Adding upstream version 86.0.1.upstream/86.0.1upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

56 files changed, 4094 insertions, 0 deletions

diff --git a/dom/midi/MIDIAccess.cpp b/dom/midi/MIDIAccess.cpp
new file mode 100644
index 0000000000..698473c20a
--- /dev/null
+++ b/dom/midi/MIDIAccess.cpp
@@ -0,0 +1,221 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim:set ts=2 sw=2 sts=2 et cindent: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "mozilla/dom/MIDIAccess.h"
+#include "mozilla/dom/MIDIAccessManager.h"
+#include "mozilla/dom/MIDIPort.h"
+#include "mozilla/dom/MIDIAccessBinding.h"
+#include "mozilla/dom/MIDIConnectionEvent.h"
+#include "mozilla/dom/MIDIOptionsBinding.h"
+#include "mozilla/dom/MIDIOutputMapBinding.h"
+#include "mozilla/dom/MIDIInputMapBinding.h"
+#include "mozilla/dom/MIDIOutputMap.h"
+#include "mozilla/dom/MIDIInputMap.h"
+#include "mozilla/dom/MIDIOutput.h"
+#include "mozilla/dom/MIDIInput.h"
+#include "mozilla/dom/MIDITypes.h"
+#include "mozilla/dom/Promise.h"
+#include "mozilla/dom/PContent.h"
+#include "mozilla/dom/Document.h"
+#include "nsPIDOMWindow.h"
+#include "nsContentPermissionHelper.h"
+#include "nsISupportsImpl.h"  // for MOZ_COUNT_CTOR, MOZ_COUNT_DTOR
+#include "IPCMessageUtils.h"
+
+namespace mozilla::dom {
+
+NS_IMPL_CYCLE_COLLECTION_CLASS(MIDIAccess)
+NS_IMPL_CYCLE_COLLECTION_TRACE_BEGIN_INHERITED(MIDIAccess, DOMEventTargetHelper)
+NS_IMPL_CYCLE_COLLECTION_TRACE_END
+
+NS_IMPL_CYCLE_COLLECTION_TRAVERSE_BEGIN_INHERITED(MIDIAccess,
+                                                  DOMEventTargetHelper)
+  NS_IMPL_CYCLE_COLLECTION_TRAVERSE(mInputMap)
+  NS_IMPL_CYCLE_COLLECTION_TRAVERSE(mOutputMap)
+  NS_IMPL_CYCLE_COLLECTION_TRAVERSE(mAccessPromise)
+NS_IMPL_CYCLE_COLLECTION_TRAVERSE_END
+
+NS_IMPL_CYCLE_COLLECTION_UNLINK_BEGIN_INHERITED(MIDIAccess,
+                                                DOMEventTargetHelper)
+  NS_IMPL_CYCLE_COLLECTION_UNLINK(mInputMap)
+  NS_IMPL_CYCLE_COLLECTION_UNLINK(mOutputMap)
+  NS_IMPL_CYCLE_COLLECTION_UNLINK(mAccessPromise)
+  tmp->Shutdown();
+NS_IMPL_CYCLE_COLLECTION_UNLINK_END
+
+NS_INTERFACE_MAP_BEGIN_CYCLE_COLLECTION(MIDIAccess)
+  NS_WRAPPERCACHE_INTERFACE_MAP_ENTRY
+NS_INTERFACE_MAP_END_INHERITING(DOMEventTargetHelper)
+
+NS_IMPL_ADDREF_INHERITED(MIDIAccess, DOMEventTargetHelper)
+NS_IMPL_RELEASE_INHERITED(MIDIAccess, DOMEventTargetHelper)
+
+MIDIAccess::MIDIAccess(nsPIDOMWindowInner* aWindow, bool aSysexEnabled,
+                       Promise* aPromise)
+    : DOMEventTargetHelper(aWindow),
+      mInputMap(new MIDIInputMap(aWindow)),
+      mOutputMap(new MIDIOutputMap(aWindow)),
+      mSysexEnabled(aSysexEnabled),
+      mAccessPromise(aPromise),
+      mHasShutdown(false) {
+  MOZ_ASSERT(aWindow);
+  MOZ_ASSERT(aPromise);
+}
+
+MIDIAccess::~MIDIAccess() { Shutdown(); }
+
+void MIDIAccess::Shutdown() {
+  if (mHasShutdown) {
+    return;
+  }
+  mDestructionObservers.Broadcast(void_t());
+  if (MIDIAccessManager::IsRunning()) {
+    MIDIAccessManager::Get()->RemoveObserver(this);
+  }
+  mHasShutdown = true;
+}
+
+void MIDIAccess::FireConnectionEvent(MIDIPort* aPort) {
+  MOZ_ASSERT(aPort);
+  MIDIConnectionEventInit init;
+  init.mPort = aPort;
+  nsAutoString id;
+  aPort->GetId(id);
+  ErrorResult rv;
+  if (aPort->State() == MIDIPortDeviceState::Disconnected) {
+    if (aPort->Type() == MIDIPortType::Input &&
+        MIDIInputMap_Binding::MaplikeHelpers::Has(mInputMap, id, rv)) {
+      MIDIInputMap_Binding::MaplikeHelpers::Delete(mInputMap, id, rv);
+    } else if (aPort->Type() == MIDIPortType::Output &&
+               MIDIOutputMap_Binding::MaplikeHelpers::Has(mOutputMap, id, rv)) {
+      MIDIOutputMap_Binding::MaplikeHelpers::Delete(mOutputMap, id, rv);
+    }
+    // Check to make sure Has()/Delete() calls haven't failed.
+    if (NS_WARN_IF(rv.Failed())) {
+      return;
+    }
+  } else {
+    // If we receive an event from a port that is not in one of our port maps,
+    // this means a port that was disconnected has been reconnected, with the
+    // port owner holding the object during that time, and we should add that
+    // port object to our maps again.
+    if (aPort->Type() == MIDIPortType::Input &&
+        !MIDIInputMap_Binding::MaplikeHelpers::Has(mInputMap, id, rv)) {
+      if (NS_WARN_IF(rv.Failed())) {
+        return;
+      }
+      MIDIInputMap_Binding::MaplikeHelpers::Set(
+          mInputMap, id, *(static_cast<MIDIInput*>(aPort)), rv);
+      if (NS_WARN_IF(rv.Failed())) {
+        return;
+      }
+    } else if (aPort->Type() == MIDIPortType::Output &&
+               !MIDIOutputMap_Binding::MaplikeHelpers::Has(mOutputMap, id,
+                                                           rv)) {
+      if (NS_WARN_IF(rv.Failed())) {
+        return;
+      }
+      MIDIOutputMap_Binding::MaplikeHelpers::Set(
+          mOutputMap, id, *(static_cast<MIDIOutput*>(aPort)), rv);
+      if (NS_WARN_IF(rv.Failed())) {
+        return;
+      }
+    }
+  }
+  RefPtr<MIDIConnectionEvent> event =
+      MIDIConnectionEvent::Constructor(this, u"statechange"_ns, init);
+  DispatchTrustedEvent(event);
+}
+
+void MIDIAccess::MaybeCreateMIDIPort(const MIDIPortInfo& aInfo,
+                                     ErrorResult& aRv) {
+  nsAutoString id(aInfo.id());
+  MIDIPortType type = static_cast<MIDIPortType>(aInfo.type());
+  RefPtr<MIDIPort> port;
+  if (type == MIDIPortType::Input) {
+    bool hasPort =
+        MIDIInputMap_Binding::MaplikeHelpers::Has(mInputMap, id, aRv);
+    if (hasPort || NS_WARN_IF(aRv.Failed())) {
+      // We already have the port in our map.
+      return;
+    }
+    port = MIDIInput::Create(GetOwner(), this, aInfo, mSysexEnabled);
+    if (NS_WARN_IF(!port)) {
+      aRv.Throw(NS_ERROR_FAILURE);
+      return;
+    }
+    MIDIInputMap_Binding::MaplikeHelpers::Set(
+        mInputMap, id, *(static_cast<MIDIInput*>(port.get())), aRv);
+    if (NS_WARN_IF(aRv.Failed())) {
+      return;
+    }
+  } else if (type == MIDIPortType::Output) {
+    bool hasPort =
+        MIDIOutputMap_Binding::MaplikeHelpers::Has(mOutputMap, id, aRv);
+    if (hasPort || NS_WARN_IF(aRv.Failed())) {
+      // We already have the port in our map.
+      return;
+    }
+    port = MIDIOutput::Create(GetOwner(), this, aInfo, mSysexEnabled);
+    if (NS_WARN_IF(!port)) {
+      aRv.Throw(NS_ERROR_FAILURE);
+      return;
+    }
+    MIDIOutputMap_Binding::MaplikeHelpers::Set(
+        mOutputMap, id, *(static_cast<MIDIOutput*>(port.get())), aRv);
+    if (NS_WARN_IF(aRv.Failed())) {
+      return;
+    }
+  } else {
+    // If we hit this, then we have some port that is neither input nor output.
+    // That is bad.
+    MOZ_CRASH("We shouldn't be here!");
+  }
+  // Set up port to listen for destruction of this access object.
+  mDestructionObservers.AddObserver(port);
+
+  // If we haven't resolved the promise for handing the MIDIAccess object to
+  // content, this means we're still populating the list of already connected
+  // devices. Don't fire events yet.
+  if (!mAccessPromise) {
+    FireConnectionEvent(port);
+  }
+}
+
+// For the MIDIAccess object, only worry about new connections, where we create
+// MIDIPort objects. When a port is removed and the MIDIPortRemove event is
+// received, that will be handled by the MIDIPort object itself, and it will
+// request removal from MIDIAccess's maps.
+void MIDIAccess::Notify(const MIDIPortList& aEvent) {
+  for (auto& port : aEvent.ports()) {
+    // Something went very wrong. Warn and return.
+    ErrorResult rv;
+    MaybeCreateMIDIPort(port, rv);
+    if (rv.Failed()) {
+      if (!mAccessPromise) {
+        return;
+      }
+      mAccessPromise->MaybeReject(std::move(rv));
+      mAccessPromise = nullptr;
+    }
+  }
+  if (!mAccessPromise) {
+    return;
+  }
+  mAccessPromise->MaybeResolve(this);
+  mAccessPromise = nullptr;
+}
+
+JSObject* MIDIAccess::WrapObject(JSContext* aCx,
+                                 JS::Handle<JSObject*> aGivenProto) {
+  return MIDIAccess_Binding::Wrap(aCx, this, aGivenProto);
+}
+
+void MIDIAccess::RemovePortListener(MIDIAccessDestructionObserver* aObs) {
+  mDestructionObservers.RemoveObserver(aObs);
+}
+
+}  // namespace mozilla::dom
diff --git a/dom/midi/MIDIAccess.h b/dom/midi/MIDIAccess.h
new file mode 100644
index 0000000000..99071aa526
--- /dev/null
+++ b/dom/midi/MIDIAccess.h
@@ -0,0 +1,116 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim:set ts=2 sw=2 sts=2 et cindent: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_dom_MIDIAccess_h
+#define mozilla_dom_MIDIAccess_h
+
+#include "mozilla/Attributes.h"
+#include "mozilla/DOMEventTargetHelper.h"
+#include "mozilla/Observer.h"
+#include "nsCycleCollectionParticipant.h"
+#include "nsWrapperCache.h"
+
+struct JSContext;
+
+namespace mozilla {
+class ErrorResult;
+
+// Predeclare void_t here, as including IPCMessageUtils brings in windows.h and
+// causes binding compilation problems.
+struct void_t;
+
+namespace dom {
+
+class MIDIAccessManager;
+class MIDIInputMap;
+struct MIDIOptions;
+class MIDIOutputMap;
+class MIDIPermissionRequest;
+class MIDIPort;
+class MIDIPortChangeEvent;
+class MIDIPortInfo;
+class MIDIPortList;
+class Promise;
+
+typedef Observer<void_t> MIDIAccessDestructionObserver;
+
+/**
+ * MIDIAccess is the DOM object that is handed to the user upon MIDI permissions
+ * being successfully granted. It manages access to MIDI ports, and fires events
+ * for device connection and disconnection.
+ *
+ * New MIDIAccess objects are created every time RequestMIDIAccess is called.
+ * MIDIAccess objects are managed via MIDIAccessManager.
+ */
+class MIDIAccess final : public DOMEventTargetHelper,
+                         public Observer<MIDIPortList> {
+  // Use the Permission Request class in MIDIAccessManager for creating
+  // MIDIAccess objects.
+  friend class MIDIPermissionRequest;
+  friend class MIDIAccessManager;
+
+ public:
+  NS_DECL_ISUPPORTS_INHERITED
+  NS_DECL_CYCLE_COLLECTION_SCRIPT_HOLDER_CLASS_INHERITED(MIDIAccess,
+                                                         DOMEventTargetHelper)
+ public:
+  virtual JSObject* WrapObject(JSContext* aCx,
+                               JS::Handle<JSObject*> aGivenProto) override;
+
+  // Return map of MIDI Input Ports
+  MIDIInputMap* Inputs() const { return mInputMap; }
+
+  // Return map of MIDI Output Ports
+  MIDIOutputMap* Outputs() const { return mOutputMap; }
+
+  // Returns true if sysex permissions were given
+  bool SysexEnabled() const { return mSysexEnabled; }
+
+  // Observer implementation for receiving port connection updates
+  void Notify(const MIDIPortList& aEvent) override;
+
+  // All MIDIPort objects observe destruction of the MIDIAccess object that
+  // created them, as the port object receives disconnection events which then
+  // must be passed up to the MIDIAccess object. If the Port object dies before
+  // the MIDIAccess object, it needs to be removed from the observer list.
+  void RemovePortListener(MIDIAccessDestructionObserver* aPort);
+
+  // Fires DOM event on port connection/disconnection
+  void FireConnectionEvent(MIDIPort* aPort);
+
+  // Notify all MIDIPorts that were created by this MIDIAccess and are still
+  // alive, and detach from the MIDIAccessManager.
+  void Shutdown();
+  IMPL_EVENT_HANDLER(statechange);
+
+ private:
+  MIDIAccess(nsPIDOMWindowInner* aWindow, bool aSysexEnabled,
+             Promise* aAccessPromise);
+  ~MIDIAccess();
+
+  // On receiving a connection event from MIDIAccessManager, create a
+  // corresponding MIDIPort object if we don't already have one.
+  void MaybeCreateMIDIPort(const MIDIPortInfo& aInfo, ErrorResult& aRv);
+
+  // Stores all known MIDIInput Ports
+  RefPtr<MIDIInputMap> mInputMap;
+  // Stores all known MIDIOutput Ports
+  RefPtr<MIDIOutputMap> mOutputMap;
+  // List of MIDIPort observers that need to be updated on destruction.
+  ObserverList<void_t> mDestructionObservers;
+  // True if user gave permissions for sysex usage to this object.
+  bool mSysexEnabled;
+  // Promise created by RequestMIDIAccess call, to be resolved after port
+  // populating is finished.
+  RefPtr<Promise> mAccessPromise;
+  // True if shutdown process has started, so we don't try to add more ports.
+  bool mHasShutdown;
+};
+
+}  // namespace dom
+}  // namespace mozilla
+
+#endif  // mozilla_dom_MIDIAccess_h
diff --git a/dom/midi/MIDIAccessManager.cpp b/dom/midi/MIDIAccessManager.cpp
new file mode 100644
index 0000000000..65c5588cd4
--- /dev/null
+++ b/dom/midi/MIDIAccessManager.cpp
@@ -0,0 +1,149 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim:set ts=2 sw=2 sts=2 et cindent: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this file,
+ * You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "mozilla/dom/MIDIAccessManager.h"
+#include "mozilla/dom/Document.h"
+#include "mozilla/dom/MIDIAccess.h"
+#include "mozilla/dom/MIDIManagerChild.h"
+#include "mozilla/dom/MIDIPermissionRequest.h"
+#include "mozilla/dom/FeaturePolicyUtils.h"
+#include "mozilla/dom/Promise.h"
+#include "nsIGlobalObject.h"
+#include "mozilla/ClearOnShutdown.h"
+#include "mozilla/ipc/PBackgroundChild.h"
+#include "mozilla/ipc/BackgroundChild.h"
+#include "mozilla/Preferences.h"
+
+using namespace mozilla::ipc;
+
+namespace mozilla::dom {
+
+namespace {
+// Singleton object for MIDIAccessManager
+StaticRefPtr<MIDIAccessManager> gMIDIAccessManager;
+}  // namespace
+
+MIDIAccessManager::MIDIAccessManager() : mHasPortList(false), mChild(nullptr) {}
+
+MIDIAccessManager::~MIDIAccessManager() = default;
+
+// static
+MIDIAccessManager* MIDIAccessManager::Get() {
+  if (!gMIDIAccessManager) {
+    gMIDIAccessManager = new MIDIAccessManager();
+    ClearOnShutdown(&gMIDIAccessManager);
+  }
+  return gMIDIAccessManager;
+}
+
+// static
+bool MIDIAccessManager::IsRunning() { return !!gMIDIAccessManager; }
+
+already_AddRefed<Promise> MIDIAccessManager::RequestMIDIAccess(
+    nsPIDOMWindowInner* aWindow, const MIDIOptions& aOptions,
+    ErrorResult& aRv) {
+  MOZ_ASSERT(NS_IsMainThread());
+  MOZ_ASSERT(aWindow);
+  nsCOMPtr<nsIGlobalObject> go = do_QueryInterface(aWindow);
+  RefPtr<Promise> p = Promise::Create(go, aRv);
+  if (NS_WARN_IF(aRv.Failed())) {
+    return nullptr;
+  }
+  nsCOMPtr<Document> doc = aWindow->GetDoc();
+  if (NS_WARN_IF(!doc)) {
+    aRv.Throw(NS_ERROR_FAILURE);
+    return nullptr;
+  }
+
+  if (!FeaturePolicyUtils::IsFeatureAllowed(doc, u"midi"_ns)) {
+    aRv.Throw(NS_ERROR_DOM_SECURITY_ERR);
+    return nullptr;
+  }
+
+  nsCOMPtr<nsIRunnable> permRunnable =
+      new MIDIPermissionRequest(aWindow, p, aOptions);
+  aRv = NS_DispatchToMainThread(permRunnable);
+  if (NS_WARN_IF(aRv.Failed())) {
+    return nullptr;
+  }
+  return p.forget();
+}
+
+bool MIDIAccessManager::AddObserver(Observer<MIDIPortList>* aObserver) {
+  // Add observer before we start the service, otherwise we can end up with
+  // device lists being received before we have observers to send them to.
+  mChangeObservers.AddObserver(aObserver);
+  // If we don't currently have a port list, that means this is a new
+  // AccessManager and we possibly need to start the MIDI Service.
+  if (!mChild) {
+    // Otherwise we must begin the PBackground initialization process and
+    // wait for the async ActorCreated() callback.
+    MOZ_ASSERT(NS_IsMainThread());
+    ::mozilla::ipc::PBackgroundChild* actor =
+        BackgroundChild::GetOrCreateForCurrentThread();
+    if (NS_WARN_IF(!actor)) {
+      return false;
+    }
+    RefPtr<MIDIManagerChild> mgr(new MIDIManagerChild());
+    PMIDIManagerChild* constructedMgr = actor->SendPMIDIManagerConstructor(mgr);
+
+    if (NS_WARN_IF(!constructedMgr)) {
+      return false;
+    }
+    MOZ_ASSERT(constructedMgr == mgr);
+    mChild = std::move(mgr);
+    // Add a ref to mChild here, that will be deref'd by
+    // BackgroundChildImpl::DeallocPMIDIManagerChild on IPC cleanup.
+    mChild->SetActorAlive();
+  }
+  return true;
+}
+
+void MIDIAccessManager::RemoveObserver(Observer<MIDIPortList>* aObserver) {
+  mChangeObservers.RemoveObserver(aObserver);
+  if (mChangeObservers.Length() == 0) {
+    // If we're out of listeners, go ahead and shut down. Make sure to cleanup
+    // the IPDL protocol also.
+    if (mChild) {
+      mChild->Shutdown();
+      mChild = nullptr;
+    }
+    gMIDIAccessManager = nullptr;
+  }
+}
+
+void MIDIAccessManager::CreateMIDIAccess(nsPIDOMWindowInner* aWindow,
+                                         bool aNeedsSysex, Promise* aPromise) {
+  MOZ_ASSERT(aWindow);
+  MOZ_ASSERT(aPromise);
+  RefPtr<MIDIAccess> a(new MIDIAccess(aWindow, aNeedsSysex, aPromise));
+  if (NS_WARN_IF(!AddObserver(a))) {
+    aPromise->MaybeReject(NS_ERROR_FAILURE);
+    return;
+  }
+  if (!mHasPortList) {
+    // Hold the access object until we get a connected device list.
+    mAccessHolder.AppendElement(a);
+  } else {
+    // If we already have a port list, just send it to the MIDIAccess object now
+    // so it can prepopulate its device list and resolve the promise.
+    a->Notify(mPortList);
+  }
+}
+
+void MIDIAccessManager::Update(const MIDIPortList& aPortList) {
+  mPortList = aPortList;
+  mChangeObservers.Broadcast(aPortList);
+  if (!mHasPortList) {
+    mHasPortList = true;
+    // Now that we've broadcast the already-connected port list, content
+    // should manage the lifetime of the MIDIAccess object, so we can clear the
+    // keep-alive array.
