root/modules/services_discovery/sap.c

/*****************************************************************************
 * sap.c :  SAP interface module
 *****************************************************************************
 * Copyright (C) 2004-2005 the VideoLAN team
 * Copyright © 2007 Rémi Denis-Courmont
 * $Id$
 *
 * Authors: Clément Stenac <zorglub@videolan.org>
 *          Rémi Denis-Courmont
 *
 * 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., 51 Franklin Street, Fifth Floor, Boston MA 02110-1301, USA.
 *****************************************************************************/

/*****************************************************************************
 * Includes
 *****************************************************************************/
#ifdef HAVE_CONFIG_H
# include "config.h"
#endif

#include <vlc_common.h>
#include <vlc_plugin.h>
#include <assert.h>

#include <vlc_demux.h>
#include <vlc_services_discovery.h>

#include <vlc_network.h>
#include <vlc_charset.h>

#include <ctype.h>
#include <errno.h>

#ifdef HAVE_UNISTD_H
#    include <unistd.h>
#endif
#ifdef HAVE_SYS_TIME_H
#    include <sys/time.h>
#endif
#ifdef HAVE_POLL
# include <poll.h>
#endif

#ifdef HAVE_ZLIB_H
#   include <zlib.h>
#endif

#ifndef WIN32
#   include <net/if.h>
#endif

/************************************************************************
 * Macros and definitions
 ************************************************************************/

#define MAX_LINE_LENGTH 256

/* SAP is always on that port */
#define SAP_PORT 9875
/* Global-scope SAP address */
#define SAP_V4_GLOBAL_ADDRESS   "224.2.127.254"
/* Organization-local SAP address */
#define SAP_V4_ORG_ADDRESS      "239.195.255.255"
/* Local (smallest non-link-local scope) SAP address */
#define SAP_V4_LOCAL_ADDRESS    "239.255.255.255"
/* Link-local SAP address */
#define SAP_V4_LINK_ADDRESS     "224.0.0.255"
#define ADD_SESSION 1

/*****************************************************************************
 * Module descriptor
 *****************************************************************************/
#define SAP_ADDR_TEXT N_( "SAP multicast address" )
#define SAP_ADDR_LONGTEXT N_( "The SAP module normally chooses itself the " \
                              "right addresses to listen to. However, you " \
                              "can specify a specific address." )
#define SAP_IPV4_TEXT N_( "IPv4 SAP" )
#define SAP_IPV4_LONGTEXT N_( \
      "Listen to IPv4 announcements on the standard addresses." )
#define SAP_IPV6_TEXT N_( "IPv6 SAP" )
#define SAP_IPV6_LONGTEXT N_( \
      "Listen to IPv6 announcements on the standard addresses." )
#define SAP_SCOPE_TEXT N_( "IPv6 SAP scope" )
#define SAP_SCOPE_LONGTEXT N_( \
       "Scope for IPv6 announcements (default is 8)." )
#define SAP_TIMEOUT_TEXT N_( "SAP timeout (seconds)" )
#define SAP_TIMEOUT_LONGTEXT N_( \
       "Delay after which SAP items get deleted if no new announcement " \
       "is received." )
#define SAP_PARSE_TEXT N_( "Try to parse the announce" )
#define SAP_PARSE_LONGTEXT N_( \
       "This enables actual parsing of the announces by the SAP module. " \
       "Otherwise, all announcements are parsed by the \"live555\" " \
       "(RTP/RTSP) module." )
#define SAP_STRICT_TEXT N_( "SAP Strict mode" )
#define SAP_STRICT_LONGTEXT N_( \
       "When this is set, the SAP parser will discard some non-compliant " \
       "announcements." )
#define SAP_CACHE_TEXT N_("Use SAP cache")
#define SAP_CACHE_LONGTEXT N_( \
       "This enables a SAP caching mechanism. " \
       "This will result in lower SAP startup time, but you could end up " \
       "with items corresponding to legacy streams." )
#define SAP_TIMESHIFT_TEXT N_("Allow timeshifting")
#define SAP_TIMESHIFT_LONGTEXT N_( "This automatically enables timeshifting " \
        "for streams discovered through SAP announcements." )

