Update Trans docs with new concurrency rules

connection.go

@@ -34,8 +34,8 @@ type Conn interface {
 }
 
 // Trans is a HOPP transaction. Methods of this interface are not safe for
-// concurrent use with the exception of the Close and ID methods. The
-// recommended use case is one goroutine per transaction.
+// concurrent use with the exception of the Write, SendWriter, Close, and ID
+// methods. The recommended use case is one goroutine per transaction.
 type Trans interface {
 	// Close closes the transaction. Any blocked operations will be
 	// unblocked and return errors. This method is safe for concurrent use.
@@ -45,13 +45,13 @@ type Trans interface {
 	// unique within the connection. This method is safe for concurrent use.
 	ID() int64
 		
-	// Send sends a message. This method is not safe for concurrent use.
+	// Send sends a message. This method is safe for concurrent use.
 	Send(method uint16, data []byte) error
 	// SendWriter sends data written to an [io.Writer]. The writer must be
 	// closed after use. Closing the writer flushes any data that hasn't
 	// been written yet. Any writer previously opened through this function
-	// will be discarded. This method is not safe for concurrent use, and
-	// neither is its result.
+	// will be discarded. This method is safe for concurrent use, but its
+	// result isn't.
 	SendWriter(method uint16) (io.WriteCloser, error)
 	// Receive receives a message. This method is not safe for concurrent
 	// use.

design/protocol.md

@@ -132,6 +132,8 @@ METADAPT-B is used over QUIC for communication over networks such as the
 Internet.
 
 ### METADAPT-A
+![Diagram of a METADAPT-A MMB.](../assets/metadapt-a-mmb-diagram.png)
+
 METADAPT-A requires a transport which offers a single full-duplex data stream
 that persists for the duration of the connection. All transactions are
 multiplexed onto this single stream. Each MMB contains a 12-octet long header,

examples/chat/client/main.go

@@ -42,11 +42,11 @@ func main() {
 			break
 		}
 		switch message := message.(type) {
-		case *chat.MessageChat:
+		case chat.MessageChat:
 			fmt.Fprintf(os.Stdout, "%s: %s\n", message.Nickname, message.Content)
-		case *chat.MessageJoinNotify:
+		case chat.MessageJoinNotify:
 			fmt.Fprintf(os.Stdout, "(i) %s joined the room\n", message.Nickname)
-		case *chat.MessageLeaveNotify:
+		case chat.MessageLeaveNotify:
 			fmt.Fprintf(os.Stdout, "(i) %s left the room\n", message.Nickname)
 		}
 	}

examples/chat/doc.go

@@ -1,6 +1,6 @@
-// Package chat implements a simple chat protocol over HOPP. To re-generate the
-// source files, run this command from within the root directory of the
-// repository:
-//
-//   go run ./cmd/hopp-generate examples/chat/protocol.pdl -o examples/chat/protocol/protocol.go
+// Package chat demonstrates a simple chat protocol.
 package chat
+
+// To use this in your own project, replace "go run ../../cmd/hopp-generate"
+// with just "hopp-generate".
+//go:generate go run ../../cmd/hopp-generate protocol.pdl -o protocol.go

examples/chat/protocol.go

@@ -57,6 +57,25 @@ func boolInt(input bool) int {
 // ensure ucontainer is always imported
 var _ hopp.Option[int]
 
+// ReceivedMessage is a sealed interface representing the value of a
+// message in this package. To determine what kind of message it is,
+// use a type switch like this:
+// 
+//   switch message := message.(type) {
+//   case MessageError:
+//           doSomething()
+//   case MessageSuccess:
+//           doSomething()
+//   case MessageJoin:
+//           doSomething()
+// 
+//   ...
+// 
+//   }
+type ReceivedMessage interface {
+	isReceivedMessage()
+}
+
 // Error is sent by a party when the other party has done something erroneous. The
 // valid error codes are:
 // 
@@ -124,6 +143,7 @@ func(this *MessageError) Decode(decoder *tape.Decoder) (n int, err error) {
 	n += nn; if err != nil { return n, err }
 	return n, nil
 }
+func (this MessageError) isReceivedMessage() { }
 
 // Success is sent by a party when it has successfully completed a task given to it
 // by the other party. The sending party must immediately close the transaction
@@ -162,6 +182,7 @@ func(this *MessageSuccess) Decode(decoder *tape.Decoder) (n int, err error) {
 	n += nn; if err != nil { return n, err }
 	return n, nil
 }
+func (this MessageSuccess) isReceivedMessage() { }
 
 // Join is sent by the client when it wishes to join a room. It must begin a new
 // transaction, and that transaction will persist while the user is in that room.
@@ -231,6 +252,7 @@ func(this *MessageJoin) Decode(decoder *tape.Decoder) (n int, err error) {
 	n += nn; if err != nil { return n, err }
 	return n, nil
 }
+func (this MessageJoin) isReceivedMessage() { }
 
