Adds trunk/talk folder of revision 359 from libjingles google code to
trunk/talk


git-svn-id: http://webrtc.googlecode.com/svn/trunk@4318 4adac7df-926f-26a2-2b94-8c16560cd09d
diff --git a/talk/session/media/mediasession.cc b/talk/session/media/mediasession.cc
new file mode 100644
index 0000000..3d00418
--- /dev/null
+++ b/talk/session/media/mediasession.cc
@@ -0,0 +1,1657 @@
+/*
+ * libjingle
+ * Copyright 2004 Google Inc.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ *  1. Redistributions of source code must retain the above copyright notice,
+ *     this list of conditions and the following disclaimer.
+ *  2. Redistributions in binary form must reproduce the above copyright notice,
+ *     this list of conditions and the following disclaimer in the documentation
+ *     and/or other materials provided with the distribution.
+ *  3. The name of the author may not be used to endorse or promote products
+ *     derived from this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR IMPLIED
+ * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO
+ * EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
+ * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS;
+ * OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
+ * WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR
+ * OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
+ * ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include "talk/session/media/mediasession.h"
+
+#include <functional>
+#include <map>
+#include <set>
+#include <utility>
+
+#include "talk/base/helpers.h"
+#include "talk/base/logging.h"
+#include "talk/base/scoped_ptr.h"
+#include "talk/base/stringutils.h"
+#include "talk/media/base/constants.h"
+#include "talk/media/base/cryptoparams.h"
+#include "talk/p2p/base/constants.h"
+#include "talk/session/media/channelmanager.h"
+#include "talk/session/media/srtpfilter.h"
+#include "talk/xmpp/constants.h"
+
+namespace {
+const char kInline[] = "inline:";
+}
+
+namespace cricket {
+
+using talk_base::scoped_ptr;
+
+// RTP Profile names
+// http://www.iana.org/assignments/rtp-parameters/rtp-parameters.xml
+// RFC4585
+const char kMediaProtocolAvpf[] = "RTP/AVPF";
+// RFC5124
+const char kMediaProtocolSavpf[] = "RTP/SAVPF";
+
+const char kMediaProtocolRtpPrefix[] = "RTP/";
+
+const char kMediaProtocolSctp[] = "SCTP";
+const char kMediaProtocolDtlsSctp[] = "DTLS/SCTP";
+
+static bool IsMediaContentOfType(const ContentInfo* content,
+                                 MediaType media_type) {
+  if (!IsMediaContent(content)) {
+    return false;
+  }
+
+  const MediaContentDescription* mdesc =
+      static_cast<const MediaContentDescription*>(content->description);
+  return mdesc && mdesc->type() == media_type;
+}
+
+static bool CreateCryptoParams(int tag, const std::string& cipher,
+                               CryptoParams *out) {
+  std::string key;
+  key.reserve(SRTP_MASTER_KEY_BASE64_LEN);
+
+  if (!talk_base::CreateRandomString(SRTP_MASTER_KEY_BASE64_LEN, &key)) {
+    return false;
+  }
+  out->tag = tag;
+  out->cipher_suite = cipher;
+  out->key_params = kInline;
+  out->key_params += key;
+  return true;
+}
+
+#ifdef HAVE_SRTP
+static bool AddCryptoParams(const std::string& cipher_suite,
+                            CryptoParamsVec *out) {
+  int size = out->size();
+
+  out->resize(size + 1);
+  return CreateCryptoParams(size, cipher_suite, &out->at(size));
+}
+
+void AddMediaCryptos(const CryptoParamsVec& cryptos,
+                     MediaContentDescription* media) {
+  for (CryptoParamsVec::const_iterator crypto = cryptos.begin();
+       crypto != cryptos.end(); ++crypto) {
+    media->AddCrypto(*crypto);
+  }
+}
+
+bool CreateMediaCryptos(const std::vector<std::string>& crypto_suites,
+                        MediaContentDescription* media) {
+  CryptoParamsVec cryptos;
+  for (std::vector<std::string>::const_iterator it = crypto_suites.begin();
+       it != crypto_suites.end(); ++it) {
+    if (!AddCryptoParams(*it, &cryptos)) {
+      return false;
+    }
+  }
+  AddMediaCryptos(cryptos, media);
+  return true;
+}
+#endif
+
+const CryptoParamsVec* GetCryptos(const MediaContentDescription* media) {
+  if (!media) {
+    return NULL;
+  }
+  return &media->cryptos();
+}
+
+bool FindMatchingCrypto(const CryptoParamsVec& cryptos,
+                        const CryptoParams& crypto,
+                        CryptoParams* out) {
+  for (CryptoParamsVec::const_iterator it = cryptos.begin();
+       it != cryptos.end(); ++it) {
+    if (crypto.Matches(*it)) {
+      *out = *it;
+      return true;
+    }
+  }
+  return false;
+}
+
+// For audio, HMAC 32 is prefered because of the low overhead.
+void GetSupportedAudioCryptoSuites(
+    std::vector<std::string>* crypto_suites) {
+#ifdef HAVE_SRTP
+  crypto_suites->push_back(CS_AES_CM_128_HMAC_SHA1_32);
+  crypto_suites->push_back(CS_AES_CM_128_HMAC_SHA1_80);
+#endif
+}
+
+void GetSupportedVideoCryptoSuites(
+    std::vector<std::string>* crypto_suites) {
+  GetSupportedDefaultCryptoSuites(crypto_suites);
+}
+
+void GetSupportedDataCryptoSuites(
+    std::vector<std::string>* crypto_suites) {
+  GetSupportedDefaultCryptoSuites(crypto_suites);
+}
+
+void GetSupportedDefaultCryptoSuites(
+    std::vector<std::string>* crypto_suites) {
+#ifdef HAVE_SRTP
+  crypto_suites->push_back(CS_AES_CM_128_HMAC_SHA1_80);
+#endif
+}
+
+// For video support only 80-bit SHA1 HMAC. For audio 32-bit HMAC is
+// tolerated unless bundle is enabled because it is low overhead. Pick the
+// crypto in the list that is supported.
+static bool SelectCrypto(const MediaContentDescription* offer,
+                         bool bundle,
+                         CryptoParams *crypto) {
+  bool audio = offer->type() == MEDIA_TYPE_AUDIO;
+  const CryptoParamsVec& cryptos = offer->cryptos();
+
+  for (CryptoParamsVec::const_iterator i = cryptos.begin();
+       i != cryptos.end(); ++i) {
+    if (CS_AES_CM_128_HMAC_SHA1_80 == i->cipher_suite ||
+        (CS_AES_CM_128_HMAC_SHA1_32 == i->cipher_suite && audio && !bundle)) {
+      return CreateCryptoParams(i->tag, i->cipher_suite, crypto);
+    }
+  }
+  return false;
+}
+
+static const StreamParams* FindFirstStreamParamsByCname(
+    const StreamParamsVec& params_vec,
+    const std::string& cname) {
+  for (StreamParamsVec::const_iterator it = params_vec.begin();
+       it != params_vec.end(); ++it) {
+    if (cname == it->cname)
+      return &*it;
+  }
+  return NULL;
+}
+
+// Generates a new CNAME or the CNAME of an already existing StreamParams
+// if a StreamParams exist for another Stream in streams with sync_label
+// sync_label.
+static bool GenerateCname(const StreamParamsVec& params_vec,
+                          const MediaSessionOptions::Streams& streams,
+                          const std::string& synch_label,
+                          std::string* cname) {
+  ASSERT(cname != NULL);
+  if (!cname)
+    return false;
+
+  // Check if a CNAME exist for any of the other synched streams.
+  for (MediaSessionOptions::Streams::const_iterator stream_it = streams.begin();
+       stream_it != streams.end() ; ++stream_it) {
+    if (synch_label != stream_it->sync_label)
+      continue;
+
+    StreamParams param;
+    // groupid is empty for StreamParams generated using
+    // MediaSessionDescriptionFactory.