/* Callbacks */
    static int  Open ( vlc_object_t * );
    static void Close( vlc_object_t * );
    static int  OpenDemux ( vlc_object_t * );
    static void CloseDemux ( vlc_object_t * );

vlc_module_begin();
    set_shortname( N_("SAP"));
    set_description( N_("SAP Announcements") );
    set_category( CAT_PLAYLIST );
    set_subcategory( SUBCAT_PLAYLIST_SD );

    add_string( "sap-addr", NULL, NULL,
                SAP_ADDR_TEXT, SAP_ADDR_LONGTEXT, true );
    add_bool( "sap-ipv4", 1 , NULL,
               SAP_IPV4_TEXT,SAP_IPV4_LONGTEXT, true );
    add_bool( "sap-ipv6", 1 , NULL,
              SAP_IPV6_TEXT, SAP_IPV6_LONGTEXT, true );
    add_integer( "sap-timeout", 1800, NULL,
                 SAP_TIMEOUT_TEXT, SAP_TIMEOUT_LONGTEXT, true );
    add_bool( "sap-parse", 1 , NULL,
               SAP_PARSE_TEXT,SAP_PARSE_LONGTEXT, true );
    add_bool( "sap-strict", 0 , NULL,
               SAP_STRICT_TEXT,SAP_STRICT_LONGTEXT, true );
#if 0
    add_bool( "sap-cache", 0 , NULL,
               SAP_CACHE_TEXT,SAP_CACHE_LONGTEXT, true );
#endif
    add_bool( "sap-timeshift", 0 , NULL,
              SAP_TIMESHIFT_TEXT,SAP_TIMESHIFT_LONGTEXT, true );

    set_capability( "services_discovery", 0 );
    set_callbacks( Open, Close );

    add_submodule();
        set_description( N_("SDP Descriptions parser") );
        add_shortcut( "sdp" );
        set_capability( "demux", 51 );
        set_callbacks( OpenDemux, CloseDemux );
vlc_module_end();


/*****************************************************************************
 * Local structures
 *****************************************************************************/

typedef struct sdp_t sdp_t;
typedef struct attribute_t attribute_t;
typedef struct sap_announce_t sap_announce_t;


struct sdp_media_t
{
    struct sdp_t           *parent;
    char                   *fmt;
    struct sockaddr_storage addr;
    socklen_t               addrlen;
    unsigned                n_addr;
    int           i_attributes;
    attribute_t  **pp_attributes;
};


/* The structure that contains sdp information */
struct  sdp_t
{
    const char *psz_sdp;

    /* o field */
    char     username[64];
    uint64_t session_id;
    uint64_t session_version;
    unsigned orig_ip_version;
    char     orig_host[1024];

    /* s= field */
    char *psz_sessionname;

    /* old cruft */
    /* "computed" URI */
    char *psz_uri;
    int           i_media_type;

    /* a= global attributes */
    int           i_attributes;
    attribute_t  **pp_attributes;

    /* medias (well, we only support one atm) */
    unsigned            mediac;
    struct sdp_media_t *mediav;
};

struct attribute_t
{
    const char *value;
    char name[];
};

struct sap_announce_t
{
    mtime_t i_last;
    mtime_t i_period;
    uint8_t i_period_trust;

    uint16_t    i_hash;
    uint32_t    i_source[4];

    /* SAP annnounces must only contain one SDP */
    sdp_t       *p_sdp;

    input_item_t * p_item;
};

struct services_discovery_sys_t
{
    vlc_thread_t thread;

    /* Socket descriptors */
    int i_fd;
    int *pi_fd;

    /* Table of announces */
    int i_announces;
    struct sap_announce_t **pp_announces;

    /* Modes */
    bool  b_strict;
    bool  b_parse;
    bool  b_timeshift;

    int i_timeout;
};

struct demux_sys_t
{
    sdp_t *p_sdp;
};

/*****************************************************************************
 * Local prototypes
 *****************************************************************************/


/* Main functions */
    static int Demux( demux_t *p_demux );
    static int Control( demux_t *, int, va_list );
    static void *Run  ( void *p_sd );

/* Main parsing functions */
    static int ParseConnection( vlc_object_t *p_obj, sdp_t *p_sdp );
    static int ParseSAP( services_discovery_t *p_sd, const uint8_t *p_buffer, size_t i_read );
    static sdp_t *ParseSDP (vlc_object_t *p_sd, const char *psz_sdp);
    static sap_announce_t *CreateAnnounce( services_discovery_t *, uint16_t, sdp_t * );
    static int RemoveAnnounce( services_discovery_t *p_sd, sap_announce_t *p_announce );