+    mAccessHolder.Clear();
+  }
+}
+
+}  // namespace mozilla::dom
diff --git a/dom/midi/MIDIAccessManager.h b/dom/midi/MIDIAccessManager.h
new file mode 100644
index 0000000000..2ffb7e6f53
--- /dev/null
+++ b/dom/midi/MIDIAccessManager.h
@@ -0,0 +1,75 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim:set ts=2 sw=2 sts=2 et cindent: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_dom_MIDIAccessManager_h
+#define mozilla_dom_MIDIAccessManager_h
+
+#include "nsPIDOMWindow.h"
+#include "mozilla/dom/MIDITypes.h"
+#include "mozilla/Observer.h"
+
+namespace mozilla {
+namespace dom {
+
+class MIDIAccess;
+class MIDIManagerChild;
+struct MIDIOptions;
+class MIDIPortChangeEvent;
+class MIDIPortInfo;
+class Promise;
+
+/**
+ * MIDIAccessManager manages creation and lifetime of MIDIAccess objects for the
+ * process it lives in. It is in charge of dealing with permission requests,
+ * creating new MIDIAccess objects, and updating live MIDIAccess objects with
+ * new device listings.
+ *
+ * While a process/window can have many MIDIAccess objects, there is only one
+ * MIDIAccessManager for any one process.
+ */
+class MIDIAccessManager final {
+ public:
+  NS_INLINE_DECL_REFCOUNTING(MIDIAccessManager);
+  // Handles requests from Navigator for MIDI permissions and MIDIAccess
+  // creation.
+  already_AddRefed<Promise> RequestMIDIAccess(nsPIDOMWindowInner* aWindow,
+                                              const MIDIOptions& aOptions,
+                                              ErrorResult& aRv);
+  // Creates a new MIDIAccess object
+  void CreateMIDIAccess(nsPIDOMWindowInner* aWindow, bool aNeedsSysex,
+                        Promise* aPromise);
+  // Getter for manager singleton
+  static MIDIAccessManager* Get();
+  // True if manager singleton has been created
+  static bool IsRunning();
+  // Send device connection updates to all known MIDIAccess objects.
+  void Update(const MIDIPortList& aEvent);
+  // Adds a device update observer (usually a MIDIAccess object)
+  bool AddObserver(Observer<MIDIPortList>* aObserver);
+  // Removes a device update observer (usually a MIDIAccess object)
+  void RemoveObserver(Observer<MIDIPortList>* aObserver);
+
+ private:
+  MIDIAccessManager();
+  ~MIDIAccessManager();
+  // True if object has received a device list from the MIDI platform service.
+  bool mHasPortList;
+  // List of known ports for the system.
+  MIDIPortList mPortList;
+  // Holds MIDIAccess objects until we've received the first list of devices
+  // from the MIDI Service.
+  nsTArray<RefPtr<MIDIAccess>> mAccessHolder;
+  // Device state update observers (usually MIDIAccess objects)
+  ObserverList<MIDIPortList> mChangeObservers;
+  // IPC Object for MIDIManager. Created on first MIDIAccess object creation,
+  // destroyed on last MIDIAccess object destruction.
+  RefPtr<MIDIManagerChild> mChild;
+};
+
+}  // namespace dom
+}  // namespace mozilla
+
+#endif  // mozilla_dom_MIDIAccessManager_h
diff --git a/dom/midi/MIDIInput.cpp b/dom/midi/MIDIInput.cpp
new file mode 100644
index 0000000000..5947f08f41
--- /dev/null
+++ b/dom/midi/MIDIInput.cpp
@@ -0,0 +1,63 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim:set ts=2 sw=2 sts=2 et cindent: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "mozilla/dom/MIDIInput.h"
+#include "mozilla/dom/Document.h"
+#include "mozilla/dom/MIDIPortChild.h"
+#include "mozilla/dom/MIDIInputBinding.h"
+#include "mozilla/dom/MIDIMessageEvent.h"
+#include "mozilla/dom/MIDIMessageEventBinding.h"
+#include "nsDOMNavigationTiming.h"
+
+namespace mozilla::dom {
+
+MIDIInput::MIDIInput(nsPIDOMWindowInner* aWindow, MIDIAccess* aMIDIAccessParent)
+    : MIDIPort(aWindow, aMIDIAccessParent) {}
+
+// static
+MIDIInput* MIDIInput::Create(nsPIDOMWindowInner* aWindow,
+                             MIDIAccess* aMIDIAccessParent,
+                             const MIDIPortInfo& aPortInfo,
+                             const bool aSysexEnabled) {
+  MOZ_ASSERT(static_cast<MIDIPortType>(aPortInfo.type()) ==
+             MIDIPortType::Input);
+  auto port = new MIDIInput(aWindow, aMIDIAccessParent);
+  if (!port->Initialize(aPortInfo, aSysexEnabled)) {
+    return nullptr;
+  }
+  return port;
+}
+
+JSObject* MIDIInput::WrapObject(JSContext* aCx,
+                                JS::Handle<JSObject*> aGivenProto) {
+  return MIDIInput_Binding::Wrap(aCx, this, aGivenProto);
+}
+
+void MIDIInput::Receive(const nsTArray<MIDIMessage>& aMsgs) {
+  nsCOMPtr<Document> doc = GetOwner() ? GetOwner()->GetDoc() : nullptr;
+  if (!doc) {
+    NS_WARNING("No document available to send MIDIMessageEvent to!");
+    return;
+  }
+  for (auto& msg : aMsgs) {
+    RefPtr<MIDIMessageEvent> event(
+        MIDIMessageEvent::Constructor(this, msg.timestamp(), msg.data()));
+    DispatchTrustedEvent(event);
+  }
+}
+
+EventHandlerNonNull* MIDIInput::GetOnmidimessage() {
+  return GetEventHandler(nsGkAtoms::onmidimessage);
+}
+
+void MIDIInput::SetOnmidimessage(EventHandlerNonNull* aCallback) {
+  SetEventHandler(nsGkAtoms::onmidimessage, aCallback);
+  if (mPort->ConnectionState() != MIDIPortConnectionState::Open) {
+    mPort->SendOpen();
+  }
+}
+
+}  // namespace mozilla::dom
diff --git a/dom/midi/MIDIInput.h b/dom/midi/MIDIInput.h
new file mode 100644
index 0000000000..df4247ffa8
--- /dev/null
+++ b/dom/midi/MIDIInput.h
@@ -0,0 +1,53 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim:set ts=2 sw=2 sts=2 et cindent: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_dom_MIDIInput_h
+#define mozilla_dom_MIDIInput_h
+
+#include "mozilla/dom/MIDIPort.h"
+
+struct JSContext;
+
+namespace mozilla {
+namespace dom {
+
+class MIDIPortInfo;
+
+/**
+ * Represents a MIDI Input Port, handles generating incoming message events.
+ *
+ */
+class MIDIInput final : public MIDIPort {
+ public:
+  static MIDIInput* Create(nsPIDOMWindowInner* aWindow,
+                           MIDIAccess* aMIDIAccessParent,
+                           const MIDIPortInfo& aPortInfo,
+                           const bool aSysexEnabled);
+  ~MIDIInput() = default;
+
+  JSObject* WrapObject(JSContext* aCx,
+                       JS::Handle<JSObject*> aGivenProto) override;
+
+  // Since we need to be able to open the port on event handler assignment, we
+  // can't use IMPL_EVENT_HANDLER. We have to implement the event handler
+  // functions ourselves.
+
+  // Getter for the event handler callback
+  EventHandlerNonNull* GetOnmidimessage();
+  // Setter for the event handler callback
+  void SetOnmidimessage(EventHandlerNonNull* aCallback);
+
+ private:
+  MIDIInput(nsPIDOMWindowInner* aWindow, MIDIAccess* aMIDIAccessParent);
+  // Takes an array of IPC MIDIMessage objects and turns them into
+  // MIDIMessageEvents, which it then fires.
+  void Receive(const nsTArray<MIDIMessage>& aMsgs) override;
+};
+
+}  // namespace dom
+}  // namespace mozilla
+
+#endif  // mozilla_dom_MIDIInput_h
diff --git a/dom/midi/MIDIInputMap.cpp b/dom/midi/MIDIInputMap.cpp
new file mode 100644
index 0000000000..aa4f57a7d3
--- /dev/null
+++ b/dom/midi/MIDIInputMap.cpp
@@ -0,0 +1,29 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this file,
+ * You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "mozilla/dom/MIDIInputMap.h"
+#include "mozilla/dom/MIDIInputMapBinding.h"
+#include "nsPIDOMWindow.h"
+#include "mozilla/dom/BindingUtils.h"
+
+namespace mozilla::dom {
+
+NS_IMPL_CYCLE_COLLECTION_WRAPPERCACHE(MIDIInputMap, mParent)
+
+NS_IMPL_CYCLE_COLLECTING_ADDREF(MIDIInputMap)
+NS_IMPL_CYCLE_COLLECTING_RELEASE(MIDIInputMap)
+
+NS_INTERFACE_MAP_BEGIN_CYCLE_COLLECTION(MIDIInputMap)
+  NS_WRAPPERCACHE_INTERFACE_MAP_ENTRY
+  NS_INTERFACE_MAP_ENTRY(nsISupports)
+NS_INTERFACE_MAP_END
+
+MIDIInputMap::MIDIInputMap(nsPIDOMWindowInner* aParent) : mParent(aParent) {}
+
+JSObject* MIDIInputMap::WrapObject(JSContext* aCx,
+                                   JS::Handle<JSObject*> aGivenProto) {
+  return MIDIInputMap_Binding::Wrap(aCx, this, aGivenProto);
+}
+
+}  // namespace mozilla::dom
diff --git a/dom/midi/MIDIInputMap.h b/dom/midi/MIDIInputMap.h
new file mode 100644
index 0000000000..ee9b749678
--- /dev/null
+++ b/dom/midi/MIDIInputMap.h
@@ -0,0 +1,40 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim:set ts=2 sw=2 sts=2 et cindent: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_dom_MIDIInputMap_h
+#define mozilla_dom_MIDIInputMap_h
+
+#include "nsCOMPtr.h"
+#include "nsWrapperCache.h"
+
+class nsPIDOMWindowInner;
+
+namespace mozilla {
+namespace dom {
+
+/**
+ * Maplike DOM object that holds a list of all MIDI input ports available for
+ * access. Almost all functions are implemented automatically by WebIDL.
+ */
+class MIDIInputMap final : public nsISupports, public nsWrapperCache {
+ public:
+  NS_DECL_CYCLE_COLLECTING_ISUPPORTS
+  NS_DECL_CYCLE_COLLECTION_SCRIPT_HOLDER_CLASS(MIDIInputMap)
+  nsPIDOMWindowInner* GetParentObject() const { return mParent; }
+
+  explicit MIDIInputMap(nsPIDOMWindowInner* aParent);
+  JSObject* WrapObject(JSContext* aCx,
+                       JS::Handle<JSObject*> aGivenProto) override;
+
+ private:
+  ~MIDIInputMap() = default;
+  nsCOMPtr<nsPIDOMWindowInner> mParent;
+};
+
+}  // namespace dom
+}  // namespace mozilla
+
+#endif  // mozilla_dom_MIDIInputMap_h
diff --git a/dom/midi/MIDIManagerChild.cpp b/dom/midi/MIDIManagerChild.cpp
new file mode 100644
index 0000000000..258a16bae3
--- /dev/null
+++ b/dom/midi/MIDIManagerChild.cpp
@@ -0,0 +1,36 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim:set ts=2 sw=2 sts=2 et cindent: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "MIDIManagerChild.h"
+#include "mozilla/dom/MIDIAccessManager.h"
+
+using namespace mozilla::dom;
+
+MIDIManagerChild::MIDIManagerChild() : mShutdown(false) {}
+
+mozilla::ipc::IPCResult MIDIManagerChild::RecvMIDIPortListUpdate(
+    const MIDIPortList& aPortList) {
+  MOZ_ASSERT(NS_IsMainThread());
+  if (mShutdown) {
+    return IPC_OK();
+  }
+  MOZ_ASSERT(MIDIAccessManager::IsRunning());
+  MIDIAccessManager::Get()->Update(aPortList);
+  return IPC_OK();
+}
+
+void MIDIManagerChild::SetActorAlive() {
+  // IPC Channels for MIDIManagers are created and managed by MIDIAccessManager,
+  // so once the actor is created, we'll need to add a reference to keep it
+  // alive until BackgroundChildImpl kills it.
+  AddRef();
+}
+
+void MIDIManagerChild::Shutdown() {
+  MOZ_ASSERT(!mShutdown);
+  mShutdown = true;
+  SendShutdown();
+}
diff --git a/dom/midi/MIDIManagerChild.h b/dom/midi/MIDIManagerChild.h
new file mode 100644
index 0000000000..eaf6f99d02
--- /dev/null
+++ b/dom/midi/MIDIManagerChild.h
@@ -0,0 +1,39 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim:set ts=2 sw=2 sts=2 et cindent: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_dom_MIDIManagerChild_h
+#define mozilla_dom_MIDIManagerChild_h
+
+#include "mozilla/dom/PMIDIManagerChild.h"
+
+namespace mozilla {
+namespace dom {
+
+/**
+ * Actor implementation for the Child side of MIDIManager (represented in DOM by
+ * MIDIAccess). Manages actor lifetime so that we know to shut down services
+ * when all MIDIManagers are gone. Also receives port list update on MIDIAccess
+ * object creation.
+ *
+ */
+class MIDIManagerChild final : public PMIDIManagerChild {
+ public:
+  NS_INLINE_DECL_REFCOUNTING(MIDIManagerChild)
+
+  MIDIManagerChild();
+  mozilla::ipc::IPCResult RecvMIDIPortListUpdate(const MIDIPortList& aPortList);
+  void SetActorAlive();
+  void Shutdown();
+
+ private:
+  ~MIDIManagerChild() = default;
+  bool mShutdown;
+};
+
+}  // namespace dom
+}  // namespace mozilla
+
+#endif  // mozilla_dom_MIDIManagerChild_h
diff --git a/dom/midi/MIDIManagerParent.cpp b/dom/midi/MIDIManagerParent.cpp
new file mode 100644
index 0000000000..a0190ff643
--- /dev/null
+++ b/dom/midi/MIDIManagerParent.cpp
@@ -0,0 +1,26 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim:set ts=2 sw=2 sts=2 et cindent: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "mozilla/dom/MIDIManagerParent.h"
+#include "mozilla/dom/MIDIPlatformService.h"
+
+namespace mozilla::dom {
+
+void MIDIManagerParent::ActorDestroy(ActorDestroyReason aWhy) {}
+
+void MIDIManagerParent::Teardown() {
+  if (MIDIPlatformService::IsRunning()) {
+    MIDIPlatformService::Get()->RemoveManager(this);
+  }
+}
+
+mozilla::ipc::IPCResult MIDIManagerParent::RecvShutdown() {
+  Teardown();
+  Unused << Send__delete__(this);
+  return IPC_OK();
+}
+
+}  // namespace mozilla::dom
diff --git a/dom/midi/MIDIManagerParent.h b/dom/midi/MIDIManagerParent.h
new file mode 100644
index 0000000000..6714ed6ab4
--- /dev/null
+++ b/dom/midi/MIDIManagerParent.h
@@ -0,0 +1,36 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim:set ts=2 sw=2 sts=2 et cindent: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_dom_MIDIManagerParent_h
+#define mozilla_dom_MIDIManagerParent_h
+
+#include "mozilla/dom/PMIDIManagerParent.h"
+
+namespace mozilla {
+namespace dom {
+
+/**
+ * Actor implementation for the Parent (PBackground thread) side of MIDIManager
+ * (represented in DOM by MIDIAccess). Manages actor lifetime so that we know
+ * to shut down services when all MIDIManagers are gone.
+ *
+ */
+class MIDIManagerParent final : public PMIDIManagerParent {
+ public:
+  NS_INLINE_DECL_REFCOUNTING(MIDIManagerParent);
+  MIDIManagerParent() = default;
+  mozilla::ipc::IPCResult RecvShutdown();
+  void Teardown();
+  void ActorDestroy(ActorDestroyReason aWhy) override;
+
+ private:
+  ~MIDIManagerParent() = default;
+};
+
+}  // namespace dom
+}  // namespace mozilla
+
+#endif  // mozilla_dom_MIDIManagerParent_h
diff --git a/dom/midi/MIDIMessageEvent.cpp b/dom/midi/MIDIMessageEvent.cpp
new file mode 100644
index 0000000000..b06b852dc5
--- /dev/null
+++ b/dom/midi/MIDIMessageEvent.cpp
@@ -0,0 +1,106 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim:set ts=2 sw=2 sts=2 et cindent: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "mozilla/dom/EventBinding.h"
+#include "mozilla/dom/MIDIMessageEvent.h"
+#include "mozilla/dom/MIDIMessageEventBinding.h"
+#include "js/GCAPI.h"
+#include "jsfriendapi.h"
+#include "mozilla/FloatingPoint.h"
+#include "mozilla/HoldDropJSObjects.h"
+#include "mozilla/dom/Nullable.h"
+#include "mozilla/dom/PrimitiveConversions.h"
+#include "mozilla/dom/TypedArray.h"
+#include "mozilla/dom/Performance.h"
+
+namespace mozilla::dom {
+
+NS_IMPL_CYCLE_COLLECTION_CLASS(MIDIMessageEvent)
+
+NS_IMPL_ADDREF_INHERITED(MIDIMessageEvent, Event)
+NS_IMPL_RELEASE_INHERITED(MIDIMessageEvent, Event)
+
+NS_IMPL_CYCLE_COLLECTION_TRAVERSE_BEGIN_INHERITED(MIDIMessageEvent, Event)
+NS_IMPL_CYCLE_COLLECTION_TRAVERSE_END
+
+NS_IMPL_CYCLE_COLLECTION_TRACE_BEGIN_INHERITED(MIDIMessageEvent, Event)
+  NS_IMPL_CYCLE_COLLECTION_TRACE_JS_MEMBER_CALLBACK(mData)
+NS_IMPL_CYCLE_COLLECTION_TRACE_END
+
+NS_IMPL_CYCLE_COLLECTION_UNLINK_BEGIN_INHERITED(MIDIMessageEvent, Event)
+  tmp->mData = nullptr;
+NS_IMPL_CYCLE_COLLECTION_UNLINK_END
+
+NS_INTERFACE_MAP_BEGIN_CYCLE_COLLECTION(MIDIMessageEvent)
+NS_INTERFACE_MAP_END_INHERITING(Event)
+
+MIDIMessageEvent::MIDIMessageEvent(mozilla::dom::EventTarget* aOwner)
+    : Event(aOwner, nullptr, nullptr) {
+  mozilla::HoldJSObjects(this);
+}
+
+MIDIMessageEvent::~MIDIMessageEvent() {
+  mData = nullptr;
+  mozilla::DropJSObjects(this);
+}
+
+JSObject* MIDIMessageEvent::WrapObjectInternal(
+    JSContext* aCx, JS::Handle<JSObject*> aGivenProto) {
+  return MIDIMessageEvent_Binding::Wrap(aCx, this, aGivenProto);
+}
+
+MIDIMessageEvent* MIDIMessageEvent::AsMIDIMessageEvent() { return this; }
+
+already_AddRefed<MIDIMessageEvent> MIDIMessageEvent::Constructor(
+    EventTarget* aOwner, const class TimeStamp& aReceivedTime,
+    const nsTArray<uint8_t>& aData) {
+  MOZ_ASSERT(aOwner);
+  RefPtr<MIDIMessageEvent> e = new MIDIMessageEvent(aOwner);
+  e->InitEvent(u"midimessage"_ns, false, false);
+  e->mEvent->mTimeStamp = aReceivedTime;
+  e->mRawData = aData.Clone();
+  e->SetTrusted(true);
+  return e.forget();
+}
+
+already_AddRefed<MIDIMessageEvent> MIDIMessageEvent::Constructor(
+    const GlobalObject& aGlobal, const nsAString& aType,
+    const MIDIMessageEventInit& aEventInitDict, ErrorResult& aRv) {
+  nsCOMPtr<EventTarget> owner = do_QueryInterface(aGlobal.GetAsSupports());
+  RefPtr<MIDIMessageEvent> e = new MIDIMessageEvent(owner);
+  bool trusted = e->Init(owner);
+  e->InitEvent(aType, aEventInitDict.mBubbles, aEventInitDict.mCancelable);
+  // Set data for event. Timestamp will always be set to Now() (default for
+  // event) using this constructor.
