Adding upstream version 124.0.1.upstream/124.0.1

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

1 files changed, 2473 insertions, 0 deletions

diff --git a/dom/media/webrtc/jsep/JsepSessionImpl.cpp b/dom/media/webrtc/jsep/JsepSessionImpl.cpp
new file mode 100644
index 0000000000..50def6eb6c
--- /dev/null
+++ b/dom/media/webrtc/jsep/JsepSessionImpl.cpp
@@ -0,0 +1,2473 @@
+/* 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 "jsep/JsepSessionImpl.h"
+
+#include <stdlib.h>
+
+#include <bitset>
+#include <iterator>
+#include <set>
+#include <string>
+#include <utility>
+
+#include "transport/logging.h"
+#include "mozilla/Preferences.h"
+#include "mozilla/Telemetry.h"
+#include "mozilla/UniquePtr.h"
+#include "mozilla/net/DataChannelProtocol.h"
+#include "nsDebug.h"
+#include "nspr.h"
+#include "nss.h"
+#include "pk11pub.h"
+
+#include "api/rtp_parameters.h"
+
+#include "jsep/JsepTrack.h"
+#include "jsep/JsepTransport.h"
+#include "sdp/HybridSdpParser.h"
+#include "sdp/SipccSdp.h"
+
+namespace mozilla {
+
+MOZ_MTLOG_MODULE("jsep")
+
+#define JSEP_SET_ERROR(error)                                 \
+  do {                                                        \
+    std::ostringstream os;                                    \
+    os << error;                                              \
+    mLastError = os.str();                                    \
+    MOZ_MTLOG(ML_ERROR, "[" << mName << "]: " << mLastError); \
+  } while (0);
+
+static std::bitset<128> GetForbiddenSdpPayloadTypes() {
+  std::bitset<128> forbidden(0);
+  forbidden[1] = true;
+  forbidden[2] = true;
+  forbidden[19] = true;
+  for (uint16_t i = 64; i < 96; ++i) {
+    forbidden[i] = true;
+  }
+  return forbidden;
+}
+
+static std::string GetRandomHex(size_t words) {
+  std::ostringstream os;
+
+  for (size_t i = 0; i < words; ++i) {
+    uint32_t rand;
+    SECStatus rv = PK11_GenerateRandom(reinterpret_cast<unsigned char*>(&rand),
+                                       sizeof(rand));
+    if (rv != SECSuccess) {
+      MOZ_CRASH();
+      return "";
+    }
+
+    os << std::hex << std::setfill('0') << std::setw(8) << rand;
+  }
+  return os.str();
+}
+
+JsepSessionImpl::JsepSessionImpl(const JsepSessionImpl& aOrig)
+    : JsepSession(aOrig),
+      JsepSessionCopyableStuff(aOrig),
+      mUuidGen(aOrig.mUuidGen->Clone()),
+      mGeneratedOffer(aOrig.mGeneratedOffer ? aOrig.mGeneratedOffer->Clone()
+                                            : nullptr),
+      mGeneratedAnswer(aOrig.mGeneratedAnswer ? aOrig.mGeneratedAnswer->Clone()
+                                              : nullptr),
+      mCurrentLocalDescription(aOrig.mCurrentLocalDescription
+                                   ? aOrig.mCurrentLocalDescription->Clone()
+                                   : nullptr),
+      mCurrentRemoteDescription(aOrig.mCurrentRemoteDescription
+                                    ? aOrig.mCurrentRemoteDescription->Clone()
+                                    : nullptr),
+      mPendingLocalDescription(aOrig.mPendingLocalDescription
+                                   ? aOrig.mPendingLocalDescription->Clone()
+                                   : nullptr),
+      mPendingRemoteDescription(aOrig.mPendingRemoteDescription
+                                    ? aOrig.mPendingRemoteDescription->Clone()
+                                    : nullptr),
+      mSdpHelper(&mLastError),
+      mParser(new HybridSdpParser()) {
+  for (const auto& codec : aOrig.mSupportedCodecs) {
+    mSupportedCodecs.emplace_back(codec->Clone());
+  }
+}
+
+nsresult JsepSessionImpl::Init() {
+  mLastError.clear();
+
+  MOZ_ASSERT(!mSessionId, "Init called more than once");
+
+  nsresult rv = SetupIds();
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  mEncodeTrackId =
+      Preferences::GetBool("media.peerconnection.sdp.encode_track_id", true);
+
+  mIceUfrag = GetRandomHex(1);
+  mIcePwd = GetRandomHex(4);
+  return NS_OK;
+}
+
+static void GetIceCredentials(
+    const Sdp& aSdp,
+    std::set<std::pair<std::string, std::string>>* aCredentials) {
+  for (size_t i = 0; i < aSdp.GetMediaSectionCount(); ++i) {
+    const SdpAttributeList& attrs = aSdp.GetMediaSection(i).GetAttributeList();
+    if (attrs.HasAttribute(SdpAttribute::kIceUfragAttribute) &&
+        attrs.HasAttribute(SdpAttribute::kIcePwdAttribute)) {
+      aCredentials->insert(
+          std::make_pair(attrs.GetIceUfrag(), attrs.GetIcePwd()));
+    }
+  }
+}
+
+std::set<std::pair<std::string, std::string>>
+JsepSessionImpl::GetLocalIceCredentials() const {
+  std::set<std::pair<std::string, std::string>> result;
+  if (mCurrentLocalDescription) {
+    GetIceCredentials(*mCurrentLocalDescription, &result);
+  }
+  if (mPendingLocalDescription) {
+    GetIceCredentials(*mPendingLocalDescription, &result);
+  }
+  return result;
+}
+
+void JsepSessionImpl::AddTransceiver(const JsepTransceiver& aTransceiver) {
+  mLastError.clear();
+  MOZ_MTLOG(ML_DEBUG,
+            "[" << mName << "]: Adding transceiver " << aTransceiver.GetUuid());
+#ifdef DEBUG
+  if (aTransceiver.GetMediaType() == SdpMediaSection::kApplication) {
+    // Make sure we don't add more than one DataChannel transceiver
+    for (const auto& transceiver : mTransceivers) {
+      MOZ_ASSERT(transceiver.GetMediaType() != SdpMediaSection::kApplication);
+    }
+  }
+#endif
+  mTransceivers.push_back(aTransceiver);
+  InitTransceiver(mTransceivers.back());
+}
+
+void JsepSessionImpl::InitTransceiver(JsepTransceiver& aTransceiver) {
+  mLastError.clear();
+
+  if (aTransceiver.GetMediaType() != SdpMediaSection::kApplication) {
+    // Make sure we have an ssrc. Might already be set.
+    aTransceiver.mSendTrack.EnsureSsrcs(mSsrcGenerator, 1U);
+    aTransceiver.mSendTrack.SetCNAME(mCNAME);
+
+    // Make sure we have identifiers for send track, just in case.
+    // (man I hate this)
+    if (mEncodeTrackId) {
+      aTransceiver.mSendTrack.SetTrackId(aTransceiver.GetUuid());
+    }
+  } else {
+    // Datachannel transceivers should always be sendrecv. Just set it instead
+    // of asserting.
+    aTransceiver.mJsDirection = SdpDirectionAttribute::kSendrecv;
+  }
+
+  aTransceiver.mSendTrack.PopulateCodecs(mSupportedCodecs);
+  aTransceiver.mRecvTrack.PopulateCodecs(mSupportedCodecs);
+  // We do not set mLevel yet, we do that either on createOffer, or setRemote
+}
+
+nsresult JsepSessionImpl::SetBundlePolicy(JsepBundlePolicy policy) {
+  mLastError.clear();
+
+  if (mBundlePolicy == policy) {
+    return NS_OK;
+  }
+
+  if (mCurrentLocalDescription) {
+    JSEP_SET_ERROR(
+        "Changing the bundle policy is only supported before the "
+        "first SetLocalDescription.");
+    return NS_ERROR_UNEXPECTED;
+  }
+
+  mBundlePolicy = policy;
+  return NS_OK;
+}
+
+nsresult JsepSessionImpl::AddDtlsFingerprint(
+    const nsACString& algorithm, const std::vector<uint8_t>& value) {
+  mLastError.clear();
+  JsepDtlsFingerprint fp;
+
+  fp.mAlgorithm = algorithm;
+  fp.mValue = value;
+
+  mDtlsFingerprints.push_back(fp);
+
+  return NS_OK;
+}
+
+nsresult JsepSessionImpl::AddRtpExtension(
+    JsepMediaType mediaType, const std::string& extensionName,
+    SdpDirectionAttribute::Direction direction) {
+  mLastError.clear();
+
+  for (auto& ext : mRtpExtensions) {
+    if (ext.mExtmap.direction == direction &&
+        ext.mExtmap.extensionname == extensionName) {
+      if (ext.mMediaType != mediaType) {
+        ext.mMediaType = JsepMediaType::kAudioVideo;
+      }
+      return NS_OK;
+    }
+  }
+
+  uint16_t freeEntry = GetNeverUsedExtmapEntry();
+
+  if (freeEntry == 0) {
+    return NS_ERROR_FAILURE;
+  }
+
+  JsepExtmapMediaType extMediaType = {
+      mediaType,
+      {freeEntry, direction,
+       // do we want to specify direction?
+       direction != SdpDirectionAttribute::kSendrecv, extensionName, ""}};
+
+  mRtpExtensions.push_back(extMediaType);
+  return NS_OK;
+}
+
+nsresult JsepSessionImpl::AddAudioRtpExtension(
+    const std::string& extensionName,
+    SdpDirectionAttribute::Direction direction) {
+  return AddRtpExtension(JsepMediaType::kAudio, extensionName, direction);
+}
+
+nsresult JsepSessionImpl::AddVideoRtpExtension(
+    const std::string& extensionName,
+    SdpDirectionAttribute::Direction direction) {
+  return AddRtpExtension(JsepMediaType::kVideo, extensionName, direction);
+}
+
+nsresult JsepSessionImpl::AddAudioVideoRtpExtension(
+    const std::string& extensionName,
+    SdpDirectionAttribute::Direction direction) {
+  return AddRtpExtension(JsepMediaType::kAudioVideo, extensionName, direction);
+}
+
+nsresult JsepSessionImpl::CreateOfferMsection(const JsepOfferOptions& options,
+                                              JsepTransceiver& transceiver,
+                                              Sdp* local) {
+  SdpMediaSection::Protocol protocol(
+      SdpHelper::GetProtocolForMediaType(transceiver.GetMediaType()));
+
+  const Sdp* answer(GetAnswer());
+  const SdpMediaSection* lastAnswerMsection = nullptr;
+
+  if (answer &&
+      (local->GetMediaSectionCount() < answer->GetMediaSectionCount())) {
+    lastAnswerMsection =
+        &answer->GetMediaSection(local->GetMediaSectionCount());
+    // Use the protocol the answer used, even if it is not what we would have
+    // used.
+    protocol = lastAnswerMsection->GetProtocol();
+  }
+
+  SdpMediaSection* msection = &local->AddMediaSection(
+      transceiver.GetMediaType(), transceiver.mJsDirection, 0, protocol,
+      sdp::kIPv4, "0.0.0.0");
+
+  // Some of this stuff (eg; mid) sticks around even if disabled
+  if (lastAnswerMsection) {
+    MOZ_ASSERT(lastAnswerMsection->GetMediaType() ==
+               transceiver.GetMediaType());
+    nsresult rv = mSdpHelper.CopyStickyParams(*lastAnswerMsection, msection);
+    NS_ENSURE_SUCCESS(rv, rv);
+  }
+
+  if (transceiver.IsStopping() || transceiver.IsStopped()) {
+    SdpHelper::DisableMsection(local, msection);
+    return NS_OK;
+  }
+
+  msection->SetPort(9);
+
+  // We don't do this in AddTransportAttributes because that is also used for
+  // making answers, and we don't want to unconditionally set rtcp-mux or
+  // rtcp-rsize there.
+  if (mSdpHelper.HasRtcp(msection->GetProtocol())) {
+    // Set RTCP-MUX.
+    msection->GetAttributeList().SetAttribute(
+        new SdpFlagAttribute(SdpAttribute::kRtcpMuxAttribute));
+    // Set RTCP-RSIZE
+    if (msection->GetMediaType() == SdpMediaSection::MediaType::kVideo &&
+        Preferences::GetBool("media.navigator.video.offer_rtcp_rsize", false)) {
+      msection->GetAttributeList().SetAttribute(
+          new SdpFlagAttribute(SdpAttribute::kRtcpRsizeAttribute));
+    }
+  }
+
+  nsresult rv = AddTransportAttributes(msection, SdpSetupAttribute::kActpass);
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  transceiver.mSendTrack.AddToOffer(mSsrcGenerator, msection);
+  transceiver.mRecvTrack.AddToOffer(mSsrcGenerator, msection);
+
+  AddExtmap(msection);
+
+  std::string mid;
+  // We do not set the mid on the transceiver, that happens when a description
+  // is set.
