Refactor socket streaming server: improve connection handling, switch to protobuf for message encoding, and optimize write operations

services/data_service/internal/server/socket_streaming_server.go

@@ -2,14 +2,16 @@ package server
 
 import (
 	"bufio"
-	"encoding/json"
+	"encoding/binary"
 	"fmt"
 	"io"
 	"net"
 	"strings"
 
 	"github.com/google/uuid"
+	pb "gitlab.michelsen.id/phillmichelsen/tessera/pkg/pb/data_service"
 	"gitlab.michelsen.id/phillmichelsen/tessera/services/data_service/internal/manager"
+	"google.golang.org/protobuf/proto"
 )
 
 type SocketStreamingServer struct {
@@ -17,17 +19,15 @@ type SocketStreamingServer struct {
 }
 
 func NewSocketStreamingServer(m *manager.Manager) *SocketStreamingServer {
-	return &SocketStreamingServer{
-		manager: m,
-	}
+	return &SocketStreamingServer{manager: m}
 }
 
-// Serve accepts a listener (TCP or Unix) and begins handling incoming connections.
+// Accepts connections and hands each off to handleConnection.
 func (s *SocketStreamingServer) Serve(lis net.Listener) error {
 	for {
 		conn, err := lis.Accept()
 		if err != nil {
-			fmt.Printf("Failed to accept connection: %v\n", err)
+			fmt.Printf("accept error: %v\n", err)
 			continue
 		}
 		go s.handleConnection(conn)
@@ -35,57 +35,112 @@ func (s *SocketStreamingServer) Serve(lis net.Listener) error {
 }
 
 func (s *SocketStreamingServer) handleConnection(conn net.Conn) {
-	defer func(conn net.Conn) {
-		err := conn.Close()
-		if err != nil {
-			fmt.Printf("Failed to close connection: %v\n", err)
+	defer func() {
+		if err := conn.Close(); err != nil {
+			fmt.Printf("conn close error: %v\n", err)
 		} else {
-			fmt.Println("Connection closed")
+			fmt.Println("connection closed")
 		}
-	}(conn)
+	}()
+
+	// Low-latency socket hints (best-effort).
+	if tc, ok := conn.(*net.TCPConn); ok {
+		_ = tc.SetNoDelay(true)
+		_ = tc.SetWriteBuffer(512 * 1024)
+		_ = tc.SetReadBuffer(512 * 1024)
+	}
+
 	reader := bufio.NewReader(conn)
 
+	// Protocol header: first line is the stream UUID.
 	raw, err := reader.ReadString('\n')
 	if err != nil {
-		fmt.Printf("Failed to read stream UUID: %v\n", err)
+		fmt.Printf("read stream UUID error: %v\n", err)
+		_, _ = fmt.Fprint(conn, "Failed to read stream UUID\n")
 		return
 	}
 	streamUUIDStr := strings.TrimSpace(raw)
 	streamUUID, err := uuid.Parse(streamUUIDStr)
 	if err != nil {
-		fmt.Fprintf(conn, "Invalid stream UUID\n")
+		_, _ = fmt.Fprint(conn, "Invalid stream UUID\n")
 		return
 	}
 
 	outCh, err := s.manager.ConnectStream(streamUUID)
 	if err != nil {
-		fmt.Fprintf(conn, "Failed to connect to stream: %v\n", err)
+		_, _ = fmt.Fprintf(conn, "Failed to connect to stream: %v\n", err)
 		return
 	}
 	defer s.manager.DisconnectStream(streamUUID)
 
+	writer := bufio.NewWriterSize(conn, 256*1024)
+	defer func(writer *bufio.Writer) {
+		err := writer.Flush()
+		if err != nil {
+			fmt.Printf("final flush error: %v\n", err)
+		}
+	}(writer)
+
+	const flushEvery = 32
+	batch := 0
+
 	for msg := range outCh {
-		payload := struct {
-			Provider string `json:"provider"`
-			Subject  string `json:"subject"`
-			Data     string `json:"data"`
-		}{
-			Provider: msg.Identifier.Provider,
-			Subject:  msg.Identifier.Subject,
-			Data:     fmt.Sprintf("%s", msg.Payload),
+		// Build protobuf payload.
+		message := pb.Message{
+			Identifier: &pb.Identifier{
+				Provider: msg.Identifier.Provider,
+				Subject:  msg.Identifier.Subject,
+			},
+			Payload:  msg.Payload,          // []byte
+			Encoding: string(msg.Encoding), // e.g., "application/json"
 		}
 
-		bytes, err := json.Marshal(payload)
+		// Marshal protobuf.
+		// Use MarshalAppend to reuse capacity and avoid an extra alloc.
+		size := proto.Size(&message)
+		buf := make([]byte, 0, size)
+		b, err := proto.MarshalOptions{}.MarshalAppend(buf, &message)
 		if err != nil {
-			fmt.Printf("Failed to encode message: %v\n", err)
+			fmt.Printf("proto marshal error: %v\n", err)
 			continue
 		}
-		_, err = conn.Write(append(bytes, '\n'))
-		if err != nil {
-			if err != io.EOF {
-				fmt.Printf("Write error: %v\n", err)
+
+		// Fixed 4-byte big-endian length prefix.
+		var hdr [4]byte
+		if len(b) > int(^uint32(0)) {
+			fmt.Printf("message too large: %d bytes\n", len(b))
+			continue
+		}
+		binary.BigEndian.PutUint32(hdr[:], uint32(len(b)))
+
+		// Write frame: [len][bytes].
+		if _, err := writer.Write(hdr[:]); err != nil {
+			if err == io.EOF {
+				return
 			}
-			break
+			fmt.Printf("write len error: %v\n", err)
+			return
+		}
+		if _, err := writer.Write(b); err != nil {
+			if err == io.EOF {
+				return
+			}
+			fmt.Printf("write body error: %v\n", err)
+			return
+		}
+
+		batch++
+		if batch >= flushEvery {
+			if err := writer.Flush(); err != nil {
+				fmt.Printf("flush error: %v\n", err)
+				return
+			}
+			batch = 0
 		}
 	}
+
+	// Final flush when channel closes.
+	if err := writer.Flush(); err != nil {
+		fmt.Printf("final flush error: %v\n", err)
+	}
 }