/* Helper functions */
    static inline attribute_t *MakeAttribute (const char *str);
    static const char *GetAttribute (attribute_t **tab, unsigned n, const char *name);
    static inline void FreeAttribute (attribute_t *a);
    static const char *FindAttribute (const sdp_t *sdp, unsigned media,
                                      const char *name);

    static bool IsSameSession( sdp_t *p_sdp1, sdp_t *p_sdp2 );
    static int InitSocket( services_discovery_t *p_sd, const char *psz_address, int i_port );
    static int Decompress( const unsigned char *psz_src, unsigned char **_dst, int i_len );
    static void FreeSDP( sdp_t *p_sdp );

static inline int min_int( int a, int b )
{
    return a > b ? b : a;
}

/*****************************************************************************
 * Open: initialize and create stuff
 *****************************************************************************/
static int Open( vlc_object_t *p_this )
{
    services_discovery_t *p_sd = ( services_discovery_t* )p_this;
    services_discovery_sys_t *p_sys  = (services_discovery_sys_t *)
                                malloc( sizeof( services_discovery_sys_t ) );
    if( !p_sys )
        return VLC_ENOMEM;

    p_sys->i_timeout = var_CreateGetInteger( p_sd, "sap-timeout" );

    p_sd->p_sys  = p_sys;

    p_sys->pi_fd = NULL;
    p_sys->i_fd = 0;

    p_sys->b_strict = var_CreateGetInteger( p_sd, "sap-strict");
    p_sys->b_parse = var_CreateGetInteger( p_sd, "sap-parse" );

#if 0
    if( var_CreateGetInteger( p_sd, "sap-cache" ) )
    {
        CacheLoad( p_sd );
    }
#endif

    /* Cache sap_timeshift value */
    p_sys->b_timeshift = var_CreateGetInteger( p_sd, "sap-timeshift" );

    /* Set our name */
    services_discovery_SetLocalizedName( p_sd, _("SAP") );

    p_sys->i_announces = 0;
    p_sys->pp_announces = NULL;
    /* TODO: create sockets here, and fix racy sockets table */
    if (vlc_clone (&p_sys->thread, Run, p_sd, VLC_THREAD_PRIORITY_LOW))
    {
        free (p_sys);
        return VLC_EGENERIC;
    }

    return VLC_SUCCESS;
}

/*****************************************************************************
 * OpenDemux: initialize and create stuff
 *****************************************************************************/
static int OpenDemux( vlc_object_t *p_this )
{
    demux_t *p_demux = (demux_t *)p_this;
    const uint8_t *p_peek;
    char *psz_sdp = NULL;
    sdp_t *p_sdp = NULL;
    int errval = VLC_EGENERIC;
    size_t i_len;

    if( !var_CreateGetInteger( p_demux, "sap-parse" ) )
    {
        /* We want livedotcom module to parse this SDP file */
        return VLC_EGENERIC;
    }

    assert( p_demux->s ); /* this is NOT an access_demux */

    /* Probe for SDP */
    if( stream_Peek( p_demux->s, &p_peek, 7 ) < 7 )
        return VLC_EGENERIC;

    if( memcmp( p_peek, "v=0\r\no=", 7 ) && memcmp( p_peek, "v=0\no=", 6 ) )
        return VLC_EGENERIC;

    /* Gather the complete sdp file */
    for( i_len = 0, psz_sdp = NULL; i_len < 65536; )
    {
        const int i_read_max = 1024;
        char *psz_sdp_new = realloc( psz_sdp, i_len + i_read_max );
        size_t i_read;
        if( psz_sdp_new == NULL )
        {
            errval = VLC_ENOMEM;
            goto error;
        }
        psz_sdp = psz_sdp_new;

        i_read = stream_Read( p_demux->s, &psz_sdp[i_len], i_read_max );
        if( (int)i_read < 0 )
        {
            msg_Err( p_demux, "cannot read SDP" );
            goto error;
        }
        i_len += i_read;

        psz_sdp[i_len] = '\0';

        if( (int)i_read < i_read_max )
            break; // EOF
    }

    p_sdp = ParseSDP( VLC_OBJECT(p_demux), psz_sdp );

    if( !p_sdp )
    {
        msg_Warn( p_demux, "invalid SDP");
        goto error;
    }

