After the week I've had, I deserve to make a commit like this lmao

metadaptb.go

@@ -0,0 +1,93 @@
+package hopp
+
+import "io"
+import "net"
+import "context"
+import "git.tebibyte.media/sashakoshka/hopp/tape"
+
+// B implements METADAPT-B over a multiplexed stream-oriented transport such as
+// QUIC.
+type b struct {
+	underlying MultiConn
+}
+
+// AdaptB returns a connection implementing METADAPT-B over a singular stream-
+// oriented transport such as TCP or UNIX domain stream sockets.
+func AdaptB(underlying MultiConn) Conn {
+	return &b {
+		underlying: underlying,
+	}
+}
+
+func (this *b) Close() error {
+	return this.underlying.Close()
+}
+
+func (this *b) OpenTrans() (Trans, error) {
+	stream, err := this.underlying.OpenStream()
+	if err != nil { return nil, err }
+	return transB { underlying: stream }, nil
+}
+
+func (this *b) AcceptTrans(ctx context.Context) (Trans, error) {
+	stream, err := this.underlying.AcceptStream(ctx)
+	if err != nil { return nil, err }
+	return transB { underlying: stream }, nil
+}
+
+type transB struct {
+	underlying Stream
+}
+
+func (trans transB) Close() error {
+	return trans.underlying.Close()
+}
+
+func (trans transB) ID() int64 {
+	return trans.underlying.ID()
+}
+
+func (trans transB) Send(method uint16, data []byte) error {
+	buffer := make([]byte, 4 + len(data))
+	tape.EncodeI16(buffer[:2], method)
+	length, ok := tape.U16CastSafe(len(data))
+	if !ok { return ErrPayloadTooLarge }
+	tape.EncodeI16(data[2:4], length)
+	copy(buffer[4:], data)
+	_, err := trans.underlying.Write(buffer)
+	return err
+}
+
+func (trans transB) Receive() (uint16, []byte, error) {
+	headerBuffer := [4]byte { }
+	_, err := io.ReadFull(trans.underlying, headerBuffer[:])
+	if err != nil { return 0, nil, err }
+	method, err := tape.DecodeI16[uint16](headerBuffer[:2])
+	if err != nil { return 0, nil, err }
+	length, err := tape.DecodeI16[uint16](headerBuffer[2:4])
+	if err != nil { return 0, nil, err }
+	payloadBuffer := make([]byte, int(length))
+	_, err = io.ReadFull(trans.underlying, payloadBuffer)
+	if err != nil { return 0, nil, err }
+	return method, payloadBuffer, nil
+}
+
+// MultiConn represens a multiplexed stream-oriented transport for use in [B].
+type MultiConn interface {
+	// See documentation for [net.Conn].
+	io.Closer
+	LocalAddr() net.Addr
+	RemoteAddr() net.Addr
+	// AcceptStream accepts the next incoming stream from the other party.
+	AcceptStream(context.Context) (Stream, error)
+	// OpenStream opens a new stream.
+	OpenStream() (Stream, error)
+}
+
+// Stream represents a single stream returned by a [MultiConn].
+type Stream interface {
+	// See documentation for [net.Conn].
+	io.ReadWriteCloser
+	// ID returns the stream ID
+	ID() int64
+}