gtsocial-umbx

writesched.go (7839B)

---

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