+  const auto& a = aEventInitDict.mData.Value();
+  a.ComputeState();
+  e->mData = Uint8Array::Create(aGlobal.Context(), owner, a.Length(), a.Data());
+  if (NS_WARN_IF(!e->mData)) {
+    aRv.Throw(NS_ERROR_OUT_OF_MEMORY);
+    return nullptr;
+  }
+
+  e->SetTrusted(trusted);
+  mozilla::HoldJSObjects(e.get());
+  return e.forget();
+}
+
+void MIDIMessageEvent::GetData(JSContext* cx,
+                               JS::MutableHandle<JSObject*> aData,
+                               ErrorResult& aRv) {
+  if (!mData) {
+    mData =
+        Uint8Array::Create(cx, this, mRawData.Length(), mRawData.Elements());
+    if (!mData) {
+      aRv.Throw(NS_ERROR_OUT_OF_MEMORY);
+      return;
+    }
+    mRawData.Clear();
+  }
+  aData.set(mData);
+}
+
+}  // namespace mozilla::dom
diff --git a/dom/midi/MIDIMessageEvent.h b/dom/midi/MIDIMessageEvent.h
new file mode 100644
index 0000000000..6422f8872a
--- /dev/null
+++ b/dom/midi/MIDIMessageEvent.h
@@ -0,0 +1,64 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim:set ts=2 sw=2 sts=2 et cindent: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_dom_MIDIMessageEvent_h
+#define mozilla_dom_MIDIMessageEvent_h
+
+#include <cstdint>
+#include "js/RootingAPI.h"
+#include "mozilla/AlreadyAddRefed.h"
+#include "mozilla/Assertions.h"
+#include "mozilla/TimeStamp.h"
+#include "mozilla/dom/Event.h"
+#include "nsCycleCollectionParticipant.h"
+#include "nsISupports.h"
+#include "nsStringFwd.h"
+#include "nsTArray.h"
+
+struct JSContext;
+namespace mozilla {
+namespace dom {
+struct MIDIMessageEventInit;
+
+/**
+ * Event that fires whenever a MIDI message is received by the MIDIInput object.
+ *
+ */
+class MIDIMessageEvent final : public Event {
+ public:
+  NS_DECL_ISUPPORTS_INHERITED
+  NS_DECL_CYCLE_COLLECTION_SCRIPT_HOLDER_CLASS_INHERITED(MIDIMessageEvent,
+                                                         Event)
+ protected:
+  explicit MIDIMessageEvent(mozilla::dom::EventTarget* aOwner);
+
+  JS::Heap<JSObject*> mData;
+
+ public:
+  virtual MIDIMessageEvent* AsMIDIMessageEvent();
+  virtual JSObject* WrapObjectInternal(
+      JSContext* aCx, JS::Handle<JSObject*> aGivenProto) override;
+  static already_AddRefed<MIDIMessageEvent> Constructor(
+      EventTarget* aOwner, const class TimeStamp& aReceivedTime,
+      const nsTArray<uint8_t>& aData);
+
+  static already_AddRefed<MIDIMessageEvent> Constructor(
+      const GlobalObject& aGlobal, const nsAString& aType,
+      const MIDIMessageEventInit& aEventInitDict, ErrorResult& aRv);
+
+  // Getter for message data
+  void GetData(JSContext* cx, JS::MutableHandle<JSObject*> aData,
+               ErrorResult& aRv);
+
+ private:
+  ~MIDIMessageEvent();
+  nsTArray<uint8_t> mRawData;
+};
+
+}  // namespace dom
+}  // namespace mozilla
+
+#endif  // mozilla_dom_MIDIMessageEvent_h
diff --git a/dom/midi/MIDIMessageQueue.cpp b/dom/midi/MIDIMessageQueue.cpp
new file mode 100644
index 0000000000..3006b225c0
--- /dev/null
+++ b/dom/midi/MIDIMessageQueue.cpp
@@ -0,0 +1,73 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim:set ts=2 sw=2 sts=2 et cindent: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "MIDIMessageQueue.h"
+#include "mozilla/dom/MIDITypes.h"
+
+namespace mozilla::dom {
+
+MIDIMessageQueue::MIDIMessageQueue() : mMutex("MIDIMessageQueue::mMutex") {}
+
+class MIDIMessageTimestampComparator {
+ public:
+  bool Equals(const MIDIMessage& a, const MIDIMessage& b) const {
+    return a.timestamp() == b.timestamp();
+  }
+  bool LessThan(const MIDIMessage& a, const MIDIMessage& b) const {
+    return a.timestamp() < b.timestamp();
+  }
+};
+
+void MIDIMessageQueue::Add(nsTArray<MIDIMessage>& aMsg) {
+  MutexAutoLock lock(mMutex);
+  for (auto msg : aMsg) {
+    mMessageQueue.InsertElementSorted(msg, MIDIMessageTimestampComparator());
+  }
+}
+
+void MIDIMessageQueue::GetMessagesBefore(TimeStamp aTimestamp,
+                                         nsTArray<MIDIMessage>& aMsgQueue) {
+  MutexAutoLock lock(mMutex);
+  int i = 0;
+  for (auto msg : mMessageQueue) {
+    if (aTimestamp < msg.timestamp()) {
+      break;
+    }
+    aMsgQueue.AppendElement(msg);
+    i++;
+  }
+  if (i > 0) {
+    mMessageQueue.RemoveElementsAt(0, i);
+  }
+}
+
+void MIDIMessageQueue::GetMessages(nsTArray<MIDIMessage>& aMsgQueue) {
+  MutexAutoLock lock(mMutex);
+  aMsgQueue.AppendElements(mMessageQueue);
+  mMessageQueue.Clear();
+}
+
+void MIDIMessageQueue::Clear() {
+  MutexAutoLock lock(mMutex);
+  mMessageQueue.Clear();
+}
+
+void MIDIMessageQueue::ClearAfterNow() {
+  MutexAutoLock lock(mMutex);
+  TimeStamp now = TimeStamp::Now();
+  int i = 0;
+  for (auto msg : mMessageQueue) {
+    if (now < msg.timestamp()) {
+      break;
+    }
+    i++;
+  }
+  if (i > 0) {
+    mMessageQueue.RemoveElementsAt(0, i);
+  }
+}
+
+}  // namespace mozilla::dom
diff --git a/dom/midi/MIDIMessageQueue.h b/dom/midi/MIDIMessageQueue.h
new file mode 100644
index 0000000000..edee2fd19b
--- /dev/null
+++ b/dom/midi/MIDIMessageQueue.h
@@ -0,0 +1,58 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim:set ts=2 sw=2 sts=2 et cindent: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_dom_MIDIMessageQueue_h
+#define mozilla_dom_MIDIMessageQueue_h
+
+#include "mozilla/Mutex.h"
+#include "nsTArray.h"
+
+// XXX Avoid including this here by moving function implementations to the cpp
+// file.
+#include "mozilla/dom/MIDITypes.h"
+
+namespace mozilla {
+
+class TimeStamp;
+
+namespace dom {
+
+class MIDIMessage;
+
+/**
+ * Since some MIDI Messages can be scheduled to be sent in the future, the
+ * MIDIMessageQueue is responsible for making sure all MIDI messages are
+ * scheduled and sent in order.
+ */
+class MIDIMessageQueue {
+ public:
+  MIDIMessageQueue();
+  ~MIDIMessageQueue() = default;
+  // Adds an array of possibly out-of-order messages to our queue.
+  void Add(nsTArray<MIDIMessage>& aMsg);
+  // Retrieve all pending messages before the time specified.
+  void GetMessagesBefore(TimeStamp aTimestamp,
+                         nsTArray<MIDIMessage>& aMsgArray);
+  // Get all pending messages.
+  void GetMessages(nsTArray<MIDIMessage>& aMsgArray);
+  // Erase all pending messages.
+  void Clear();
+  // Erase all pending messages that would be sent in the future. Useful for
+  // when ports are closed, as we must send all messages with timestamps in the
+  // past.
+  void ClearAfterNow();
+
+ private:
+  // Array of messages to be sent.
+  nsTArray<MIDIMessage> mMessageQueue;
+  // Mutex for coordinating cross thread array access.
+  Mutex mMutex;
+};
+
+}  // namespace dom
+}  // namespace mozilla
+
+#endif  // mozilla_dom_MIDIMessageQueue_h
diff --git a/dom/midi/MIDIOutput.cpp b/dom/midi/MIDIOutput.cpp
new file mode 100644
index 0000000000..c7148e174c
--- /dev/null
+++ b/dom/midi/MIDIOutput.cpp
@@ -0,0 +1,100 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim:set ts=2 sw=2 sts=2 et cindent: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "mozilla/dom/MIDIOutput.h"
+#include "mozilla/dom/MIDIPortChild.h"
+#include "mozilla/dom/MIDITypes.h"
+#include "mozilla/dom/MIDIOutputBinding.h"
+#include "mozilla/dom/MIDIUtils.h"
+#include "nsDOMNavigationTiming.h"
+#include "mozilla/ErrorResult.h"
+#include "mozilla/TimeStamp.h"
+#include "mozilla/dom/Document.h"
+#include "mozilla/dom/Performance.h"
+
+using namespace mozilla;
+using namespace mozilla::dom;
+
+MIDIOutput::MIDIOutput(nsPIDOMWindowInner* aWindow,
+                       MIDIAccess* aMIDIAccessParent)
+    : MIDIPort(aWindow, aMIDIAccessParent) {}
+
+// static
+MIDIOutput* MIDIOutput::Create(nsPIDOMWindowInner* aWindow,
+                               MIDIAccess* aMIDIAccessParent,
+                               const MIDIPortInfo& aPortInfo,
+                               const bool aSysexEnabled) {
+  MOZ_ASSERT(static_cast<MIDIPortType>(aPortInfo.type()) ==
+             MIDIPortType::Output);
+  auto port = new MIDIOutput(aWindow, aMIDIAccessParent);
+  if (NS_WARN_IF(!port->Initialize(aPortInfo, aSysexEnabled))) {
+    return nullptr;
+  }
+  return port;
+}
+
+JSObject* MIDIOutput::WrapObject(JSContext* aCx,
+                                 JS::Handle<JSObject*> aGivenProto) {
+  return MIDIOutput_Binding::Wrap(aCx, this, aGivenProto);
+}
+
+void MIDIOutput::Send(const Sequence<uint8_t>& aData,
+                      const Optional<double>& aTimestamp, ErrorResult& aRv) {
+  if (mPort->DeviceState() == MIDIPortDeviceState::Disconnected) {
+    aRv.Throw(NS_ERROR_DOM_INVALID_STATE_ERR);
+    return;
+  }
+  // The timestamp passed to us is a DOMHighResTimestamp, which is in relation
+  // to the start of navigation timing. This needs to be turned into a
+  // TimeStamp before it hits the platform specific MIDI service.
+  //
+  // If timestamp is either not set or zero, set timestamp to now and send the
+  // message ASAP.
+  TimeStamp timestamp;
+  if (aTimestamp.WasPassed() && aTimestamp.Value() != 0) {
+    nsCOMPtr<Document> doc = GetOwner()->GetDoc();
+    if (!doc) {
+      aRv.Throw(NS_ERROR_DOM_INVALID_STATE_ERR);
+      return;
+    }
+    TimeDuration ts_diff = TimeDuration::FromMilliseconds(aTimestamp.Value());
+    timestamp = GetOwner()
+                    ->GetPerformance()
+                    ->GetDOMTiming()
+                    ->GetNavigationStartTimeStamp() +
+                ts_diff;
+  } else {
+    timestamp = TimeStamp::Now();
+  }
+
+  nsTArray<MIDIMessage> msgArray;
+  MIDIUtils::ParseMessages(aData, timestamp, msgArray);
+  // Our translation of the spec is that invalid messages in a multi-message
+  // sequence will be thrown out, but that valid messages will still be used.
+  if (msgArray.IsEmpty()) {
+    aRv.ThrowTypeError("Empty message array");
+    return;
+  }
+
+  // TODO Move this check back to parse message so we don't have to iterate
+  // twice.
+  if (!SysexEnabled()) {
+    for (auto& msg : msgArray) {
+      if (MIDIUtils::IsSysexMessage(msg)) {
+        aRv.Throw(NS_ERROR_DOM_INVALID_ACCESS_ERR);
+        return;
+      }
+    }
+  }
+  mPort->SendSend(msgArray);
+}
+
+void MIDIOutput::Clear() {
+  if (mPort->ConnectionState() == MIDIPortConnectionState::Closed) {
+    return;
+  }
+  mPort->SendClear();
+}
diff --git a/dom/midi/MIDIOutput.h b/dom/midi/MIDIOutput.h
new file mode 100644
index 0000000000..72d0efb55e
--- /dev/null
+++ b/dom/midi/MIDIOutput.h
@@ -0,0 +1,52 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim:set ts=2 sw=2 sts=2 et cindent: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_dom_MIDIOutput_h
+#define mozilla_dom_MIDIOutput_h
+
+#include "mozilla/dom/MIDIPort.h"
+#include "mozilla/Attributes.h"
+#include "nsWrapperCache.h"
+
+struct JSContext;
+
+namespace mozilla {
+class ErrorResult;
+
+namespace dom {
+
+class MIDIPortInfo;
+class MIDIMessage;
+
+/**
+ * Represents a MIDI Output Port, handles sending message to devices.
+ *
+ */
+class MIDIOutput final : public MIDIPort {
+ public:
+  static MIDIOutput* Create(nsPIDOMWindowInner* aWindow,
+                            MIDIAccess* aMIDIAccessParent,
+                            const MIDIPortInfo& aPortInfo,
+                            const bool aSysexEnabled);
+  ~MIDIOutput() = default;
+
+  JSObject* WrapObject(JSContext* aCx,
+                       JS::Handle<JSObject*> aGivenProto) override;
+
+  // Send a message to an output port
+  void Send(const Sequence<uint8_t>& aData, const Optional<double>& aTimestamp,
+            ErrorResult& aRv);
+  // Clear any partially sent messages from the send queue
+  void Clear();
+
+ private:
+  MIDIOutput(nsPIDOMWindowInner* aWindow, MIDIAccess* aMIDIAccessParent);
+};
+
+}  // namespace dom
+}  // namespace mozilla
+
+#endif  // mozilla_dom_MIDIOutput_h
diff --git a/dom/midi/MIDIOutputMap.cpp b/dom/midi/MIDIOutputMap.cpp
new file mode 100644
index 0000000000..d7840827f2
--- /dev/null
+++ b/dom/midi/MIDIOutputMap.cpp
@@ -0,0 +1,29 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this file,
+ * You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "mozilla/dom/MIDIOutputMap.h"
+#include "mozilla/dom/MIDIOutputMapBinding.h"
+#include "nsPIDOMWindow.h"
+#include "mozilla/dom/BindingUtils.h"
+
+namespace mozilla::dom {
+
+NS_IMPL_CYCLE_COLLECTION_WRAPPERCACHE(MIDIOutputMap, mParent)
+
+NS_IMPL_CYCLE_COLLECTING_ADDREF(MIDIOutputMap)
+NS_IMPL_CYCLE_COLLECTING_RELEASE(MIDIOutputMap)
+
+NS_INTERFACE_MAP_BEGIN_CYCLE_COLLECTION(MIDIOutputMap)
+  NS_WRAPPERCACHE_INTERFACE_MAP_ENTRY
+  NS_INTERFACE_MAP_ENTRY(nsISupports)
+NS_INTERFACE_MAP_END
+
+MIDIOutputMap::MIDIOutputMap(nsPIDOMWindowInner* aParent) : mParent(aParent) {}
+
+JSObject* MIDIOutputMap::WrapObject(JSContext* aCx,
+                                    JS::Handle<JSObject*> aGivenProto) {
+  return MIDIOutputMap_Binding::Wrap(aCx, this, aGivenProto);
+}
+
+}  // namespace mozilla::dom
diff --git a/dom/midi/MIDIOutputMap.h b/dom/midi/MIDIOutputMap.h
new file mode 100644
index 0000000000..16c8957669
--- /dev/null
+++ b/dom/midi/MIDIOutputMap.h
@@ -0,0 +1,43 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim:set ts=2 sw=2 sts=2 et cindent: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_dom_MIDIOutputMap_h
+#define mozilla_dom_MIDIOutputMap_h
+
+#include "nsCOMPtr.h"
+#include "nsWrapperCache.h"
+
+class nsPIDOMWindowInner;
+
+namespace mozilla {
+namespace dom {
+
+/**
+ * Maplike DOM object that holds a list of all MIDI output ports available for
+ * access. Almost all functions are implemented automatically by WebIDL.
+ *
+ */
+class MIDIOutputMap final : public nsISupports, public nsWrapperCache {
+ public:
+  NS_DECL_CYCLE_COLLECTING_ISUPPORTS
+  NS_DECL_CYCLE_COLLECTION_SCRIPT_HOLDER_CLASS(MIDIOutputMap)
+
+  explicit MIDIOutputMap(nsPIDOMWindowInner* aParent);
+
+  nsPIDOMWindowInner* GetParentObject() const { return mParent; }
+
+  JSObject* WrapObject(JSContext* aCx,
+                       JS::Handle<JSObject*> aGivenProto) override;
+
+ private:
+  ~MIDIOutputMap() = default;
+  nsCOMPtr<nsPIDOMWindowInner> mParent;
+};
+
+}  // namespace dom
+}  // namespace mozilla
+
+#endif  // mozilla_dom_MIDIOutputMap_h
diff --git a/dom/midi/MIDIPermissionRequest.cpp b/dom/midi/MIDIPermissionRequest.cpp
new file mode 100644
index 0000000000..a26c730aff
--- /dev/null
+++ b/dom/midi/MIDIPermissionRequest.cpp
@@ -0,0 +1,98 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim:set ts=2 sw=2 sts=2 et cindent: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this file,
+ * You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "mozilla/dom/MIDIPermissionRequest.h"
+#include "mozilla/dom/Document.h"
+#include "mozilla/dom/MIDIAccessManager.h"
+#include "mozilla/dom/MIDIOptionsBinding.h"
+#include "nsIGlobalObject.h"
+#include "mozilla/Preferences.h"
+#include "nsContentUtils.h"
+
+//-------------------------------------------------
+// MIDI Permission Requests
+//-------------------------------------------------
+
+using namespace mozilla::dom;
+
+NS_IMPL_CYCLE_COLLECTION_INHERITED(MIDIPermissionRequest,
+                                   ContentPermissionRequestBase, mPromise)
+
+NS_IMPL_QUERY_INTERFACE_CYCLE_COLLECTION_INHERITED(MIDIPermissionRequest,
+                                                   ContentPermissionRequestBase,
+                                                   nsIRunnable)
+
+NS_IMPL_ADDREF_INHERITED(MIDIPermissionRequest, ContentPermissionRequestBase)
+NS_IMPL_RELEASE_INHERITED(MIDIPermissionRequest, ContentPermissionRequestBase)
+
+MIDIPermissionRequest::MIDIPermissionRequest(nsPIDOMWindowInner* aWindow,
+                                             Promise* aPromise,
+                                             const MIDIOptions& aOptions)
+    : ContentPermissionRequestBase(
+          aWindow->GetDoc()->NodePrincipal(), aWindow,
+          ""_ns,  // We check prefs in a custom way here
+          "midi"_ns),
+      mPromise(aPromise),
+      mNeedsSysex(aOptions.mSysex) {
+  MOZ_ASSERT(aWindow);
+  MOZ_ASSERT(aPromise, "aPromise should not be null!");
+  MOZ_ASSERT(aWindow->GetDoc());
+  mPrincipal = aWindow->GetDoc()->NodePrincipal();
+  MOZ_ASSERT(mPrincipal);
+}
+
+NS_IMETHODIMP
+MIDIPermissionRequest::GetTypes(nsIArray** aTypes) {
+  NS_ENSURE_ARG_POINTER(aTypes);
+  nsTArray<nsString> options;
+  if (mNeedsSysex) {
+    options.AppendElement(u"sysex"_ns);
+  }
+  return nsContentPermissionUtils::CreatePermissionArray(mType, options,
+                                                         aTypes);
+}
+
+NS_IMETHODIMP
+MIDIPermissionRequest::Cancel() {
+  mPromise->MaybeReject(NS_ERROR_DOM_SECURITY_ERR);
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+MIDIPermissionRequest::Allow(JS::HandleValue aChoices) {
+  MOZ_ASSERT(aChoices.isUndefined());
+  MIDIAccessManager* mgr = MIDIAccessManager::Get();
+  mgr->CreateMIDIAccess(mWindow, mNeedsSysex, mPromise);
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+MIDIPermissionRequest::Run() {
+  // If the testing flag is true, skip dialog
+  if (Preferences::GetBool("midi.prompt.testing", false)) {
+    bool allow =
+        Preferences::GetBool("media.navigator.permission.disabled", false);
+    if (allow) {
+      Allow(JS::UndefinedHandleValue);
+    } else {
+      Cancel();
+    }
+    return NS_OK;
+  }
+
+  // If we already have sysex perms, allow.
+  if (nsContentUtils::IsExactSitePermAllow(mPrincipal, "midi-sysex"_ns)) {
+    Allow(JS::UndefinedHandleValue);
+    return NS_OK;
+  }
+
+  // If we have no perms, or only have midi and are asking for sysex, pop dialog
+  if (NS_FAILED(nsContentPermissionUtils::AskPermission(this, mWindow))) {
+    Cancel();
+    return NS_ERROR_FAILURE;
+  }
+  return NS_OK;
+}
diff --git a/dom/midi/MIDIPermissionRequest.h b/dom/midi/MIDIPermissionRequest.h
new file mode 100644
index 0000000000..558f14bcf0
--- /dev/null
+++ b/dom/midi/MIDIPermissionRequest.h
@@ -0,0 +1,48 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim:set ts=2 sw=2 sts=2 et cindent: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this file,
+ * You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_dom_MIDIPermissionRequest_h
+#define mozilla_dom_MIDIPermissionRequest_h
+
+#include "mozilla/dom/Promise.h"
+#include "nsContentPermissionHelper.h"
+
+namespace mozilla {
+namespace dom {
+
+struct MIDIOptions;
+
+/**
+ * Handles permission dialog management when requesting MIDI permissions.
