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+[#]: subject: "Boost the power of C with these open source libraries"
+[#]: via: "https://opensource.com/article/22/5/libsoup-gobject-c"
+[#]: author: "Joël Krähemann https://opensource.com/users/joel2001k"
+[#]: collector: "lkxed"
+[#]: translator: " "
+[#]: reviewer: " "
+[#]: publisher: " "
+[#]: url: " "
+
+Boost the power of C with these open source libraries
+======
+GObject and libsoup do a lot of work for you, so you can turn your attention to inventing amazing applications in C.
+
+![Why and how to handle exceptions in Python Flask][1]
+（Image by: Image from Unsplash.com, Creative Commons Zero）
+
+The [GLib Object System (GObject)][2] is a library providing a flexible and extensible object-oriented framework for C. In this article, I demonstrate using the 2.4 version of the library.
+
+The GObject libraries extend the ANSI C standard, with typedefs for common types such as:
+
+* gchar: a character type
+* guchar: an unsigned character type
+* gunichar: a fixed 32 bit width unichar type
+* gboolean: a boolean type
+* gint8, gint16, gint32, gint64: 8, 16, 32, and 64 bit integers
+* guint8, guint16, guint32, guint64: unsigned 8, 16, 32, and 64 bit integers
+* gfloat: an IEEE Standard 754 single precision floating point number
+* gdouble: an IEEE Standard 754 double precision floating point number
+* gpointer: a generic pointer type
+
+### Function pointers
+
+GObject also introduces a type and object system with classes and interfaces. This is possible because the ANSI C language understands function pointers.
+
+To declare a function pointer, you can do this:
+
+```c
+void (*my_callback)(gpointer data);
+```
+
+But first, you need to assign the `my_callback` variable:
+
+```c
+void my_callback_func(gpointer data)
+{
+  //do something
+}
+
+my_callback = my_callback_func;
+```
+
+The function pointer `my_callback` can be invoked like this:
+
+```c
+gpointer data;
+data = g_malloc(512 * sizeof(gint16));
+my_callback(data);
+```
+
+### Object classes
+
+The GObject base class consists of 2 structs (`GObject` and `GObjectClass` ) which you inherit to implement your very own objects.
+
+You embed GObject and GObjectClass as the first struct field:
+
+```c
+struct _MyObject
+{
+  GObject gobject;
+  //your fields
+};
+
+struct _MyObjectClass
+{
+  GObjectClass gobject;
+  //your class methods
+};
+
+GType my_object_get_type(void);
+```
+
+The object’s implementation contains fields, which might be exposed as properties. GObject provides a solution to private fields, too. This is actually a struct in the C source file, instead of the header file. The class usually contains function pointers only.
+
+An interface can’t be derived from another interface and is implemented as following:
+
+```c
+struct _MyInterface
+{
+  GInterface ginterface;
+  //your interface methods
+};
+```
+
+Properties are accessed by `g_object_get()` and `g_object_set()` function calls. To get a property, you must provide the return location of the specific type. It’s recommended that you initialize the return location first:
+
+```c
+gchar *str
+
+str = NULL;
+
+g_object_get(gobject,
+  "my-name", &str,
+  NULL);
+```
+
+Or you might want to set the property:
+
+```c
+g_object_set(gobject,
+  "my-name", "Anderson",
+  NULL);
+```
+
+### The libsoup HTTP library
+
+The `libsoup` project provides an HTTP client and server library for GNOME. It uses GObjects and the glib main loop to integrate with GNOME applications, and also has a synchronous API for use in command-line tools. First, create a `libsoup` session with an authentication callback specified. You can also make use of cookies.
+
+```c
+SoupSession *soup_session;
+SoupCookieJar *jar;
+
+soup_session = soup_session_new_with_options(SOUP_SESSION_ADD_FEATURE_BY_TYPE, SOUP_TYPE_AUTH_BASIC,
+  SOUP_SESSION_ADD_FEATURE_BY_TYPE, SOUP_TYPE_AUTH_DIGEST,
+  NULL);
+
+jar = soup_cookie_jar_text_new("cookies.txt",
+  FALSE);     
+
+soup_session_add_feature(soup_session, jar);
+g_signal_connect(soup_session, "authenticate",
+  G_CALLBACK(my_authenticate_callback), NULL);
+```
+
+Then you can create a HTTP GET request like the following:
+
+```c
+SoupMessage *msg;
+SoupMessageHeaders *response_headers;
+SoupMessageBody *response_body;
+guint status;
+GError *error;
+
+msg = soup_form_request_new("GET",
+  "http://127.0.0.1:8080/my-xmlrpc",
+  NULL);
+
+status = soup_session_send_message(soup_session,
+  msg);
+
+response_headers = NULL;
+response_body = NULL;
+
+g_object_get(msg,
+  "response-headers", &response_headers,
+  "response-body", &response_body,
+  NULL);
+
+g_message("status %d", status);
+cookie = NULL;
+soup_message_headers_iter_init(&iter,
+response_headers);
+
+while(soup_message_headers_iter_next(&iter, &name, &value)){    
+  g_message("%s: %s", name, value);
+}
+
+g_message("%s", response_body->data);
+if(status == 200){
+  cookie = soup_cookies_from_response(msg);
+  while(cookie != NULL){
+    char *cookie_name;
+    cookie_name = soup_cookie_get_name(cookie->data);
+    //parse cookies
+    cookie = cookie->next;
+  }
+}
+```
+
+The authentication callback is called as the web server asks for authentication.
