diff --git a/core/app.js b/core/app.js
index 9f9f520d..fdf8357d 100644
--- a/core/app.js
+++ b/core/app.js
@@ -7,71 +7,11 @@
 
 /** \cond */
 import * as core from './core.js';
-
-export {App};
 /** \endcond */
 
 /** A sequence number of apps. */
 let g_session_index = 0;
 
-/**
- ** App constructor.
- ** @return An app instance.
- */
-function App() {
-	this._send_queue = [];
-	this.calls = {};
-	this._next_call_id = 1;
-	return this;
-}
-
-/**
- ** Create a function wrapper that when called invokes a function on the app
- ** itself.
- ** @param api The function and argument names.
- ** @return A function.
- */
-App.prototype.makeFunction = function (api) {
-	let self = this;
-	let result = function () {
-		let id = self._next_call_id++;
-		while (!id || self.calls[id]) {
-			id = self._next_call_id++;
-		}
-		let promise = new Promise(function (resolve, reject) {
-			self.calls[id] = {resolve: resolve, reject: reject};
-		});
-		let message = {
-			action: 'tfrpc',
-			method: api[0],
-			params: [...arguments],
-			id: id,
-		};
-		self.send(message);
-		return promise;
-	};
-	Object.defineProperty(result, 'name', {value: api[0], writable: false});
-	return result;
-};
-
-/**
- ** Send a message to the app.
- ** @param message The message to send.
- */
-App.prototype.send = function (message) {
-	if (this._send_queue) {
-		if (this._on_output) {
-			this._send_queue.forEach((x) => this._on_output(x));
-			this._send_queue = null;
-		} else if (message) {
-			this._send_queue.push(message);
-		}
-	}
-	if (message && this._on_output) {
-		this._on_output(message);
-	}
-};
-
 /**
  ** App socket handler.
  ** @param request The HTTP request of the WebSocket connection.
diff --git a/core/core.js b/core/core.js
index ec76a39c..6d801926 100644
--- a/core/core.js
+++ b/core/core.js
@@ -6,7 +6,7 @@
  */
 
 /** \cond */
-import * as app from './app.js';
+import * as app_module from './app.js';
 
 export {invoke, getProcessBlob};
 /** \endcond */
@@ -22,6 +22,64 @@ let g_update_accounts_scheduled;
 /** Time between pings, in milliseconds. */
 const k_ping_interval = 60 * 1000;
 
+/**
+ ** App constructor.
+ ** @return An app instance.
+ */
+function App() {
+	this._send_queue = [];
+	this.calls = {};
+	this._next_call_id = 1;
+	return this;
+}
+
+/**
+ ** Create a function wrapper that when called invokes a function on the app
+ ** itself.
+ ** @param api The function and argument names.
+ ** @return A function.
+ */
+App.prototype.makeFunction = function (api) {
+	let self = this;
+	let result = function () {
+		let id = self._next_call_id++;
+		while (!id || self.calls[id]) {
+			id = self._next_call_id++;
+		}
+		let promise = new Promise(function (resolve, reject) {
+			self.calls[id] = {resolve: resolve, reject: reject};
+		});
+		let message = {
+			action: 'tfrpc',
+			method: api[0],
+			params: [...arguments],
+			id: id,
+		};
+		self.send(message);
+		return promise;
+	};
+	Object.defineProperty(result, 'name', {value: api[0], writable: false});
+	return result;
+};
+
+/**
+ ** Send a message to the app.
+ ** @param message The message to send.
+ */
+App.prototype.send = function (message) {
+	if (this._send_queue) {
+		if (this._on_output) {
+			this._send_queue.forEach((x) => this._on_output(x));
+			this._send_queue = null;
+		} else if (message) {
+			this._send_queue.push(message);
+		}
+	}
+	if (message && this._on_output) {
+		this._on_output(message);
+	}
+};
+
 /**
  * Print an error.
  * @param error The error.
@@ -183,7 +241,7 @@ async function getProcessBlob(blobId, key, options) {
 			process.url = options?.url;
 			process.eventHandlers = {};
 			if (!options?.script || options?.script === 'app.js') {
-				process.app = new app.App();
+				process.app = new App();
 			}
 			process.lastActive = Date.now();
 			process.lastPing = null;
diff --git a/src/httpd.app.c b/src/httpd.app.c
index caaf6c90..4b4c50cb 100644
--- a/src/httpd.app.c
+++ b/src/httpd.app.c
@@ -291,7 +291,42 @@ static void _http_json_send(tf_http_request_t* request, JSContext* context, JSVa
 
