Router is the core component of Valum. It dispatches request to the right handler and processes certain error conditions described in Redirection and Error.

The router is constituted of a sequence of Route objects which may or may not match incoming requests and perform the process described in their handlers.


The most basic and explicit way of attaching a handler is Router.route, which attach the provided Route object to the sequence.

app.route (new RuleRoute (Method.GET, "/", null, () => {}));

Route are simple objects which combine a matching and handling processes. The following sections implicitly treat of route objects such such as RuleRoute and RegexRoute.


New in version 0.3.

The Method flag provide a list of HTTP methods and some useful masks used into route definitions.

Flag Description
Method.SAFE safe methods
Method.IDEMPOTENT idempotent methods (e.g. SAFE and PUT)
Method.CACHEABLE cacheable methods (e.g. HEAD, GET and POST)
Method.ALL all standard HTTP methods
Method.OTHER any non-standard HTTP methods
Method.ANY anything, including non-standard methods
Method.PROVIDED indicate that the route provide its methods
Method.META mask for all meta flags like Method.PROVIDED


Safe, idempotent and cacheable methods are defined in section 4.2 of RFC 7231.

Using a flag makes it really convenient to capture multiple methods with the | binary operator.

app.rule (Method.GET | Method.POST, "/", (req, res) => {
    // matches GET and POST

Method.GET is defined as Method.ONLY_GET | Method.HEAD such that defining the former will also provide a HEAD implementation. In general, it’s recommended to check the method in order to skip a body that won’t be considered by the user agent.

app.get ("/", () => {
    res.headers.set_content_type ("text/plain", null);
    if (req.method == Request.HEAD) {
        return res.end (); // skip unnecessary I/O
    return res.expand_utf8 ("Hello world!");

To provide only the GET part, use Method.ONLY_GET.

app.rule (Method.ONLY_GET, "/", () => {
    res.headers.set_content_type ("text/plain", null);
    return res.expand_utf8 ("Hello world!");

Per definition, POST is considered cacheable, but if it’s not desirable, it may be removed from the mask with the unary ~ operator.

app.rule (Method.CACHEABLE & ~Method.POST, "/", () => {
    res.headers.set_content_type ("text/plain", null);
    return res.expand_utf8 ("Hello world!");

Non-standard method

To handle non-standard HTTP method, use the Method.OTHER along with an explicit check.

app.method (Method.OTHER, "/rule", (req, res) => {
    if (req.method != "CUSTOM")
        return next ();


New in version 0.3.

Some route implementations can be reversed into URLs by calling Route.to_url or the alternative Route.to_urlv and Route.to_url_from_hash. It may optionally take parameters which, in the case of the rule-based route, correspond to the named captures.


The router introspect the route sequence to determine what methods are allowed for a given URI and thus produce a nice Allow header. To mark a method as provided, the Method.PROVIDED flag has to be used. This is automatically done for the helpers and the Router.rule function described below.

Additionally, the OPTIONS and TRACE are automatically handled if not specified for a path. The OPTIONS will produce a Allow header and TRACE will feedback the request into the response payload.

Named route

New in version 0.3.

Few of the helpers provided by the router also accept an additional parameter to name the created route object. This can then be used to generate reverse URLs with Router.url_for.


This feature is only support for the rule-based and path-based route implementations.

var app = new Router ();

app.get ("/", (req, res) => {
    return res.expand_utf8 ("Hello world! %s".printf (app.url_for ("home")));
}, "home");

Likewise to to_url, it’s possible to pass additional parameters as varidic arguments. The following example show how one can serve relocatable static resources and generate URLs in a Compose template.

using Compose.HTML5;
using Valum;
using Valum.Static;

var app = new Router ();

app.get ("/", () => {
    return res.expand_utf8 (
        html (
            head (
                title ("Hello world!"),
                link ("stylesheet",
                      app.url_for ("static",
                                   "path", "bootstrap/dist/css/bootstrap.min.css"))),
            body ()));

app.get ("/static/<path>", serve_from_path ("static"), "static");

Other helpers are provided to pass a GLib.HashTable via Router.url_for_hash or explicit varidic arguments via Router.url_for_valist.