    if( ParseConnection( VLC_OBJECT( p_demux ), p_sdp ) )
    {
        p_sdp->psz_uri = NULL;
    }
    switch (p_sdp->i_media_type)
    {   /* Should be in sync with modules/demux/rtp.c */
        case  0: /* PCMU/8000 */
        case  8: /* PCMA/8000 */
        case 10: /* L16/44100/2 */
        case 11: /* L16/44100 */
        case 14: /* MPA/90000 */
        case 32: /* MPV/90000 */
        case 33: /* MP2/90000 */
            break;
        default:
            goto error;
    }
    if( p_sdp->psz_uri == NULL ) goto error;

    p_demux->p_sys = (demux_sys_t *)malloc( sizeof(demux_sys_t) );
    p_demux->p_sys->p_sdp = p_sdp;
    p_demux->pf_control = Control;
    p_demux->pf_demux = Demux;

    FREENULL( psz_sdp );
    return VLC_SUCCESS;

error:
    FREENULL( psz_sdp );
    if( p_sdp ) FreeSDP( p_sdp ); p_sdp = NULL;
    stream_Seek( p_demux->s, 0 );
    return errval;
}

/*****************************************************************************
 * Close:
 *****************************************************************************/
static void Close( vlc_object_t *p_this )
{
    services_discovery_t *p_sd = ( services_discovery_t* )p_this;
    services_discovery_sys_t    *p_sys  = p_sd->p_sys;
    int i;

    vlc_cancel (p_sys->thread);
    vlc_join (p_sys->thread, NULL);

    for( i = p_sys->i_fd-1 ; i >= 0 ; i-- )
    {
        net_Close( p_sys->pi_fd[i] );
    }
    FREENULL( p_sys->pi_fd );

#if 0
    if( config_GetInt( p_sd, "sap-cache" ) )
    {
        CacheSave( p_sd );
    }
#endif

    for( i = p_sys->i_announces  - 1;  i>= 0; i-- )
    {
        RemoveAnnounce( p_sd, p_sys->pp_announces[i] );
    }
    FREENULL( p_sys->pp_announces );

    free( p_sys );
}

/*****************************************************************************
 * CloseDemux: Close the demuxer
 *****************************************************************************/
static void CloseDemux( vlc_object_t *p_this )
{
    demux_t *p_demux = (demux_t *)p_this;
    if( p_demux->p_sys )
    {
        if( p_demux->p_sys->p_sdp ) { FreeSDP( p_demux->p_sys->p_sdp ); p_demux->p_sys->p_sdp = NULL; }
        free( p_demux->p_sys );
    }
}

/*****************************************************************************
 * Run: main SAP thread
 *****************************************************************************
 * Listens to SAP packets, and sends them to packet_handle
 *****************************************************************************/
#define MAX_SAP_BUFFER 5000

static void *Run( void *data )
{
    services_discovery_t *p_sd = data;
    char *psz_addr;
    int i;
    int timeout = -1;
    int canc = vlc_savecancel ();

    /* Braindead Winsock DNS resolver will get stuck over 2 seconds per failed
     * DNS queries, even if the DNS server returns an error with milliseconds.
     * You don't want to know why the bug (as of XP SP2) wasn't fixed since
     * Winsock 1.1 from Windows 95, if not Windows 3.1.
     * Anyway, to avoid a 30 seconds delay for failed IPv6 socket creation,
     * we have to open sockets in Run() rather than Open(). */
    if( var_CreateGetInteger( p_sd, "sap-ipv4" ) )
    {
        InitSocket( p_sd, SAP_V4_GLOBAL_ADDRESS, SAP_PORT );
        InitSocket( p_sd, SAP_V4_ORG_ADDRESS, SAP_PORT );
        InitSocket( p_sd, SAP_V4_LOCAL_ADDRESS, SAP_PORT );
        InitSocket( p_sd, SAP_V4_LINK_ADDRESS, SAP_PORT );
    }
    if( var_CreateGetInteger( p_sd, "sap-ipv6" ) )
    {
        char psz_address[NI_MAXNUMERICHOST] = "ff02::2:7ffe%";

#ifndef WIN32
        struct if_nameindex *l = if_nameindex ();
        if (l != NULL)
        {
            char *ptr = strchr (psz_address, '%') + 1;
            for (unsigned i = 0; l[i].if_index; i++)
            {
                strcpy (ptr, l[i].if_name);
                InitSocket (p_sd, psz_address, SAP_PORT);
            }
            if_freenameindex (l);
        }
#else
        /* this is the Winsock2 equivalant of SIOCGIFCONF on BSD stacks,
           which if_nameindex uses internally anyway */