+    if (GetStreamByIds(params_vec, "", stream_it->id,
+                       &param)) {
+      *cname = param.cname;
+      return true;
+    }
+  }
+  // No other stream seems to exist that we should sync with.
+  // Generate a random string for the RTCP CNAME, as stated in RFC 6222.
+  // This string is only used for synchronization, and therefore is opaque.
+  do {
+    if (!talk_base::CreateRandomString(16, cname)) {
+      ASSERT(false);
+      return false;
+    }
+  } while (FindFirstStreamParamsByCname(params_vec, *cname));
+
+  return true;
+}
+
+// Generate random SSRC values that are not already present in |params_vec|.
+// Either 2 or 1 ssrcs will be generated based on |include_rtx_stream| being
+// true or false. The generated values are added to |ssrcs|.
+static void GenerateSsrcs(const StreamParamsVec& params_vec,
+                          bool include_rtx_stream,
+                          std::vector<uint32>* ssrcs) {
+  unsigned int num_ssrcs = include_rtx_stream ? 2 : 1;
+  for (unsigned int i = 0; i < num_ssrcs; i++) {
+    uint32 candidate;
+    do {
+      candidate = talk_base::CreateRandomNonZeroId();
+    } while (GetStreamBySsrc(params_vec, candidate, NULL) ||
+             std::count(ssrcs->begin(), ssrcs->end(), candidate) > 0);
+    ssrcs->push_back(candidate);
+  }
+}
+
+// Returns false if we exhaust the range of SIDs.
+static bool GenerateSctpSid(const StreamParamsVec& params_vec,
+                            uint32* sid) {
+  if (params_vec.size() > kMaxSctpSid) {
+    LOG(LS_WARNING) <<
+        "Could not generate an SCTP SID: too many SCTP streams.";
+    return false;
+  }
+  while (true) {
+    uint32 candidate = talk_base::CreateRandomNonZeroId() % kMaxSctpSid;
+    if (!GetStreamBySsrc(params_vec, candidate, NULL)) {
+      *sid = candidate;
+      return true;
+    }
+  }
+}
+
+static bool GenerateSctpSids(const StreamParamsVec& params_vec,
+                             std::vector<uint32>* sids) {
+  uint32 sid;
+  if (!GenerateSctpSid(params_vec, &sid)) {
+    LOG(LS_WARNING) << "Could not generated an SCTP SID.";
+    return false;
+  }
+  sids->push_back(sid);
+  return true;
+}
+
+// Finds all StreamParams of all media types and attach them to stream_params.
+static void GetCurrentStreamParams(const SessionDescription* sdesc,
+                                   StreamParamsVec* stream_params) {
+  if (!sdesc)
+    return;
+
+  const ContentInfos& contents = sdesc->contents();
+  for (ContentInfos::const_iterator content = contents.begin();
+       content != contents.end(); ++content) {
+    if (!IsMediaContent(&*content)) {
+      continue;
+    }
+    const MediaContentDescription* media =
+        static_cast<const MediaContentDescription*>(
+            content->description);
+    const StreamParamsVec& streams = media->streams();
+    for (StreamParamsVec::const_iterator it = streams.begin();
+         it != streams.end(); ++it) {
+      stream_params->push_back(*it);
+    }
+  }
+}
+
+template <typename IdStruct>
+class UsedIds {
+ public:
+  UsedIds(int min_allowed_id, int max_allowed_id)
+      : min_allowed_id_(min_allowed_id),
+        max_allowed_id_(max_allowed_id),
+        next_id_(max_allowed_id) {
+  }
+
+  // Loops through all Id in |ids| and changes its id if it is
+  // already in use by another IdStruct. Call this methods with all Id
+  // in a session description to make sure no duplicate ids exists.
+  // Note that typename Id must be a type of IdStruct.
+  template <typename Id>
+  void FindAndSetIdUsed(std::vector<Id>* ids) {
+    for (typename std::vector<Id>::iterator it = ids->begin();
+         it != ids->end(); ++it) {
+      FindAndSetIdUsed(&*it);
+    }
+  }
+
+  // Finds and sets an unused id if the |idstruct| id is already in use.
+  void FindAndSetIdUsed(IdStruct* idstruct) {
+    const int original_id = idstruct->id;
+    int new_id = idstruct->id;
+
+    if (original_id > max_allowed_id_ || original_id < min_allowed_id_) {
+      // If the original id is not in range - this is an id that can't be
+      // dynamically changed.
+      return;
+    }
+
+    if (IsIdUsed(original_id)) {
+      new_id = FindUnusedId();
+      LOG(LS_WARNING) << "Duplicate id found. Reassigning from " << original_id
+          << " to " << new_id;
+      idstruct->id = new_id;
+    }
+    SetIdUsed(new_id);
+  }
+
+ private:
+  // Returns the first unused id in reverse order.
+  // This hopefully reduce the risk of more collisions. We want to change the
+  // default ids as little as possible.
+  int FindUnusedId() {
+    while (IsIdUsed(next_id_) && next_id_ >= min_allowed_id_) {
+      --next_id_;
+    }
+    ASSERT(next_id_ >= min_allowed_id_);
+    return next_id_;
+  }
+
+  bool IsIdUsed(int new_id) {
+    return id_set_.find(new_id) != id_set_.end();
+  }
+
+  void SetIdUsed(int new_id) {
+    id_set_.insert(new_id);
+  }
+
+  const int min_allowed_id_;
+  const int max_allowed_id_;
+  int next_id_;
+  std::set<int> id_set_;
+};
+
+// Helper class used for finding duplicate RTP payload types among audio, video
+// and data codecs. When bundle is used the payload types may not collide.
+class UsedPayloadTypes : public UsedIds<Codec> {
+ public:
+  UsedPayloadTypes()
+      : UsedIds<Codec>(kDynamicPayloadTypeMin, kDynamicPayloadTypeMax) {
+  }
+
+
+ private:
+  static const int kDynamicPayloadTypeMin = 96;
+  static const int kDynamicPayloadTypeMax = 127;
+};
+
+// Helper class used for finding duplicate RTP Header extension ids among
+// audio and video extensions.
+class UsedRtpHeaderExtensionIds : public UsedIds<RtpHeaderExtension> {
+ public:
+  UsedRtpHeaderExtensionIds()
+      : UsedIds<RtpHeaderExtension>(kLocalIdMin, kLocalIdMax) {
+  }
+
+ private:
+  // Min and Max local identifier as specified by RFC5285.
+  static const int kLocalIdMin = 1;
+  static const int kLocalIdMax = 255;
+};
+
+static bool IsSctp(const MediaContentDescription* desc) {
+  return ((desc->protocol() == kMediaProtocolSctp) ||
+          (desc->protocol() == kMediaProtocolDtlsSctp));
+}
+
+// Adds a StreamParams for each Stream in Streams with media type
+// media_type to content_description.
+// |current_params| - All currently known StreamParams of any media type.
+template <class C>
+static bool AddStreamParams(
+    MediaType media_type,
+    const MediaSessionOptions::Streams& streams,
+    StreamParamsVec* current_streams,
+    MediaContentDescriptionImpl<C>* content_description,
+    const bool add_legacy_stream) {
+  const bool include_rtx_stream =
+    ContainsRtxCodec(content_description->codecs());
+
+  if (streams.empty() && add_legacy_stream) {
+    // TODO(perkj): Remove this legacy stream when all apps use StreamParams.
+    std::vector<uint32> ssrcs;
+    if (IsSctp(content_description)) {
+      GenerateSctpSids(*current_streams, &ssrcs);
+    } else {
+      GenerateSsrcs(*current_streams, include_rtx_stream, &ssrcs);
+    }
+    if (include_rtx_stream) {
+      content_description->AddLegacyStream(ssrcs[0], ssrcs[1]);
+      content_description->set_multistream(true);
+    } else {
+      content_description->AddLegacyStream(ssrcs[0]);
+    }
+    return true;
+  }
+
+  MediaSessionOptions::Streams::const_iterator stream_it;
+  for (stream_it = streams.begin();
+       stream_it != streams.end(); ++stream_it) {
+    if (stream_it->type != media_type)
+      continue;  // Wrong media type.
