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### 5.34 libnet

#### 5.34.1 Overview

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

#### 5.34.2 API

Function: int lw6net_is_connectable (const char * ip, int port)

  ip: IP address

  port: IP port

  Tells wether we’re likely to be able to connect on a given host and port. This is to save ressources, any call to connect which fails will register an entry that says "OK this is rotten, don’t try it before some time, you’ll waste your ressources trying to do this".

  Return value: 1 if connectable, 0 if not.

Function: void lw6net_set_connectable (const char * ip, int port, int status)

  ip: IP address

  port: IP port

  status: status, set to 1 if connectable, 0 if not

  Registers a destination ip: port as connectable or not. Connectable means, there are chances that a connect on this might return true. The information will be kept in a cache. This is to avoid too many low-level calls to connect, the information will be kept in cache "for some time", and this way connect will return "can’t connect" right away and not even try to connect, therefore saving ressources.

  Return value: none.

Function: int lw6net_dns_is_ip (const 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 (const 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 (const 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. Socket descriptor is closed on the fly on connection problem.

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

Function: int lw6net_send_line_tcp (int * sock, const 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. Socket descriptor is closed on the fly on connection problem.

  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, const char * line, const 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, const 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. This function will take a pointer on the socket, this is done on purpose, the idea is to make sure once the socket is closed it’s never used again within the code, so we modify the pointed value in place.

  Return value: none.

Function: int lw6net_tcp_listen (const char * ip, int port)

  ip: IP address to bind to

  port: IP port to listen on

  Listens in TCP on a given port.

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

Function: int lw6net_tcp_accept (char ** incoming_ip, int * incoming_port, int listening_sock, int delay_msec)

  incoming_ip: address of remote peer (out param, dynamically allocated)

  incoming_port: port of remote peer (out param)

  listening_sock: socket to listen on

  delay_msec: delay, in msec, after which we stop accepting

  Accepts for a connexion on the given socket.

  Return value: the new socket (>=0) if accepted, else -1

Function: int lw6net_tcp_connect (const char * ip, int port, int delay_msec)

  ip: address to connect to

  port: port to connect to

  delay_msec: delay before we consider it’s too late

  Tries to connect on a given socket.

  Return value: socket (>=0) on success, else -1

Function: int lw6net_tcp_send (int * sock, const char * buf, int len, int delay_msec, int loop)

  sock: socket to use

  buf: data buffer

  len: data buffer length

  delay_msec: delay after which we give up

  loop: accept to do several calls if needed

  Will send data, possibly looping until all is send, and waiting for a maximum time of delay_msec. If the send reveals a socket closed by peer or other serious problem, socket is closed and sock set to -1.

  Return value: 1 on success, 0 on failure.

Function: int lw6net_tcp_peek (int * sock, char * buf, int len, int delay_msec)

  sock: socket to use

  buf: data buffer

  len: data buffer length

  delay_msec: maximum time to wait

  Tells wether data is available. Will actually fill the buffer with the data, but not remove it from the fifo list. If the peel reveals a socket closed by peer or other serious problem, socket is closed and sock set to -1.

  Return value: number of bytes available, 0 when nothing

Function: int lw6net_tcp_recv (int * sock, char * buf, int len, int delay_msec, int loop)

  sock: socket to use

  buf: data buffer

  len: data buffer length

  delay_msec: maximum time to wait

  loop: wether to loop or not

  If data is available, put it in buffer. If needed, will loop until `delay_msec` is elapsed. Data is removed from queue. If the peel reveals a socket closed by peer or other serious problem, socket is closed and sock set to -1.

  Return value: number of bytes received, 0 when nothing

Function: int lw6net_tcp_is_alive (int * sock)

  sock: socket to test

  Tells wether a socket is alive and able to send data. This function will attempt a write to test if it’s really usable. If not, will close in on the fly.

  Return value: 1 if alive, 0 if not.

Function: int lw6net_test_register (int mode)

  mode: test mode (bitmask)

  Registers all tests for the libnet module.

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

Function: int lw6net_test_run (int mode)

  mode: test mode (bitmask)

  Runs the `net` module test suite, testing most (if not all...) functions.

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

Function: int lw6net_udp_client ()

  Creates an UDP client socket, that is, creates it and does not bind it to any address.

  Return value: socket (>=0) on success, else -1

Function: int lw6net_udp_server (const char * ip, int port)

  ip: IP address to bind to

  port: IP port to listen on

  Creates an UDP listening socket, that is, creates it and binds it on a given address.

  Return value: socket (>=0) on success, else -1

Function: int lw6net_udp_send (int sock, const char * buf, int len, const char * ip, int port)

  sock: socket to use

  buf: data buffer

  len: data buffer length

  ip: IP address to send data to

  port: IP port to send data to

  Sends an UDP datagram. Size can’t be longer than about 1400 bytes, see problems about MTU, in practice all values arround 1000 are quite safe, 500 is pretty much garanteed to work everywhere, and for various reasons 1452 is a good maximum bet.

  Return value: number of bytes sent

Function: int lw6net_udp_peek (int sock, char * buf, int len, char ** incoming_ip, int * incoming_port)

  sock: socket to use

  buf: data buffer

  len: data buffer length

  Peeks for a UDP datagram. Will not remove the data from queue.

  Return value: number of bytes received

Function: int lw6net_udp_recv (int sock, char * buf, int len, char ** incoming_ip, int * incoming_port)

  sock: socket to use

  buf: data buffer

  len: data buffer length

  Receives a UDP datagram. Will remove the data from queue.

  Return value: number of bytes received

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