Log how often DTLS negotiation failed because of incompatible ciphersuites.

webrtc/base/opensslstreamadapter.cc

 /*
  *  Copyright 2004 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 836 matching lines @@
       }
       break;
 
     case SSL_ERROR_WANT_WRITE:
       LOG(LS_VERBOSE) << " -- error want write";
       break;
 
     case SSL_ERROR_ZERO_RETURN:
     default:
       LOG(LS_VERBOSE) << " -- error " << code;
+      SSLHandshakeError ssl_handshake_err = SSLHandshakeError::UNKNOWN;
+      int err_code = ERR_peek_last_error();
+      if (err_code != 0 && ERR_GET_REASON(err_code) == SSL_R_NO_SHARED_CIPHER) {
+        ssl_handshake_err = SSLHandshakeError::INCOMPATIBLE_CIPHERSUITE;
+      }
+      SignalSSLHandshakeError(ssl_handshake_err);

[skvlad, 2016/07/27 00:29:18]

I wonder if it could be better to directly log the ERR_GET_REASON values instead
of translating it into our own enums? That way we won't need to extend it to
other types of errors; on the other hand we'll need OpenSSL headers to interpret
this data correctly.

[honghaiz3, 2016/07/27 17:11:48]

Are we potentially interested in knowing other types of SSL errors?
If yes, we may want to use the return value from ERR_GET_REASON. The range of
that is pretty big though, up to 2^12. 

[Zhi Huang, 2016/07/27 21:04:13]

I will remove the new defined enum and use the error code directly from
ERR_GET_REASON(). Since in this issue we are more interested in
incompatible-ciphersuite, I will just log that for now. It won't be too hard to
extend the histogram if we become interested in other types.

       return (ssl_error != 0) ? ssl_error : -1;
   }
 
   return 0;
 }
 
 void OpenSSLStreamAdapter::Error(const char* context, int err, bool signal) {
   LOG(LS_WARNING) << "OpenSSLStreamAdapter::Error("
                   << context << ", " << err << ")";
   state_ = SSL_ERROR;
@@ skipping 352 matching lines @@
         return true;
     }
   }
 
   return false;
 }
 
 }  // namespace rtc
 
 #endif  // HAVE_OPENSSL_SSL_H