 // Chat is sent by the client when it wishes to post a message to the room. It is
 // also relayed by the server to other clients to notify them of the message. It
@@ -299,6 +321,7 @@ func(this *MessageChat) Decode(decoder *tape.Decoder) (n int, err error) {
 	n += nn; if err != nil { return n, err }
 	return n, nil
 }
+func (this MessageChat) isReceivedMessage() { }
 
 // JoinNotify is sent by the server when another client joins the room. It must be
 // sent within a room transaction.
@@ -351,6 +374,7 @@ func(this *MessageJoinNotify) Decode(decoder *tape.Decoder) (n int, err error) {
 	n += nn; if err != nil { return n, err }
 	return n, nil
 }
+func (this MessageJoinNotify) isReceivedMessage() { }
 
 // LeaveNotify is sent by the server when another client leaves the room. It must
 // be sent within a room transaction.
@@ -403,6 +427,7 @@ func(this *MessageLeaveNotify) Decode(decoder *tape.Decoder) (n int, err error)
 	n += nn; if err != nil { return n, err }
 	return n, nil
 }
+func (this MessageLeaveNotify) isReceivedMessage() { }
 
 func decodeBranch_1d505103df99c95e6bed0800d0ea881a_MessageError(this *MessageError, decoder *tape.Decoder, tag tape.Tag) (n int, err error) {
 	var nn int
@@ -693,16 +718,11 @@ func decodeBranch_68c536511e6d598462efc482144438e9_MessageLeaveNotify(this *Mess
 
 // Receive decodes a message from a transaction and returns it as a value.
 // Use a type switch to determine what type of message it is.
-func Receive(trans hopp.Trans) (message any, n int, err error) {
+func Receive(trans hopp.Trans) (message ReceivedMessage, n int, err error) {
 	method, reader, err := trans.ReceiveReader()
-	decoder := tape.NewDecoder(reader)
 	if err != nil { return nil, n, err }
+	decoder := tape.NewDecoder(reader)
 	switch method {
-	case 0x0401:
-		var message MessageLeaveNotify
-		nn, err := message.Decode(decoder)
-		n += nn; if err != nil { return nil, n, err }
-		return message, n, nil
 	case 0x0000:
 		var message MessageError
 		nn, err := message.Decode(decoder)
@@ -728,6 +748,11 @@ func Receive(trans hopp.Trans) (message any, n int, err error) {
 		nn, err := message.Decode(decoder)
 		n += nn; if err != nil { return nil, n, err }
 		return message, n, nil
+	case 0x0401:
+		var message MessageLeaveNotify
+		nn, err := message.Decode(decoder)
+		n += nn; if err != nil { return nil, n, err }
+		return message, n, nil
 	}
 	return nil, n, fmt.Errorf("%w: M%04X", hopp.ErrUnknownMethod, method)
 }

examples/chat/server/main.go

@@ -98,20 +98,27 @@ func (this *client) transTalk(trans hopp.Trans, initial *chat.MessageJoin) error
 	err := this.joinRoom(trans, room)
 	if err != nil { return err }
 	defer this.leaveRoom(trans, room)
+
+	_, err = chat.Send(trans, &chat.MessageChat {
+		Content: "(i) joined " + room,
+		Nickname: "SYSTEM",
+	})
+	if err != nil { return err }
+	
 	for {
 		message, _, err := chat.Receive(trans)
 		if err != nil { return err }
 		switch message := message.(type) {
-		case *chat.MessageChat:
+		case chat.MessageChat:
 			err := this.handleMessageChat(trans, room, message)
 			if err != nil { return err }
-		case *chat.MessageError:
-			return message
+		case chat.MessageError:
+			return &message
 		}
 	}
 }
 
-func (this *client) handleMessageChat(trans hopp.Trans, room string, message *chat.MessageChat) error {
+func (this *client) handleMessageChat(trans hopp.Trans, room string, message chat.MessageChat) error {
 	log.Printf("(). %s #%s: %s", this.nickname, room, message.Content)
 	clients, done := clients.RBorrow()
 	defer done()
@@ -124,11 +131,11 @@ func (this *client) handleMessageChat(trans hopp.Trans, room string, message *ch
 	return nil
 }
 
-func (this *client) relayMessage(room string, message *chat.MessageChat) error {
+func (this *client) relayMessage(room string, message chat.MessageChat) error {
 	rooms, done := this.rooms.RBorrow()
 	defer done()
 	if trans, ok := rooms[room]; ok {
-		_, err := chat.Send(trans, message)
+		_, err := chat.Send(trans, &message)
 		if err != nil {
 			return fmt.Errorf("could not relay message: %w", err)
 		}

examples/ping/client/main.go

@@ -25,12 +25,11 @@ func main() {
 
 	go func() {
 		message := ping.MessagePing(0)
-		for {
+		for _ = range time.Tick(time.Second) {
 			log.Printf("<-- ping (%d)", message)
 			_, err := ping.Send(trans, &message)
 			handleErr(1, err)
 			message ++
-			time.Sleep(time.Second)
 		}
 	}()
 
