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stream.go
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stream.go
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package zerocopy
import (
"bytes"
"context"
"io"
"sync"
)
// defaultBufferSize is the default buffer size to use
// when neither the reader nor the writer has buffer size requirements.
// It's the same default as io.Copy.
const defaultBufferSize = 32768
// ReaderInfo contains information about a reader.
type ReaderInfo struct {
Headroom Headroom
// MinPayloadBufferSizePerRead is the minimum size of payload buffer
// the ReadZeroCopy method requires for an unbuffered read.
//
// This is usually required by chunk-based protocols to be able to read
// whole chunks without needing internal caching.
MinPayloadBufferSizePerRead int
}
// Reader provides a stream interface for reading.
type Reader interface {
// ReaderInfo returns information about the reader.
ReaderInfo() ReaderInfo
// ReadZeroCopy uses b as buffer space to initiate a read operation.
//
// b must have at least [ReaderInfo.Headroom.Front] bytes before payloadBufStart
// and [ReaderInfo.Headroom.Rear] bytes after payloadBufStart + payloadBufLen.
//
// payloadBufLen must be at least [ReaderInfo.MinPayloadBufferSizePerRead].
//
// The read operation may use the whole space of b.
// The actual payload will be confined in [payloadBufStart, payloadBufLen).
//
// If no error occurs, the returned payload is b[payloadBufStart : payloadBufStart+payloadLen].
ReadZeroCopy(b []byte, payloadBufStart, payloadBufLen int) (payloadLen int, err error)
}
// WriterInfo contains information about a writer.
type WriterInfo struct {
Headroom Headroom
// MaxPayloadSizePerWrite is the maximum size of payload
// the WriteZeroCopy method can write at a time.
//
// This is usually required by chunk-based protocols to be able to write
// one chunk at a time without needing to break up the payload.
//
// 0 means no size limit.
MaxPayloadSizePerWrite int
}
// Writer provides a stream interface for writing.
type Writer interface {
// WriterInfo returns information about the writer.
WriterInfo() WriterInfo
// WriteZeroCopy uses b as buffer space to initiate a write operation.
//
// b must have at least [WriterInfo.Headroom.Front] bytes before payloadBufStart
// and [WriterInfo.Headroom.Rear] bytes after payloadBufStart + payloadBufLen.
//
// payloadLen must not exceed [WriterInfo.MaxPayloadSizePerWrite].
//
// The write operation may use the whole space of b.
WriteZeroCopy(b []byte, payloadStart, payloadLen int) (payloadWritten int, err error)
}
// DirectReader provides access to the underlying [io.Reader].
type DirectReader interface {
// DirectReader returns the underlying reader for direct reads.
DirectReader() io.Reader
}
// DirectWriter provides access to the underlying [io.Writer].
type DirectWriter interface {
// DirectWriter returns the underlying writer for direct writes.
DirectWriter() io.Writer
}
// Relay reads from r and writes to w using zero-copy methods.
// It returns the number of bytes transferred, and any error occurred during transfer.
func Relay(w Writer, r Reader) (n int64, err error) {
// Use direct read/write when possible.
if dr, ok := r.(DirectReader); ok {
if dw, ok := w.(DirectWriter); ok {
r := dr.DirectReader()
w := dw.DirectWriter()
return io.Copy(w, r)
}
}
// Process reader and writer info.
ri := r.ReaderInfo()
wi := w.WriterInfo()
headroom := MaxHeadroom(ri.Headroom, wi.Headroom)
// Check payload buffer size requirement compatibility.
if wi.MaxPayloadSizePerWrite > 0 && ri.MinPayloadBufferSizePerRead > wi.MaxPayloadSizePerWrite {
return relayFallback(w, r, headroom.Front, headroom.Rear, ri.MinPayloadBufferSizePerRead, wi.MaxPayloadSizePerWrite)
}
payloadBufSize := ri.MinPayloadBufferSizePerRead
if payloadBufSize == 0 {
payloadBufSize = wi.MaxPayloadSizePerWrite
if payloadBufSize == 0 {
payloadBufSize = defaultBufferSize
}
}
// Make buffer.
b := make([]byte, headroom.Front+payloadBufSize+headroom.Rear)
// Main relay loop.
for {
var payloadLen int
payloadLen, err = r.ReadZeroCopy(b, headroom.Front, payloadBufSize)
if payloadLen == 0 {
if err == io.EOF {
err = nil
}
return
}
payloadWritten, werr := w.WriteZeroCopy(b, headroom.Front, payloadLen)
n += int64(payloadWritten)
if werr != nil {
err = werr
return
}
if err != nil {
if err == io.EOF {
err = nil
}
return
}
}
}
// relayFallback uses copying to handle situations where the reader requires more payload buffer space than the writer can handle in one write call.