+  if (transceiver.IsAssociated()) {
+    mid = transceiver.GetMid();
+  } else {
+    mid = GetNewMid();
+  }
+
+  msection->GetAttributeList().SetAttribute(
+      new SdpStringAttribute(SdpAttribute::kMidAttribute, mid));
+
+  return NS_OK;
+}
+
+void JsepSessionImpl::SetupBundle(Sdp* sdp) const {
+  std::vector<std::string> mids;
+  std::set<SdpMediaSection::MediaType> observedTypes;
+
+  // This has the effect of changing the bundle level if the first m-section
+  // goes from disabled to enabled. This is kinda inefficient.
+
+  for (size_t i = 0; i < sdp->GetMediaSectionCount(); ++i) {
+    auto& attrs = sdp->GetMediaSection(i).GetAttributeList();
+    if ((sdp->GetMediaSection(i).GetPort() != 0) &&
+        attrs.HasAttribute(SdpAttribute::kMidAttribute)) {
+      bool useBundleOnly = false;
+      switch (mBundlePolicy) {
+        case kBundleMaxCompat:
+          // We don't use bundle-only for max-compat
+          break;
+        case kBundleBalanced:
+          // balanced means we use bundle-only on everything but the first
+          // m-section of a given type
+          if (observedTypes.count(sdp->GetMediaSection(i).GetMediaType())) {
+            useBundleOnly = true;
+          }
+          observedTypes.insert(sdp->GetMediaSection(i).GetMediaType());
+          break;
+        case kBundleMaxBundle:
+          // max-bundle means we use bundle-only on everything but the first
+          // m-section
+          useBundleOnly = !mids.empty();
+          break;
+      }
+
+      if (useBundleOnly) {
+        attrs.SetAttribute(
+            new SdpFlagAttribute(SdpAttribute::kBundleOnlyAttribute));
+        // Set port to 0 for sections with bundle-only attribute. (mjf)
+        sdp->GetMediaSection(i).SetPort(0);
+      }
+
+      mids.push_back(attrs.GetMid());
+    }
+  }
+
+  if (!mids.empty()) {
+    UniquePtr<SdpGroupAttributeList> groupAttr(new SdpGroupAttributeList);
+    groupAttr->PushEntry(SdpGroupAttributeList::kBundle, mids);
+    sdp->GetAttributeList().SetAttribute(groupAttr.release());
+  }
+}
+
+JsepSession::Result JsepSessionImpl::CreateOffer(
+    const JsepOfferOptions& options, std::string* offer) {
+  mLastError.clear();
+
+  if (mState != kJsepStateStable && mState != kJsepStateHaveLocalOffer) {
+    JSEP_SET_ERROR("Cannot create offer in state " << GetStateStr(mState));
+    // Spec doesn't seem to say this is an error. It probably should.
+    return dom::PCError::InvalidStateError;
+  }
+
+  // This is one of those places where CreateOffer sets some state.
+  SetIceRestarting(options.mIceRestart.isSome() && *(options.mIceRestart));
+
+  UniquePtr<Sdp> sdp;
+
+  // Make the basic SDP that is common to offer/answer.
+  nsresult rv = CreateGenericSDP(&sdp);
+  NS_ENSURE_SUCCESS(rv, dom::PCError::OperationError);
+
+  for (size_t level = 0;
+       Maybe<JsepTransceiver> transceiver = GetTransceiverForLocal(level);
+       ++level) {
+    rv = CreateOfferMsection(options, *transceiver, sdp.get());
+    NS_ENSURE_SUCCESS(rv, dom::PCError::OperationError);
+    SetTransceiver(*transceiver);
+  }
+
+  SetupBundle(sdp.get());
+
+  if (mCurrentLocalDescription && GetAnswer()) {
+    rv = CopyPreviousTransportParams(*GetAnswer(), *mCurrentLocalDescription,
+                                     *sdp, sdp.get());
+    NS_ENSURE_SUCCESS(rv, dom::PCError::OperationError);
+  }
+
+  *offer = sdp->ToString();
+  mGeneratedOffer = std::move(sdp);
+  ++mSessionVersion;
+  MOZ_MTLOG(ML_DEBUG, "[" << mName << "]: CreateOffer \nSDP=\n" << *offer);
+
+  return Result();
+}
+
+std::string JsepSessionImpl::GetLocalDescription(
+    JsepDescriptionPendingOrCurrent type) const {
+  std::ostringstream os;
+  mozilla::Sdp* sdp = GetParsedLocalDescription(type);
+  if (sdp) {
+    sdp->Serialize(os);
+  }
+  return os.str();
+}
+
+std::string JsepSessionImpl::GetRemoteDescription(
+    JsepDescriptionPendingOrCurrent type) const {
+  std::ostringstream os;
+  mozilla::Sdp* sdp = GetParsedRemoteDescription(type);
+  if (sdp) {
+    sdp->Serialize(os);
+  }
+  return os.str();
+}
+
+void JsepSessionImpl::AddExtmap(SdpMediaSection* msection) {
+  auto extensions = GetRtpExtensions(*msection);
+
+  if (!extensions.empty()) {
+    SdpExtmapAttributeList* extmap = new SdpExtmapAttributeList;
+    extmap->mExtmaps = extensions;
+    msection->GetAttributeList().SetAttribute(extmap);
+  }
+}
+
+std::vector<SdpExtmapAttributeList::Extmap> JsepSessionImpl::GetRtpExtensions(
+    const SdpMediaSection& msection) {
+  std::vector<SdpExtmapAttributeList::Extmap> result;
+  JsepMediaType mediaType = JsepMediaType::kNone;
+  switch (msection.GetMediaType()) {
+    case SdpMediaSection::kAudio:
+      mediaType = JsepMediaType::kAudio;
+      break;
+    case SdpMediaSection::kVideo:
+      mediaType = JsepMediaType::kVideo;
+      if (msection.GetAttributeList().HasAttribute(
+              SdpAttribute::kRidAttribute)) {
+        // We need RID support
+        // TODO: Would it be worth checking that the direction is sane?
+        AddVideoRtpExtension(webrtc::RtpExtension::kRidUri,
+                             SdpDirectionAttribute::kSendonly);
+
+        if (mRtxIsAllowed &&
+            Preferences::GetBool("media.peerconnection.video.use_rtx", false)) {
+          AddVideoRtpExtension(webrtc::RtpExtension::kRepairedRidUri,
+                               SdpDirectionAttribute::kSendonly);
+        }
+      }
+      break;
+    default:;
+  }
+  if (mediaType != JsepMediaType::kNone) {
+    for (auto ext = mRtpExtensions.begin(); ext != mRtpExtensions.end();
+         ++ext) {
+      if (ext->mMediaType == mediaType ||
+          ext->mMediaType == JsepMediaType::kAudioVideo) {
+        result.push_back(ext->mExtmap);
+      }
+    }
+  }
+  return result;
+}
+
+std::string JsepSessionImpl::GetNewMid() {
+  std::string mid;
+
+  do {
+    std::ostringstream osMid;
+    osMid << mMidCounter++;
+    mid = osMid.str();
+  } while (mUsedMids.count(mid));
+
+  mUsedMids.insert(mid);
+  return mid;
+}
+
+void JsepSessionImpl::AddCommonExtmaps(const SdpMediaSection& remoteMsection,
+                                       SdpMediaSection* msection) {
+  auto negotiatedRtpExtensions = GetRtpExtensions(*msection);
+  mSdpHelper.NegotiateAndAddExtmaps(remoteMsection, negotiatedRtpExtensions,
+                                    msection);
+}
+
+uint16_t JsepSessionImpl::GetNeverUsedExtmapEntry() {
+  uint16_t result = 1;
+
+  // Walk the set in order, and return the first "hole" we find
+  for (const auto used : mExtmapEntriesEverUsed) {
+    if (result != used) {
+      MOZ_ASSERT(result < used);
+      break;
+    }
+
+    // RFC 5285 says entries >= 4096 are used in offers to force the answerer
+    // to pick, so we do not want to actually use these
+    if (used == 4095) {
+      JSEP_SET_ERROR(
+          "Too many rtp extensions have been added. "
+          "That's 4095. Who _does_ that?");
+      return 0;
+    }
+
+    result = used + 1;
+  }
+
+  mExtmapEntriesEverUsed.insert(result);
+  return result;
+}
+
+JsepSession::Result JsepSessionImpl::CreateAnswer(
+    const JsepAnswerOptions& options, std::string* answer) {
+  mLastError.clear();
+
+  if (mState != kJsepStateHaveRemoteOffer) {
+    JSEP_SET_ERROR("Cannot create answer in state " << GetStateStr(mState));
+    return dom::PCError::InvalidStateError;
+  }
+
+  UniquePtr<Sdp> sdp;
+
+  // Make the basic SDP that is common to offer/answer.
+  nsresult rv = CreateGenericSDP(&sdp);
+  NS_ENSURE_SUCCESS(rv, dom::PCError::OperationError);
+
+  const Sdp& offer = *mPendingRemoteDescription;
+
+  // Copy the bundle groups into our answer
+  UniquePtr<SdpGroupAttributeList> groupAttr(new SdpGroupAttributeList);
+  mSdpHelper.GetBundleGroups(offer, &groupAttr->mGroups);
+  sdp->GetAttributeList().SetAttribute(groupAttr.release());
+
+  for (size_t i = 0; i < offer.GetMediaSectionCount(); ++i) {
+    // The transceivers are already in place, due to setRemote
+    Maybe<JsepTransceiver> transceiver(GetTransceiverForLevel(i));
+    if (!transceiver) {
+      JSEP_SET_ERROR("No transceiver for level " << i);
+      MOZ_ASSERT(false);
+      return dom::PCError::OperationError;
+    }
+    rv = CreateAnswerMsection(options, *transceiver, offer.GetMediaSection(i),
+                              sdp.get());
+    NS_ENSURE_SUCCESS(rv, dom::PCError::OperationError);
+    SetTransceiver(*transceiver);
+  }
+
+  // Ensure that each bundle-group starts with a mid that has a transport, in
+  // case we've disabled what the offerer wanted to use. If the group doesn't
+  // contain anything that has a transport, remove it.
+  groupAttr.reset(new SdpGroupAttributeList);
+  std::vector<SdpGroupAttributeList::Group> bundleGroups;
+  mSdpHelper.GetBundleGroups(*sdp, &bundleGroups);
+  for (auto& group : bundleGroups) {
+    for (auto& mid : group.tags) {
+      const SdpMediaSection* msection =
+          mSdpHelper.FindMsectionByMid(offer, mid);
+
+      if (msection && !msection->GetAttributeList().HasAttribute(
+                          SdpAttribute::kBundleOnlyAttribute)) {
+        std::swap(group.tags[0], mid);
+        groupAttr->mGroups.push_back(group);
+        break;
+      }
+    }
+  }
+  sdp->GetAttributeList().SetAttribute(groupAttr.release());
+
+  if (mCurrentLocalDescription) {
+    // per discussion with bwc, 3rd parm here should be offer, not *sdp. (mjf)
+    rv = CopyPreviousTransportParams(*GetAnswer(), *mCurrentRemoteDescription,
+                                     offer, sdp.get());
+    NS_ENSURE_SUCCESS(rv, dom::PCError::OperationError);
+  }
+
+  *answer = sdp->ToString();
+  mGeneratedAnswer = std::move(sdp);
+  ++mSessionVersion;
+  MOZ_MTLOG(ML_DEBUG, "[" << mName << "]: CreateAnswer \nSDP=\n" << *answer);
+
+  return Result();
+}
+
+nsresult JsepSessionImpl::CreateAnswerMsection(
+    const JsepAnswerOptions& options, JsepTransceiver& transceiver,
+    const SdpMediaSection& remoteMsection, Sdp* sdp) {
+  MOZ_ASSERT(transceiver.GetMediaType() == remoteMsection.GetMediaType());
+  SdpDirectionAttribute::Direction direction =
+      reverse(remoteMsection.GetDirection()) & transceiver.mJsDirection;
+  SdpMediaSection& msection =
+      sdp->AddMediaSection(remoteMsection.GetMediaType(), direction, 9,
+                           remoteMsection.GetProtocol(), sdp::kIPv4, "0.0.0.0");
+
+  nsresult rv = mSdpHelper.CopyStickyParams(remoteMsection, &msection);
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  if (mSdpHelper.MsectionIsDisabled(remoteMsection)) {
+    SdpHelper::DisableMsection(sdp, &msection);
+    return NS_OK;
+  }
+
+  MOZ_ASSERT(transceiver.IsAssociated());
+  if (msection.GetAttributeList().GetMid().empty()) {
+    msection.GetAttributeList().SetAttribute(new SdpStringAttribute(
+        SdpAttribute::kMidAttribute, transceiver.GetMid()));
+  }
+
+  MOZ_ASSERT(transceiver.GetMid() == msection.GetAttributeList().GetMid());
+
+  SdpSetupAttribute::Role role;
+  if (transceiver.mTransport.mDtls && !IsIceRestarting()) {
+    role = (transceiver.mTransport.mDtls->mRole ==
+            JsepDtlsTransport::kJsepDtlsClient)
+               ? SdpSetupAttribute::kActive
+               : SdpSetupAttribute::kPassive;
+  } else {
+    rv = DetermineAnswererSetupRole(remoteMsection, &role);
+    NS_ENSURE_SUCCESS(rv, rv);
+  }
+
+  rv = AddTransportAttributes(&msection, role);
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  transceiver.mSendTrack.AddToAnswer(remoteMsection, mSsrcGenerator, &msection);
+  transceiver.mRecvTrack.AddToAnswer(remoteMsection, mSsrcGenerator, &msection);
+
+  // Add extmap attributes. This logic will probably be moved to the track,
+  // since it can be specified on a per-sender basis in JS.
