Add mjpeg server to screenshotr (danielpaulus#213)

start a simple mjpeg server by running
`ios screenshot --stream` on 0.0.0.0:3333. If you provide the port argument like so: 
`ios screenshot --stream --port=8082` the server will run on your specified port. Then watch a slow stream in your browser. 
This is only a fun feature or to use in debugging if all else fails. Screenshotr is too slow to be really useable on Retina/High Res devices because it sends huge PNG files. Those reach memory bandwith limits on the device. Also it is too unstable to be used in production scenarios. For useable mjpeg streams, use WebDriverAgent's built in server. 
On older devices, this works quite well though :-D

Author: danielpaulus

ios/screenshotr/mjpeg_server.go

@@ -0,0 +1,108 @@
+package screenshotr
+
+import (
+	"bufio"
+	"bytes"
+	"fmt"
+	"github.com/danielpaulus/go-ios/ios"
+	log "github.com/sirupsen/logrus"
+	"image/jpeg"
+	"image/png"
+	"io"
+	"net/http"
+	"sync"
+	"time"
+)
+
+var consumers sync.Map
+var conversionQueue = make(chan []byte, 20)
+
+func StartStreamingServer(device ios.DeviceEntry, port string) error {
+	conn, err := New(device)
+	if err != nil {
+		return err
+	}
+	go startScreenshotting(conn)
+	go startConversionQueue()
+	http.HandleFunc("/", mjpegHandler)
+	location := fmt.Sprintf("0.0.0.0:%s", port)
+	log.WithFields(log.Fields{"host": "0.0.0.0", "port": port}).Infof("starting server, open your browser here: http://%s/", location)
+	return http.ListenAndServe(location, nil)
+}
+func startConversionQueue() {
+	var opt jpeg.Options
+	opt.Quality = 80
+
+	for {
+		pngBytes := <-conversionQueue
+		start := time.Now()
+		img, err := png.Decode(bytes.NewReader(pngBytes))
+		if err != nil {
+			log.Warnf("failed decoding png %v", err)
+			continue
+		}
+		var b bytes.Buffer
+		foo := bufio.NewWriter(&b)
+		err = jpeg.Encode(foo, img, &opt)
+		if err != nil {
+			log.Warnf("failed encoding jpg %v", err)
+			continue
+		}
+		elapsed := time.Since(start)
+		log.Debugf("conversion took %fs", elapsed.Seconds())
+		consumers.Range(func(key, value interface{}) bool {
+			c := value.(chan []byte)
+			go func() { c <- b.Bytes() }()
+			return true
+		})
+	}
+}
+func startScreenshotting(conn *Connection) {
+	for {
+		start := time.Now()
+		pngBytes, err := conn.TakeScreenshot()
+		if err != nil {
+			log.Fatal("screenshotr failed", err)
+		}
+		elapsed := time.Since(start)
+		log.Debugf("shot took %fs", elapsed.Seconds())
+		conversionQueue <- pngBytes
+	}
+}
+
+const mjpegFrameFooter = "\r\n\r\n"
+const mjpegFrameHeader = "--BoundaryString\r\nContent-type: image/jpg\r\nContent-Length: %d\r\n\r\n"
+
+func mjpegHandler(w http.ResponseWriter, r *http.Request) {
+	log.Infof("starting mjpeg stream for new client")
+	c := make(chan []byte)
+	consumers.Store(r, c)
+	w.Header().Add("Server", "go-ios-screenshotr-mjpeg-stream")
+	w.Header().Add("Connection", "Close")
+	w.Header().Add("Content-Type", "multipart/x-mixed-replace; boundary=--BoundaryString")
+	w.Header().Add("Max-Age", "0")
+	w.Header().Add("Expires", "0")
+	w.Header().Add("Cache-Control", "no-cache, private")
+	w.Header().Add("Pragma", "no-cache")
+
+	//io.WriteString(w, mjpegStreamHeader)
+	w.WriteHeader(200)
+	for {
+		jpg := <-c
+		_, err := io.WriteString(w, fmt.Sprintf(mjpegFrameHeader, len(jpg)))
+		if err != nil {
+			break
+		}
+		_, err = w.Write(jpg)
+		if err != nil {
+			break
+		}
+		_, err = io.WriteString(w, mjpegFrameFooter)
+		if err != nil {
+			break
+		}
+	}
+	consumers.Delete(r)
+	close(c)
+	log.Info("client disconnected")
+}

main.go

@@ -66,7 +66,7 @@ Usage:
   ios image mount [--path=<imagepath>] [options]
   ios image auto [--basedir=<where_dev_images_are_stored>] [options]
   ios syslog [options]
-  ios screenshot [options] [--output=<outfile>]
+  ios screenshot [options] [--output=<outfile>] [--stream] [--port=<port>]
   ios instruments notifications [options]
   ios crash ls [<pattern>] [options]
   ios crash cp <srcpattern> <target> [options]
@@ -132,7 +132,8 @@ The commands work as following:
    >                                                                  You can specify a dir where images should be cached.
    >                                                                  The default is the current dir. 
    ios syslog [options]                                               Prints a device's log output
-   ios screenshot [options] [--output=<outfile>]                      Takes a screenshot and writes it to the current dir or to <outfile>
+   ios screenshot [options] [--output=<outfile>] [--stream] [--port=<port>]  Takes a screenshot and writes it to the current dir or to <outfile>  If --stream is supplied it
+   >                                                                  starts an mjpeg server at 0.0.0.0:3333. Use --port to set another port.
    ios instruments notifications [options]                            Listen to application state notifications                                    
    ios crash ls [<pattern>] [options]                                 run "ios crash ls" to get all crashreports in a list, 
    >                                                                  or use a pattern like 'ios crash ls "*ips*"' to filter
@@ -377,7 +378,17 @@ The commands work as following:
 
 	b, _ = arguments.Bool("screenshot")
 	if b {
+		stream, _ := arguments.Bool("--stream")
+		port, _ := arguments.String("--port")
 		path, _ := arguments.String("--output")
+		if stream {
+			if port == "" {
+				port = "3333"
+			}
+			err := screenshotr.StartStreamingServer(device, port)
+			exitIfError("failed starting mjpeg", err)
+			return
+		}
 		saveScreenshot(device, path)
 		return
 	}