func relayFallback(w Writer, r Reader, frontHeadroom, rearHeadroom, readMaxPayloadSize, writeMaxPayloadSize int) (n int64, err error) {
br := make([]byte, frontHeadroom+readMaxPayloadSize+rearHeadroom)
bw := make([]byte, frontHeadroom+writeMaxPayloadSize+rearHeadroom)
for {
var payloadLen int
payloadLen, err = r.ReadZeroCopy(br, frontHeadroom, readMaxPayloadSize)
if payloadLen == 0 {
if err == io.EOF {
err = nil
}
return
}
// Short-circuit to avoid copying if payload can fit in one write.
if payloadLen <= writeMaxPayloadSize {
payloadWritten, werr := w.WriteZeroCopy(br, frontHeadroom, payloadLen)
n += int64(payloadWritten)
if werr != nil {
err = werr
}
if err != nil {
return
}
continue
}
// Loop until all of br[frontHeadroom : frontHeadroom+payloadLen] is written.
for i, j := 0, 0; i < payloadLen; i += j {
j = copy(bw[frontHeadroom:frontHeadroom+writeMaxPayloadSize], br[frontHeadroom+i:frontHeadroom+payloadLen])
payloadWritten, werr := w.WriteZeroCopy(bw, frontHeadroom, j)
n += int64(payloadWritten)
if werr != nil {
err = werr
return
}
}
if err != nil {
if err == io.EOF {
err = nil
}
return
}
}
}
// CloseRead provides the CloseRead method.
type CloseRead interface {
// CloseRead indicates to the underlying reader that no further reads will happen.
CloseRead() error
}
// CloseWrite provides the CloseWrite method.
type CloseWrite interface {
// CloseWrite indicates to the underlying writer that no further writes will happen.
CloseWrite() error
}
// ReadWriter provides a stream interface for reading and writing.
type ReadWriter interface {
Reader
Writer
CloseRead
CloseWrite
io.Closer
}
// TwoWayRelay relays data between left and right using zero-copy methods.
// It returns the number of bytes sent from left to right, from right to left,
// and any error occurred during transfer.
func TwoWayRelay(left, right ReadWriter) (nl2r, nr2l int64, err error) {
var l2rErr error
l2rDone := make(chan struct{})
go func() {
nl2r, l2rErr = Relay(right, left)
right.CloseWrite()
close(l2rDone)
}()
nr2l, err = Relay(left, right)
left.CloseWrite()
<-l2rDone
if l2rErr != nil {
err = l2rErr
}
return
}
// DirectReadWriteCloser extends io.ReadWriteCloser with CloseRead and CloseWrite.
type DirectReadWriteCloser interface {
io.ReadWriteCloser
CloseRead
CloseWrite
}
// DirectTwoWayRelay relays data between left and right using [io.Copy].
// It returns the number of bytes sent from left to right, from right to left,
// and any error occurred during transfer.
func DirectTwoWayRelay(left, right DirectReadWriteCloser) (nl2r, nr2l int64, err error) {
var l2rErr error
l2rDone := make(chan struct{})
go func() {
nl2r, l2rErr = io.Copy(right, left)
right.CloseWrite()
close(l2rDone)
}()
nr2l, err = io.Copy(left, right)
left.CloseWrite()
<-l2rDone
if l2rErr != nil {
err = l2rErr
}
return
}
// DirectReadWriteCloserOpener provides the Open method to open a [DirectReadWriteCloser].
type DirectReadWriteCloserOpener interface {
// Open opens a [DirectReadWriteCloser] with the specified initial payload.
Open(ctx context.Context, b []byte) (DirectReadWriteCloser, error)
}
// SimpleDirectReadWriteCloserOpener wraps a [DirectReadWriteCloser] for the Open method to return.
type SimpleDirectReadWriteCloserOpener struct {
DirectReadWriteCloser
}
// Open implements the DirectReadWriteCloserOpener Open method.
func (o *SimpleDirectReadWriteCloserOpener) Open(ctx context.Context, b []byte) (DirectReadWriteCloser, error) {
_, err := o.DirectReadWriteCloser.Write(b)
return o.DirectReadWriteCloser, err
}
// ReadWriterTestFunc tests the left and right ReadWriters by performing 2 writes
// on each ReadWriter and validating the read results.