+  // We will need some validation to ensure that the ids are identical for
+  // RTP streams that are bundled together, though (bug 1406529).
+  AddCommonExtmaps(remoteMsection, &msection);
+
+  if (msection.GetFormats().empty()) {
+    // Could not negotiate anything. Disable m-section.
+    SdpHelper::DisableMsection(sdp, &msection);
+  }
+
+  return NS_OK;
+}
+
+nsresult JsepSessionImpl::DetermineAnswererSetupRole(
+    const SdpMediaSection& remoteMsection, SdpSetupAttribute::Role* rolep) {
+  // Determine the role.
+  // RFC 5763 says:
+  //
+  //   The endpoint MUST use the setup attribute defined in [RFC4145].
+  //   The endpoint that is the offerer MUST use the setup attribute
+  //   value of setup:actpass and be prepared to receive a client_hello
+  //   before it receives the answer.  The answerer MUST use either a
+  //   setup attribute value of setup:active or setup:passive.  Note that
+  //   if the answerer uses setup:passive, then the DTLS handshake will
+  //   not begin until the answerer is received, which adds additional
+  //   latency. setup:active allows the answer and the DTLS handshake to
+  //   occur in parallel.  Thus, setup:active is RECOMMENDED.  Whichever
+  //   party is active MUST initiate a DTLS handshake by sending a
+  //   ClientHello over each flow (host/port quartet).
+  //
+  //   We default to assuming that the offerer is passive and we are active.
+  SdpSetupAttribute::Role role = SdpSetupAttribute::kActive;
+
+  if (remoteMsection.GetAttributeList().HasAttribute(
+          SdpAttribute::kSetupAttribute)) {
+    switch (remoteMsection.GetAttributeList().GetSetup().mRole) {
+      case SdpSetupAttribute::kActive:
+        role = SdpSetupAttribute::kPassive;
+        break;
+      case SdpSetupAttribute::kPassive:
+      case SdpSetupAttribute::kActpass:
+        role = SdpSetupAttribute::kActive;
+        break;
+      case SdpSetupAttribute::kHoldconn:
+        // This should have been caught by ParseSdp
+        MOZ_ASSERT(false);
+        JSEP_SET_ERROR(
+            "The other side used an illegal setup attribute"
+            " (\"holdconn\").");
+        return NS_ERROR_INVALID_ARG;
+    }
+  }
+
+  *rolep = role;
+  return NS_OK;
+}
+
+JsepSession::Result JsepSessionImpl::SetLocalDescription(
+    JsepSdpType type, const std::string& constSdp) {
+  mLastError.clear();
+  std::string sdp = constSdp;
+
+  MOZ_MTLOG(ML_DEBUG, "[" << mName << "]: SetLocalDescription type=" << type
+                          << "\nSDP=\n"
+                          << sdp);
+
+  switch (type) {
+    case kJsepSdpOffer:
+      if (!mGeneratedOffer) {
+        JSEP_SET_ERROR(
+            "Cannot set local offer when createOffer has not been called.");
+        return dom::PCError::InvalidModificationError;
+      }
+      if (sdp.empty()) {
+        sdp = mGeneratedOffer->ToString();
+      }
+      if (mState == kJsepStateHaveLocalOffer) {
+        // Rollback previous offer before applying the new one.
+        SetLocalDescription(kJsepSdpRollback, "");
+        MOZ_ASSERT(mState == kJsepStateStable);
+      }
+      break;
+    case kJsepSdpAnswer:
+    case kJsepSdpPranswer:
+      if (!mGeneratedAnswer) {
+        JSEP_SET_ERROR(
+            "Cannot set local answer when createAnswer has not been called.");
+        return dom::PCError::InvalidModificationError;
+      }
+      if (sdp.empty()) {
+        sdp = mGeneratedAnswer->ToString();
+      }
+      break;
+    case kJsepSdpRollback:
+      if (mState != kJsepStateHaveLocalOffer) {
+        JSEP_SET_ERROR("Cannot rollback local description in "
+                       << GetStateStr(mState));
+        // Currently, spec allows this in any state except stable, and
+        // sRD(rollback) and sLD(rollback) do exactly the same thing.
+        return dom::PCError::InvalidStateError;
+      }
+
+      mPendingLocalDescription.reset();
+      SetState(kJsepStateStable);
+      RollbackLocalOffer();
+      return Result();
+  }
+
+  switch (mState) {
+    case kJsepStateStable:
+      if (type != kJsepSdpOffer) {
+        JSEP_SET_ERROR("Cannot set local answer in state "
+                       << GetStateStr(mState));
+        return dom::PCError::InvalidStateError;
+      }
+      break;
+    case kJsepStateHaveRemoteOffer:
+      if (type != kJsepSdpAnswer && type != kJsepSdpPranswer) {
+        JSEP_SET_ERROR("Cannot set local offer in state "
+                       << GetStateStr(mState));
+        return dom::PCError::InvalidStateError;
+      }
+      break;
+    default:
+      JSEP_SET_ERROR("Cannot set local offer or answer in state "
+                     << GetStateStr(mState));
+      return dom::PCError::InvalidStateError;
+  }
+
+  UniquePtr<Sdp> parsed;
+  nsresult rv = ParseSdp(sdp, &parsed);
+  // Needs to be RTCError with sdp-syntax-error
+  NS_ENSURE_SUCCESS(rv, dom::PCError::OperationError);
+
+  // Check that content hasn't done anything unsupported with the SDP
+  rv = ValidateLocalDescription(*parsed, type);
+  NS_ENSURE_SUCCESS(rv, dom::PCError::InvalidModificationError);
+
+  switch (type) {
+    case kJsepSdpOffer:
+      rv = ValidateOffer(*parsed);
+      break;
+    case kJsepSdpAnswer:
+    case kJsepSdpPranswer:
+      rv = ValidateAnswer(*mPendingRemoteDescription, *parsed);
+      break;
+    case kJsepSdpRollback:
+      MOZ_CRASH();  // Handled above
+  }
+  NS_ENSURE_SUCCESS(rv, dom::PCError::InvalidAccessError);
+
+  if (type == kJsepSdpOffer) {
+    // Save in case we need to rollback
+    mOldTransceivers = mTransceivers;
+  }
+
+  SdpHelper::BundledMids bundledMids;
+  rv = mSdpHelper.GetBundledMids(*parsed, &bundledMids);
+  NS_ENSURE_SUCCESS(rv, dom::PCError::OperationError);
+
+  SdpHelper::BundledMids remoteBundledMids;
+  if (type != kJsepSdpOffer) {
+    rv = mSdpHelper.GetBundledMids(*mPendingRemoteDescription,
+                                   &remoteBundledMids);
+    NS_ENSURE_SUCCESS(rv, dom::PCError::OperationError);
+  }
+
+  for (size_t i = 0; i < parsed->GetMediaSectionCount(); ++i) {
+    Maybe<JsepTransceiver> transceiver(GetTransceiverForLevel(i));
+    if (!transceiver) {
+      MOZ_ASSERT(false);
+      JSEP_SET_ERROR("No transceiver for level " << i);
+      return dom::PCError::OperationError;
+    }
+
+    const auto& msection = parsed->GetMediaSection(i);
+    transceiver->Associate(msection.GetAttributeList().GetMid());
+    transceiver->mRecvTrack.RecvTrackSetLocal(msection);
+
+    if (mSdpHelper.MsectionIsDisabled(msection)) {
+      transceiver->mTransport.Close();
+      SetTransceiver(*transceiver);
+      continue;
+    }
+
+    bool hasOwnTransport = mSdpHelper.OwnsTransport(
+        msection, bundledMids,
+        (type == kJsepSdpOffer) ? sdp::kOffer : sdp::kAnswer);
+    if (type != kJsepSdpOffer) {
+      const auto& remoteMsection =
+          mPendingRemoteDescription->GetMediaSection(i);
+      // Don't allow the answer to override what the offer allowed for
+      hasOwnTransport &= mSdpHelper.OwnsTransport(
+          remoteMsection, remoteBundledMids, sdp::kOffer);
+    }
+
+    if (hasOwnTransport) {
+      EnsureHasOwnTransport(parsed->GetMediaSection(i), *transceiver);
+    }
+
+    if (type == kJsepSdpOffer) {
+      if (!hasOwnTransport) {
+        auto it = bundledMids.find(transceiver->GetMid());
+        if (it != bundledMids.end()) {
+          transceiver->SetBundleLevel(it->second->GetLevel());
+        }
+      }
+    } else {
+      auto it = remoteBundledMids.find(transceiver->GetMid());
+      if (it != remoteBundledMids.end()) {
+        transceiver->SetBundleLevel(it->second->GetLevel());
+      }
+    }
+    SetTransceiver(*transceiver);
+  }
+
+  CopyBundleTransports();
+
+  switch (type) {
+    case kJsepSdpOffer:
+      rv = SetLocalDescriptionOffer(std::move(parsed));
+      break;
+    case kJsepSdpAnswer:
+    case kJsepSdpPranswer:
+      rv = SetLocalDescriptionAnswer(type, std::move(parsed));
+      break;
+    case kJsepSdpRollback:
+      MOZ_CRASH();  // Handled above
+  }
+
+  NS_ENSURE_SUCCESS(rv, dom::PCError::OperationError);
+  return Result();
+}
+
+nsresult JsepSessionImpl::SetLocalDescriptionOffer(UniquePtr<Sdp> offer) {
+  MOZ_ASSERT(mState == kJsepStateStable);
+  mPendingLocalDescription = std::move(offer);
+  mIsPendingOfferer = Some(true);
+  SetState(kJsepStateHaveLocalOffer);
+  return NS_OK;
+}
+
+nsresult JsepSessionImpl::SetLocalDescriptionAnswer(JsepSdpType type,
+                                                    UniquePtr<Sdp> answer) {
+  MOZ_ASSERT(mState == kJsepStateHaveRemoteOffer);
+  mPendingLocalDescription = std::move(answer);
+
+  nsresult rv = HandleNegotiatedSession(mPendingLocalDescription,
+                                        mPendingRemoteDescription);
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  mCurrentRemoteDescription = std::move(mPendingRemoteDescription);
+  mCurrentLocalDescription = std::move(mPendingLocalDescription);
+  MOZ_ASSERT(mIsPendingOfferer.isSome() && !*mIsPendingOfferer);
+  mIsPendingOfferer.reset();
+  mIsCurrentOfferer = Some(false);
+
+  SetState(kJsepStateStable);
+  return NS_OK;
+}
+
+JsepSession::Result JsepSessionImpl::SetRemoteDescription(
+    JsepSdpType type, const std::string& sdp) {
+  mLastError.clear();
+
+  MOZ_MTLOG(ML_DEBUG, "[" << mName << "]: SetRemoteDescription type=" << type
+                          << "\nSDP=\n"
+                          << sdp);
+
+  if (mState == kJsepStateHaveRemoteOffer && type == kJsepSdpOffer) {
+    // Rollback previous offer before applying the new one.