+
+    StreamParams param;
+    // groupid is empty for StreamParams generated using
+    // MediaSessionDescriptionFactory.
+    if (!GetStreamByIds(*current_streams, "", stream_it->id,
+                        &param)) {
+      // This is a new stream.
+      // Get a CNAME. Either new or same as one of the other synched streams.
+      std::string cname;
+      if (!GenerateCname(*current_streams, streams, stream_it->sync_label,
+                         &cname)) {
+        return false;
+      }
+
+      std::vector<uint32> ssrcs;
+      if (IsSctp(content_description)) {
+        GenerateSctpSids(*current_streams, &ssrcs);
+      } else {
+        GenerateSsrcs(*current_streams, include_rtx_stream, &ssrcs);
+      }
+      StreamParams stream_param;
+      stream_param.id = stream_it->id;
+      stream_param.ssrcs.push_back(ssrcs[0]);
+      if (include_rtx_stream) {
+        stream_param.AddFidSsrc(ssrcs[0], ssrcs[1]);
+        content_description->set_multistream(true);
+      }
+      stream_param.cname = cname;
+      stream_param.sync_label = stream_it->sync_label;
+      content_description->AddStream(stream_param);
+
+      // Store the new StreamParams in current_streams.
+      // This is necessary so that we can use the CNAME for other media types.
+      current_streams->push_back(stream_param);
+    } else {
+      content_description->AddStream(param);
+    }
+  }
+  return true;
+}
+
+// Updates the transport infos of the |sdesc| according to the given
+// |bundle_group|. The transport infos of the content names within the
+// |bundle_group| should be updated to use the ufrag and pwd of the first
+// content within the |bundle_group|.
+static bool UpdateTransportInfoForBundle(const ContentGroup& bundle_group,
+                                         SessionDescription* sdesc) {
+  // The bundle should not be empty.
+  if (!sdesc || !bundle_group.FirstContentName()) {
+    return false;
+  }
+
+  // We should definitely have a transport for the first content.
+  std::string selected_content_name = *bundle_group.FirstContentName();
+  const TransportInfo* selected_transport_info =
+      sdesc->GetTransportInfoByName(selected_content_name);
+  if (!selected_transport_info) {
+    return false;
+  }
+
+  // Set the other contents to use the same ICE credentials.
+  const std::string selected_ufrag =
+      selected_transport_info->description.ice_ufrag;
+  const std::string selected_pwd =
+      selected_transport_info->description.ice_pwd;
+  for (TransportInfos::iterator it =
+           sdesc->transport_infos().begin();
+       it != sdesc->transport_infos().end(); ++it) {
+    if (bundle_group.HasContentName(it->content_name) &&
+        it->content_name != selected_content_name) {
+      it->description.ice_ufrag = selected_ufrag;
+      it->description.ice_pwd = selected_pwd;
+    }
+  }
+  return true;
+}
+
+// Gets the CryptoParamsVec of the given |content_name| from |sdesc|, and
+// sets it to |cryptos|.
+static bool GetCryptosByName(const SessionDescription* sdesc,
+                             const std::string& content_name,
+                             CryptoParamsVec* cryptos) {
+  if (!sdesc || !cryptos) {
+    return false;
+  }
+
+  const ContentInfo* content = sdesc->GetContentByName(content_name);
+  if (!IsMediaContent(content) || !content->description) {
+    return false;
+  }
+
+  const MediaContentDescription* media_desc =
+      static_cast<const MediaContentDescription*>(content->description);
+  *cryptos = media_desc->cryptos();
+  return true;
+}
+
+// Predicate function used by the remove_if.
+// Returns true if the |crypto|'s cipher_suite is not found in |filter|.
+static bool CryptoNotFound(const CryptoParams crypto,
+                           const CryptoParamsVec* filter) {
+  if (filter == NULL) {
+    return true;
+  }
+  for (CryptoParamsVec::const_iterator it = filter->begin();
+       it != filter->end(); ++it) {
+    if (it->cipher_suite == crypto.cipher_suite) {
+      return false;
+    }
+  }
+  return true;
+}
+
+// Prunes the |target_cryptos| by removing the crypto params (cipher_suite)
+// which are not available in |filter|.
+static void PruneCryptos(const CryptoParamsVec& filter,
+                         CryptoParamsVec* target_cryptos) {
+  if (!target_cryptos) {
+    return;
+  }
+  target_cryptos->erase(std::remove_if(target_cryptos->begin(),
+                                       target_cryptos->end(),
+                                       bind2nd(ptr_fun(CryptoNotFound),
+                                               &filter)),
+                        target_cryptos->end());
+}
+
+static bool IsRtpContent(SessionDescription* sdesc,
+                         const std::string& content_name) {
+  bool is_rtp = false;
+  ContentInfo* content = sdesc->GetContentByName(content_name);
+  if (IsMediaContent(content)) {
+    MediaContentDescription* media_desc =
+        static_cast<MediaContentDescription*>(content->description);
+    if (!media_desc) {
+      return false;
+    }
+    is_rtp = media_desc->protocol().empty() ||
+             talk_base::starts_with(media_desc->protocol().data(),
+                                    kMediaProtocolRtpPrefix);
+  }
+  return is_rtp;
+}
+
+// Updates the crypto parameters of the |sdesc| according to the given
+// |bundle_group|. The crypto parameters of all the contents within the
+// |bundle_group| should be updated to use the common subset of the
+// available cryptos.
+static bool UpdateCryptoParamsForBundle(const ContentGroup& bundle_group,
+                                        SessionDescription* sdesc) {
+  // The bundle should not be empty.
+  if (!sdesc || !bundle_group.FirstContentName()) {
+    return false;
+  }
+
+  // Get the common cryptos.
+  const ContentNames& content_names = bundle_group.content_names();
+  CryptoParamsVec common_cryptos;
+  for (ContentNames::const_iterator it = content_names.begin();
+       it != content_names.end(); ++it) {
+    if (!IsRtpContent(sdesc, *it)) {
+      continue;
+    }
+    if (it == content_names.begin()) {
+      // Initial the common_cryptos with the first content in the bundle group.
+      if (!GetCryptosByName(sdesc, *it, &common_cryptos)) {
+        return false;
+      }
+      if (common_cryptos.empty()) {
+        // If there's no crypto params, we should just return.
+        return true;
+      }
+    } else {
+      CryptoParamsVec cryptos;
+      if (!GetCryptosByName(sdesc, *it, &cryptos)) {
+        return false;
+      }
+      PruneCryptos(cryptos, &common_cryptos);
+    }
+  }
+
+  if (common_cryptos.empty()) {
+    return false;
+  }
+
+  // Update to use the common cryptos.
+  for (ContentNames::const_iterator it = content_names.begin();
+       it != content_names.end(); ++it) {
+    if (!IsRtpContent(sdesc, *it)) {
+      continue;
+    }
+    ContentInfo* content = sdesc->GetContentByName(*it);
+    if (IsMediaContent(content)) {
+      MediaContentDescription* media_desc =
+          static_cast<MediaContentDescription*>(content->description);
+      if (!media_desc) {
+        return false;
+      }
+      media_desc->set_cryptos(common_cryptos);
+    }
+  }
+  return true;
+}
+
+template <class C>
+static bool ContainsRtxCodec(const std::vector<C>& codecs) {
+  typename std::vector<C>::const_iterator it;
+  for (it = codecs.begin(); it != codecs.end(); ++it) {
+    if (IsRtxCodec(*it)) {
+      return true;
+    }
+  }
+  return false;
+}
+
+template <class C>
+static bool IsRtxCodec(const C& codec) {
+  return stricmp(codec.name.c_str(), kRtxCodecName) == 0;
+}
+
+// Create a media content to be offered in a session-initiate,
+// according to the given options.rtcp_mux, options.is_muc,
+// options.streams, codecs, secure_transport, crypto, and streams.  If we don't
+// currently have crypto (in current_cryptos) and it is enabled (in
+// secure_policy), crypto is created (according to crypto_suites).  If
+// add_legacy_stream is true, and current_streams is empty, a legacy
+// stream is created.  The created content is added to the offer.