@@ -44,7 +43,7 @@ func main() {
 			break
 		}
 		switch message := message.(type) {
-		case *ping.MessagePong:
+		case ping.MessagePong:
 			log.Printf("--> pong (%d) from %v", message, address)
 		}
 	}

examples/ping/doc.go

@@ -0,0 +1,6 @@
+// Example ping demonstrates a simple ping/pong protocol.
+package ping
+
+// To use this in your own project, replace "go run ../../cmd/hopp-generate"
+// with just "hopp-generate".
+//go:generate go run ../../cmd/hopp-generate protocol.pdl -o protocol.go

examples/ping/protocol.go

@@ -57,6 +57,20 @@ func boolInt(input bool) int {
 // ensure ucontainer is always imported
 var _ hopp.Option[int]
 
+// ReceivedMessage is a sealed interface representing the value of a
+// message in this package. To determine what kind of message it is,
+// use a type switch like this:
+// 
+//   switch message := message.(type) {
+//   case MessagePing:
+//           doSomething()
+//   case MessagePong:
+//           doSomething()
+//   }
+type ReceivedMessage interface {
+	isReceivedMessage()
+}
+
 // Ping is sent by the client to the server. It may contain any number. This
 // number will be returned to the client via a [Pong] message.
 type MessagePing int32
@@ -88,6 +102,7 @@ func(this *MessagePing) Decode(decoder *tape.Decoder) (n int, err error) {
 	*this = MessagePing(destination_2)
 	return n, nil
 }
+func (this MessagePing) isReceivedMessage() { }
 
 // Pong is sent by the server to the client in response to a [Ping] message, It
 // will contain the same number as that message.
@@ -120,13 +135,14 @@ func(this *MessagePong) Decode(decoder *tape.Decoder) (n int, err error) {
 	*this = MessagePong(destination_4)
 	return n, nil
 }
+func (this MessagePong) isReceivedMessage() { }
 
 // Receive decodes a message from a transaction and returns it as a value.
 // Use a type switch to determine what type of message it is.
-func Receive(trans hopp.Trans) (message any, n int, err error) {
+func Receive(trans hopp.Trans) (message ReceivedMessage, n int, err error) {
 	method, reader, err := trans.ReceiveReader()
-	decoder := tape.NewDecoder(reader)
 	if err != nil { return nil, n, err }
+	decoder := tape.NewDecoder(reader)
 	switch method {
 	case 0x0000:
 		var message MessagePing

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)

generate/generate.go

@@ -114,6 +114,8 @@ func (this *Generator) Generate(protocol *Protocol) (n int, err error) {
 	n += nn; if err != nil { return n, err }
 
 	// type definitions
+	nn, err = this.generateMessageValueInterface()
+	n += nn; if err != nil { return n, err }
 	for _, name := range slices.Sorted(maps.Keys(protocol.Types)) {
 		nn, err := this.generateTypedef(name, protocol.Types[name])
 		n += nn; if err != nil { return n, err }
@@ -140,6 +142,42 @@ func (this *Generator) Generate(protocol *Protocol) (n int, err error) {
 	return n, nil
 }
 
+func (this *Generator) generateMessageValueInterface() (n int, err error) {
+	keys := slices.Sorted(maps.Keys(this.protocol.Messages))
+	nn, err := this.iprint(
+		"\n// ReceivedMessage is a sealed interface representing the value of a\n" +
+		"// message in this package. To determine what kind of message it is,\n" +
+		"// use a type switch like this:\n" +
+		"// \n" +
+		"//   switch message := message.(type) {\n")
+	n += nn; if err != nil { return n, err }
+	for index, method := range keys {
+		if index > 2 {
+			nn, err := this.iprint("// \n//   ...\n// \n")
+			n += nn; if err != nil { return n, err }
+			break
+		}
+		nn, err := this.iprintf("//   case %s:\n",
+			this.resolveMessageName(this.protocol.Messages[method].Name))
+		n += nn; if err != nil { return n, err }
+		nn, err = this.iprintf("//           doSomething()\n")
+		n += nn; if err != nil { return n, err }
+	}
+	nn, err = this.iprintf("//   }\n")
+	n += nn; if err != nil { return n, err }
+	
+	nn, err = this.iprintf("type ReceivedMessage interface {\n")
+	n += nn; if err != nil { return n, err }
+	this.push()
+		nn, err = this.iprintf("isReceivedMessage()\n")
+		n += nn; if err != nil { return n, err }
+	this.pop()
+	nn, err = this.iprintf("}\n")
+	n += nn; if err != nil { return n, err }
+	
+	return n, nil
+}
+
 func (this *Generator) generateTypedef(name string, typedef Typedef) (n int, err error) {
 	typ := typedef.Type
 