+    SetRemoteDescription(kJsepSdpRollback, "");
+    MOZ_ASSERT(mState == kJsepStateStable);
+  }
+
+  if (type == kJsepSdpRollback) {
+    if (mState != kJsepStateHaveRemoteOffer) {
+      JSEP_SET_ERROR("Cannot rollback remote description in "
+                     << GetStateStr(mState));
+      return dom::PCError::InvalidStateError;
+    }
+
+    mPendingRemoteDescription.reset();
+    SetState(kJsepStateStable);
+    RollbackRemoteOffer();
+
+    return Result();
+  }
+
+  switch (mState) {
+    case kJsepStateStable:
+      if (type != kJsepSdpOffer) {
+        JSEP_SET_ERROR("Cannot set remote answer in state "
+                       << GetStateStr(mState));
+        return dom::PCError::InvalidStateError;
+      }
+      break;
+    case kJsepStateHaveLocalOffer:
+    case kJsepStateHaveRemotePranswer:
+      if (type != kJsepSdpAnswer && type != kJsepSdpPranswer) {
+        JSEP_SET_ERROR("Cannot set remote offer in state "
+                       << GetStateStr(mState));
+        return dom::PCError::InvalidStateError;
+      }
+      break;
+    default:
+      JSEP_SET_ERROR("Cannot set remote offer or answer in current state "
+                     << GetStateStr(mState));
+      return dom::PCError::InvalidStateError;
+  }
+
+  // Parse.
+  UniquePtr<Sdp> parsed;
+  nsresult rv = ParseSdp(sdp, &parsed);
+  // Needs to be RTCError with sdp-syntax-error
+  NS_ENSURE_SUCCESS(rv, dom::PCError::OperationError);
+
+  rv = ValidateRemoteDescription(*parsed);
+  NS_ENSURE_SUCCESS(rv, dom::PCError::InvalidAccessError);
+
+  switch (type) {
+    case kJsepSdpOffer:
+      rv = ValidateOffer(*parsed);
+      break;
+    case kJsepSdpAnswer:
+    case kJsepSdpPranswer:
+      rv = ValidateAnswer(*mPendingLocalDescription, *parsed);
+      break;
+    case kJsepSdpRollback:
+      MOZ_CRASH();  // Handled above
+  }
+  NS_ENSURE_SUCCESS(rv, dom::PCError::InvalidAccessError);
+
+  bool iceLite =
+      parsed->GetAttributeList().HasAttribute(SdpAttribute::kIceLiteAttribute);
+
+  // check for mismatch ufrag/pwd indicating ice restart
+  // can't just check the first one because it might be disabled
+  bool iceRestarting = false;
+  if (mCurrentRemoteDescription.get()) {
+    for (size_t i = 0; !iceRestarting &&
+                       i < mCurrentRemoteDescription->GetMediaSectionCount();
+         ++i) {
+      const SdpMediaSection& newMsection = parsed->GetMediaSection(i);
+      const SdpMediaSection& oldMsection =
+          mCurrentRemoteDescription->GetMediaSection(i);
+
+      if (mSdpHelper.MsectionIsDisabled(newMsection) ||
+          mSdpHelper.MsectionIsDisabled(oldMsection)) {
+        continue;
+      }
+
+      iceRestarting = mSdpHelper.IceCredentialsDiffer(newMsection, oldMsection);
+    }
+  }
+
+  std::vector<std::string> iceOptions;
+  if (parsed->GetAttributeList().HasAttribute(
+          SdpAttribute::kIceOptionsAttribute)) {
+    iceOptions = parsed->GetAttributeList().GetIceOptions().mValues;
+  }
+
+  if (type == kJsepSdpOffer) {
+    // Save in case we need to rollback.
+    mOldTransceivers = mTransceivers;
+    for (auto& transceiver : mTransceivers) {
+      if (!transceiver.IsNegotiated()) {
+        // We chose a level for this transceiver, but never negotiated it.
+        // Discard this state.
+        transceiver.ClearLevel();
+      }
+    }
+  }
+
+  // TODO(bug 1095780): Note that we create remote tracks even when
+  // They contain only codecs we can't negotiate or other craziness.
+  rv = UpdateTransceiversFromRemoteDescription(*parsed);
+  NS_ENSURE_SUCCESS(rv, dom::PCError::OperationError);
+
+  for (size_t i = 0; i < parsed->GetMediaSectionCount(); ++i) {
+    MOZ_ASSERT(GetTransceiverForLevel(i));
+  }
+
+  switch (type) {
+    case kJsepSdpOffer:
+      rv = SetRemoteDescriptionOffer(std::move(parsed));
+      break;
+    case kJsepSdpAnswer:
+    case kJsepSdpPranswer:
+      rv = SetRemoteDescriptionAnswer(type, std::move(parsed));
+      break;
+    case kJsepSdpRollback:
+      MOZ_CRASH();  // Handled above
+  }
+
+  NS_ENSURE_SUCCESS(rv, dom::PCError::OperationError);
+
+  mRemoteIsIceLite = iceLite;
+  mIceOptions = iceOptions;
+  SetIceRestarting(iceRestarting);
+  return Result();
+}
+
+nsresult JsepSessionImpl::HandleNegotiatedSession(
+    const UniquePtr<Sdp>& local, const UniquePtr<Sdp>& remote) {
+  // local ufrag/pwd has been negotiated; we will never go back to the old ones
+  mOldIceUfrag.clear();
+  mOldIcePwd.clear();
+
+  bool remoteIceLite =
+      remote->GetAttributeList().HasAttribute(SdpAttribute::kIceLiteAttribute);
+
+  mIceControlling = remoteIceLite || *mIsPendingOfferer;
+
+  const Sdp& answer = *mIsPendingOfferer ? *remote : *local;
+
+  SdpHelper::BundledMids bundledMids;
+  nsresult rv = mSdpHelper.GetBundledMids(answer, &bundledMids);
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  // First, set the bundle level on the transceivers
+  for (auto& [mid, transportOwner] : bundledMids) {
+    Maybe<JsepTransceiver> bundledTransceiver = GetTransceiverForMid(mid);
+    if (!bundledTransceiver) {
+      JSEP_SET_ERROR("No transceiver for bundled mid " << mid);
+      return NS_ERROR_INVALID_ARG;
+    }
+    bundledTransceiver->SetBundleLevel(transportOwner->GetLevel());
+    SetTransceiver(*bundledTransceiver);
+  }
+
+  // Now walk through the m-sections, perform negotiation, and update the
+  // transceivers.
+  for (size_t i = 0; i < local->GetMediaSectionCount(); ++i) {
+    Maybe<JsepTransceiver> transceiver(GetTransceiverForLevel(i));
+    if (!transceiver) {
+      MOZ_ASSERT(false);
+      JSEP_SET_ERROR("No transceiver for level " << i);
+      return NS_ERROR_FAILURE;
+    }
+
+    if (mSdpHelper.MsectionIsDisabled(local->GetMediaSection(i))) {
+      transceiver->SetRemoved();
+    }
+
+    // Skip disabled m-sections.
+    if (answer.GetMediaSection(i).GetPort() == 0) {
+      transceiver->mTransport.Close();
+      transceiver->SetStopped();
+      transceiver->Disassociate();
+      transceiver->ClearBundleLevel();
+      transceiver->mSendTrack.SetActive(false);
+      transceiver->mRecvTrack.SetActive(false);
+      transceiver->SetCanRecycleMyMsection();
+      SetTransceiver(*transceiver);
+      // Do not clear mLevel yet! That will happen on the next negotiation.
+      continue;
+    }
+
+    rv = MakeNegotiatedTransceiver(remote->GetMediaSection(i),
+                                   local->GetMediaSection(i), *transceiver);
+    NS_ENSURE_SUCCESS(rv, rv);
+    SetTransceiver(*transceiver);
+  }
+
+  CopyBundleTransports();
+
+  std::vector<JsepTrack*> remoteTracks;
+  for (auto& transceiver : mTransceivers) {
+    remoteTracks.push_back(&transceiver.mRecvTrack);
+  }
+  JsepTrack::SetUniquePayloadTypes(remoteTracks);
+
+  mNegotiations++;
+
+  mGeneratedAnswer.reset();
+  mGeneratedOffer.reset();
+
+  return NS_OK;
+}
+
+nsresult JsepSessionImpl::MakeNegotiatedTransceiver(
+    const SdpMediaSection& remote, const SdpMediaSection& local,
+    JsepTransceiver& transceiver) {
+  const SdpMediaSection& answer = *mIsPendingOfferer ? remote : local;
+
+  bool sending = false;
+  bool receiving = false;
+
+  // We do not pay any attention to whether the transceiver is stopped here,
+  // because that is only a signal to the JSEP engine to _attempt_ to reject
+  // the corresponding m-section the next time we're the offerer.
+  if (*mIsPendingOfferer) {
+    receiving = answer.IsSending();
+    sending = answer.IsReceiving();
+  } else {
+    sending = answer.IsSending();
+    receiving = answer.IsReceiving();
+  }
+
+  MOZ_MTLOG(ML_DEBUG, "[" << mName << "]: Negotiated m= line"
+                          << " index=" << local.GetLevel() << " type="
+                          << local.GetMediaType() << " sending=" << sending
+                          << " receiving=" << receiving);
+
+  transceiver.SetNegotiated();
+
+  // Ensure that this is finalized in case we need to copy it below
+  nsresult rv =
+      FinalizeTransport(remote.GetAttributeList(), answer.GetAttributeList(),
+                        &transceiver.mTransport);
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  transceiver.mSendTrack.SetActive(sending);
+  rv = transceiver.mSendTrack.Negotiate(answer, remote, local);
+  if (NS_FAILED(rv)) {
+    JSEP_SET_ERROR("Answer had no codecs in common with offer in m-section "
+                   << local.GetLevel());
+    return rv;
+  }
+
+  JsepTrack& recvTrack = transceiver.mRecvTrack;
+  recvTrack.SetActive(receiving);
+  rv = recvTrack.Negotiate(answer, remote, local);
+  if (NS_FAILED(rv)) {
+    JSEP_SET_ERROR("Answer had no codecs in common with offer in m-section "
+                   << local.GetLevel());
+    return rv;
+  }
+
+  if (transceiver.HasBundleLevel() && recvTrack.GetSsrcs().empty() &&
+      recvTrack.GetMediaType() != SdpMediaSection::kApplication) {
+    // TODO(bug 1105005): Once we have urn:ietf:params:rtp-hdrext:sdes:mid
+    // support, we should only fire this warning if that extension was not
+    // negotiated.
+    MOZ_MTLOG(ML_ERROR, "[" << mName
+                            << "]: Bundled m-section has no ssrc "
+                               "attributes. This may cause media packets to be "
+                               "dropped.");
+  }
+
+  if (transceiver.mTransport.mComponents == 2) {
+    // RTCP MUX or not.
+    // TODO(bug 1095743): verify that the PTs are consistent with mux.
+    MOZ_MTLOG(ML_DEBUG, "[" << mName << "]: RTCP-MUX is off");
+  }
+
+  if (answer.GetAttributeList().HasAttribute(SdpAttribute::kExtmapAttribute)) {
+    const auto extmaps = answer.GetAttributeList().GetExtmap().mExtmaps;
+    for (const auto& negotiatedExtension : extmaps) {
+      if (negotiatedExtension.entry == 0) {
+        MOZ_ASSERT(false, "This should have been caught sooner");
+        continue;
+      }
+
+      mExtmapEntriesEverNegotiated[negotiatedExtension.entry] =
+          negotiatedExtension.extensionname;
+
+      for (auto& originalExtension : mRtpExtensions) {
+        if (negotiatedExtension.extensionname ==
+            originalExtension.mExtmap.extensionname) {
+          // Update extmap to match what was negotiated
+          originalExtension.mExtmap.entry = negotiatedExtension.entry;
+          mExtmapEntriesEverUsed.insert(negotiatedExtension.entry);
+        } else if (originalExtension.mExtmap.entry ==
+                   negotiatedExtension.entry) {
+          // If this extmap entry was claimed for a different extension, update
+          // it to a new value so we don't end up with a duplicate.
+          originalExtension.mExtmap.entry = GetNeverUsedExtmapEntry();
+        }
+      }
+    }
+  }
+
+  return NS_OK;
+}
+
+void JsepSessionImpl::EnsureHasOwnTransport(const SdpMediaSection& msection,
+                                            JsepTransceiver& transceiver) {
+  JsepTransport& transport = transceiver.mTransport;
+
+  if (!transceiver.HasOwnTransport()) {
+    // Transceiver didn't own this transport last time, it won't now either
+    transport.Close();
+  }
+
+  transport.mLocalUfrag = msection.GetAttributeList().GetIceUfrag();
+  transport.mLocalPwd = msection.GetAttributeList().GetIcePwd();
+
+  transceiver.ClearBundleLevel();
+
+  if (!transport.mComponents) {
+    if (mSdpHelper.HasRtcp(msection.GetProtocol())) {
+      transport.mComponents = 2;
+    } else {
+      transport.mComponents = 1;
+    }
+  }
+
+  if (transport.mTransportId.empty()) {
+    // TODO: Once we use different ICE ufrag/pass for each m-section, we can
+    // use that here.
