blob: 83c3829826ae6b7171f31c3f50d079b2eb90981a [file] [log] [blame]
/*
*
* Copyright 2014 gRPC authors.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*
*/
package transport
import (
"bytes"
"errors"
"fmt"
"net"
"runtime"
"strconv"
"sync"
"sync/atomic"
"golang.org/x/net/http2"
"golang.org/x/net/http2/hpack"
"google.golang.org/grpc/internal/grpclog"
"google.golang.org/grpc/internal/grpcutil"
"google.golang.org/grpc/status"
)
var updateHeaderTblSize = func(e *hpack.Encoder, v uint32) {
e.SetMaxDynamicTableSizeLimit(v)
}
type itemNode struct {
it any
next *itemNode
}
type itemList struct {
head *itemNode
tail *itemNode
}
func (il *itemList) enqueue(i any) {
n := &itemNode{it: i}
if il.tail == nil {
il.head, il.tail = n, n
return
}
il.tail.next = n
il.tail = n
}
// peek returns the first item in the list without removing it from the
// list.
func (il *itemList) peek() any {
return il.head.it
}
func (il *itemList) dequeue() any {
if il.head == nil {
return nil
}
i := il.head.it
il.head = il.head.next
if il.head == nil {
il.tail = nil
}
return i
}
func (il *itemList) dequeueAll() *itemNode {
h := il.head
il.head, il.tail = nil, nil
return h
}
func (il *itemList) isEmpty() bool {
return il.head == nil
}
// The following defines various control items which could flow through
// the control buffer of transport. They represent different aspects of
// control tasks, e.g., flow control, settings, streaming resetting, etc.
// maxQueuedTransportResponseFrames is the most queued "transport response"
// frames we will buffer before preventing new reads from occurring on the
// transport. These are control frames sent in response to client requests,
// such as RST_STREAM due to bad headers or settings acks.
const maxQueuedTransportResponseFrames = 50
type cbItem interface {
isTransportResponseFrame() bool
}
// registerStream is used to register an incoming stream with loopy writer.
type registerStream struct {
streamID uint32
wq *writeQuota
}
func (*registerStream) isTransportResponseFrame() bool { return false }
// headerFrame is also used to register stream on the client-side.
type headerFrame struct {
streamID uint32
hf []hpack.HeaderField
endStream bool // Valid on server side.
initStream func(uint32) error // Used only on the client side.
onWrite func()
wq *writeQuota // write quota for the stream created.
cleanup *cleanupStream // Valid on the server side.
onOrphaned func(error) // Valid on client-side
}
func (h *headerFrame) isTransportResponseFrame() bool {
return h.cleanup != nil && h.cleanup.rst // Results in a RST_STREAM
}
type cleanupStream struct {
streamID uint32
rst bool
rstCode http2.ErrCode
onWrite func()
}
func (c *cleanupStream) isTransportResponseFrame() bool { return c.rst } // Results in a RST_STREAM
type earlyAbortStream struct {
httpStatus uint32
streamID uint32
contentSubtype string
status *status.Status
rst bool
}
func (*earlyAbortStream) isTransportResponseFrame() bool { return false }
type dataFrame struct {
streamID uint32
endStream bool
h []byte
d []byte
// onEachWrite is called every time
// a part of d is written out.