//
// The left and right ReadWriters must be connected with a duplex pipe.
func ReadWriterTestFunc(t tester, l, r ReadWriter) {
defer r.Close()
defer l.Close()
var (
hello = []byte{'h', 'e', 'l', 'l', 'o'}
world = []byte{'w', 'o', 'r', 'l', 'd'}
)
lri := l.ReaderInfo()
lwi := l.WriterInfo()
lwmax := lwi.MaxPayloadSizePerWrite
if lwmax == 0 {
lwmax = 5
}
lrmin := lri.MinPayloadBufferSizePerRead
if lrmin == 0 {
lrmin = 5
}
lwbuf := make([]byte, lwi.Headroom.Front+lwmax+lwi.Headroom.Rear)
lrbuf := make([]byte, lri.Headroom.Front+lrmin+lri.Headroom.Rear)
rri := r.ReaderInfo()
rwi := r.WriterInfo()
rwmax := rwi.MaxPayloadSizePerWrite
if rwmax == 0 {
rwmax = 5
}
rrmin := rri.MinPayloadBufferSizePerRead
if rrmin == 0 {
rrmin = 5
}
rwbuf := make([]byte, rwi.Headroom.Front+rwmax+rwi.Headroom.Rear)
rrbuf := make([]byte, rri.Headroom.Front+rrmin+rri.Headroom.Rear)
var wg sync.WaitGroup
wg.Add(2)
// Start read goroutines.
go func() {
defer wg.Done()
pl, err := l.ReadZeroCopy(lrbuf, lri.Headroom.Front, lrmin)
if err != nil {
t.Error(err)
}
if pl != 5 {
t.Errorf("Expected payloadLen 5, got %d", pl)
}
p := lrbuf[lri.Headroom.Front : lri.Headroom.Front+pl]
if !bytes.Equal(p, world) {
t.Errorf("Expected payload %v, got %v", world, p)
}
pl, err = l.ReadZeroCopy(lrbuf, lri.Headroom.Front, lrmin)
if err != nil {
t.Error(err)
}
if pl != 5 {
t.Errorf("Expected payloadLen 5, got %d", pl)
}
p = lrbuf[lri.Headroom.Front : lri.Headroom.Front+pl]
if !bytes.Equal(p, hello) {
t.Errorf("Expected payload %v, got %v", hello, p)
}
pl, err = l.ReadZeroCopy(lrbuf, lri.Headroom.Front, lrmin)
if err != io.EOF {
t.Errorf("Expected io.EOF, got %v", err)
}
if pl != 0 {
t.Errorf("Expected payloadLen 0, got %v", pl)
}
}()
go func() {
defer wg.Done()
pl, err := r.ReadZeroCopy(rrbuf, rri.Headroom.Front, rrmin)
if err != nil {
t.Error(err)
}
if pl != 5 {
t.Errorf("Expected payloadLen 5, got %d", pl)
}
p := rrbuf[rri.Headroom.Front : rri.Headroom.Front+pl]
if !bytes.Equal(p, hello) {
t.Errorf("Expected payload %v, got %v", hello, p)
}
pl, err = r.ReadZeroCopy(rrbuf, rri.Headroom.Front, rrmin)
if err != nil {
t.Error(err)
}
if pl != 5 {
t.Errorf("Expected payloadLen 5, got %d", pl)
}
p = rrbuf[rri.Headroom.Front : rri.Headroom.Front+pl]
if !bytes.Equal(p, world) {
t.Errorf("Expected payload %v, got %v", world, p)
}
pl, err = r.ReadZeroCopy(rrbuf, rri.Headroom.Front, rrmin)
if err != io.EOF {
t.Errorf("Expected io.EOF, got %v", err)
}
if pl != 0 {
t.Errorf("Expected payloadLen 0, got %v", pl)
}
}()
// Write from left to right.
n := copy(lwbuf[lwi.Headroom.Front:], hello)
written, err := l.WriteZeroCopy(lwbuf, lwi.Headroom.Front, n)
if err != nil {
t.Error(err)
}
if written != n {
t.Errorf("Expected bytes written: %d, got %d", n, written)
}
n = copy(lwbuf[lwi.Headroom.Front:], world)
written, err = l.WriteZeroCopy(lwbuf, lwi.Headroom.Front, n)
if err != nil {
t.Error(err)
}
if written != n {
t.Errorf("Expected bytes written: %d, got %d", n, written)
}
err = l.CloseWrite()
if err != nil {
t.Error(err)
}
// Write from right to left.