+    std::ostringstream os;
+    os << "transport_" << mTransportIdCounter++;
+    transport.mTransportId = os.str();
+  }
+}
+
+void JsepSessionImpl::CopyBundleTransports() {
+  for (auto& transceiver : mTransceivers) {
+    if (transceiver.HasBundleLevel()) {
+      MOZ_MTLOG(ML_DEBUG,
+                "[" << mName << "] Transceiver " << transceiver.GetLevel()
+                    << " is in a bundle; transceiver "
+                    << transceiver.BundleLevel() << " owns the transport.");
+      Maybe<const JsepTransceiver> transportOwner =
+          GetTransceiverForLevel(transceiver.BundleLevel());
+      MOZ_ASSERT(transportOwner);
+      if (transportOwner) {
+        transceiver.mTransport = transportOwner->mTransport;
+      }
+    } else if (transceiver.HasLevel()) {
+      MOZ_MTLOG(ML_DEBUG, "[" << mName << "] Transceiver "
+                              << transceiver.GetLevel()
+                              << " is not necessarily in a bundle.");
+    }
+    if (transceiver.HasLevel()) {
+      MOZ_MTLOG(ML_DEBUG,
+                "[" << mName << "] Transceiver " << transceiver.GetLevel()
+                    << " transport-id: " << transceiver.mTransport.mTransportId
+                    << " components: " << transceiver.mTransport.mComponents);
+    }
+  }
+}
+
+nsresult JsepSessionImpl::FinalizeTransport(const SdpAttributeList& remote,
+                                            const SdpAttributeList& answer,
+                                            JsepTransport* transport) const {
+  if (!transport->mComponents) {
+    return NS_OK;
+  }
+
+  if (!transport->mIce || transport->mIce->mUfrag != remote.GetIceUfrag() ||
+      transport->mIce->mPwd != remote.GetIcePwd()) {
+    UniquePtr<JsepIceTransport> ice = MakeUnique<JsepIceTransport>();
+    transport->mDtls = nullptr;
+
+    // We do sanity-checking for these in ParseSdp
+    ice->mUfrag = remote.GetIceUfrag();
+    ice->mPwd = remote.GetIcePwd();
+    transport->mIce = std::move(ice);
+  }
+
+  if (remote.HasAttribute(SdpAttribute::kCandidateAttribute)) {
+    transport->mIce->mCandidates = remote.GetCandidate();
+  }
+
+  if (!transport->mDtls) {
+    // RFC 5763 says:
+    //
+    //   The endpoint MUST use the setup attribute defined in [RFC4145].
+    //   The endpoint that is the offerer MUST use the setup attribute
+    //   value of setup:actpass and be prepared to receive a client_hello
+    //   before it receives the answer.  The answerer MUST use either a
+    //   setup attribute value of setup:active or setup:passive.  Note that
+    //   if the answerer uses setup:passive, then the DTLS handshake will
+    //   not begin until the answerer is received, which adds additional
+    //   latency. setup:active allows the answer and the DTLS handshake to
+    //   occur in parallel.  Thus, setup:active is RECOMMENDED.  Whichever
+    //   party is active MUST initiate a DTLS handshake by sending a
+    //   ClientHello over each flow (host/port quartet).
+    UniquePtr<JsepDtlsTransport> dtls = MakeUnique<JsepDtlsTransport>();
+    dtls->mFingerprints = remote.GetFingerprint();
+    if (!answer.HasAttribute(mozilla::SdpAttribute::kSetupAttribute)) {
+      dtls->mRole = *mIsPendingOfferer ? JsepDtlsTransport::kJsepDtlsServer
+                                       : JsepDtlsTransport::kJsepDtlsClient;
+    } else {
+      if (*mIsPendingOfferer) {
+        dtls->mRole = (answer.GetSetup().mRole == SdpSetupAttribute::kActive)
+                          ? JsepDtlsTransport::kJsepDtlsServer
+                          : JsepDtlsTransport::kJsepDtlsClient;
+      } else {
+        dtls->mRole = (answer.GetSetup().mRole == SdpSetupAttribute::kActive)
+                          ? JsepDtlsTransport::kJsepDtlsClient
+                          : JsepDtlsTransport::kJsepDtlsServer;
+      }
+    }
+
+    transport->mDtls = std::move(dtls);
+  }
+
+  if (answer.HasAttribute(SdpAttribute::kRtcpMuxAttribute)) {
+    transport->mComponents = 1;
+  }
+
+  return NS_OK;
+}
+
+nsresult JsepSessionImpl::AddTransportAttributes(
+    SdpMediaSection* msection, SdpSetupAttribute::Role dtlsRole) {
+  if (mIceUfrag.empty() || mIcePwd.empty()) {
+    JSEP_SET_ERROR("Missing ICE ufrag or password");
+    return NS_ERROR_FAILURE;
+  }
+
+  SdpAttributeList& attrList = msection->GetAttributeList();
+  attrList.SetAttribute(
+      new SdpStringAttribute(SdpAttribute::kIceUfragAttribute, mIceUfrag));
+  attrList.SetAttribute(
+      new SdpStringAttribute(SdpAttribute::kIcePwdAttribute, mIcePwd));
+
+  msection->GetAttributeList().SetAttribute(new SdpSetupAttribute(dtlsRole));
+
+  return NS_OK;
+}
+
+nsresult JsepSessionImpl::CopyPreviousTransportParams(
+    const Sdp& oldAnswer, const Sdp& offerersPreviousSdp, const Sdp& newOffer,
+    Sdp* newLocal) {
+  for (size_t i = 0; i < oldAnswer.GetMediaSectionCount(); ++i) {
+    if (!mSdpHelper.MsectionIsDisabled(newLocal->GetMediaSection(i)) &&
+        mSdpHelper.AreOldTransportParamsValid(oldAnswer, offerersPreviousSdp,
+                                              newOffer, i)) {
+      // If newLocal is an offer, this will be the number of components we used
+      // last time, and if it is an answer, this will be the number of
+      // components we've decided we're using now.
+      Maybe<const JsepTransceiver> transceiver(GetTransceiverForLevel(i));
+      if (!transceiver) {
+        MOZ_ASSERT(false);
+        JSEP_SET_ERROR("No transceiver for level " << i);
+        return NS_ERROR_FAILURE;
+      }
+      size_t numComponents = transceiver->mTransport.mComponents;
+      nsresult rv = mSdpHelper.CopyTransportParams(
+          numComponents, mCurrentLocalDescription->GetMediaSection(i),
+          &newLocal->GetMediaSection(i));
+      NS_ENSURE_SUCCESS(rv, rv);
+    }
+  }
+
+  return NS_OK;
+}
+
+nsresult JsepSessionImpl::ParseSdp(const std::string& sdp,
+                                   UniquePtr<Sdp>* parsedp) {
+  auto results = mParser->Parse(sdp);
+  auto parsed = std::move(results->Sdp());
+  mLastSdpParsingErrors = results->Errors();
+  if (!parsed) {
+    std::string error = results->ParserName() + " Failed to parse SDP: ";
+    mSdpHelper.AppendSdpParseErrors(mLastSdpParsingErrors, &error);
+    JSEP_SET_ERROR(error);
+    return NS_ERROR_INVALID_ARG;
+  }
+  // Verify that the JSEP rules for all SDP are followed
+  for (size_t i = 0; i < parsed->GetMediaSectionCount(); ++i) {
+    if (mSdpHelper.MsectionIsDisabled(parsed->GetMediaSection(i))) {
+      // Disabled, let this stuff slide.
+      continue;
+    }
+
+    const SdpMediaSection& msection(parsed->GetMediaSection(i));
+    auto& mediaAttrs = msection.GetAttributeList();
+
+    if (mediaAttrs.HasAttribute(SdpAttribute::kMidAttribute) &&
+        mediaAttrs.GetMid().length() > 16) {
+      JSEP_SET_ERROR(
+          "Invalid description, mid length greater than 16 "
+          "unsupported until 2-byte rtp header extensions are "
+          "supported in webrtc.org");
+      return NS_ERROR_INVALID_ARG;
+    }
+
+    if (mediaAttrs.HasAttribute(SdpAttribute::kExtmapAttribute)) {
+      std::set<uint16_t> extIds;
+      for (const auto& ext : mediaAttrs.GetExtmap().mExtmaps) {
+        uint16_t id = ext.entry;
+
+        if (id < 1 || id > 14) {
+          JSEP_SET_ERROR("Description contains invalid extension id "
+                         << id << " on level " << i
+                         << " which is unsupported until 2-byte rtp"
+                            " header extensions are supported in webrtc.org");
+          return NS_ERROR_INVALID_ARG;
+        }
+
+        if (extIds.find(id) != extIds.end()) {
+          JSEP_SET_ERROR("Description contains duplicate extension id "
+                         << id << " on level " << i);
+          return NS_ERROR_INVALID_ARG;
+        }
+        extIds.insert(id);
+      }
+    }
+
+    static const std::bitset<128> forbidden = GetForbiddenSdpPayloadTypes();
+    if (msection.GetMediaType() == SdpMediaSection::kAudio ||
+        msection.GetMediaType() == SdpMediaSection::kVideo) {
+      // Sanity-check that payload type can work with RTP
+      for (const std::string& fmt : msection.GetFormats()) {
+        uint16_t payloadType;
+        if (!SdpHelper::GetPtAsInt(fmt, &payloadType)) {
+          JSEP_SET_ERROR("Payload type \""
+                         << fmt << "\" is not a 16-bit unsigned int at level "
+                         << i);
+          return NS_ERROR_INVALID_ARG;
+        }
+        if (payloadType > 127) {
+          JSEP_SET_ERROR("audio/video payload type \""
+                         << fmt << "\" is too large at level " << i);
+          return NS_ERROR_INVALID_ARG;
+        }
+        if (forbidden.test(payloadType)) {
+          JSEP_SET_ERROR("Illegal audio/video payload type \""
+                         << fmt << "\" at level " << i);
+          return NS_ERROR_INVALID_ARG;
+        }
+      }
+    }
+  }
+
+  *parsedp = std::move(parsed);
+  return NS_OK;
+}
+
+nsresult JsepSessionImpl::SetRemoteDescriptionOffer(UniquePtr<Sdp> offer) {
+  MOZ_ASSERT(mState == kJsepStateStable);
+
+  mPendingRemoteDescription = std::move(offer);
+  mIsPendingOfferer = Some(false);
+
+  SetState(kJsepStateHaveRemoteOffer);
+  return NS_OK;
+}
+
+nsresult JsepSessionImpl::SetRemoteDescriptionAnswer(JsepSdpType type,
+                                                     UniquePtr<Sdp> answer) {
+  MOZ_ASSERT(mState == kJsepStateHaveLocalOffer ||
+             mState == kJsepStateHaveRemotePranswer);
+
+  mPendingRemoteDescription = std::move(answer);
+
+  nsresult rv = HandleNegotiatedSession(mPendingLocalDescription,
+                                        mPendingRemoteDescription);
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  mCurrentRemoteDescription = std::move(mPendingRemoteDescription);
+  mCurrentLocalDescription = std::move(mPendingLocalDescription);
+  MOZ_ASSERT(mIsPendingOfferer.isSome() && *mIsPendingOfferer);
+  mIsPendingOfferer.reset();
+  mIsCurrentOfferer = Some(true);
+
+  SetState(kJsepStateStable);
+  return NS_OK;
+}
+
+Maybe<JsepTransceiver> JsepSessionImpl::GetTransceiverForLevel(
+    size_t level) const {
+  return FindTransceiver([level](const JsepTransceiver& transceiver) {
+    return transceiver.HasLevel() && (transceiver.GetLevel() == level);
+  });
+}
+
+Maybe<JsepTransceiver> JsepSessionImpl::GetTransceiverForMid(
+    const std::string& mid) const {
+  return FindTransceiver([mid](const JsepTransceiver& transceiver) {
+    return transceiver.IsAssociated() && (transceiver.GetMid() == mid);
+  });
+}
+
+Maybe<JsepTransceiver> JsepSessionImpl::GetTransceiverForLocal(size_t level) {
+  if (Maybe<JsepTransceiver> transceiver = GetTransceiverForLevel(level)) {
+    if (transceiver->CanRecycleMyMsection() &&
+        transceiver->GetMediaType() != SdpMediaSection::kApplication) {
+      // Attempt to recycle. If this fails, the old transceiver stays put.
