Changes :

libcli.c

• add naive custom implementation of char *strchrnul(const char *s, int c)

Makefile

• use gcc-9 instead, as gcc aliases to clang on macOS
• set CFLAGS to --std=gnu99

Original README.md

Libcli provides a shared C library for including a Cisco-like command-line interface into other software.

It’s a telnet interface which supports command-line editing, history, authentication and callbacks for a user-definable function tree.

To compile:

$ make
$ make install

This will install libcli.so into /usr/local/lib. If you want to change the location, edit Makefile.

There is a test application built called clitest. Run this and telnet to port 8000.

By default, a single username and password combination is enabled.

Username: fred
Password: nerk

Get help by entering help or hitting ?.

libcli provides support for using the arrow keys for command-line editing. Up and Down arrows will cycle through the command history, and Left & Right can be used for editing the current command line.

libcli also works out the shortest way of entering a command, so if you have a command show users | grep foobar defined, you can enter sh us | g foobar if that is the shortest possible way of doing it.

Enter sh? at the command line to get a list of commands starting with sh

A few commands are defined in every libcli program:

• help
• quit
• exit
• logout
• history

Use in your own code:

First of all, make sure you #include <libcli.h> in your C code, and link with -lcli.

If you have any trouble with this, have a look at clitest.c for a demonstration.

Start your program off with a cli_init(). This sets up the internal data structures required.

When a user connects, they are presented with a greeting if one is set using the cli_set_banner(banner) function.

By default, the command-line session is not authenticated, which means users will get full access as soon as they connect. As this may not be always the best thing, 2 methods of authentication are available.

First, you can add username / password combinations with the cli_allow_user(username, password) function. When a user connects, they can connect with any of these username / password combinations.

Secondly, you can add a callback using the cli_set_auth_callback(callback) function. This function is passed the username and password as char *, and must return CLI_OK if the user is to have access and CLI_ERROR if they are not.

The library itself will take care of prompting the user for credentials.

Commands are built using a tree-like structure. You define commands with the cli_register_command(parent, command, callback, privilege, mode, help) function.

parent is a cli_command * reference to a previously added command. Using a parent you can build up complex commands.

e.g. to provide commands show users, show sessions and show people, use the following sequence:

cli_command *c = cli_register_command(NULL, "show", NULL, PRIVILEGE_UNPRIVILEGED, MODE_EXEC, NULL);
cli_register_command(c, "sessions", fn_sessions, PRIVILEGE_UNPRIVILEGED, MODE_EXEC, "Show the sessions connected");
cli_register_command(c, "users", fn_users, PRIVILEGE_UNPRIVILEGED, MODE_EXEC, "Show the users connected");
cli_register_command(c, "people", fn_people, PRIVILEGE_UNPRIVILEGED, MODE_EXEC, "Show a list of the people I like");

If callback is NULL, the command can be used as part of a tree, but cannot be individually run.

If you decide later that you don't want a command to be run, you can call cli_unregister_command(command). You can use this to build dynamic command trees.

It is possible to carry along a user-defined context to all command callbacks using cli_set_context(cli, context) and cli_get_context(cli) functions.

You are responsible for accepting a TCP connection, and for creating a process or thread to run the cli. Once you are ready to process the connection, call cli_loop(cli, sock) to interact with the user on the given socket.

This function will return when the user exits the cli, either by breaking the connection or entering quit.

Call cli_done() to free the data structures.