Allow name and message in errors

Set the name of the error by setting the error's dbusName property.

E.g.

    var error = new Error('This is the message');
    error.dbusName = 'test.dbus.TestService.ErrorCode';
    callback(error);

If error.dbusName is not set, it defaults to DBUS_ERROR_FAILED[1]

This matches closer with what people expect the error message to be, and
prevents the following error when a `new Error('Human readable
message')` is returned.

```
process 16776: arguments to dbus_message_new_error() were incorrect,
assertion "_dbus_check_is_valid_error_name (error_name)" failed in file
../../dbus/dbus-message.c line 1480.

This is normally a bug in some application using the D-Bus library.
```

[1]: https://dbus.freedesktop.org/doc/api/html/group__DBusProtocol.html#gabb62fd6340d0787fbd56ff8dd2f326c7

Author: bryanburgers

examples/service.js

@@ -17,7 +17,9 @@ iface1.addMethod('Dummy', {}, function(callback) {
 });
 
 iface1.addMethod('MakeError', { out: DBus.Define(String) }, function(callback) {
-	callback(new Error('nodejs.dbus.ExampleService.ErrorTest'));
+	var error = new Error('Some error');
+	error.dbusName = 'nodejs.dbus.ExampleService.ErrorTest';
+	callback(error);
 });
 
 iface1.addMethod('Hello', { out: DBus.Define(String) }, function(callback) {

lib/service_interface.js

@@ -95,7 +95,8 @@ ServiceInterface.prototype.call = function(method, message, args) {
 
 		// Error handling
 		if (value instanceof Error) {
-			self.object.service.bus.dbus._sendErrorMessageReply(message, value.message);
+			var name = value.dbusName || 'org.freedesktop.DBus.Error.Failed';
+			self.object.service.bus.dbus._sendErrorMessageReply(message, name, value.message);
 			return;
 		}
 

test/client-call-error.test.js

@@ -0,0 +1,29 @@
+var withService = require('./with-service');
+var tap = require('tap');
+var DBus = require('../');
+
+tap.plan(6);
+withService('service.js', function(err, done) {
+	if (err) throw err;
+
+	var dbus = new DBus();
+	var bus = dbus.getBus('session');
+
+	bus.getInterface('test.dbus.TestService', '/test/dbus/TestService', 'test.dbus.TestService.Interface1', function(err, iface) {
+		iface.ThrowsError({ timeout: 1000 }, function(err, result) {
+			tap.notSame(err, null);
+			tap.same(result, null);
+			// tap.match(err.message, /from service/);
+			tap.match(err.message, 'org.freedesktop.DBus.Error.Failed');
+
+			iface.ThrowsCustomError({ timeout: 1000 }, function(err, result) {
+				tap.notSame(err, null);
+				tap.same(result, null);
+				// tap.match(err.message, /from service/);
+				tap.match(err.message, 'test.dbus.TestService.Error');
+				done();
+				bus.disconnect();
+			});
+		});
+	});
+});

test/client-property-error.test.js

@@ -0,0 +1,22 @@
+var withService = require('./with-service');
+var tap = require('tap');
+var DBus = require('../');
+
+tap.plan(3);
+withService('service.js', function(err, done) {
+	if (err) throw err;
+
+	var dbus = new DBus();
+	var bus = dbus.getBus('session');
+
+	bus.getInterface('test.dbus.TestService', '/test/dbus/TestService', 'test.dbus.TestService.Interface1', function(err, iface) {
+		iface.getProperty('ErrorProperty', function(err, value) {
+			tap.notSame(err, null);
+			tap.same(value, null);
+			//tap.match(err.message, /from service/);
+			tap.match(err.message, 'org.freedesktop.DBus.Error.Failed');
+			done();
+			bus.disconnect();
+		});
+	});
+});

test/client-property.test.js

@@ -21,6 +21,7 @@ withService('service.js', function(err, done) {
 						tap.equal(value, 'http://stem.mandice.org');
 
 						iface.getProperties(function(err, props) {
+							console.log(props);
 							tap.equal(props.Author, 'Douglas Adams');
 							tap.equal(props.URL, 'http://stem.mandice.org');
 							done();

test/service.js

@@ -24,6 +24,20 @@ iface1.addMethod('LongProcess', { out: DBus.Define(Number) }, function(callback)
 	}, 5000).unref();
 });
 
+iface1.addMethod('ThrowsError', { out: DBus.Define(Number) }, function(callback) {
+	setTimeout(function() {
+		callback(new Error('This is an error thrown from the service'));
+	}, 100);
+});
+
+iface1.addMethod('ThrowsCustomError', { out: DBus.Define(Number) }, function(callback) {
+	setTimeout(function() {
+		var error = new Error('This is an error thrown from the service');
+		error.dbusName = 'test.dbus.TestService.Error';
+		callback(error);
+	}, 100);
+});
+
 var author = 'Fred Chien';
 iface1.addProperty('Author', {
 	type: DBus.Define(String),
@@ -46,6 +60,14 @@ iface1.addProperty('URL', {
 	}
 });
 
+// Read-only property
+iface1.addProperty('ErrorProperty', {
+	type: DBus.Define(String),
+	getter: function(callback) {
+		callback(new Error('This is an error thrown from the service'));
+	}
+});
+
 // Signal
 var counter = 0;
 iface1.addSignal('pump', {