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