Add SdpHelper for more reliable codec configuration in WebrtcTransport.

remoting/protocol/sdp_message.cc

Index: remoting/protocol/sdp_message.cc
diff --git a/remoting/protocol/sdp_message.cc b/remoting/protocol/sdp_message.cc
new file mode 100644
index 0000000000000000000000000000000000000000..3cd8354ec35012e88567fe4596b5957b598b5485
--- /dev/null
+++ b/remoting/protocol/sdp_message.cc
@@ -0,0 +1,66 @@
+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "remoting/protocol/sdp_message.h"
+
+#include "base/strings/string_split.h"
+#include "base/strings/string_util.h"
+
+namespace remoting {
+namespace protocol {
+
+SdpMessage::SdpMessage(const std::string& sdp) {
+  sdp_lines_ =
+      SplitString(sdp, "\n", base::TRIM_WHITESPACE, base::SPLIT_WANT_NONEMPTY);
+  for (const auto& line : sdp_lines_) {
+    if (base::StartsWith(line, "m=audio", base::CompareCase::SENSITIVE))
+      has_audio_ = true;
+    if (base::StartsWith(line, "m=video", base::CompareCase::SENSITIVE))
+      has_video_ = true;
+  }
+}
+
+SdpMessage::~SdpMessage() {}
+
+std::string SdpMessage::ToString() const {
+  return base::JoinString(sdp_lines_, "\n") + "\n";
+}
+
+bool SdpMessage::AddCodecParameter(const std::string& codec,
+                                   const std::string& parameters_to_add) {
+  int line_num;
+  std::string payload_type;
+  bool codec_found = FindCodec(codec, &line_num, &payload_type);
+  if (!codec_found) {
+    return false;
+  }
+  sdp_lines_.insert(sdp_lines_.begin() + line_num + 1,
+                    "a=fmtp:" + payload_type + ' ' + parameters_to_add);
+  return true;
+}
+
+bool SdpMessage::FindCodec(const std::string& codec,
+                           int* line_num,
+                           std::string* payload_type) const {
+  const std::string kRtpMapPrefix = "a=rtpmap:";
+  for (size_t i = 0; i < sdp_lines_.size(); ++i) {
+    const auto& line = sdp_lines_[i];
+    if (!base::StartsWith(line, kRtpMapPrefix, base::CompareCase::SENSITIVE))
+      continue;
+    size_t space_pos = line.find(' ');
+    if (space_pos == std::string::npos)
+      continue;
+    if (line.substr(space_pos + 1, codec.size()) == codec &&
+        line[space_pos + 1 + codec.size()] == '/') {
+      *line_num = i;
+      *payload_type =
+          line.substr(kRtpMapPrefix.size(), space_pos - kRtpMapPrefix.size());
+      return true;
+    }
+  }
+  return false;
+}
+
+}  // namespace protocol
+}  // namespace remoting