+      transceiver->Disassociate();
+      Maybe<JsepTransceiver> newTransceiver =
+          FindUnassociatedTransceiver(transceiver->GetMediaType(), false);
+      if (newTransceiver) {
+        newTransceiver->SetLevel(level);
+        transceiver->ClearLevel();
+        transceiver->mSendTrack.ClearRids();
+        SetTransceiver(*newTransceiver);
+        SetTransceiver(*transceiver);
+        return newTransceiver;
+      }
+    }
+
+    SetTransceiver(*transceiver);
+    return transceiver;
+  }
+
+  // There is no transceiver for |level| right now.
+
+  // Look for an RTP transceiver (spec requires us to give the lower levels to
+  // new RTP transceivers)
+  for (auto& transceiver : mTransceivers) {
+    if (transceiver.GetMediaType() != SdpMediaSection::kApplication &&
+        transceiver.IsFreeToUse()) {
+      transceiver.SetLevel(level);
+      return Some(transceiver);
+    }
+  }
+
+  // Ok, look for a datachannel
+  for (auto& transceiver : mTransceivers) {
+    if (transceiver.IsFreeToUse()) {
+      transceiver.SetLevel(level);
+      return Some(transceiver);
+    }
+  }
+
+  return Nothing();
+}
+
+Maybe<JsepTransceiver> JsepSessionImpl::GetTransceiverForRemote(
+    const SdpMediaSection& msection) {
+  size_t level = msection.GetLevel();
+  Maybe<JsepTransceiver> transceiver = GetTransceiverForLevel(level);
+  if (transceiver) {
+    if (!transceiver->CanRecycleMyMsection()) {
+      return transceiver;
+    }
+    transceiver->Disassociate();
+    transceiver->ClearLevel();
+    transceiver->mSendTrack.ClearRids();
+    SetTransceiver(*transceiver);
+  }
+
+  // No transceiver for |level|
+  transceiver = FindUnassociatedTransceiver(msection.GetMediaType(), true);
+  if (transceiver) {
+    transceiver->SetLevel(level);
+    SetTransceiver(*transceiver);
+    return transceiver;
+  }
+
+  // Make a new transceiver
+  JsepTransceiver newTransceiver(msection.GetMediaType(), *mUuidGen,
+                                 SdpDirectionAttribute::kRecvonly);
+  newTransceiver.SetLevel(level);
+  newTransceiver.SetOnlyExistsBecauseOfSetRemote(true);
+  AddTransceiver(newTransceiver);
+  return Some(mTransceivers.back());
+}
+
+Maybe<JsepTransceiver> JsepSessionImpl::GetTransceiverWithTransport(
+    const std::string& transportId) const {
+  for (const auto& transceiver : mTransceivers) {
+    if (transceiver.HasOwnTransport() &&
+        (transceiver.mTransport.mTransportId == transportId)) {
+      MOZ_ASSERT(transceiver.HasLevel(),
+                 "Transceiver has a transport, but no level!");
+      return Some(transceiver);
+    }
+  }
+
+  return Nothing();
+}
+
+nsresult JsepSessionImpl::UpdateTransceiversFromRemoteDescription(
+    const Sdp& remote) {
+  // Iterate over the sdp, updating remote tracks as we go
+  for (size_t i = 0; i < remote.GetMediaSectionCount(); ++i) {
+    const SdpMediaSection& msection = remote.GetMediaSection(i);
+
+    Maybe<JsepTransceiver> transceiver(GetTransceiverForRemote(msection));
+    if (!transceiver) {
+      return NS_ERROR_FAILURE;
+    }
+
+    if (!mSdpHelper.MsectionIsDisabled(msection)) {
+      if (msection.GetAttributeList().HasAttribute(
+              SdpAttribute::kMidAttribute)) {
+        transceiver->Associate(msection.GetAttributeList().GetMid());
+      }
+      if (!transceiver->IsAssociated()) {
+        transceiver->Associate(GetNewMid());
+      } else {
+        mUsedMids.insert(transceiver->GetMid());
+      }
+    } else {
+      // We do not disassociate here, that happens when negotiation completes
+      // These things cannot be rolled back.
+      transceiver->mTransport.Close();
+      transceiver->SetStopped();
+      SetTransceiver(*transceiver);
+      continue;
+    }
+
+    if (msection.GetMediaType() == SdpMediaSection::MediaType::kApplication) {
+      SetTransceiver(*transceiver);
+      continue;
+    }
+
+    transceiver->mSendTrack.SendTrackSetRemote(mSsrcGenerator, msection);
+
+    // Interop workaround for endpoints that don't support msid.
+    // Ensures that there is a default stream id set, provided the remote is
+    // sending.
+    // TODO(bug 1426005): Remove this, or at least move it to JsepTrack.
+    transceiver->mRecvTrack.UpdateStreamIds({mDefaultRemoteStreamId});
+
+    // This will process a=msid if present, or clear the stream ids if the
+    // msection is not sending. If the msection is sending, and there are no
+    // a=msid, the previously set default will stay.
+    transceiver->mRecvTrack.RecvTrackSetRemote(remote, msection);
+    SetTransceiver(*transceiver);
+  }
+
+  return NS_OK;
+}
+
+Maybe<JsepTransceiver> JsepSessionImpl::FindUnassociatedTransceiver(
+    SdpMediaSection::MediaType type, bool magic) {
+  // Look through transceivers that are not mapped to an m-section
+  for (auto& transceiver : mTransceivers) {
+    if (type == SdpMediaSection::kApplication &&
+        type == transceiver.GetMediaType()) {
+      transceiver.RestartDatachannelTransceiver();
+      return Some(transceiver);
+    }
+    if (transceiver.IsFreeToUse() &&
+        (!magic || transceiver.HasAddTrackMagic()) &&
+        (transceiver.GetMediaType() == type)) {
+      return Some(transceiver);
+    }
+  }
+
+  return Nothing();
+}
+
+void JsepSessionImpl::RollbackLocalOffer() {
+  for (size_t i = 0; i < mTransceivers.size(); ++i) {
+    auto& transceiver = mTransceivers[i];
+    if (mOldTransceivers.size() > i) {
+      transceiver.Rollback(mOldTransceivers[i], false);
+      mOldTransceivers[i] = transceiver;
+      continue;
+    }
+
+    JsepTransceiver temp(transceiver.GetMediaType(), *mUuidGen);
+    InitTransceiver(temp);
+    transceiver.Rollback(temp, false);
+    mOldTransceivers.push_back(transceiver);
+  }
+
+  mTransceivers = std::move(mOldTransceivers);
+}
+
+void JsepSessionImpl::RollbackRemoteOffer() {
+  for (size_t i = 0; i < mTransceivers.size(); ++i) {
+    auto& transceiver = mTransceivers[i];
+    if (mOldTransceivers.size() > i) {
+      // Some stuff cannot be rolled back. Save this information.
+      transceiver.Rollback(mOldTransceivers[i], true);
+      mOldTransceivers[i] = transceiver;
+      continue;
+    }
+
+    if (transceiver.HasLevel()) {
+      // New transceiver, that was either created by the remote offer, or
+      // attached to the remote offer.
+      // We rollback even for transceivers we will remove, just to ensure we end
+      // up at the starting state.
+      JsepTransceiver temp(transceiver.GetMediaType(), *mUuidGen);
+      InitTransceiver(temp);
+      transceiver.Rollback(temp, true);
+
+      if (transceiver.OnlyExistsBecauseOfSetRemote()) {
+        transceiver.SetStopped();
+        transceiver.Disassociate();
+        transceiver.SetRemoved();
+      } else {
+        // Oof. This hangs around because of addTrack. Make it magic!
+        transceiver.SetAddTrackMagic();
+      }
+    }  // else, _we_ added this and it is not attached to the remote offer yet
+
+    mOldTransceivers.push_back(transceiver);
+  }
+
+  mTransceivers = std::move(mOldTransceivers);
+}
+
+nsresult JsepSessionImpl::ValidateLocalDescription(const Sdp& description,
+                                                   JsepSdpType type) {
+  Sdp* generated = nullptr;
+  // TODO(bug 1095226): Better checking.
+  if (type == kJsepSdpOffer) {
+    generated = mGeneratedOffer.get();
+  } else {
+    generated = mGeneratedAnswer.get();
+  }
+
+  if (!generated) {
+    JSEP_SET_ERROR(
+        "Calling SetLocal without first calling CreateOffer/Answer"
+        " is not supported.");
+    return NS_ERROR_UNEXPECTED;
+  }
+
+  if (description.GetMediaSectionCount() != generated->GetMediaSectionCount()) {
+    JSEP_SET_ERROR("Changing the number of m-sections is not allowed");
+    return NS_ERROR_INVALID_ARG;
+  }
+
+  for (size_t i = 0; i < description.GetMediaSectionCount(); ++i) {
+    auto& origMsection = generated->GetMediaSection(i);
+    auto& finalMsection = description.GetMediaSection(i);
+    if (origMsection.GetMediaType() != finalMsection.GetMediaType()) {
+      JSEP_SET_ERROR("Changing the media-type of m-sections is not allowed");
+      return NS_ERROR_INVALID_ARG;
+    }
+
+    // These will be present in reoffer
+    if (!mCurrentLocalDescription) {
+      if (finalMsection.GetAttributeList().HasAttribute(
+              SdpAttribute::kCandidateAttribute)) {
+        JSEP_SET_ERROR("Adding your own candidate attributes is not supported");
+        return NS_ERROR_INVALID_ARG;
+      }
+
+      if (finalMsection.GetAttributeList().HasAttribute(
+              SdpAttribute::kEndOfCandidatesAttribute)) {
+        JSEP_SET_ERROR("Why are you trying to set a=end-of-candidates?");
+        return NS_ERROR_INVALID_ARG;
+      }
+    }
+
+    if (mSdpHelper.MsectionIsDisabled(finalMsection)) {
+      continue;
+    }
+
+    if (!finalMsection.GetAttributeList().HasAttribute(
+            SdpAttribute::kMidAttribute)) {
+      JSEP_SET_ERROR("Local descriptions must have a=mid attributes.");
+      return NS_ERROR_INVALID_ARG;
+    }
+
+    if (finalMsection.GetAttributeList().GetMid() !=
+        origMsection.GetAttributeList().GetMid()) {
+      JSEP_SET_ERROR("Changing the mid of m-sections is not allowed.");
+      return NS_ERROR_INVALID_ARG;
+    }
+
+    // TODO(bug 1095218): Check msid
+    // TODO(bug 1095226): Check ice-ufrag and ice-pwd
+    // TODO(bug 1095226): Check fingerprints
+    // TODO(bug 1095226): Check payload types (at least ensure that payload
+    // types we don't actually support weren't added)
+    // TODO(bug 1095226): Check ice-options?
