path: root/rfc822.c

/*****************************************************************************

NAME:
   rfc822.c -- code for slicing and dicing RFC822 mail headers

ENTRY POINTS:
   nextaddr() -- parse the next address out of an RFC822 header
   reply_hack() -- append hostname to local header addresses 

THEORY:
   How to parse RFC822 headers in C. This is not a fully conformant
implementation of RFC822 or RFC2822, but it has been in production use
in a widely-deployed MTA (fetcmail) since 1996 without complaints.
Really perverse combinations of quoting and commenting could break it.

AUTHOR:
   Eric S. Raymond <esr@thyrsus.com>, 1997.  This source code example
is part of fetchmail and the Unix Cookbook, and are released under the
MIT license.  Compile with -DMAIN to build the demonstrator.

******************************************************************************/
#include  <stdio.h>
#include  <ctype.h>
#include  <string.h>
#include  <stdlib.h>

#include "fetchmail.h"

#ifndef MAIN
#include "i18n.h"
#else
#include  <unistd.h>
static int verbose;
const char *program_name = "rfc822";
#endif /* MAIN */

#ifndef TRUE
#define TRUE 1
#define FALSE 0
#endif

#define HEADER_END(p)	((p)[0] == '\n' && ((p)[1] != ' ' && (p)[1] != '\t'))

#define BEFORE_EOL(s)	strcspn((s), "\r\n"))

char *reply_hack(
	char *buf		/* header to be hacked */,
	const char *host	/* server hostname */,
	size_t *length)
/* hack message headers so replies will work properly */
{
    char *from, *cp, last_nws = '\0', *parens_from = NULL;
    int parendepth, state, has_bare_name_part, has_host_part;
#ifndef MAIN
    int addresscount = 1;
#endif /* MAIN */

    if (strncasecmp("From:", buf, 5)
	&& strncasecmp("To:", buf, 3)
	&& strncasecmp("Reply-To:", buf, 9)
	&& strncasecmp("Return-Path:", buf, 12)
	&& strncasecmp("Cc:", buf, 3)
	&& strncasecmp("Bcc:", buf, 4)
	&& strncasecmp("Resent-From:", buf, 12)
	&& strncasecmp("Resent-To:", buf, 10)
	&& strncasecmp("Resent-Cc:", buf, 10)
	&& strncasecmp("Resent-Bcc:", buf, 11)
	&& strncasecmp("Apparently-From:", buf, 16)
	&& strncasecmp("Apparently-To:", buf, 14)
	&& strncasecmp("Sender:", buf, 7)
	&& strncasecmp("Resent-Sender:", buf, 14)
       ) {
	return(buf);
    }

#ifndef MAIN
    if (outlevel >= O_DEBUG)
	report_build(stdout, GT_("About to rewrite %.*s...\n"),
			(int)BEFORE_EOL(buf), buf);

    /* make room to hack the address; buf must be malloced */
    for (cp = buf; *cp; cp++)
	if (*cp == ',' || isspace((unsigned char)*cp))
	    addresscount++;
    buf = (char *)xrealloc(buf, strlen(buf) + addresscount * (strlen(host) + 1) + 1);
#endif /* MAIN */

    /*
     * This is going to foo up on some ill-formed addresses.
     * Note that we don't rewrite the fake address <> in order to
     * avoid screwing up bounce suppression with a null Return-Path.
     */

    parendepth = state = 0;
    has_host_part = has_bare_name_part = FALSE;
    for (from = buf; *from; from++)
    {
#ifdef MAIN
	if (verbose)
	{
	    printf("state %d: %s", state, buf);
	    printf("%*s^\n", (int)(from - buf + 10), " ");
	}
#endif /* MAIN */
	if (state != 2)
	{
	    if (*from == '(')
		++parendepth;
	    else if (*from == ')')
		--parendepth;
	}

	if (!parendepth && !has_host_part)
	    switch (state)
	    {
	    case 0:	/* before header colon */
		if (*from == ':')
		    state = 1;
		break;

	    case 1:	/* we've seen the colon, we're looking for addresses */
		if (!isspace((unsigned char)*from))
		    last_nws = *from;
		if (*from == '<')
		    state = 3;
		else if (*from == '@' || *from == '!')
		    has_host_part = TRUE;
		else if (*from == '"')
		    state = 2;
		/*
		 * Not expanding on last non-WS == ';' deals with groupnames,
		 * an obscure misfeature described in sections
		 * 6.1, 6.2.6, and A.1.5 of the RFC822 standard.
		 */
		else if ((*from == ',' || HEADER_END(from))
			 && has_bare_name_part
			 && !has_host_part
			 && last_nws != ';')
		{
		    int hostlen;
		    char *p;

