Using SILC Client Library
Introduction
SILC Client library is a full featured SILC Client protocol implementation. The library has been designed to be complete SILC client without actual user interface. The library provides the API for the appliation which it can use to implement generally whatever user interface it wants. The SILC Client Library recides in the lib/silcclient/ directory. It uses common and core component of SILC protocol from the lib/silccore, SKE from lib/silcske and general utility routines from lib/silcutil.
The `silcclient.h' file defines the function prototypes that application must implement in order to be able to create the user interface with the library. The idea is that the application can implement whatever user interface routines in the functions and display the data whatever way it wants. The library is entirely transparent to the user interface and it does not include any user interface specific issues such as window handling or item handling on the screen etc. These does not interest the library. The `silcclient.h' also defines the client libary interface the application can call. The interface includes for example functions for sending channel and private messages, client and channel retrieval and other utility functions.
Including Library Headers
Your application must include the following includes in your sources to get access all SILC Client Library routines:
`#include "silcincludes.h"
#include "silcclient.h"`
Network Initialization on Win32
If you are programming your SILC client application on Windows system, you will need to initialize the network routines in order to be able to use the client library. The network initialization is done by calling the silc_net_win32_init at the start of your Windows application. Usually this is done either in main() or WinMain() function, or other similar place. This function should be called before calling any other SILC routine.
`if (silc_net_win32_init() == FALSE)
exit_with_error();`
This function is available only on Win32 platforms, and on other platforms the network routines are initialized automatically by the operating system.
Creating Client
The client is context or entity based, so several client entitites can be created in the application if needed. However, it should be noted that they are completely independent from each other and can be seen as different applications. Usually only one client entity is needed per application.
The client object is SilcClient which is usually allocated in following manner:
`SilcClient client = silc_client_alloc(&ops, params, context, silc_version_string);`
`ops' is the static structure of client operations that library will call. `context' can be some application specific context that will be saved into the SilcClient object. It is up to the caller to free this context. SilcClient is always passed to the application thus the application specific context can be retrieved from the SilcClient object. See `client.h' file for detailed definition of SilcClient object.
The `silc_version_string' is the current protocol version string, and you can get it by including `silcversion.h' header in your source code.
`ops' can be defined for example as follows:
`SilcClientOperations ops = {
silc_say,
silc_channel_message,
silc_private_message,
silc_notify,
silc_command,
silc_command_reply,
silc_connect,
silc_disconnect,
silc_get_auth_method,
silc_verify_public_key,
silc_ask_passphrase,
silc_failure,
silc_key_agreement,
};
`
Please see the `client_ops_example.c' source file in lib/silcclient/ directory for predefined structure and stub functions for your convenience. It is provided for programmers so that they can copy it and use it directly in their application.
Initializing the Client
The client must be initialized before running. However, there are also some other tasks that must be done before initializing the client. The following pointers must be set by the application before calling the initializing function:
`client->username
client->hostname
client->realname
client->pkcs
client->public_key
client->private_key`
You may also set client->nickname if you want. If it is set then the library will change the nickname to that one after the client is connected to the server. If not set, then server will initially give the nickname which is same as the username.
After setting the pointers one must call:
`silc_client_init(client);`
which then initializes the client library for the `client'. If the pointers mentioned above are not initialized the silc_client_init will fail. The application should check the return value of the silc_client_init function.
Running the Client
The client is run by calling silc_client_run. The function will call the scheduler from utility library that will be run until the program is ended. When silc_client_run returns the application is ended. Thus, to run the client, call:
`silc_client_run(client);`
Usually application may do some other initializations before calling this function. For example before calling this function application should initialize the user interface.
Running the Client in GUI application
Many GUI applications has their own main loop or event loop, which they would like to use or are forced to use by the underlaying system. If you are developing for example GUI application on Unix system, and you are using GTK+ or QT as GUI library you would probably like to use their own main loop. SILC Client can be run under external main loop as well. The interface provides a function silc_client_run_one which will run the client library once, and returns immediately. During that running it can process incoming data and send outgoing data, but it is guaranteed that it will not block the calling process.
It is suggested that you would call this function as many times in a second as possible to provide smooth action for the client library. You can use an timeout task, or an idle task provided by your GUI library to accomplish this. After you have initialized the client library with silc_client_init, you should register the timeout task or idle task that will call the silc_client_run_one periodically. In the Toolkit package there is GTK-- GUI example in silcer/ directory. That example calls the silc_client_run_one every 50 milliseconds, and it should be sufficient for smooth working.
For Win32 the silc_client_run can be used instead of using the Windows's own event loop. However, if you would like to use the silc_client_run_one also on Win32 systems it is possible.
Running Client in GTK--
Here is a short example how to run the SILC Client libary under the Gnome/GTK--'s main loop:
`gint YourClass::silc_scheduler()
{
// Run the SILC client once, and return immediately. This function
// is called every 50 milliseconds by the Gnome main loop, to process
// SILC stuff. This function will read data, and write data to network,
// etc. Makes the client library tick! :)
silc_client_run_one(silc_client);
return 1;
}
`
then, during initialization of the SILC Client call:
`// Setup SILC scheduler as timeout task. This will handle the SILC
// client library every 50 milliseconds. It will actually make the
// SILC client work on background.
Gnome::Main::timeout.connect(slot(this, &YourClass::silc_scheduler), 50);
`
This will call the function silc_scheduler every 50 millisecconds, which on the otherhand will call silc_client_run_one, which will make the SILC Client library work on the background of the GUI application.
Creating Connection to Server
Connection to remote SILC server is done by calling:
`silc_client_connect_to_server(client, port, hostname, context);`
The function will create the connection asynchronously to the server, ie. the function will return before the actual connection is created. After the connection is created the client->ops->connect operation is called.
Generally speaking the connections are associated with windows' on the screen. IRC is usually implemented this way, however it is not the necessary way to associate the client's connections. SilcClientConnection object is provided by the library (and is always passed to the application) that can be used in the application to associate the connection from the library. Application specific context can be saved to the SilcClientConnection object which then can be retrieved in the application, thus perhaps associate the connection with what ever object in application (window or something else).
Using Own Connecting
Application might not want to use silc_client_connect_to_server function if it wants to perform its own connecting for some reason. In this case application must call function silc_client_start_key_exchange after it has created the connection by itself. This function starts the key exhange protocol between the client and server and the library takes care of everything after that.
After connection has been created application must call:
`SilcClientConnection conn;
/* Add new connection to client */
conn = silc_client_add_connection(client, hostname, port, context);
/* Start key exchange and let the library handle everything
after this point on. */
silc_client_start_key_exchange(client, conn, sock);`
NOTE: These calls are performed only and only if application did not call silc_client_connect_to_server function, but performed the connecting process manually.
Debugging
Being able to debug what you have coded is important when troubles occurs during coding, and they always do. SILC supports extensive debugging capabilities which are also available for client library user. You should have compiled the Toolkit with --enable-debug option so that run-time debugging is enabled.
Then, to say in your application you would like to use the debugging use the SILC_ENABLE_DEBUG macro. Put this macro to your main header file, or some other file that needs the debugging enabled. After using this macro you are able to use the debugging routines provided by the SILC Toolkit. Note that, the Toolkit library must be compiled with --enable-debug for this macro to have any effect.
To turn on the run-time debugging set the global variable "silc_debug" to TRUE. To see packet hexdumps you can set also "silc_debug_hexdump" to TRUE. Hexdumps can create more debug log so not setting it to TRUE by default is probably best. To get debug messages out of specific modules you can set a debug string with silc_log_set_debug_string function. The function takes regex string as argument, for example:
`silc_debug = TRUE;
silc_log_set_debug_string("*");
`
This piece of code turns on the debugging and sets "*" as debug string. This means that all debug messages are printed. To get debugging out of only for example SILC Client Library the debug string could be "silc_client*". The debug string matches to function names and filenames so it is possible to get debugging out of specific files, and specific functions. Other examples could be:
`silc_log_set_debug_string("silc_client*,*socket*,*ske*");
`
By default, all debug messages are printed to standard error output (stderr). If you want to redirect the debug messages somewhere else you can set your own debug callback with silc_log_set_debug_callbacks function:
`silc_log_set_debug_callbacks(my_debug_callback, my_context, my_hexdump_callback, my_context);
`
See the lib/silcutil/silclog.h for definition of the callbacks. See the same file for other logging and debugging information.
You can also use SILC debugging capabilities in your own application. To produce debug messages you can use SILC_LOG_DEBUG and SILC_LOG_HEXDUMP macros in your application. The SILC_LOG_DEBUG can print out normal debug messages with variable argument list, for example:
`SILC_LOG_DEBUG(("Start"));
SILC_LOG_DEBUG(("Packet length %d", packet_len));
SILC_LOG_DEBUG(("The remote is %s on %d", sock->ip, sock->port));`
The SILC_LOG_HEXDUMP macro can be used dump data which couldn't be printed out otherwise, for example binary data.
`SILC_LOG_HEXDUMP(("Packet"), packet->data, packet->len);
SILC_LOG_HEXDUMP(("Packet, size=%d", size), packet->data, packet->len);`
Note that the variable arguments in SILC_LOG_HEXDUMP are before the second last parenthesis, and the last two arguments are the data, and its length that are hexdumped.
Example Client
This section includes an example SILC client implementation in pseudo-like C code. It creates and initializes the client and sets up an imaginary user interface. The user will use the user interface then to create the connections. The SilcClientOperations are expected to be implemented.