        // first create a dummy socket to pin down the protocol family
        SOCKET s = socket(PF_INET6, SOCK_DGRAM, IPPROTO_UDP);
        if( s != INVALID_SOCKET )
        {
            INTERFACE_INFO ifaces[10]; // Assume there will be no more than 10 IP interfaces
            size_t len = sizeof(ifaces);

            if( SOCKET_ERROR != WSAIoctl(s, SIO_GET_INTERFACE_LIST, NULL, 0, &ifaces, len, &len, NULL, NULL) )
            {
                unsigned ifcount = len/sizeof(INTERFACE_INFO);
                char *ptr = strchr (psz_address, '%') + 1;
                for(unsigned i = 1; i<=ifcount; ++i )
                {
                    // append link-local zone identifier
                    sprintf(ptr, "%d", i);
                }
            }
            closesocket(s);
        }
#endif
        *strchr (psz_address, '%') = '\0';

        static const char ipv6_scopes[] = "1456789ABCDE";
        for (const char *c_scope = ipv6_scopes; *c_scope; c_scope++)
        {
            psz_address[3] = *c_scope;
            InitSocket( p_sd, psz_address, SAP_PORT );
        }
    }

    psz_addr = var_CreateGetString( p_sd, "sap-addr" );
    if( psz_addr && *psz_addr )
        InitSocket( p_sd, psz_addr, SAP_PORT );
    free( psz_addr );

    if( p_sd->p_sys->i_fd == 0 )
    {
        msg_Err( p_sd, "unable to listen on any address" );
        return NULL;
    }

    /* read SAP packets */
    for (;;)
    {
        vlc_restorecancel (canc);
        unsigned n = p_sd->p_sys->i_fd;
        struct pollfd ufd[n];

        for (unsigned i = 0; i < n; i++)
        {
            ufd[i].fd = p_sd->p_sys->pi_fd[i];
            ufd[i].events = POLLIN;
            ufd[i].revents = 0;
        }

        int val = poll (ufd, n, timeout);
        canc = vlc_savecancel ();
        if (val > 0)
        {
            for (unsigned i = 0; i < n; i++)
            {
                if (ufd[i].revents)
                {
                    uint8_t p_buffer[MAX_SAP_BUFFER+1];
                    ssize_t i_read;

                    i_read = net_Read (p_sd, ufd[i].fd, NULL, p_buffer,
                                       MAX_SAP_BUFFER, false);
                    if (i_read < 0)
                        msg_Warn (p_sd, "receive error: %m");
                    if (i_read > 6)
                    {
                        /* Parse the packet */
                        p_buffer[i_read] = '\0';
                        ParseSAP (p_sd, p_buffer, i_read);
                    }
                }
            }
        }

        mtime_t now = mdate();

        /* A 1 hour timeout correspong to the RFC Implicit timeout.
         * This timeout is tuned in the following loop. */
        timeout = 1000 * 60 * 60;

        /* Check for items that need deletion */
        for( i = 0; i < p_sd->p_sys->i_announces; i++ )
        {
            mtime_t i_timeout = ( mtime_t ) 1000000 * p_sd->p_sys->i_timeout;
            sap_announce_t * p_announce = p_sd->p_sys->pp_announces[i];
            mtime_t i_last_period = now - p_announce->i_last;

            /* Remove the annoucement, if the last announcement was 1 hour ago
             * or if the last packet emitted was 3 times the average time
             * between two packets */
            if( ( p_announce->i_period_trust > 5 && i_last_period > 3 * p_announce->i_period ) ||
                i_last_period > i_timeout )
            {
                RemoveAnnounce( p_sd, p_announce );
            }
            else
            {
                /* Compute next timeout */
                if( p_announce->i_period_trust > 5 )
                    timeout = min_int((3 * p_announce->i_period - i_last_period) / 1000, timeout);
                timeout = min_int((i_timeout - i_last_period)/1000, timeout);
            }
        }

        if( !p_sd->p_sys->i_announces )
            timeout = -1; /* We can safely poll indefinitly. */
        else if( timeout < 200 )
            timeout = 200; /* Don't wakeup too fast. */
    }
    assert (0);
}

