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package ttrpc
import (
"bufio"
"context"
"encoding/binary"
"io"
"net"
"sync"
"github.com/pkg/errors"
"google.golang.org/grpc/codes"
"google.golang.org/grpc/status"
)
const (
messageHeaderLength = 10
messageLengthMax = 4 << 20
)
type messageType uint8
const (
messageTypeRequest messageType = 0x1
messageTypeResponse messageType = 0x2
)
// messageHeader represents the fixed-length message header of 10 bytes sent
// with every request.
type messageHeader struct {
Length uint32 // length excluding this header. b[:4]
StreamID uint32 // identifies which request stream message is a part of. b[4:8]
Type messageType // message type b[8]
Flags uint8 // reserved b[9]
}
func readMessageHeader(p []byte, r io.Reader) (messageHeader, error) {
_, err := io.ReadFull(r, p[:messageHeaderLength])
if err != nil {
return messageHeader{}, err
}
return messageHeader{
Length: binary.BigEndian.Uint32(p[:4]),
StreamID: binary.BigEndian.Uint32(p[4:8]),
Type: messageType(p[8]),
Flags: p[9],
}, nil
}
func writeMessageHeader(w io.Writer, p []byte, mh messageHeader) error {
binary.BigEndian.PutUint32(p[:4], mh.Length)
binary.BigEndian.PutUint32(p[4:8], mh.StreamID)
p[8] = byte(mh.Type)
p[9] = mh.Flags
_, err := w.Write(p[:])
return err
}
var buffers sync.Pool
type channel struct {
conn net.Conn
bw *bufio.Writer
br *bufio.Reader
hrbuf [messageHeaderLength]byte // avoid alloc when reading header
hwbuf [messageHeaderLength]byte
}
func newChannel(conn net.Conn) *channel {
return &channel{
conn: conn,
bw: bufio.NewWriter(conn),
br: bufio.NewReader(conn),
}
}
// recv a message from the channel. The returned buffer contains the message.
//
// If a valid grpc status is returned, the message header
// returned will be valid and caller should send that along to
// the correct consumer. The bytes on the underlying channel
// will be discarded.
func (ch *channel) recv(ctx context.Context) (messageHeader, []byte, error) {
mh, err := readMessageHeader(ch.hrbuf[:], ch.br)
if err != nil {
return messageHeader{}, nil, err
}
if mh.Length > uint32(messageLengthMax) {
if _, err := ch.br.Discard(int(mh.Length)); err != nil {
return mh, nil, errors.Wrapf(err, "failed to discard after receiving oversized message")
}
return mh, nil, status.Errorf(codes.ResourceExhausted, "message length %v exceed maximum message size of %v", mh.Length, messageLengthMax)
}
p := ch.getmbuf(int(mh.Length))
if _, err := io.ReadFull(ch.br, p); err != nil {
return messageHeader{}, nil, errors.Wrapf(err, "failed reading message")
}
return mh, p, nil
}
func (ch *channel) send(ctx context.Context, streamID uint32, t messageType, p []byte) error {
if err := writeMessageHeader(ch.bw, ch.hwbuf[:], messageHeader{Length: uint32(len(p)), StreamID: streamID, Type: t}); err != nil {
return err
}
_, err := ch.bw.Write(p)
if err != nil {
return err
}
return ch.bw.Flush()
}
func (ch *channel) getmbuf(size int) []byte {
// we can't use the standard New method on pool because we want to allocate
// based on size.
b, ok := buffers.Get().(*[]byte)
if !ok || cap(*b) < size {
// TODO(stevvooe): It may be better to allocate these in fixed length
// buckets to reduce fragmentation but its not clear that would help
// with performance. An ilogb approach or similar would work well.
bb := make([]byte, size)
b = &bb
} else {
*b = (*b)[:size]
}
return *b
}
func (ch *channel) putmbuf(p []byte) {
buffers.Put(&p)
}
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