+template <class C>
+static bool CreateMediaContentOffer(
+    const MediaSessionOptions& options,
+    const std::vector<C>& codecs,
+    const SecureMediaPolicy& secure_policy,
+    const CryptoParamsVec* current_cryptos,
+    const std::vector<std::string>& crypto_suites,
+    const RtpHeaderExtensions& rtp_extensions,
+    bool add_legacy_stream,
+    StreamParamsVec* current_streams,
+    MediaContentDescriptionImpl<C>* offer) {
+  offer->AddCodecs(codecs);
+  offer->SortCodecs();
+
+  offer->set_crypto_required(secure_policy == SEC_REQUIRED);
+  offer->set_rtcp_mux(options.rtcp_mux_enabled);
+  offer->set_multistream(options.is_muc);
+  offer->set_rtp_header_extensions(rtp_extensions);
+
+  if (!AddStreamParams(
+          offer->type(), options.streams, current_streams,
+          offer, add_legacy_stream)) {
+    return false;
+  }
+
+#ifdef HAVE_SRTP
+  if (secure_policy != SEC_DISABLED) {
+    if (current_cryptos) {
+      AddMediaCryptos(*current_cryptos, offer);
+    }
+    if (offer->cryptos().empty()) {
+      if (!CreateMediaCryptos(crypto_suites, offer)) {
+        return false;
+      }
+    }
+  }
+#endif
+
+  if (offer->crypto_required() && offer->cryptos().empty()) {
+    return false;
+  }
+  return true;
+}
+
+template <class C>
+static void NegotiateCodecs(const std::vector<C>& local_codecs,
+                            const std::vector<C>& offered_codecs,
+                            std::vector<C>* negotiated_codecs) {
+  typename std::vector<C>::const_iterator ours;
+  for (ours = local_codecs.begin();
+       ours != local_codecs.end(); ++ours) {
+    typename std::vector<C>::const_iterator theirs;
+    for (theirs = offered_codecs.begin();
+         theirs != offered_codecs.end(); ++theirs) {
+      if (ours->Matches(*theirs)) {
+        C negotiated = *ours;
+        negotiated.IntersectFeedbackParams(*theirs);
+        if (IsRtxCodec(negotiated)) {
+          // Only negotiate RTX if kCodecParamAssociatedPayloadType has been
+          // set.
+          std::string apt_value;
+          if (!theirs->GetParam(kCodecParamAssociatedPayloadType, &apt_value)) {
+            LOG(LS_WARNING) << "RTX missing associated payload type.";
+            continue;
+          }
+          negotiated.SetParam(kCodecParamAssociatedPayloadType, apt_value);
+        }
+        negotiated.id = theirs->id;
+        negotiated_codecs->push_back(negotiated);
+      }
+    }
+  }
+}
+
+template <class C>
+static bool FindMatchingCodec(const std::vector<C>& codecs,
+                              const C& codec_to_match,
+                              C* found_codec) {
+  for (typename std::vector<C>::const_iterator it = codecs.begin();
+       it  != codecs.end(); ++it) {
+    if (it->Matches(codec_to_match)) {
+      if (found_codec != NULL) {
+        *found_codec= *it;
+      }
+      return true;
+    }
+  }
+  return false;
+}
+
+// Adds all codecs from |reference_codecs| to |offered_codecs| that dont'
+// already exist in |offered_codecs| and ensure the payload types don't
+// collide.
+template <class C>
+static void FindCodecsToOffer(
+    const std::vector<C>& reference_codecs,
+    std::vector<C>* offered_codecs,
+    UsedPayloadTypes* used_pltypes) {
+
+  typedef std::map<int, C> RtxCodecReferences;
+  RtxCodecReferences new_rtx_codecs;
+
+  // Find all new RTX codecs.
+  for (typename std::vector<C>::const_iterator it = reference_codecs.begin();
+       it != reference_codecs.end(); ++it) {
+    if (!FindMatchingCodec<C>(*offered_codecs, *it, NULL) && IsRtxCodec(*it)) {
+      C rtx_codec = *it;
+      int referenced_pl_type =
+          talk_base::FromString<int>(
+              rtx_codec.params[kCodecParamAssociatedPayloadType]);
+      new_rtx_codecs.insert(std::pair<int, C>(referenced_pl_type,
+                                              rtx_codec));
+    }
+  }
+
+  // Add all new codecs that are not RTX codecs.
+  for (typename std::vector<C>::const_iterator it = reference_codecs.begin();
+       it != reference_codecs.end(); ++it) {
+    if (!FindMatchingCodec<C>(*offered_codecs, *it, NULL) && !IsRtxCodec(*it)) {
+      C codec = *it;
+      int original_payload_id = codec.id;
+      used_pltypes->FindAndSetIdUsed(&codec);
+      offered_codecs->push_back(codec);
+
+      // If this codec is referenced by a new RTX codec, update the reference
+      // in the RTX codec with the new payload type.
+      typename RtxCodecReferences::iterator rtx_it =
+          new_rtx_codecs.find(original_payload_id);
+      if (rtx_it != new_rtx_codecs.end()) {
+        C& rtx_codec = rtx_it->second;
+        rtx_codec.params[kCodecParamAssociatedPayloadType] =
+            talk_base::ToString(codec.id);
+      }
+    }
+  }
+
+  // Add all new RTX codecs.
+  for (typename RtxCodecReferences::iterator it = new_rtx_codecs.begin();
+       it != new_rtx_codecs.end(); ++it) {
+    C& rtx_codec = it->second;
+    used_pltypes->FindAndSetIdUsed(&rtx_codec);
+    offered_codecs->push_back(rtx_codec);
+  }
+}
+
+
+static bool FindByUri(const RtpHeaderExtensions& extensions,
+                      const RtpHeaderExtension& ext_to_match,
+                      RtpHeaderExtension* found_extension) {
+  for (RtpHeaderExtensions::const_iterator it = extensions.begin();
+       it  != extensions.end(); ++it) {
+    // We assume that all URIs are given in a canonical format.
+    if (it->uri == ext_to_match.uri) {
+      if (found_extension != NULL) {
+        *found_extension= *it;
+      }
+      return true;
+    }
+  }
+  return false;
+}
+
+static void FindAndSetRtpHdrExtUsed(
+  const RtpHeaderExtensions& reference_extensions,
+  RtpHeaderExtensions* offered_extensions,
+  UsedRtpHeaderExtensionIds* used_extensions) {
+  for (RtpHeaderExtensions::const_iterator it = reference_extensions.begin();
+      it != reference_extensions.end(); ++it) {
+    if (!FindByUri(*offered_extensions, *it, NULL)) {
+      RtpHeaderExtension ext = *it;
+      used_extensions->FindAndSetIdUsed(&ext);
+      offered_extensions->push_back(ext);
+    }
+  }
+}
+
+static void NegotiateRtpHeaderExtensions(
+    const RtpHeaderExtensions& local_extensions,
+    const RtpHeaderExtensions& offered_extensions,
+    RtpHeaderExtensions* negotiated_extenstions) {
+  RtpHeaderExtensions::const_iterator ours;
+  for (ours = local_extensions.begin();
+       ours != local_extensions.end(); ++ours) {
+    RtpHeaderExtension theirs;
+    if (FindByUri(offered_extensions, *ours, &theirs)) {
+      // We respond with their RTP header extension id.