/**********************************************************************
 * Demux: reads and demuxes data packets
 * Return -1 if error, 0 if EOF, 1 else
 **********************************************************************/
static int Demux( demux_t *p_demux )
{
    sdp_t *p_sdp = p_demux->p_sys->p_sdp;
    input_thread_t *p_input;
    input_item_t *p_parent_input;

    p_input = (input_thread_t *)vlc_object_find( p_demux, VLC_OBJECT_INPUT,
                                                 FIND_PARENT );
    assert( p_input );
    if( !p_input )
    {
        msg_Err( p_demux, "parent input could not be found" );
        return VLC_EGENERIC;
    }

    /* This item hasn't been held by input_GetItem
     * don't release it */
    p_parent_input = input_GetItem( p_input );

    input_item_SetURI( p_parent_input, p_sdp->psz_uri );
    input_item_SetName( p_parent_input, p_sdp->psz_sessionname );

    vlc_mutex_lock( &p_parent_input->lock );

    p_parent_input->i_type = ITEM_TYPE_NET;

    vlc_mutex_unlock( &p_parent_input->lock );
    return VLC_SUCCESS;
}

static int Control( demux_t *p_demux, int i_query, va_list args )
{
    VLC_UNUSED(p_demux); VLC_UNUSED(i_query); VLC_UNUSED(args);
    return VLC_EGENERIC;
}

/**************************************************************
 * Local functions
 **************************************************************/

/* i_read is at least > 6 */
static int ParseSAP( services_discovery_t *p_sd, const uint8_t *buf,
                     size_t len )
{
    int i;
    const char          *psz_sdp;
    const uint8_t *end = buf + len;
    sdp_t               *p_sdp;

    assert (buf[len] == '\0');

    if (len < 4)
        return VLC_EGENERIC;

    uint8_t flags = buf[0];

    /* First, check the sap announce is correct */
    if ((flags >> 5) != 1)
        return VLC_EGENERIC;

    bool b_ipv6 = (flags & 0x10) != 0;
    bool b_need_delete = (flags & 0x04) != 0;

    if (flags & 0x02)
    {
        msg_Dbg( p_sd, "encrypted packet, unsupported" );
        return VLC_EGENERIC;
    }

    bool b_compressed = (flags & 0x01) != 0;

    uint16_t i_hash = U16_AT (buf + 2);

    if( p_sd->p_sys->b_strict && i_hash == 0 )
    {
        msg_Dbg( p_sd, "strict mode, discarding announce with null id hash");
        return VLC_EGENERIC;
    }

    // Skips source address and auth data
    buf += 4 + (b_ipv6 ? 16 : 4) + buf[1];
    if (buf > end)
        return VLC_EGENERIC;

    uint8_t *decomp = NULL;
    if( b_compressed )
    {
        int newsize = Decompress (buf, &decomp, end - buf);
        if (newsize < 0)
        {
            msg_Dbg( p_sd, "decompression of SAP packet failed" );
            return VLC_EGENERIC;
        }

        decomp = realloc (decomp, newsize + 1);
        decomp[newsize] = '\0';
        psz_sdp = (const char *)decomp;
        len = newsize;
    }
    else
    {
        psz_sdp = (const char *)buf;
        len = end - buf;
    }

    /* len is a strlen here here. both buf and decomp are len+1 where the 1 should be a \0 */
    assert( psz_sdp[len] == '\0');

    /* Skip payload type */
    /* SAPv1 has implicit "application/sdp" payload type: first line is v=0 */
    if (strncmp (psz_sdp, "v=0", 3))
    {
        size_t clen = strlen (psz_sdp) + 1;

        if (strcmp (psz_sdp, "application/sdp"))
        {
            msg_Dbg (p_sd, "unsupported content type: %s", psz_sdp);
            return VLC_EGENERIC;
        }

        // skips content type
        if (len <= clen)
            return VLC_EGENERIC;

        len -= clen;
        psz_sdp += clen;
    }

    /* Parse SDP info */
    p_sdp = ParseSDP( VLC_OBJECT(p_sd), psz_sdp );

    if( p_sdp == NULL )
        return VLC_EGENERIC;

    p_sdp->psz_sdp = psz_sdp;

    /* Decide whether we should add a playlist item for this SDP */
    /* Parse connection information (c= & m= ) */
    if( ParseConnection( VLC_OBJECT(p_sd), p_sdp ) )
        p_sdp->psz_uri = NULL;