Vala also support the : syntax for passing varidic argument in a key-value style if the key is a glib-2.0/string which is the case for Router.url_for and Route.to_url.

var bootstrap_url = app.url_for ("static", path: "bootstrap/dist/css/bootstrap.min.css");


New in version 0.3.

To perform initialization or just call some middleware once, use Router.once.

Gda.Connection database;

app.once ((req, res, next) => {
    database = new Gda.Connection.from_string ("mysql", ...);
    return next ();

app.get ("/", (req, res) => {
    return res.expand_utf8 ("Hello world!");


New in version 0.3.

The simplest way to attach a handler is Router.use, which unconditionally apply the route on the request.

app.use ((req, res, next) => {
    var params = new HashTable<string, string> (str_hash, str_equal);
    params["charset"] = "iso-8859-1";
    res.headers.set_content_type ("text/xhtml+xml", params);
    return next ();

It is typically used to mount a Middlewares on the router.


New in version 0.3.

The special * URI is handled by the Router.asterisk helper. It is typically used along with the OPTIONS method to provide a self-description of the Web service or application.

app.asterisk (Method.OPTIONS, () => {
    return true;


Changed in version 0.3: Rule helpers (e.g. get, post, rule) must explicitly be provided with a leading slash.

The rule syntax has been greatly improved to support groups, optionals and wildcards.

The de facto way of attaching handler callbacks is based on the rule system. The Router.rule as well as all HTTP method helpers use it.

app.rule (Method.ALL, "/rule" (req, res) => {
    return true;

The syntax for rules is given by the following EBNF grammar:

rule      = piece | parameter | group | optional | wildcard, [ rule ];
group     = '(', rule, ')';
optional  = (piece | parameter | group), '?';
wildcard  = '*';
parameter = '<', [ type, ':' ], name, '>'; (* considered as a terminal *)
type      = ? any sequence of word character ?;
name      = ? any sequence of word character ?;
piece     = ? any sequence of URL-encoded character ?;


  • a piece is a single character, so /users/? only indicates that the / is optional
  • the wildcard * matches anything, just like the .* regular expression

The following table show valid rules and their corresponding regular expressions. Note that rules are matching the whole path as they are automatically anchored.

Rule Regular expression
/user ^/user$
/user/<id> ^/user/(?<id>\w+)$
/user/<int:id> ^/user/(?<id>\d+)$
/user(/<int:id>)? ^/user(?:/(?<id>\d+))?$


Valum provides built-in types initialized in the Router constructor. The following table details these types and what they match.

Type Regex Description
int \d+ matches non-negative integers like a database primary key
string \w+ matches any word character
path (?:\.?[\w/-\s/])+ matches a piece of route including slashes, but not ..

Undeclared types default to string, which matches any word characters.

It is possible to specify or overwrite types using the types map in Router. This example will define the path type matching words and slashes using a regular expression literal.

app.register_type ("path", new Regex ("[\w/]+", RegexCompileFlags.OPTIMIZE));

If you would like ìnt to match negatives integer, you may just do:

app.register_type ("int", new Regex ("-?\d+", RegexCompileFlags.OPTIMIZE));

Rule parameters are available from the routing context by their name.

app.get ("/<controller>/<action>", (req, res, next, context) => {
    var controller = context["controller"].get_string ();
    var action     = context["action"].get_string ();


Helpers for the methods defined in the HTTP/1.1 protocol and the extra TRACE methods are included. The path is matched according to the rule system defined previously.

app.get ("/", (req, res) => {
    return res.expand_utf8 ("Hello world!");

The following example deal with a POST request providing using libsoup-2.4/Soup.Form to decode the payload. ("/login", (req, res) => {
    var data = Soup.Form.decode (req.flatten_utf8 ());

    var username = data["username"];
    var password = data["password"];

    // assuming you have a session implementation in your app
    var session = new Session.authenticated_by (username, password);

    return true;

Regular expression

Changed in version 0.3: The regex helper must be provided with an explicit leading slash.

