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Zack Williamse940c7a2019-08-21 14:25:39 -07001// Copyright 2014 The Go Authors. All rights reserved.
2// Use of this source code is governed by a BSD-style
3// license that can be found in the LICENSE file.
4
5package http2
6
7import "fmt"
8
9// WriteScheduler is the interface implemented by HTTP/2 write schedulers.
10// Methods are never called concurrently.
11type WriteScheduler interface {
12 // OpenStream opens a new stream in the write scheduler.
13 // It is illegal to call this with streamID=0 or with a streamID that is
14 // already open -- the call may panic.
15 OpenStream(streamID uint32, options OpenStreamOptions)
16
17 // CloseStream closes a stream in the write scheduler. Any frames queued on
18 // this stream should be discarded. It is illegal to call this on a stream
19 // that is not open -- the call may panic.
20 CloseStream(streamID uint32)
21
22 // AdjustStream adjusts the priority of the given stream. This may be called
23 // on a stream that has not yet been opened or has been closed. Note that
24 // RFC 7540 allows PRIORITY frames to be sent on streams in any state. See:
25 // https://tools.ietf.org/html/rfc7540#section-5.1
26 AdjustStream(streamID uint32, priority PriorityParam)
27
28 // Push queues a frame in the scheduler. In most cases, this will not be
29 // called with wr.StreamID()!=0 unless that stream is currently open. The one
30 // exception is RST_STREAM frames, which may be sent on idle or closed streams.
31 Push(wr FrameWriteRequest)
32
33 // Pop dequeues the next frame to write. Returns false if no frames can
34 // be written. Frames with a given wr.StreamID() are Pop'd in the same
35 // order they are Push'd.
36 Pop() (wr FrameWriteRequest, ok bool)
37}
38
39// OpenStreamOptions specifies extra options for WriteScheduler.OpenStream.
40type OpenStreamOptions struct {
41 // PusherID is zero if the stream was initiated by the client. Otherwise,
42 // PusherID names the stream that pushed the newly opened stream.
43 PusherID uint32
44}
45
46// FrameWriteRequest is a request to write a frame.
47type FrameWriteRequest struct {
48 // write is the interface value that does the writing, once the
49 // WriteScheduler has selected this frame to write. The write
50 // functions are all defined in write.go.
51 write writeFramer
52
53 // stream is the stream on which this frame will be written.
54 // nil for non-stream frames like PING and SETTINGS.
55 stream *stream
56
57 // done, if non-nil, must be a buffered channel with space for
58 // 1 message and is sent the return value from write (or an
59 // earlier error) when the frame has been written.
60 done chan error
61}
62
63// StreamID returns the id of the stream this frame will be written to.
64// 0 is used for non-stream frames such as PING and SETTINGS.
65func (wr FrameWriteRequest) StreamID() uint32 {
66 if wr.stream == nil {
67 if se, ok := wr.write.(StreamError); ok {
68 // (*serverConn).resetStream doesn't set
69 // stream because it doesn't necessarily have
70 // one. So special case this type of write
71 // message.
72 return se.StreamID
73 }
74 return 0
75 }
76 return wr.stream.id
77}
78
79// DataSize returns the number of flow control bytes that must be consumed
80// to write this entire frame. This is 0 for non-DATA frames.
81func (wr FrameWriteRequest) DataSize() int {
82 if wd, ok := wr.write.(*writeData); ok {
83 return len(wd.p)
84 }
85 return 0
86}
87
88// Consume consumes min(n, available) bytes from this frame, where available
89// is the number of flow control bytes available on the stream. Consume returns
90// 0, 1, or 2 frames, where the integer return value gives the number of frames
91// returned.
92//
93// If flow control prevents consuming any bytes, this returns (_, _, 0). If
94// the entire frame was consumed, this returns (wr, _, 1). Otherwise, this
95// returns (consumed, rest, 2), where 'consumed' contains the consumed bytes and
96// 'rest' contains the remaining bytes. The consumed bytes are deducted from the
97// underlying stream's flow control budget.
98func (wr FrameWriteRequest) Consume(n int32) (FrameWriteRequest, FrameWriteRequest, int) {
99 var empty FrameWriteRequest
100
101 // Non-DATA frames are always consumed whole.
102 wd, ok := wr.write.(*writeData)
103 if !ok || len(wd.p) == 0 {
104 return wr, empty, 1
105 }
106
107 // Might need to split after applying limits.
