V2: review comment

internal/profiling/profiling.go

@@ -221,3 +221,10 @@ func InitStats(streamStatsSize uint32) error {
 
 	return nil
 }
+
+const (
+	// StreamStats have a 12-byte metadata byte slice that is a big-endian
+	// concatenation of a stream's connection ID (first eight bytes) and stream
+	// ID (next four bytes).
+	StreamStatMetadataSize = 12
+)

internal/transport/http2_client.go

@@ -572,7 +572,9 @@ func (t *http2Client) NewStream(ctx context.Context, callHdr *CallHdr) (_ *Strea
 
 	if profiling.IsEnabled() {
 		s.stat = profiling.NewStat("client")
-		s.stat.Metadata = make([]byte, 12)
+		s.stat.Metadata = make([]byte, profiling.StreamStatMetadataSize)
+		// See comment above StreamStatMetadataSize definition for more information
+		// on this encoding.
 		binary.BigEndian.PutUint64(s.stat.Metadata[0:8], t.connectionID)
 		// Stream ID will be set when loopy writer actually establishes the stream
 		// and obtains a stream ID

internal/transport/http2_server.go

@@ -335,10 +335,10 @@ func (t *http2Server) operateHeaders(frame *http2.MetaHeadersFrame, handle func(
 	}
 
 	if profiling.IsEnabled() {
-		// This is where the concept of a stream is first established within a gRPC
-		// server, so let's create an associated Stat object.
 		s.stat = profiling.NewStat("server")
-		s.stat.Metadata = make([]byte, 12)
+		// See comment above StreamStatMetadataSize definition for more information
+		// on this encoding.
+		s.stat.Metadata = make([]byte, profiling.StreamStatMetadataSize)
 		binary.BigEndian.PutUint64(s.stat.Metadata[0:8], t.connectionID)
 		binary.BigEndian.PutUint32(s.stat.Metadata[8:12], streamID)
 		profiling.StreamStats.Push(s.stat)

profiling/cmd/catapult.go

@@ -124,6 +124,8 @@ func streamStatsCatapultJSONSingle(stat *ppb.Stat, baseSec int64, baseNsec int32
 		return nil
 	}
 
+	// See comment above StreamStatMetadataSize definition for more information
+	// on this encoding.
 	connectionCounter := binary.BigEndian.Uint64(stat.Metadata[0:8])
 	streamID := binary.BigEndian.Uint32(stat.Metadata[8:12])
 	opid := fmt.Sprintf("/%s/%d/%d", stat.Tags, connectionCounter, streamID)