If the rule system does not suit your needs, it is always possible to use regular expression. Regular expression will be automatically scoped, anchored and optimized.

app.regex (Method.GET, new Regex ("/home/?", RegexCompileFlags.OPTIMIZE), (req, res) => {
    return res.body.write_all ("Matched using a regular expression.".data, true);

Named captures are registered on the routing context.

app.regex (new Regex ("/(?<word>\w+)", RegexCompileFlags.OPTIMIZE), (req, res, next, ctx) => {
    var word = ctx["word"].get_string ();

Matcher callback

Request can be matched by a simple callback typed by the MatcherCallback delegate.

app.matcher (Method.GET, (req) => { return req.uri.get_path () == "/home"; }, (req, res) => {
    // matches /home


Changed in version 0.3: The scope feature does not include a slash, instead you should scope with a leading slash like shown in the following examples.

Scoping is a powerful prefixing mechanism for rules and regular expressions. Route declarations within a scope will be prefixed by <scope>.

The Router maintains a scope stack so that when the program flow enter a scope, it pushes the fragment on top of that stack and pops it when it exits.

app.scope ("/admin", (admin) => {
    // admin is a scoped Router
    app.get ("/users", (req, res) => {
        // matches /admin/users

app.get ("/users", (req, res) => {
    // matches /users

To literally mount an application on a prefix, see the Basepath middleware.


New in version 0.3.

During the routing, states can obtained from a previous handler or passed to the next one using the routing context.

Keys are resolved recursively in the tree of context by looking at the parent context if it’s missing.

app.get ("/", (req, res, next, context) => {
    context["some key"] = "some value";
    return next ();

app.get ("/", (req, res, next, context) => {
    var some_value = context["some key"]; // or context.parent["some key"]
    return return res.body.write_all (, null);

Error handling

New in version 0.2.1: Prior to this release, any unhandled error would crash the main loop iteration.

Changed in version 0.3: Error and status codes are now handled with a catch block or using the Status middleware.

Changed in version 0.3: The default handling is not ensured by the Basic middleware.

Changed in version 0.3: Thrown errors are forwarded to VSGI, which process them essentially the same way. See VSGI for more details.

Similarly to status codes, errors are propagated in the HandlerCallback and NextCallback delegate signatures and can be handled in a catch block.

app.use (() => {
    try {
        return next ();
    } catch (IOError err) {
        res.status = 500;
        return res.expand_utf8 (err.message);

app.get ("/", (req, res) => {
    throw new IOError.FAILED ("I/O failed some some reason.");

Thrown status code can also be caught this way, but it’s much more convenient to use the Status middleware.


Since VSGI.ApplicationCallback is type compatible with HandlerCallback, it is possible to delegate request handling to another VSGI-compliant application.

In particular, it is possible to treat Router.handle like any handling callback.


This feature is a key design of the router and is intended to be used for a maximum inter-operability with other frameworks based on VSGI.

The following example delegates all GET requests to another router which will process in isolation with its own routing context.

var app = new Router ();
var api = new Router ();

// delegate all GET requests to api router
app.get ("*", api.handle);

One common pattern with subrouting is to attempt another router and fallback on next.

var app = new Router ();
var api = new Router ();

app.get ("/some-resource", (req, res) => {
    return api.handle (req, res) || next ();

Cleaning up route logic

Performing a lot of route bindings can get messy, particularly if you want to split an application several reusable modules. Encapsulation can be achieved by subclassing Router and performing initialization in a construct block:

public class AdminRouter : Router {

    construct {
        rule (Method.GET,               "/admin/user",          view);
        rule (Method.GET | Method.POST, "/admin/user/<int:id>", edit);

    public bool view (Request req, Response res) {
        return render_template ("users", Users.all ());

    public bool edit (Request req, Response res) {
        var user = User.find (ctx["id"]);
        if (req.method == "POST") {
            user.values (Soup.Form.decode (req.flatten_utf8 ()));
            user.update ();
        return render_template ("user", user);

Using subrouting, it can be assembled to a parent router given a rule (or any matching process described in this document). This way, incoming request having the /admin/ path prefix will be delegated to the admin router.

var app = new Router ();

app.rule (Method.ALL, "/admin/*", new AdminRouter ().handle);

The Basepath middleware provide very handy path isolation so that the router can be simply written upon the leading / and rebased on any basepath. In that case, we can strip the leading /admin in router’s rules.

var app = new Router ();

// captures '/admin/users' and '/admin/user/<int:id>'
app.use (basepath ("/admin", new AdminRouter ().handle));