+      negotiated_extenstions->push_back(theirs);
+    }
+  }
+}
+
+static void StripCNCodecs(AudioCodecs* audio_codecs) {
+  AudioCodecs::iterator iter = audio_codecs->begin();
+  while (iter != audio_codecs->end()) {
+    if (stricmp(iter->name.c_str(), kComfortNoiseCodecName) == 0) {
+      iter = audio_codecs->erase(iter);
+    } else {
+      ++iter;
+    }
+  }
+}
+
+// Create a media content to be answered in a session-accept,
+// according to the given options.rtcp_mux, options.streams, codecs,
+// crypto, and streams.  If we don't currently have crypto (in
+// current_cryptos) and it is enabled (in secure_policy), crypto is
+// created (according to crypto_suites).  If add_legacy_stream is
+// true, and current_streams is empty, a legacy stream is created.
+// The codecs, rtcp_mux, and crypto are all negotiated with the offer
+// from the incoming session-initiate.  If the negotiation fails, this
+// method returns false.  The created content is added to the offer.
+template <class C>
+static bool CreateMediaContentAnswer(
+    const MediaContentDescriptionImpl<C>* offer,
+    const MediaSessionOptions& options,
+    const std::vector<C>& local_codecs,
+    const SecureMediaPolicy& sdes_policy,
+    const CryptoParamsVec* current_cryptos,
+    const RtpHeaderExtensions& local_rtp_extenstions,
+    StreamParamsVec* current_streams,
+    bool add_legacy_stream,
+    bool bundle_enabled,
+    MediaContentDescriptionImpl<C>* answer) {
+  std::vector<C> negotiated_codecs;
+  NegotiateCodecs(local_codecs, offer->codecs(), &negotiated_codecs);
+  answer->AddCodecs(negotiated_codecs);
+  answer->SortCodecs();
+  answer->set_protocol(offer->protocol());
+  RtpHeaderExtensions negotiated_rtp_extensions;
+  NegotiateRtpHeaderExtensions(local_rtp_extenstions,
+                               offer->rtp_header_extensions(),
+                               &negotiated_rtp_extensions);
+  answer->set_rtp_header_extensions(negotiated_rtp_extensions);
+
+  answer->set_rtcp_mux(options.rtcp_mux_enabled && offer->rtcp_mux());
+
+  if (sdes_policy != SEC_DISABLED) {
+    CryptoParams crypto;
+    if (SelectCrypto(offer, bundle_enabled, &crypto)) {
+      if (current_cryptos) {
+        FindMatchingCrypto(*current_cryptos, crypto, &crypto);
+      }
+      answer->AddCrypto(crypto);
+    }
+  }
+
+  if (answer->cryptos().empty() &&
+      (offer->crypto_required() || sdes_policy == SEC_REQUIRED)) {
+    return false;
+  }
+
+  if (!AddStreamParams(
+          answer->type(), options.streams, current_streams,
+          answer, add_legacy_stream)) {
+    return false;  // Something went seriously wrong.
+  }
+
+  // Make sure the answer media content direction is per default set as
+  // described in RFC3264 section 6.1.
+  switch (offer->direction()) {
+    case MD_INACTIVE:
+      answer->set_direction(MD_INACTIVE);
+      break;
+    case MD_SENDONLY:
+      answer->set_direction(MD_RECVONLY);
+      break;
+    case MD_RECVONLY:
+      answer->set_direction(MD_SENDONLY);
+      break;
+    case MD_SENDRECV:
+      answer->set_direction(MD_SENDRECV);
+      break;
+    default:
+      break;
+  }
+
+  return true;
+}
+
+static bool IsMediaProtocolSupported(MediaType type,
+                                     const std::string& protocol) {
+  // Data channels can have a protocol of SCTP or SCTP/DTLS.
+  if (type == MEDIA_TYPE_DATA &&
+      (protocol == kMediaProtocolSctp ||
+       protocol == kMediaProtocolDtlsSctp)) {
+    return true;
+  }
+  // Since not all applications serialize and deserialize the media protocol,
+  // we will have to accept |protocol| to be empty.
+  return protocol == kMediaProtocolAvpf || protocol == kMediaProtocolSavpf ||
+      protocol.empty();
+}
+
+static void SetMediaProtocol(bool secure_transport,
+                             MediaContentDescription* desc) {
+  if (!desc->cryptos().empty() || secure_transport)
+    desc->set_protocol(kMediaProtocolSavpf);
+  else
+    desc->set_protocol(kMediaProtocolAvpf);
+}
+
+void MediaSessionOptions::AddStream(MediaType type,
+                                    const std::string& id,
+                                    const std::string& sync_label) {
+  streams.push_back(Stream(type, id, sync_label));
+
+  if (type == MEDIA_TYPE_VIDEO)
+    has_video = true;
+  else if (type == MEDIA_TYPE_AUDIO)
+    has_audio = true;
+  // If we haven't already set the data_channel_type, and we add a
+  // stream, we assume it's an RTP data stream.
+  else if (type == MEDIA_TYPE_DATA && data_channel_type == DCT_NONE)
+    data_channel_type = DCT_RTP;
+}
+
+void MediaSessionOptions::RemoveStream(MediaType type,
+                                       const std::string& id) {
+  Streams::iterator stream_it = streams.begin();
+  for (; stream_it != streams.end(); ++stream_it) {
+    if (stream_it->type == type && stream_it->id == id) {
+      streams.erase(stream_it);
+      return;
+    }
+  }
+  ASSERT(false);
+}
+
+MediaSessionDescriptionFactory::MediaSessionDescriptionFactory(
+    const TransportDescriptionFactory* transport_desc_factory)
+    : secure_(SEC_DISABLED),
+      add_legacy_(true),
+      transport_desc_factory_(transport_desc_factory) {
+}
+
+MediaSessionDescriptionFactory::MediaSessionDescriptionFactory(
+    ChannelManager* channel_manager,
+    const TransportDescriptionFactory* transport_desc_factory)
+    : secure_(SEC_DISABLED),
+      add_legacy_(true),
+      transport_desc_factory_(transport_desc_factory) {
+  channel_manager->GetSupportedAudioCodecs(&audio_codecs_);
+  channel_manager->GetSupportedAudioRtpHeaderExtensions(&audio_rtp_extensions_);
+  channel_manager->GetSupportedVideoCodecs(&video_codecs_);
+  channel_manager->GetSupportedVideoRtpHeaderExtensions(&video_rtp_extensions_);
+  channel_manager->GetSupportedDataCodecs(&data_codecs_);
+}
+
+SessionDescription* MediaSessionDescriptionFactory::CreateOffer(
+    const MediaSessionOptions& options,
+    const SessionDescription* current_description) const {
+  bool secure_transport = (transport_desc_factory_->secure() != SEC_DISABLED);
+
+  scoped_ptr<SessionDescription> offer(new SessionDescription());
+
+  StreamParamsVec current_streams;
+  GetCurrentStreamParams(current_description, &current_streams);
+
+  AudioCodecs audio_codecs;
+  VideoCodecs video_codecs;
+  DataCodecs data_codecs;
+  GetCodecsToOffer(current_description, &audio_codecs, &video_codecs,
+                   &data_codecs);
+
+  if (!options.vad_enabled) {
+    // If application doesn't want CN codecs in offer.
+    StripCNCodecs(&audio_codecs);
+  }
+
+  RtpHeaderExtensions audio_rtp_extensions;
+  RtpHeaderExtensions video_rtp_extensions;
+  GetRtpHdrExtsToOffer(current_description, &audio_rtp_extensions,
+                       &video_rtp_extensions);
+
+  // Handle m=audio.
+  if (options.has_audio) {
+    scoped_ptr<AudioContentDescription> audio(new AudioContentDescription());
+    std::vector<std::string> crypto_suites;
+    GetSupportedAudioCryptoSuites(&crypto_suites);
+    if (!CreateMediaContentOffer(
+            options,
+            audio_codecs,
+            secure(),
+            GetCryptos(GetFirstAudioContentDescription(current_description)),
+            crypto_suites,
+            audio_rtp_extensions,
+            add_legacy_,
+            &current_streams,
+            audio.get())) {
+      return NULL;
+    }
+
+    audio->set_lang(lang_);
+    SetMediaProtocol(secure_transport, audio.get());
+    offer->AddContent(CN_AUDIO, NS_JINGLE_RTP, audio.release());
+    if (!AddTransportOffer(CN_AUDIO, options.transport_options,
+                           current_description, offer.get())) {
+      return NULL;
+    }
+  }
+
+  // Handle m=video.
