# Generic Network Communication

    /*
    **	(c) COPYRIGHT MIT 1995.
    **	Please first read the full copyright statement in the file COPYRIGH.
    */

This module has the common code for handling TCP/IP and DECnet connections etc. The main topics of functions in this module are:

- Connection establishment
- Cache of host names
- Errno Messages
- Host and mail addresses
- Signal Handling

This module is implemented by HTTCP.c, and it is a part of the W3C Reference Library.

    #ifndef HTTCP_H
    #define HTTCP_H
    #include "HTReq.h"
    #include "HTNet.h"

## Connection Management

All connections are established through the following functions.

### Active Connection Establishment

This makes an active connect to the specified host. The HTNet structure is parsed in order to handle errors. Default port might be overwritten by any port indication in the URL specified as <host>:<port> If it is a multihomed host then HTDoConnect measures the time to do the connection and updates the calculated weights in the cache of visited hosts.

    extern int HTDoConnect (HTNet * net, char * url, u_short default_port);

### Passive Connection Establishment

This function makes a non-blocking accept on a port. The net must contain a valid socket to accept on. If accept is OK then the socket descripter in the Net object is swapped to the new one.

    extern int HTDoAccept (HTNet * net);

### Listen on a Socket

Listens on the specified port. 0 means that we don't care and a temporary one will be assigned. If `master`==INVSOC then we listen on all local interfaces (using a wildcard). If !INVSOC then use this as the local interface. `backlog` is the number of connections that can be queued on the socket - you can use `HT_BACKLOG` for a platform dependent value (typically 5 on BSD and 32 on SVR4). Returns HT_ERROR or HT_OK.

    extern int HTDoListen (HTNet * net, u_short port, SOCKET master, int backlog);

## System Description of Error Message

Return error message corresponding to errno number given. We need to pass the error number as a parameter as we on some platforms get different codes from sockets and local file access.

    extern CONST char * HTErrnoString	(int errnum);
    extern int HTInetStatus			(int errnum, char * where);

### Parse a Cardinal Value

    /*	Parse a cardinal value				       parse_cardinal()
    **	----------------------
    **
    ** On entry:
    ** 	*pp points to first character to be interpreted, terminated by
    ** 	non 0..9 character.
    ** 	*pstatus points to status already valid,
    ** 	maxvalue gives the largest allowable value.
    **
    ** On exit:
    ** 	*pp points to first unread character,
    ** 	*pstatus points to status updated iff bad
    */

    extern unsigned int HTCardinal (int *		pstatus,
    				char **		pp,
    				unsigned int	max_value);

## Internet Name Server Functions

The following functions are available to get information about a specified host.

### Produce a string for an internet address

This function is equivalent to the BSD system call inet_ntoa in that it converts a numeric 32-bit IP-address to a dotted-notation decimal string. The pointer returned points to static memory which must be copied if it is to be kept.

    extern CONST char * HTInetString (struct sockaddr_in * sin);

### Get Name of This Machine

This function returns a CONET char pointer to a static location containing the name of this host or NULL if not available.

    extern CONST char * HTGetHostName (void);

### Set Name of This Machine

This function overwrites any other value of current host name. This might be set by the user to change the value in the ID value parsed to a news host when posting. The change doesn't influence the Mail Address as they are stored in two different locations. If, however, the change is done before the first call to HTGetMailAddress() then this function will use the new host and domain name.

    extern void HTSetHostName (char * host);

### Cleanup Memory

Called from HTLibTerminate

    extern void HTFreeHostName (void);

### Get Domain Name of This Machine

This function rerturns the domain name part of the host name as returned by HTGetHostName() function. Changing the domain name requires a call to HTSetHostname().

    extern CONST char *HTGetDomainName (void);

### Get User Mail Address

This functions returns a char pointer to a static location containing the mail address of the current user. The static location is different from the one of the current host name so different values can be assigned. The default value is <USER>@hostname where hostname is as returned by HTGetHostName().

    extern CONST char * HTGetMailAddress (void);

### Set User Mail Address

This function overwrites any other value of current mail address. This might be set by the user to change the value in the From field in the HTTP Protocol.

    extern void HTSetMailAddress (char * address);

### Free Memory

Called by HTLibTerminate

    extern void HTFreeMailAddress (void);

## Signal Handling

This is only necessary to compile on a few platforms and only if the application does not have its own signal handling. It is required on Solaris 2.3 (and other SVR4 platforms?) due to a bug in the TCP kernel. When a `connect()` is tried to a illegal port, solaris gives a SIGPIPE signal instead of returning Connection refused.

    #ifdef WWWLIB_SIG
    extern void HTSetSignal (void);
    #endif

    #endif   /* HTTCP_H */

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