		    p = from;
		    if (parens_from)
			from = parens_from;
		    while (isspace((unsigned char)*from) || (*from == ','))
			--from;
		    from++;
		    hostlen = strlen(host);
		    for (cp = from + strlen(from); cp >= from; --cp)
			cp[hostlen+1] = *cp;
		    *from++ = '@';
		    memcpy(from, host, hostlen);
		    from = p + hostlen + 1;
		    has_host_part = TRUE;
		} 
		else if (from[1] == '('
			 && has_bare_name_part
			 && !has_host_part
			 && last_nws != ';' && last_nws != ')')
		{
		    parens_from = from;
		} 
		else if (!isspace((unsigned char)*from))
		    has_bare_name_part = TRUE;
		break;

	    case 2:	/* we're in a string */
		if (*from == '"')
		{
		    char	*bp;
		    int		bscount;

		    bscount = 0;
		    for (bp = from - 1; *bp == '\\'; bp--)
			bscount++;
		    if (!(bscount % 2))
			state = 1;
		}
		break;

	    case 3:	/* we're in a <>-enclosed address */
		if (*from == '@' || *from == '!')
		    has_host_part = TRUE;
		else if (*from == '>' && (from > buf && from[-1] != '<'))
		{
		    state = 1;
		    if (!has_host_part)
		    {
			int hostlen;

			hostlen = strlen(host);
			for (cp = from + strlen(from); cp >= from; --cp)
			    cp[hostlen+1] = *cp;
			*from++ = '@';
			memcpy(from, host, hostlen);
			from += hostlen;
			has_host_part = TRUE;
		    }
		}
		break;
	    }

	/*
	 * If we passed a comma, reset everything.
	 */
	if ((from > buf && from[-1] == ',') && !parendepth) {
	  has_host_part = has_bare_name_part = FALSE;
	  parens_from = NULL;
	}
    }

#ifndef MAIN
    if (outlevel >= O_DEBUG)
	report_complete(stdout, GT_("...rewritten version is %.*s.\n"),
			(int)BEFORE_EOL(buf), buf);
#endif /* MAIN */
    *length = strlen(buf);
    return(buf);
}

char *nxtaddr(const char *hdr /* header to be parsed, NUL to continue previous hdr */)
/* parse addresses in succession out of a specified RFC822 header */
{
    static char address[BUFSIZ];
    static size_t tp;
    static const char *hp;
    static int	state, oldstate;
#ifdef MAIN
    static const char *orighdr;
#endif /* MAIN */
    int parendepth = 0;

#define START_HDR	0	/* before header colon */
#define SKIP_JUNK	1	/* skip whitespace, \n, and junk */
#define BARE_ADDRESS	2	/* collecting address without delimiters */
#define INSIDE_DQUOTE	3	/* inside double quotes */
#define INSIDE_PARENS	4	/* inside parentheses */
#define INSIDE_BRACKETS	5	/* inside bracketed address */
#define ENDIT_ALL	6	/* after last address */

#define NEXTTP()	((tp < sizeof(address)-1) ? tp++ : tp)

    if (hdr)
    {
	hp = hdr;
	state = START_HDR;
#ifdef MAIN
	orighdr = hdr;
#endif /* MAIN */
	tp = 0;
    }

    if (!hp) return NULL;

    for (; *hp; hp++)
    {
#ifdef MAIN
	if (verbose)
	{
	    printf("state %d: %s", state, orighdr);
	    printf("%*s^\n", (int)(hp - orighdr + 10), " ");
	}
#endif /* MAIN */

	if (state == ENDIT_ALL)		/* after last address */
	    return(NULL);
	else if (HEADER_END(hp))
	{
	    state = ENDIT_ALL;
	    if (tp)
	    {
		while (tp > 0 && isspace((unsigned char)address[tp - 1]))
		    tp--;
		address[tp] = '\0';
		tp = 0;
		return (address);
	    }
	    return(NULL);
	}
	else if (*hp == '\\')		/* handle RFC822 escaping */
	{
	    if (state != INSIDE_PARENS)
	    {
		address[NEXTTP()] = *hp++;	/* take the escape */
		address[NEXTTP()] = *hp;	/* take following unsigned char */
	    }
	}
	else switch (state)
	{
	case START_HDR:   /* before header colon */
	    if (*hp == ':')
		state = SKIP_JUNK;
	    break;

