Initial Commit

streampb/stream.go

@@ -0,0 +1,89 @@
+package streampb
+
+import (
+	"encoding/binary"
+	"io"
+
+	"github.com/gogo/protobuf/proto"
+	"github.com/pkg/errors"
+)
+
+const (
+	// prefixSize is the number of bytes we preallocate for storing
+	// our big endian lenth prefix buffer.
+	prefixSize = 8
+)
+
+// NewEncoder creates a streaming protobuf encoder.
+func NewEncoder(w io.Writer) *Encoder {
+	return &Encoder{w: w, prefixBuf: make([]byte, prefixSize)}
+}
+
+// Encoder wraps an underlying io.Writer and allows you to stream
+// proto encodings on it.
+type Encoder struct {
+	w         io.Writer
+	prefixBuf []byte
+}
+
+// Encode takes any proto.Message and streams it to the underlying writer.
+// Messages are framed with a length prefix.
+func (e *Encoder) Encode(msg proto.Message) error {
+	buf, err := proto.Marshal(msg)
+	if err != nil {
+		return err
+	}
+	binary.BigEndian.PutUint64(e.prefixBuf, uint64(len(buf)))
+
+	if _, err := e.w.Write(e.prefixBuf); err != nil {
+		return errors.Wrap(err, "failed writing length prefix")
+	}
+
+	_, err = e.w.Write(buf)
+	return errors.Wrap(err, "failed writing marshaled data")
+}
+
+// NewDecoder creates a streaming protobuf decoder.
+func NewDecoder(r io.Reader) *Decoder {
+	return &Decoder{
+		r:         r,
+		prefixBuf: make([]byte, prefixSize),
+	}
+}
+
+// Decoder wraps an underlying io.Reader and allows you to stream
+// proto decodings on it.
+type Decoder struct {
+	r         io.Reader
+	prefixBuf []byte
+}
+
+// Decode takes a proto.Message and unmarshals the next payload in the
+// underlying io.Reader. It returns an EOF when it's done.
+func (d *Decoder) Decode(v proto.Message) error {
+	_, err := io.ReadFull(d.r, d.prefixBuf)
+	if err != nil {
+		return err
+	}
+
+	n := binary.BigEndian.Uint64(d.prefixBuf)
+
+	buf := make([]byte, n)
+
+	idx := uint64(0)
+	for idx < n {
+		m, err := d.r.Read(buf[idx:n])
+		if err != nil {
+			return errors.Wrap(translateError(err), "failed reading marshaled data")
+		}
+		idx += uint64(m)
+	}
+	return proto.Unmarshal(buf[:n], v)
+}
+
+func translateError(err error) error {
+	if err == io.EOF {
+		return io.ErrUnexpectedEOF
+	}
+	return err
+}