onEachWrite func()
}
func (*dataFrame) isTransportResponseFrame() bool { return false }
type incomingWindowUpdate struct {
streamID uint32
increment uint32
}
func (*incomingWindowUpdate) isTransportResponseFrame() bool { return false }
type outgoingWindowUpdate struct {
streamID uint32
increment uint32
}
func (*outgoingWindowUpdate) isTransportResponseFrame() bool {
return false // window updates are throttled by thresholds
}
type incomingSettings struct {
ss []http2.Setting
}
func (*incomingSettings) isTransportResponseFrame() bool { return true } // Results in a settings ACK
type outgoingSettings struct {
ss []http2.Setting
}
func (*outgoingSettings) isTransportResponseFrame() bool { return false }
type incomingGoAway struct {
}
func (*incomingGoAway) isTransportResponseFrame() bool { return false }
type goAway struct {
code http2.ErrCode
debugData []byte
headsUp bool
closeConn error // if set, loopyWriter will exit, resulting in conn closure
}
func (*goAway) isTransportResponseFrame() bool { return false }
type ping struct {
ack bool
data [8]byte
}
func (*ping) isTransportResponseFrame() bool { return true }
type outFlowControlSizeRequest struct {
resp chan uint32
}
func (*outFlowControlSizeRequest) isTransportResponseFrame() bool { return false }
// closeConnection is an instruction to tell the loopy writer to flush the
// framer and exit, which will cause the transport's connection to be closed
// (by the client or server). The transport itself will close after the reader
// encounters the EOF caused by the connection closure.
type closeConnection struct{}
func (closeConnection) isTransportResponseFrame() bool { return false }
type outStreamState int
const (
active outStreamState = iota
empty
waitingOnStreamQuota
)
type outStream struct {
id uint32
state outStreamState
itl *itemList
bytesOutStanding int
wq *writeQuota
next *outStream
prev *outStream
}
func (s *outStream) deleteSelf() {
if s.prev != nil {
s.prev.next = s.next
}
if s.next != nil {
s.next.prev = s.prev
}
s.next, s.prev = nil, nil
}
type outStreamList struct {
// Following are sentinel objects that mark the
// beginning and end of the list. They do not
// contain any item lists. All valid objects are
// inserted in between them.
// This is needed so that an outStream object can
// deleteSelf() in O(1) time without knowing which
// list it belongs to.
head *outStream
tail *outStream
}
func newOutStreamList() *outStreamList {
head, tail := new(outStream), new(outStream)
head.next = tail
tail.prev = head
return &outStreamList{
head: head,
tail: tail,
}
}
func (l *outStreamList) enqueue(s *outStream) {
e := l.tail.prev
e.next = s
s.prev = e
s.next = l.tail
l.tail.prev = s
}
// remove from the beginning of the list.
func (l *outStreamList) dequeue() *outStream {
b := l.head.next
if b == l.tail {
return nil
}
b.deleteSelf()
return b
}
// controlBuffer is a way to pass information to loopy.
// Information is passed as specific struct types called control frames.
// A control frame not only represents data, messages or headers to be sent out
// but can also be used to instruct loopy to update its internal state.
// It shouldn't be confused with an HTTP2 frame, although some of the control frames
// like dataFrame and headerFrame do go out on wire as HTTP2 frames.
type controlBuffer struct {
ch chan struct{}
done <-chan struct{}
mu sync.Mutex
consumerWaiting bool
list *itemList
err error
// transportResponseFrames counts the number of queued items that represent
// the response of an action initiated by the peer. trfChan is created
// when transportResponseFrames >= maxQueuedTransportResponseFrames and is
// closed and nilled when transportResponseFrames drops below the
// threshold. Both fields are protected by mu.
transportResponseFrames int
trfChan atomic.Value // chan struct{}
}
func newControlBuffer(done <-chan struct{}) *controlBuffer {
return &controlBuffer{
ch: make(chan struct{}, 1),
list: &itemList{},
done: done,
}
}
// throttle blocks if there are too many incomingSettings/cleanupStreams in the
// controlbuf.
func (c *controlBuffer) throttle() {
ch, _ := c.trfChan.Load().(chan struct{})
if ch != nil {
select {
case <-ch:
case <-c.done:
}
}
}
func (c *controlBuffer) put(it cbItem) error {
_, err := c.executeAndPut(nil, it)
return err
}
func (c *controlBuffer) executeAndPut(f func(it any) bool, it cbItem) (bool, error) {
var wakeUp bool
c.mu.Lock()
if c.err != nil {
c.mu.Unlock()
return false, c.err
}
if f != nil {
if !f(it) { // f wasn't successful
c.mu.Unlock()
return false, nil
}
}
if c.consumerWaiting {
wakeUp = true
c.consumerWaiting = false
}
c.list.enqueue(it)
if it.isTransportResponseFrame() {
c.transportResponseFrames++
if c.transportResponseFrames == maxQueuedTransportResponseFrames {
// We are adding the frame that puts us over the threshold; create
// a throttling channel.
