internal/testutil: Add ConnRecorder which records net.Conn writes

examples/ping/server/main.go

@@ -57,9 +57,9 @@ func runTrans(conn hopp.Conn, trans hopp.Trans) {
 			return
 		}
 		switch message := message.(type) {
-		case *ping.MessagePing:
+		case ping.MessagePing:
 			log.Printf("--> ping (%d) from %v", message, conn.RemoteAddr())
-			response := ping.MessagePong(*message)
+			response := ping.MessagePong(message)
 			_, err := ping.Send(trans, &response)
 			if err != nil {
 				log.Printf("XXX failed to send message: %v", err)

internal/testutil/conn-recorder.go

@@ -0,0 +1,45 @@
+package testutil
+
+import "net"
+import "fmt"
+import "strings"
+
+var _ net.Conn = new(ConnRecorder)
+
+// ConnRecorder records write/flush actions performed on a net.Conn.
+type ConnRecorder struct {
+	net.Conn
+	// A []byte means data was written, and untyped nil
+	// means data was flushed.
+	Log []any
+}
+
+func RecordConn(underlying net.Conn) *ConnRecorder {
+	return &ConnRecorder {
+		Conn: underlying,
+	}
+}
+
+func (this *ConnRecorder) Write(data []byte) (n int, err error) {
+	this.Log = append(this.Log, data)
+	return len(data), nil
+}
+
+func (this *ConnRecorder) Flush() error {
+	this.Log = append(this.Log, nil)
+	return nil
+}
+
+func (this *ConnRecorder) Dump() string {
+	builder := strings.Builder { }
+	for index, item := range this.Log {
+		fmt.Fprintf(&builder, "%06d ", index)
+		switch item := item.(type) {
+		case nil:
+			fmt.Fprintln(&builder, "FLUSH")
+		case []byte:
+			fmt.Fprintln(&builder, HexBytes(item))
+		}
+	}
+	return builder.String()
+}

internal/testutil/conn-recorder_test.go

@@ -0,0 +1,44 @@
+package testutil
+
+import "net"
+import "testing"
+
+func TestConnRecorder(test *testing.T) {
+	// server
+	listener, err := net.Listen("tcp", "localhost:9999")
+	if err != nil { test.Fatal(err) }
+	defer listener.Close()
+	go func() {
+		conn, err := listener.Accept()
+		defer conn.Close()
+		if err != nil { test.Fatal(err) }
+		buf := [16]byte { }
+		for {
+			_, err := conn.Read(buf[:])
+			if err != nil { break }
+		}
+	}()
+
+	// client
+	conn, err := net.Dial("tcp", "localhost:9999")
+	if err != nil { test.Fatal(err) }
+	defer conn.Close()
+	recorder := RecordConn(conn)
+	
+	_, err = recorder.Write([]byte("hello"))
+	if err != nil { test.Fatal(err) }
+	_, err = recorder.Write([]byte("world!"))
+	if err != nil { test.Fatal(err) }
+	err = recorder.Flush()
+	if err != nil { test.Fatal(err) }
+
+	test.Log("GOT:\n" + recorder.Dump())
+
+	if len(recorder.Log) != 3 { test.Fatal("wrong length") }
+	if string(recorder.Log[0].([]byte)) != "hello" {
+		test.Fatal("not equal")
+	}
+	if string(recorder.Log[1].([]byte)) != "world!" {
+		test.Fatal("not equal")
+	}
+}