@@ -327,6 +365,10 @@ func (this *Generator) generateMessage(method uint16, message Message) (n int, e
 	this.pop()
 	nn, err = this.iprintf("}\n")
 	n += nn; if err != nil { return n, err }
+
+	// isReceivedMessage method
+	nn, err = this.iprintf("func (this %s) isReceivedMessage() { }\n", this.resolveMessageName(message.Name))
+	n += nn; if err != nil { return n, err }
 	
 	return n, nil
 }
@@ -1207,15 +1249,15 @@ func (this *Generator) generateReceive() (n int, err error) {
 		"// Use a type switch to determine what type of message it is.\n")
 	n += nn; if err != nil { return n, err }
 	nn, err = this.iprintf(
-		"func Receive(trans hopp.Trans) (message any, n int, err error) {\n")
+		"func Receive(trans hopp.Trans) (message ReceivedMessage, n int, err error) {\n")
 	n += nn; if err != nil { return n, err }
 	this.push()
 		nn, err = this.iprintf("method, reader, err := trans.ReceiveReader()\n")
 		n += nn; if err != nil { return n, err }
-		nn, err = this.iprintf("decoder := tape.NewDecoder(reader)\n")
-		n += nn; if err != nil { return n, err }
 		nn, err = this.iprintf("if err != nil { return nil, n, err }\n")
 		n += nn; if err != nil { return n, err }
+		nn, err = this.iprintf("decoder := tape.NewDecoder(reader)\n")
+		n += nn; if err != nil { return n, err }
 		nn, err = this.iprintf("switch method {\n")
 		n += nn; if err != nil { return n, err }
 		for method, message := range this.protocol.Messages {

generate/generate_test.go

@@ -7,8 +7,10 @@ import "testing"
 // generator is equal to something specific
 
 var exampleProtocol = defaultProtocol()
+var pingProtocol    = defaultProtocol()
 
 func init() {
+	// example protocol
 	exampleProtocol.Messages[0x0000] = Message {
 		Name: "Connect",
 		Type: TypeTableDefined {
@@ -121,6 +123,16 @@ func init() {
 			},
 		},
 	}
+	
+	// ping protocol
+	pingProtocol.Messages[0x0000] = Message {
+		Name: "Ping",
+		Type: TypeInt { Bits: 32, Signed: true },
+	}
+	pingProtocol.Messages[0x0001] = Message {
+		Name: "Pong",
+		Type: TypeInt { Bits: 32, Signed: true },
+	}
 }
 