c.trfChan.Store(make(chan struct{}))
}
}
c.mu.Unlock()
if wakeUp {
select {
case c.ch <- struct{}{}:
default:
}
}
return true, nil
}
// Note argument f should never be nil.
func (c *controlBuffer) execute(f func(it any) bool, it any) (bool, error) {
c.mu.Lock()
if c.err != nil {
c.mu.Unlock()
return false, c.err
}
if !f(it) { // f wasn't successful
c.mu.Unlock()
return false, nil
}
c.mu.Unlock()
return true, nil
}
func (c *controlBuffer) get(block bool) (any, error) {
for {
c.mu.Lock()
if c.err != nil {
c.mu.Unlock()
return nil, c.err
}
if !c.list.isEmpty() {
h := c.list.dequeue().(cbItem)
if h.isTransportResponseFrame() {
if c.transportResponseFrames == maxQueuedTransportResponseFrames {
// We are removing the frame that put us over the
// threshold; close and clear the throttling channel.
ch := c.trfChan.Load().(chan struct{})
close(ch)
c.trfChan.Store((chan struct{})(nil))
}
c.transportResponseFrames--
}
c.mu.Unlock()
return h, nil
}
if !block {
c.mu.Unlock()
return nil, nil
}
c.consumerWaiting = true
c.mu.Unlock()
select {
case <-c.ch:
case <-c.done:
return nil, errors.New("transport closed by client")
}
}
}
func (c *controlBuffer) finish() {
c.mu.Lock()
if c.err != nil {
c.mu.Unlock()
return
}
c.err = ErrConnClosing
// There may be headers for streams in the control buffer.
// These streams need to be cleaned out since the transport
// is still not aware of these yet.
for head := c.list.dequeueAll(); head != nil; head = head.next {
hdr, ok := head.it.(*headerFrame)
if !ok {
continue
}
if hdr.onOrphaned != nil { // It will be nil on the server-side.
hdr.onOrphaned(ErrConnClosing)
}
}
// In case throttle() is currently in flight, it needs to be unblocked.
// Otherwise, the transport may not close, since the transport is closed by
// the reader encountering the connection error.
ch, _ := c.trfChan.Load().(chan struct{})
if ch != nil {
close(ch)
}
c.trfChan.Store((chan struct{})(nil))
c.mu.Unlock()
}
type side int
const (
clientSide side = iota
serverSide
)
// Loopy receives frames from the control buffer.
// Each frame is handled individually; most of the work done by loopy goes
// into handling data frames. Loopy maintains a queue of active streams, and each
// stream maintains a queue of data frames; as loopy receives data frames
// it gets added to the queue of the relevant stream.
// Loopy goes over this list of active streams by processing one node every iteration,
// thereby closely resemebling to a round-robin scheduling over all streams. While
// processing a stream, loopy writes out data bytes from this stream capped by the min
// of http2MaxFrameLen, connection-level flow control and stream-level flow control.
type loopyWriter struct {
side side
cbuf *controlBuffer
sendQuota uint32
oiws uint32 // outbound initial window size.
// estdStreams is map of all established streams that are not cleaned-up yet.
// On client-side, this is all streams whose headers were sent out.
// On server-side, this is all streams whose headers were received.
estdStreams map[uint32]*outStream // Established streams.
// activeStreams is a linked-list of all streams that have data to send and some
// stream-level flow control quota.