+ */
+class MIDIPermissionRequest final : public ContentPermissionRequestBase,
+                                    public nsIRunnable {
+ public:
+  MIDIPermissionRequest(nsPIDOMWindowInner* aWindow, Promise* aPromise,
+                        const MIDIOptions& aOptions);
+
+  NS_DECL_ISUPPORTS_INHERITED
+  NS_DECL_NSIRUNNABLE
+  NS_DECL_CYCLE_COLLECTION_CLASS_INHERITED(MIDIPermissionRequest,
+                                           ContentPermissionRequestBase)
+  // nsIContentPermissionRequest
+  NS_IMETHOD Cancel(void) override;
+  NS_IMETHOD Allow(JS::HandleValue choices) override;
+  NS_IMETHOD GetTypes(nsIArray** aTypes) override;
+
+ private:
+  ~MIDIPermissionRequest() = default;
+
+  // Promise for returning MIDIAccess on request success
+  RefPtr<Promise> mPromise;
+  // True if sysex permissions should be requested
+  bool mNeedsSysex;
+};
+
+}  // namespace dom
+}  // namespace mozilla
+
+#endif  // mozilla_dom_MIDIPermissionRequest_h
diff --git a/dom/midi/MIDIPlatformRunnables.cpp b/dom/midi/MIDIPlatformRunnables.cpp
new file mode 100644
index 0000000000..debc555e74
--- /dev/null
+++ b/dom/midi/MIDIPlatformRunnables.cpp
@@ -0,0 +1,49 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim:set ts=2 sw=2 sts=2 et cindent: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "mozilla/dom/MIDIPlatformRunnables.h"
+#include "mozilla/dom/MIDIPlatformService.h"
+#include "mozilla/dom/MIDIPortParent.h"
+#include "mozilla/ipc/BackgroundParent.h"
+
+namespace mozilla::dom {
+
+NS_IMETHODIMP
+MIDIBackgroundRunnable::Run() {
+  ::mozilla::ipc::AssertIsOnBackgroundThread();
+  if (!MIDIPlatformService::IsRunning()) {
+    return NS_OK;
+  }
+  RunInternal();
+  return NS_OK;
+}
+
+void ReceiveRunnable::RunInternal() {
+  MIDIPlatformService::Get()->CheckAndReceive(mPortId, mMsgs);
+}
+
+void AddPortRunnable::RunInternal() {
+  MIDIPlatformService::Get()->AddPortInfo(mPortInfo);
+}
+
+void RemovePortRunnable::RunInternal() {
+  MIDIPlatformService::Get()->RemovePortInfo(mPortInfo);
+}
+
+void SetStatusRunnable::RunInternal() {
+  MIDIPlatformService::Get()->UpdateStatus(mPortId, mState, mConnection);
+}
+
+void SendPortListRunnable::RunInternal() {
+  // Unlike other runnables, SendPortListRunnable should just exit quietly if
+  // the service has died.
+  if (!MIDIPlatformService::IsRunning()) {
+    return;
+  }
+  MIDIPlatformService::Get()->SendPortList();
+}
+
+}  // namespace mozilla::dom
diff --git a/dom/midi/MIDIPlatformRunnables.h b/dom/midi/MIDIPlatformRunnables.h
new file mode 100644
index 0000000000..0a5e1d0583
--- /dev/null
+++ b/dom/midi/MIDIPlatformRunnables.h
@@ -0,0 +1,127 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim:set ts=2 sw=2 sts=2 et cindent: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_dom_MIDIPlatformRunnables_h
+#define mozilla_dom_MIDIPlatformRunnables_h
+
+#include "mozilla/dom/MIDITypes.h"
+
+namespace mozilla {
+namespace dom {
+
+enum class MIDIPortConnectionState : uint8_t;
+enum class MIDIPortDeviceState : uint8_t;
+
+class MIDIPortParent;
+class MIDIMessage;
+class MIDIPortInfo;
+
+/**
+ * Base class for runnables to be fired to the platform-specific MIDI service
+ * thread in PBackground.
+ */
+class MIDIBackgroundRunnable : public Runnable {
+ public:
+  MIDIBackgroundRunnable(const char* aName) : Runnable(aName) {}
+  virtual ~MIDIBackgroundRunnable() = default;
+  NS_IMETHOD Run() override;
+  virtual void RunInternal() = 0;
+};
+
+/**
+ * Runnable fired from platform-specific MIDI service thread to PBackground
+ * Thread whenever messages need to be sent to a MIDI device.
+ *
+ */
+class ReceiveRunnable final : public MIDIBackgroundRunnable {
+ public:
+  ReceiveRunnable(const nsAString& aPortId, const nsTArray<MIDIMessage>& aMsgs)
+      : MIDIBackgroundRunnable("ReceiveRunnable"),
+        mMsgs(aMsgs.Clone()),
+        mPortId(aPortId) {}
+  // Used in tests
+  ReceiveRunnable(const nsAString& aPortId, const MIDIMessage& aMsgs)
+      : MIDIBackgroundRunnable("ReceiveRunnable"), mPortId(aPortId) {
+    mMsgs.AppendElement(aMsgs);
+  }
+  ~ReceiveRunnable() = default;
+  void RunInternal() override;
+
+ private:
+  nsTArray<MIDIMessage> mMsgs;
+  nsString mPortId;
+};
+
+/**
+ * Runnable fired from platform-specific MIDI service thread to PBackground
+ * Thread whenever a device is connected.
+ *
+ */
+class AddPortRunnable final : public MIDIBackgroundRunnable {
+ public:
+  explicit AddPortRunnable(const MIDIPortInfo& aPortInfo)
+      : MIDIBackgroundRunnable("AddPortRunnable"), mPortInfo(aPortInfo) {}
+  ~AddPortRunnable() = default;
+  void RunInternal() override;
+
+ private:
+  MIDIPortInfo mPortInfo;
+};
+
+/**
+ * Runnable fired from platform-specific MIDI service thread to PBackground
+ * Thread whenever a device is disconnected.
+ *
+ */
+class RemovePortRunnable final : public MIDIBackgroundRunnable {
+ public:
+  explicit RemovePortRunnable(const MIDIPortInfo& aPortInfo)
+      : MIDIBackgroundRunnable("RemovePortRunnable"), mPortInfo(aPortInfo) {}
+  ~RemovePortRunnable() = default;
+  void RunInternal() override;
+
+ private:
+  MIDIPortInfo mPortInfo;
+};
+
+/**
+ * Runnable used to delay calls to SendPortList, which is requires to make sure
+ * MIDIManager actor initialization happens correctly. Also used for testing.
+ *
+ */
+class SendPortListRunnable final : public MIDIBackgroundRunnable {
+ public:
+  SendPortListRunnable() : MIDIBackgroundRunnable("SendPortListRunnable") {}
+  ~SendPortListRunnable() = default;
+  void RunInternal() override;
+};
+
+/**
+ * Runnable fired from platform-specific MIDI service thread to PBackground
+ * Thread whenever a device is disconnected.
+ *
+ */
+class SetStatusRunnable final : public MIDIBackgroundRunnable {
+ public:
+  SetStatusRunnable(const nsAString& aPortId, MIDIPortDeviceState aState,
+                    MIDIPortConnectionState aConnection)
+      : MIDIBackgroundRunnable("SetStatusRunnable"),
+        mPortId(aPortId),
+        mState(aState),
+        mConnection(aConnection) {}
+  ~SetStatusRunnable() = default;
+  void RunInternal() override;
+
+ private:
+  nsString mPortId;
+  MIDIPortDeviceState mState;
+  MIDIPortConnectionState mConnection;
+};
+
+}  // namespace dom
+}  // namespace mozilla
+
+#endif  // mozilla_dom_MIDIPlatformRunnables_h
diff --git a/dom/midi/MIDIPlatformService.cpp b/dom/midi/MIDIPlatformService.cpp
new file mode 100644
index 0000000000..940cdf8541
--- /dev/null
+++ b/dom/midi/MIDIPlatformService.cpp
@@ -0,0 +1,261 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim:set ts=2 sw=2 sts=2 et cindent: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "MIDIPlatformService.h"
+#include "MIDIMessageQueue.h"
+#include "TestMIDIPlatformService.h"
+#include "mozilla/ErrorResult.h"
+#include "mozilla/StaticPtr.h"
+#include "mozilla/Unused.h"
+#include "mozilla/dom/MIDIManagerParent.h"
+#include "mozilla/dom/MIDIPlatformRunnables.h"
+#include "mozilla/dom/MIDIUtils.h"
+#include "mozilla/dom/PMIDIManagerParent.h"
+#include "mozilla/ipc/BackgroundParent.h"
+#include "mozilla/dom/MIDIPortParent.h"
+
+using namespace mozilla;
+using namespace mozilla::dom;
+
+MIDIPlatformService::MIDIPlatformService()
+    : mHasSentPortList(false),
+      mMessageQueueMutex("MIDIPlatformServce::mMessageQueueMutex") {}
+
+MIDIPlatformService::~MIDIPlatformService() = default;
+
+void MIDIPlatformService::CheckAndReceive(const nsAString& aPortId,
+                                          const nsTArray<MIDIMessage>& aMsgs) {
+  ::mozilla::ipc::AssertIsOnBackgroundThread();
+  for (auto& port : mPorts) {
+    // TODO Clean this up when we split input/output port arrays
+    if (port->MIDIPortInterface::Id() != aPortId ||
+        port->Type() != MIDIPortType::Input ||
+        port->ConnectionState() != MIDIPortConnectionState::Open) {
+      continue;
+    }
+    if (!port->SysexEnabled()) {
+      nsTArray<MIDIMessage> msgs;
+      for (auto& msg : aMsgs) {
+        if (!MIDIUtils::IsSysexMessage(msg)) {
+          msgs.AppendElement(msg);
+        }
+      }
+      Unused << port->SendReceive(msgs);
+    } else {
+      Unused << port->SendReceive(aMsgs);
+    }
+  }
+}
+
+void MIDIPlatformService::AddPort(MIDIPortParent* aPort) {
+  MOZ_ASSERT(aPort);
+  ::mozilla::ipc::AssertIsOnBackgroundThread();
+  mPorts.AppendElement(aPort);
+}
+
+void MIDIPlatformService::RemovePort(MIDIPortParent* aPort) {
+  // This should only be called from the background thread, when a MIDIPort
+  // actor has been destroyed.
+  ::mozilla::ipc::AssertIsOnBackgroundThread();
+  MOZ_ASSERT(aPort);
+  mPorts.RemoveElement(aPort);
+  MaybeStop();
+}
+
+void MIDIPlatformService::BroadcastState(const MIDIPortInfo& aPortInfo,
+                                         const MIDIPortDeviceState& aState) {
+  ::mozilla::ipc::AssertIsOnBackgroundThread();
+  for (auto& p : mPorts) {
+    if (p->MIDIPortInterface::Id() == aPortInfo.id() &&
+        p->DeviceState() != aState) {
+      p->SendUpdateStatus(aState, p->ConnectionState());
+    }
+  }
+}
+
+void MIDIPlatformService::QueueMessages(const nsAString& aId,
+                                        nsTArray<MIDIMessage>& aMsgs) {
+  ::mozilla::ipc::AssertIsOnBackgroundThread();
+  {
+    MutexAutoLock lock(mMessageQueueMutex);
+    MIDIMessageQueue* msgQueue = mMessageQueues.LookupOrAdd(aId);
+    msgQueue->Add(aMsgs);
+    ScheduleSend(aId);
+  }
+}
+
+void MIDIPlatformService::SendPortList() {
+  ::mozilla::ipc::AssertIsOnBackgroundThread();
+  mHasSentPortList = true;
+  MIDIPortList l;
+  for (auto& el : mPortInfo) {
+    l.ports().AppendElement(el);
+  }
+  for (auto& mgr : mManagers) {
+    Unused << mgr->SendMIDIPortListUpdate(l);
+  }
+}
+
+void MIDIPlatformService::Clear(MIDIPortParent* aPort) {
+  ::mozilla::ipc::AssertIsOnBackgroundThread();
+  MOZ_ASSERT(aPort);
+  {
+    MutexAutoLock lock(mMessageQueueMutex);
+    MIDIMessageQueue* msgQueue =
+        mMessageQueues.Get(aPort->MIDIPortInterface::Id());
+    if (msgQueue) {
+      msgQueue->Clear();
+    }
+  }
+}
+
+void MIDIPlatformService::AddPortInfo(MIDIPortInfo& aPortInfo) {
+  ::mozilla::ipc::AssertIsOnBackgroundThread();
+  MOZ_ASSERT(XRE_IsParentProcess());
+
+  mPortInfo.AppendElement(aPortInfo);
+
+  // ORDER MATTERS HERE.
+  //
+  // When MIDI hardware is disconnected, all open MIDIPort objects revert to a
+  // "pending" state, and they are removed from the port maps of MIDIAccess
+  // objects. We need to send connection updates to all living ports first, THEN
+  // we can send port list updates to all of the live MIDIAccess objects. We
+  // have to go in this order because if a port object is still held live but is
+  // disconnected, it needs to readd itself to its originating MIDIAccess
+  // object. Running SendPortList first would cause MIDIAccess to create a new
+  // MIDIPort object, which would conflict (i.e. old disconnected object != new
+  // object in port map, which is against spec).
+  for (auto& port : mPorts) {
+    if (port->MIDIPortInterface::Id() == aPortInfo.id()) {
+      port->SendUpdateStatus(MIDIPortDeviceState::Connected,
+                             port->ConnectionState());
+    }
+  }
+  if (mHasSentPortList) {
+    SendPortList();
+  }
+}
+
+void MIDIPlatformService::RemovePortInfo(MIDIPortInfo& aPortInfo) {
+  ::mozilla::ipc::AssertIsOnBackgroundThread();
+  mPortInfo.RemoveElement(aPortInfo);
+  BroadcastState(aPortInfo, MIDIPortDeviceState::Disconnected);
+  if (mHasSentPortList) {
+    SendPortList();
+  }
+}
+
+StaticRefPtr<MIDIPlatformService> gMIDIPlatformService;
+
+// static
+bool MIDIPlatformService::IsRunning() {
+  return gMIDIPlatformService != nullptr;
+}
+
+void MIDIPlatformService::Close(mozilla::dom::MIDIPortParent* aPort) {
+  ::mozilla::ipc::AssertIsOnBackgroundThread();
+  {
+    MutexAutoLock lock(mMessageQueueMutex);
+    MIDIMessageQueue* msgQueue =
+        mMessageQueues.Get(aPort->MIDIPortInterface::Id());
+    if (msgQueue) {
+      msgQueue->ClearAfterNow();
+    }
+  }
+  // Send all messages before sending a close request
+  ScheduleSend(aPort->MIDIPortInterface::Id());
+  // TODO We should probably have the send function schedule closing
+  ScheduleClose(aPort);
+}
+
+// static
+MIDIPlatformService* MIDIPlatformService::Get() {
+  // We should never touch the platform service in a child process.
+  MOZ_ASSERT(XRE_IsParentProcess());
+  ::mozilla::ipc::AssertIsOnBackgroundThread();
+  if (!IsRunning()) {
+    ErrorResult rv;
+    // Uncomment once we have an actual platform library to test.
+    //
+    // bool useTestService = false;
+    // rv = Preferences::GetRootBranch()->GetBoolPref("midi.testing",
+    // &useTestService);
+    gMIDIPlatformService = new TestMIDIPlatformService();
+    gMIDIPlatformService->Init();
+  }
+  return gMIDIPlatformService;
+}
+
+void MIDIPlatformService::MaybeStop() {
+  ::mozilla::ipc::AssertIsOnBackgroundThread();
+  if (!IsRunning()) {
+    // Service already stopped or never started. Exit.
+    return;
+  }
+  // If we have any ports or managers left, we should still be alive.
+  if (!mPorts.IsEmpty() || !mManagers.IsEmpty()) {
+    return;
+  }
+  Stop();
+  gMIDIPlatformService = nullptr;
+}
+
+void MIDIPlatformService::AddManager(MIDIManagerParent* aManager) {
+  ::mozilla::ipc::AssertIsOnBackgroundThread();
+  mManagers.AppendElement(aManager);
+  // Managers add themselves during construction. We have to wait for the
+  // protocol construction to finish before we send them a port list. The
+  // runnable calls SendPortList, which iterates through the live manager list,
+  // so this saves us from having to worry about Manager pointer validity at
+  // time of runnable execution.
+  nsCOMPtr<nsIRunnable> r(new SendPortListRunnable());
+  NS_DispatchToCurrentThread(r);
+}
+
+void MIDIPlatformService::RemoveManager(MIDIManagerParent* aManager) {
+  ::mozilla::ipc::AssertIsOnBackgroundThread();
+  mManagers.RemoveElement(aManager);
+  MaybeStop();
+}
+
+void MIDIPlatformService::UpdateStatus(
+    const nsAString& aPortId, const MIDIPortDeviceState& aDeviceState,
+    const MIDIPortConnectionState& aConnectionState) {
+  ::mozilla::ipc::AssertIsOnBackgroundThread();
+  for (auto port : mPorts) {
+    if (port->MIDIPortInterface::Id() == aPortId) {
+      port->SendUpdateStatus(aDeviceState, aConnectionState);
+    }
+  }
+}
+
+void MIDIPlatformService::GetMessages(const nsAString& aPortId,
+                                      nsTArray<MIDIMessage>& aMsgs) {
+  // Can run on either background thread or platform specific IO Thread.
+  {
+    MutexAutoLock lock(mMessageQueueMutex);
+    MIDIMessageQueue* msgQueue;
+    if (!mMessageQueues.Get(aPortId, &msgQueue)) {
+      return;
+    }
+    msgQueue->GetMessages(aMsgs);
+  }
+}
+
+void MIDIPlatformService::GetMessagesBefore(const nsAString& aPortId,
+                                            const TimeStamp& aTimeStamp,
+                                            nsTArray<MIDIMessage>& aMsgs) {
+  // Can run on either background thread or platform specific IO Thread.
+  {
+    MutexAutoLock lock(mMessageQueueMutex);
+    MIDIMessageQueue* msgQueue;
+    if (!mMessageQueues.Get(aPortId, &msgQueue)) {
+      return;
+    }
+    msgQueue->GetMessagesBefore(aTimeStamp, aMsgs);
+  }
+}
diff --git a/dom/midi/MIDIPlatformService.h b/dom/midi/MIDIPlatformService.h
new file mode 100644
index 0000000000..74ca04b3b8
--- /dev/null
+++ b/dom/midi/MIDIPlatformService.h
@@ -0,0 +1,162 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim:set ts=2 sw=2 sts=2 et cindent: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_dom_MIDIPlatformService_h
+#define mozilla_dom_MIDIPlatformService_h
+
+#include "nsClassHashtable.h"
+#include "mozilla/Mutex.h"
+#include "mozilla/dom/MIDIPortBinding.h"
+#include "nsHashKeys.h"
+
+// XXX Avoid including this here by moving function implementations to the cpp
+// file.
+#include "mozilla/dom/MIDIMessageQueue.h"
+
+namespace mozilla {
+namespace dom {
+
+class MIDIManagerParent;
+class MIDIPortParent;
+class MIDIMessage;
+class MIDIMessageQueue;
+class MIDIPortInfo;
+
+/**
+ * Base class for platform specific MIDI implementations. Handles aggregation of
+ * IPC service objects, as well as sending/receiving updates about port
+ * connection events and messages.
+ *
+ */
+class MIDIPlatformService {
+ public:
+  NS_INLINE_DECL_REFCOUNTING(MIDIPlatformService);
+  // Adds info about MIDI Port that has been connected.
+  void AddPortInfo(MIDIPortInfo& aPortInfo);
+
+  // Removes info of MIDI Port that has been disconnected.
+  void RemovePortInfo(MIDIPortInfo& aPortInfo);
+
+  // Adds a newly created manager protocol object to manager array.
+  void AddManager(MIDIManagerParent* aParent);
+
+  // Removes a deleted manager protocol object from manager array.
+  void RemoveManager(MIDIManagerParent* aParent);
+
+  // Adds a newly created port protocol object to port array.
+  void AddPort(MIDIPortParent* aPort);
+
+  // Removes a deleted port protocol object from port array.
+  void RemovePort(MIDIPortParent* aPort);
+
+  // Platform specific init function.
+  virtual void Init() = 0;
+
+  // Platform specific MIDI port opening function.
+  virtual void Open(MIDIPortParent* aPort) = 0;
+
+  // Clears all queued MIDI messages for a port.
+  void Clear(MIDIPortParent* aPort);
+
+  // Puts in a request to destroy the singleton MIDIPlatformService object.
+  // Object will only be destroyed if there are no more MIDIManager and MIDIPort
+  // protocols left to communicate with.
+  void MaybeStop();
+
+  // True if service is live.