+  }
+
+  if (description.GetAttributeList().HasAttribute(
+          SdpAttribute::kIceLiteAttribute)) {
+    JSEP_SET_ERROR("Running ICE in lite mode is unsupported");
+    return NS_ERROR_INVALID_ARG;
+  }
+
+  return NS_OK;
+}
+
+nsresult JsepSessionImpl::ValidateRemoteDescription(const Sdp& description) {
+  if (!mCurrentLocalDescription) {
+    // Initial offer; nothing to validate besides the stuff in ParseSdp
+    return NS_OK;
+  }
+
+  if (mCurrentLocalDescription->GetMediaSectionCount() >
+      description.GetMediaSectionCount()) {
+    JSEP_SET_ERROR(
+        "New remote description has fewer m-sections than the "
+        "previous remote description.");
+    return NS_ERROR_INVALID_ARG;
+  }
+
+  for (size_t i = 0; i < description.GetMediaSectionCount(); ++i) {
+    const SdpAttributeList& attrs =
+        description.GetMediaSection(i).GetAttributeList();
+
+    if (attrs.HasAttribute(SdpAttribute::kExtmapAttribute)) {
+      for (const auto& ext : attrs.GetExtmap().mExtmaps) {
+        if (mExtmapEntriesEverNegotiated.count(ext.entry) &&
+            mExtmapEntriesEverNegotiated[ext.entry] != ext.extensionname) {
+          JSEP_SET_ERROR(
+              "Remote description attempted to remap RTP extension id "
+              << ext.entry << " from "
+              << mExtmapEntriesEverNegotiated[ext.entry] << " to "
+              << ext.extensionname);
+          return NS_ERROR_INVALID_ARG;
+        }
+      }
+    }
+  }
+
+  if (!mCurrentRemoteDescription) {
+    // No further checking for initial answers
+    return NS_OK;
+  }
+
+  // These are solely to check that bundle is valid
+  SdpHelper::BundledMids bundledMids;
+  nsresult rv = GetNegotiatedBundledMids(&bundledMids);
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  SdpHelper::BundledMids newBundledMids;
+  rv = mSdpHelper.GetBundledMids(description, &newBundledMids);
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  // check for partial ice restart, which is not supported
+  Maybe<bool> iceCredsDiffer;
+  for (size_t i = 0; i < mCurrentRemoteDescription->GetMediaSectionCount();
+       ++i) {
+    const SdpMediaSection& newMsection = description.GetMediaSection(i);
+    const SdpMediaSection& oldMsection =
+        mCurrentRemoteDescription->GetMediaSection(i);
+
+    if (mSdpHelper.MsectionIsDisabled(newMsection) ||
+        mSdpHelper.MsectionIsDisabled(oldMsection)) {
+      continue;
+    }
+
+    if (oldMsection.GetMediaType() != newMsection.GetMediaType()) {
+      JSEP_SET_ERROR("Remote description changes the media type of m-line "
+                     << i);
+      return NS_ERROR_INVALID_ARG;
+    }
+
+    bool differ = mSdpHelper.IceCredentialsDiffer(newMsection, oldMsection);
+
+    if (mIsPendingOfferer.isSome() && *mIsPendingOfferer && differ &&
+        !IsIceRestarting()) {
+      JSEP_SET_ERROR(
+          "Remote description indicates ICE restart but offer did not "
+          "request ICE restart (new remote description changes either "
+          "the ice-ufrag or ice-pwd)");
+      return NS_ERROR_INVALID_ARG;
+    }
+
+    // Detect whether all the creds are the same or all are different
+    if (!iceCredsDiffer.isSome()) {
+      // for the first msection capture whether creds are different or same
+      iceCredsDiffer = mozilla::Some(differ);
+    } else if (iceCredsDiffer.isSome() && *iceCredsDiffer != differ) {
+      // subsequent msections must match the first sections
+      JSEP_SET_ERROR(
+          "Partial ICE restart is unsupported at this time "
+          "(new remote description changes either the ice-ufrag "
+          "or ice-pwd on fewer than all msections)");
+      return NS_ERROR_INVALID_ARG;
+    }
+  }
+
+  return NS_OK;
+}
+
+nsresult JsepSessionImpl::ValidateOffer(const Sdp& offer) {
+  return mSdpHelper.ValidateTransportAttributes(offer, sdp::kOffer);
+}
+
+nsresult JsepSessionImpl::ValidateAnswer(const Sdp& offer, const Sdp& answer) {
+  if (offer.GetMediaSectionCount() != answer.GetMediaSectionCount()) {
+    JSEP_SET_ERROR("Offer and answer have different number of m-lines "
+                   << "(" << offer.GetMediaSectionCount() << " vs "
+                   << answer.GetMediaSectionCount() << ")");
+    return NS_ERROR_INVALID_ARG;
+  }
+
+  nsresult rv = mSdpHelper.ValidateTransportAttributes(answer, sdp::kAnswer);
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  for (size_t i = 0; i < offer.GetMediaSectionCount(); ++i) {
+    const SdpMediaSection& offerMsection = offer.GetMediaSection(i);
+    const SdpMediaSection& answerMsection = answer.GetMediaSection(i);
+
+    if (offerMsection.GetMediaType() != answerMsection.GetMediaType()) {
+      JSEP_SET_ERROR("Answer and offer have different media types at m-line "
+                     << i);
+      return NS_ERROR_INVALID_ARG;
+    }
+
+    if (mSdpHelper.MsectionIsDisabled(answerMsection)) {
+      continue;
+    }
+
+    if (mSdpHelper.MsectionIsDisabled(offerMsection)) {
+      JSEP_SET_ERROR(
+          "Answer tried to enable an m-section that was disabled in the offer");
+      return NS_ERROR_INVALID_ARG;
+    }
+
+    if (!offerMsection.IsSending() && answerMsection.IsReceiving()) {
+      JSEP_SET_ERROR("Answer tried to set recv when offer did not set send");
+      return NS_ERROR_INVALID_ARG;
+    }
+
+    if (!offerMsection.IsReceiving() && answerMsection.IsSending()) {
+      JSEP_SET_ERROR("Answer tried to set send when offer did not set recv");
+      return NS_ERROR_INVALID_ARG;
+    }
+
+    const SdpAttributeList& answerAttrs(answerMsection.GetAttributeList());
+    const SdpAttributeList& offerAttrs(offerMsection.GetAttributeList());
+    if (answerAttrs.HasAttribute(SdpAttribute::kMidAttribute) &&
+        offerAttrs.HasAttribute(SdpAttribute::kMidAttribute) &&
+        offerAttrs.GetMid() != answerAttrs.GetMid()) {
+      JSEP_SET_ERROR("Answer changes mid for level, was \'"
+                     << offerMsection.GetAttributeList().GetMid()
+                     << "\', now \'"
+                     << answerMsection.GetAttributeList().GetMid() << "\'");
+      return NS_ERROR_INVALID_ARG;
+    }
+
+    // Sanity check extmap
+    if (answerAttrs.HasAttribute(SdpAttribute::kExtmapAttribute)) {
+      if (!offerAttrs.HasAttribute(SdpAttribute::kExtmapAttribute)) {
+        JSEP_SET_ERROR("Answer adds extmap attributes to level " << i);
+        return NS_ERROR_INVALID_ARG;
+      }
+
+      for (const auto& ansExt : answerAttrs.GetExtmap().mExtmaps) {
+        bool found = false;
+        for (const auto& offExt : offerAttrs.GetExtmap().mExtmaps) {
+          if (ansExt.extensionname == offExt.extensionname) {
+            if ((ansExt.direction & reverse(offExt.direction)) !=
+                ansExt.direction) {
+              // FIXME we do not return an error here, because Chrome up to
+              // version 57 is actually tripping over this if they are the
+              // answerer. See bug 1355010 for details.
+              MOZ_MTLOG(ML_WARNING,
+                        "[" << mName
+                            << "]: Answer has inconsistent"
+                               " direction on extmap attribute at level "
+                            << i << " (" << ansExt.extensionname
+                            << "). Offer had " << offExt.direction
+                            << ", answer had " << ansExt.direction << ".");
+              // return NS_ERROR_INVALID_ARG;
+            }
+
+            if (offExt.entry < 4096 && (offExt.entry != ansExt.entry)) {
+              JSEP_SET_ERROR("Answer changed id for extmap attribute at level "
+                             << i << " (" << offExt.extensionname << ") from "
+                             << offExt.entry << " to " << ansExt.entry << ".");
+              return NS_ERROR_INVALID_ARG;
+            }
+
+            if (ansExt.entry >= 4096) {
+              JSEP_SET_ERROR("Answer used an invalid id ("
+                             << ansExt.entry
+                             << ") for extmap attribute at level " << i << " ("
+                             << ansExt.extensionname << ").");
+              return NS_ERROR_INVALID_ARG;
+            }
+
+            found = true;
+            break;
+          }
+        }
+
+        if (!found) {
+          JSEP_SET_ERROR("Answer has extmap "
+                         << ansExt.extensionname
+                         << " at "
+                            "level "
+                         << i << " that was not present in offer.");
+          return NS_ERROR_INVALID_ARG;
+        }
+      }
+    }
+  }
+
+  return NS_OK;
+}
+
+nsresult JsepSessionImpl::CreateGenericSDP(UniquePtr<Sdp>* sdpp) {
+  // draft-ietf-rtcweb-jsep-08 Section 5.2.1:
+  //  o  The second SDP line MUST be an "o=" line, as specified in
+  //     [RFC4566], Section 5.2.  The value of the <username> field SHOULD
+  //     be "-".  The value of the <sess-id> field SHOULD be a
+  //     cryptographically random number.  To ensure uniqueness, this
+  //     number SHOULD be at least 64 bits long.  The value of the <sess-
+  //     version> field SHOULD be zero.  The value of the <nettype>
+  //     <addrtype> <unicast-address> tuple SHOULD be set to a non-
+  //     meaningful address, such as IN IP4 0.0.0.0, to prevent leaking the
+  //     local address in this field.  As mentioned in [RFC4566], the
+  //     entire o= line needs to be unique, but selecting a random number
+  //     for <sess-id> is sufficient to accomplish this.
+  //
+  // Historical note: we used to report the actual version number here, after
+  // "SDPARTA-", but that becomes a problem starting with version 100, since
+  // some services parse 100 as "10" and give us legacy/broken behavior. So
+  // we're freezing the version number at 99.0 in this string.
+  auto origin = SdpOrigin("mozilla...THIS_IS_SDPARTA-99.0", mSessionId,
+                          mSessionVersion, sdp::kIPv4, "0.0.0.0");
+
+  UniquePtr<Sdp> sdp = MakeUnique<SipccSdp>(origin);
+
+  if (mDtlsFingerprints.empty()) {
+    JSEP_SET_ERROR("Missing DTLS fingerprint");
+    return NS_ERROR_FAILURE;
+  }
+
+  UniquePtr<SdpFingerprintAttributeList> fpl =
+      MakeUnique<SdpFingerprintAttributeList>();
+  for (auto& dtlsFingerprint : mDtlsFingerprints) {
+    fpl->PushEntry(dtlsFingerprint.mAlgorithm, dtlsFingerprint.mValue);
+  }
+  sdp->GetAttributeList().SetAttribute(fpl.release());
+
+  auto* iceOpts = new SdpOptionsAttribute(SdpAttribute::kIceOptionsAttribute);
+  iceOpts->PushEntry("trickle");
+  sdp->GetAttributeList().SetAttribute(iceOpts);
+
+  // This assumes content doesn't add a bunch of msid attributes with a
+  // different semantic in mind.
+  std::vector<std::string> msids;
+  msids.push_back("*");
+  mSdpHelper.SetupMsidSemantic(msids, sdp.get());
+
+  *sdpp = std::move(sdp);
+  return NS_OK;
+}
+
+nsresult JsepSessionImpl::SetupIds() {
+  SECStatus rv = PK11_GenerateRandom(
+      reinterpret_cast<unsigned char*>(&mSessionId), sizeof(mSessionId));
+  // RFC 3264 says that session-ids MUST be representable as a _signed_
+  // 64 bit number, meaning the MSB cannot be set.
+  mSessionId = mSessionId >> 1;
+  if (rv != SECSuccess) {
+    JSEP_SET_ERROR("Failed to generate session id: " << rv);
+    return NS_ERROR_FAILURE;
+  }
+
+  if (!mUuidGen->Generate(&mDefaultRemoteStreamId)) {
+    JSEP_SET_ERROR("Failed to generate default uuid for streams");
+    return NS_ERROR_FAILURE;
+  }
+
+  if (!mUuidGen->Generate(&mCNAME)) {
+    JSEP_SET_ERROR("Failed to generate CNAME");
+    return NS_ERROR_FAILURE;
+  }
+
+  return NS_OK;
+}
+
+void JsepSessionImpl::SetDefaultCodecs(
+    const std::vector<UniquePtr<JsepCodecDescription>>& aPreferredCodecs) {
+  mSupportedCodecs.clear();
+
+  for (const auto& codec : aPreferredCodecs) {
+    mSupportedCodecs.emplace_back(codec->Clone());
+  }
+}
+
+void JsepSessionImpl::SetState(JsepSignalingState state) {
+  if (state == mState) return;
+
+  MOZ_MTLOG(ML_NOTICE, "[" << mName << "]: " << GetStateStr(mState) << " -> "
+                           << GetStateStr(state));
+  mState = state;
+}
+
+JsepSession::Result JsepSessionImpl::AddRemoteIceCandidate(
+    const std::string& candidate, const std::string& mid,
+    const Maybe<uint16_t>& level, const std::string& ufrag,
+    std::string* transportId) {
+  mLastError.clear();
+  if (!mCurrentRemoteDescription && !mPendingRemoteDescription) {
+    JSEP_SET_ERROR("Cannot add ICE candidate when there is no remote SDP");
+    return dom::PCError::InvalidStateError;
+  }
+
+  if (mid.empty() && !level.isSome() && candidate.empty()) {
+    // Set end-of-candidates on SDP
+    if (mCurrentRemoteDescription) {
+      nsresult rv = mSdpHelper.SetIceGatheringComplete(
+          mCurrentRemoteDescription.get(), ufrag);
+      NS_ENSURE_SUCCESS(rv, dom::PCError::OperationError);
+    }
+
+    if (mPendingRemoteDescription) {
+      // If we had an error when adding the candidate to the current
+      // description, we stomp them here. This is deliberate.
