Automatically update remote files on change

This extends the automatic watching of graph definition files across the
remote SSH boundary.

configwatch.go

@@ -24,9 +24,64 @@ import (
 	"math"
 	"path"
 	"strings"
+	"sync"
 	"syscall"
 )
 
+// ConfigWatcher returns events on a channel anytime one of its files events.
+type ConfigWatcher struct {
+	ch        chan string
+	wg        sync.WaitGroup
+	closechan chan struct{}
+}
+
+// NewConfigWatcher creates a new ConfigWatcher struct.
+func NewConfigWatcher() *ConfigWatcher {
+	return &ConfigWatcher{
+		ch:        make(chan string),
+		closechan: make(chan struct{}),
+	}
+}
+
+// The Add method adds a new file path to watch for events on.
+func (obj *ConfigWatcher) Add(file string) {
+	obj.wg.Add(1)
+	go func() {
+		defer obj.wg.Done()
+		ch := ConfigWatch(file)
+		for {
+			select {
+			case <-ch:
+				obj.ch <- file
+				continue
+			case <-obj.closechan:
+				return
+			}
+		}
+	}()
+}
+
+// Events returns a channel to listen on for file events. It closes when it is
+// emptied after the Close() method is called. You can test for closure with the
+// f, more := <-obj.Events() pattern.
+func (obj *ConfigWatcher) Events() chan string {
+	return obj.ch
+}
+
+// Close shuts down the ConfigWatcher object. It closes the Events channel after
+// all the currently pending events have been emptied.
+func (obj *ConfigWatcher) Close() {
+	if obj.ch == nil {
+		return
+	}
+	close(obj.closechan)
+	obj.wg.Wait() // wait until everyone is done sending on obj.ch
+	//obj.ch <- "" // send finished message
+	close(obj.ch)
+	obj.ch = nil
+}
+
+// ConfigWatch writes on the channel everytime an event is seen for the path.
 // XXX: it would be great if we could reuse code between this and the file resource
 // XXX: patch this to submit it as part of go-fsnotify if they're interested...
 func ConfigWatch(file string) chan bool {
@@ -51,8 +106,9 @@ func ConfigWatch(file string) chan bool {
 			if current == "" { // the empty string top is the root dir ("/")
 				current = "/"
 			}
+			if DEBUG {
 				log.Printf("Watching: %v", current) // attempting to watch...
-
+			}
 			// initialize in the loop so that we can reset on rm-ed handles
 			err = watcher.Add(current)
 			if err != nil {
@@ -97,7 +153,10 @@ func ConfigWatch(file string) chan bool {
 				// if we have what we wanted, awesome, send an event...
 				if event.Name == safename {
 					//log.Println("Event!")
+					// TODO: filter out some of the events, is Write a sufficient minimum?
+					if event.Op&fsnotify.Write == fsnotify.Write {
 						send = true
+					}
 
 					// file removed, move the watch upwards
 					if deltaDepth >= 0 && (event.Op&fsnotify.Remove == fsnotify.Remove) {

main.go

@@ -262,12 +262,23 @@ func run(c *cli.Context) error {
 		}
 	}()
 
+	configWatcher := NewConfigWatcher()
+	events := configWatcher.Events()
+	if !c.Bool("no-watch") {
+		for _, f := range c.StringSlice("remote") { // add all the files...
+			configWatcher.Add(f)
+		}
+	} else {
+		events = nil // signal that no-watch is true
+	}
+
 	// build remotes struct for remote ssh
 	remotes := NewRemotes(
 		EmbdEtcd.LocalhostClientURLs().StringSlice(),
 		[]string{DefaultClientURL},
 		noop,
 		c.StringSlice("remote"), // list of files
+		events,                  // watch for file changes
 		cConns,
 		c.Bool("allow-interactive"),
 		c.String("ssh-priv-id-rsa"),
@@ -288,6 +299,7 @@ func run(c *cli.Context) error {
 
 	log.Println("Destroy...")
 
+	configWatcher.Close() // stop sending file changes to remotes
 	remotes.Exit()        // tell all the remote connections to shutdown; waits!
 
