Fix race condition that could cause pairing state to be lost

If a mDNS response for a host happened during the period where we
had removed the host from discovery, it would be re-added by mDNS
without the pairing cert. Now we no longer completely remove the host
and instead just remember that it's paused.

Limelight/Network/DiscoveryManager.h

@@ -24,6 +24,8 @@
 - (void) resetDiscoveryState;
 - (BOOL) addHostToDiscovery:(TemporaryHost*)host;
 - (void) removeHostFromDiscovery:(TemporaryHost*)host;
+- (void) pauseDiscoveryForHost:(TemporaryHost *)host;
+- (void) resumeDiscoveryForHost:(TemporaryHost *)host;
 - (void) discoverHost:(NSString*)hostAddress withCallback:(void (^)(TemporaryHost*, NSString*))callback;
 
 @end

Limelight/Network/DiscoveryManager.m

@@ -17,6 +17,7 @@
 
 @implementation DiscoveryManager {
     NSMutableArray* _hostQueue;
+    NSMutableSet* _pausedHosts;
     id<DiscoveryCallback> _callback;
     MDNSManager* _mdnsMan;
     NSOperationQueue* _opQueue;
@@ -33,6 +34,7 @@
     _callback = callback;
     shouldDiscover = NO;
     _hostQueue = [NSMutableArray array];
+    _pausedHosts = [NSMutableSet set];
     for (TemporaryHost* host in hosts)
     {
         [self addHostToDiscovery:host];
@@ -85,9 +87,11 @@
     
     @synchronized (_hostQueue) {
         for (TemporaryHost* host in _hostQueue) {
+            if (![_pausedHosts containsObject:host]) {
                 [_opQueue addOperation:[self createWorkerForHost:host]];
             }
         }
+    }
 }
 
 - (void) stopDiscovery {
@@ -168,6 +172,33 @@
         }
         
         [_hostQueue removeObject:host];
+        [_pausedHosts removeObject:host];
+    }
+}
+
+- (void) pauseDiscoveryForHost:(TemporaryHost *)host {
+    @synchronized (_hostQueue) {
+        // Stop any worker for the host
+        for (DiscoveryWorker* worker in [_opQueue operations]) {
+            if ([worker getHost] == host) {
+                [worker cancel];
+            }
+        }
+        
+        // Add it to the paused hosts list
+        [_pausedHosts addObject:host];
+    }
+}
+
+- (void) resumeDiscoveryForHost:(TemporaryHost *)host {
+    @synchronized (_hostQueue) {
+        // Remove it from the paused hosts list
+        [_pausedHosts removeObject:host];
+        
+        // Start discovery again
+        if (shouldDiscover) {
+            [_opQueue addOperation:[self createWorkerForHost:host]];
+        }
     }
 }
 

Limelight/ViewControllers/MainFrameViewController.m

@@ -133,6 +133,10 @@ static NSMutableSet* hostList;
     // Capture the host here because it can change once we
     // leave the main thread
     TemporaryHost* host = _selectedHost;
+    if (host == nil) {
+        [self hideLoadingFrame: nil];
+        return;
+    }
     
     if ([host.appList count] > 0) {
         usingCachedAppList = true;
@@ -149,11 +153,11 @@ static NSMutableSet* hostList;
     Log(LOG_I, @"Using cached app list: %d", usingCachedAppList);
     dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
         // Exempt this host from discovery while handling the applist query
-        [self->_discMan removeHostFromDiscovery:host];
+        [self->_discMan pauseDiscoveryForHost:host];
         
         AppListResponse* appListResp = [ConnectionHelper getAppListForHostWithHostIP:host.activeAddress serverCert:host.serverCert uniqueID:self->_uniqueId];
         
-        [self->_discMan addHostToDiscovery:host];
+        [self->_discMan resumeDiscoveryForHost:host];
 
         if (![appListResp isStatusOk] || [appListResp getAppList] == nil) {
             Log(LOG_W, @"Failed to get applist: %@", appListResp.statusMessage);
@@ -340,10 +344,10 @@ static NSMutableSet* hostList;
             ServerInfoResponse* serverInfoResp = [[ServerInfoResponse alloc] init];
             
             // Exempt this host from discovery while handling the serverinfo request
-            [self->_discMan removeHostFromDiscovery:host];
+            [self->_discMan pauseDiscoveryForHost:host];
             [hMan executeRequestSynchronously:[HttpRequest requestForResponse:serverInfoResp withUrlRequest:[hMan newServerInfoRequest:false]
                                                                 fallbackError:401 fallbackRequest:[hMan newHttpServerInfoRequest]]];
-            [self->_discMan addHostToDiscovery:host];
+            [self->_discMan resumeDiscoveryForHost:host];
             
             if (![serverInfoResp isStatusOk]) {
                 Log(LOG_W, @"Failed to get server info: %@", serverInfoResp.statusMessage);
@@ -612,7 +616,7 @@ static NSMutableSet* hostList;
                                                 HttpRequest* quitRequest = [HttpRequest requestForResponse: quitResponse withUrlRequest:[hMan newQuitAppRequest]];
                                                 
                                                 // Exempt this host from discovery while handling the quit operation
-                                                [self->_discMan removeHostFromDiscovery:app.host];
+                                                [self->_discMan pauseDiscoveryForHost:app.host];
                                                 [hMan executeRequestSynchronously:quitRequest];
                                                 if (quitResponse.statusCode == 200) {
                                                     ServerInfoResponse* serverInfoResp = [[ServerInfoResponse alloc] init];
@@ -629,7 +633,7 @@ static NSMutableSet* hostList;
                                                         [serverInfoResp populateHost:app.host];
                                                     }
                                                 }
-                                                [self->_discMan addHostToDiscovery:app.host];
+                                                [self->_discMan resumeDiscoveryForHost:app.host];
 
                                                 // If it fails, display an error and stop the current operation
                                                 if (quitResponse.statusCode != 200) {