Bug 1667775 - Add a telemetry probe for the reason why a transaction is restarted r=necko-reviewers,dragana

Differential Revision: https://phabricator.services.mozilla.com/D91595

netwerk/protocol/http/nsHttpTransaction.cpp

@@ -1396,6 +1396,11 @@ void nsHttpTransaction::Close(nsresult reason) {
       mSentData = false;
       mReceivedData = false;
       LOG(("transaction force restarted\n"));
+      // Only record the first restart attempt.
+      if (!mRestartCount) {
+        Telemetry::Accumulate(Telemetry::HTTP_TRANSACTION_RESTART_REASON,
+                              TRANSACTION_RESTART_FORCED);
+      }
       return;
     }
 
@@ -1439,11 +1444,34 @@ void nsHttpTransaction::Close(nsresult reason) {
       // Note that when echConfig is enabled, it's possible that we don't have a
       // usable connection info to retry.
       if (mConnInfo && NS_SUCCEEDED(Restart())) {
+        // Only record the first restart attempt.
+        if (!mRestartCount) {
+          if (restartToFallbackConnInfo) {
+            Telemetry::Accumulate(Telemetry::HTTP_TRANSACTION_RESTART_REASON,
+                                  TRANSACTION_RESTART_HTTPSSVC_INVOLVED);
+          } else if (!reallySentData) {
+            Telemetry::Accumulate(Telemetry::HTTP_TRANSACTION_RESTART_REASON,
+                                  TRANSACTION_RESTART_NO_DATA_SENT);
+          } else if (reason == psm::GetXPCOMFromNSSError(
+                                   SSL_ERROR_DOWNGRADE_WITH_EARLY_DATA)) {
+            Telemetry::Accumulate(
+                Telemetry::HTTP_TRANSACTION_RESTART_REASON,
+                TRANSACTION_RESTART_DOWNGRADE_WITH_EARLY_DATA);
+          } else {
+            Telemetry::Accumulate(Telemetry::HTTP_TRANSACTION_RESTART_REASON,
+                                  TRANSACTION_RESTART_OTHERS);
+          }
+        }
         return;
       }
     }
   }
 
+  if (!mRestartCount) {
+    Telemetry::Accumulate(Telemetry::HTTP_TRANSACTION_RESTART_REASON,
+                          TRANSACTION_RESTART_NONE);
+  }
+
   if (!mResponseIsComplete && NS_SUCCEEDED(reason) && isHttp2or3) {
     // Responses without content-length header field are still complete if
     // they are transfered over http2 or http3 and the stream is properly

netwerk/protocol/http/nsHttpTransaction.h

@@ -490,6 +490,17 @@ class nsHttpTransaction final : public nsAHttpTransaction,
   bool mFastFallbackTriggered = false;
   nsCOMPtr<nsITimer> mFastFallbackTimer;
   nsCOMPtr<nsISVCBRecord> mFastFallbackRecord;
+
+  // IMPORTANT: when adding new values, always add them to the end, otherwise
+  // it will mess up telemetry.
+  enum TRANSACTION_RESTART_REASON : uint32_t {
+    TRANSACTION_RESTART_NONE = 0,    // The transacion was not restarted.
+    TRANSACTION_RESTART_FORCED = 1,  // The transaction was forced to restart.
+    TRANSACTION_RESTART_HTTPSSVC_INVOLVED = 2,
+    TRANSACTION_RESTART_NO_DATA_SENT = 3,
+    TRANSACTION_RESTART_DOWNGRADE_WITH_EARLY_DATA = 4,
+    TRANSACTION_RESTART_OTHERS = 5,
+  };
 };
 
 }  // namespace net

toolkit/components/telemetry/Histograms.json

@@ -15879,5 +15879,15 @@
     ],
     "releaseChannelCollection": "opt-out",
     "description": "Ratio of used and unused resources preloaded with link rel=preload tag or response header, broken down by supported resource type."
+  },
+  "HTTP_TRANSACTION_RESTART_REASON": {
+    "record_in_processes": ["main"],
+    "products": ["firefox"],
+    "expires_in_version": "never",
+    "n_values": 50,
+    "bug_numbers": [1667775],
+    "alert_emails": ["necko@mozilla.com", "kershaw@mozilla.com"],
+    "kind": "enumerated",
+    "description": "The reason why a HTTP transaction is restarted."
   }
 }