prime_hash.c

/*
 * Copyright (C) 2007 1&1 Internet AG
 *
 * This file is part of opensips, a free SIP server.
 *
 * opensips 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
 *
 * opensips 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., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301  USA
 */

/*!
 * \file
 * \brief
 * Functions for determinung a pseudo random number over a message's
 * header field, based on CRC32 or a prime number algorithm.
 */

#include "sr_module.h"
#include "parser/parse_uri.h"
#include "parser/parse_to.h"
#include "parser/parse_from.h"
#include "crc.h"

#include <ctype.h>

#include "prime_hash.h"


static int determine_source(struct sip_msg *msg, enum hash_source source,
                            str *source_string);
static int validate_msg(struct sip_msg * msg);
static int determine_call_id (struct sip_msg *msg, str *source_string);
static int determine_fromto_uri (struct to_body *fromto, str *source_string);
static int determine_fromto_user (struct to_body *fromto, str *source_string);
static int first_token (str *source_string);


int hash_func (struct sip_msg * msg,
                         enum hash_source source, int denominator) {
	int ret;
	unsigned int hash;
	str source_string;

	if(determine_source (msg, source, &source_string) == -1) {
		return -1;
	}
	crc32_uint(&source_string, &hash);

	ret = hash % denominator;
	LM_DBG("hash: %u %% %i = %i\n", hash, denominator, ret);
	return ret;
}

int prime_hash_func(struct sip_msg * msg,
                              enum hash_source source, int denominator) {
	str source_string;
	if(source != shs_from_user && source != shs_to_user) {
		LM_ERR("chosen hash source not usable (may contain letters)\n");
		return -1;
	}
	if (determine_source (msg, source, &source_string) == -1) {
		return -1;
	}

	static const int INT_DIGIT_LIMIT = 18;
	static const int PRIME_NUMBER = 51797;
	uint64_t number = 0;
	uint64_t p10;
	int i, j, limit = 0;
	int ret;
	char source_number_s[INT_DIGIT_LIMIT + 1];

	i = INT_DIGIT_LIMIT - 1;
	j = source_string.len - 1;
	source_number_s[INT_DIGIT_LIMIT] ='\0';

	while(i >= 0 && j >= 0) {
		if(isdigit(source_string.s[j])) {
			source_number_s[i] = source_string.s[j];
			i--;
		}
		j--;
	}
	limit = i;

	for(i=INT_DIGIT_LIMIT - 1, p10=1; i>limit; i--, p10=p10*10) {
		number += (source_number_s[i] - '0') * p10;
	}

	LM_DBG("source_string is %.*s, source_number_s "
	    "is: %s, number is %llu\n", source_string.len, source_string.s,
	    source_number_s + (limit + 1), (long long unsigned int)number);
	ret = number % PRIME_NUMBER;
	ret = ret % denominator + 1;
	LM_DBG("calculated hash is: %i\n", ret);
	return ret;
}

static int determine_source (struct sip_msg *msg, enum hash_source source,
                             str *source_string) {
	source_string->s = NULL;
	source_string->len = 0;

	if(validate_msg(msg) < 0) {
		return -1;
	}

	switch (source) {
			case shs_call_id:
			return determine_call_id (msg, source_string);
			case shs_from_uri:
			return determine_fromto_uri (get_from(msg), source_string);
			case shs_from_user:
			return determine_fromto_user (get_from(msg), source_string);
			case shs_to_uri:
			return determine_fromto_uri (get_to(msg), source_string);
			case shs_to_user:
			return determine_fromto_user (get_to(msg), source_string);
			default:
			LM_ERR("unknown hash source %i.\n",
			     (int) source);
			return -1;
	}
}

static int validate_msg(struct sip_msg * msg) {
	if(!msg->callid && ((parse_headers(msg, HDR_CALLID_F, 0) == -1) || !msg->callid)) {
		LM_ERR("Message has no Call-ID header\n");
		return -1;
	}
	if(!msg->to && ((parse_headers(msg, HDR_TO_F, 0) == -1) || !msg->to)) {
		LM_ERR("Message has no To header\n");
		return -1;
	}
	if(!msg->from && ((parse_headers(msg, HDR_FROM_F, 0) == -1) || !msg->from)) {
		LM_ERR("Message has no From header\n");
		return -1;
	}
	//TODO it would make more sense to do the parsing just if its needed
	//     but parse_from_header is smart enough, so its probably not a huge problem
	if (parse_from_header(msg) < 0) {
		LM_ERR("Error while parsing From header field\n");
		return -1;
	}
	return 0;
}

static int determine_call_id (struct sip_msg *msg, str *source_string) {
	source_string->s = msg->callid->body.s;
	source_string->len = msg->callid->body.len;
	first_token (source_string);
	return 0;
}

static int determine_fromto_uri (struct to_body *fromto, str *source_string) {
	if (fromto == NULL) {
		LM_ERR("fromto is NULL!\n");
		return -1;
	}
	source_string->s = fromto->uri.s;
	source_string->len = fromto->uri.len;
	return 0;
}

static int determine_fromto_user (struct to_body *fromto, str *source_string) {
	struct sip_uri uri;

	if (fromto == NULL) {
		LM_ERR("fromto is NULL!\n");
		return -1;
	}
	if (parse_uri (fromto->uri.s, fromto->uri.len, &uri) < 0) {
		LM_ERR("Failed to parse From or To URI.\n");
		return -1;
	}
	source_string->s = uri.user.s;
	source_string->len = uri.user.len;
	return 0;
}

static int first_token (str *source_string) {
	size_t len;

	if (source_string->s == NULL || source_string->len == 0) {
		return 0;
	}

	while (source_string->len > 0 && isspace (*source_string->s)) {
		++source_string->s;
		--source_string->len;
	}
	for (len = 0; len < source_string->len; ++len) {
		if (isspace (source_string->s[len])) {
			source_string->len = len;
			break;
		}
	}
	return 0;
}