| 1 | // Copyright 2020 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 jsonrpc2 |
| 6 | |
| 7 | import ( |
| 8 | "context" |
| 9 | "fmt" |
| 10 | "io" |
| 11 | "runtime" |
| 12 | "sync" |
| 13 | "sync/atomic" |
| 14 | "time" |
| 15 | ) |
| 16 | |
| 17 | // Listener is implemented by protocols to accept new inbound connections. |
| 18 | type Listener interface { |
| 19 | // Accept accepts an inbound connection to a server. |
| 20 | // It blocks until either an inbound connection is made, or the listener is closed. |
| 21 | Accept(context.Context) (io.ReadWriteCloser, error) |
| 22 | |
| 23 | // Close closes the listener. |
| 24 | // Any blocked Accept or Dial operations will unblock and return errors. |
| 25 | Close() error |
| 26 | |
| 27 | // Dialer returns a dialer that can be used to connect to this listener |
| 28 | // locally. |
| 29 | // If a listener does not implement this it will return nil. |
| 30 | Dialer() Dialer |
| 31 | } |
| 32 | |
| 33 | // Dialer is used by clients to dial a server. |
| 34 | type Dialer interface { |
| 35 | // Dial returns a new communication byte stream to a listening server. |
| 36 | Dial(ctx context.Context) (io.ReadWriteCloser, error) |
| 37 | } |
| 38 | |
| 39 | // Server is a running server that is accepting incoming connections. |
| 40 | type Server struct { |
| 41 | listener Listener |
| 42 | binder Binder |
| 43 | async *async |
| 44 | |
| 45 | shutdownOnce sync.Once |
| 46 | closing int32 // atomic: set to nonzero when Shutdown is called |
| 47 | } |
| 48 | |
| 49 | // Dial uses the dialer to make a new connection, wraps the returned |
| 50 | // reader and writer using the framer to make a stream, and then builds |
| 51 | // a connection on top of that stream using the binder. |
| 52 | // |
| 53 | // The returned Connection will operate independently using the Preempter and/or |
| 54 | // Handler provided by the Binder, and will release its own resources when the |
| 55 | // connection is broken, but the caller may Close it earlier to stop accepting |
| 56 | // (or sending) new requests. |
| 57 | func Dial(ctx context.Context, dialer Dialer, binder Binder) (*Connection, error) { |
| 58 | // dial a server |
| 59 | rwc, err := dialer.Dial(ctx) |
| 60 | if err != nil { |
| 61 | return nil, err |
| 62 | } |
| 63 | return newConnection(ctx, rwc, binder, nil), nil |
| 64 | } |
| 65 | |
| 66 | // NewServer starts a new server listening for incoming connections and returns |
| 67 | // it. |
| 68 | // This returns a fully running and connected server, it does not block on |
| 69 | // the listener. |
| 70 | // You can call Wait to block on the server, or Shutdown to get the sever to |
| 71 | // terminate gracefully. |
| 72 | // To notice incoming connections, use an intercepting Binder. |
| 73 | func NewServer(ctx context.Context, listener Listener, binder Binder) *Server { |
| 74 | server := &Server{ |
| 75 | listener: listener, |
| 76 | binder: binder, |
| 77 | async: newAsync(), |
| 78 | } |
| 79 | go server.run(ctx) |
| 80 | return server |
| 81 | } |
| 82 | |
| 83 | // Wait returns only when the server has shut down. |
| 84 | func (s *Server) Wait() error { |
| 85 | return s.async.wait() |
| 86 | } |
| 87 | |
| 88 | // Shutdown informs the server to stop accepting new connections. |
| 89 | func (s *Server) Shutdown() { |
| 90 | s.shutdownOnce.Do(func() { |
| 91 | atomic.StoreInt32(&s.closing, 1) |
| 92 | s.listener.Close() |
| 93 | }) |
| 94 | } |
| 95 | |
| 96 | // run accepts incoming connections from the listener, |
| 97 | // If IdleTimeout is non-zero, run exits after there are no clients for this |
| 98 | // duration, otherwise it exits only on error. |
| 99 | func (s *Server) run(ctx context.Context) { |
| 100 | defer s.async.done() |
| 101 | |
| 102 | var activeConns sync.WaitGroup |
| 103 | for { |
| 104 | rwc, err := s.listener.Accept(ctx) |
| 105 | if err != nil { |
| 106 | // Only Shutdown closes the listener. If we get an error after Shutdown is |
| 107 | // called, assume that that was the cause and don't report the error; |
| 108 | // otherwise, report the error in case it is unexpected. |
| 109 | if atomic.LoadInt32(&s.closing) == 0 { |
| 110 | s.async.setError(err) |