 	G.Exit() // tell all the children to exit

remote.go

@@ -87,6 +87,7 @@ type SSH struct {
 	clientURLs []string // list of urls where the local server is listening
 	remoteURLs []string // list of urls where the remote server connects to
 	noop       bool     // whether to run the remote process with --noop
+	noWatch    bool     // whether to run the remote process with --no-watch
 
 	caching bool   // whether to try and cache the copy of the binary
 	prefix  string // location we're allowed to put data on the remote server
@@ -241,7 +242,7 @@ func (obj *SSH) Sftp() error {
 	// TODO: should future versions use torrent for this copy and updates?
 	obj.filepath = path.Join(obj.remotewd, path.Base(obj.file)) // same filename
 	log.Println("Remote: Copying graph definition...")
-	_, err = obj.SftpCopy(obj.file, obj.filepath)
+	_, err = obj.SftpGraphCopy()
 	if err != nil {
 		// TODO: cleanup
 		return fmt.Errorf("Error copying graph: %s", err)
@@ -250,6 +251,14 @@ func (obj *SSH) Sftp() error {
 	return nil
 }
 
+// SftpGraphCopy is a helper function used for re-copying the graph definition.
+func (obj *SSH) SftpGraphCopy() (int64, error) {
+	if obj.filepath == "" {
+		return -1, fmt.Errorf("Sftp session isn't ready yet!")
+	}
+	return obj.SftpCopy(obj.file, obj.filepath)
+}
+
 // SftpCopy is a simple helper function that runs a local -> remote sftp copy.
 func (obj *SSH) SftpCopy(src, dst string) (int64, error) {
 	if obj.sftp == nil {
@@ -473,6 +482,9 @@ func (obj *SSH) Exec() error {
 	if obj.noop {
 		args = append(args, "--noop")
 	}
+	if obj.noWatch {
+		args = append(args, "--no-watch")
+	}
 
 	// TODO: add --converged-timeout support for group
 
@@ -648,6 +660,7 @@ type Remotes struct {
 	remoteURLs   []string // list of urls where the remote server connects to
 	noop         bool     // whether to run in noop mode
 	remotes      []string // list of remote graph definition files to run
+	fileWatch    chan string
 	cConns       uint16 // number of concurrent ssh connections, zero means unlimited
 	interactive  bool   // allow interactive prompting
 	sshPrivIdRsa string // path to ~/.ssh/id_rsa
@@ -662,12 +675,13 @@ type Remotes struct {
 }
 
 // The NewRemotes function builds a Remotes struct.
-func NewRemotes(clientURLs, remoteURLs []string, noop bool, remotes []string, cConns uint16, interactive bool, sshPrivIdRsa string, caching bool, prefix string) *Remotes {
+func NewRemotes(clientURLs, remoteURLs []string, noop bool, remotes []string, fileWatch chan string, cConns uint16, interactive bool, sshPrivIdRsa string, caching bool, prefix string) *Remotes {
 	return &Remotes{
 		clientURLs:   clientURLs,
 		remoteURLs:   remoteURLs,
 		noop:         noop,
-		remotes:      remotes,
+		remotes:      StrRemoveDuplicatesInList(remotes),
+		fileWatch:    fileWatch,
 		cConns:       cConns,
 		interactive:  interactive,
 		sshPrivIdRsa: sshPrivIdRsa,
@@ -748,6 +762,7 @@ func (obj *Remotes) NewSSH(file string) (*SSH, error) {
 		clientURLs: obj.clientURLs,
 		remoteURLs: obj.remoteURLs,
 		noop:       obj.noop,
+		noWatch:    obj.fileWatch == nil,
 		caching:    obj.caching,
 		prefix:     obj.prefix,
 	}, nil
@@ -827,6 +842,31 @@ func (obj *Remotes) passwordCallback(user, host string) func() (string, error) {
 // The Run method of the Remotes struct kicks it all off. It is usually run from
 // a go routine.
 func (obj *Remotes) Run() {
+	// kick off the file change notifications
+	if obj.fileWatch != nil {
+		go func() {
+			for {
+				f, more := <-obj.fileWatch // read from channel
+				if !more {
+					return
+				}
+				obj.lock.Lock()
+				sshobj, exists := obj.sshmap[f]
+				if !exists || sshobj == nil {
+					continue // skip, this hasn't happened yet
+				}
+				// NOTE: if this errors because the session isn't
+				// ready yet, it's fine, because we haven't copied
+				// the file yet, so the update notification isn't
+				// wasted, in fact, it's premature and redundant.
+				if _, err := sshobj.SftpGraphCopy(); err == nil { // push new copy
+					log.Printf("Remote: Copied over new graph definition: %s", f)
+				} // ignore errors
+				obj.lock.Unlock()
+			}
+		}()
+	}
+
 	// the semaphore provides the max simultaneous connection limit
 	for _, f := range obj.remotes {
 		if obj.cConns != 0 {