251 lines
7.6 KiB
Go
251 lines
7.6 KiB
Go
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// Copyright 2014 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package http2
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import "fmt"
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// WriteScheduler is the interface implemented by HTTP/2 write schedulers.
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// Methods are never called concurrently.
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type WriteScheduler interface {
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// OpenStream opens a new stream in the write scheduler.
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// It is illegal to call this with streamID=0 or with a streamID that is
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// already open -- the call may panic.
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OpenStream(streamID uint32, options OpenStreamOptions)
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// CloseStream closes a stream in the write scheduler. Any frames queued on
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// this stream should be discarded. It is illegal to call this on a stream
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// that is not open -- the call may panic.
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CloseStream(streamID uint32)
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// AdjustStream adjusts the priority of the given stream. This may be called
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// on a stream that has not yet been opened or has been closed. Note that
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// RFC 7540 allows PRIORITY frames to be sent on streams in any state. See:
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// https://tools.ietf.org/html/rfc7540#section-5.1
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AdjustStream(streamID uint32, priority PriorityParam)
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// Push queues a frame in the scheduler. In most cases, this will not be
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// called with wr.StreamID()!=0 unless that stream is currently open. The one
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// exception is RST_STREAM frames, which may be sent on idle or closed streams.
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Push(wr FrameWriteRequest)
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// Pop dequeues the next frame to write. Returns false if no frames can
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// be written. Frames with a given wr.StreamID() are Pop'd in the same
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// order they are Push'd, except RST_STREAM frames. No frames should be
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// discarded except by CloseStream.
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Pop() (wr FrameWriteRequest, ok bool)
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}
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// OpenStreamOptions specifies extra options for WriteScheduler.OpenStream.
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type OpenStreamOptions struct {
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// PusherID is zero if the stream was initiated by the client. Otherwise,
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// PusherID names the stream that pushed the newly opened stream.
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PusherID uint32
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}
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// FrameWriteRequest is a request to write a frame.
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type FrameWriteRequest struct {
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// write is the interface value that does the writing, once the
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// WriteScheduler has selected this frame to write. The write
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// functions are all defined in write.go.
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write writeFramer
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// stream is the stream on which this frame will be written.
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// nil for non-stream frames like PING and SETTINGS.
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// nil for RST_STREAM streams, which use the StreamError.StreamID field instead.
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stream *stream
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// done, if non-nil, must be a buffered channel with space for
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// 1 message and is sent the return value from write (or an
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// earlier error) when the frame has been written.
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done chan error
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}
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// StreamID returns the id of the stream this frame will be written to.
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// 0 is used for non-stream frames such as PING and SETTINGS.
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func (wr FrameWriteRequest) StreamID() uint32 {
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if wr.stream == nil {
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if se, ok := wr.write.(StreamError); ok {
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// (*serverConn).resetStream doesn't set
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// stream because it doesn't necessarily have
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// one. So special case this type of write
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// message.
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return se.StreamID
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}
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return 0
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}
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return wr.stream.id
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}
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// isControl reports whether wr is a control frame for MaxQueuedControlFrames
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// purposes. That includes non-stream frames and RST_STREAM frames.
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func (wr FrameWriteRequest) isControl() bool {
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return wr.stream == nil
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}
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// DataSize returns the number of flow control bytes that must be consumed
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// to write this entire frame. This is 0 for non-DATA frames.
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func (wr FrameWriteRequest) DataSize() int {
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if wd, ok := wr.write.(*writeData); ok {
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return len(wd.p)
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}
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return 0
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}
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// Consume consumes min(n, available) bytes from this frame, where available
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// is the number of flow control bytes available on the stream. Consume returns
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// 0, 1, or 2 frames, where the integer return value gives the number of frames
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// returned.
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//
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// If flow control prevents consuming any bytes, this returns (_, _, 0). If
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// the entire frame was consumed, this returns (wr, _, 1). Otherwise, this
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// returns (consumed, rest, 2), where 'consumed' contains the consumed bytes and
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// 'rest' contains the remaining bytes. The consumed bytes are deducted from the
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// underlying stream's flow control budget.
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func (wr FrameWriteRequest) Consume(n int32) (FrameWriteRequest, FrameWriteRequest, int) {
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var empty FrameWriteRequest
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// Non-DATA frames are always consumed whole.