// Each of these streams internally have a list of data items(and perhaps trailers
// on the server-side) to be sent out.
activeStreams *outStreamList
framer *framer
hBuf *bytes.Buffer // The buffer for HPACK encoding.
hEnc *hpack.Encoder // HPACK encoder.
bdpEst *bdpEstimator
draining bool
conn net.Conn
logger *grpclog.PrefixLogger
// Side-specific handlers
ssGoAwayHandler func(*goAway) (bool, error)
}
func newLoopyWriter(s side, fr *framer, cbuf *controlBuffer, bdpEst *bdpEstimator, conn net.Conn, logger *grpclog.PrefixLogger) *loopyWriter {
var buf bytes.Buffer
l := &loopyWriter{
side: s,
cbuf: cbuf,
sendQuota: defaultWindowSize,
oiws: defaultWindowSize,
estdStreams: make(map[uint32]*outStream),
activeStreams: newOutStreamList(),
framer: fr,
hBuf: &buf,
hEnc: hpack.NewEncoder(&buf),
bdpEst: bdpEst,
conn: conn,
logger: logger,
}
return l
}
const minBatchSize = 1000
// run should be run in a separate goroutine.
// It reads control frames from controlBuf and processes them by:
// 1. Updating loopy's internal state, or/and
// 2. Writing out HTTP2 frames on the wire.
//
// Loopy keeps all active streams with data to send in a linked-list.
// All streams in the activeStreams linked-list must have both:
// 1. Data to send, and
// 2. Stream level flow control quota available.
//
// In each iteration of run loop, other than processing the incoming control
// frame, loopy calls processData, which processes one node from the
// activeStreams linked-list. This results in writing of HTTP2 frames into an
// underlying write buffer. When there's no more control frames to read from
// controlBuf, loopy flushes the write buffer. As an optimization, to increase
// the batch size for each flush, loopy yields the processor, once if the batch
// size is too low to give stream goroutines a chance to fill it up.
//
// Upon exiting, if the error causing the exit is not an I/O error, run()
// flushes the underlying connection. The connection is always left open to
// allow different closing behavior on the client and server.
func (l *loopyWriter) run() (err error) {
defer func() {
if l.logger.V(logLevel) {
l.logger.Infof("loopyWriter exiting with error: %v", err)
}
if !isIOError(err) {
l.framer.writer.Flush()
}
l.cbuf.finish()
}()
for {
it, err := l.cbuf.get(true)
if err != nil {
return err
}
if err = l.handle(it); err != nil {
return err
}
if _, err = l.processData(); err != nil {
return err
}
gosched := true
hasdata:
for {
it, err := l.cbuf.get(false)
if err != nil {
return err
}
if it != nil {
if err = l.handle(it); err != nil {
return err
}
if _, err = l.processData(); err != nil {
return err
}
continue hasdata
}
isEmpty, err := l.processData()
if err != nil {
return err
}
if !isEmpty {
continue hasdata
}
if gosched {
gosched = false
if l.framer.writer.offset < minBatchSize {
runtime.Gosched()
continue hasdata
}
}
l.framer.writer.Flush()
break hasdata
}
}
}
func (l *loopyWriter) outgoingWindowUpdateHandler(w *outgoingWindowUpdate) error {
return l.framer.fr.WriteWindowUpdate(w.streamID, w.increment)
}
func (l *loopyWriter) incomingWindowUpdateHandler(w *incomingWindowUpdate) {
// Otherwise update the quota.
if w.streamID == 0 {
l.sendQuota += w.increment
return
}
// Find the stream and update it.
if str, ok := l.estdStreams[w.streamID]; ok {
str.bytesOutStanding -= int(w.increment)
if strQuota := int(l.oiws) - str.bytesOutStanding; strQuota > 0 && str.state == waitingOnStreamQuota {
str.state = active
l.activeStreams.enqueue(str)
return
}
}
}
func (l *loopyWriter) outgoingSettingsHandler(s *outgoingSettings) error {
return l.framer.fr.WriteSettings(s.ss...)
