Merge branch 't/decoder_latency'

[paraslash.git] / vss.c

/*
 * Copyright (C) 1997-2010 Andre Noll <maan@systemlinux.org>
 *
 * Licensed under the GPL v2. For licencing details see COPYING.
 */

/** \file vss.c The virtual streaming system.
 *
 * This contains the audio streaming code of para_server which is independent
 * of the current audio format, audio file selector and of the activated
 * senders.
 */

#include <regex.h>
#include <dirent.h>
#include <osl.h>

#include "para.h"
#include "error.h"
#include "portable_io.h"
#include "fec.h"
#include "string.h"
#include "afh.h"
#include "afs.h"
#include "server.h"
#include "net.h"
#include "server.cmdline.h"
#include "list.h"
#include "send.h"
#include "vss.h"
#include "ipc.h"
#include "fd.h"
#include "sched.h"

extern struct misc_meta_data *mmd;

extern void dccp_send_init(struct sender *);
extern void http_send_init(struct sender *);
extern void udp_send_init(struct sender *);

/** The list of supported senders. */
struct sender senders[] = {
        {
                .name = "http",
                .init = http_send_init,
        },
        {
                .name = "dccp",
                .init = dccp_send_init,
        },
        {
                .name = "udp",
                .init = udp_send_init,
        },
        {
                .name = NULL,
        }
};

/** The possible states of the afs socket. */
enum afs_socket_status {
        /** Socket is inactive. */
        AFS_SOCKET_READY,
        /** Socket fd was included in the write fd set for select(). */
        AFS_SOCKET_CHECK_FOR_WRITE,
        /** vss wrote a request to the socket and waits for reply from afs. */
        AFS_SOCKET_AFD_PENDING
};

/** The task structure for the virtual streaming system. */
struct vss_task {
        /** Copied from the -announce_time command line option. */
        struct timeval announce_tv;
        /** End of the announcing interval. */
        struct timeval data_send_barrier;
        /** End of the EOF interval. */
        struct timeval eof_barrier;
        /** Only used if --autoplay_delay was given. */
        struct timeval autoplay_barrier;
        /** Used for afs-server communication. */
        int afs_socket;
        /** The current state of \a afs_socket. */
        enum afs_socket_status afsss;
        /** The memory mapped audio file. */
        char *map;
        /** Used by the scheduler. */
        struct task task;
        /** Pointer to the header of the mapped audio file. */
        const char *header_buf;
        /** Length of the audio file header. */
        size_t header_len;
        /** Time between audio file headers are sent. */
        struct timeval header_interval;
};

/**
 * The list of currently connected fec clients.
 *
 * Senders may use \ref vss_add_fec_client() to add entries to the list.
 */
static struct list_head fec_client_list;

/**
 * Data associated with one FEC group.
 *
 * A FEC group consists of a fixed number of slices and this number is given by
 * the \a slices_per_group parameter of struct \ref fec_client_parms. Each FEC
 * group contains a number of chunks of the current audio file.
 *
 * FEC slices directly correspond to the data packages sent by the paraslash
 * senders that use FEC. Each slice is identified by its group number and its
 * number within the group. All slices have the same size, but the last slice
 * of the group may not be filled entirely.
 */
struct fec_group {
        /** The number of the FEC group. */
        uint32_t num;
        /** Number of bytes in this group. */
        uint32_t bytes;
        /** The first chunk of the current audio file belonging to the group. */
        uint32_t first_chunk;
        /** The number of chunks contained in this group. */
        uint32_t num_chunks;
        /** When the first chunk was sent. */
        struct timeval start;
        /** The duration of the full group. */
        struct timeval duration;
        /** The group duration divided by the number of slices. */
        struct timeval slice_duration;
        /** Group contains the audio file header that occupies that many slices. */
        uint8_t num_header_slices;
};

enum fec_client_state {
        FEC_STATE_NONE = 0,     /**< not initialized and not enabled */
        FEC_STATE_DISABLED,     /**< temporarily disabled */
        FEC_STATE_READY_TO_RUN  /**< initialized and enabled */
};

/**
 * Describes one connected FEC client.
 */
struct fec_client {
        /** Current state of the client */
        enum fec_client_state state;
        /** The connected sender client (transport layer). */
        struct sender_client *sc;
        /** Parameters requested by the client. */
        struct fec_client_parms *fcp;
        /** Used by the core FEC code. */
        struct fec_parms *parms;
        /** The position of this client in the fec client list. */
        struct list_head node;
        /** When the first slice for this client was sent. */
        struct timeval stream_start;
        /** The first chunk sent to this FEC client. */
        int first_stream_chunk;
        /** Describes the current group. */
        struct fec_group group;
        /** The current slice. */
        uint8_t current_slice_num;
        /** The data to be FEC-encoded (point to a region within the mapped audio file). */
        const unsigned char **src_data;
        /** Last time an audio  header was sent. */
        struct timeval next_header_time;
        /** Used for the last source pointer of an audio file. */
        unsigned char *extra_src_buf;
        /** Extra slices needed to store largest chunk + header. */
        int num_extra_slices;
        /** Contains the FEC-encoded data. */
        unsigned char *enc_buf;
};