+  if (options.has_video) {
+    scoped_ptr<VideoContentDescription> video(new VideoContentDescription());
+    std::vector<std::string> crypto_suites;
+    GetSupportedVideoCryptoSuites(&crypto_suites);
+    if (!CreateMediaContentOffer(
+            options,
+            video_codecs,
+            secure(),
+            GetCryptos(GetFirstVideoContentDescription(current_description)),
+            crypto_suites,
+            video_rtp_extensions,
+            add_legacy_,
+            &current_streams,
+            video.get())) {
+      return NULL;
+    }
+
+    video->set_bandwidth(options.video_bandwidth);
+    SetMediaProtocol(secure_transport, video.get());
+    offer->AddContent(CN_VIDEO, NS_JINGLE_RTP, video.release());
+    if (!AddTransportOffer(CN_VIDEO, options.transport_options,
+                           current_description, offer.get())) {
+      return NULL;
+    }
+  }
+
+  // Handle m=data.
+  if (options.has_data()) {
+    scoped_ptr<DataContentDescription> data(new DataContentDescription());
+    bool is_sctp = (options.data_channel_type == DCT_SCTP);
+
+    std::vector<std::string> crypto_suites;
+    cricket::SecurePolicy sdes_policy = secure();
+    if (is_sctp) {
+      // SDES doesn't make sense for SCTP, so we disable it, and we only
+      // get SDES crypto suites for RTP-based data channels.
+      sdes_policy = cricket::SEC_DISABLED;
+      // Unlike SetMediaProtocol below, we need to set the protocol
+      // before we call CreateMediaContentOffer.  Otherwise,
+      // CreateMediaContentOffer won't know this is SCTP and will
+      // generate SSRCs rather than SIDs.
+      data->set_protocol(
+          secure_transport ? kMediaProtocolDtlsSctp : kMediaProtocolSctp);
+    } else {
+      GetSupportedDataCryptoSuites(&crypto_suites);
+    }
+
+    if (!CreateMediaContentOffer(
+            options,
+            data_codecs,
+            sdes_policy,
+            GetCryptos(GetFirstDataContentDescription(current_description)),
+            crypto_suites,
+            RtpHeaderExtensions(),
+            add_legacy_,
+            &current_streams,
+            data.get())) {
+      return NULL;
+    }
+
+    if (is_sctp) {
+      offer->AddContent(CN_DATA, NS_JINGLE_DRAFT_SCTP, data.release());
+    } else {
+      data->set_bandwidth(options.data_bandwidth);
+      SetMediaProtocol(secure_transport, data.get());
+      offer->AddContent(CN_DATA, NS_JINGLE_RTP, data.release());
+    }
+    if (!AddTransportOffer(CN_DATA, options.transport_options,
+                           current_description, offer.get())) {
+      return NULL;
+    }
+  }
+
+  // Bundle the contents together, if we've been asked to do so, and update any
+  // parameters that need to be tweaked for BUNDLE.
+  if (options.bundle_enabled) {
+    ContentGroup offer_bundle(GROUP_TYPE_BUNDLE);
+    for (ContentInfos::const_iterator content = offer->contents().begin();
+       content != offer->contents().end(); ++content) {
+      offer_bundle.AddContentName(content->name);
+    }
+    offer->AddGroup(offer_bundle);
+    if (!UpdateTransportInfoForBundle(offer_bundle, offer.get())) {
+      LOG(LS_ERROR) << "CreateOffer failed to UpdateTransportInfoForBundle.";
+      return NULL;
+    }
+    if (!UpdateCryptoParamsForBundle(offer_bundle, offer.get())) {
+      LOG(LS_ERROR) << "CreateOffer failed to UpdateCryptoParamsForBundle.";
+      return NULL;
+    }
+  }
+
+  return offer.release();
+}
+
+SessionDescription* MediaSessionDescriptionFactory::CreateAnswer(
+    const SessionDescription* offer, const MediaSessionOptions& options,
+    const SessionDescription* current_description) const {
+  // The answer contains the intersection of the codecs in the offer with the
+  // codecs we support, ordered by our local preference. As indicated by
+  // XEP-0167, we retain the same payload ids from the offer in the answer.
+  scoped_ptr<SessionDescription> answer(new SessionDescription());
+
+  StreamParamsVec current_streams;
+  GetCurrentStreamParams(current_description, &current_streams);
+
+  bool bundle_enabled =
+      offer->HasGroup(GROUP_TYPE_BUNDLE) && options.bundle_enabled;
+
+  // Handle m=audio.
+  const ContentInfo* audio_content = GetFirstAudioContent(offer);
+  if (audio_content) {
+    scoped_ptr<TransportDescription> audio_transport(
+        CreateTransportAnswer(audio_content->name, offer,
+                              options.transport_options,
+                              current_description));
+    if (!audio_transport) {
+      return NULL;
+    }
+
+    AudioCodecs audio_codecs = audio_codecs_;
+    if (!options.vad_enabled) {
+      StripCNCodecs(&audio_codecs);
+    }
+
+    scoped_ptr<AudioContentDescription> audio_answer(
+        new AudioContentDescription());
+    // Do not require or create SDES cryptos if DTLS is used.
+    cricket::SecurePolicy sdes_policy =
+        audio_transport->secure() ? cricket::SEC_DISABLED : secure();
+    if (!CreateMediaContentAnswer(
+            static_cast<const AudioContentDescription*>(
+                audio_content->description),
+            options,
+            audio_codecs,
+            sdes_policy,
+            GetCryptos(GetFirstAudioContentDescription(current_description)),
+            audio_rtp_extensions_,
+            &current_streams,
+            add_legacy_,
+            bundle_enabled,
+            audio_answer.get())) {
+      return NULL;  // Fails the session setup.
+    }
+
+    bool rejected = !options.has_audio || audio_content->rejected ||
+          !IsMediaProtocolSupported(MEDIA_TYPE_AUDIO,
+                                    audio_answer->protocol());
+    if (!rejected) {
+      AddTransportAnswer(audio_content->name, *(audio_transport.get()),
+                         answer.get());
+    } else {
+      // RFC 3264
+      // The answer MUST contain the same number of m-lines as the offer.
+      LOG(LS_INFO) << "Audio is not supported in the answer.";
+    }
+
+    answer->AddContent(audio_content->name, audio_content->type, rejected,
+                       audio_answer.release());
+  } else {
+    LOG(LS_INFO) << "Audio is not available in the offer.";
+  }
+
+  // Handle m=video.
+  const ContentInfo* video_content = GetFirstVideoContent(offer);
+  if (video_content) {
+    scoped_ptr<TransportDescription> video_transport(
+        CreateTransportAnswer(video_content->name, offer,
+                              options.transport_options,
+                              current_description));
+    if (!video_transport) {
+      return NULL;
+    }
+
+    scoped_ptr<VideoContentDescription> video_answer(
+        new VideoContentDescription());
+    // Do not require or create SDES cryptos if DTLS is used.
+    cricket::SecurePolicy sdes_policy =
+        video_transport->secure() ? cricket::SEC_DISABLED : secure();
+    if (!CreateMediaContentAnswer(
+            static_cast<const VideoContentDescription*>(
+                video_content->description),
+            options,
+            video_codecs_,
+            sdes_policy,
+            GetCryptos(GetFirstVideoContentDescription(current_description)),
+            video_rtp_extensions_,
+            &current_streams,
+            add_legacy_,
+            bundle_enabled,
+            video_answer.get())) {
+      return NULL;
+    }
+    bool rejected = !options.has_video || video_content->rejected ||
+        !IsMediaProtocolSupported(MEDIA_TYPE_VIDEO, video_answer->protocol());
+    if (!rejected) {
+      if (!AddTransportAnswer(video_content->name, *(video_transport.get()),
+                              answer.get())) {
+        return NULL;
+      }
+      video_answer->set_bandwidth(options.video_bandwidth);
+    } else {
+      // RFC 3264
+      // The answer MUST contain the same number of m-lines as the offer.
