1 files changed, 171 insertions, 0 deletions
diff --git a/dom/ipc/TabContext.h b/dom/ipc/TabContext.h
new file mode 100644
index 0000000000..00bf69c2a2
--- /dev/null
+++ b/dom/ipc/TabContext.h
@@ -0,0 +1,171 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=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/. */
+
+#ifndef mozilla_dom_TabContext_h
+#define mozilla_dom_TabContext_h
+
+#include "nsCOMPtr.h"
+#include "mozilla/BasePrincipal.h"
+#include "nsPIDOMWindow.h"
+#include "nsPIWindowRoot.h"
+
+namespace mozilla::dom {
+
+class IPCTabContext;
+
+/**
+ * TabContext encapsulates information about an iframe.
+ *
+ * BrowserParent and BrowserChild both inherit from TabContext, and you can also
+ * have standalone TabContext objects.
+ *
+ * This class is immutable except by calling one of the protected
+ * SetTabContext*() methods (and those methods can only be called once).  See
+ * also MutableTabContext.
+ */
+class TabContext {
+ public:
+  TabContext();
+
+  /* (The implicit copy-constructor and operator= are fine.) */
+
+  /**
+   * Generates IPCTabContext of type BrowserFrameIPCTabContext from this
+   * TabContext's information.
+   */
+  IPCTabContext AsIPCTabContext() const;
+
+  uint64_t ChromeOuterWindowID() const;
+
+  uint32_t MaxTouchPoints() const { return mMaxTouchPoints; }
+
+ protected:
+  friend class MaybeInvalidTabContext;
+
+  /**
+   * These protected mutator methods let you modify a TabContext once.  Further
+   * attempts to modify a given TabContext will fail (the method will return
+   * false).
+   *
+   * These mutators will also fail if the TabContext was created with anything
+   * other than the no-args constructor.
+   */
+
+  /**
+   * Set this TabContext to match the given TabContext.
+   */
+  bool SetTabContext(const TabContext& aContext);
+
+  bool SetTabContext(uint64_t aChromeOuterWindowID, uint32_t aMaxTouchPoints);
+
+  /**
+   * Modify this TabContext to match the given TabContext.  This is a special
+   * case triggered by nsFrameLoader::SwapWithOtherRemoteLoader which may have
+   * caused the owner content to change.
+   *
+   * This special case only allows the field `mChromeOuterWindowID` to be
+   * changed.  If any other fields have changed, the update is ignored and
+   * returns false.
+   */
+  bool UpdateTabContextAfterSwap(const TabContext& aContext);
+
+  void SetMaxTouchPoints(uint32_t aMaxTouchPoints) {
+    mMaxTouchPoints = aMaxTouchPoints;
+  }
+
+ private:
+  /**
+   * Has this TabContext been initialized?  If so, mutator methods will fail.
+   */
+  bool mInitialized;
+
+  /**
+   * The outerWindowID of the window hosting the remote frameloader.
+   */
+  uint64_t mChromeOuterWindowID;
+
+  /**
+   * Maximum number of touch points.
+   */
+  uint32_t mMaxTouchPoints;
+};
+
+/**
+ * MutableTabContext is the same as MaybeInvalidTabContext, except the mutation
+ * methods are public instead of protected.  You can still only call these
+ * mutation methods once on a given object.
+ */
+class MutableTabContext : public TabContext {
+ public:
+  bool SetTabContext(const TabContext& aContext) {
+    return TabContext::SetTabContext(aContext);
+  }
+
+  bool SetTabContext(uint64_t aChromeOuterWindowID, uint32_t aMaxTouchPoints) {
+    return TabContext::SetTabContext(aChromeOuterWindowID, aMaxTouchPoints);
+  }
+};
+
+/**
+ * MaybeInvalidTabContext is a simple class that lets you transform an
+ * IPCTabContext into a TabContext.
+ *
+ * The issue is that an IPCTabContext is not necessarily valid.  So to convert
+ * an IPCTabContext into a TabContext, you construct a MaybeInvalidTabContext,
+ * check whether it's valid, and, if so, read out your TabContext.
+ *
+ * Example usage:
+ *
+ *   void UseTabContext(const TabContext& aTabContext);
+ *
+ *   void CreateTab(const IPCTabContext& aContext) {
+ *     MaybeInvalidTabContext tc(aContext);
+ *     if (!tc.IsValid()) {
+ *       NS_ERROR(nsPrintfCString("Got an invalid IPCTabContext: %s",
+ *                                tc.GetInvalidReason()));
+ *       return;
+ *     }
+ *     UseTabContext(tc.GetTabContext());
+ *   }
+ */
+class MaybeInvalidTabContext {
+ public:
+  /**
+   * This constructor copies the information in aContext and sets IsValid() as
+   * appropriate.
+   */
+  explicit MaybeInvalidTabContext(const IPCTabContext& aContext);
+
+  /**
+   * Was the IPCTabContext we received in our constructor valid?
+   */
+  bool IsValid();
+
+  /**
+   * If IsValid(), this function returns null.  Otherwise, it returns a
+   * human-readable string indicating why the IPCTabContext passed to our
+   * constructor was not valid.
+   */
+  const char* GetInvalidReason();
+
+  /**
+   * If IsValid(), this function returns a reference to a TabContext
+   * corresponding to the IPCTabContext passed to our constructor.  If
+   * !IsValid(), this function crashes.
+   */
+  const TabContext& GetTabContext();
+
+ private:
+  MaybeInvalidTabContext(const MaybeInvalidTabContext&) = delete;
+  MaybeInvalidTabContext& operator=(const MaybeInvalidTabContext&) = delete;
+
+  const char* mInvalidReason;
+  MutableTabContext mTabContext;
+};
+
+}  // namespace mozilla::dom
+
+#endif