 func TestGenerateRunEncodeDecode(test *testing.T) {
@@ -485,3 +497,119 @@ func TestGenerateRunDecodeWrongType(test *testing.T) {
 		}
 	`)
 }
+
+func TestGenerateRunSendReceive(test *testing.T) {
+	testGenerateRun(test, &pingProtocol, "send-receive", `
+		// imports
+		import "git.tebibyte.media/sashakoshka/hopp/internal/mock"
+	`, `
+		log.Println("Send"); {
+			message := MessagePing(77)
+			trans   := mock.Trans { }
+			_, err := Send(&trans, &message)
+			if err != nil { log.Fatal(err) }
+			gotMethod, gotPayload := trans.Methods[0], trans.Messages[0]
+			log.Printf("method M%04X", gotMethod)
+			log.Println("payload", tu.HexBytes(gotPayload))
+			if gotMethod != 0x0000 {
+				log.Fatalln("wrong method")
+			}
+			if ok, n := snake.L(0x43, 0x00, 0x00, 0x00, 0x4D).Check(gotPayload); !ok {
+				log.Fatalln("not equal at:", n)
+			}
+		}
+
+		log.Println("Receive"); {
+			trans := mock.Trans {
+				Methods:  []uint16 { 1 },
+				Messages: [][]byte { []byte { 0x43, 0x00, 0x00, 0x00, 0x4E } },
+			}
+			gotMessage, n, err := Receive(&trans)
+			if err != nil { log.Fatal(err) }
+			log.Println("message", gotMessage)
+			log.Println("n",       n)
+			casted, ok := gotMessage.(MessagePong)
+			if !ok          { log.Fatalln("expected MessagePong") }
+			if casted != 78 { log.Fatalln("wrong message value") }
+			if n != 5       { log.Fatalln("wrong n value") }
+		}
+	`)
+}
+
+func TestGenerateRunConn(test *testing.T) {
+	testGenerateRun(test, &pingProtocol, "send-receive", `
+		// imports
+		import "sync"
+		import "context"
+		import "git.tebibyte.media/sashakoshka/hopp"
+	`, `
+		group := sync.WaitGroup { }
+		group.Add(2)
+	
+		// server
+		listener, err := hopp.Listen("tcp", "localhost:43957", nil)
+		if err != nil { log.Fatalln("SERVER listen:", err) }
+		go func() {
+			defer listener.Close()
+			defer group.Done()
+			
+			conn, err := listener.Accept()
+			if err != nil { log.Fatalln("SERVER accept:", err) }
+			trans, err := conn.AcceptTrans()
+			if err != nil { log.Fatalln("SERVER accept trans:", err) }
+			
+			message, n, err := Receive(trans)
+			if err != nil { log.Fatalln("SERVER receive:", err) }
+			log.Println("SERVER got message", message)
+			log.Println("SERVER got n",       n)
+			casted, ok := message.(MessagePing)
+			if !ok          { log.Fatalln("SERVER expected MessagePong") }
+			if casted != 77 { log.Fatalln("SERVER wrong message value") }
+			if n != 5       { log.Fatalln("SERVER wrong n value") }
+			
+			message, n, err = Receive(trans)
+			if err != nil { log.Fatalln("SERVER receive:", err) }
+			log.Println("SERVER got message", message)
+			log.Println("SERVER got n",       n)
+			casted, ok = message.(MessagePing)
+			if !ok          { log.Fatalln("SERVER expected MessagePong") }
+			if casted != 78 { log.Fatalln("SERVER wrong message value") }
+			if n != 5       { log.Fatalln("SERVER wrong n value") }
+		}()
+
+		// client
+		go func() {
+			defer group.Done()
+
+			log.Println("CLIENT dialing")
+			conn, err := hopp.Dial(
+				context.Background(),
+				"tcp", "localhost:43957",
+				nil)
+			if err != nil { log.Fatalln("CLIENT dial:", err) }
+			defer conn.Close()
+			log.Println("CLIENT connected")
+
+			log.Println("CLIENT opening trans")
+			trans, err := conn.OpenTrans()
+			if err != nil { log.Fatalln("CLIENT open trans:", err) }
+			
+			message := MessagePing(77)
+			log.Println("CLIENT sending message")
+			n, err := Send(trans, &message)
+			if err != nil { log.Fatalln("CLIENT send:", err) }
+			log.Println("CLIENT sent n", n)
+			if n != 5 { log.Fatalln("CLIENT wrong n value") }
+			
+			message = MessagePing(78)
+			log.Println("CLIENT sending message")
+			n, err = Send(trans, &message)
+			if err != nil { log.Fatalln("CLIENT send:", err) }
+			log.Println("CLIENT sent n", n)
+			if n != 5 { log.Fatalln("CLIENT wrong n value") }
+		}()
+
+		group.Wait()
+	`)
+	
+}

internal/mock/connection.go

@@ -0,0 +1,64 @@
+package mock
+
+import "io"
+import "time"
+import "bytes"
+import "git.tebibyte.media/sashakoshka/hopp"
+
+var _ hopp.Trans = new(Trans)
+
+// Trans is a mock transaction implementation.
+type Trans struct {
+	// These arrays must be the same length. You can load this up
+	// with messages to read, or deposit messages and retrieve them
+	// here later.
+	Methods  []uint16
+	Messages [][]byte
+}
+
+func (this *Trans) Close() error { return nil }
+
+func (this *Trans) ID() int64 { return 56 }
+
+func (this *Trans) Send(method uint16, data []byte) error {
+	this.Methods  = append(this.Methods,  method)
+	this.Messages = append(this.Messages, data)
+	return nil
+}
+
+func (this *Trans) SendWriter(method uint16) (io.WriteCloser, error) {
+	return &transWriter {
+		Buffer: new(bytes.Buffer),
+		method: method,
+		parent: this,
+	}, nil
+}
+
+func (this *Trans) Receive() (method uint16, data []byte, err error) {
+	if len(this.Methods) == 0 {
+		return 0, nil, io.EOF
+	}
+	method = this.Methods[0]
+	data   = this.Messages[0]
+	this.Methods  = this.Methods[1:]
+	this.Messages = this.Messages[1:]
+	return method, data, nil
+}
+
+func (this *Trans) ReceiveReader() (method uint16, reader io.Reader, err error) {
+	method, data, err := this.Receive()
+	if err != nil { return 0, nil, err }
+	return method, bytes.NewBuffer(data), nil
+}
+
+func (this *Trans) SetDeadline(time.Time) error { return nil }
+
+type transWriter struct {
+	*bytes.Buffer
+	method uint16
+	parent *Trans
+}
+
+func (this *transWriter) Close() error {
+	return this.parent.Send(this.method, this.Bytes())
+}

