fix: Add exponential backoff interval on consecutive screenshot failures (#1119)

Author: mykola-mokhnach

WebDriverAgentLib/Utilities/FBMjpegServer.m

@@ -21,6 +21,8 @@
 
 static const NSUInteger MAX_FPS = 60;
 static const NSTimeInterval FRAME_TIMEOUT = 1.;
+static const NSTimeInterval FAILURE_BACKOFF_MIN = 1.0;
+static const NSTimeInterval FAILURE_BACKOFF_MAX = 10.0;
 
 static NSString *const SERVER_NAME = @"WDA MJPEG Server";
 static const char *QUEUE_NAME = "JPEG Screenshots Provider Queue";
@@ -32,6 +34,7 @@ @interface FBMjpegServer()
 @property (nonatomic, readonly) NSMutableArray<GCDAsyncSocket *> *listeningClients;
 @property (nonatomic, readonly) FBImageProcessor *imageProcessor;
 @property (nonatomic, readonly) long long mainScreenID;
+@property (nonatomic, assign) NSUInteger consecutiveScreenshotFailures;
 
 @end
 
@@ -41,6 +44,7 @@ @implementation FBMjpegServer
 - (instancetype)init
 {
   if ((self = [super init])) {
+    _consecutiveScreenshotFailures = 0;
     _listeningClients = [NSMutableArray array];
     dispatch_queue_attr_t queueAttributes = dispatch_queue_attr_make_with_qos_class(DISPATCH_QUEUE_SERIAL, QOS_CLASS_UTILITY, 0);
     _backgroundQueue = dispatch_queue_create(QUEUE_NAME, queueAttributes);
@@ -91,10 +95,16 @@ - (void)streamScreenshot
                                                                         error:&error];
   if (nil == screenshotData) {
     [FBLogger logFmt:@"%@", error.description];
-    [self scheduleNextScreenshotWithInterval:timerInterval timeStarted:timeStarted];
+    self.consecutiveScreenshotFailures++;
+    NSTimeInterval backoffSeconds = MIN(FAILURE_BACKOFF_MAX,
+                                        FAILURE_BACKOFF_MIN * (1 << MIN(self.consecutiveScreenshotFailures, 4)));
+    uint64_t backoffInterval = (uint64_t)(backoffSeconds * NSEC_PER_SEC);
+    [self scheduleNextScreenshotWithInterval:backoffInterval timeStarted:timeStarted];
     return;
   }
 
+  self.consecutiveScreenshotFailures = 0;
+
   CGFloat scalingFactor = FBConfiguration.mjpegScalingFactor / 100.0;
   [self.imageProcessor submitImageData:screenshotData
                          scalingFactor:scalingFactor

lib/webdriveragent.ts

@@ -315,11 +315,13 @@ export class WebDriverAgent {
 
   private async parseBundleId(wdaBundlePath: string): Promise<string> {
     const infoPlistPath = path.join(wdaBundlePath, 'Info.plist');
-    const infoPlist = await plist.parsePlist(await fs.readFile(infoPlistPath));
+    const infoPlist = (await plist.parsePlist(await fs.readFile(infoPlistPath))) as {
+      CFBundleIdentifier?: string;
+    };
     if (!infoPlist.CFBundleIdentifier) {
       throw new Error(`Could not find bundle id in '${infoPlistPath}'`);
     }
-    return infoPlist.CFBundleIdentifier as string;
+    return infoPlist.CFBundleIdentifier;
   }
 
   private async fetchWDABundle(): Promise<string> {