fix(azure-iot-device): invalid body on received on a device method invoke throws (#856)

If somehow an invalid body is pushed through on a device method invocation, the device client side
will throw when it trys to json parse that body.

device/core/src/internal_client.ts

@@ -396,18 +396,25 @@ export abstract class InternalClient extends EventEmitter {
   private _addMethodCallback(methodName: string, callback: (request: DeviceMethodRequest, response: DeviceMethodResponse) => void): void {
     const self = this;
     this._transport.onDeviceMethod(methodName, (message) => {
-      // build the request object
-      const request = new DeviceMethodRequest(
-        message.requestId,
-        message.methods.methodName,
-        message.body
-      );
-
       // build the response object
       const response = new DeviceMethodResponse(message.requestId, self._transport);
 
-      // Codes_SRS_NODE_INTERNAL_CLIENT_13_001: [ The onDeviceMethod method shall cause the callback function to be invoked when a cloud-to-device method invocation signal is received from the IoT Hub service. ]
-      callback(request, response);
+      // build the request object
+      try {
+        const request = new DeviceMethodRequest(
+          message.requestId,
+          message.methods.methodName,
+          message.body
+        );
+        // Codes_SRS_NODE_INTERNAL_CLIENT_13_001: [ The onDeviceMethod method shall cause the callback function to be invoked when a cloud-to-device method invocation signal is received from the IoT Hub service. ]
+        callback(request, response);
+      } catch (err) {
+        response.send(400, 'Invalid request format: ' + err.message, (err) => {
+          if (err) {
+            debug('Error sending invalid request response back to application');
+          }
+        });
+      }
     });
   }
 

device/core/test/_module_client_test.js

@@ -832,12 +832,34 @@ describe('ModuleClient', function () {
           done();
         });
       });
-      2
-
       // test
       transport.emitMethodCall('reboot');
     });
 
+    it('calls response send with 400 status when method call contains invalid body', function (done) {
+      // setup
+      var transport = new FakeMethodTransport();
+      var client = new ModuleClient(transport);
+      client.open(function () {
+        client.onMethod('reboot', function () {
+          assert.fail('Should not reach here.');
+        });
+      });
+      var responseSpy = sinon.spy(transport, 'sendMethodResponse');
+      // test
+      transport.emit('method_' + 'reboot', {
+        methods: {
+          methodName: 'reboot'
+        },
+        body: '{',
+        requestId: '42'
+      });
+
+      transport.emitMethodCall('reboot');
+      assert.strictEqual(responseSpy.args[0][0].status, 400);
+      done();
+    });
+
     // Tests_SRS_NODE_MODULE_CLIENT_13_003: [ The client shall start listening for method calls from the service whenever there is a listener subscribed for a method callback. ]
     it('registers callback on transport when a method event is subscribed to', function () {
       // setup