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")
+	}
+}

metadapta.go

@@ -6,6 +6,7 @@ import "fmt"
 import "net"
 import "sync"
 import "time"
+import "bytes"
 import "context"
 import "sync/atomic"
 import "git.tebibyte.media/sashakoshka/go-util/sync"
@@ -17,6 +18,12 @@ const closeMethod = 0xFFFF
 const int64Max = int64((^uint64(0)) >> 1)
 const defaultChunkSize = 0x1000
 
+var bufferPool = sync.Pool {
+	New: func() any {
+		return &bytes.Buffer { }
+	},
+}
+
 // Party represents a side of a connection.
 type Party bool; const (
 	ServerSide Party = false
@@ -222,12 +229,12 @@ type transA struct {
 	parent        *a
 	id            int64
 	incoming      usync.Gate[incomingMessage]
-	currentReader io.Reader
-	currentWriter io.Closer
-	writeBuffer   []byte
 	closed        atomic.Bool
 	closeErr      error
 	
+	currentReader  io.Reader
+	currentWriter  usync.Monitor[io.Closer]
+	
 	deadline      *time.Timer
 	deadlineLock  sync.Mutex
 }
@@ -263,23 +270,24 @@ func (this *transA) Send(method uint16, data []byte) error {
 }
 
 func (this *transA) SendWriter(method uint16) (io.WriteCloser, error) {
+	currentWriter, done := this.currentWriter.BorrowReturn()
+	defer done(&currentWriter)
+
 	// close previous writer if necessary
-	if this.currentWriter != nil {
-		this.currentWriter.Close()
-		this.currentWriter = nil
+	if currentWriter != nil {
+		currentWriter.Close()
+		currentWriter = nil
 	}
 
 	// create new writer
 	writer := &writerA {
 		parent: this,
-		// there is only ever one writer at a time, so they can all
-		// share a buffer
-		buffer: this.writeBuffer[:0],
+		buffer: bufferPool.Get().(*bytes.Buffer),
 		method: method,
 		chunkSize: defaultChunkSize,
 		open: true,
 	}
-	this.currentWriter = writer
+	currentWriter = writer
 	return writer, nil
 }
 
@@ -406,7 +414,7 @@ func (this *readerA) Read(buffer []byte) (int, error) {
 
 type writerA struct {
 	parent    *transA
-	buffer    []byte
+	buffer    *bytes.Buffer
 	method    uint16
 	chunkSize int64
 	open      bool
@@ -425,8 +433,18 @@ func (this *writerA) Write(data []byte) (n int, err error) {
 }
 
 func (this *writerA) Close() error {
-	this.flush(0)
-	this.open = false
+	if this.buffer != nil {
+		// flush if needed
+		if this.buffer.Len() > 0 {
+			this.flush(0)
+		}
+		this.open = false
+
+		// reset the buffer and put it back in the pool
+		this.buffer.Reset()
+		bufferPool.Put(this.buffer)
+		this.buffer = nil
+	}
 	return nil
 }
 
@@ -434,11 +452,11 @@ func (this *writerA) writeOne(data []byte) (n int, err error) {
 	data = data[:min(len(data), int(this.chunkSize))]
 	
 	// if there is more room, append to the buffer and exit
-	if int64(len(this.buffer) + len(data)) <= this.chunkSize {
-		this.buffer = append(this.buffer, data...)
+	if int64(this.buffer.Len() + len(data)) <= this.chunkSize {
+		this.buffer.Write(data)
 		n = len(data)
 		// if have a full chunk, flush
-		if int64(len(this.buffer)) == this.chunkSize {
+		if int64(this.buffer.Len()) == this.chunkSize {
 			err = this.flush(1)
 			if err != nil { return n, err }
 		}
@@ -448,12 +466,17 @@ func (this *writerA) writeOne(data []byte) (n int, err error) {
 	// if not, flush and store as much as we can in the buffer
 	err = this.flush(1)
 	if err != nil { return n, err }
-	this.buffer = append(this.buffer, data...)
+	n = int(min(int64(len(data)), this.chunkSize))
+	this.buffer.Write(data[:n])
 	return n, nil
 }
 
 func (this *writerA) flush(ccb uint64) error {
-	return this.parent.parent.sendMessageSafe(this.parent.id, this.method, ccb, this.buffer)
+	err := this.parent.parent.sendMessageSafe(
+		this.parent.id, this.method, ccb,
+		this.buffer.Bytes())
+	this.buffer.Reset()
+	return err
 }
 
 type incomingMessage struct {

metadapta_test.go

@@ -1,11 +1,14 @@
 package hopp
 
 import "io"
+import "net"
+import "sync"
 import "bytes"
 import "errors"
 import "slices"
 import "testing"
 import "context"
+import tu "git.tebibyte.media/sashakoshka/hopp/internal/testutil"
 