n = copy(rwbuf[rwi.Headroom.Front:], world)
written, err = r.WriteZeroCopy(rwbuf, rwi.Headroom.Front, n)
if err != nil {
t.Error(err)
}
if written != n {
t.Errorf("Expected bytes written: %d, got %d", n, written)
}
n = copy(rwbuf[rwi.Headroom.Front:], hello)
written, err = r.WriteZeroCopy(rwbuf, rwi.Headroom.Front, n)
if err != nil {
t.Error(err)
}
if written != n {
t.Errorf("Expected bytes written: %d, got %d", n, written)
}
err = r.CloseWrite()
if err != nil {
t.Error(err)
}
wg.Wait()
}
// CopyReadWriter wraps a ReadWriter and provides the io.ReadWriter Read and Write methods
// by copying from and to internal buffers and using the zerocopy methods on them.
//
// The io.ReaderFrom ReadFrom method is implemented using the internal write buffer without copying.
type CopyReadWriter struct {
ReadWriter
readHeadroom Headroom
writeHeadroom Headroom
readBuf []byte
readBufStart int
readBufLength int
writeBuf []byte
}
func NewCopyReadWriter(rw ReadWriter) *CopyReadWriter {
ri := rw.ReaderInfo()
wi := rw.WriterInfo()
readBufSize := ri.MinPayloadBufferSizePerRead
if readBufSize == 0 {
readBufSize = defaultBufferSize
}
writeBufSize := wi.MaxPayloadSizePerWrite
if writeBufSize == 0 {
writeBufSize = defaultBufferSize
}
return &CopyReadWriter{
ReadWriter: rw,
readHeadroom: ri.Headroom,
writeHeadroom: wi.Headroom,
readBuf: make([]byte, ri.Headroom.Front+readBufSize+ri.Headroom.Front),
writeBuf: make([]byte, wi.Headroom.Front+writeBufSize+wi.Headroom.Rear),
}
}
// Read implements the io.Reader Read method.
func (rw *CopyReadWriter) Read(b []byte) (n int, err error) {
if rw.readBufLength == 0 {
rw.readBufStart = rw.readHeadroom.Front
rw.readBufLength = len(rw.readBuf) - rw.readHeadroom.Front - rw.readHeadroom.Rear
rw.readBufLength, err = rw.ReadWriter.ReadZeroCopy(rw.readBuf, rw.readBufStart, rw.readBufLength)
if err != nil {
return
}
}
n = copy(b, rw.readBuf[rw.readBufStart:rw.readBufStart+rw.readBufLength])
rw.readBufStart += n
rw.readBufLength -= n
return n, nil
}
// Write implements the io.Writer Write method.
func (rw *CopyReadWriter) Write(b []byte) (n int, err error) {
payloadBuf := rw.writeBuf[rw.writeHeadroom.Front : len(rw.writeBuf)-rw.writeHeadroom.Rear]
for n < len(b) {
payloadLength := copy(payloadBuf, b[n:])
var payloadWritten int
payloadWritten, err = rw.ReadWriter.WriteZeroCopy(rw.writeBuf, rw.writeHeadroom.Front, payloadLength)
n += payloadWritten
if err != nil {
return
}
}
return
}
// ReadFrom implements the io.ReaderFrom ReadFrom method.
func (rw *CopyReadWriter) ReadFrom(r io.Reader) (n int64, err error) {
for {
nr, err := r.Read(rw.writeBuf[rw.writeHeadroom.Front : len(rw.writeBuf)-rw.writeHeadroom.Rear])
n += int64(nr)
switch err {
case nil:
case io.EOF:
return n, nil
default:
return n, err
}
_, err = rw.ReadWriter.WriteZeroCopy(rw.writeBuf, rw.writeHeadroom.Front, nr)
if err != nil {
return n, err
}
}
}
func CopyWriteOnce(w Writer, b []byte) (n int, err error) {
wi := w.WriterInfo()
writeBufSize := wi.MaxPayloadSizePerWrite
if writeBufSize == 0 {
writeBufSize = defaultBufferSize
}
if writeBufSize > len(b) {
writeBufSize = len(b)
}
writeBuf := make([]byte, wi.Headroom.Front+writeBufSize+wi.Headroom.Rear)
payloadBuf := writeBuf[wi.Headroom.Front : wi.Headroom.Front+writeBufSize]
for n < len(b) {
payloadLength := copy(payloadBuf, b[n:])
var payloadWritten int
payloadWritten, err = w.WriteZeroCopy(writeBuf, wi.Headroom.Front, payloadLength)
n += payloadWritten
if err != nil {
return
}
}
return
}