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### 5.28 libnet

#### 5.28.1 Overview

View lcov test coverage results on http://www.gnu.org/software/liquidwar6/coverage/src/lib/net/index.html.

#### 5.28.2 API

— Function: int lw6net_dns_is_ip (char * ip)

> ip: the string to check

> Tests if a given string is a valid IP (IPV4). Test is only syntaxic, it's just to know if we're likely to need to query the DNS, it does not mean the IP is *really* valid.

> Return value: 1 if it's an IP, O if not.

— Function: char * lw6net_dns_gethostbyname (char * name)

> name: name of the host

> A wrapper over the standard gethostbyname function, will even accept an IP as an input (in this case, will copy it...) and allocate a new string for the result.

> Return value: an IP if success, NULL on error.

— Function: int lw6net_dns_lock ()

> Locks access to dns function `lw6net_dns_gethostbyname`. This is because `gethostbyname` isn't reentrant plus, even if we didn't use it but its multithreadable equivalent (which is however not standard and always available) other libs (such as `libcurl` not to name it) might use this function too so in a general manner it's a good idea to use a mutex to protect multiple accesses to this.

> Return value: an IP if success, 0 on error.

— Function: int lw6net_dns_unlock ()

> Unlocks access to dns function `lw6net_dns_gethostbyname`.

> Return value: an IP if success, 0 on error.

— Function: int lw6net_last_error ()

> Reports the last network error. This is basically a debug function, designed mostly for Microsoft Winsock API, but can be safely called on any platform.

> Return value: the last error code, has no universal meaning, depends on the platform you're working on.

— Function: char * lw6net_if_guess_local ()

> Guess the local IP address. This is not fool-proof, and it probably cannot be as we can't handle all user-specific configs involving multiple IP addresses, virtual private networks, and so on. But this is just to provide a default public IP address when starting a network game, saavy users can always specify the right interface/address if needed. Will return NULL if interface can't be guessed.

> Return value: the IP as a string, dynamically allocated

— Function: char * lw6net_if_guess_public_url (char * bind_ip, int bind_port)

> bind_ip: the IP address used to bind on

> bind_port: the IP port used to bind on

> Guess the server public url, based on `lw6net_if_guess_local` which tries to find a valid local IP address which is not loopback. This is only in case `bind_ip` is 0.0.0.0 (listen on all addresses) else it will just use `bind_ip` as you would expect. Function isn't foolproof, that's why one can override its default with a user settings.

> Return value: the IP as a string, dynamically allocated

— Function: char * lw6net_recv_line_tcp (int sock)

> sock: the socket descriptor

> Receives a line terminated by LF ("\n", chr(10)) or CR/LF ("\r\n", chr(10)chr(13)) on a TCP socket, that is, stream oriented. If there's no complete line available, function returns immediately with NULL. Same if socket is closed, broken, whatever. Only if there's something consistent will the function return non-NULL.

> Return value: a dynamically allocated string with the content received. The tailing (CR)/LF is stripped.

— Function: int lw6net_send_line_tcp (int sock, char * line)

> sock: the socket descriptor

> line: the line to be sent, without the "\n" at the end

> Sends a line terminated by LF ("\n", chr(10)) on a TCP socket, that is, stream oriented. The "\n" is automatically added, do not bother sending it.

> Return value: non-zero if success

— Function: char * lw6net_recv_line_udp (int sock, char ** incoming_ip, int * incoming_port)

> sock: the socket descriptor

> incoming_ip: the IP address of the sender (returned)

> incoming_port: the IP port of the sender (returned)

> Receives a line terminated by LF ("\n", chr(10)) or CR/LF ("\r\n", chr(10)chr(13)) on a UDP socket, that is, datagram oriented. If there's no complete line available, function returns immediately with NULL. Same if socket is closed, broken, whatever. Only if there's something consistent will the function return non-NULL. By-value parameters allow the caller to know where the data come from.

> Return value: a dynamically allocated string with the content received. The tailing (CR)/LF is stripped.

— Function: lw6sys_list_t * lw6net_recv_lines_udp (int sock, char ** incoming_ip, int * incoming_port)

> sock: the socket descriptor

> incoming_ip: the IP address of the sender (returned)

> incoming_port: the IP port of the sender (returned)

> Receives several lines terminated by LF ("\n", chr(10)) or CR/LF ("\r\n", chr(10)chr(13)) on a UDP socket, that is, datagram oriented. If there's no complete line available, function returns immediately with NULL. Same if socket is closed, broken, whatever. Only if there's something consistent will the function return non-NULL. By-value parameters allow the caller to know where the data come from. This variant of `lw6net_recv_line_tcp` will return a list of lines, this is mandatory since in UDP we can't call recv several times.

> Return value: a list of dynamically allocated strings. The tailing (CR)/LF is stripped from strings.

— Function: int lw6net_send_line_udp (int sock, char * line, char * ip, int port)

> sock: the socket descriptor

> line: the line to be sent, without the "\n" at the end

> ip: the IP address of the target

> port: the IP port of the target

> Sends a line terminated by LF ("\n", chr(10)) on a UDP socket, that is, datagram oriented. The "\n" is automatically added, do not bother sending it.

> Return value: the number of bytes sent, 0 if failure

— Function: int lw6net_init (int argc, char * [] argv, int net_log)

> argc: argc as passed to `main`

> argv: argv as passed to `main`

> net_log: 1 if you want to enable net log, 0 if not

> Initializes the low-level network API, you must call this before calling any other network related function, for it allocates a dynamic context which is in turn used by every function.

> Return value: non-zero if success

— Function: void lw6net_quit ()

> Frees memory, joins active threads, and releases everything set up by network code.

> Return value: void

— Function: int lw6net_socket_set_blocking_mode (int sock, int mode)

> sock: the socket to modify

> mode: the mode to use (1 -> blocking mode, 0 -> non-blocking)

> Sets the blocking mode of a socket, the reason we use this is that `ioctl` isn't portable (`ioctlsocket` on MS-Windows).

> Return value: 1 on success, 0 on failure.

— Function: int lw6net_socket_is_valid (int sock)

> sock: the socket to test

> Tells if a socket is valid or not. This does not mean the socket is opened/connected and/or the peer is reachable, it just checks the socket is a valid descriptor. In practice it's just to avoid copy/pasting if (sock>=0)" everywhere.

> Return value: 1 if valid, 0 if not

— Function: void lw6net_socket_close (int sock)

> sock: the socket to close

> Closes a socket, that is, stop activity and free its descriptor.

> Return value: none.

— Function: int lw6net_test (int mode)

> mode: 0 for check only, 1 for full test

> Runs the `net` module test suite. This one could fail if some sockets are already bound, for instance. It's still run even in check-only (mode=0) mode.

> Return value: 1 if test is successfull, 0 on error.