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streamer.go
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streamer.go
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// Copyright (c) 2017 Badoo Tech. All rights reserved.
// Use of this source code is governed by a MIT license
// that can be found in the LICENSE file
// BUG(denkoren@corp.badoo.com): on kqueue systems (like MacOS X, for example) file_streamer can't stream named pipes.
// 'kqueue' can't notify about FIFO file events, so fsNotify just does not provide any signals on data writes to a FIFO
// file.
// Package file_streamer provides a file streaming service that streams all data from a file into a buffered writer.
//
// It uses fsNotify for detecting changes in files, reads that changes (new data) and writes them into a buffered writer.
package file_streamer
import (
"errors"
"fmt"
"github.com/fsnotify/fsnotify"
"io"
"log"
"os"
"sync"
"time"
)
const (
stateStopped uint8 = 1 << iota
stateStarting
stateRunning
stateStopping
)
type empty struct{}
// Maps watched file to the list of channels (readers) to be notified about changes detection.
type subscriptions map[string]map[newDataChan]empty
// Streamer is a main package instance that provides streaming service to all Listeners
type Streamer struct {
mu sync.Mutex
logger *log.Logger
fsNotify *fsnotify.Watcher
changedFileNames chan string
subscriptions subscriptions
subscribe chan *Listener
unsubscribe chan *Listener
threads sync.WaitGroup
state uint8
}
var (
// ErrNotRunning is an error returned when action can't be finished because Streamer service is not running yet
// Streamer.Start() was not called
ErrNotRunning = errors.New("streamer is not running")
// ErrRunning is an error returned when action can't be finished because Streamer service is in running state
ErrRunning = errors.New("streamer is running")
// ErrListenerClosed is an error returned when Listener can't be used for streaming because it is already closed.
ErrListenerClosed = errors.New("listener is closed")
)
// New creates new instance of file streamer. Usually, you don't need more than one instance of Streamer.
func New(logger *log.Logger) *Streamer {
if logger == nil {
logger = log.New(os.Stdout, "", log.LstdFlags)
}
s := &Streamer{
logger: logger,
subscriptions: make(subscriptions),
subscribe: make(chan *Listener),
unsubscribe: make(chan *Listener),
state: stateStopped,
}
return s
}
// read all fs notifications and send changed file names to eventsRouter()
func (s *Streamer) sendChangeEvents() {
defer close(s.changedFileNames)
defer s.threads.Done()
for {
fileEvent, isOpen := <-s.fsNotify.Events
if !isOpen {
// We're not listening file changes any more (watcher is closed and no events left in pool)
return
}
s.changedFileNames <- fileEvent.Name
}
}
// We have to read notify errors in a separate goroutine to make sure all data is read from fsNotify.Errors,
// fsnotify.Watcher.Errors channel is unbuffered and that may cause memory leaks.
func (s *Streamer) logNotifyErrors() {
defer s.threads.Done()
for {
notificationError, isOpen := <-s.fsNotify.Errors
if !isOpen {
// We're not listening file changes any more (watcher is closed and no errors left in pool)
return
}
s.logger.Printf("FS notifications error: %s", notificationError)
}
}
// eventsRouter will notify all subscribed channels about changes in particular file.
// subscribeListener adds listener's 'new data' notification channel to subscriptions list.
func (s *Streamer) subscribeListener(listener *Listener) {
// if it's a first subscription for the given file - prepare subscriptions map and start to listen for file events
if _, subscriptionExists := s.subscriptions[listener.file.Name()]; !subscriptionExists {
s.subscriptions[listener.file.Name()] = make(map[newDataChan]empty)
err := s.fsNotify.Add(listener.file.Name())
if err != nil {
s.logger.Printf("Failed to register new fsNotify listener for file '%s': %v", listener.file.Name(), err)
}
}
// subscribe
s.logger.Printf("New listener for '%s' file", listener.file.Name())
s.subscriptions[listener.file.Name()][listener.newDataNotifications] = empty{}
// force initial file read after subscription
if len(listener.newDataNotifications) < cap(listener.newDataNotifications) {
listener.newDataNotifications <- newDataEvent{}
}
}
// unsubscribeListener removes listener's 'new data' notification channel from subscriptions list.
func (s *Streamer) unsubscribeListener(listener *Listener) {
// unsubscribe
delete(s.subscriptions[listener.file.Name()], listener.newDataNotifications)
s.logger.Printf("File '%s' listener unsubscribed", listener.file.Name())
// when it was a last listener for the given file - stop listening and forget about file
if len(s.subscriptions[listener.file.Name()]) == 0 {
delete(s.subscriptions, listener.file.Name())
err := s.fsNotify.Remove(listener.file.Name())
if err != nil {
s.logger.Printf("Failed stop listening fsNotify events of file '%s': %v", listener.file.Name(), err)
}
}
}
// eventsRouter receives filesystem events from fsNotify and sends 'new data' notifications to all subscribers.