}
func (l *loopyWriter) incomingSettingsHandler(s *incomingSettings) error {
l.applySettings(s.ss)
return l.framer.fr.WriteSettingsAck()
}
func (l *loopyWriter) registerStreamHandler(h *registerStream) {
str := &outStream{
id: h.streamID,
state: empty,
itl: &itemList{},
wq: h.wq,
}
l.estdStreams[h.streamID] = str
}
func (l *loopyWriter) headerHandler(h *headerFrame) error {
if l.side == serverSide {
str, ok := l.estdStreams[h.streamID]
if !ok {
if l.logger.V(logLevel) {
l.logger.Infof("Unrecognized streamID %d in loopyWriter", h.streamID)
}
return nil
}
// Case 1.A: Server is responding back with headers.
if !h.endStream {
return l.writeHeader(h.streamID, h.endStream, h.hf, h.onWrite)
}
// else: Case 1.B: Server wants to close stream.
if str.state != empty { // either active or waiting on stream quota.
// add it str's list of items.
str.itl.enqueue(h)
return nil
}
if err := l.writeHeader(h.streamID, h.endStream, h.hf, h.onWrite); err != nil {
return err
}
return l.cleanupStreamHandler(h.cleanup)
}
// Case 2: Client wants to originate stream.
str := &outStream{
id: h.streamID,
state: empty,
itl: &itemList{},
wq: h.wq,
}
return l.originateStream(str, h)
}
func (l *loopyWriter) originateStream(str *outStream, hdr *headerFrame) error {
// l.draining is set when handling GoAway. In which case, we want to avoid
// creating new streams.
if l.draining {
// TODO: provide a better error with the reason we are in draining.
hdr.onOrphaned(errStreamDrain)
return nil
}
if err := hdr.initStream(str.id); err != nil {
return err
}
if err := l.writeHeader(str.id, hdr.endStream, hdr.hf, hdr.onWrite); err != nil {
return err
}
l.estdStreams[str.id] = str
return nil
}
func (l *loopyWriter) writeHeader(streamID uint32, endStream bool, hf []hpack.HeaderField, onWrite func()) error {
if onWrite != nil {
onWrite()
}
l.hBuf.Reset()
for _, f := range hf {
if err := l.hEnc.WriteField(f); err != nil {
if l.logger.V(logLevel) {
l.logger.Warningf("Encountered error while encoding headers: %v", err)
}
}
}
var (
err error
endHeaders, first bool
)
first = true
for !endHeaders {
size := l.hBuf.Len()
if size > http2MaxFrameLen {
size = http2MaxFrameLen
} else {
endHeaders = true
}
if first {
first = false
err = l.framer.fr.WriteHeaders(http2.HeadersFrameParam{
StreamID: streamID,
BlockFragment: l.hBuf.Next(size),
EndStream: endStream,
EndHeaders: endHeaders,
})
} else {
err = l.framer.fr.WriteContinuation(
streamID,
endHeaders,
l.hBuf.Next(size),
)
}
if err != nil {
return err
}
}
return nil
}
func (l *loopyWriter) preprocessData(df *dataFrame) {
str, ok := l.estdStreams[df.streamID]
if !ok {
return
}
// If we got data for a stream it means that
// stream was originated and the headers were sent out.
str.itl.enqueue(df)
if str.state == empty {
str.state = active
l.activeStreams.enqueue(str)
}
}
func (l *loopyWriter) pingHandler(p *ping) error {
if !p.ack {
l.bdpEst.timesnap(p.data)
}
return l.framer.fr.WritePing(p.ack, p.data)
}
func (l *loopyWriter) outFlowControlSizeRequestHandler(o *outFlowControlSizeRequest) {
o.resp <- l.sendQuota
}
func (l *loopyWriter) cleanupStreamHandler(c *cleanupStream) error {
c.onWrite()
if str, ok := l.estdStreams[c.streamID]; ok {
// On the server side it could be a trailers-only response or
// a RST_STREAM before stream initialization thus the stream might
// not be established yet.