/**
 * Get the chunk time of the current audio file.
 *
 * \return A pointer to a struct containing the chunk time, or NULL,
 * if currently no audio file is selected.
 */
struct timeval *vss_chunk_time(void)
{
        if (mmd->afd.afhi.chunk_tv.tv_sec == 0 &&
                        mmd->afd.afhi.chunk_tv.tv_usec == 0)
                return NULL;
        return &mmd->afd.afhi.chunk_tv;
}

/**
 * Write a fec header to a buffer.
 *
 * \param buf The buffer to write to.
 * \param h The fec header to write.
 */
static void write_fec_header(struct fec_client *fc, struct vss_task *vsst)
{
        char *buf = (char *)fc->enc_buf;
        struct fec_group *g = &fc->group;
        struct fec_client_parms *p = fc->fcp;

        write_u32(buf, FEC_MAGIC);

        write_u8(buf + 4, p->slices_per_group + fc->num_extra_slices);
        write_u8(buf + 5, p->data_slices_per_group + fc->num_extra_slices);
        write_u32(buf + 6, g->num_header_slices? vsst->header_len : 0);

        write_u32(buf + 10, g->num);
        write_u32(buf + 14, g->bytes);

        write_u8(buf + 18, fc->current_slice_num);
        write_u16(buf + 20, p->max_slice_bytes - FEC_HEADER_SIZE);
        write_u8(buf + 22, g->first_chunk? 0 : 1);
        write_u8(buf + 23, vsst->header_len? 1 : 0);
        memset(buf + 24, 0, 7);
}

static int need_audio_header(struct fec_client *fc, struct vss_task *vsst)
{
        if (!mmd->current_chunk) {
                tv_add(now, &vsst->header_interval, &fc->next_header_time);
                return 0;
        }
        if (!vsst->header_buf)
                return 0;
        if (!vsst->header_len)
                return 0;
        if (fc->group.num && tv_diff(&fc->next_header_time, now, NULL) > 0)
                return 0;
        tv_add(now, &vsst->header_interval, &fc->next_header_time);
        return 1;
}

static int num_slices(long unsigned bytes, struct fec_client *fc, uint8_t *result)
{
        unsigned long m = fc->fcp->max_slice_bytes - FEC_HEADER_SIZE;
        unsigned rv, redundant_slices = fc->fcp->slices_per_group
                - fc->fcp->data_slices_per_group;

        if (!m)
                return -E_BAD_CT;
        rv = (bytes + m - 1) / m;
        if (rv + redundant_slices > 255)
                return -E_BAD_CT;
        *result = rv;
        return 1;
}

/* set group start and group duration */
static void set_group_timing(struct fec_client *fc, struct fec_group *g)
{
        struct timeval *chunk_tv = vss_chunk_time();

        tv_scale(g->num_chunks, chunk_tv, &g->duration);
        tv_divide(fc->fcp->slices_per_group + fc->num_extra_slices,
                &g->duration, &g->slice_duration);
        PARA_DEBUG_LOG("durations (group/chunk/slice): %lu/%lu/%lu\n",
                tv2ms(&g->duration), tv2ms(chunk_tv), tv2ms(&g->slice_duration));
}

static int setup_next_fec_group(struct fec_client *fc, struct vss_task *vsst)
{
        int ret, i, k, data_slices;
        size_t len;
        const char *buf, *start_buf;
        struct fec_group *g = &fc->group;
        unsigned slice_bytes = fc->fcp->max_slice_bytes - FEC_HEADER_SIZE;
        uint32_t max_data_size;

        if (fc->first_stream_chunk < 0) {
                uint8_t hs, ds; /* needed header/data slices */
                uint8_t rs = fc->fcp->slices_per_group
                        - fc->fcp->data_slices_per_group; /* redundant slices */
                int n;

