Ensure Simulator publishes mDNS records (#6696)

* Ensure Simulator publishes mDNS records on loopback interface.

shell/platform/darwin/ios/framework/Source/FlutterObservatoryPublisher.mm

@@ -4,6 +4,16 @@
 
 #define FML_USED_ON_EMBEDDER
 
+#import <TargetConditionals.h>
+
+// NSNetService works fine on physical devices, but doesn't expose the services to regular mDNS
+// queries on the Simulator.  We can work around this by using the lower level C API, but that's
+// only available from iOS 9.3+/macOS 10.11.4+.
+#if TARGET_IPHONE_SIMULATOR
+#include <dns_sd.h>  // nogncheck
+#include <net/if.h>  // nogncheck
+#endif               // TARGET_IPHONE_SIMLUATOR
+
 #import "FlutterObservatoryPublisher.h"
 
 #include "flutter/fml/logging.h"
@@ -26,7 +36,11 @@
 @end
 
 @implementation FlutterObservatoryPublisher {
+#if TARGET_IPHONE_SIMULATOR
+  DNSServiceRef _dnsServiceRef;
+#else   // TARGET_IPHONE_SIMULATOR
   fml::scoped_nsobject<NSNetService> _netService;
+#endif  // TARGET_IPHONE_SIMULATOR
 
   blink::DartServiceIsolate::CallbackHandle _callbackHandle;
   std::unique_ptr<fml::WeakPtrFactory<FlutterObservatoryPublisher>> _weakFactory;
@@ -54,14 +68,29 @@
 }
 
 - (void)dealloc {
+#if TARGET_IPHONE_SIMULATOR
+  if (_dnsServiceRef) {
+    DNSServiceRefDeallocate(_dnsServiceRef);
+    _dnsServiceRef = NULL;
+  }
+#else   // TARGET_IPHONE_SIMULATOR
   [_netService.get() stop];
+#endif  // TARGET_IPHONE_SIMULATOR
+
   blink::DartServiceIsolate::RemoveServerStatusCallback(std::move(_callbackHandle));
   [super dealloc];
 }
 
 - (void)publishServiceProtocolPort:(std::string)uri {
+#if TARGET_IPHONE_SIMULATOR
+  if (_dnsServiceRef) {
+    DNSServiceRefDeallocate(_dnsServiceRef);
+    _dnsServiceRef = NULL;
+  }
+#else   // TARGET_IPHONE_SIMULATOR
+  [_netService.get() stop];
+#endif  // TARGET_IPHONE_SIMULATOR
   if (uri.empty()) {
-    [_netService.get() stop];
     return;
   }
   // uri comes in as something like 'http://127.0.0.1:XXXXX/' where XXXXX is the port
@@ -69,28 +98,37 @@
   NSURL* url =
       [[[NSURL alloc] initWithString:[NSString stringWithUTF8String:uri.c_str()]] autorelease];
 
-  // DNS name has to be a max of 63 bytes.  Prefer to cut off the app name rather than
-  // the device hostName. e.g. 'io.flutter.example@someones-iphone', or
-  // 'ongAppNameBecauseThisCouldHappenAtSomePoint@somelongname-iphone'
-  NSString* serviceName = [NSString
-      stringWithFormat:@"%@@%@",
-                       [[[NSBundle mainBundle] infoDictionary] objectForKey:@"CFBundleIdentifier"],
-                       [NSProcessInfo processInfo].hostName];
-  if ([serviceName length] > 63) {
-    serviceName = [serviceName substringFromIndex:[serviceName length] - 63];
-  }
+  NSString* serviceName =
+      [[[NSBundle mainBundle] infoDictionary] objectForKey:@"CFBundleIdentifier"];
 
+#if TARGET_IPHONE_SIMULATOR
+  DNSServiceFlags flags = kDNSServiceFlagsDefault;
+  uint32_t interfaceIndex = if_nametoindex("lo0");
+  const char* registrationType = "_dartobservatory._tcp";
+  const char* domain = "local.";  // default domain
+  uint16_t port = [[url port] intValue];
+
+  int err = DNSServiceRegister(&_dnsServiceRef, flags, interfaceIndex, [serviceName UTF8String],
+                               registrationType, domain, NULL, htons(port), 0, NULL,
+                               registrationCallback, NULL);
+
+  if (err != 0) {
+    FML_LOG(ERROR) << "Failed to register observatory port with mDNS.";
+  } else {
+    DNSServiceProcessResult(_dnsServiceRef);
+  }
+#else   // TARGET_IPHONE_SIMULATOR
   _netService.reset([[NSNetService alloc] initWithDomain:@"local."
                                                     type:@"_dartobservatory._tcp."
                                                     name:serviceName
                                                     port:[[url port] intValue]]);
-
   [_netService.get() setDelegate:self];
   [_netService.get() publish];
+#endif  // TARGET_IPHONE_SIMULATOR
 }
 
 - (void)netServiceDidPublish:(NSNetService*)sender {
-  FML_DLOG(INFO) << "FlutterObservatoryPublisher is ready!";
+  FML_LOG(INFO) << "FlutterObservatoryPublisher is ready!";
 }
 
 - (void)netService:(NSNetService*)sender didNotPublish:(NSDictionary*)errorDict {
@@ -98,6 +136,23 @@
                     "network settings and relaunch the application.";
 }
 
+#if TARGET_IPHONE_SIMULATOR
+static void DNSSD_API registrationCallback(DNSServiceRef sdRef,
+                                           DNSServiceFlags flags,
+                                           DNSServiceErrorType errorCode,
+                                           const char* name,
+                                           const char* regType,
+                                           const char* domain,
+                                           void* context) {
+  if (errorCode == kDNSServiceErr_NoError) {
+    FML_LOG(ERROR) << "FlutterObservatoryPublisher is ready!";
+  } else {
+    FML_LOG(ERROR) << "Could not register as server for FlutterObservatoryPublisher. Check your "
+                      "network settings and relaunch the application.";
+  }
+}
+#endif  // TARGET_IPHONE_SIMULATOR
+
 #endif  // FLUTTER_RUNTIME_MODE != FLUTTER_RUNTIME_MODE_RELEASE && FLUTTER_RUNTIME_MODE !=
         // FLUTTER_RUNTIME_MODE_DYNAMIC_RELEASE