delete(l.estdStreams, c.streamID)
str.deleteSelf()
}
if c.rst { // If RST_STREAM needs to be sent.
if err := l.framer.fr.WriteRSTStream(c.streamID, c.rstCode); err != nil {
return err
}
}
if l.draining && len(l.estdStreams) == 0 {
// Flush and close the connection; we are done with it.
return errors.New("finished processing active streams while in draining mode")
}
return nil
}
func (l *loopyWriter) earlyAbortStreamHandler(eas *earlyAbortStream) error {
if l.side == clientSide {
return errors.New("earlyAbortStream not handled on client")
}
// In case the caller forgets to set the http status, default to 200.
if eas.httpStatus == 0 {
eas.httpStatus = 200
}
headerFields := []hpack.HeaderField{
{Name: ":status", Value: strconv.Itoa(int(eas.httpStatus))},
{Name: "content-type", Value: grpcutil.ContentType(eas.contentSubtype)},
{Name: "grpc-status", Value: strconv.Itoa(int(eas.status.Code()))},
{Name: "grpc-message", Value: encodeGrpcMessage(eas.status.Message())},
}
if err := l.writeHeader(eas.streamID, true, headerFields, nil); err != nil {
return err
}
if eas.rst {
if err := l.framer.fr.WriteRSTStream(eas.streamID, http2.ErrCodeNo); err != nil {
return err
}
}
return nil
}
func (l *loopyWriter) incomingGoAwayHandler(*incomingGoAway) error {
if l.side == clientSide {
l.draining = true
if len(l.estdStreams) == 0 {
// Flush and close the connection; we are done with it.
return errors.New("received GOAWAY with no active streams")
}
}
return nil
}
func (l *loopyWriter) goAwayHandler(g *goAway) error {
// Handling of outgoing GoAway is very specific to side.
if l.ssGoAwayHandler != nil {
draining, err := l.ssGoAwayHandler(g)
if err != nil {
return err
}
l.draining = draining
}
return nil
}
func (l *loopyWriter) handle(i any) error {
switch i := i.(type) {
case *incomingWindowUpdate:
l.incomingWindowUpdateHandler(i)
case *outgoingWindowUpdate:
return l.outgoingWindowUpdateHandler(i)
case *incomingSettings:
return l.incomingSettingsHandler(i)
case *outgoingSettings:
return l.outgoingSettingsHandler(i)
case *headerFrame:
return l.headerHandler(i)
case *registerStream:
l.registerStreamHandler(i)
case *cleanupStream:
return l.cleanupStreamHandler(i)
case *earlyAbortStream:
return l.earlyAbortStreamHandler(i)
case *incomingGoAway:
return l.incomingGoAwayHandler(i)
case *dataFrame:
l.preprocessData(i)
case *ping:
return l.pingHandler(i)
case *goAway:
return l.goAwayHandler(i)
case *outFlowControlSizeRequest:
l.outFlowControlSizeRequestHandler(i)
case closeConnection:
// Just return a non-I/O error and run() will flush and close the
// connection.
return ErrConnClosing
default:
return fmt.Errorf("transport: unknown control message type %T", i)
}
return nil
}
func (l *loopyWriter) applySettings(ss []http2.Setting) {
for _, s := range ss {
switch s.ID {
case http2.SettingInitialWindowSize:
o := l.oiws
l.oiws = s.Val
if o < l.oiws {
// If the new limit is greater make all depleted streams active.
for _, stream := range l.estdStreams {
if stream.state == waitingOnStreamQuota {
stream.state = active
l.activeStreams.enqueue(stream)
}
}
}
case http2.SettingHeaderTableSize:
updateHeaderTblSize(l.hEnc, s.Val)
}
}
}
// processData removes the first stream from active streams, writes out at most 16KB
// of its data and then puts it at the end of activeStreams if there's still more data
// to be sent and stream has some stream-level flow control.
func (l *loopyWriter) processData() (bool, error) {
if l.sendQuota == 0 {
return true, nil
}
str := l.activeStreams.dequeue() // Remove the first stream.
if str == nil {
return true, nil
}
dataItem := str.itl.peek().(*dataFrame) // Peek at the first data item this stream.
