fixed: setBroadcast hangs on Android

It seems we must not call `setBroadcast()` after receiving thread was started.
At least on my setup (Android emulator or Samsung Galaxy S8 running on Android API 28)
this will result in deadlock.

Therefore I removed automatic start of receive on bind and introduced new method
`startReveiving()`.

It can be called like this:

```
let udpClient = dgram.createSocket('udp4')
this.udpClient.on('bound', () => {
  this.udpClient.setBroadcast(true)
  this.udpClient.startReceiving()
})
udpClient.bind()
```

See issue: tradle#82

UdpSocket.js

@@ -85,7 +85,7 @@ UdpSocket.prototype.bind = function(...args) {
 
   if (!port) port = 0
 
-  if (callback) this.once('listening', callback.bind(this))
+  if (callback) this.once('bound', callback.bind(this))
 
   this._state = STATE.BINDING
   this._debug('binding, address:', address, 'port:', port)
@@ -109,7 +109,23 @@ UdpSocket.prototype.bind = function(...args) {
     self._address = addr.address
     self._port = addr.port
     self._state = STATE.BOUND
-    self.emit('listening')
+    self.emit('bound')
+  })
+}
+
+UdpSocket.prototype.startReceiving = function(callback=noop) {
+  if (this._state !== STATE.BOUND) {
+    throw new Error('you must bind before startReceiving()')
+  }
+
+  this.once('listening', callback)
+
+  Sockets.startReceiving(this._id, err => {
+    err = normalizeError(err)
+    if (err) return this.emit('error', err)
+
+    this._debug('listening')
+    this.emit('listening')
   })
 }
 

android/build.gradle

@@ -32,7 +32,7 @@ android {
 dependencies {
     def supportLibVersion = project.hasProperty('supportLibVersion') ? project.supportLibVersion : DEFAULT_SUPPORT_LIB_VERSION
 
-    compile fileTree(dir: 'libs', include: ['*.jar'])
-    compile "com.android.support:appcompat-v7:$supportLibVersion"
-    compile 'com.facebook.react:react-native:+'
+    implementation fileTree(dir: 'libs', include: ['*.jar'])
+    implementation "com.android.support:appcompat-v7:$supportLibVersion"
+    compileOnly 'com.facebook.react:react-native:+'
 }

android/src/main/java/com/tradle/react/UdpSocketClient.java

@@ -82,6 +82,17 @@ public void bind(Integer port, @Nullable String address) throws IOException {
 
         mSocket.setReuseAddress(mReuseAddress);
         mSocket.bind(socketAddress);
+    }
+
+    /**
+     * Start receiving thread.
+     *
+     * @throws IllegalStateException if socket is not bound.
+     */
+    public void startReceiving() throws IllegalStateException {
+        if (null == mSocket || !mSocket.isBound() || mReceiverTask == null) {
+            throw new IllegalStateException("Socket is not bound.");
+        }
 
         // begin listening for data in the background
         mReceiverTask.executeOnExecutor(AsyncTask.THREAD_POOL_EXECUTOR,

android/src/main/java/com/tradle/react/UdpSockets.java

@@ -157,6 +157,30 @@ protected void doInBackgroundGuarded(Void... params) {
         }.execute();
     }
 
+    /**
+     * Start receiving thread.
+     */
+    @ReactMethod
+    public void startReceiving(final Integer cId, final Callback callback) {
+        new GuardedAsyncTask<Void, Void>(getReactApplicationContext()) {
+            @Override
+            protected void doInBackgroundGuarded(Void... params) {
+                UdpSocketClient client = findClient(cId, callback);
+                if (client == null) {
+                    return;
+                }
+
+                try {
+                    client.startReceiving();
+                    callback.invoke();
+                } catch (IllegalStateException ise) {
+                    // Socket is not bound or a problem occurred during starting thread
+                    callback.invoke(UdpErrorUtil.getError(null, ise.getMessage()));
+                }
+            }
+        }.execute();
+    }
+
     /**
      * Joins a multi-cast group
      */

ios/UdpSocketClient.h

@@ -66,6 +66,11 @@ typedef enum RCTUDPError RCTUDPError;
  */
 - (BOOL)bind:(u_int16_t) port address:(NSString*)address options:(NSDictionary *)options error:(NSError**)error;
 
+/**
+ * Start receiving thread
+ */
+ - (BOOL)startReceiving:(NSError **) error;
+
 /**
  * Join multicast groupt
  *

ios/UdpSocketClient.m

@@ -93,13 +93,13 @@ - (BOOL)bind:(u_int16_t)port address:(NSString *)address options:(NSDictionary *
   _address = address;
 
   _udpSocket = [[GCDAsyncUdpSocket alloc] initWithDelegate:self delegateQueue:[self methodQueue]];
-  
+
   [_udpSocket setMaxReceiveIPv4BufferSize:UINT16_MAX];
   [_udpSocket setMaxReceiveIPv6BufferSize:UINT16_MAX];
 
   BOOL reusePort = options[@"reusePort"] ?: NO;
   [_udpSocket enableReusePort:reusePort error:error];
-  
+
   BOOL result;
   if (address) {
     struct sockaddr_in ip;
@@ -114,7 +114,12 @@ - (BOOL)bind:(u_int16_t)port address:(NSString *)address options:(NSDictionary *
     result = [_udpSocket bindToPort:_port error:error];
   }
 
-  return result && [_udpSocket beginReceiving:error];
+  return result;
+}
+
+- (BOOL)startReceiving:(NSError **) error
+{
+    return [_udpSocket beginReceiving:error];
 }
 
 - (BOOL)joinMulticastGroup:(NSString *)address error:(NSError **) error

ios/UdpSockets.m

@@ -70,6 +70,22 @@ - (void)dealloc
     callback(@[[NSNull null], [client address]]);
 }
 
+RCT_EXPORT_METHOD(startReceiving:(nonnull NSNumber*)cId
+                  callback:(RCTResponseSenderBlock)callback)
+{
+    UdpSocketClient* client = [self findClient:cId callback:callback];
+    if (!client) return;
+
+    NSError *error = nil;
+    if (![client startReceiving:&error])
+    {
+        NSString *msg = error.localizedFailureReason ?: error.localizedDescription;
+        callback(@[msg ?: @"unknown error when startReceiving"]);
+        return;
+    }
+    callback(@[[NSNull null]]);
+}
+
 RCT_EXPORT_METHOD(send:(nonnull NSNumber*)cId
                   string:(NSString*)base64String
                   port:(int)port
@@ -108,19 +124,19 @@ - (void)dealloc
 RCT_EXPORT_METHOD(addMembership:(nonnull NSNumber*)cId
                   multicastAddress:(NSString *)address) {
      UdpSocketClient *client = _clients[cId];
-    
+
     if (!client) return;
-    
+
     NSError *error = nil;
     [client joinMulticastGroup:address error:&error];
 }
 
 RCT_EXPORT_METHOD(dropMembership:(nonnull NSNumber*)cId
                   multicastAddress:(NSString *)address) {
     UdpSocketClient *client = _clients[cId];
-    
+
     if (!client) return;
-    
+
     NSError *error = nil;
     [client leaveMulticastGroup:address error:&error];
 }