+  static bool IsRunning();
+
+  // Returns a pointer to the MIDIPlatformService object, creating it and
+  // starting the platform specific service if it is not currently running.
+  static MIDIPlatformService* Get();
+
+  // Sends a list of all currently connected ports in order to populate a new
+  // MIDIAccess object.
+  void SendPortList();
+
+  // Receives a new set of messages from an MIDI Input Port, and checks their
+  // validity.
+  void CheckAndReceive(const nsAString& aPortID,
+                       const nsTArray<MIDIMessage>& aMsgs);
+
+  // Sends connection/disconnect/open/closed/etc status updates about a MIDI
+  // Port to all port listeners.
+  void UpdateStatus(MIDIPortParent* aPort,
+                    const MIDIPortDeviceState& aDeviceState,
+                    const MIDIPortConnectionState& aConnectionState);
+  void UpdateStatus(const nsAString& aPortId,
+                    const MIDIPortDeviceState& aDeviceState,
+                    const MIDIPortConnectionState& aConnectionState);
+
+  // Adds outgoing messages to the sorted message queue, for sending later.
+  void QueueMessages(const nsAString& aId, nsTArray<MIDIMessage>& aMsgs);
+
+  // Clears all messages later than now, sends all outgoing message scheduled
+  // before/at now, and schedules MIDI Port connection closing.
+  void Close(MIDIPortParent* aPort);
+
+ protected:
+  MIDIPlatformService();
+  virtual ~MIDIPlatformService();
+  // Platform specific MIDI service shutdown method.
+  virtual void Stop() = 0;
+
+  // When device state of a MIDI Port changes, broadcast to all IPC port
+  // objects.
+  void BroadcastState(const MIDIPortInfo& aPortInfo,
+                      const MIDIPortDeviceState& aState);
+
+  // Platform specific MIDI port closing function. Named "Schedule" due to the
+  // fact that it needs to happen in the context of the I/O thread for the
+  // platform MIDI implementation, and therefore will happen async.
+  virtual void ScheduleClose(MIDIPortParent* aPort) = 0;
+
+  // Platform specific MIDI message sending function. Named "Schedule" due to
+  // the fact that it needs to happen in the context of the I/O thread for the
+  // platform MIDI implementation, and therefore will happen async.
+  virtual void ScheduleSend(const nsAString& aPortId) = 0;
+
+  // Allows platform specific IO Threads to retrieve all messages to be sent.
+  // Handles mutex locking.
+  void GetMessages(const nsAString& aPortId, nsTArray<MIDIMessage>& aMsgs);
+
+  // Allows platform specific IO Threads to retrieve all messages to be sent
+  // before a certain timestamp. Handles mutex locking.
+  void GetMessagesBefore(const nsAString& aPortId, const TimeStamp& aTimeStamp,
+                         nsTArray<MIDIMessage>& aMsgs);
+
+ private:
+  // When the MIDIPlatformService is created, we need to know whether or not the
+  // corresponding IPC MIDIManager objects have received the MIDIPort list after
+  // it is populated. This is set to True when that is done, so we don't
+  // constantly spam MIDIManagers with port lists.
+  bool mHasSentPortList;
+
+  // Array of MIDIManager IPC objects. This array manages the lifetime of
+  // MIDIManager objects in the parent process, and IPC will call
+  // RemoveManager() end lifetime when IPC channel is destroyed.
+  nsTArray<RefPtr<MIDIManagerParent>> mManagers;
+
+  // Array of information for currently connected Ports
+  nsTArray<MIDIPortInfo> mPortInfo;
+
+  // Array of MIDIPort IPC objects. May contain ports not listed in mPortInfo,
+  // as we can hold port objects even after they are disconnected.
+  //
+  // TODO Split this into input and output ports. Will make life easier.
+  nsTArray<RefPtr<MIDIPortParent>> mPorts;
+
+  // Per-port message queue hashtable. Handles scheduling messages for sending.
+  nsClassHashtable<nsStringHashKey, MIDIMessageQueue> mMessageQueues;
+
+  // Mutex for managing access to message queue objects.
+  Mutex mMessageQueueMutex;
+};
+
+}  // namespace dom
+}  // namespace mozilla
+
+#endif  // mozilla_dom_MIDIPlatformService_h
diff --git a/dom/midi/MIDIPort.cpp b/dom/midi/MIDIPort.cpp
new file mode 100644
index 0000000000..662c7ca7b1
--- /dev/null
+++ b/dom/midi/MIDIPort.cpp
@@ -0,0 +1,197 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim:set ts=2 sw=2 sts=2 et cindent: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "mozilla/dom/MIDIPort.h"
+#include "mozilla/dom/MIDIConnectionEvent.h"
+#include "mozilla/dom/MIDIPortChild.h"
+#include "mozilla/dom/MIDIAccess.h"
+#include "mozilla/dom/MIDITypes.h"
+#include "mozilla/ipc/PBackgroundChild.h"
+#include "mozilla/ipc/BackgroundChild.h"
+#include "mozilla/dom/Promise.h"
+#include "mozilla/dom/MIDITypes.h"
+#include "mozilla/Unused.h"
+#include "nsISupportsImpl.h"  // for MOZ_COUNT_CTOR, MOZ_COUNT_DTOR
+
+using namespace mozilla::ipc;
+
+namespace mozilla::dom {
+
+NS_IMPL_CYCLE_COLLECTION_INHERITED(MIDIPort, DOMEventTargetHelper,
+                                   mOpeningPromise, mClosingPromise)
+
+NS_IMPL_CYCLE_COLLECTION_TRACE_BEGIN_INHERITED(MIDIPort, DOMEventTargetHelper)
+NS_IMPL_CYCLE_COLLECTION_TRACE_END
+
+NS_INTERFACE_MAP_BEGIN_CYCLE_COLLECTION(MIDIPort)
+  NS_WRAPPERCACHE_INTERFACE_MAP_ENTRY
+NS_INTERFACE_MAP_END_INHERITING(DOMEventTargetHelper)
+
+NS_IMPL_ADDREF_INHERITED(MIDIPort, DOMEventTargetHelper)
+NS_IMPL_RELEASE_INHERITED(MIDIPort, DOMEventTargetHelper)
+
+MIDIPort::MIDIPort(nsPIDOMWindowInner* aWindow, MIDIAccess* aMIDIAccessParent)
+    : DOMEventTargetHelper(aWindow), mMIDIAccessParent(aMIDIAccessParent) {
+  MOZ_ASSERT(aWindow);
+  MOZ_ASSERT(aMIDIAccessParent);
+}
+
+MIDIPort::~MIDIPort() {
+  if (mMIDIAccessParent) {
+    mMIDIAccessParent->RemovePortListener(this);
+    mMIDIAccessParent = nullptr;
+  }
+  if (mPort) {
+    // If the IPC port channel is still alive at this point, it means we're
+    // probably CC'ing this port object. Send the shutdown message to also clean
+    // up the IPC channel.
+    mPort->SendShutdown();
+    // This will unset the IPC Port pointer. Don't call anything after this.
+    mPort->Teardown();
+  }
+}
+
+bool MIDIPort::Initialize(const MIDIPortInfo& aPortInfo, bool aSysexEnabled) {
+  RefPtr<MIDIPortChild> port =
+      new MIDIPortChild(aPortInfo, aSysexEnabled, this);
+  PBackgroundChild* b = BackgroundChild::GetForCurrentThread();
+  MOZ_ASSERT(b,
+             "Should always have a valid BackgroundChild when creating a port "
+             "object!");
+  if (!b->SendPMIDIPortConstructor(port, aPortInfo, aSysexEnabled)) {
+    return false;
+  }
+  mPort = port;
+  // Make sure to increase the ref count for the port, so it can be cleaned up
+  // by the IPC manager.
+  mPort->SetActorAlive();
+  return true;
+}
+
+void MIDIPort::UnsetIPCPort() { mPort = nullptr; }
+
+void MIDIPort::GetId(nsString& aRetVal) const {
+  MOZ_ASSERT(mPort);
+  aRetVal = mPort->MIDIPortInterface::Id();
+}
+
+void MIDIPort::GetManufacturer(nsString& aRetVal) const {
+  MOZ_ASSERT(mPort);
+  aRetVal = mPort->Manufacturer();
+}
+
+void MIDIPort::GetName(nsString& aRetVal) const {
+  MOZ_ASSERT(mPort);
+  aRetVal = mPort->Name();
+}
+
+void MIDIPort::GetVersion(nsString& aRetVal) const {
+  MOZ_ASSERT(mPort);
+  aRetVal = mPort->Version();
+}
+
+MIDIPortType MIDIPort::Type() const {
+  MOZ_ASSERT(mPort);
+  return mPort->Type();
+}
+
+MIDIPortConnectionState MIDIPort::Connection() const {
+  MOZ_ASSERT(mPort);
+  return mPort->ConnectionState();
+}
+
+MIDIPortDeviceState MIDIPort::State() const {
+  MOZ_ASSERT(mPort);
+  return mPort->DeviceState();
+}
+
+bool MIDIPort::SysexEnabled() const {
+  MOZ_ASSERT(mPort);
+  return mPort->SysexEnabled();
+}
+
+already_AddRefed<Promise> MIDIPort::Open() {
+  MOZ_ASSERT(mPort);
+  RefPtr<Promise> p;
+  if (mOpeningPromise) {
+    p = mOpeningPromise;
+    return p.forget();
+  }
+  ErrorResult rv;
+  nsCOMPtr<nsIGlobalObject> go = do_QueryInterface(GetOwner());
+  p = Promise::Create(go, rv);
+  if (rv.Failed()) {
+    return nullptr;
+  }
+  mOpeningPromise = p;
+  mPort->SendOpen();
+  return p.forget();
+}
+
+already_AddRefed<Promise> MIDIPort::Close() {
+  MOZ_ASSERT(mPort);
+  RefPtr<Promise> p;
+  if (mClosingPromise) {
+    p = mClosingPromise;
+    return p.forget();
+  }
+  ErrorResult rv;
+  nsCOMPtr<nsIGlobalObject> go = do_QueryInterface(GetOwner());
+  p = Promise::Create(go, rv);
+  if (rv.Failed()) {
+    return nullptr;
+  }
+  mClosingPromise = p;
+  mPort->SendClose();
+  return p.forget();
+}
+
+void MIDIPort::Notify(const void_t& aVoid) {
+  // If we're getting notified, it means the MIDIAccess parent object is dead.
+  // Nullify our copy.
+  mMIDIAccessParent = nullptr;
+}
+
+void MIDIPort::FireStateChangeEvent() {
+  MOZ_ASSERT(mPort);
+  if (mPort->ConnectionState() == MIDIPortConnectionState::Open ||
+      mPort->ConnectionState() == MIDIPortConnectionState::Pending) {
+    if (mOpeningPromise) {
+      mOpeningPromise->MaybeResolve(this);
+      mOpeningPromise = nullptr;
+    }
+  } else if (mPort->ConnectionState() == MIDIPortConnectionState::Closed) {
+    if (mOpeningPromise) {
+      mOpeningPromise->MaybeReject(NS_ERROR_DOM_INVALID_ACCESS_ERR);
+      mOpeningPromise = nullptr;
+    }
+    if (mClosingPromise) {
+      mClosingPromise->MaybeResolve(this);
+      mClosingPromise = nullptr;
+    }
+  }
+  if (mPort->DeviceState() == MIDIPortDeviceState::Connected &&
+      mPort->ConnectionState() == MIDIPortConnectionState::Pending) {
+    mPort->SendOpen();
+  }
+  // Fire MIDIAccess events first so that the port is no longer in the port
+  // maps.
+  if (mMIDIAccessParent) {
+    mMIDIAccessParent->FireConnectionEvent(this);
+  }
+
+  MIDIConnectionEventInit init;
+  init.mPort = this;
+  RefPtr<MIDIConnectionEvent> event(
+      MIDIConnectionEvent::Constructor(this, u"statechange"_ns, init));
+  DispatchTrustedEvent(event);
+}
+
+void MIDIPort::Receive(const nsTArray<MIDIMessage>& aMsg) {
+  MOZ_CRASH("We should never get here!");
+}
+
+}  // namespace mozilla::dom
diff --git a/dom/midi/MIDIPort.h b/dom/midi/MIDIPort.h
new file mode 100644
index 0000000000..1d12030a71
--- /dev/null
+++ b/dom/midi/MIDIPort.h
@@ -0,0 +1,97 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim:set ts=2 sw=2 sts=2 et cindent: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_dom_MIDIPort_h
+#define mozilla_dom_MIDIPort_h
+
+#include "nsWrapperCache.h"
+#include "mozilla/Attributes.h"
+#include "mozilla/Observer.h"
+#include "mozilla/DOMEventTargetHelper.h"
+#include "mozilla/dom/MIDIAccess.h"
+#include "mozilla/dom/MIDIPortInterface.h"
+
+struct JSContext;
+
+namespace mozilla {
+namespace dom {
+
+class Promise;
+class MIDIPortInfo;
+class MIDIAccess;
+class MIDIPortChangeEvent;
+class MIDIPortChild;
+class MIDIMessage;
+
+/**
+ * Implementation of WebIDL DOM MIDIPort class. Handles all port representation
+ * and communication.
+ *
+ */
+class MIDIPort : public DOMEventTargetHelper,
+                 public MIDIAccessDestructionObserver {
+ public:
+  NS_DECL_ISUPPORTS_INHERITED
+  NS_DECL_CYCLE_COLLECTION_SCRIPT_HOLDER_CLASS_INHERITED(MIDIPort,
+                                                         DOMEventTargetHelper)
+ protected:
+  MIDIPort(nsPIDOMWindowInner* aWindow, MIDIAccess* aMIDIAccessParent);
+  bool Initialize(const MIDIPortInfo& aPortInfo, bool aSysexEnabled);
+  virtual ~MIDIPort();
+
+ public:
+  nsPIDOMWindowInner* GetParentObject() const { return GetOwner(); }
+
+  // Getters
+  void GetId(nsString& aRetVal) const;
+  void GetManufacturer(nsString& aRetVal) const;
+  void GetName(nsString& aRetVal) const;
+  void GetVersion(nsString& aRetVal) const;
+  MIDIPortType Type() const;
+  MIDIPortConnectionState Connection() const;
+  MIDIPortDeviceState State() const;
+  bool SysexEnabled() const;
+
+  already_AddRefed<Promise> Open();
+  already_AddRefed<Promise> Close();
+
+  // MIDIPorts observe the death of their parent MIDIAccess object, and delete
+  // their reference accordingly.
+  virtual void Notify(const void_t& aVoid) override;
+
+  void FireStateChangeEvent();
+
+  virtual void Receive(const nsTArray<MIDIMessage>& aMsg);
+
+  // This object holds a pointer to its corresponding IPC MIDIPortChild actor.
+  // If the IPC actor is deleted, it cleans itself up via this method.
+  void UnsetIPCPort();
+
+  IMPL_EVENT_HANDLER(statechange)
+ protected:
+  // IPC Actor corresponding to this class
+  RefPtr<MIDIPortChild> mPort;
+
+ private:
+  // MIDIAccess object that created this MIDIPort object, which we need for
+  // firing port connection events. There is a chance this MIDIPort object can
+  // outlive its parent MIDIAccess object, so this is a weak reference that must
+  // be handled properly. It is set on construction of the MIDIPort object, and
+  // set to null when the parent MIDIAccess object is destroyed, which fires an
+  // notification we observe.
+  MIDIAccess* mMIDIAccessParent;
+  // Promise object generated on Open() call, that needs to be resolved once the
+  // platform specific Open() function has completed.
+  RefPtr<Promise> mOpeningPromise;
+  // Promise object generated on Close() call, that needs to be resolved once
+  // the platform specific Close() function has completed.
+  RefPtr<Promise> mClosingPromise;
+};
+
+}  // namespace dom
+}  // namespace mozilla
+
+#endif  // mozilla_dom_MIDIPort_h
diff --git a/dom/midi/MIDIPortChild.cpp b/dom/midi/MIDIPortChild.cpp
new file mode 100644
index 0000000000..1540c8cae4
--- /dev/null
+++ b/dom/midi/MIDIPortChild.cpp
@@ -0,0 +1,57 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim:set ts=2 sw=2 sts=2 et cindent: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "mozilla/dom/MIDIPortChild.h"
+#include "mozilla/dom/MIDIPort.h"
+#include "mozilla/dom/MIDIPortInterface.h"
+
+using namespace mozilla;
+using namespace mozilla::dom;
+
+MIDIPortChild::MIDIPortChild(const MIDIPortInfo& aPortInfo, bool aSysexEnabled,
+                             MIDIPort* aPort)
+    : MIDIPortInterface(aPortInfo, aSysexEnabled),
+      mDOMPort(aPort),
+      mActorWasAlive(false) {}
+
+void MIDIPortChild::Teardown() {
+  if (mDOMPort) {
+    mDOMPort->UnsetIPCPort();
+    mDOMPort = nullptr;
+  }
+  MIDIPortInterface::Shutdown();
+}
+
+void MIDIPortChild::ActorDestroy(ActorDestroyReason aWhy) {}
+
+mozilla::ipc::IPCResult MIDIPortChild::RecvReceive(
+    nsTArray<MIDIMessage>&& aMsgs) {
+  if (mDOMPort) {
+    mDOMPort->Receive(aMsgs);
+  }
+  return IPC_OK();
+}
+
+mozilla::ipc::IPCResult MIDIPortChild::RecvUpdateStatus(
+    const uint32_t& aDeviceState, const uint32_t& aConnectionState) {
+  // Either a device is connected, and can have any connection state, or a
+  // device is disconnected, and can only be closed or pending.
+  MOZ_ASSERT(mDeviceState == MIDIPortDeviceState::Connected ||
+             (mConnectionState == MIDIPortConnectionState::Closed ||
+              mConnectionState == MIDIPortConnectionState::Pending));
+  mDeviceState = static_cast<MIDIPortDeviceState>(aDeviceState);
+  mConnectionState = static_cast<MIDIPortConnectionState>(aConnectionState);
+  if (mDOMPort) {
+    mDOMPort->FireStateChangeEvent();
+  }
+  return IPC_OK();
+}
+
+void MIDIPortChild::SetActorAlive() {
+  MOZ_ASSERT(!mActorWasAlive);
+  mActorWasAlive = true;
+  AddRef();
+}
diff --git a/dom/midi/MIDIPortChild.h b/dom/midi/MIDIPortChild.h
new file mode 100644
index 0000000000..e0d1e5a247
--- /dev/null
+++ b/dom/midi/MIDIPortChild.h
@@ -0,0 +1,52 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim:set ts=2 sw=2 sts=2 et cindent: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_dom_MIDIPortChild_h
+#define mozilla_dom_MIDIPortChild_h
+
+#include "mozilla/dom/PMIDIPortChild.h"
+#include "mozilla/dom/MIDIPortInterface.h"
+
+namespace mozilla {
+namespace dom {
+
+class MIDIPort;
+class MIDIPortInfo;
+
+/**
+ * Child actor for a MIDIPort object. Each MIDIPort DOM object in JS has a its
+ * own child actor. The lifetime of the actor object is dependent on the
+ * lifetime of the JS object.
+ *
+ */
+class MIDIPortChild final : public PMIDIPortChild, public MIDIPortInterface {
+ public:
+  NS_INLINE_DECL_REFCOUNTING(MIDIPortChild);
+  mozilla::ipc::IPCResult RecvReceive(nsTArray<MIDIMessage>&& aMsgs);
+
+  virtual void ActorDestroy(ActorDestroyReason aWhy) override;
+
+  mozilla::ipc::IPCResult RecvUpdateStatus(const uint32_t& aDeviceState,
+                                           const uint32_t& aConnectionState);
+
+  MIDIPortChild(const MIDIPortInfo& aPortInfo, bool aSysexEnabled,
+                MIDIPort* aPort);
+  // virtual void Shutdown() override;
+  void SetActorAlive();
+
+  void Teardown();
+
+ private:
+  ~MIDIPortChild() = default;
+  // Pointer to the DOM object this actor represents. The actor cannot outlive
+  // the DOM object.
+  MIDIPort* mDOMPort;
+  bool mActorWasAlive;
+};
+}  // namespace dom
+}  // namespace mozilla
+
+#endif
diff --git a/dom/midi/MIDIPortInterface.cpp b/dom/midi/MIDIPortInterface.cpp
new file mode 100644
index 0000000000..42411b81a8
--- /dev/null
+++ b/dom/midi/MIDIPortInterface.cpp
@@ -0,0 +1,27 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim:set ts=2 sw=2 sts=2 et cindent: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "mozilla/dom/MIDIPortInterface.h"
+#include "mozilla/dom/MIDIPlatformService.h"
+#include "mozilla/dom/MIDITypes.h"
+
+mozilla::dom::MIDIPortInterface::MIDIPortInterface(
+    const MIDIPortInfo& aPortInfo, bool aSysexEnabled)
+    : mId(aPortInfo.id()),
+      mName(aPortInfo.name()),
+      mManufacturer(aPortInfo.manufacturer()),
+      mVersion(aPortInfo.version()),
+      mSysexEnabled(aSysexEnabled),
+      mType((MIDIPortType)aPortInfo.type()),
+      // We'll never initialize a port object that's not connected
+      mDeviceState(MIDIPortDeviceState::Connected),
+      // Open everything on connection
+      mConnectionState(MIDIPortConnectionState::Open),
+      mShuttingDown(false) {}
+
+mozilla::dom::MIDIPortInterface::~MIDIPortInterface() { Shutdown(); }
+
+void mozilla::dom::MIDIPortInterface::Shutdown() { mShuttingDown = true; }
diff --git a/dom/midi/MIDIPortInterface.h b/dom/midi/MIDIPortInterface.h
new file mode 100644
index 0000000000..dbbea382ed
--- /dev/null
+++ b/dom/midi/MIDIPortInterface.h
@@ -0,0 +1,50 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim:set ts=2 sw=2 sts=2 et cindent: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_dom_MIDIPortInterface_h
+#define mozilla_dom_MIDIPortInterface_h
+
+#include "mozilla/dom/MIDIPortBinding.h"
+
+namespace mozilla {
+namespace dom {
+class MIDIPortInfo;
+/**
+ * Base class for MIDIPort Parent/Child Actors. Makes sure both sides of the
+ * MIDIPort IPC connection need to a synchronized set of info/state.
