120 lines
3.1 KiB
Go
120 lines
3.1 KiB
Go
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// Copyright 2013 The GoMPD Authors. All rights reserved.
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// Use of this source code is governed by the MIT
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// license that can be found in the LICENSE file.
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package mpd
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// Watcher represents a MPD client connection that can be watched for events.
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type Watcher struct {
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conn *Client // client connection to MPD
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exit chan bool // channel used to ask loop to terminate
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done chan bool // channel indicating loop has terminated
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names chan []string // channel to set new subsystems to watch
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Event chan string // event channel
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Error chan error // error channel
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}
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// NewWatcher connects to MPD server and watches for changes in subsystems
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// names. If no subsystem is specified, all changes are reported.
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//
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// See http://www.musicpd.org/doc/protocol/command_reference.html#command_idle
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// for valid subsystem names.
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func NewWatcher(net, addr, passwd string, names ...string) (w *Watcher, err error) {
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conn, err := DialAuthenticated(net, addr, passwd)
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if err != nil {
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return
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}
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w = &Watcher{
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conn: conn,
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Event: make(chan string),
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Error: make(chan error),
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done: make(chan bool),
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// Buffer channels to avoid race conditions with noIdle
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names: make(chan []string, 1),
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exit: make(chan bool, 1),
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}
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go w.watch(names...)
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return
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}
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func (w *Watcher) watch(names ...string) {
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defer w.closeChans()
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// We can block in two places: idle and sending on Event/Error channels.
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// We need to check w.exit and w.names after each.
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for {
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changed, err := w.conn.idle(names...)
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select {
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case <-w.exit:
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// If Close interrupted idle with a noidle, and we don't
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// exit now, we will block trying to send on Event/Error.
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return
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case names = <-w.names:
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// Received new subsystems to watch. Ignore results.
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changed = []string{}
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err = nil
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default: // continue
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}
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switch {
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case err != nil:
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w.Error <- err
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default:
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for _, name := range changed {
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w.Event <- name
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}
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}
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select {
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case <-w.exit:
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// If Close unblocks us from sending on Event/Error channels,
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// we should exit now because noidle might be sent out
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// before we get to idle.
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return
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case names = <-w.names:
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// If method Subsystems unblocks us from sending on Event/Error
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// channels, the next call to idle should be on the new names.
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default: // continue
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}
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}
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}
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func (w *Watcher) closeChans() {
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close(w.Event)
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close(w.Error)
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close(w.names)
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close(w.exit)
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close(w.done)
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}
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func (w *Watcher) consume() {
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for {
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select {
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case <-w.Event:
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case <-w.Error:
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default:
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return
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}
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}
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}
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// Subsystems interrupts watching current subsystems, consumes all
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// outstanding values from Event and Error channels, and then
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// changes the subsystems to watch for to names.
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func (w *Watcher) Subsystems(names ...string) {
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w.names <- names
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w.consume()
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w.conn.noIdle()
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}
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// Close closes Event and Error channels, and the connection to MPD server.
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func (w *Watcher) Close() error {
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w.exit <- true
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w.consume()
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w.conn.noIdle()
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<-w.done // wait for idle to finish and channels to close
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// At this point, watch goroutine has ended,
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// so it's safe to close connection.
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return w.conn.Close()
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}
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