+
+Here’s a function signature:
+
+```c
+#define MY_AUTHENTICATE_LOGIN "my-username"
+#define MY_AUTHENTICATE_PASSWORD "my-password"
+
+void my_authenticate_callback(SoupSession *session,
+  SoupMessage *msg,
+  SoupAuth *auth,
+  gboolean retrying,
+  gpointer user_data)
+{
+  g_message("authenticate: ****");
+  soup_auth_authenticate(auth,
+                         MY_AUTHENTICATE_LOGIN,
+                         MY_AUTHENTICATE_PASSWORD);
+}
+```
+
+### A libsoup server
+
+For basic HTTP authentication to work, you must specify a callback and server context path. Then you add a handler with another callback.
+
+This example listens to any IPv4 address on localhost port 8080:
+
+```c
+SoupServer *soup_server;
+SoupAuthDomain *auth_domain;
+GSocket *ip4_socket;
+GSocketAddress *ip4_address;
+MyObject *my_object;
+GError *error;
+
+soup_server = soup_server_new(NULL);
+auth_domain = soup_auth_domain_basic_new(SOUP_AUTH_DOMAIN_REALM, "my-realm",
+  SOUP_AUTH_DOMAIN_BASIC_AUTH_CALLBACK, my_xmlrpc_server_auth_callback,
+  SOUP_AUTH_DOMAIN_BASIC_AUTH_DATA, my_object,
+  SOUP_AUTH_DOMAIN_ADD_PATH, "my-xmlrpc",
+  NULL);
+
+soup_server_add_auth_domain(soup_server, auth_domain);
+soup_server_add_handler(soup_server,
+  "my-xmlrpc",
+  my_xmlrpc_server_callback,
+  my_object,
+  NULL);
+
+ip4_socket = g_socket_new(G_SOCKET_FAMILY_IPV4,
+  G_SOCKET_TYPE_STREAM,
+  G_SOCKET_PROTOCOL_TCP,
+  &error);
+
+ip4_address = g_inet_socket_address_new(g_inet_address_new_any(G_SOCKET_FAMILY_IPV4),
+  8080);
+error = NULL;
+g_socket_bind(ip4_socket,
+  ip4_address,
+  TRUE,
+  &error);
+error = NULL;
+g_socket_listen(ip4_socket, &error);
+
+error = NULL;
+soup_server_listen_socket(soup_server,
+  ip4_socket, 0, &error);
+```
+
+In this example code, there are two callbacks. One handles authentication, and the other handles the request itself.
+
+Suppose you want a web server to allow a login with the credentials username **my-username** and the password **my-password**, and to set a session cookie with a random unique user ID (UUID) string.
+
+```c
+gboolean my_xmlrpc_server_auth_callback(SoupAuthDomain *domain,
+  SoupMessage *msg,
+  const char *username,
+  const char *password,
+  MyObject *my_object)
+{
+  if(username == NULL || password == NULL){
+    return(FALSE);
+  }
+
+  if(!strcmp(username, "my-username") &&
+     !strcmp(password, "my-password")){
+    SoupCookie *session_cookie;
+    GSList *cookie;
+    gchar *security_token;
+    cookie = NULL;
+
+    security_token = g_uuid_string_random();
+    session_cookie = soup_cookie_new("my-srv-security-token",
+      security_token,
+      "localhost",
+      "my-xmlrpc",
+      -1);
+
+     cookie = g_slist_prepend(cookie,
+       session_cookie);  
+     soup_cookies_to_request(cookie,
+       msg);
+    return(TRUE);
+  }
+  return(FALSE);
+}
+```
+
+A handler for the context path **my-xmlrpc**:
+
+```c
+void my_xmlrpc_server_callback(SoupServer *soup_server,
+  SoupMessage *msg,
+  const char *path,
+  GHashTable *query,
+  SoupClientContext *client,
+  MyObject *my_object)
+{
+  GSList *cookie;
+  cookie = soup_cookies_from_request(msg);
+  //check cookies
+}
+```
+
+### A more powerful C
+
+I hope my examples show how the GObject and libsoup projects give C a very real boost. Libraries like these extend C in a literal sense, and by doing so they make C more approachable. They do a lot of work for you, so you can turn your attention to inventing amazing applications in the simple, direct, and timeless C language.
+
+--------------------------------------------------------------------------------
+
+via: https://opensource.com/article/22/5/libsoup-gobject-c
+
+作者：[Joël Krähemann][a]
+选题：[lkxed][b]
+译者：[译者ID](https://github.com/译者ID)
+校对：[校对者ID](https://github.com/校对者ID)
+
+本文由 [LCTT](https://github.com/LCTT/TranslateProject) 原创编译，[Linux中国](https://linux.cn/) 荣誉推出
+
+[a]: https://opensource.com/users/joel2001k
+[b]: https://github.com/lkxed
+[1]: https://opensource.com/sites/default/files/lead-images/computer_code_programming_laptop.jpg
+[2]: https://docs.gtk.org/gobject/concepts.html