func (s *Streamer) eventsRouter() {
defer s.threads.Done()
routeEvents:
for {
select {
case listener := <-s.subscribe:
s.subscribeListener(listener)
case listener := <-s.unsubscribe:
s.unsubscribeListener(listener)
case filename, isOpen := <-s.changedFileNames:
if !isOpen {
break routeEvents
}
if _, exists := s.subscriptions[filename]; !exists || len(s.subscriptions[filename]) == 0 {
s.logger.Printf("No listeners subscribed for '%s' file events", filename)
continue
}
for toNotify := range s.subscriptions[filename] {
if len(toNotify) < cap(toNotify) {
toNotify <- newDataEvent{}
}
}
}
}
// Wait for all subscriptions to be finished
for len(s.subscriptions) != 0 {
select {
case listener := <-s.subscribe:
s.subscribeListener(listener)
case listener := <-s.unsubscribe:
s.unsubscribeListener(listener)
}
}
}
// SetLogger changes main Streamer logger
func (s *Streamer) SetLogger(l *log.Logger) {
s.logger = l
}
// initialize Streamer instance before each .Start()
func (s *Streamer) init() error {
watcher, err := fsnotify.NewWatcher()
if err != nil {
return err
}
s.fsNotify = watcher // we closed it during Stop() process
s.changedFileNames = make(chan string, 1000) // we closed it during Stop() process
return nil
}
// Start streamer.
//
// Makes Streamer's .StreamTo() available for Listeners. After return from this function Streamer is able to stream
// files into buffered writers.
//
// Thread safe.
func (s *Streamer) Start() error {
s.mu.Lock()
if s.state != stateStopped {
s.mu.Unlock()
return ErrRunning
}
s.state = stateStarting
s.mu.Unlock()
err := s.init()
if err != nil {
return err
}
// Attach to fs notification system
s.threads.Add(2)
go s.sendChangeEvents()
go s.logNotifyErrors()
// Start streaming service
s.threads.Add(1)
go s.eventsRouter()
s.mu.Lock()
s.state = stateRunning
s.mu.Unlock()
return nil
}
// Stop streamer.
//
// Prevents new streams creation, finishes all existing subscriptions and stops all internal goroutines.
//
// Thread safe.
func (s *Streamer) Stop() error {
s.mu.Lock()
if s.state != stateRunning {
s.mu.Unlock()
return ErrNotRunning
}
s.state = stateStopping
s.mu.Unlock()
s.fsNotify.Close() // trigger stop chain: fsNotify -> (sendChangeEvents,logNotifyErrors) -> eventsRouter
s.threads.Wait()
s.mu.Lock()
s.state = stateStopped
s.mu.Unlock()
return nil
}
// IsRunning is a thread-safe way to check Streamer is in 'Running' state.
//
// 'Running' state means Streamer reads fsNotify events on files, reads data from files and streams it to
// buffered writers.
func (s *Streamer) IsRunning() bool {
s.mu.Lock()
isRunning := s.state == stateRunning
s.mu.Unlock()
return isRunning
}
// StreamTo makes streamer to start data streaming for Listener.
// StreamTo will block until <listener> is closed (listener.Close() is called) or file is not modified more than
// <timeout> time.
//
// Zero value ('0') as <timeout> disables timeout at all, making Streamer to stream data until Listener is closed
// (by .Close() call)
//
// returns ErrNotRunning when Streamer is not ready for streaming data (was not Start()'ed, or was Stop()'ed)
//
// returns ErrListenerClosed when listener is not ready for accepting data.
//
func (s *Streamer) StreamTo(listener *Listener, timeout time.Duration) error {
if !s.IsRunning() {
return ErrNotRunning
}
if listener.IsClosed() {
return ErrListenerClosed
}
s.subscribe <- listener
defer func() { s.unsubscribe <- listener }()
listenerBufSize := listener.writeDataTo.Available() + listener.writeDataTo.Buffered()
buf := make([]byte, listenerBufSize)
timeoutTimer := getTimer(timeout)
for {
select {
case _, isOpen := <-listener.newDataNotifications:
if !isOpen {
return nil
}
listener.file.Seek(0, 1) // re-set current position to be able to read to EOF again
for {
n, err := listener.file.Read(buf)
if err == io.EOF {
break
}
if err != nil {
fmt.Fprintf(listener.writeDataTo, "Could not read file: %s", err.Error())
_ = listener.writeDataTo.Flush()
s.logger.Printf("File '%s' read error: %v", listener.file.Name(), err)
return err
}
_, err = listener.writeDataTo.Write(buf[:n])
if err != nil {
s.logger.Printf("Failed to send file '%s' contents to client: %v", listener.file.Name(), err)
return err
}
}
// Force all data to be sent to client
err := listener.writeDataTo.Flush()
if err != nil {
s.logger.Printf("Failed to send file '%s' contents to client: %v", listener.file.Name(), err)
return err
}
// Is file exist? If not - just stop streaming
if _, err = os.Stat(listener.file.Name()); err != nil {
return nil
}
case <-timeoutTimer.C:
// Just stop streaming after <timeout> of inactivity (no changes in file)
return nil
}
if timeout != 0 {
timeoutTimer.Reset(timeout)
}
}
}