Scott Baker | eee8dd8 | 2019-09-24 12:52:34 -0700 | [diff] [blame^] | 1 | // 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 | |
| 5 | package http2 |
| 6 | |
| 7 | import ( |
| 8 | "errors" |
| 9 | "io" |
| 10 | "sync" |
| 11 | ) |
| 12 | |
| 13 | // pipe is a goroutine-safe io.Reader/io.Writer pair. It's like |
| 14 | // io.Pipe except there are no PipeReader/PipeWriter halves, and the |
| 15 | // underlying buffer is an interface. (io.Pipe is always unbuffered) |
| 16 | type pipe struct { |
| 17 | mu sync.Mutex |
| 18 | c sync.Cond // c.L lazily initialized to &p.mu |
| 19 | b pipeBuffer // nil when done reading |
| 20 | err error // read error once empty. non-nil means closed. |
| 21 | breakErr error // immediate read error (caller doesn't see rest of b) |
| 22 | donec chan struct{} // closed on error |
| 23 | readFn func() // optional code to run in Read before error |
| 24 | } |
| 25 | |
| 26 | type pipeBuffer interface { |
| 27 | Len() int |
| 28 | io.Writer |
| 29 | io.Reader |
| 30 | } |
| 31 | |
| 32 | func (p *pipe) Len() int { |
| 33 | p.mu.Lock() |
| 34 | defer p.mu.Unlock() |
| 35 | if p.b == nil { |
| 36 | return 0 |
| 37 | } |
| 38 | return p.b.Len() |
| 39 | } |
| 40 | |
| 41 | // Read waits until data is available and copies bytes |
| 42 | // from the buffer into p. |
| 43 | func (p *pipe) Read(d []byte) (n int, err error) { |
| 44 | p.mu.Lock() |
| 45 | defer p.mu.Unlock() |
| 46 | if p.c.L == nil { |
| 47 | p.c.L = &p.mu |
| 48 | } |
| 49 | for { |
| 50 | if p.breakErr != nil { |
| 51 | return 0, p.breakErr |
| 52 | } |
| 53 | if p.b != nil && p.b.Len() > 0 { |
| 54 | return p.b.Read(d) |
| 55 | } |
| 56 | if p.err != nil { |
| 57 | if p.readFn != nil { |
| 58 | p.readFn() // e.g. copy trailers |
| 59 | p.readFn = nil // not sticky like p.err |
| 60 | } |
| 61 | p.b = nil |
| 62 | return 0, p.err |
| 63 | } |
| 64 | p.c.Wait() |
| 65 | } |
| 66 | } |
| 67 | |
| 68 | var errClosedPipeWrite = errors.New("write on closed buffer") |
| 69 | |
| 70 | // Write copies bytes from p into the buffer and wakes a reader. |
| 71 | // It is an error to write more data than the buffer can hold. |
| 72 | func (p *pipe) Write(d []byte) (n int, err error) { |
| 73 | p.mu.Lock() |
| 74 | defer p.mu.Unlock() |
| 75 | if p.c.L == nil { |
| 76 | p.c.L = &p.mu |
| 77 | } |
| 78 | defer p.c.Signal() |
| 79 | if p.err != nil { |
| 80 | return 0, errClosedPipeWrite |
| 81 | } |
| 82 | if p.breakErr != nil { |
| 83 | return len(d), nil // discard when there is no reader |
| 84 | } |
| 85 | return p.b.Write(d) |
| 86 | } |
| 87 | |
| 88 | // CloseWithError causes the next Read (waking up a current blocked |
| 89 | // Read if needed) to return the provided err after all data has been |
| 90 | // read. |
| 91 | // |
| 92 | // The error must be non-nil. |
| 93 | func (p *pipe) CloseWithError(err error) { p.closeWithError(&p.err, err, nil) } |
| 94 | |
| 95 | // BreakWithError causes the next Read (waking up a current blocked |
| 96 | // Read if needed) to return the provided err immediately, without |
| 97 | // waiting for unread data. |
| 98 | func (p *pipe) BreakWithError(err error) { p.closeWithError(&p.breakErr, err, nil) } |
| 99 | |
| 100 | // closeWithErrorAndCode is like CloseWithError but also sets some code to run |
| 101 | // in the caller's goroutine before returning the error. |
| 102 | func (p *pipe) closeWithErrorAndCode(err error, fn func()) { p.closeWithError(&p.err, err, fn) } |
| 103 | |
| 104 | func (p *pipe) closeWithError(dst *error, err error, fn func()) { |
| 105 | if err == nil { |
| 106 | panic("err must be non-nil") |
| 107 | } |
| 108 | p.mu.Lock() |
| 109 | defer p.mu.Unlock() |
| 110 | if p.c.L == nil { |
| 111 | p.c.L = &p.mu |
| 112 | } |
| 113 | defer p.c.Signal() |
| 114 | if *dst != nil { |
| 115 | // Already been done. |
| 116 | return |
| 117 | } |
| 118 | p.readFn = fn |
| 119 | if dst == &p.breakErr { |
| 120 | p.b = nil |
| 121 | } |
| 122 | *dst = err |
| 123 | p.closeDoneLocked() |
| 124 | } |
| 125 | |
| 126 | // requires p.mu be held. |
| 127 | func (p *pipe) closeDoneLocked() { |
| 128 | if p.donec == nil { |
| 129 | return |
| 130 | } |
| 131 | // Close if unclosed. This isn't racy since we always |
| 132 | // hold p.mu while closing. |
| 133 | select { |
| 134 | case <-p.donec: |
| 135 | default: |
| 136 | close(p.donec) |
| 137 | } |
| 138 | } |
| 139 | |
| 140 | // Err returns the error (if any) first set by BreakWithError or CloseWithError. |
| 141 | func (p *pipe) Err() error { |
| 142 | p.mu.Lock() |
| 143 | defer p.mu.Unlock() |
| 144 | if p.breakErr != nil { |
| 145 | return p.breakErr |
| 146 | } |
| 147 | return p.err |
| 148 | } |
| 149 | |
| 150 | // Done returns a channel which is closed if and when this pipe is closed |
| 151 | // with CloseWithError. |
| 152 | func (p *pipe) Done() <-chan struct{} { |
| 153 | p.mu.Lock() |
| 154 | defer p.mu.Unlock() |
| 155 | if p.donec == nil { |
| 156 | p.donec = make(chan struct{}) |
| 157 | if p.err != nil || p.breakErr != nil { |
| 158 | // Already hit an error. |
| 159 | p.closeDoneLocked() |
| 160 | } |
| 161 | } |
| 162 | return p.donec |
| 163 | } |