108 allowed := wr.stream.flow.available()
109 if n < allowed {
110 allowed = n
111 }
112 if wr.stream.sc.maxFrameSize < allowed {
113 allowed = wr.stream.sc.maxFrameSize
114 }
115 if allowed <= 0 {
116 return empty, empty, 0
117 }
118 if len(wd.p) > int(allowed) {
119 wr.stream.flow.take(allowed)
120 consumed := FrameWriteRequest{
121 stream: wr.stream,
122 write: &writeData{
123 streamID: wd.streamID,
124 p: wd.p[:allowed],
125 // Even if the original had endStream set, there
126 // are bytes remaining because len(wd.p) > allowed,
127 // so we know endStream is false.
128 endStream: false,
129 },
130 // Our caller is blocking on the final DATA frame, not
131 // this intermediate frame, so no need to wait.
132 done: nil,
133 }
134 rest := FrameWriteRequest{
135 stream: wr.stream,
136 write: &writeData{
137 streamID: wd.streamID,
138 p: wd.p[allowed:],
139 endStream: wd.endStream,
140 },
141 done: wr.done,
142 }
143 return consumed, rest, 2
144 }
145
146 // The frame is consumed whole.
147 // NB: This cast cannot overflow because allowed is <= math.MaxInt32.
148 wr.stream.flow.take(int32(len(wd.p)))
149 return wr, empty, 1
150}
151
152// String is for debugging only.
153func (wr FrameWriteRequest) String() string {
154 var des string
155 if s, ok := wr.write.(fmt.Stringer); ok {
156 des = s.String()
157 } else {
158 des = fmt.Sprintf("%T", wr.write)
159 }
160 return fmt.Sprintf("[FrameWriteRequest stream=%d, ch=%v, writer=%v]", wr.StreamID(), wr.done != nil, des)
161}
162
163// replyToWriter sends err to wr.done and panics if the send must block
164// This does nothing if wr.done is nil.
165func (wr *FrameWriteRequest) replyToWriter(err error) {
166 if wr.done == nil {
167 return
168 }
169 select {
170 case wr.done <- err:
171 default:
172 panic(fmt.Sprintf("unbuffered done channel passed in for type %T", wr.write))
173 }
174 wr.write = nil // prevent use (assume it's tainted after wr.done send)
175}
176
177// writeQueue is used by implementations of WriteScheduler.
178type writeQueue struct {
179 s []FrameWriteRequest
180}
181
182func (q *writeQueue) empty() bool { return len(q.s) == 0 }
183
184func (q *writeQueue) push(wr FrameWriteRequest) {
185 q.s = append(q.s, wr)
186}
187
188func (q *writeQueue) shift() FrameWriteRequest {
189 if len(q.s) == 0 {
190 panic("invalid use of queue")
191 }
192 wr := q.s[0]
193 // TODO: less copy-happy queue.
194 copy(q.s, q.s[1:])
195 q.s[len(q.s)-1] = FrameWriteRequest{}
196 q.s = q.s[:len(q.s)-1]
197 return wr
198}
199
200// consume consumes up to n bytes from q.s[0]. If the frame is
201// entirely consumed, it is removed from the queue. If the frame
202// is partially consumed, the frame is kept with the consumed
203// bytes removed. Returns true iff any bytes were consumed.
204func (q *writeQueue) consume(n int32) (FrameWriteRequest, bool) {
205 if len(q.s) == 0 {
206 return FrameWriteRequest{}, false
207 }
208 consumed, rest, numresult := q.s[0].Consume(n)
209 switch numresult {
210 case 0:
211 return FrameWriteRequest{}, false
212 case 1:
213 q.shift()
214 case 2:
215 q.s[0] = rest
216 }
217 return consumed, true
218}
219
220type writeQueuePool []*writeQueue
221
222// put inserts an unused writeQueue into the pool.
223func (p *writeQueuePool) put(q *writeQueue) {
224 for i := range q.s {
225 q.s[i] = FrameWriteRequest{}
226 }
227 q.s = q.s[:0]
228 *p = append(*p, q)
229}
230
231// get returns an empty writeQueue.
232func (p *writeQueuePool) get() *writeQueue {
233 ln := len(*p)
234 if ln == 0 {
235 return new(writeQueue)
236 }
237 x := ln - 1
238 q := (*p)[x]
239 (*p)[x] = nil
240 *p = (*p)[:x]
241 return q
242}