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wd, ok := wr.write.(*writeData)
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if !ok || len(wd.p) == 0 {
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return wr, empty, 1
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}
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// Might need to split after applying limits.
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allowed := wr.stream.flow.available()
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if n < allowed {
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allowed = n
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}
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if wr.stream.sc.maxFrameSize < allowed {
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allowed = wr.stream.sc.maxFrameSize
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}
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if allowed <= 0 {
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return empty, empty, 0
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}
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if len(wd.p) > int(allowed) {
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wr.stream.flow.take(allowed)
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consumed := FrameWriteRequest{
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stream: wr.stream,
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write: &writeData{
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streamID: wd.streamID,
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p: wd.p[:allowed],
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// Even if the original had endStream set, there
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// are bytes remaining because len(wd.p) > allowed,
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// so we know endStream is false.
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endStream: false,
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},
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// Our caller is blocking on the final DATA frame, not
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// this intermediate frame, so no need to wait.
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done: nil,
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}
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rest := FrameWriteRequest{
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stream: wr.stream,
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write: &writeData{
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streamID: wd.streamID,
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p: wd.p[allowed:],
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endStream: wd.endStream,
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},
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done: wr.done,
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}
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return consumed, rest, 2
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}
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// The frame is consumed whole.
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// NB: This cast cannot overflow because allowed is <= math.MaxInt32.
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wr.stream.flow.take(int32(len(wd.p)))
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return wr, empty, 1
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}
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// String is for debugging only.
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func (wr FrameWriteRequest) String() string {
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var des string
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if s, ok := wr.write.(fmt.Stringer); ok {
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des = s.String()
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} else {
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des = fmt.Sprintf("%T", wr.write)
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}
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return fmt.Sprintf("[FrameWriteRequest stream=%d, ch=%v, writer=%v]", wr.StreamID(), wr.done != nil, des)
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}
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// replyToWriter sends err to wr.done and panics if the send must block
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// This does nothing if wr.done is nil.
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func (wr *FrameWriteRequest) replyToWriter(err error) {
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if wr.done == nil {
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return
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}
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select {
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case wr.done <- err:
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default:
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panic(fmt.Sprintf("unbuffered done channel passed in for type %T", wr.write))
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}
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wr.write = nil // prevent use (assume it's tainted after wr.done send)
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}
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// writeQueue is used by implementations of WriteScheduler.
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type writeQueue struct {
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s []FrameWriteRequest
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}
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func (q *writeQueue) empty() bool { return len(q.s) == 0 }
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func (q *writeQueue) push(wr FrameWriteRequest) {
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q.s = append(q.s, wr)
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}
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func (q *writeQueue) shift() FrameWriteRequest {
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if len(q.s) == 0 {
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panic("invalid use of queue")
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}
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wr := q.s[0]
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// TODO: less copy-happy queue.
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copy(q.s, q.s[1:])
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q.s[len(q.s)-1] = FrameWriteRequest{}
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q.s = q.s[:len(q.s)-1]
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return wr
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}
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// consume consumes up to n bytes from q.s[0]. If the frame is
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// entirely consumed, it is removed from the queue. If the frame
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// is partially consumed, the frame is kept with the consumed
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// bytes removed. Returns true iff any bytes were consumed.
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func (q *writeQueue) consume(n int32) (FrameWriteRequest, bool) {
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if len(q.s) == 0 {
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return FrameWriteRequest{}, false
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}
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consumed, rest, numresult := q.s[0].Consume(n)
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switch numresult {
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case 0:
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return FrameWriteRequest{}, false
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case 1:
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q.shift()
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case 2:
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q.s[0] = rest
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}
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return consumed, true
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}
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type writeQueuePool []*writeQueue
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// put inserts an unused writeQueue into the pool.
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func (p *writeQueuePool) put(q *writeQueue) {
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for i := range q.s {
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q.s[i] = FrameWriteRequest{}
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}
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q.s = q.s[:0]
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*p = append(*p, q)
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}
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// get returns an empty writeQueue.
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func (p *writeQueuePool) get() *writeQueue {
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ln := len(*p)
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if ln == 0 {
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return new(writeQueue)
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}
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x := ln - 1
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q := (*p)[x]
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(*p)[x] = nil
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*p = (*p)[:x]
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return q
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}
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