 // some of these tests spawn goroutines that can signal a failure.
 // abide by the documentation for testing.T (https://pkg.go.dev/testing#T):
@@ -149,21 +152,23 @@ func TestReadWriteA(test *testing.T) {
 			gotPayloadBytes, err := io.ReadAll(gotReader)
 			if err != nil { test.Fatal("CLIENT", err) }
 			gotPayload := string(gotPayloadBytes)
-			test.Log("CLIENT m:", gotMethod, "p:", gotPayload)
+			test.Log("CLIENT m:", gotMethod, "p:", tu.HexBytes(gotPayloadBytes))
 			if int(gotMethod) != method {
-				test.Errorf("CLIENT method not equal")
+				test.Error("CLIENT method not equal, expected", method)
 			}
 			if gotPayload != payload {
-				test.Errorf("CLIENT payload not equal")
+				test.Error(
+					"CLIENT payload not equal, expected",
+					tu.HexBytes([]byte(payload)))
 			}
 		}
 		test.Log("CLIENT waiting for transaction close...")
 		gotMethod, gotPayload, err := trans.Receive()
 		if !errors.Is(err, io.EOF) {
 			test.Error("CLIENT wrong error:", err)
-			test.Error("CLIENT method:", gotMethod)
-			test.Error("CLIENT payload:", gotPayload)
-			test.Fatal("CLIENT ok byeeeeeeeeeeeee")
+			test.Error("CLIENT    method:", gotMethod)
+			test.Error("CLIENT    payload:", tu.HexBytes(gotPayload))
+			test.Fatal("CLIENT    (expected io.EOF and no message)")
 		}
 		test.Log("CLIENT transaction has closed")
 	}
@@ -174,7 +179,7 @@ func TestReadWriteA(test *testing.T) {
 		if err != nil { test.Error("SERVER", err); return }
 		test.Cleanup(func() { trans.Close() })
 		for method, payload := range payloads {
-			test.Log("SERVER m:", method, "p:", payload)
+			test.Log("SERVER m:", method, "p:", tu.HexBytes([]byte(payload)))
 			func() {
 				writer, err := trans.SendWriter(uint16(method))
 				if err != nil { test.Error("SERVER", err); return }
@@ -271,6 +276,225 @@ func TestEncodeDecodeMessageA(test *testing.T) {
 	}
 }
 