	case SKIP_JUNK:		/* looking for address start */
	    if (*hp == '"')	/* quoted string */
	    {
		oldstate = SKIP_JUNK;
	        state = INSIDE_DQUOTE;
		address[NEXTTP()] = *hp;
	    }
	    else if (*hp == '(')	/* address comment -- ignore */
	    {
		parendepth = 1;
		oldstate = SKIP_JUNK;
		state = INSIDE_PARENS;    
	    }
	    else if (*hp == '<')	/* begin <address> */
	    {
		state = INSIDE_BRACKETS;
		tp = 0;
	    }
	    else if (*hp != ',' && !isspace((unsigned char)*hp))
	    {
		--hp;
	        state = BARE_ADDRESS;
	    }
	    break;

	case BARE_ADDRESS:   	/* collecting address without delimiters */
	    if (*hp == ',')  	/* end of address */
	    {
		if (tp)
		{
		    address[NEXTTP()] = '\0';
		    state = SKIP_JUNK;
		    tp = 0;
		    return(address);
		}
	    }
	    else if (*hp == '(')  	/* beginning of comment */
	    {
		parendepth = 1;
		oldstate = BARE_ADDRESS;
		state = INSIDE_PARENS;    
	    }
	    else if (*hp == '<')  	/* beginning of real address */
	    {
		state = INSIDE_BRACKETS;
		tp = 0;
	    }
	    else if (*hp == '"')        /* quoted word, copy verbatim */
	    {
	        oldstate = state;
		state = INSIDE_DQUOTE;
                address[NEXTTP()] = *hp;
            }
	    else if (!isspace((unsigned char)*hp)) 	/* just take it, ignoring whitespace */
		address[NEXTTP()] = *hp;
	    break;

	case INSIDE_DQUOTE:	/* we're in a quoted string, copy verbatim */
	    address[NEXTTP()] = *hp;
	    if (*hp == '"')
		state = oldstate;
	    break;

	case INSIDE_PARENS:	/* we're in a parenthesized comment, ignore */
	    if (*hp == '(')
		++parendepth;
	    else if (*hp == ')')
		--parendepth;
	    if (parendepth == 0)
		state = oldstate;
	    break;

	case INSIDE_BRACKETS:	/* possible <>-enclosed address */
	    if (*hp == '>')	/* end of address */
	    {
		address[NEXTTP()] = '\0';
		state = SKIP_JUNK;
		++hp;
		tp = 0;
		return(address);
	    }
	    else if (*hp == '<')	/* nested <> */
	        tp = 0;
	    else if (*hp == '"')	/* quoted address */
	    {
	        address[NEXTTP()] = *hp;
		oldstate = INSIDE_BRACKETS;
		state = INSIDE_DQUOTE;
	    }
	    else			/* just copy address */
		address[NEXTTP()] = *hp;
	    break;
	}
    }

    return(NULL);
}

#ifdef MAIN
static void parsebuf(char *longbuf, int reply)
{
    char	*cp;
    size_t	dummy;

    if (reply)
    {
	reply_hack(longbuf, "HOSTNAME.NET", &dummy);
	printf("Rewritten buffer: %s", (char *)longbuf);
    }
    else
	if ((cp = nxtaddr(longbuf)) != (char *)NULL)
	    do {
		printf("\t-> \"%s\"\n", (char *)cp);
	    } while
		((cp = nxtaddr((char *)NULL)) != (char *)NULL);
}



int main(int argc, char *argv[])
{
    char	buf[BUFSIZ], longbuf[BUFSIZ];
    int		ch, reply;
    
    verbose = reply = FALSE;
    while ((ch = getopt(argc, argv, "rv")) != EOF)
	switch(ch)
	{
	case 'r':
	    reply = TRUE;
	    break;

	case 'v':
	    verbose = TRUE;
	    break;
	}

    while (fgets(buf, sizeof(buf)-1, stdin))
    {
	if (buf[0] == ' ' || buf[0] == '\t')
	    strlcat(longbuf, buf, sizeof(longbuf));
	else if (!strncasecmp("From: ", buf, 6)
		    || !strncasecmp("To: ", buf, 4)
		    || !strncasecmp("Reply-", buf, 6)
		    || !strncasecmp("Cc: ", buf, 4)
		    || !strncasecmp("Bcc: ", buf, 5))
	    strlcpy(longbuf, buf, sizeof(longbuf));
	else if (longbuf[0])
	{
	    if (verbose)
		fputs(longbuf, stdout);
	    parsebuf(longbuf, reply);
	    longbuf[0] = '\0';
	}
    }
    if (longbuf[0])
    {
	if (verbose)
	    fputs(longbuf, stdout);
	parsebuf(longbuf, reply);
    }
    exit(0);
}
#endif /* MAIN */

/* rfc822.c end */