// A data item is represented by a dataFrame, since it later translates into
// multiple HTTP2 data frames.
// Every dataFrame has two buffers; h that keeps grpc-message header and d that is actual data.
// As an optimization to keep wire traffic low, data from d is copied to h to make as big as the
// maximum possible HTTP2 frame size.
if len(dataItem.h) == 0 && len(dataItem.d) == 0 { // Empty data frame
// Client sends out empty data frame with endStream = true
if err := l.framer.fr.WriteData(dataItem.streamID, dataItem.endStream, nil); err != nil {
return false, err
}
str.itl.dequeue() // remove the empty data item from stream
if str.itl.isEmpty() {
str.state = empty
} else if trailer, ok := str.itl.peek().(*headerFrame); ok { // the next item is trailers.
if err := l.writeHeader(trailer.streamID, trailer.endStream, trailer.hf, trailer.onWrite); err != nil {
return false, err
}
if err := l.cleanupStreamHandler(trailer.cleanup); err != nil {
return false, err
}
} else {
l.activeStreams.enqueue(str)
}
return false, nil
}
var (
buf []byte
)
// Figure out the maximum size we can send
maxSize := http2MaxFrameLen
if strQuota := int(l.oiws) - str.bytesOutStanding; strQuota <= 0 { // stream-level flow control.
str.state = waitingOnStreamQuota
return false, nil
} else if maxSize > strQuota {
maxSize = strQuota
}
if maxSize > int(l.sendQuota) { // connection-level flow control.
maxSize = int(l.sendQuota)
}
// Compute how much of the header and data we can send within quota and max frame length
hSize := min(maxSize, len(dataItem.h))
dSize := min(maxSize-hSize, len(dataItem.d))
if hSize != 0 {
if dSize == 0 {
buf = dataItem.h
} else {
// We can add some data to grpc message header to distribute bytes more equally across frames.
// Copy on the stack to avoid generating garbage
var localBuf [http2MaxFrameLen]byte
copy(localBuf[:hSize], dataItem.h)
copy(localBuf[hSize:], dataItem.d[:dSize])
buf = localBuf[:hSize+dSize]
}
} else {
buf = dataItem.d
}
size := hSize + dSize
// Now that outgoing flow controls are checked we can replenish str's write quota
str.wq.replenish(size)
var endStream bool
// If this is the last data message on this stream and all of it can be written in this iteration.
if dataItem.endStream && len(dataItem.h)+len(dataItem.d) <= size {
endStream = true
}
if dataItem.onEachWrite != nil {
dataItem.onEachWrite()
}
if err := l.framer.fr.WriteData(dataItem.streamID, endStream, buf[:size]); err != nil {
return false, err
}
str.bytesOutStanding += size
l.sendQuota -= uint32(size)
dataItem.h = dataItem.h[hSize:]
dataItem.d = dataItem.d[dSize:]
if len(dataItem.h) == 0 && len(dataItem.d) == 0 { // All the data from that message was written out.
str.itl.dequeue()
}
if str.itl.isEmpty() {
str.state = empty
} else if trailer, ok := str.itl.peek().(*headerFrame); ok { // The next item is trailers.
if err := l.writeHeader(trailer.streamID, trailer.endStream, trailer.hf, trailer.onWrite); err != nil {
return false, err
}
if err := l.cleanupStreamHandler(trailer.cleanup); err != nil {
return false, err
}
} else if int(l.oiws)-str.bytesOutStanding <= 0 { // Ran out of stream quota.
str.state = waitingOnStreamQuota
} else { // Otherwise add it back to the list of active streams.
l.activeStreams.enqueue(str)
}
return false, nil
}
func min(a, b int) int {
if a < b {
return a
}
return b
}