communication.h

/* See LICENSE file for copyright and license details. */
#ifndef COMMUNICATION_H
#define COMMUNICATION_H

#include <stdio.h>
#include <stdlib.h>

#ifndef GCC_ONLY
# if defined(__GNUC__) && !defined(__clang__)
#  define GCC_ONLY(...) __VA_ARGS__
# else
#  define GCC_ONLY(...) /* nothing */
# endif
#endif

/**
 * Construct a message
 * 
 * @param  bufp:char**            Output parameter for the buffer, must not have side-effects
 * @param  np:size_t*             Output parameter for the size of the buffer sans `extra`
 * @param  extra:size_t           The extra number for bytes to allocate to the buffer
 * @param  format:string-literal  Message format string
 * @param  ...                    Message formatting arguments
 */
#define MAKE_MESSAGE(bufp, np, extra, format, ...)\
	do {\
		ssize_t m__;\
		snprintf(NULL, 0, format "%zn", __VA_ARGS__, &m__);\
		*(bufp) = malloc((size_t)(extra) + (size_t)m__ + (size_t)1);\
		if (!*(bufp))\
			return -1;\
		sprintf(*(bufp), format, __VA_ARGS__);\
		*(np) = (size_t)m__;\
	} while (0)

/**
 * Send a custom error without an error number
 * 
 * @param   ...  The error description to send
 * @return       1: Client disconnected
 *               0: Success (possibily delayed)
 *               -1: An error occurred
 */
#define send_error(...) ((send_error)(conn, message_id, __VA_ARGS__))

/**
 * Send a standard error
 * 
 * @param   ...  The value of `errno`, 0 to indicate success
 * @return       1: Client disconnected
 *               0: Success (possibily delayed)
 *               -1: An error occurred
 */
#define send_errno(...) ((send_errno)(conn, message_id, __VA_ARGS__))

/**
 * Send a message
 * 
 * @param   conn  The index of the connection
 * @param   buf   The data to send
 * @param   n     The size of `buf`
 * @return        Zero on success, -1 on error, 1 if disconncted
 *                EINTR, EAGAIN, EWOULDBLOCK, and ECONNRESET count
 *                as success (ECONNRESET cause 1 to be returned),
 *                and are handled appropriately.
 */
int send_message(size_t conn, char *restrict buf, size_t n);

/**
 * Send a custom error without an error number
 * 
 * @param   conn        The index of the connection
 * @param   message_id  The ID of the message to which this message is a response
 * @param   desc        The error description to send
 * @return              1: Client disconnected
 *                      0: Success (possibily delayed)
 *                      -1: An error occurred
 */
GCC_ONLY(__attribute__((__nonnull__)))
int (send_error)(size_t conn, const char *restrict message_id, const char *restrict desc);

/**
 * Send a standard error
 * 
 * @param   conn        The index of the connection
 * @param   message_id  The ID of the message to which this message is a response
 * @param   number      The value of `errno`, 0 to indicate success
 * @return              1: Client disconnected
 *                      0: Success (possibily delayed)
 *                      -1: An error occurred
 */
GCC_ONLY(__attribute__((__nonnull__)))
int (send_errno)(size_t conn, const char *restrict message_id, int number);

/**
 * Continue sending the queued messages
 * 
 * @param   conn  The index of the connection
 * @return        Zero on success, -1 on error, 1 if disconncted
 *                EINTR, EAGAIN, EWOULDBLOCK, and ECONNRESET count
 *                as success (ECONNRESET cause 1 to be returned),
 *                and are handled appropriately.
 */
static inline int
continue_send(size_t conn)
{
	return send_message(conn, NULL, 0);
}

#endif