sems/apps/sbc/HeaderFilter.cpp

/*
 * Copyright (C) 2010 Stefan Sayer
 *
 * This file is part of SEMS, a free SIP media server.
 *
 * SEMS 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.
 *
 * For a license to use the SEMS software under conditions
 * other than those described here, or to purchase support for this
 * software, please contact iptel.org by e-mail at the following addresses:
 *    info@iptel.org
 *
 * SEMS 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., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 */

#include "HeaderFilter.h"
#include "sip/parse_common.h"
#include "log.h"
#include "AmUtils.h"
#include <algorithm>
#include <fnmatch.h>

const char* FilterType2String(FilterType ft) {
    switch (ft)
	{
		case Transparent: return "transparent";
		case Whitelist: return "whitelist";
		case Blacklist: return "blacklist";
		default: return "unknown";
    };
}

FilterType String2FilterType(const char* ft) {
    if (!ft)
        return Undefined;

    if (!strcasecmp(ft,"transparent"))
        return Transparent;

    if (!strcasecmp(ft,"whitelist"))
        return Whitelist;

    if (!strcasecmp(ft,"blacklist"))
        return Blacklist;

    return Undefined;
}

bool isActiveFilter(FilterType ft) {
    return (ft != Undefined) && (ft != Transparent);
}

/** @return whether successful */
bool readFilter(AmConfigReader& cfg, const char* cfg_key_filter, const char* cfg_key_list,
        vector<FilterEntry>& filter_list, bool keep_transparent_entry) {

    string filter = cfg.getParameter(cfg_key_filter);
    if (filter.empty())
        return true;

    FilterEntry hf;
    hf.filter_type = String2FilterType(filter.c_str());
    if (Undefined == hf.filter_type) {
        ERROR("invalid %s mode '%s'\n", cfg_key_filter, filter.c_str());
        return false;
    }

    /* no transparent filter */
    if (!keep_transparent_entry && hf.filter_type==Transparent)
        return true;

    vector<string> elems = explode(cfg.getParameter(cfg_key_list), ",");
    for (vector<string>::iterator it=elems.begin(); it != elems.end(); it++) {
        string c = *it;
        std::transform(c.begin(), c.end(), c.begin(), ::tolower);
        hf.filter_list.insert(c);
    }

    filter_list.push_back(hf);
    return true;
}

int skip_header(std::string& hdr, size_t start_pos,
        size_t& name_end, size_t& val_begin,
        size_t& val_end, size_t& hdr_end) {
    /* adapted from sip/parse_header.cpp */

    name_end = val_begin = val_end = start_pos;
    hdr_end = hdr.length();

    /*
     * Header states
     */
    enum {
        H_NAME=0,
        H_HCOLON,
        H_VALUE_SWS,
        H_VALUE,
    };

    int st = H_NAME;
    int saved_st = 0;

    /* iterate till actual name, if space(s)/tab(s) in front of hf name */
    bool iteration_till_name = true;

    size_t p = start_pos;
    for ( ; p < hdr.length() && st != ST_LF && st != ST_CRLF; p++)
    {
        switch (st)
        {
            case H_NAME:
                switch (hdr[p])
                {
                    case_CR_LF;

                    case HCOLON:
                        st = H_VALUE_SWS;
                        name_end = p;
                        break;

                    case SP:
                    case HTAB:
                        /* skip spaces/tabs at the beginning of the line (if now expected hf name) */
                        if (!iteration_till_name) {
                            st = H_HCOLON;
                            name_end = p;
                        } else {
                            /* remove space from the name */
                            hdr.erase(p--, 1);
                        }
                        break;

                    /* other letters apart space, tab and colon */
                    default:
                        /* means - no spaces at the beginning of hf name found, start reading the name */
                        iteration_till_name = false;
                }
                break;

            case H_VALUE_SWS:
                switch (hdr[p])
                {
                    case_CR_LF;

                    case SP:
                    case HTAB:
                        break;

                    default:
                        st = H_VALUE;
                        val_begin = p;
                        break;
                };
                break;

            case H_VALUE:
                switch (hdr[p])
                {
                    case_CR_LF;
                };