+      LOG(LS_INFO) << "Video is not supported in the answer.";
+    }
+    answer->AddContent(video_content->name, video_content->type, rejected,
+                       video_answer.release());
+  } else {
+    LOG(LS_INFO) << "Video is not available in the offer.";
+  }
+
+  // Handle m=data.
+  const ContentInfo* data_content = GetFirstDataContent(offer);
+  if (data_content) {
+    scoped_ptr<TransportDescription> data_transport(
+        CreateTransportAnswer(data_content->name, offer,
+                              options.transport_options,
+                              current_description));
+    if (!data_transport) {
+      return NULL;
+    }
+    scoped_ptr<DataContentDescription> data_answer(
+        new DataContentDescription());
+    // Do not require or create SDES cryptos if DTLS is used.
+    cricket::SecurePolicy sdes_policy =
+        data_transport->secure() ? cricket::SEC_DISABLED : secure();
+    if (!CreateMediaContentAnswer(
+            static_cast<const DataContentDescription*>(
+                data_content->description),
+            options,
+            data_codecs_,
+            sdes_policy,
+            GetCryptos(GetFirstDataContentDescription(current_description)),
+            RtpHeaderExtensions(),
+            &current_streams,
+            add_legacy_,
+            bundle_enabled,
+            data_answer.get())) {
+      return NULL;  // Fails the session setup.
+    }
+
+    bool rejected = !options.has_data() || data_content->rejected ||
+        !IsMediaProtocolSupported(MEDIA_TYPE_DATA, data_answer->protocol());
+    if (!rejected) {
+      data_answer->set_bandwidth(options.data_bandwidth);
+      if (!AddTransportAnswer(data_content->name, *(data_transport.get()),
+                              answer.get())) {
+        return NULL;
+      }
+    } else {
+      // RFC 3264
+      // The answer MUST contain the same number of m-lines as the offer.
+      LOG(LS_INFO) << "Data is not supported in the answer.";
+    }
+    answer->AddContent(data_content->name, data_content->type, rejected,
+                       data_answer.release());
+  } else {
+    LOG(LS_INFO) << "Data is not available in the offer.";
+  }
+
+  // If the offer supports BUNDLE, and we want to use it too, create a BUNDLE
+  // group in the answer with the appropriate content names.
+  if (offer->HasGroup(GROUP_TYPE_BUNDLE) && options.bundle_enabled) {
+    const ContentGroup* offer_bundle = offer->GetGroupByName(GROUP_TYPE_BUNDLE);
+    ContentGroup answer_bundle(GROUP_TYPE_BUNDLE);
+    for (ContentInfos::const_iterator content = answer->contents().begin();
+       content != answer->contents().end(); ++content) {
+      if (!content->rejected && offer_bundle->HasContentName(content->name)) {
+        answer_bundle.AddContentName(content->name);
+      }
+    }
+    if (answer_bundle.FirstContentName()) {
+      answer->AddGroup(answer_bundle);
+
+      // Share the same ICE credentials and crypto params across all contents,
+      // as BUNDLE requires.
+      if (!UpdateTransportInfoForBundle(answer_bundle, answer.get())) {
+        LOG(LS_ERROR) << "CreateAnswer failed to UpdateTransportInfoForBundle.";
+        return NULL;
+      }
+
+      if (!UpdateCryptoParamsForBundle(answer_bundle, answer.get())) {
+        LOG(LS_ERROR) << "CreateAnswer failed to UpdateCryptoParamsForBundle.";
+        return NULL;
+      }
+    }
+  }
+
+  return answer.release();
+}
+
+// Gets the TransportInfo of the given |content_name| from the
+// |current_description|. If doesn't exist, returns a new one.
+static const TransportDescription* GetTransportDescription(
+    const std::string& content_name,
+    const SessionDescription* current_description) {
+  const TransportDescription* desc = NULL;
+  if (current_description) {
+    const TransportInfo* info =
+        current_description->GetTransportInfoByName(content_name);
+    if (info) {
+      desc = &info->description;
+    }
+  }
+  return desc;
+}
+
+void MediaSessionDescriptionFactory::GetCodecsToOffer(
+    const SessionDescription* current_description,
+    AudioCodecs* audio_codecs,
+    VideoCodecs* video_codecs,
+    DataCodecs* data_codecs) const {
+  UsedPayloadTypes used_pltypes;
+  audio_codecs->clear();
+  video_codecs->clear();
+  data_codecs->clear();
+
+
+  // First - get all codecs from the current description if the media type
+  // is used.
+  // Add them to |used_pltypes| so the payloadtype is not reused if a new media
+  // type is added.
+  if (current_description) {
+    const AudioContentDescription* audio =
+        GetFirstAudioContentDescription(current_description);
+    if (audio) {
+      *audio_codecs = audio->codecs();
+      used_pltypes.FindAndSetIdUsed<AudioCodec>(audio_codecs);
+    }
+    const VideoContentDescription* video =
+        GetFirstVideoContentDescription(current_description);
+    if (video) {
+      *video_codecs = video->codecs();
+      used_pltypes.FindAndSetIdUsed<VideoCodec>(video_codecs);
+    }
+    const DataContentDescription* data =
+        GetFirstDataContentDescription(current_description);
+    if (data) {
+      *data_codecs = data->codecs();
+      used_pltypes.FindAndSetIdUsed<DataCodec>(data_codecs);
+    }
+  }
+
+  // Add our codecs that are not in |current_description|.
+  FindCodecsToOffer<AudioCodec>(audio_codecs_, audio_codecs, &used_pltypes);
+  FindCodecsToOffer<VideoCodec>(video_codecs_, video_codecs, &used_pltypes);
+  FindCodecsToOffer<DataCodec>(data_codecs_, data_codecs, &used_pltypes);
+}
+
+void MediaSessionDescriptionFactory::GetRtpHdrExtsToOffer(
+    const SessionDescription* current_description,
+    RtpHeaderExtensions* audio_extensions,
+    RtpHeaderExtensions* video_extensions) const {
+  UsedRtpHeaderExtensionIds used_ids;
+  audio_extensions->clear();
+  video_extensions->clear();
+
+  // First - get all extensions from the current description if the media type
+  // is used.
+  // Add them to |used_ids| so the local ids are not reused if a new media
+  // type is added.
+  if (current_description) {
+    const AudioContentDescription* audio =
+        GetFirstAudioContentDescription(current_description);
+    if (audio) {
+      *audio_extensions = audio->rtp_header_extensions();
+      used_ids.FindAndSetIdUsed(audio_extensions);
+    }
+    const VideoContentDescription* video =
+        GetFirstVideoContentDescription(current_description);
+    if (video) {
+      *video_extensions = video->rtp_header_extensions();
+      used_ids.FindAndSetIdUsed(video_extensions);
+    }
+  }
+
+  // Add our default RTP header extensions that are not in
+  // |current_description|.
