Add pgproto3.Backend

backend.go

@@ -0,0 +1,74 @@
+package pgproto3
+
+import (
+	"encoding/binary"
+	"errors"
+	"fmt"
+	"io"
+
+	"github.com/jackc/pgx/chunkreader"
+)
+
+type Backend struct {
+	cr *chunkreader.ChunkReader
+	w  io.Writer
+
+	// Frontend message flyweights
+	bind            Bind
+	describe        Describe
+	execute         Execute
+	parse           Parse
+	passwordMessage PasswordMessage
+	query           Query
+	sync            Sync
+	terminate       Terminate
+}
+
+func NewBackend(r io.Reader, w io.Writer) (*Backend, error) {
+	cr := chunkreader.NewChunkReader(r)
+	return &Backend{cr: cr, w: w}, nil
+}
+
+func (b *Backend) Send(msg BackendMessage) error {
+	return errors.New("not implemented")
+}
+
+func (b *Backend) Receive() (FrontendMessage, error) {
+	header, err := b.cr.Next(5)
+	if err != nil {
+		return nil, err
+	}
+
+	msgType := header[0]
+	bodyLen := int(binary.BigEndian.Uint32(header[1:])) - 4
+
+	var msg FrontendMessage
+	switch msgType {
+	case 'B':
+		msg = &b.bind
+	case 'D':
+		msg = &b.describe
+	case 'E':
+		msg = &b.execute
+	case 'P':
+		msg = &b.parse
+	case 'p':
+		msg = &b.passwordMessage
+	case 'Q':
+		msg = &b.query
+	case 'S':
+		msg = &b.sync
+	case 'X':
+		msg = &b.terminate
+	default:
+		return nil, fmt.Errorf("unknown message type: %c", msgType)
+	}
+
+	msgBody, err := b.cr.Next(bodyLen)
+	if err != nil {
+		return nil, err
+	}
+
+	err = msg.Decode(msgBody)
+	return msg, err
+}