+ *
+ */
+class MIDIPortInterface {
+ public:
+  MIDIPortInterface(const MIDIPortInfo& aPortInfo, bool aSysexEnabled);
+  const nsString& Id() const { return mId; }
+  const nsString& Name() const { return mName; }
+  const nsString& Manufacturer() const { return mManufacturer; }
+  const nsString& Version() const { return mVersion; }
+  bool SysexEnabled() const { return mSysexEnabled; }
+  MIDIPortType Type() const { return mType; }
+  MIDIPortDeviceState DeviceState() const { return mDeviceState; }
+  MIDIPortConnectionState ConnectionState() const { return mConnectionState; }
+  bool IsShutdown() const { return mShuttingDown; }
+  virtual void Shutdown();
+
+ protected:
+  virtual ~MIDIPortInterface();
+  nsString mId;
+  nsString mName;
+  nsString mManufacturer;
+  nsString mVersion;
+  bool mSysexEnabled;
+  MIDIPortType mType;
+  MIDIPortDeviceState mDeviceState;
+  MIDIPortConnectionState mConnectionState;
+  bool mShuttingDown;
+};
+
+}  // namespace dom
+}  // namespace mozilla
+
+#endif  // mozilla_dom_MIDIPortInterface_h
diff --git a/dom/midi/MIDIPortParent.cpp b/dom/midi/MIDIPortParent.cpp
new file mode 100644
index 0000000000..2da91d7653
--- /dev/null
+++ b/dom/midi/MIDIPortParent.cpp
@@ -0,0 +1,108 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim:set ts=2 sw=2 sts=2 et cindent: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "mozilla/dom/MIDIPortParent.h"
+#include "mozilla/dom/MIDIPlatformService.h"
+#include "nsContentUtils.h"
+
+// C++ file contents
+namespace mozilla::dom {
+
+// Keep an internal ID that we can use for passing information about specific
+// MIDI ports back and forth to the Rust libraries.
+static uint32_t gId = 0;
+
+mozilla::ipc::IPCResult MIDIPortParent::RecvSend(
+    nsTArray<MIDIMessage>&& aMsgs) {
+  if (mConnectionState != MIDIPortConnectionState::Open) {
+    mMessageQueue.AppendElements(aMsgs);
+    if (MIDIPlatformService::IsRunning()) {
+      MIDIPlatformService::Get()->Open(this);
+    }
+    return IPC_OK();
+  }
+  if (MIDIPlatformService::IsRunning()) {
+    MIDIPlatformService::Get()->QueueMessages(MIDIPortInterface::mId, aMsgs);
+  }
+  return IPC_OK();
+}
+
+mozilla::ipc::IPCResult MIDIPortParent::RecvOpen() {
+  if (MIDIPlatformService::IsRunning()) {
+    MIDIPlatformService::Get()->Open(this);
+  }
+  return IPC_OK();
+}
+
+mozilla::ipc::IPCResult MIDIPortParent::RecvClose() {
+  if (mConnectionState != MIDIPortConnectionState::Closed) {
+    if (MIDIPlatformService::IsRunning()) {
+      MIDIPlatformService::Get()->Close(this);
+    }
+  }
+  return IPC_OK();
+}
+
+mozilla::ipc::IPCResult MIDIPortParent::RecvClear() {
+  if (MIDIPlatformService::IsRunning()) {
+    MIDIPlatformService::Get()->Clear(this);
+  }
+  return IPC_OK();
+}
+
+mozilla::ipc::IPCResult MIDIPortParent::RecvShutdown() {
+  if (mShuttingDown) {
+    return IPC_OK();
+  }
+  Teardown();
+  Unused << Send__delete__(this);
+  return IPC_OK();
+}
+
+void MIDIPortParent::Teardown() {
+  mMessageQueue.Clear();
+  MIDIPortInterface::Shutdown();
+  if (MIDIPlatformService::IsRunning()) {
+    MIDIPlatformService::Get()->RemovePort(this);
+  }
+}
+
+void MIDIPortParent::ActorDestroy(ActorDestroyReason) {}
+
+bool MIDIPortParent::SendUpdateStatus(
+    const MIDIPortDeviceState& aDeviceState,
+    const MIDIPortConnectionState& aConnectionState) {
+  if (mShuttingDown) {
+    return true;
+  }
+  mDeviceState = aDeviceState;
+  mConnectionState = aConnectionState;
+  if (aConnectionState == MIDIPortConnectionState::Open &&
+      aDeviceState == MIDIPortDeviceState::Disconnected) {
+    mConnectionState = MIDIPortConnectionState::Pending;
+  } else if (aConnectionState == MIDIPortConnectionState::Open &&
+             aDeviceState == MIDIPortDeviceState::Connected &&
+             !mMessageQueue.IsEmpty()) {
+    if (MIDIPlatformService::IsRunning()) {
+      MIDIPlatformService::Get()->QueueMessages(MIDIPortInterface::mId,
+                                                mMessageQueue);
+    }
+    mMessageQueue.Clear();
+  }
+  return PMIDIPortParent::SendUpdateStatus(
+      static_cast<uint32_t>(mDeviceState),
+      static_cast<uint32_t>(mConnectionState));
+}
+
+MIDIPortParent::MIDIPortParent(const MIDIPortInfo& aPortInfo,
+                               const bool aSysexEnabled)
+    : MIDIPortInterface(aPortInfo, aSysexEnabled), mInternalId(++gId) {
+  MOZ_ASSERT(MIDIPlatformService::IsRunning(),
+             "Shouldn't be able to add MIDI port without MIDI service!");
+  MIDIPlatformService::Get()->AddPort(this);
+}
+
+}  // namespace mozilla::dom
diff --git a/dom/midi/MIDIPortParent.h b/dom/midi/MIDIPortParent.h
new file mode 100644
index 0000000000..946e457928
--- /dev/null
+++ b/dom/midi/MIDIPortParent.h
@@ -0,0 +1,51 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim:set ts=2 sw=2 sts=2 et cindent: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_dom_MIDIPortParent_h
+#define mozilla_dom_MIDIPortParent_h
+
+#include "mozilla/dom/PMIDIPortParent.h"
+#include "mozilla/dom/MIDIPortBinding.h"
+#include "mozilla/dom/MIDIPortInterface.h"
+
+// Header file contents
+namespace mozilla {
+namespace dom {
+
+/**
+ * Actor representing the parent (PBackground thread) side of a MIDIPort object.
+ *
+ */
+class MIDIPortParent final : public PMIDIPortParent, public MIDIPortInterface {
+ public:
+  NS_INLINE_DECL_REFCOUNTING(MIDIPortParent);
+  void ActorDestroy(ActorDestroyReason) override;
+  mozilla::ipc::IPCResult RecvSend(nsTArray<MIDIMessage>&& aMsg);
+  mozilla::ipc::IPCResult RecvOpen();
+  mozilla::ipc::IPCResult RecvClose();
+  mozilla::ipc::IPCResult RecvClear();
+  mozilla::ipc::IPCResult RecvShutdown();
+  MOZ_IMPLICIT MIDIPortParent(const MIDIPortInfo& aPortInfo,
+                              const bool aSysexEnabled);
+  // Sends the current port status to the child actor. May also send message
+  // buffer if required.
+  bool SendUpdateStatus(const MIDIPortDeviceState& aState,
+                        const MIDIPortConnectionState& aConnection);
+  uint32_t GetInternalId() const { return mInternalId; }
+  void Teardown();
+
+ protected:
+  ~MIDIPortParent() = default;
+  // Queue of messages that needs to be sent. Since sending a message on a
+  // closed port opens it, we sometimes have to buffer messages from the time
+  // Send() is called until the time we get a device state change to Opened.
+  nsTArray<MIDIMessage> mMessageQueue;
+  const uint32_t mInternalId;
+};
+}  // namespace dom
+}  // namespace mozilla
+
+#endif
diff --git a/dom/midi/MIDITypes.ipdlh b/dom/midi/MIDITypes.ipdlh
new file mode 100644
index 0000000000..9694ca12c3
--- /dev/null
+++ b/dom/midi/MIDITypes.ipdlh
@@ -0,0 +1,31 @@
+/* -*- Mode: C++; c-basic-offset: 4; indent-tabs-mode: nil; tab-width: 8 -*- */
+/* vim: set sw=4 ts=8 et tw=80 ft=cpp : */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+using mozilla::TimeStamp from "mozilla/TimeStamp.h";
+
+namespace mozilla {
+namespace dom {
+
+comparable struct MIDIPortInfo {
+    nsString id;
+    nsString name;
+    nsString manufacturer;
+    nsString version;
+    //Actually a MIDIPortType enum
+    uint32_t type;
+};
+
+struct MIDIMessage {
+    uint8_t[] data;
+    TimeStamp timestamp;
+};
+
+struct MIDIPortList {
+    MIDIPortInfo[] ports;
+};
+
+} // namespace dom
+} // namespace mozilla
diff --git a/dom/midi/MIDIUtils.cpp b/dom/midi/MIDIUtils.cpp
new file mode 100644
index 0000000000..6e2a7f75af
--- /dev/null
+++ b/dom/midi/MIDIUtils.cpp
@@ -0,0 +1,124 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim:set ts=2 sw=2 sts=2 et cindent: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "mozilla/dom/MIDITypes.h"
+#include "mozilla/dom/MIDIUtils.h"
+#include "mozilla/UniquePtr.h"
+
+// Taken from MIDI IMPLEMENTATION CHART INSTRUCTIONS, MIDI Spec v1.0, Pg. 97
+static const uint8_t kCommandByte = 0x80;
+static const uint8_t kSysexMessageStart = 0xF0;
+static const uint8_t kSystemMessage = 0xF0;
+static const uint8_t kSysexMessageEnd = 0xF7;
+static const uint8_t kSystemRealtimeMessage = 0xF8;
+// Represents the length of all possible command messages.
+// Taken from MIDI Spec, Pg. 101v 1.0, Table 2
+static const uint8_t kCommandLengths[] = {3, 3, 3, 3, 2, 2, 3};
+// Represents the length of all possible system messages. The length of sysex
+// messages is variable, so we just put zero since it won't be checked anyways.
+// Taken from MIDI Spec v1.0, Pg. 105, Table 5
+static const uint8_t kSystemLengths[] = {0, 2, 3, 2, 1, 1, 1, 1};
+
+namespace mozilla::dom::MIDIUtils {
+
+// Checks validity of MIDIMessage passed to it. Throws debug warnings and
+// returns false if message is not valid.
+bool IsValidMessage(const MIDIMessage* aMsg) {
+  if (NS_WARN_IF(!aMsg)) {
+    return false;
+  }
+  // Assert on parser problems
+  MOZ_ASSERT(aMsg->data().Length() > 0,
+             "Created a MIDI Message of Length 0. This should never happen!");
+  uint8_t cmd = aMsg->data()[0];
+  // If first byte isn't a command, something is definitely wrong.
+  MOZ_ASSERT((cmd & kCommandByte) == kCommandByte,
+             "Constructed a MIDI packet where first byte is not command!");
+  if (cmd == kSysexMessageStart) {
+    // All we can do with sysex is make sure it starts and  ends with the
+    // correct command bytes.
+    if (aMsg->data()[aMsg->data().Length() - 1] != kSysexMessageEnd) {
+      NS_WARNING("Last byte of Sysex Message not 0xF7!");
+      return false;
+    }
+    return true;
+  }
+  // For system realtime messages, the length should always be 1.
+  if ((cmd & kSystemRealtimeMessage) == kSystemRealtimeMessage) {
+    return aMsg->data().Length() == 1;
+  }
+  // Otherwise, just use the correct array for testing lengths. We can't tell
+  // much about message validity other than that.
+  if ((cmd & kSystemMessage) == kSystemMessage) {
+    if (cmd - kSystemMessage >=
+        static_cast<uint8_t>(ArrayLength(kSystemLengths))) {
+      NS_WARNING("System Message Command byte not valid!");
+      return false;
+    }
+    return aMsg->data().Length() == kSystemLengths[cmd - kSystemMessage];
+  }
+  // For non system commands, we only care about differences in the high nibble
+  // of the first byte. Shift this down to give the index of the expected packet
+  // length.
+  uint8_t cmdIndex = (cmd - kCommandByte) >> 4;
+  if (cmdIndex >= ArrayLength(kCommandLengths)) {
+    // If our index is bigger than our array length, command byte is unknown;
+    NS_WARNING("Unknown MIDI command!");
+    return false;
+  }
+  return aMsg->data().Length() == kCommandLengths[cmdIndex];
+}
+
+uint32_t ParseMessages(const nsTArray<uint8_t>& aByteBuffer,
+                       const TimeStamp& aTimestamp,
+                       nsTArray<MIDIMessage>& aMsgArray) {
+  uint32_t bytesRead = 0;
+  bool inSysexMessage = false;
+  UniquePtr<MIDIMessage> currentMsg;
+  for (auto& byte : aByteBuffer) {
+    bytesRead++;
+    if ((byte & kSystemRealtimeMessage) == kSystemRealtimeMessage) {
+      MIDIMessage rt_msg;
+      rt_msg.data().AppendElement(byte);
+      rt_msg.timestamp() = aTimestamp;
+      aMsgArray.AppendElement(rt_msg);
+      continue;
+    }
+    if (byte == kSysexMessageEnd) {
+      if (!inSysexMessage) {
+        MOZ_ASSERT(inSysexMessage);
+        NS_WARNING(
+            "Got sysex message end with no sysex message being processed!");
+      }
+      inSysexMessage = false;
+    } else if (byte & kCommandByte) {
+      if (currentMsg && IsValidMessage(currentMsg.get())) {
+        aMsgArray.AppendElement(*currentMsg);
+      }
+      currentMsg = MakeUnique<MIDIMessage>();
+      currentMsg->timestamp() = aTimestamp;
+    }
+    currentMsg->data().AppendElement(byte);
+    if (byte == kSysexMessageStart) {
+      inSysexMessage = true;
+    }
+  }
+  if (currentMsg && IsValidMessage(currentMsg.get())) {
+    aMsgArray.AppendElement(*currentMsg);
+  }
+  return bytesRead;
+}
+
+bool IsSysexMessage(const MIDIMessage& aMsg) {
+  if (aMsg.data().Length() == 0) {
+    return false;
+  }
+  if (aMsg.data()[0] == kSysexMessageStart) {
+    return true;
+  }
+  return false;
+}
+}  // namespace mozilla::dom::MIDIUtils
diff --git a/dom/midi/MIDIUtils.h b/dom/midi/MIDIUtils.h
new file mode 100644
index 0000000000..43cc294b90
--- /dev/null
+++ b/dom/midi/MIDIUtils.h
@@ -0,0 +1,29 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim:set ts=2 sw=2 sts=2 et cindent: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "nsTArray.h"
+#include "mozilla/TimeStamp.h"
+
+namespace mozilla {
+namespace dom {
+class MIDIMessage;
+
+/**
+ * Set of utility functions for dealing with MIDI Messages.
+ *
+ */
+namespace MIDIUtils {
+
+// Takes a nsTArray of bytes and parses it into zero or more MIDI messages.
+// Returns number of bytes parsed.
+uint32_t ParseMessages(const nsTArray<uint8_t>& aByteBuffer,
+                       const TimeStamp& aTimestamp,
+                       nsTArray<MIDIMessage>& aMsgArray);
+// Returns true if a message is a sysex message.
+bool IsSysexMessage(const MIDIMessage& a);
+}  // namespace MIDIUtils
+}  // namespace dom
+}  // namespace mozilla
diff --git a/dom/midi/PMIDIManager.ipdl b/dom/midi/PMIDIManager.ipdl
new file mode 100644
index 0000000000..eb5f363fd4
--- /dev/null
+++ b/dom/midi/PMIDIManager.ipdl
@@ -0,0 +1,25 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+include protocol PBackground;
+include MIDITypes;
+
+namespace mozilla {
+namespace dom {
+
+async protocol PMIDIManager
+{
+  manager PBackground;
+parent:
+  async Shutdown();
+child:
+  /*
+   * Send an updated list of MIDI ports to the child
+   */
+  async MIDIPortListUpdate(MIDIPortList aPortList);
+  async __delete__();
+};
+
+} // namespace ipc
+} // namespace mozilla
diff --git a/dom/midi/PMIDIPort.ipdl b/dom/midi/PMIDIPort.ipdl
new file mode 100644
index 0000000000..ebdb9c644d
--- /dev/null
+++ b/dom/midi/PMIDIPort.ipdl
@@ -0,0 +1,31 @@
+/* -*- Mode: c++; c-basic-offset: 2; indent-tabs-mode: nil; tab-width: 40 -*- */
+/* vim: set ts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this file,
+ * You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+include protocol PBackground;
+include MIDITypes;
+
+namespace mozilla {
+namespace dom {
+
+async protocol PMIDIPort
+{
+  manager PBackground;
+parent:
+  async Shutdown();
+  async Send(MIDIMessage[] msg);
+  async Open();
+  async Close();
+  async Clear();
+child:
+  async Receive(MIDIMessage[] msg);
+  // Actually takes a MIDIDeviceConnectionState and MIDIPortConnectionState
+  // respectively.
+  async UpdateStatus(uint32_t deviceState, uint32_t connectionState);
+  async __delete__();
+};
+
+}
+}
diff --git a/dom/midi/TestMIDIPlatformService.cpp b/dom/midi/TestMIDIPlatformService.cpp
new file mode 100644
index 0000000000..22cd57a2e4
--- /dev/null
+++ b/dom/midi/TestMIDIPlatformService.cpp
@@ -0,0 +1,244 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this file,
+ * You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "TestMIDIPlatformService.h"
+#include "mozilla/dom/MIDIPort.h"
+#include "mozilla/dom/MIDITypes.h"
+#include "mozilla/dom/MIDIPortInterface.h"
+#include "mozilla/dom/MIDIPortParent.h"
+#include "mozilla/dom/MIDIPlatformRunnables.h"
+#include "mozilla/dom/MIDIUtils.h"
+#include "mozilla/ipc/BackgroundParent.h"
+#include "mozilla/Unused.h"
+#include "nsIThread.h"
+
+using namespace mozilla;
+using namespace mozilla::dom;
+using namespace mozilla::ipc;
+
+/**
+ * Runnable used for making sure ProcessMessages only happens on the IO thread.
+ *
+ */
+class ProcessMessagesRunnable : public mozilla::Runnable {
+ public:
+  explicit ProcessMessagesRunnable(const nsAString& aPortID)
+      : Runnable("ProcessMessagesRunnable"), mPortID(aPortID) {}
+  ~ProcessMessagesRunnable() = default;
+  NS_IMETHOD Run() {
+    // If service is no longer running, just exist without processing.
+    if (!MIDIPlatformService::IsRunning()) {
+      return NS_OK;
+    }
+    TestMIDIPlatformService* srv =
+        static_cast<TestMIDIPlatformService*>(MIDIPlatformService::Get());
+    srv->ProcessMessages(mPortID);
+    return NS_OK;
+  }
+
+ private:
+  nsString mPortID;
+};
+
+/**
+ * Runnable used for allowing IO thread to queue more messages for processing,
+ * since it can't access the service object directly.