    /* Multi-media or no-parse -> pass to LIVE.COM */
    if( ( p_sdp->i_media_type != 14
       && p_sdp->i_media_type != 32
       && p_sdp->i_media_type != 33)
     || p_sd->p_sys->b_parse == false )
    {
        free( p_sdp->psz_uri );
        if (asprintf( &p_sdp->psz_uri, "sdp://%s", p_sdp->psz_sdp ) == -1)
            p_sdp->psz_uri = NULL;
    }

    if( p_sdp->psz_uri == NULL )
    {
        FreeSDP( p_sdp );
        return VLC_EGENERIC;
    }

    for( i = 0 ; i< p_sd->p_sys->i_announces ; i++ )
    {
        sap_announce_t * p_announce = p_sd->p_sys->pp_announces[i];
        /* FIXME: slow */
        /* FIXME: we create a new announce each time the sdp changes */
        if( IsSameSession( p_announce->p_sdp, p_sdp ) )
        {
            /* We don't support delete announcement as they can easily
             * Be used to highjack an announcement by a third party.
             * Intead we cleverly implement Implicit Announcement removal.
             *
             * if( b_need_delete )
             *    RemoveAnnounce( p_sd, p_sd->p_sys->pp_announces[i]);
             * else
             */

            if( !b_need_delete )
            {
                /* No need to go after six, as we start to trust the
                 * average period at six */
                if( p_announce->i_period_trust <= 5 )
                    p_announce->i_period_trust++;

                /* Compute the average period */
                mtime_t now = mdate();
                p_announce->i_period = (p_announce->i_period + (now - p_announce->i_last)) / 2;
                p_announce->i_last = now;
            }
            FreeSDP( p_sdp ); p_sdp = NULL;
            return VLC_SUCCESS;
        }
    }

    CreateAnnounce( p_sd, i_hash, p_sdp );

    FREENULL (decomp);
    return VLC_SUCCESS;
}

sap_announce_t *CreateAnnounce( services_discovery_t *p_sd, uint16_t i_hash,
                                sdp_t *p_sdp )
{
    input_item_t *p_input;
    const char *psz_value;
    sap_announce_t *p_sap = (sap_announce_t *)malloc(
                                        sizeof(sap_announce_t ) );
    services_discovery_sys_t *p_sys;
    if( p_sap == NULL )
        return NULL;

    p_sys = p_sd->p_sys;

    p_sap->i_last = mdate();
    p_sap->i_period = 0;
    p_sap->i_period_trust = 0;
    p_sap->i_hash = i_hash;
    p_sap->p_sdp = p_sdp;

    /* Released in RemoveAnnounce */
    p_input = input_item_NewWithType( VLC_OBJECT(p_sd),
                                     p_sap->p_sdp->psz_uri,
                                     p_sdp->psz_sessionname,
                                     0, NULL, -1, ITEM_TYPE_NET );
    p_sap->p_item = p_input;
    if( !p_input )
    {
        free( p_sap );
        return NULL;
    }

    if( p_sys->b_timeshift )
        input_item_AddOption( p_input, ":access-filter=timeshift" );

    psz_value = GetAttribute( p_sap->p_sdp->pp_attributes, p_sap->p_sdp->i_attributes, "tool" );
    if( psz_value != NULL )
    {
        input_item_AddInfo( p_input, _("Session"), _("Tool"), "%s", psz_value );
    }
    if( strcmp( p_sdp->username, "-" ) )
    {
        input_item_AddInfo( p_input, _("Session"), _("User"), "%s",
                           p_sdp->username );
    }

    /* Handle group */
    if (p_sap->p_sdp->mediac >= 1)
        psz_value = FindAttribute (p_sap->p_sdp, 0, "x-plgroup");
    else
        psz_value = GetAttribute( p_sap->p_sdp->pp_attributes, p_sap->p_sdp->i_attributes, "x-plgroup" );

    services_discovery_AddItem( p_sd, p_input, psz_value /* category name */ );

    TAB_APPEND( p_sys->i_announces, p_sys->pp_announces, p_sap );

    return p_sap;
}


static const char *FindAttribute (const sdp_t *sdp, unsigned media,
                                  const char *name)
{
    /* Look for media attribute, and fallback to session */
    return GetAttribute (sdp->mediav[media].pp_attributes,
                         sdp->mediav[media].i_attributes, name)
        ?: GetAttribute (sdp->pp_attributes, sdp->i_attributes, name);
}


/* Fill p_sdp->psz_uri */