+      nsresult rv = mSdpHelper.SetIceGatheringComplete(
+          mPendingRemoteDescription.get(), ufrag);
+      NS_ENSURE_SUCCESS(rv, dom::PCError::OperationError);
+    }
+    return Result();
+  }
+
+  Maybe<JsepTransceiver> transceiver;
+  if (!mid.empty()) {
+    transceiver = GetTransceiverForMid(mid);
+  } else if (level.isSome()) {
+    transceiver = GetTransceiverForLevel(level.value());
+  }
+
+  if (!transceiver) {
+    JSEP_SET_ERROR("Cannot set ICE candidate for level="
+                   << level << " mid=" << mid << ": No such transceiver.");
+    return dom::PCError::OperationError;
+  }
+
+  if (level.isSome() && transceiver->GetLevel() != level.value()) {
+    MOZ_MTLOG(ML_WARNING, "Mismatch between mid and level - \""
+                              << mid << "\" is not the mid for level "
+                              << level);
+  }
+
+  *transportId = transceiver->mTransport.mTransportId;
+  nsresult rv = NS_ERROR_UNEXPECTED;
+  if (mCurrentRemoteDescription) {
+    rv =
+        mSdpHelper.AddCandidateToSdp(mCurrentRemoteDescription.get(), candidate,
+                                     transceiver->GetLevel(), ufrag);
+  }
+
+  if (mPendingRemoteDescription) {
+    // If we had an error when adding the candidate to the current description,
+    // we stomp them here. This is deliberate.
+    rv =
+        mSdpHelper.AddCandidateToSdp(mPendingRemoteDescription.get(), candidate,
+                                     transceiver->GetLevel(), ufrag);
+  }
+
+  NS_ENSURE_SUCCESS(rv, dom::PCError::OperationError);
+  return Result();
+}
+
+nsresult JsepSessionImpl::AddLocalIceCandidate(const std::string& candidate,
+                                               const std::string& transportId,
+                                               const std::string& ufrag,
+                                               uint16_t* level,
+                                               std::string* mid,
+                                               bool* skipped) {
+  mLastError.clear();
+  *skipped = true;
+  if (!mCurrentLocalDescription && !mPendingLocalDescription) {
+    JSEP_SET_ERROR("Cannot add ICE candidate when there is no local SDP");
+    return NS_ERROR_UNEXPECTED;
+  }
+
+  Maybe<const JsepTransceiver> transceiver =
+      GetTransceiverWithTransport(transportId);
+  if (!transceiver || !transceiver->IsAssociated()) {
+    // mainly here to make some testing less complicated, but also just in case
+    return NS_OK;
+  }
+
+  *level = transceiver->GetLevel();
+  *mid = transceiver->GetMid();
+
+  nsresult rv = NS_ERROR_INVALID_ARG;
+  if (mCurrentLocalDescription) {
+    rv = mSdpHelper.AddCandidateToSdp(mCurrentLocalDescription.get(), candidate,
+                                      *level, ufrag);
+  }
+
+  if (mPendingLocalDescription) {
+    // If we had an error when adding the candidate to the current description,
+    // we stomp them here. This is deliberate.
+    rv = mSdpHelper.AddCandidateToSdp(mPendingLocalDescription.get(), candidate,
+                                      *level, ufrag);
+  }
+
+  *skipped = false;
+  return rv;
+}
+
+nsresult JsepSessionImpl::UpdateDefaultCandidate(
+    const std::string& defaultCandidateAddr, uint16_t defaultCandidatePort,
+    const std::string& defaultRtcpCandidateAddr,
+    uint16_t defaultRtcpCandidatePort, const std::string& transportId) {
+  mLastError.clear();
+
+  mozilla::Sdp* sdp =
+      GetParsedLocalDescription(kJsepDescriptionPendingOrCurrent);
+
+  if (!sdp) {
+    JSEP_SET_ERROR("Cannot add ICE candidate in state " << GetStateStr(mState));
+    return NS_ERROR_UNEXPECTED;
+  }
+
+  for (const auto& transceiver : mTransceivers) {
+    // We set the default address for bundled m-sections, but not candidate
+    // attributes. Ugh.
+    if (transceiver.mTransport.mTransportId == transportId) {
+      MOZ_ASSERT(transceiver.HasLevel(),
+                 "Transceiver has a transport, but no level! "
+                 "This should never happen.");
+      std::string defaultRtcpCandidateAddrCopy(defaultRtcpCandidateAddr);
+      if (mState == kJsepStateStable) {
+        if (transceiver.mTransport.mComponents == 1) {
+          // We know we're doing rtcp-mux by now. Don't create an rtcp attr.
+          defaultRtcpCandidateAddrCopy = "";
+          defaultRtcpCandidatePort = 0;
+        }
+      }
+
+      size_t level = transceiver.GetLevel();
+      if (level >= sdp->GetMediaSectionCount()) {
+        MOZ_ASSERT(false, "Transceiver's level is too large!");
+        JSEP_SET_ERROR("Transceiver's level is too large!");
+        return NS_ERROR_FAILURE;
+      }
+
+      auto& msection = sdp->GetMediaSection(level);
+
+      // Do not add default candidate to a bundle-only m-section, sinice that
+      // might confuse endpoints that do not support bundle-only.
+      if (!msection.GetAttributeList().HasAttribute(
+              SdpAttribute::kBundleOnlyAttribute)) {
+        mSdpHelper.SetDefaultAddresses(
+            defaultCandidateAddr, defaultCandidatePort,
+            defaultRtcpCandidateAddrCopy, defaultRtcpCandidatePort, &msection);
+      }
+    }
+  }
+
+  return NS_OK;
+}
+
+nsresult JsepSessionImpl::GetNegotiatedBundledMids(
+    SdpHelper::BundledMids* bundledMids) {
+  const Sdp* answerSdp = GetAnswer();
+
+  if (!answerSdp) {
+    return NS_OK;
+  }
+
+  return mSdpHelper.GetBundledMids(*answerSdp, bundledMids);
+}
+
+mozilla::Sdp* JsepSessionImpl::GetParsedLocalDescription(
+    JsepDescriptionPendingOrCurrent type) const {
+  if (type == kJsepDescriptionPending) {
+    return mPendingLocalDescription.get();
+  } else if (mPendingLocalDescription &&
+             type == kJsepDescriptionPendingOrCurrent) {
+    return mPendingLocalDescription.get();
+  }
+  return mCurrentLocalDescription.get();
+}
+
+mozilla::Sdp* JsepSessionImpl::GetParsedRemoteDescription(
+    JsepDescriptionPendingOrCurrent type) const {
+  if (type == kJsepDescriptionPending) {
+    return mPendingRemoteDescription.get();
+  } else if (mPendingRemoteDescription &&
+             type == kJsepDescriptionPendingOrCurrent) {
+    return mPendingRemoteDescription.get();
+  }
+  return mCurrentRemoteDescription.get();
+}
+
+const Sdp* JsepSessionImpl::GetAnswer() const {
+  return (mIsCurrentOfferer.isSome() && *mIsCurrentOfferer)
+             ? mCurrentRemoteDescription.get()
+             : mCurrentLocalDescription.get();
+}
+
+void JsepSessionImpl::SetIceRestarting(bool restarting) {
+  if (restarting) {
+    // not restarting -> restarting
+    if (!IsIceRestarting()) {
+      // We don't set this more than once, so the old ufrag/pwd is preserved
+      // even if we CreateOffer({iceRestart:true}) multiple times in a row.
+      mOldIceUfrag = mIceUfrag;
+      mOldIcePwd = mIcePwd;
+    }
+    mIceUfrag = GetRandomHex(1);
+    mIcePwd = GetRandomHex(4);
+  } else if (IsIceRestarting()) {
+    // restarting -> not restarting, restore old ufrag/pwd
+    mIceUfrag = mOldIceUfrag;
+    mIcePwd = mOldIcePwd;
+    mOldIceUfrag.clear();
+    mOldIcePwd.clear();
+  }
+}
+
+nsresult JsepSessionImpl::Close() {
+  mLastError.clear();
+  SetState(kJsepStateClosed);
+  return NS_OK;
+}
+
+const std::string JsepSessionImpl::GetLastError() const { return mLastError; }
+
+const std::vector<std::pair<size_t, std::string>>&
+JsepSessionImpl::GetLastSdpParsingErrors() const {
+  return mLastSdpParsingErrors;
+}
+
+bool JsepSessionImpl::CheckNegotiationNeeded() const {
+  MOZ_ASSERT(mState == kJsepStateStable);
+
+  for (const auto& transceiver : mTransceivers) {
+    if (transceiver.IsStopped()) {
+      // Nothing to do with this
+      continue;
+    }
+
+    if (transceiver.IsStopping()) {
+      MOZ_MTLOG(ML_DEBUG, "[" << mName
+                              << "]: Negotiation needed because of "
+                                 "transceiver we need to stop");
+      return true;
+    }
+
+    if (!transceiver.IsAssociated()) {
+      MOZ_MTLOG(ML_DEBUG, "[" << mName
+                              << "]: Negotiation needed because of "
+                                 "transceiver we need to associate.");
+      return true;
+    }
+
+    MOZ_ASSERT(transceiver.IsAssociated() && !transceiver.IsStopping() &&
+               !transceiver.IsStopped());
+
+    if (!mCurrentLocalDescription || !mCurrentRemoteDescription) {
+      MOZ_CRASH(
+          "Transceivers should not be associated if we're in stable "
+          "before the first negotiation.");
+      continue;
+    }
+
+    if (!transceiver.HasLevel()) {
+      MOZ_CRASH("Associated transceivers should always have a level.");
+      continue;
+    }
+
+    if (transceiver.GetMediaType() == SdpMediaSection::kApplication) {
+      continue;
+    }
+
+    size_t level = transceiver.GetLevel();
+    if (NS_WARN_IF(mCurrentLocalDescription->GetMediaSectionCount() <= level) ||
+        NS_WARN_IF(mCurrentRemoteDescription->GetMediaSectionCount() <=
+                   level)) {
+      MOZ_ASSERT(false);
+      continue;
+    }
+
+    const SdpMediaSection& local =
+        mCurrentLocalDescription->GetMediaSection(level);
+    const SdpMediaSection& remote =
+        mCurrentRemoteDescription->GetMediaSection(level);
+
+    if (transceiver.mJsDirection & sdp::kSend) {
+      std::vector<std::string> sdpMsids;
+      if (local.GetAttributeList().HasAttribute(SdpAttribute::kMsidAttribute)) {
+        for (const auto& msidAttr : local.GetAttributeList().GetMsid().mMsids) {
+          if (msidAttr.identifier != "-") {
+            sdpMsids.push_back(msidAttr.identifier);
+          }
+        }
+      }
+      std::sort(sdpMsids.begin(), sdpMsids.end());
+
+      std::vector<std::string> jsepMsids;
+      for (const auto& jsepMsid : transceiver.mSendTrack.GetStreamIds()) {
+        jsepMsids.push_back(jsepMsid);
+      }
+      std::sort(jsepMsids.begin(), jsepMsids.end());
+
+      if (!std::equal(sdpMsids.begin(), sdpMsids.end(), jsepMsids.begin(),
+                      jsepMsids.end())) {
+        MOZ_MTLOG(ML_DEBUG,
+                  "[" << mName
+                      << "]: Negotiation needed because transceiver "
+                         "is sending, and the local SDP has different "
+                         "msids than the send track");
+        MOZ_MTLOG(ML_DEBUG, "[" << mName << "]: SDP msids = [");
+        for (const auto& msid : sdpMsids) {
+          MOZ_MTLOG(ML_DEBUG, msid << ", ");
+        }
+        MOZ_MTLOG(ML_DEBUG, "]");
+        MOZ_MTLOG(ML_DEBUG, "[" << mName << "]: JSEP msids = [");
+        for (const auto& msid : jsepMsids) {
+          MOZ_MTLOG(ML_DEBUG, msid << ", ");
+        }
+        MOZ_MTLOG(ML_DEBUG, "]");
+        return true;
+      }
+    }
+
+    if (mIsCurrentOfferer.isSome() && *mIsCurrentOfferer) {
+      if ((local.GetDirection() != transceiver.mJsDirection) &&
+          reverse(remote.GetDirection()) != transceiver.mJsDirection) {
+        MOZ_MTLOG(ML_DEBUG, "[" << mName
+                                << "]: Negotiation needed because "
+                                   "the direction on our offer, and the remote "
+                                   "answer, does not "
+                                   "match the direction on a transceiver.");
+        return true;
+      }
+    } else if (local.GetDirection() !=
+               (transceiver.mJsDirection & reverse(remote.GetDirection()))) {
+      MOZ_MTLOG(
+          ML_DEBUG,
+          "[" << mName
+              << "]: Negotiation needed because "
+                 "the direction on our answer doesn't match the direction on a "
+                 "transceiver, even though the remote offer would have allowed "
+                 "it.");
+      return true;
+    }
+  }
+
+  return false;
+}
+
+}  // namespace mozilla