VSGI is a middleware that interfaces different Web server technologies under a common and simple set of abstractions.

For the moment, it is developed along with Valum to target the needs of a Web framework, but it will eventually be extracted and distributed as a shared library.

VSGI produces process-based applications that are able to communicate with various HTTP servers using standardized protocols.


The entry point of any VSGI application implement the vsgi-0.3/VSGI.Handler abstract class. It provides a function of two arguments: a Request and a Response that return a boolean indicating if the request has been or will be processed. It may also raise an error.

using VSGI;

public class App : Handler {

    public override handle (Request req, Response res) throws Error {
        // process the request and produce the response...
        return true;

Server.new ("http", handler: new App ()).run ();

If a handler indicate that the request has not been processed, it’s up to the server implementation to decide what will happen.

From now on, examples will consist of vsgi-0.3/VSGI.Handler.handle content to remain more concise.

Error handling

New in version 0.3.

At any moment, an error can be raised and handled by the server implementation which will in turn teardown the connection appropriately.

throw new IOError.FAILED ("some I/O failed");

Asynchronous processing

The asynchronous processing model follows the RAII pattern and wraps all resources in a connection that inherits from gio-2.0/GLib.IOStream. It is therefore important that the said connection is kept alive as long as the streams are being used.

The Request holds a reference to the said connection and the Response indirectly does as it holds a reference to the request. Generally speaking, holding a reference on any of these two instances is sufficient to keep the streams usable.


As VSGI relies on reference counting to free the resources underlying a request, you must keep a reference to either the Request or Response during the processing, including in asynchronous callbacks.

It is important that the connection persist until all streams operations are done as the following example demonstrates:

res.body.write_async.begin ("Hello world!",
                            (body, result) => {
    // the response reference will make the connection persist
    var written = res.body.write_async.end (result);

Dynamic loading

New in version 0.3.

It could be handy to dynamically load handlers the same way Server are.

Fortunately, this can be performed with the HandlerModule by providing a directory and name for the shared library containing a dynamically loadable application.

var module = var new HandlerModule ("<directory>", "<name>");

Server.new ("http", handler: Object.new (module.handler_type)).run ();

The only required definition is a handler_init symbol that return the type of some Handler. In this case, the library should be located in <directory>/lib<name>.so, although the actual name is system-dependant.

public Type handler_init (TypeModule type_module) {
    return typeof (App);

public class App : Handler {

    public bool handle (Request req, Response res) {
        return res.expand_utf8 ("Hello world!");

Eventually, this will be used to provide a utility to run arbitrary applications with support for live-reloading.