VSGI

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.

Handler

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 bool 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.

Asynchronous handling

New in version 0.4.

To go asynchronous, one can override the vsgi-0.3/VSGI.Handler.handle_async symbol instead.

using VSGI;

public class App : Handler {

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

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

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");

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.

[ModuleInit]
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!");
    }
}

Loader

New in version 0.4.

VSGI provide the vsgi-loader utility designed to serve handlers written as gmodule-2.0/GLib.Module from any supported implementation, no recompilation needed.

Furthermore, it also provide a live-reloader based on gio-2.0/GLib.FileMonitor to remove the necessity of restarting the server if the application code changes.

Usage

The vsgi-loader program can be used as follow:

vsgi-loader [--directory=<directory>] [--server=<server>] [--live-reload] <module_name> -- <server_arguments>
  • the directory where the shared library is located or default system path
  • the server implementation which is either http, fastcgi or scgi and defaults to http
  • if --live-reload is set, the server will automatically reload the shared library on change
  • the name of the library without the lib prefix and .so extension
  • arguments for the server implementation specified by the --server flag and delimited by --

Warning

Arguments for the server implementation must be separated by a -- indicator, otherwise they will be interpreted by vsgi-loader.

vsgi-loader --directory=build/examples/loader loader -- --port=3005

Additional arguments are described in vsgi-loader --help.

vsgi-loader --help

For details about server-specific options, the --help flag can be passed beyond.

vsgi-loader --server=fastcgi app -- --help

Initialization

To perform initialization, one can implement the gio-2.0/GLib.Initable interface, it will automatically be called by the loader.

[ModuleInit]
public Type handler_init (TypeModule type_module) {
    return typeof (App);
}

public class App : Handler, Initable {

    public Gda.Connection database { get; construct; }

    public bool init (Cancellable? cancellable = null) throws Error {
        database.open ();
    }

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