+ *
+ */
+class QueueMessagesRunnable : public MIDIBackgroundRunnable {
+ public:
+  QueueMessagesRunnable(const nsAString& aPortID,
+                        const nsTArray<MIDIMessage>& aMsgs)
+      : MIDIBackgroundRunnable("QueueMessagesRunnable"),
+        mPortID(aPortID),
+        mMsgs(aMsgs.Clone()) {}
+  ~QueueMessagesRunnable() = default;
+  virtual void RunInternal() {
+    AssertIsOnBackgroundThread();
+    MIDIPlatformService::Get()->QueueMessages(mPortID, mMsgs);
+  }
+
+ private:
+  nsString mPortID;
+  nsTArray<MIDIMessage> mMsgs;
+};
+
+TestMIDIPlatformService::TestMIDIPlatformService()
+    : mBackgroundThread(NS_GetCurrentThread()),
+      mControlInputPort(u"b744eebe-f7d8-499b-872b-958f63c8f522"_ns,
+                        u"Test Control MIDI Device Input Port"_ns,
+                        u"Test Manufacturer"_ns, u"1.0.0"_ns,
+                        static_cast<uint32_t>(MIDIPortType::Input)),
+      mControlOutputPort(u"ab8e7fe8-c4de-436a-a960-30898a7c9a3d"_ns,
+                         u"Test Control MIDI Device Output Port"_ns,
+                         u"Test Manufacturer"_ns, u"1.0.0"_ns,
+                         static_cast<uint32_t>(MIDIPortType::Output)),
+      mStateTestInputPort(u"a9329677-8588-4460-a091-9d4a7f629a48"_ns,
+                          u"Test State MIDI Device Input Port"_ns,
+                          u"Test Manufacturer"_ns, u"1.0.0"_ns,
+                          static_cast<uint32_t>(MIDIPortType::Input)),
+      mStateTestOutputPort(u"478fa225-b5fc-4fa6-a543-d32d9cb651e7"_ns,
+                           u"Test State MIDI Device Output Port"_ns,
+                           u"Test Manufacturer"_ns, u"1.0.0"_ns,
+                           static_cast<uint32_t>(MIDIPortType::Output)),
+      mAlwaysClosedTestOutputPort(u"f87d0c76-3c68-49a9-a44f-700f1125c07a"_ns,
+                                  u"Always Closed MIDI Device Output Port"_ns,
+                                  u"Test Manufacturer"_ns, u"1.0.0"_ns,
+                                  static_cast<uint32_t>(MIDIPortType::Output)),
+      mIsInitialized(false) {
+  AssertIsOnBackgroundThread();
+}
+
+TestMIDIPlatformService::~TestMIDIPlatformService() {
+  AssertIsOnBackgroundThread();
+}
+
+void TestMIDIPlatformService::Init() {
+  AssertIsOnBackgroundThread();
+
+  if (mIsInitialized) {
+    return;
+  }
+  mIsInitialized = true;
+
+  // Treat all of our special ports as always connected. When the service comes
+  // up, prepopulate the port list with them.
+  MIDIPlatformService::Get()->AddPortInfo(mControlInputPort);
+  MIDIPlatformService::Get()->AddPortInfo(mControlOutputPort);
+  MIDIPlatformService::Get()->AddPortInfo(mAlwaysClosedTestOutputPort);
+  nsCOMPtr<nsIRunnable> r(new SendPortListRunnable());
+
+  // Start the IO Thread.
+  NS_DispatchToCurrentThread(r);
+}
+
+void TestMIDIPlatformService::Open(MIDIPortParent* aPort) {
+  MOZ_ASSERT(aPort);
+  MIDIPortConnectionState s = MIDIPortConnectionState::Open;
+  if (aPort->MIDIPortInterface::Id() == mAlwaysClosedTestOutputPort.id()) {
+    // If it's the always closed testing port, act like it's already opened
+    // exclusively elsewhere.
+    s = MIDIPortConnectionState::Closed;
+  }
+  // Connection events are just simulated on the background thread, no need to
+  // push to IO thread.
+  nsCOMPtr<nsIRunnable> r(new SetStatusRunnable(aPort->MIDIPortInterface::Id(),
+                                                aPort->DeviceState(), s));
+  NS_DispatchToCurrentThread(r);
+}
+
+void TestMIDIPlatformService::ScheduleClose(MIDIPortParent* aPort) {
+  MOZ_ASSERT(aPort);
+  if (aPort->ConnectionState() == MIDIPortConnectionState::Open) {
+    // Connection events are just simulated on the background thread, no need to
+    // push to IO thread.
+    nsCOMPtr<nsIRunnable> r(new SetStatusRunnable(
+        aPort->MIDIPortInterface::Id(), aPort->DeviceState(),
+        MIDIPortConnectionState::Closed));
+    NS_DispatchToCurrentThread(r);
+  }
+}
+
+void TestMIDIPlatformService::Stop() { AssertIsOnBackgroundThread(); }
+
+void TestMIDIPlatformService::ScheduleSend(const nsAString& aPortId) {
+  nsCOMPtr<nsIRunnable> r(new ProcessMessagesRunnable(aPortId));
+  NS_DispatchToCurrentThread(r);
+}
+
+void TestMIDIPlatformService::ProcessMessages(const nsAString& aPortId) {
+  nsTArray<MIDIMessage> msgs;
+  GetMessagesBefore(aPortId, TimeStamp::Now(), msgs);
+
+  for (MIDIMessage msg : msgs) {
+    // receiving message from test control port
+    if (aPortId == mControlOutputPort.id()) {
+      switch (msg.data()[0]) {
+        // Hit a note, get a test!
+        case 0x90:
+          switch (msg.data()[1]) {
+            // Echo data/timestamp back through output port
+            case 0x00: {
+              nsCOMPtr<nsIRunnable> r(
+                  new ReceiveRunnable(mControlInputPort.id(), msg));
+              mBackgroundThread->Dispatch(r, NS_DISPATCH_NORMAL);
+              break;
+            }
+            // Cause control test ports to connect
+            case 0x01: {
+              nsCOMPtr<nsIRunnable> r1(
+                  new AddPortRunnable(mStateTestInputPort));
+              mBackgroundThread->Dispatch(r1, NS_DISPATCH_NORMAL);
+              break;
+            }
+            // Cause control test ports to disconnect
+            case 0x02: {
+              nsCOMPtr<nsIRunnable> r1(
+                  new RemovePortRunnable(mStateTestInputPort));
+              mBackgroundThread->Dispatch(r1, NS_DISPATCH_NORMAL);
+              break;
+            }
+            // Test for packet timing
+            case 0x03: {
+              // Append a few echo command packets in reverse timing order,
+              // should come out in correct order on other end.
+              nsTArray<MIDIMessage> newMsgs;
+              nsTArray<uint8_t> msg;
+              msg.AppendElement(0x90);
+              msg.AppendElement(0x00);
+              msg.AppendElement(0x00);
+              // PR_Now() returns nanosecods, and we need a double with
+              // fractional milliseconds.
+              TimeStamp currentTime = TimeStamp::Now();
+              for (int i = 0; i <= 5; ++i) {
+                // Insert messages with timestamps in reverse order, to make
+                // sure we're sorting correctly.
+                newMsgs.AppendElement(MIDIMessage(
+                    msg, currentTime - TimeDuration::FromMilliseconds(i * 2)));
+              }
+              nsCOMPtr<nsIRunnable> r(
+                  new QueueMessagesRunnable(aPortId, newMsgs));
+              mBackgroundThread->Dispatch(r, NS_DISPATCH_NORMAL);
+              break;
+            }
+            default:
+              NS_WARNING("Unknown Test MIDI message received!");
+          }
+          break;
+          // Sysex tests
+        case 0xF0:
+          switch (msg.data()[1]) {
+              // Echo data/timestamp back through output port
+            case 0x00: {
+              nsCOMPtr<nsIRunnable> r(
+                  new ReceiveRunnable(mControlInputPort.id(), msg));
+              mBackgroundThread->Dispatch(r, NS_DISPATCH_NORMAL);
+              break;
+            }
+            // Test for system real time messages in the middle of sysex
+            // messages.
+            case 0x01: {
+              nsTArray<uint8_t> msgs;
+              const uint8_t msg[] = {0xF0, 0x01, 0xF8, 0x02, 0x03,
+                                     0x04, 0xF9, 0x05, 0xF7};
+              // Can't use AppendElements on an array here, so just do range
+              // based loading.
+              for (auto& s : msg) {
+                msgs.AppendElement(s);
+              }
+              nsTArray<MIDIMessage> newMsgs;
+              MIDIUtils::ParseMessages(msgs, TimeStamp::Now(), newMsgs);
+              nsCOMPtr<nsIRunnable> r(
+                  new ReceiveRunnable(mControlInputPort.id(), newMsgs));
+              mBackgroundThread->Dispatch(r, NS_DISPATCH_NORMAL);
+              break;
+            }
+            default:
+              NS_WARNING("Unknown Test Sysex MIDI message received!");
+          }
+          break;
+      }
+    }
+  }
+}
diff --git a/dom/midi/TestMIDIPlatformService.h b/dom/midi/TestMIDIPlatformService.h
new file mode 100644
index 0000000000..984afce032
--- /dev/null
+++ b/dom/midi/TestMIDIPlatformService.h
@@ -0,0 +1,64 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim:set ts=2 sw=2 sts=2 et cindent: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_dom_TestMIDIPlatformService_h
+#define mozilla_dom_TestMIDIPlatformService_h
+
+#include "mozilla/dom/MIDIPlatformService.h"
+#include "mozilla/dom/MIDITypes.h"
+
+class nsIThread;
+
+namespace mozilla {
+namespace dom {
+
+class MIDIPortInterface;
+
+/**
+ * Platform service implementation used for mochitests. Emulates what a real
+ * platform service should look like, including using an internal IO thread for
+ * message IO.
+ *
+ */
+class TestMIDIPlatformService : public MIDIPlatformService {
+ public:
+  TestMIDIPlatformService();
+  virtual void Init() override;
+  virtual void Open(MIDIPortParent* aPort) override;
+  virtual void Stop() override;
+  virtual void ScheduleSend(const nsAString& aPort) override;
+  virtual void ScheduleClose(MIDIPortParent* aPort) override;
+  // MIDI Service simulation function. Can take specially formed sysex messages
+  // in order to trigger device connection events and state changes,
+  // interrupting messages for high priority sysex sends, etc...
+  void ProcessMessages(const nsAString& aPort);
+
+ private:
+  virtual ~TestMIDIPlatformService();
+  // Convenience object for sending runnables to the background thread. All
+  // runnables are pushed to the background thread, and check for existence of a
+  // manager object on the thread before running.
+  nsCOMPtr<nsIThread> mBackgroundThread;
+  // Port that takes test control messages
+  MIDIPortInfo mControlInputPort;
+  // Port that returns test status messages
+  MIDIPortInfo mControlOutputPort;
+  // Used for testing input connection/disconnection
+  MIDIPortInfo mStateTestInputPort;
+  // Used for testing output connection/disconnection
+  MIDIPortInfo mStateTestOutputPort;
+  // Used for testing open() call failures
+  MIDIPortInfo mAlwaysClosedTestOutputPort;
+  // IO Simulation thread. Runs all instances of ProcessMessages().
+  nsCOMPtr<nsIThread> mClientThread;
+  // True if server has been brought up already.
+  bool mIsInitialized;
+};
+
+}  // namespace dom
+}  // namespace mozilla
+
+#endif  // mozilla_dom_TestMIDIPlatformService_h
diff --git a/dom/midi/moz.build b/dom/midi/moz.build
new file mode 100644
index 0000000000..11723dcfad
--- /dev/null
+++ b/dom/midi/moz.build
@@ -0,0 +1,63 @@
+# -*- Mode: python; c-basic-offset: 4; indent-tabs-mode: nil; tab-width: 40 -*-
+# vim: set filetype=python:
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+IPDL_SOURCES += [
+    "MIDITypes.ipdlh",
+    "PMIDIManager.ipdl",
+    "PMIDIPort.ipdl",
+]
+
+EXPORTS.mozilla.dom += [
+    "MIDIAccess.h",
+    "MIDIAccessManager.h",
+    "MIDIInput.h",
+    "MIDIInputMap.h",
+    "MIDIManagerChild.h",
+    "MIDIManagerParent.h",
+    "MIDIMessageEvent.h",
+    "MIDIMessageQueue.h",
+    "MIDIOutput.h",
+    "MIDIOutputMap.h",
+    "MIDIPermissionRequest.h",
+    "MIDIPlatformRunnables.h",
+    "MIDIPlatformService.h",
+    "MIDIPort.h",
+    "MIDIPortChild.h",
+    "MIDIPortInterface.h",
+    "MIDIPortParent.h",
+    "MIDIUtils.h",
+]
+
+UNIFIED_SOURCES = [
+    "MIDIAccess.cpp",
+    "MIDIAccessManager.cpp",
+    "MIDIInput.cpp",
+    "MIDIInputMap.cpp",
+    "MIDIManagerChild.cpp",
+    "MIDIManagerParent.cpp",
+    "MIDIMessageEvent.cpp",
+    "MIDIMessageQueue.cpp",
+    "MIDIOutput.cpp",
+    "MIDIOutputMap.cpp",
+    "MIDIPermissionRequest.cpp",
+    "MIDIPlatformRunnables.cpp",
+    "MIDIPlatformService.cpp",
+    "MIDIPort.cpp",
+    "MIDIPortChild.cpp",
+    "MIDIPortInterface.cpp",
+    "MIDIPortParent.cpp",
+    "MIDIUtils.cpp",
+    "TestMIDIPlatformService.cpp",
+]
+
+include("/ipc/chromium/chromium-config.mozbuild")
+
+FINAL_LIBRARY = "xul"
+LOCAL_INCLUDES += [
+    "/dom/base",
+]
+
+MOCHITEST_MANIFESTS += ["tests/mochitest.ini"]
diff --git a/dom/midi/tests/.eslintrc.js b/dom/midi/tests/.eslintrc.js
new file mode 100644
index 0000000000..845ed3f013
--- /dev/null
+++ b/dom/midi/tests/.eslintrc.js
@@ -0,0 +1,5 @@
+"use strict";
+
+module.exports = {
+  extends: ["plugin:mozilla/mochitest-test"],
+};
diff --git a/dom/midi/tests/MIDITestUtils.js b/dom/midi/tests/MIDITestUtils.js
new file mode 100644
index 0000000000..4d516fc2e4
--- /dev/null
+++ b/dom/midi/tests/MIDITestUtils.js
@@ -0,0 +1,63 @@
+/* eslint-env mozilla/frame-script */
+var MIDITestUtils = {
+  permissionSetup: allow => {
+    let permPromiseRes;
+    let permPromise = new Promise((res, rej) => {
+      permPromiseRes = res;
+    });
+    SpecialPowers.pushPrefEnv(
+      {
+        set: [
+          ["dom.webmidi.enabled", true],
+          ["midi.testing", true],
+          ["midi.prompt.testing", true],
+          ["media.navigator.permission.disabled", allow],
+        ],
+      },
+      () => {
+        permPromiseRes();
+      }
+    );
+    return permPromise;
+  },
+  // This list needs to stay synced with the ports in
+  // dom/midi/TestMIDIPlatformService.
+  inputInfo: {
+    id: "b744eebe-f7d8-499b-872b-958f63c8f522",
+    name: "Test Control MIDI Device Input Port",
+    manufacturer: "Test Manufacturer",
+    version: "1.0.0",
+  },
+  outputInfo: {
+    id: "ab8e7fe8-c4de-436a-a960-30898a7c9a3d",
+    name: "Test Control MIDI Device Output Port",
+    manufacturer: "Test Manufacturer",
+    version: "1.0.0",
+  },
+  stateTestInputInfo: {
+    id: "a9329677-8588-4460-a091-9d4a7f629a48",
+    name: "Test State MIDI Device Input Port",
+    manufacturer: "Test Manufacturer",
+    version: "1.0.0",
+  },
+  stateTestOutputInfo: {
+    id: "478fa225-b5fc-4fa6-a543-d32d9cb651e7",
+    name: "Test State MIDI Device Output Port",
+    manufacturer: "Test Manufacturer",
+    version: "1.0.0",
+  },
+  alwaysClosedTestOutputInfo: {
+    id: "f87d0c76-3c68-49a9-a44f-700f1125c07a",
+    name: "Always Closed MIDI Device Output Port",
+    manufacturer: "Test Manufacturer",
+    version: "1.0.0",
+  },
+  checkPacket: (expected, actual) => {
+    if (expected.length != actual.length) {
+      ok(false, "Packet " + expected + " length not same as packet " + actual);
+    }
+    for (var i = 0; i < expected.length; ++i) {
+      is(expected[i], actual[i], "Packet value " + expected[i] + " matches.");
+    }
+  },
+};
diff --git a/dom/midi/tests/mochitest.ini b/dom/midi/tests/mochitest.ini
new file mode 100644
index 0000000000..6682a30c9f
--- /dev/null
+++ b/dom/midi/tests/mochitest.ini
@@ -0,0 +1,19 @@
+[DEFAULT]
+support-files =
+  MIDITestUtils.js
+scheme = https
+
+
+[test_midi_permission_prompt.html]
+[test_midi_permission_allow.html]
+[test_midi_permission_deny.html]
+[test_midi_device_enumeration.html]
+[test_midi_device_implicit_open_close.html]
+[test_midi_device_explicit_open_close.html]
+[test_midi_device_sysex.html]
+[test_midi_device_system_rt.html]
+[test_midi_packet_timing_sorting.html]
+[test_midi_device_connect_disconnect.html]
+disabled = Bug 1437204
+[test_midi_device_pending.html]
+disabled = Bug 1437204
diff --git a/dom/midi/tests/test_midi_device_connect_disconnect.html b/dom/midi/tests/test_midi_device_connect_disconnect.html
new file mode 100644
index 0000000000..9b5143921d
--- /dev/null
+++ b/dom/midi/tests/test_midi_device_connect_disconnect.html
@@ -0,0 +1,54 @@
+<html>
+  <head>
+    <title>WebMIDI Listener Test</title>
+    <script type="text/javascript" src="/MochiKit/MochiKit.js"></script>
+    <script src="/tests/SimpleTest/SimpleTest.js"></script>
+    <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css" />
+    <script type="application/javascript" src="MIDITestUtils.js"></script>
+  </head>
+
+  <body onload="runTests()">
+    <script class="testbody" type="application/javascript">
+     SimpleTest.waitForExplicitFinish();
+
+     async function runTests() {
+       await MIDITestUtils.permissionSetup(true);
+       let output;
+
+       let midi_access;
+       try {
+         midi_access = await navigator.requestMIDIAccess({ "sysex": false });
+         ok(true, "MIDI Access Request successful");
+       } catch (e) {
+         ok(false, "MIDI Access Request failed!");
+         SimpleTest.finish();
+         return;
+       }
+       is(midi_access.sysexEnabled, false, "Sysex should be false");
+       output = midi_access.outputs.get(MIDITestUtils.outputInfo.id);
+       let statePromiseRes;
+       let statePromise = new Promise((res) => { statePromiseRes = res; });
+       await output.open();
+       let stateChangeHandler = (event) => {
+         if (event.port == output) {
+           return;
+         }
+         statePromiseRes(event.port);
+       };
+       midi_access.addEventListener("statechange", stateChangeHandler);
+       // Send command to connect new port.
+       output.send([0x90, 0x01, 0x00]);
+       let p = await statePromise;
+       is(p.state, "connected", "Device " + p.name + " connected");
+
+       // Rebuild our promise, we'll need to await another one.
+       statePromise = new Promise((res) => { statePromiseRes = res; });
+       output.send([0x90, 0x02, 0x00]);
+       p = await statePromise;
+       is(p.state, "disconnected", "Device " + p.name + " disconnected");
+       midi_access.removeEventListener("statechange", stateChangeHandler);
+       SimpleTest.finish();
+     }
+    </script>
+  </body>
+</html>
diff --git a/dom/midi/tests/test_midi_device_enumeration.html b/dom/midi/tests/test_midi_device_enumeration.html
new file mode 100644
index 0000000000..0702228c73
--- /dev/null
+++ b/dom/midi/tests/test_midi_device_enumeration.html
@@ -0,0 +1,46 @@
+<html>
+  <head>
+    <title>WebMIDI Listener Test</title>
+    <script type="text/javascript" src="/MochiKit/MochiKit.js"></script>
+    <script src="/tests/SimpleTest/SimpleTest.js"></script>
+    <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css" />
+    <script type="application/javascript" src="MIDITestUtils.js"></script>
+  </head>
+
+  <body onload="runTests()">
+    <script class="testbody" type="application/javascript">
+     SimpleTest.waitForExplicitFinish();
+
+     let objectCompare = (type, props, obj) => {
+       for (var prop in props) {
+         is(props[prop], obj[prop], type + " property value " + prop + " is " + props[prop]);
+       }
+     };
+     let failOnCall = (event) => {
+       ok(false, "No connect/state events should be received on startup!");
+     };
+     async function runTests () {
+       await MIDITestUtils.permissionSetup(true);
+       // Request access without sysex.