| 111 | } |
| 112 | // We are done generating new connections for good. |
| 113 | break |
| 114 | } |
| 115 | |
| 116 | // A new inbound connection. |
| 117 | activeConns.Add(1) |
| 118 | _ = newConnection(ctx, rwc, s.binder, activeConns.Done) // unregisters itself when done |
| 119 | } |
| 120 | activeConns.Wait() |
| 121 | } |
| 122 | |
| 123 | // NewIdleListener wraps a listener with an idle timeout. |
| 124 | // |
| 125 | // When there are no active connections for at least the timeout duration, |
| 126 | // calls to Accept will fail with ErrIdleTimeout. |
| 127 | // |
| 128 | // A connection is considered inactive as soon as its Close method is called. |
| 129 | func NewIdleListener(timeout time.Duration, wrap Listener) Listener { |
| 130 | l := &idleListener{ |
| 131 | wrapped: wrap, |
| 132 | timeout: timeout, |
| 133 | active: make(chan int, 1), |
| 134 | timedOut: make(chan struct{}), |
| 135 | idleTimer: make(chan *time.Timer, 1), |
| 136 | } |
| 137 | l.idleTimer <- time.AfterFunc(l.timeout, l.timerExpired) |
| 138 | return l |
| 139 | } |
| 140 | |
| 141 | type idleListener struct { |
| 142 | wrapped Listener |
| 143 | timeout time.Duration |
| 144 | |
| 145 | // Only one of these channels is receivable at any given time. |
| 146 | active chan int // count of active connections; closed when Close is called if not timed out |
| 147 | timedOut chan struct{} // closed when the idle timer expires |
| 148 | idleTimer chan *time.Timer // holds the timer only when idle |
| 149 | } |
| 150 | |
| 151 | // Accept accepts an incoming connection. |
| 152 | // |
| 153 | // If an incoming connection is accepted concurrent to the listener being closed |
| 154 | // due to idleness, the new connection is immediately closed. |
| 155 | func (l *idleListener) Accept(ctx context.Context) (io.ReadWriteCloser, error) { |
| 156 | rwc, err := l.wrapped.Accept(ctx) |
| 157 | |
| 158 | select { |
| 159 | case n, ok := <-l.active: |
| 160 | if err != nil { |
| 161 | if ok { |
| 162 | l.active <- n |
| 163 | } |
| 164 | return nil, err |
| 165 | } |
| 166 | if ok { |
| 167 | l.active <- n + 1 |
| 168 | } else { |
| 169 | // l.wrapped.Close Close has been called, but Accept returned a |
| 170 | // connection. This race can occur with concurrent Accept and Close calls |
| 171 | // with any net.Listener, and it is benign: since the listener was closed |
| 172 | // explicitly, it can't have also timed out. |
| 173 | } |
| 174 | return l.newConn(rwc), nil |
| 175 | |
| 176 | case <-l.timedOut: |
| 177 | if err == nil { |
| 178 | // Keeping the connection open would leave the listener simultaneously |
| 179 | // active and closed due to idleness, which would be contradictory and |
| 180 | // confusing. Close the connection and pretend that it never happened. |
| 181 | rwc.Close() |
| 182 | } else { |
| 183 | // In theory the timeout could have raced with an unrelated error return |
| 184 | // from Accept. However, ErrIdleTimeout is arguably still valid (since we |
| 185 | // would have closed due to the timeout independent of the error), and the |
| 186 | // harm from returning a spurious ErrIdleTimeout is negliglible anyway. |
| 187 | } |
| 188 | return nil, ErrIdleTimeout |
| 189 | |
| 190 | case timer := <-l.idleTimer: |
| 191 | if err != nil { |
| 192 | // The idle timer doesn't run until it receives itself from the idleTimer |
| 193 | // channel, so it can't have called l.wrapped.Close yet and thus err can't |
| 194 | // be ErrIdleTimeout. Leave the idle timer as it was and return whatever |
| 195 | // error we got. |
| 196 | l.idleTimer <- timer |
| 197 | return nil, err |
| 198 | } |
| 199 | |
| 200 | if !timer.Stop() { |
| 201 | // Failed to stop the timer — the timer goroutine is in the process of |
| 202 | // firing. Send the timer back to the timer goroutine so that it can |
| 203 | // safely close the timedOut channel, and then wait for the listener to |
| 204 | // actually be closed before we return ErrIdleTimeout. |
| 205 | l.idleTimer <- timer |
| 206 | rwc.Close() |
| 207 | <-l.timedOut |
| 208 | return nil, ErrIdleTimeout |
| 209 | } |
| 210 | |
| 211 | l.active <- 1 |
| 212 | return l.newConn(rwc), nil |