+func TestConsecutiveSend(test *testing.T) {
+	packets := [][]byte {
+		[]byte {
+			0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x01,
+			0x00, 0x00,
+			0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x05,
+			0x43, 0x00, 0x00, 0x00, 0x07 },
+		
+		[]byte {
+			0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x01,
+			0x00, 0x00,
+			0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x05,
+			0x43, 0x00, 0x00, 0x00, 0x08 },
+	}
+	payloads := [][]byte {
+		[]byte { 0x43, 0x00, 0x00, 0x00, 0x07 },
+		[]byte { 0x43, 0x00, 0x00, 0x00, 0x08 },
+	}
+
+	var group sync.WaitGroup
+	group.Add(2)
+
+	// server
+	listener, err := net.Listen("tcp", "localhost:9999")
+	if err != nil { test.Fatal("SERVER", err) }
+	go func() {
+		defer group.Done()
+		defer listener.Close()
+		conn, err := listener.Accept()
+		if err != nil { test.Fatal("SERVER", err) }
+		defer conn.Close()
+		
+		buf := [16]byte { }
+		for {
+			_, err := conn.Read(buf[:])
+			if err != nil { break }
+		}
+	}()
+
+	// client
+	go func() {
+		defer group.Done()
+		conn, err := net.Dial("tcp", "localhost:9999")
+		if err != nil { test.Fatal("CLIENT", err) }
+		defer conn.Close()
+		recorder := tu.RecordConn(conn)
+
+		a := AdaptA(recorder, ClientSide)
+		trans, err := a.OpenTrans()
+		if err != nil { test.Fatal("CLIENT", err) }
+
+		for _, payload := range payloads {
+			err := trans.Send(0x0000, payload)
+			if err != nil { test.Fatal("CLIENT", err) }
+		}
+
+		test.Log("CLIENT recorded output:\n" + recorder.Dump())
+		if len(recorder.Log) != 2 { test.Fatal("wrong length") }
+		if !slices.Equal(recorder.Log[0].([]byte), packets[0]) {
+			test.Fatal("not equal")
+		}
+		if !slices.Equal(recorder.Log[1].([]byte), packets[1]) {
+			test.Fatal("not equal")
+		}
+	}()
+
+	group.Wait()
+}
+
+func TestConsecutiveWrite(test *testing.T) {
+	packets := [][]byte {
+		[]byte {
+			0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x01,
+			0x00, 0x00,
+			0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x05,
+			0x43, 0x00, 0x00, 0x00, 0x07 },
+		
+		[]byte {
+			0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x01,
+			0x00, 0x00,
+			0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x05,
+			0x43, 0x00, 0x00, 0x00, 0x08 },
+	}
+	payloads := [][]byte {
+		[]byte { 0x43, 0x00, 0x00, 0x00, 0x07 },
+		[]byte { 0x43, 0x00, 0x00, 0x00, 0x08 },
+	}
+
+	var group sync.WaitGroup
+	group.Add(2)
+
+	// server
+	listener, err := net.Listen("tcp", "localhost:9999")
+	if err != nil { test.Fatal("SERVER", err) }
+	go func() {
+		defer group.Done()
+		defer listener.Close()
+		conn, err := listener.Accept()
+		if err != nil { test.Fatal("SERVER", err) }
+		defer conn.Close()
+		
+		buf := [16]byte { }
+		for {
+			_, err := conn.Read(buf[:])
+			if err != nil { break }
+		}
+	}()
+
+	// client
+	go func() {
+		defer group.Done()
+		conn, err := net.Dial("tcp", "localhost:9999")
+		if err != nil { test.Fatal("CLIENT", err) }
+		defer conn.Close()
+		recorder := tu.RecordConn(conn)
+
+		a := AdaptA(recorder, ClientSide)
+		trans, err := a.OpenTrans()
+		if err != nil { test.Fatal("CLIENT", err) }
+
+		for _, payload := range payloads {
+			func() {
+				writer, err := trans.SendWriter(0x0000)
+				if err != nil { test.Fatal("CLIENT", err) }
+				_, err = writer.Write(payload)
+				if err != nil { test.Fatal("CLIENT", err) }
+				writer.Close()	
+			}()
+		}
+
+		test.Log("CLIENT recorded output:\n" + recorder.Dump())
+		if len(recorder.Log) != 2 { test.Fatal("wrong length") }
+		if !slices.Equal(recorder.Log[0].([]byte), packets[0]) {
+			test.Fatal("not equal")
+		}
+		if !slices.Equal(recorder.Log[1].([]byte), packets[1]) {
+			test.Fatal("not equal")
+		}
+	}()
+
+	group.Wait()
+}
+
+func TestConsecutiveReceive(test *testing.T) {
+	stream := []byte {
+		0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x01,
+		0x00, 0x00,
+		0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x05,
+		0x43, 0x00, 0x00, 0x00, 0x07,
+
+		0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x01,
+		0x00, 0x00,
+		0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x05,
+		0x43, 0x00, 0x00, 0x00, 0x08,
+	}
+	payloads := [][]byte {
+		[]byte { 0x43, 0x00, 0x00, 0x00, 0x07 },
+		[]byte { 0x43, 0x00, 0x00, 0x00, 0x08 },
+	}
+
+	var group sync.WaitGroup
+	group.Add(2)
+
+	// server
+	listener, err := net.Listen("tcp", "localhost:9999")
+	if err != nil { test.Fatal("SERVER", err) }
+	go func() {
+		defer group.Done()
+		defer listener.Close()
+		conn, err := listener.Accept()
+		if err != nil { test.Fatal("SERVER", err) }
+		defer conn.Close()
+		
+		a := AdaptA(conn, ServerSide)
+		trans, err := a.AcceptTrans()
+		if err != nil { test.Fatal("SERVER", err) }
+		index := 0
+		for {
+			method, data, err := trans.Receive()
+			if err != nil {
+				if !errors.Is(err, io.EOF) {
+					test.Fatal("SERVER", err)
+				}
+				break
+			}
+			test.Logf("SERVER GOT: M%04X %s", method, tu.HexBytes(data))
+			if index >= len(payloads) {
+				test.Fatalf(
+					"SERVER we weren't supposed to receive %d messages",
+					index + 1)
+			}
+			if method != 0 {
+				test.Fatal("SERVER", "method not equal")
+			}
+			if !slices.Equal(data, payloads[index]) {
+				test.Fatal("SERVER", "data not equal")
+			}
+			index ++
+		}
+		if index != len(payloads) {
+			test.Fatalf(
+				"SERVER we weren't supposed to receive %d messages",
+				index + 1)
+		}
+	}()
+
+	// client
+	go func() {
+		defer group.Done()
+		conn, err := net.Dial("tcp", "localhost:9999")
+		if err != nil { test.Fatal("CLIENT", err) }
+		defer conn.Close()
+		_, err = conn.Write(stream)
+		if err != nil { test.Fatal("CLIENT", err) }
+	}()
+
+	group.Wait()
+}
+
 func clientServerEnvironment(test *testing.T, clientFunc func(conn Conn), serverFunc func(conn Conn)) {
 	network := "tcp"
 	addr := "localhost:7959"