    #include "silcincludes.h"
    #include "silcclient.h"

    int main()
    {
    	SilcClientOperations ops = {
    	  silc_say,
    	  silc_channel_message,
    	  silc_private_message,
    	  silc_notify,
    	  silc_command,
    	  silc_command_reply,
    	  silc_connect,
    	  silc_disconnect,
    	  silc_get_auth_method,
    	  silc_verify_public_key,
    	  silc_ask_passphrase,
    	  silc_failure,
    	  silc_key_agreement,
    	  silc_ftp,
    	  silc_detach
    	};

    	SilcClient client;

    	/* Allocate SILC client. The `silc_version_string' is defined
    	   in includes/version.h file. */
    	client = silc_client_alloc(&ops, NULL, NULL, silc_version_string);

    	/* Set the mandatory pointers, read public and private key from
    	   files (or somewhere) and return pointers and PKCS context. */
    	client->username = silc_get_username();
    	client->hostname = silc_net_localhost();
    	client->realname = silc_get_real_name();
    	client->pkcs = get_public_and_private_key(&client->public_key,
    						  &client->private_key);

    	/* If the keys does not exist, create a key pair since we must
    	   provide key pair to the library. */
    	if (!client->pkcs)
    	  generate_key_new_key_pair(client);

    	/* Iinitialize client */
    	if (!silc_client_init(client))
    	  fatal_error("Could not initialize client");

    	/* Initialize user interface. The user interface can be generally
    	   initialized at any phase, including before actually allocating
    	   and initializing the client, if wished. */
    	InitUserInterface();
    	DoCoolThings();

    	/* Start the client. This will start the scheduler. At this phase
    	   the user might have the user interface in front of him already.
    	   He will use the user interface to create the connection to the
    	   server for example. When this function returns the program is
    	  ended. */
    	silc_client_run(client);

    	/* Client is ended */
    	return 0;
    }