+  FindAndSetRtpHdrExtUsed(audio_rtp_header_extensions(), audio_extensions,
+                          &used_ids);
+  FindAndSetRtpHdrExtUsed(video_rtp_header_extensions(), video_extensions,
+                          &used_ids);
+}
+
+bool MediaSessionDescriptionFactory::AddTransportOffer(
+  const std::string& content_name,
+  const TransportOptions& transport_options,
+  const SessionDescription* current_desc,
+  SessionDescription* offer_desc) const {
+  if (!transport_desc_factory_)
+     return false;
+  const TransportDescription* current_tdesc =
+      GetTransportDescription(content_name, current_desc);
+  talk_base::scoped_ptr<TransportDescription> new_tdesc(
+      transport_desc_factory_->CreateOffer(transport_options, current_tdesc));
+  bool ret = (new_tdesc.get() != NULL &&
+      offer_desc->AddTransportInfo(TransportInfo(content_name, *new_tdesc)));
+  if (!ret) {
+    LOG(LS_ERROR)
+        << "Failed to AddTransportOffer, content name=" << content_name;
+  }
+  return ret;
+}
+
+TransportDescription* MediaSessionDescriptionFactory::CreateTransportAnswer(
+    const std::string& content_name,
+    const SessionDescription* offer_desc,
+    const TransportOptions& transport_options,
+    const SessionDescription* current_desc) const {
+  if (!transport_desc_factory_)
+    return NULL;
+  const TransportDescription* offer_tdesc =
+      GetTransportDescription(content_name, offer_desc);
+  const TransportDescription* current_tdesc =
+      GetTransportDescription(content_name, current_desc);
+  return
+      transport_desc_factory_->CreateAnswer(offer_tdesc, transport_options,
+                                            current_tdesc);
+}
+
+bool MediaSessionDescriptionFactory::AddTransportAnswer(
+    const std::string& content_name,
+    const TransportDescription& transport_desc,
+    SessionDescription* answer_desc) const {
+  if (!answer_desc->AddTransportInfo(TransportInfo(content_name,
+                                                   transport_desc))) {
+    LOG(LS_ERROR)
+        << "Failed to AddTransportAnswer, content name=" << content_name;
+    return false;
+  }
+  return true;
+}
+
+bool IsMediaContent(const ContentInfo* content) {
+  return (content &&
+          (content->type == NS_JINGLE_RTP ||
+           content->type == NS_JINGLE_DRAFT_SCTP));
+}
+
+bool IsAudioContent(const ContentInfo* content) {
+  return IsMediaContentOfType(content, MEDIA_TYPE_AUDIO);
+}
+
+bool IsVideoContent(const ContentInfo* content) {
+  return IsMediaContentOfType(content, MEDIA_TYPE_VIDEO);
+}
+
+bool IsDataContent(const ContentInfo* content) {
+  return IsMediaContentOfType(content, MEDIA_TYPE_DATA);
+}
+
+static const ContentInfo* GetFirstMediaContent(const ContentInfos& contents,
+                                               MediaType media_type) {
+  for (ContentInfos::const_iterator content = contents.begin();
+       content != contents.end(); content++) {
+    if (IsMediaContentOfType(&*content, media_type)) {
+      return &*content;
+    }
+  }
+  return NULL;
+}
+
+const ContentInfo* GetFirstAudioContent(const ContentInfos& contents) {
+  return GetFirstMediaContent(contents, MEDIA_TYPE_AUDIO);
+}
+
+const ContentInfo* GetFirstVideoContent(const ContentInfos& contents) {
+  return GetFirstMediaContent(contents, MEDIA_TYPE_VIDEO);
+}
+
+const ContentInfo* GetFirstDataContent(const ContentInfos& contents) {
+  return GetFirstMediaContent(contents, MEDIA_TYPE_DATA);
+}
+
+static const ContentInfo* GetFirstMediaContent(const SessionDescription* sdesc,
+                                               MediaType media_type) {
+  if (sdesc == NULL)
+    return NULL;
+
+  return GetFirstMediaContent(sdesc->contents(), media_type);
+}
+
+const ContentInfo* GetFirstAudioContent(const SessionDescription* sdesc) {
+  return GetFirstMediaContent(sdesc, MEDIA_TYPE_AUDIO);
+}
+
+const ContentInfo* GetFirstVideoContent(const SessionDescription* sdesc) {
+  return GetFirstMediaContent(sdesc, MEDIA_TYPE_VIDEO);
+}
+
+const ContentInfo* GetFirstDataContent(const SessionDescription* sdesc) {
+  return GetFirstMediaContent(sdesc, MEDIA_TYPE_DATA);
+}
+
+const MediaContentDescription* GetFirstMediaContentDescription(
+    const SessionDescription* sdesc, MediaType media_type) {
+  const ContentInfo* content = GetFirstMediaContent(sdesc, media_type);
+  const ContentDescription* description = content ? content->description : NULL;
+  return static_cast<const MediaContentDescription*>(description);
+}
+
+const AudioContentDescription* GetFirstAudioContentDescription(
+    const SessionDescription* sdesc) {
+  return static_cast<const AudioContentDescription*>(
+      GetFirstMediaContentDescription(sdesc, MEDIA_TYPE_AUDIO));
+}
+
+const VideoContentDescription* GetFirstVideoContentDescription(
+    const SessionDescription* sdesc) {
+  return static_cast<const VideoContentDescription*>(
+      GetFirstMediaContentDescription(sdesc, MEDIA_TYPE_VIDEO));
+}
+
+const DataContentDescription* GetFirstDataContentDescription(
+    const SessionDescription* sdesc) {
+  return static_cast<const DataContentDescription*>(
+      GetFirstMediaContentDescription(sdesc, MEDIA_TYPE_DATA));
+}
+
+bool GetMediaChannelNameFromComponent(
+    int component, MediaType media_type, std::string* channel_name) {
+  if (media_type == MEDIA_TYPE_AUDIO) {
+    if (component == ICE_CANDIDATE_COMPONENT_RTP) {
+      *channel_name = GICE_CHANNEL_NAME_RTP;
+      return true;
+    } else if (component == ICE_CANDIDATE_COMPONENT_RTCP) {
+      *channel_name = GICE_CHANNEL_NAME_RTCP;
+      return true;
+    }
+  } else if (media_type == MEDIA_TYPE_VIDEO) {
+    if (component == ICE_CANDIDATE_COMPONENT_RTP) {
+      *channel_name = GICE_CHANNEL_NAME_VIDEO_RTP;
+      return true;
+    } else if (component == ICE_CANDIDATE_COMPONENT_RTCP) {
+      *channel_name = GICE_CHANNEL_NAME_VIDEO_RTCP;
+      return true;
+    }
+  } else if (media_type == MEDIA_TYPE_DATA) {
+    if (component == ICE_CANDIDATE_COMPONENT_RTP) {
+      *channel_name = GICE_CHANNEL_NAME_DATA_RTP;
+      return true;
+    } else if (component == ICE_CANDIDATE_COMPONENT_RTCP) {
+      *channel_name = GICE_CHANNEL_NAME_DATA_RTCP;
+      return true;
+    }
+  }
+
+  return false;
+}
+
+bool GetMediaComponentFromChannelName(
+    const std::string& channel_name, int* component) {
+  if (channel_name == GICE_CHANNEL_NAME_RTP ||
+      channel_name == GICE_CHANNEL_NAME_VIDEO_RTP ||
+      channel_name == GICE_CHANNEL_NAME_DATA_RTP) {
+    *component = ICE_CANDIDATE_COMPONENT_RTP;
+    return true;
+  } else if (channel_name == GICE_CHANNEL_NAME_RTCP ||
+             channel_name == GICE_CHANNEL_NAME_VIDEO_RTCP ||
+             channel_name == GICE_CHANNEL_NAME_DATA_RTP) {
+    *component = ICE_CANDIDATE_COMPONENT_RTCP;
+    return true;
+  }
+
+  return false;
+}
+
+bool GetMediaTypeFromChannelName(
+    const std::string& channel_name, MediaType* media_type) {
+  if (channel_name == GICE_CHANNEL_NAME_RTP ||
+      channel_name == GICE_CHANNEL_NAME_RTCP) {
+    *media_type = MEDIA_TYPE_AUDIO;
+    return true;
+  } else if (channel_name == GICE_CHANNEL_NAME_VIDEO_RTP ||
+             channel_name == GICE_CHANNEL_NAME_VIDEO_RTCP) {
+    *media_type = MEDIA_TYPE_VIDEO;
+    return true;
+  } else if (channel_name == GICE_CHANNEL_NAME_DATA_RTP ||
+             channel_name == GICE_CHANNEL_NAME_DATA_RTCP) {
+    *media_type = MEDIA_TYPE_DATA;
+    return true;
+  }
+
+  return false;
+}
+
+}  // namespace cricket