| 213 | } |
| 214 | } |
| 215 | |
| 216 | func (l *idleListener) Close() error { |
| 217 | select { |
| 218 | case _, ok := <-l.active: |
| 219 | if ok { |
| 220 | close(l.active) |
| 221 | } |
| 222 | |
| 223 | case <-l.timedOut: |
| 224 | // Already closed by the timer; take care not to double-close if the caller |
| 225 | // only explicitly invokes this Close method once, since the io.Closer |
| 226 | // interface explicitly leaves doubled Close calls undefined. |
| 227 | return ErrIdleTimeout |
| 228 | |
| 229 | case timer := <-l.idleTimer: |
| 230 | if !timer.Stop() { |
| 231 | // Couldn't stop the timer. It shouldn't take long to run, so just wait |
| 232 | // (so that the Listener is guaranteed to be closed before we return) |
| 233 | // and pretend that this call happened afterward. |
| 234 | // That way we won't leak any timers or goroutines when Close returns. |
| 235 | l.idleTimer <- timer |
| 236 | <-l.timedOut |
| 237 | return ErrIdleTimeout |
| 238 | } |
| 239 | close(l.active) |
| 240 | } |
| 241 | |
| 242 | return l.wrapped.Close() |
| 243 | } |
| 244 | |
| 245 | func (l *idleListener) Dialer() Dialer { |
| 246 | return l.wrapped.Dialer() |
| 247 | } |
| 248 | |
| 249 | func (l *idleListener) timerExpired() { |
| 250 | select { |
| 251 | case n, ok := <-l.active: |
| 252 | if ok { |
| 253 | panic(fmt.Sprintf("jsonrpc2: idleListener idle timer fired with %d connections still active", n)) |
| 254 | } else { |
| 255 | panic("jsonrpc2: Close finished with idle timer still running") |
| 256 | } |
| 257 | |
| 258 | case <-l.timedOut: |
| 259 | panic("jsonrpc2: idleListener idle timer fired more than once") |
| 260 | |
| 261 | case <-l.idleTimer: |
| 262 | // The timer for this very call! |
| 263 | } |
| 264 | |
| 265 | // Close the Listener with all channels still blocked to ensure that this call |
| 266 | // to l.wrapped.Close doesn't race with the one in l.Close. |
| 267 | defer close(l.timedOut) |
| 268 | l.wrapped.Close() |
| 269 | } |
| 270 | |
| 271 | func (l *idleListener) connClosed() { |
| 272 | select { |
| 273 | case n, ok := <-l.active: |
| 274 | if !ok { |
| 275 | // l is already closed, so it can't close due to idleness, |
| 276 | // and we don't need to track the number of active connections any more. |
| 277 | return |
| 278 | } |
| 279 | n-- |
| 280 | if n == 0 { |
| 281 | l.idleTimer <- time.AfterFunc(l.timeout, l.timerExpired) |
| 282 | } else { |
| 283 | l.active <- n |
| 284 | } |
| 285 | |
| 286 | case <-l.timedOut: |
| 287 | panic("jsonrpc2: idleListener idle timer fired before last active connection was closed") |
| 288 | |
| 289 | case <-l.idleTimer: |
| 290 | panic("jsonrpc2: idleListener idle timer active before last active connection was closed") |
| 291 | } |
| 292 | } |
| 293 | |
| 294 | type idleListenerConn struct { |
| 295 | wrapped io.ReadWriteCloser |
| 296 | l *idleListener |
| 297 | closeOnce sync.Once |
| 298 | } |
| 299 | |
| 300 | func (l *idleListener) newConn(rwc io.ReadWriteCloser) *idleListenerConn { |
| 301 | c := &idleListenerConn{ |
| 302 | wrapped: rwc, |
| 303 | l: l, |
| 304 | } |
| 305 | |
| 306 | // A caller that forgets to call Close may disrupt the idleListener's |
| 307 | // accounting, even though the file descriptor for the underlying connection |
| 308 | // may eventually be garbage-collected anyway. |
| 309 | // |
| 310 | // Set a (best-effort) finalizer to verify that a Close call always occurs. |
| 311 | // (We will clear the finalizer explicitly in Close.) |
| 312 | runtime.SetFinalizer(c, func(c *idleListenerConn) { |
| 313 | panic("jsonrpc2: IdleListener connection became unreachable without a call to Close") |
| 314 | }) |
| 315 | |
| 316 | return c |
| 317 | } |
| 318 | |
| 319 | func (c *idleListenerConn) Read(p []byte) (int, error) { return c.wrapped.Read(p) } |
| 320 | func (c *idleListenerConn) Write(p []byte) (int, error) { return c.wrapped.Write(p) } |
| 321 | |
| 322 | func (c *idleListenerConn) Close() error { |
| 323 | defer c.closeOnce.Do(func() { |
| 324 | c.l.connClosed() |
| 325 | runtime.SetFinalizer(c, nil) |
| 326 | }) |
| 327 | return c.wrapped.Close() |
| 328 | } |
| 329 |
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