Bug 1484024: add Telemetry histogram for DTLS ciphers on RTCPeerConnection r=francois,mt

Added a Telemetry histrogram which collects which DTLS cipher got
negotiated when a RTCPeerConnection connected.

Differential Revision: https://phabricator.services.mozilla.com/D3551

--HG--
extra : moz-landing-system : lando

media/mtransport/transportlayerdtls.cpp

@@ -885,6 +885,8 @@ void TransportLayerDtls::Handshake() {
     }
 
     TL_SET_STATE(TS_OPEN);
+
+    RecordCipherTelemetry();
   } else {
     int32_t err = PR_GetError();
     switch(err) {
@@ -1332,4 +1334,65 @@ TransportLayerDtls::RecordHandshakeCompletionTelemetry(
   }
 }
 
+void
+TransportLayerDtls::RecordCipherTelemetry() {
+  uint16_t cipher;
+
+  nsresult rv = GetCipherSuite(&cipher);
+
+  if (NS_FAILED(rv)) {
+    MOZ_MTLOG(ML_ERROR, "Failed to get cipher suite");
+    return;
+  }
+
+  uint16_t t_cipher = 0;
+
+  switch (cipher) {
+    /* Old DHE ciphers: candidates for removal, see bug 1227519 */
+    case TLS_DHE_RSA_WITH_AES_128_CBC_SHA:
+      t_cipher = 1;
+      break;
+    case TLS_DHE_RSA_WITH_AES_256_CBC_SHA:
+      t_cipher = 2;
+      break;
+    /* Current ciphers */
+    case TLS_ECDHE_ECDSA_WITH_AES_128_CBC_SHA:
+      t_cipher = 3;
+      break;
+    case TLS_ECDHE_ECDSA_WITH_AES_256_CBC_SHA:
+      t_cipher = 4;
+      break;
+    case TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA:
+      t_cipher = 5;
+      break;
+    case TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA:
+      t_cipher = 6;
+      break;
+    case TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256:
+      t_cipher = 7;
+      break;
+    case TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256:
+      t_cipher = 8;
+      break;
+    case TLS_ECDHE_RSA_WITH_CHACHA20_POLY1305_SHA256:
+      t_cipher = 9;
+      break;
+    case TLS_ECDHE_ECDSA_WITH_CHACHA20_POLY1305_SHA256:
+      t_cipher = 10;
+      break;
+    /* TLS 1.3 ciphers */
+    case TLS_AES_128_GCM_SHA256:
+      t_cipher = 11;
+      break;
+    case TLS_CHACHA20_POLY1305_SHA256:
+      t_cipher = 12;
+      break;
+    case TLS_AES_256_GCM_SHA384:
+      t_cipher = 13;
+      break;
+  }
+
+  Telemetry::Accumulate(Telemetry::WEBRTC_DTLS_CIPHER, t_cipher);
+}
+
 }  // close namespace

media/mtransport/transportlayerdtls.h

@@ -161,6 +161,7 @@ class TransportLayerDtls final : public TransportLayer {
                         UniqueCERTCertificate& cert) const;
 
   void RecordHandshakeCompletionTelemetry(TransportLayer::State endState);
+  void RecordCipherTelemetry();
 
   RefPtr<DtlsIdentity> identity_;
   // What ALPN identifiers are permitted.

toolkit/components/telemetry/Histograms.json

@@ -8653,6 +8653,15 @@
     "n_buckets": 20,
     "description": "The length of time (in milliseconds) it took for a server DTLS handshake to complete, given that it failed."
   },
+  "WEBRTC_DTLS_CIPHER": {
+    "record_in_processes": ["content"],
+    "alert_emails": ["webrtc-dtls-telemetry-alerts@mozilla.com", "nohlmeier@mozilla.com"],
+    "bug_numbers": [1484024],
+    "expires_in_version": "66",
+    "kind": "enumerated",
+    "n_values": 14,
+    "description": "The DTLS cipher (as integer) negotiated for a RTCPeerConnection. See TransportLayerDtls::RecordCipherTelemetry for the meaning of the values"
+  },
   "WEBRTC_ICE_FINAL_CONNECTION_STATE": {
     "record_in_processes": ["main", "content"],
     "alert_emails": ["webrtc-ice-telemetry-alerts@mozilla.com, nohlmeier@mozilla.com"],