 static JSValue _httpd_app_on_tfrpc(JSContext* context, JSValueConst this_val, int argc, JSValueConst* argv, int magic, JSValue* func_data)
 {
-	tf_printf("TODO: TFRPC\n");
+	const char* id = tf_util_get_property_as_string(context, argv[0], "id");
+	if (id)
+	{
+		JSClassID class_id = 0;
+		app_t* app = JS_GetAnyOpaque(func_data[0], &class_id);
+		JSValue process_app = JS_GetPropertyStr(context, app->process, "app");
+		JSValue calls = JS_IsObject(process_app) ? JS_GetPropertyStr(context, process_app, "calls") : JS_UNDEFINED;
+		JSValue call = JS_IsObject(calls) ? JS_GetPropertyStr(context, calls, id) : JS_UNDEFINED;
+		if (!JS_IsUndefined(call))
+		{
+			JSValue error = JS_GetPropertyStr(context, argv[0], "error");
+			if (!JS_IsUndefined(error))
+			{
+				JSValue reject = JS_GetPropertyStr(context, call, "reject");
+				JSValue result = JS_Call(context, reject, JS_UNDEFINED, 1, &error);
+				tf_util_report_error(context, result);
+				JS_FreeValue(context, result);
+				JS_FreeValue(context, reject);
+			}
+			else
+			{
+				JSValue resolve = JS_GetPropertyStr(context, call, "resolve");
+				JSValue message_result = JS_GetPropertyStr(context, argv[0], "result");
+				JSValue result = JS_Call(context, resolve, JS_UNDEFINED, 1, &message_result);
+				JS_FreeValue(context, message_result);
+				tf_util_report_error(context, result);
+				JS_FreeValue(context, result);
+				JS_FreeValue(context, resolve);
+			}
+			JS_FreeValue(context, error);
+		}
+		JS_FreeValue(context, call);
+		JS_FreeValue(context, calls);
+		JS_FreeValue(context, process_app);
+	}
+	JS_FreeCString(context, id);
 	return JS_UNDEFINED;
 }
 
@@ -311,7 +346,6 @@ static JSValue _httpd_app_on_process_start(JSContext* context, JSValueConst this
 	JSClassID class_id = 0;
 	app_t* app = JS_GetAnyOpaque(func_data[0], &class_id);
 	app->process = JS_DupValue(context, argv[0]);
-	tf_printf("ON START %p => %s\n", app, app->request->path);
 
 	JSValue client_api = JS_GetPropertyStr(context, app->process, "client_api");
 	JSValue tfrpc = JS_NewCFunctionData(context, _httpd_app_on_tfrpc, 1, 0, 1, func_data);
@@ -319,10 +353,16 @@ static JSValue _httpd_app_on_process_start(JSContext* context, JSValueConst this
 	JS_FreeValue(context, client_api);
 
 	JSValue process_app = JS_GetPropertyStr(context, app->process, "app");
-	JSValue send = JS_NewCFunctionData(context, _httpd_app_on_output, 1, 0, 1, func_data);
-	JS_SetPropertyStr(context, process_app, "_on_output", send);
+	JSValue on_output = JS_NewCFunctionData(context, _httpd_app_on_output, 1, 0, 1, func_data);
+	JS_SetPropertyStr(context, process_app, "_on_output", on_output);
 	JS_FreeValue(context, process_app);
 
+	JSValue send = JS_GetPropertyStr(context, process_app, "send");
+	JSValue result = JS_Call(context, send, process_app, 0, NULL);
+	JS_FreeValue(context, send);
+	tf_util_report_error(context, result);
+	JS_FreeValue(context, result);
+
 	return JS_UNDEFINED;
 }