Cache a ClientHello received before the DTLS handshake has started.

webrtc/p2p/base/dtlstransportchannel.cc

 /*
  *  Copyright 2011 The WebRTC Project Authors. All rights reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
@@ skipping 19 matching lines @@
 static const size_t kMinRtpPacketLen = 12;
 
 // Maximum number of pending packets in the queue. Packets are read immediately
 // after they have been written, so a capacity of "1" is sufficient.
 static const size_t kMaxPendingPackets = 1;
 
 static bool IsDtlsPacket(const char* data, size_t len) {
   const uint8_t* u = reinterpret_cast<const uint8_t*>(data);
   return (len >= kDtlsRecordHeaderLen && (u[0] > 19 && u[0] < 64));
 }
+static bool IsDtlsClientHelloPacket(const char* data, size_t len) {
+  if (!IsDtlsPacket(data, len)) {
+    return false;
+  }
+  const uint8_t* u = reinterpret_cast<const uint8_t*>(data);
+  return len > 17 && u[0] == 22 && u[13] == 1;
+}
 static bool IsRtpPacket(const char* data, size_t len) {
   const uint8_t* u = reinterpret_cast<const uint8_t*>(data);
   return (len >= kMinRtpPacketLen && (u[0] & 0xC0) == 0x80);
 }
 
 StreamInterfaceChannel::StreamInterfaceChannel(TransportChannel* channel)
     : channel_(channel),
       state_(rtc::SS_OPEN),
       packets_(kMaxPendingPackets, kMaxDtlsPacketLen) {
 }
@@ skipping 413 matching lines @@
 
   if (!dtls_active_) {
     // Not doing DTLS.
     SignalReadPacket(this, data, size, packet_time, 0);
     return;
   }
 
   switch (dtls_state()) {
     case DTLS_TRANSPORT_NEW:
       if (dtls_) {
-        // Drop packets received before DTLS has actually started.
-        LOG_J(LS_INFO, this) << "Dropping packet received before DTLS started.";
+        LOG_J(LS_INFO, this) << "Packet received before DTLS started.";
       } else {
-        // Currently drop the packet, but we might in future
-        // decide to take this as evidence that the other
-        // side is ready to do DTLS and start the handshake
-        // on our end.
-        LOG_J(LS_WARNING, this) << "Received packet before we know if we are "
-                                << "doing DTLS or not; dropping.";
+        LOG_J(LS_WARNING, this) << "Packet received before we know if we are "
+                                << "doing DTLS or not.";
+      }
+      // Cache a client hello packet received before DTLS has actually started.
+      if (IsDtlsClientHelloPacket(data, size)) {
+        LOG_J(LS_INFO, this) << "Caching DTLS ClientHello packet until DTLS is "
+                             << "started.";
+        cached_client_hello_.SetData(data, size);
+      } else {
+        LOG_J(LS_INFO, this) << "Not a DTLS ClientHello packet; dropping.";
       }
       break;
 
     case DTLS_TRANSPORT_CONNECTING:
     case DTLS_TRANSPORT_CONNECTED:
       // We should only get DTLS or SRTP packets; STUN's already been demuxed.
       // Is this potentially a DTLS packet?
       if (IsDtlsPacket(data, size)) {
         if (!HandleDtlsPacket(data, size)) {
           LOG_J(LS_ERROR, this) << "Failed to handle DTLS packet.";
@@ skipping 78 matching lines @@
 bool DtlsTransportChannelWrapper::MaybeStartDtls() {
   if (dtls_ && channel_->writable()) {
     if (dtls_->StartSSLWithPeer()) {
       LOG_J(LS_ERROR, this) << "Couldn't start DTLS handshake";
       set_dtls_state(DTLS_TRANSPORT_FAILED);
       return false;
     }
     LOG_J(LS_INFO, this)
       << "DtlsTransportChannelWrapper: Started DTLS handshake";
     set_dtls_state(DTLS_TRANSPORT_CONNECTING);
+    // Now that the handshake has started, we can process a cached ClientHello
+    // (if one exists).
+    if (cached_client_hello_.size()) {
+      if (ssl_role_ == rtc::SSL_SERVER) {
+        LOG_J(LS_INFO, this) << "Handling cached DTLS ClientHello packet.";
+        if (!HandleDtlsPacket(cached_client_hello_.data<char>(),
+                              cached_client_hello_.size())) {
+          LOG_J(LS_ERROR, this) << "Failed to handle DTLS packet.";
+        }
+      } else {
+        LOG_J(LS_WARNING, this) << "Discarding cached DTLS ClientHello packet "
+                                << "because we don't have the server role.";
+      }
+      cached_client_hello_.Clear();
+    }
   }
   return true;
 }
 
 // Called from OnReadPacket when a DTLS packet is received.
 bool DtlsTransportChannelWrapper::HandleDtlsPacket(const char* data,
                                                    size_t size) {
   // Sanity check we're not passing junk that
   // just looks like DTLS.
   const uint8_t* tmp_data = reinterpret_cast<const uint8_t*>(data);
@@ skipping 64 matching lines @@
 
 void DtlsTransportChannelWrapper::Reconnect() {
   set_dtls_state(DTLS_TRANSPORT_NEW);
   set_writable(false);
   if (channel_->writable()) {
     OnWritableState(channel_);
   }
 }
 
 }  // namespace cricket