+       let access = await navigator.requestMIDIAccess({ "sysex": false });
+       ok(true, "MIDI Access Request successful");
+       is(access.sysexEnabled, false, "Sysex should be false");
+       access.addEventListener("statechange", failOnCall);
+       var input_id = MIDITestUtils.inputInfo.id;
+       var output_id = MIDITestUtils.outputInfo.id;
+       var inputs = access.inputs;
+       var outputs = access.outputs;
+       is(inputs.size, 1, "Should have one input");
+       is(outputs.size, 2, "Should have two outputs");
+       ok(inputs.has(input_id), "input list should contain input id");
+       ok(outputs.has(output_id), "output list should contain output id");
+       var input = access.inputs.get(input_id);
+       var output = access.outputs.get(output_id);
+       objectCompare("input", MIDITestUtils.inputInfo, input);
+       objectCompare("output", MIDITestUtils.outputInfo, output);
+       access.removeEventListener("statechange", failOnCall);
+       SimpleTest.finish();
+     };
+    </script>
+  </body>
+</html>
diff --git a/dom/midi/tests/test_midi_device_explicit_open_close.html b/dom/midi/tests/test_midi_device_explicit_open_close.html
new file mode 100644
index 0000000000..db4e17f619
--- /dev/null
+++ b/dom/midi/tests/test_midi_device_explicit_open_close.html
@@ -0,0 +1,95 @@
+<html>
+  <head>
+    <title>WebMIDI Device Open/Close Test</title>
+    <script type="text/javascript" src="/MochiKit/MochiKit.js"></script>
+    <script src="/tests/SimpleTest/SimpleTest.js"></script>
+    <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css" />
+    <script type="application/javascript" src="MIDITestUtils.js"></script>
+  </head>
+
+  <body onload="runTests()">
+    <script class="testbody" type="application/javascript">
+     SimpleTest.waitForExplicitFinish();
+
+     async function runTests() {
+       await MIDITestUtils.permissionSetup(true);
+
+       let access;
+       try {
+         access = await navigator.requestMIDIAccess({ "sysex": false })
+       } catch (e) {
+         ok(false, "MIDI Access Request Failed!");
+         SimpleTest.finish();
+       }
+
+       ok(true, "MIDI Access Request successful");
+       let input = access.inputs.get(MIDITestUtils.inputInfo.id);
+       let portEventRes;
+       let accessEventRes;
+       let portEventPromise = new Promise((resolve, reject) => { portEventRes = resolve; });
+       let accessEventPromise = new Promise((resolve, reject) => { accessEventRes = resolve; });
+       let shouldClose = false;
+       let checkPort = (event) => {
+         ok(input === event.port, "input port object and event port object are same object");
+         ok(true, "port connection event fired");
+         ok(event.port.connection === (!shouldClose ? "open" : "closed"), "connection registered correctly");
+       };
+       let inputEventHandler = (event) => {
+         checkPort(event);
+         portEventRes();
+       };
+       let accessEventHandler = (event) => {
+         checkPort(event);
+         accessEventRes();
+       };
+       input.addEventListener("statechange", inputEventHandler);
+       access.addEventListener("statechange", accessEventHandler);
+       await input.open();
+       ok(true, "connection successful");
+       ok(input.connection === "open", "connection registered as open");
+       await Promise.all([portEventPromise, accessEventPromise]);
+       input.removeEventListener("statechange", inputEventHandler);
+       access.removeEventListener("statechange", accessEventHandler);
+       ok(true, "MIDI Port Open Test finished.");
+       ok(true, "Testing open failure");
+       let out_access;
+       try {
+         out_access = await navigator.requestMIDIAccess({ "sysex": false });
+       } catch (e) {
+         ok(false, "MIDI Access Request Failed!");
+         SimpleTest.finish();
+       }
+       let outputEventRes;
+       let outputEventHandler = (event) => {
+         ok(output_opened === event.port, "output port object and event port object are same object");
+         ok(true, "access connection event fired");
+         ok(event.port.connection === "closed", "connection registered as closed");
+       };
+       out_access.addEventListener("statechange", outputEventHandler);
+       let output_opened = out_access.outputs.get(MIDITestUtils.alwaysClosedTestOutputInfo.id);
+       try {
+         await output_opened.open();
+         ok(false, "Should've failed to open port!");
+       } catch(err) {
+         is(err.name, "InvalidAccessError", "error name " + err.name + " should be InvalidAccessError");
+         ok(output_opened.connection == "closed", "connection registered as closed");
+         ok(true, "Port not opened, test succeeded");
+       } finally {
+         out_access.removeEventListener("statechange", outputEventHandler);
+       }
+       ok(true, "Starting MIDI port closing test");
+       portEventPromise = new Promise((resolve, reject) => { portEventRes = resolve; });
+       accessEventPromise = new Promise((resolve, reject) => { accessEventRes = resolve; });
+       input.addEventListener("statechange", inputEventHandler);
+       access.addEventListener("statechange", accessEventHandler);
+       shouldClose = true;
+       await input.close();
+       ok(input.connection === "closed", "connection registered as closed");
+       await Promise.all([portEventPromise, accessEventPromise]);
+       input.removeEventListener("statechange", inputEventHandler);
+       access.removeEventListener("statechange", accessEventHandler);
+       SimpleTest.finish();
+     }
+    </script>
+  </body>
+</html>
diff --git a/dom/midi/tests/test_midi_device_implicit_open_close.html b/dom/midi/tests/test_midi_device_implicit_open_close.html
new file mode 100644
index 0000000000..f2c064dc6c
--- /dev/null
+++ b/dom/midi/tests/test_midi_device_implicit_open_close.html
@@ -0,0 +1,67 @@
+<html>
+  <head>
+    <title>WebMIDI Listener Test</title>
+    <script type="text/javascript" src="/MochiKit/MochiKit.js"></script>
+    <script src="/tests/SimpleTest/SimpleTest.js"></script>
+    <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css" />
+    <script type="application/javascript" src="MIDITestUtils.js"></script>
+  </head>
+
+  <body onload="runTests()">
+    <script class="testbody" type="application/javascript">
+     SimpleTest.waitForExplicitFinish();
+
+     async function runTests() {
+       await MIDITestUtils.permissionSetup(true);
+       let access = await navigator.requestMIDIAccess({ "sysex": false });
+       ok(true, "MIDI Access Request successful");
+       is(access.sysexEnabled, false, "Sysex should be false");
+
+       var checkCount = 0;
+       var reopened = false;
+       var input;
+       var output;
+       function checkCallbacks(port) {
+         ok(true, "Got port " + port.connection + " for " + port.name);
+         if (port.connection == "open") {
+           checkCount++;
+         } else {
+           if (!reopened) {
+             reopened = true;
+             // Ports are closed. Fire rest of tests.
+             input.onmidimessage = checkReturn;
+             output.send([0x90, 0x00, 0x7F]);
+           }
+         }
+         if (checkCount == 3) {
+           input.onstatechange = undefined;
+           output.onstatechange = undefined;
+           input.close();
+           output.close();
+           SimpleTest.finish();
+         }
+       }
+       function checkReturn(event) {
+         checkCount++;
+         ok(true, "Got echo message back");
+         MIDITestUtils.checkPacket(event.data, [0x90, 0x00, 0x7f]);
+         if (checkCount == 3) {
+           input.onstatechange = undefined;
+           output.onstatechange = undefined;
+           input.close();
+           output.close();
+           SimpleTest.finish();
+         }
+       }
+
+       input = access.inputs.get(MIDITestUtils.inputInfo.id);
+       output = access.outputs.get(MIDITestUtils.outputInfo.id);
+       // We automatically open ports, so close them first.
+       input.onstatechange = (event) => { checkCallbacks(event.port); };
+       output.onstatechange = (event) => { checkCallbacks(event.port); };
+       input.close();
+       output.close();
+     }
+    </script>
+  </body>
+</html>
diff --git a/dom/midi/tests/test_midi_device_pending.html b/dom/midi/tests/test_midi_device_pending.html
new file mode 100644
index 0000000000..cc179cfdcc
--- /dev/null
+++ b/dom/midi/tests/test_midi_device_pending.html
@@ -0,0 +1,122 @@
+<html>
+  <head>
+    <title>WebMIDI Listener Test</title>
+    <script type="text/javascript" src="/MochiKit/MochiKit.js"></script>
+    <script src="/tests/SimpleTest/SimpleTest.js"></script>
+    <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css" />
+    <script type="application/javascript" src="MIDITestUtils.js"></script>
+  </head>
+
+  <body onload="runTests()">
+    <script class="testbody" type="application/javascript">
+     SimpleTest.waitForExplicitFinish();
+
+     async function runTests() {
+       await MIDITestUtils.permissionSetup(true);
+
+
+       var checkCount = 0;
+       var state = "connecting";
+       var output;
+       var test_ports = [];
+       let access;
+
+       let accessRes;
+       let accessRej;
+       let accessPromise;
+       let portRes;
+       let portRej;
+       let portPromise;
+
+       function resetPromises() {
+         accessPromise = new Promise((res, rej) => { accessRes = res; accessRej = rej; });
+         portPromise = new Promise((res, rej) => { portRes = res; portRej = rej; });
+       }
+
+       function accessStateChangeHandler(event) {
+         var p = event.port;
+         // We'll get an open event for the output control port. Ignore it.
+         if (p.name == MIDITestUtils.outputInfo.name) {
+           return;
+         }
+         accessRes(event);
+       }
+
+       function portStateChangeHandler(event) {
+         var p = event.port;
+         // We'll get an open event for the output control port. Ignore it.
+         if (p.name == MIDITestUtils.outputInfo.name) {
+           return;
+         }
+         portRes(event);
+       }
+
+       // Part 1: Create MIDIAccess object, attach state change listener to list for new connections
+       access = await navigator.requestMIDIAccess({ "sysex": false });
+       ok(true, "MIDI Access Request successful");
+       is(access.sysexEnabled, false, "Sysex should be false");
+       access.addEventListener("statechange", accessStateChangeHandler);
+
+       // Part 2: open test device, make sure it connects, attach event handler to device object
+       output = access.outputs.get(MIDITestUtils.outputInfo.id);
+       resetPromises();
+       output.send([0x90, 0x01, 0x00]);
+       let accessEvent = await accessPromise;
+       let testPort = accessEvent.port;
+       test_ports.push(testPort);
+       testPort.addEventListener("statechange", portStateChangeHandler);
+       is(testPort.state, "connected", "Device " + testPort.name + " connected");
+
+       // Part 3: Listen for port status change on open as both an access event
+       // and a port event.
+       resetPromises();
+       testPort.open();
+       accessEvent = await accessPromise;
+       is(testPort.connection, "open", "Connection " + testPort.name + " opened");
+       let portEvent = await portPromise;
+       is(testPort.connection, "open", "Connection " + testPort.name + " opened");
+
+       // Part 4: Disconnect port but don't close, check status to make sure we're pending.
+       resetPromises();
+       output.send([0x90, 0x02, 0x00]);
+       accessEvent = await accessPromise;
+       is(testPort.connection, "pending", "Connection " + testPort.name + " pending");
+       is(access.inputs.has(testPort.id), false, "port removed from input map while pending");
+       portEvent = await portPromise;
+       is(testPort.connection, "pending", "Connection " + testPort.name + " pending");
+
+       // Part 5: Connect ports again, make sure we return to the right status. The events will
+       // fire because the device has been readded to the device maps in the access object.
+       resetPromises();
+       output.send([0x90, 0x01, 0x00]);
+       accessEvent = await accessPromise;
+       var port = access.inputs.get(testPort.id);
+       is(port, accessEvent.port, "port in map and port in event should be the same");
+       is(testPort.connection, "pending", "Connection " + testPort.name + " pending");
+       portEvent = await portPromise;
+       is(testPort.connection, "pending", "Connection " + testPort.name + " pending");
+
+       // Part 6: Close out everything and clean up.
+       resetPromises();
+       accessEvent = await accessPromise;
+       is(accessEvent.port.connection, "open", "Connection " + testPort.name + " opened");
+       portEvent = await portPromise;
+       is(portEvent.port.connection, "open", "Connection " + testPort.name + " opened");
+
+       /* for (let port of test_ports) {
+        *   port.removeEventListener("statechange", checkDevices);
+        * }
+        * access.removeEventListener("statechange", checkDevices);*/
+       output.send([0x90, 0x02, 0x00]);
+       testPort.removeEventListener("statechange", portStateChangeHandler);
+       access.removeEventListener("statechange", accessStateChangeHandler);
+       access = undefined;
+       output = undefined;
+       testPort = undefined;
+       accessEvent = undefined;
+       portEvent = undefined;
+       SimpleTest.finish();
+     }
+    </script>
+  </body>
+</html>
diff --git a/dom/midi/tests/test_midi_device_sysex.html b/dom/midi/tests/test_midi_device_sysex.html
new file mode 100644
index 0000000000..60ee741e60
--- /dev/null
+++ b/dom/midi/tests/test_midi_device_sysex.html
@@ -0,0 +1,57 @@
+<html>
+  <head>
+    <title>WebMIDI Listener Test</title>
+    <script type="text/javascript" src="/MochiKit/MochiKit.js"></script>
+    <script src="/tests/SimpleTest/SimpleTest.js"></script>
+    <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css" />
+    <script type="application/javascript" src="MIDITestUtils.js"></script>
+  </head>
+
+  <body onload="runTests()">
+    <script class="testbody" type="application/javascript">
+     SimpleTest.waitForExplicitFinish();
+
+     async function runTests() {
+       await MIDITestUtils.permissionSetup(true);
+       var sysexCheckCount = 0;
+       var checkCount = 0;
+       var input;
+       var output;
+       function checkSysexReceive(event) {
+         checkCount++;
+         sysexCheckCount++;
+         if (sysexCheckCount == 1) {
+           is(event.data[0], 0xF0, "Echoed sysex message via sysex port");
+         } else {
+           is(event.data[0], 0x90, "Echoed regular message via sysex port");
+         }
+         if (checkCount == 5) {
+           SimpleTest.finish();
+         }
+       }
+
+       function checkNoSysexReceive(event) {
+         checkCount++;
+         is(event.data[0], 0x90, "Echoed regular message via non-sysex port");
+         if (checkCount == 5) {
+           SimpleTest.finish()
+         }
+       }
+
+       // Request access without sysex.
+       let access_regular = await navigator.requestMIDIAccess({ "sysex": false });
+       let access_sysex = await navigator.requestMIDIAccess({ "sysex": true });
+       ok(true, "MIDI Access Request successful");
+       ok(true, "Check for sysex message drop");
+       input = access_regular.inputs.get(MIDITestUtils.inputInfo.id);
+       output = access_sysex.outputs.get(MIDITestUtils.outputInfo.id);
+       input_sysex = access_sysex.inputs.get(MIDITestUtils.inputInfo.id);
+       input_sysex.onmidimessage = checkSysexReceive;
+       input.onmidimessage = checkNoSysexReceive;
+       output.send([0xF0, 0x00, 0xF7]);
+       output.send([0x90, 0x00, 0x01]);
+       output.send([0x90, 0x00, 0x01]);
+     }
+    </script>
+  </body>
+</html>
diff --git a/dom/midi/tests/test_midi_device_system_rt.html b/dom/midi/tests/test_midi_device_system_rt.html
new file mode 100644
index 0000000000..399f42f915
--- /dev/null
+++ b/dom/midi/tests/test_midi_device_system_rt.html
@@ -0,0 +1,39 @@
+<html>
+  <head>
+    <title>WebMIDI Listener Test</title>
+    <script type="text/javascript" src="/MochiKit/MochiKit.js"></script>
+    <script src="/tests/SimpleTest/SimpleTest.js"></script>
+    <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css" />
+    <script type="application/javascript" src="MIDITestUtils.js"></script>
+  </head>
+
+  <body onload="runTests()">
+    <script class="testbody" type="application/javascript">
+     SimpleTest.waitForExplicitFinish();
+
+     async function runTests() {
+       await MIDITestUtils.permissionSetup(true);
+       var checkCount = 0;
+
+       function checkReturn(msg) {
+         checkCount++;
+         if (checkCount == 1) {
+           MIDITestUtils.checkPacket(msg.data, [0xF8]);
+         } else if (checkCount == 2) {
+           MIDITestUtils.checkPacket(msg.data, [0xF9]);
+         } else if (checkCount == 3) {
+           MIDITestUtils.checkPacket(msg.data, [0xF0, 0x01, 0x02, 0x03, 0x04, 0x05, 0xF7]);
+           SimpleTest.finish();
+         }
+       }
+
+       // Request access without sysex.
+       let access_sysex = await navigator.requestMIDIAccess({ "sysex": true });
+       let input_sysex = access_sysex.inputs.get(MIDITestUtils.inputInfo.id);
+       input_sysex.onmidimessage = checkReturn;
+       let output_sysex = access_sysex.outputs.get(MIDITestUtils.outputInfo.id);
+       output_sysex.send([0xF0, 0x01, 0xF7]);
+     }
+    </script>
+  </body>
+</html>
diff --git a/dom/midi/tests/test_midi_packet_timing_sorting.html b/dom/midi/tests/test_midi_packet_timing_sorting.html
new file mode 100644
index 0000000000..904929e532
--- /dev/null
+++ b/dom/midi/tests/test_midi_packet_timing_sorting.html
@@ -0,0 +1,48 @@
+<html>
+  <head>
+    <title>WebMIDI Listener Test</title>
+    <script type="text/javascript" src="/MochiKit/MochiKit.js"></script>
+    <script src="/tests/SimpleTest/SimpleTest.js"></script>
+    <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css" />
+    <script type="application/javascript" src="MIDITestUtils.js"></script>
+  </head>
+
+  <body onload="runTests()">
+    <script class="testbody" type="application/javascript">
+     SimpleTest.waitForExplicitFinish();
+
+     async function runTests() {
+       await MIDITestUtils.permissionSetup(true);
+       await SpecialPowers.pushPrefEnv({"set": [["privacy.resistFingerprinting.reduceTimerPrecision.jitter", false]]});
+       var checkCount = 0;
+       var lastTime = 0;
+       var reopened = false;
+       var input;
+       var output;
+       function checkReturn(event) {
+         ok(event.timeStamp > lastTime, "Received timestamp " + event.timeStamp + " should be greater than " + lastTime);
+         lastTime = event.timeStamp;
+         checkCount++;
+
+         if (checkCount == 6) {
+           input.close();
+           output.close();
+           SimpleTest.finish();
+         }
+       }
+       ok("Testing MIDI packet reordering based on timestamps");
+       // Request access without sysex.
+       let access = await navigator.requestMIDIAccess({ "sysex": false });
+       ok(true, "MIDI Access Request successful");
+       is(access.sysexEnabled, false, "Sysex should be false");
+
+       input = access.inputs.get(MIDITestUtils.inputInfo.id);
+       output = access.outputs.get(MIDITestUtils.outputInfo.id);
+       input.onmidimessage = checkReturn;
+       // trigger the packet timing sorting tests
+       output.send([0x90, 0x03, 0x00], 0);
+       ok(true, "Waiting on packets");
+     }
+    </script>
+  </body>
+</html>
diff --git a/dom/midi/tests/test_midi_permission_allow.html b/dom/midi/tests/test_midi_permission_allow.html
new file mode 100644
index 0000000000..84578cfeae
--- /dev/null
+++ b/dom/midi/tests/test_midi_permission_allow.html
@@ -0,0 +1,26 @@
+<html>
+  <head>
+    <title>WebMIDI Listener Test</title>
+    <script src="/tests/SimpleTest/SimpleTest.js"></script>
+    <script type="application/javascript" src="MIDITestUtils.js"></script>
+  </head>
+
+  <body onload="runTests()">
+    <script class="testbody" type="application/javascript">
+     SimpleTest.waitForExplicitFinish();
+
+     async function runTests() {
+       await MIDITestUtils.permissionSetup(true);
+       // Request access without sysex.
+       try {
+         await navigator.requestMIDIAccess({ "sysex": false })
+         ok(true, "MIDI Access Request successful");
+         SimpleTest.finish();
+       } catch (ex) {
+         ok(false, "MIDI Access Request Failed!");
+         SimpleTest.finish();
+       }
+     }
+    </script>
+  </body>
+</html>
diff --git a/dom/midi/tests/test_midi_permission_deny.html b/dom/midi/tests/test_midi_permission_deny.html
new file mode 100644
index 0000000000..8e3043a49a
--- /dev/null
+++ b/dom/midi/tests/test_midi_permission_deny.html
@@ -0,0 +1,26 @@
+<html>
+  <head>
+    <title>WebMIDI Listener Test</title>
+    <script src="/tests/SimpleTest/SimpleTest.js"></script>
+    <script type="application/javascript" src="MIDITestUtils.js"></script>
+  </head>
+
+  <body onload="runTests()">
+    <script class="testbody" type="application/javascript">
+     SimpleTest.waitForExplicitFinish();
+
+     async function runTests() {
+       await MIDITestUtils.permissionSetup(false);
+       // Request access without sysex.
+       try {
+         await navigator.requestMIDIAccess({ "sysex": false });
+         ok(false, "MIDI Access Request Deny failed");
+         SimpleTest.finish();
+       } catch (ex) {
+         ok(true, "MIDI Access Request Deny successful!");
+         SimpleTest.finish();
+       }
+     }
+    </script>
+  </body>
+</html>
diff --git a/dom/midi/tests/test_midi_permission_prompt.html b/dom/midi/tests/test_midi_permission_prompt.html
new file mode 100644
index 0000000000..26a6b3d789
--- /dev/null
+++ b/dom/midi/tests/test_midi_permission_prompt.html
@@ -0,0 +1,24 @@
+<html>
+  <head>
+    <title>WebMIDI Listener Test</title>
+    <script src="/tests/SimpleTest/SimpleTest.js"></script>
+    <script type="application/javascript" src="MIDITestUtils.js"></script>
+  </head>
+
+  <body onload="runTests()">
+    <script class="testbody" type="application/javascript">
+     SimpleTest.waitForExplicitFinish();
+
+     async function runTests() {
+       await MIDITestUtils.permissionSetup(true);
+       try {
+         await navigator.requestMIDIAccess({ "sysex": false });
+         ok(true, "Prompting for permissions succeeded!");
+       } catch (e) {
+         ok(false, "Prompting for permissions failed!");
+       }
+       SimpleTest.finish();
+     }
+    </script>
+  </body>
+</html>