Vala JSON Samples

Gisgraphy Web Service

This sample shows usage of json-glib combined with libsoup as a HTTP client. The sample uses the Gisgraphy web service as a source for a sample JSON document.

Requires Vala >= 0.11.0

void main () {
    var uri = "".printf ("asakusa");

    var session = new Soup.Session ();
    var message = new Soup.Message ("GET", uri);
    session.send_message (message);

    try {
        var parser = new Json.Parser ();
        parser.load_from_data ((string) message.response_body.flatten ().data, -1);

        var root_object = parser.get_root ().get_object ();
        var response = root_object.get_object_member ("response");
        var results = response.get_array_member ("docs");
        int64 count = results.get_length ();
        int64 total = response.get_int_member ("numFound");
        stdout.printf ("got %lld out of %lld results:\n\n", count, total);

        foreach (var geonode in results.get_elements ()) {
            var geoname = geonode.get_object ();
            stdout.printf ("%s\n%s\n%f\n%f\n\n",
                          geoname.get_string_member ("name"),
                          geoname.get_string_member ("country_name"),
                          geoname.get_double_member ("lng"),
                          geoname.get_double_member ("lat"));
    } catch (Error e) {
        stderr.printf ("I guess something is not working...\n");

Compile and Run

$ valac --thread --pkg libsoup-2.4 --pkg json-glib-1.0 json-sample.vala
$ ./jsonsample

Glosbe translation API

This sample uses libsoup and json-glib to translate text via the Glosbe API.

Requires Vala >= 0.11.0

string translate (string text, string input_language, string output_language) throws Error {
    string uri = "";
    string full_uri = "%s?phrase=%s&from=%s&dest=%s&format=json&pretty=true".printf (uri,
                                 Soup.URI.encode (text, null),
                                 input_language, output_language);

    var session = new Soup.Session ();
    var message = new Soup.Message ("GET", full_uri);
    session.send_message (message);

    var parser = new Json.Parser ();
    parser.load_from_data ((string) message.response_body.flatten ().data, -1);

    var root_object = parser.get_root ().get_object ();
    string translated_text = root_object.get_array_member ("tuc")
                                        .get_object_element (0)
                                        .get_object_member ("phrase")
                                        .get_string_member ("text");

    return translated_text;

void main () {
    try {
        string original_text = "Hello World";
        string translated_text = translate (original_text, "eng", "spa");
        stdout.printf ("Translated text: %s\n", translated_text);
    } catch (Error e) {
        stderr.printf ("I think something went wrong!\n");

Compile and Run

$ valac --thread --pkg libsoup-2.4 --pkg json-glib-1.0 json-translator.vala
$ ./json-translator

Transmission RPC Interface

This example generates a JSON request object which is send via HTTP to the transmission-daemon which in turn returns the torrent data as JSON.

using Soup;
using Json;

class Transmission {
   private SessionAsync session;
   private string user;
   private string password;
   private string path;
   private string sessionid;
   private static string[] std_fields = { "id","name","percentDone","rateDownload","rateUpload","sizeWhenDone"};

   public Transmission(string host, int port, string? user, string? password) {
      if(user != null && password != null) {
         this.user = user; this.password = password;
      path = @"http://$host:$port/transmission/rpc";
      session = new SessionAsync();
      //In case you setup Transmission with authentication this sets a callback for handling it

      //Newer Transmission versions require a sessionid to be carried with each request. Get one!
      var msg = new Message("GET", path);
      sessionid = msg.response_headers.get("X-Transmission-Session-Id");
      if(sessionid == null)
         error("Transmission version to old or not configured on that port");

   public void request_list() {
      size_t length;
      string json;

      var msg = new Message("POST", path);
      //Start a Generator and setup some fields for it
      var gen = new Generator();
      var root = new Json.Node(NodeType.OBJECT);
      var object = new Json.Object();

      var args = new Json.Object();
      object.set_object_member("arguments", args);
      object.set_string_member("method", "torrent-get");

      var fields = new Json.Array();
      foreach(string s in std_fields)
      args.set_array_member("fields", fields);

      //Send the request json to the server and carry the sessionid along with the request
      json = gen.to_data(out length);
      msg.request_body.append(MemoryUse.COPY, json, length);
      msg.request_headers.append("X-Transmission-Session-Id", sessionid);

      try {
         //Setup a Parser and load the data from the transmission response
         var parser = new Json.Parser();
         parser.load_from_data(msg.response_body.flatten().data, -1);
         //This basically iterates the whole json tree of elements down to the one with the torrent informations
         var info = parser.get_root().get_object().get_object_member("arguments").get_array_member("torrents").get_elements();
         foreach(var node in info) {
            var obj = node.get_object();
            stdout.printf("%d: %s - %.2f%% [%.2f/%.2f] %d byte\n",
      catch(Error e) {
         error("%s", e.message);
   private void auth(Message msg, Auth auth, bool retry) {
      if(user != null && password != null)
         auth.authenticate(user, password);
      else if(retry)
         error("Wrong username/password");
         error("Transmission server requires authentication");

   public static void main() {
      var t = new Transmission("", 9091, null, null);

Compile and Run

$ valac --thread --pkg libsoup-2.4 --pkg json-glib-1.0 transmission-rpc.vala
$ ./transmission-rpc


Projects/Vala/JsonSample (last edited 2014-03-04 13:27:43 by StefanTalpalaru)