dates.c

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/* 
   Date manipulation routines
   Copyright (C) 1999, Joe Orton <[e-mail]>
                                                                     
   This program is free software; you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation; either version 2 of the License, or
   (at your option) any later version.
  
   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License for more details.
  
   You should have received a copy of the GNU General Public License
   along with this program; if not, write to the Free Software
   Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
*/

#ifdef HAVE_CONFIG_H
#include <config.h>
#endif

#include <sys/types.h>

#include <time.h>
#ifdef HAVE_STDLIB_H
#include <stdlib.h>
#endif
#include <stdio.h>

#include <dates.h>

/* Generic date manipulation routines. */

/* RFC1123: Sun, 06 Nov 1994 08:49:37 GMT */
#define RFC1123_FORMAT "%3s, %02d %3s %4d %02d:%02d:%02d GMT"
/* RFC850:  Sunday, 06-Nov-94 08:49:37 GMT */
#define RFC1036_FORMAT "%s, %2d-%3s-%2d %2d:%2d:%2d GMT"
/* asctime: Wed Jun 30 21:49:08 1993 */
#define ASCTIME_FORMAT "%3s %3s %2d %2d:%2d:%2d %4d"

const char *rfc1123_weekdays[7] = { 
    "Sun", "Mon", "Tue", "Wed", "Thu", "Fri", "Sat" 
};
const char *short_months[12] = { 
    "Jan", "Feb", "Mar", "Apr", "May", "Jun",
    "Jul", "Aug", "Sep", "Oct", "Nov", "Dec"
};

/* Returns the time/date GMT, in RFC1123-type format: eg
 *  Sun, 06 Nov 1994 08:49:37 GMT. */
char *rfc1123_date( const time_t anytime ) {
    struct tm *gmt;
    char *ret;
    gmt = gmtime( &anytime );
    ret = malloc( 29 + 1 ); /* dates are 29 chars long */
/*  it goes: Sun, 06 Nov 1994 08:49:37 GMT */
    snprintf( ret, 30, RFC1123_FORMAT,
	      rfc1123_weekdays[gmt->tm_wday], gmt->tm_mday, 
	      short_months[gmt->tm_mon], 1900 + gmt->tm_year, 
	      gmt->tm_hour, gmt->tm_min, gmt->tm_sec );
    
    return ret;
}

/* Takes an RFC1123-formatted date string and returns the time_t.
 * Returns (time_t)-1 if the parse fails. */
time_t rfc1123_parse( const char *date ) {
    struct tm gmt = {0};
    static char wkday[4], mon[4];
    int n;
/*  it goes: Sun, 06 Nov 1994 08:49:37 GMT */
    n = sscanf( date, RFC1123_FORMAT,
	    wkday, &gmt.tm_mday, mon, &gmt.tm_year, &gmt.tm_hour,
	    &gmt.tm_min, &gmt.tm_sec );
    /* Is it portable to check n==7 here? */
    gmt.tm_year -= 1900;
    for( n=0; n<12; n++ )
	if( strcmp( mon, short_months[n] ) == 0 )
	    break;
    /* tm_mon comes out as 12 if the month is corrupt, which is desired,
     * since the mktime will then fail */
    gmt.tm_mon = n;
    return mktime( &gmt );
}

/* Takes a string containing a RFC1036-style date and returns the time_t */
time_t rfc1036_parse( const char *date ) {
    struct tm gmt = {0};
    int n;
    static char wkday[10], mon[4];
    /* RFC850/1036 style dates: Sunday, 06-Nov-94 08:49:37 GMT */
    n = sscanf( RFC1036_FORMAT,
		wkday, &gmt.tm_mday, mon, &gmt.tm_year,
		&gmt.tm_hour, &gmt.tm_min, &gmt.tm_sec );
    /* portable to check n here? */
    for( n=0; n<12; n++ )
	if( strcmp( mon, short_months[n] ) == 0 )
	    break;
    /* tm_mon comes out as 12 if the month is corrupt, which is desired,
     * since the mktime will then fail */
    gmt.tm_mon = n;
    return mktime( &gmt );
}


/* (as)ctime dates are like:
 *    Wed Jun 30 21:49:08 1993
 */
time_t asctime_parse( const char *date ) {
    struct tm gmt = {0};
    int n;
    static char wkday[4], mon[4];
    n = sscanf( ASCTIME_FORMAT,
		wkday, mon, &gmt.tm_mday, 
		&gmt.tm_hour, &gmt.tm_min, &gmt.tm_sec,
		&gmt.tm_year );
    /* portable to check n here? */
    for( n=0; n<12; n++ )
	if( strcmp( mon, short_months[n] ) == 0 )
	    break;
    /* tm_mon comes out as 12 if the month is corrupt, which is desired,
     * since the mktime will then fail */
    gmt.tm_mon = n;
    return mktime( &gmt );
}

#undef RFC1036_FORMAT
#undef ASCTIME_FORMAT
#undef RFC1123_FORMAT

#ifdef RFC1123_TEST

int main( int argc, char **argv ) {
    time_t now, in;
    char *out;
    if( argc > 1 ) {
	printf( "Got: %s\n", argv[1] );
	in = rfc1123_parse( argv[1] );
	printf( "Parsed: %d\n", in );
	out = rfc1123_date( in );
	printf( "Back again: %s\n", out );
    } else {
	now = time(NULL);
	out = rfc1123_date(now);
	in = rfc1123_parse(out);
	printf( "time(NULL) = %d\n", now );
	printf( "RFC1123 Time: [%s]\n", out );
	printf( "Parsed = %d\n", in );
	out = rfc1123_date( in );
	printf( "Back again: [%s]\n", out );
    }
    return 0;
}

#endif