Cache a ClientHello received before the DTLS handshake has started.

webrtc/p2p/base/dtlstransportchannel.cc

Index: webrtc/p2p/base/dtlstransportchannel.cc
diff --git a/webrtc/p2p/base/dtlstransportchannel.cc b/webrtc/p2p/base/dtlstransportchannel.cc
index 88a11928cc205aebaf5cde89a8d5d7606cc57caf..51f1429ee86aa89ce410214329a39b0b3c0be3e8 100644
--- a/webrtc/p2p/base/dtlstransportchannel.cc
+++ b/webrtc/p2p/base/dtlstransportchannel.cc
@@ -469,15 +469,18 @@ void DtlsTransportChannelWrapper::OnReadPacket(
   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 the last DTLS packet (should be a client hello) received before
+      // DTLS has actually started.
+      if (IsDtlsPacket(data, size)) {

[juberti2, 2016/04/25 20:40:18]

We should probably also verify this is a CLIENT HELLO, at least for logging. 

[Taylor Brandstetter, 2016/04/26 22:55:58]

Done.

+        LOG_J(LS_INFO, this) << "Caching DTLS packet until DTLS is started.";
+        cached_dtls_packet_.SetData(data, size);
+      } else {
+        LOG_J(LS_INFO, this) << "Not a DTLS packet; dropping.";
       }
       break;
 
@@ -576,6 +579,21 @@ bool DtlsTransportChannelWrapper::MaybeStartDtls() {
     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 packet
+    // (if one exists).
+    if (cached_dtls_packet_.size()) {
+      if (ssl_role_ == rtc::SSL_SERVER) {
+        LOG_J(LS_INFO, this) << "Handling cached DTLS packet.";
+        if (!HandleDtlsPacket(cached_dtls_packet_.data<char>(),
+                              cached_dtls_packet_.size())) {
+          LOG_J(LS_ERROR, this) << "Failed to handle DTLS packet.";
+        }
+      } else {
+        LOG_J(LS_WARNING, this) << "Discarding cached DTLS packet because "

[juberti2, 2016/04/25 20:40:18]

Log text could be clearer to indicate this is a real malfunction by the remote
side as opposed to just a race condition or some such.

[Taylor Brandstetter, 2016/04/26 22:55:58]

Now that the message is changed to "discarding cached ClientHello because we're
not the server" is it more clear?

+                                << "we don't have the server role.";
+      }
+      cached_dtls_packet_.Clear();
+    }
   }
   return true;
 }