                /* trying to guess, if this is a multi-line header */
                if (st == ST_CR || st == ST_LF) {

                    /* if next line of SIP message begins with a space, then we should check for a multi-value */
                    if (hdr[p] == CR && hdr[p+1] == LF && (hdr[p+2] == SP || hdr[p+2] == HTAB))
                    {
                        printf("Checking whether the value is multi-line\n");

                        /* next line must not contain colon. No colon - is a clear sign of multi-line value */
                        size_t tmp = p;
                        tmp += 2;

                        bool colon_found = false;
                        for ( ; tmp < hdr.length() && hdr[tmp] != CR && hdr[tmp] != LF; tmp++)
                        {
                            if (hdr[tmp] == HCOLON) {
                                colon_found = true;
                                break;
                            }
                        }

                        if (colon_found) {
                            /* next line is definitely another header, stop parsing as a value */
                            val_end = p;
                        } else {
                            /* next line is a part of multi-line value */
                            hdr.erase(p, 2); /* remove CR and LF from the string */
                            st = H_VALUE;
                        }

                        break;

                    /* definitely not a multi-value */
                    } else {
                        val_end = p;
                    }
                }

                /* Beginning of the next part of multi-line value.
                 * By RFC3261 (section 7.4.1), as well as by RFC2616, multi-line value of hf,
                 * must begin either with at least one space or tab.
                 */
                if (hdr[p] == SP || hdr[p] == HTAB) {
                    while (hdr[p]  == SP || hdr[p] == HTAB)
                        p++;
                }
                break;

            case H_HCOLON:
                switch (hdr[p])
                {
                    case HCOLON:
                        st = H_VALUE_SWS;
                        val_begin = p;
                        break;

                    case SP:
                    case HTAB:
                        break;

                default:
                    DBG("Missing ':' after header name\n");
                    return MALFORMED_SIP_MSG;
            }
            break;

            case_ST_CR(hdr[p]);

            st = saved_st;
            hdr_end = p;
            break;
        }
    }
    
    hdr_end = p;
    if (p == hdr.length() && st == H_VALUE) {
        val_end = p;
    }

    return 0;
}

int inplaceHeaderFilter(string& hdrs, const vector<FilterEntry>& filter_list) {
    if (!hdrs.length() || ! filter_list.size())
        return 0;

    DBG("Applying '%zd' header filters\n", filter_list.size());

    for (vector<FilterEntry>::const_iterator fe = filter_list.begin();
        fe != filter_list.end(); fe++)
    {
        const set<string>& headerfilter_list = fe->filter_list;
        const FilterType& f_type = fe->filter_type;

        if (!isActiveFilter(f_type))
            continue;

        /* todo: multi-line header support */

        size_t start_pos = 0;
        while (start_pos < hdrs.length())
        {
            size_t name_end, val_begin, val_end, hdr_end;
            int res;

            if ((res = skip_header(hdrs, start_pos, name_end, val_begin,
                                    val_end, hdr_end)) != 0) {
                return res;
            }

            string hdr_name = hdrs.substr(start_pos, name_end - start_pos);
            std::transform(hdr_name.begin(), hdr_name.end(), hdr_name.begin(), ::tolower);
            bool erase = (f_type == Whitelist);

            string hdr_value = hdrs.substr(val_begin, val_end - val_begin);

            /* DBG("hdr name parsed: '%s'\n", hdr_name.c_str()); */
            /* DBG("hdr value parsed: '%s'\n", hdr_value.c_str()); */

            for (set<string>::iterator it = headerfilter_list.begin();
                it != headerfilter_list.end(); ++it)
            {
                if (fnmatch(it->c_str(), hdr_name.c_str(), 0) == 0) {
                    erase = (f_type != Whitelist);
                    break;
                }
            }

            if (erase) {
                DBG("erasing header '%s' by filter '%s'\n", hdr_name.c_str(), FilterType2String(f_type));
                hdrs.erase(start_pos, hdr_end-start_pos);
            } else {
                /* DBG("header accepted '%s' by filter '%s'\n", hdr_name.c_str(), FilterType2String(f_type)); */
                start_pos = hdr_end;
            }
        }
    }

    return 0;
}