                ret = num_slices(vsst->header_len, fc, &hs);
                if (ret < 0)
                        return ret;
                ret = num_slices(afh_get_largest_chunk_size(&mmd->afd.afhi),
                        fc, &ds);
                if (ret < 0)
                        return ret;
                k = (int)hs + ds;
                if (k > 255)
                        return -E_BAD_CT;
                if (k < fc->fcp->data_slices_per_group)
                        k = fc->fcp->data_slices_per_group;
                n = k + rs;
                fc->num_extra_slices = k - fc->fcp->data_slices_per_group;
                PARA_NOTICE_LOG("fec parms %d:%d:%d (%d extra slices)\n",
                        slice_bytes, k, n, fc->num_extra_slices);
                fec_free(fc->parms);
                fc->src_data = para_realloc(fc->src_data, k * sizeof(char *));
                ret = fec_new(k, n, &fc->parms);
                if (ret < 0)
                        return ret;
                fc->stream_start = *now;
                fc->first_stream_chunk = mmd->current_chunk;
                g->first_chunk = mmd->current_chunk;
                g->num = 0;
                g->start = *now;
        } else {
                struct timeval tmp;
                if (g->first_chunk + g->num_chunks >= mmd->afd.afhi.chunks_total)
                        return 0;
                /*
                 * Start and duration of this group depend only on the previous
                 * group. Compute the new group start as g->start += g->duration.
                 */
                tmp = g->start;
                tv_add(&tmp, &g->duration, &g->start);
                k = fc->fcp->data_slices_per_group + fc->num_extra_slices;
                set_group_timing(fc, g);
                g->first_chunk += g->num_chunks;
                g->num++;
        }
        if (need_audio_header(fc, vsst)) {
                ret = num_slices(vsst->header_len, fc, &g->num_header_slices);
                if (ret < 0)
                        return ret;
        } else
                g->num_header_slices = 0;
        afh_get_chunk(g->first_chunk, &mmd->afd.afhi, vsst->map, &start_buf,
                &len);
        data_slices = k - g->num_header_slices;
        assert(data_slices);
        max_data_size = slice_bytes * data_slices;
        g->bytes = 0;
        for (i = g->first_chunk; i < mmd->afd.afhi.chunks_total; i++) {
                afh_get_chunk(i, &mmd->afd.afhi, vsst->map, &buf, &len);
                if (g->bytes + len > max_data_size)
                        break;
                g->bytes += len;
        }
        g->num_chunks = i - g->first_chunk;
        assert(g->num_chunks);
        fc->current_slice_num = 0;
        if (g->num == 0)
                set_group_timing(fc, g);

        /* setup header slices */
        buf = vsst->header_buf;
        for (i = 0; i < g->num_header_slices; i++) {
                fc->src_data[i] = (const unsigned char *)buf;
                buf += slice_bytes;
        }

        /* setup data slices */
        buf = start_buf;
        for (i = g->num_header_slices; i < k; i++) {
                if (buf + slice_bytes > vsst->map + mmd->size)
                        /*
                         * Can not use the memory mapped audio file for this
                         * slice as it goes beyond the map. This slice will not
                         * be fully used.
                         */
                        break;
                fc->src_data[i] = (const unsigned char *)buf;
                buf += slice_bytes;
        }
        if (i < k) {
                uint32_t payload_size = vsst->map + mmd->size - buf;
                memcpy(fc->extra_src_buf, buf, payload_size);
                fc->src_data[i] = fc->extra_src_buf;
                i++;
                /* use arbitrary data for all remaining slices */
                buf = vsst->map;
                for (; i < k; i++)
                        fc->src_data[i] = (const unsigned char *)buf;
        }
        PARA_DEBUG_LOG("FEC group %d: %d chunks (%d - %d), "
                "%d header slices, %d data slices\n",
                g->num, g->num_chunks, g->first_chunk,
                g->first_chunk + g->num_chunks - 1,
                g->num_header_slices, data_slices
        );
        return 1;
}

static int compute_next_fec_slice(struct fec_client *fc, struct vss_task *vsst)
{
        if (fc->first_stream_chunk < 0 || fc->current_slice_num
                        == fc->fcp->slices_per_group + fc->num_extra_slices) {
                int ret = setup_next_fec_group(fc, vsst);
                if (ret == 0)
                        return 0;
                if (ret < 0) {
                        PARA_ERROR_LOG("%s\n", para_strerror(-ret));
                        PARA_ERROR_LOG("FEC client temporarily disabled\n");
                        fc->state = FEC_STATE_DISABLED;
                        return ret;
                }
        }
        write_fec_header(fc, vsst);
        fec_encode(fc->parms, fc->src_data, fc->enc_buf + FEC_HEADER_SIZE,
                fc->current_slice_num,
                fc->fcp->max_slice_bytes - FEC_HEADER_SIZE);
        return 1;
}

/**
 * Return a buffer that marks the end of the stream.
 *
 * \param buf Result pointer.
 * \return The length of the eof buffer.
 *
 * This is used for (multicast) udp streaming where closing the socket on the
 * sender might not give rise to an eof condition at the peer.
 */
size_t vss_get_fec_eof_packet(const char **buf)
{
        static const char fec_eof_packet[FEC_HEADER_SIZE] = FEC_EOF_PACKET;
        *buf = fec_eof_packet;
        return FEC_HEADER_SIZE;
}

/**
 * Add one entry to the list of active fec clients.
 *
 * \param sc  Generic sender_client data of the transport layer.
 * \param fcp FEC parameters as supplied by the transport layer.
 *
 * \return Newly allocated fec_client struct.
 */
struct fec_client *vss_add_fec_client(struct sender_client *sc,
                                      struct fec_client_parms *fcp)
{
        struct fec_client *fc = para_calloc(sizeof(*fc));

        fc->sc  = sc;
        fc->fcp = fcp;
        para_list_add(&fc->node, &fec_client_list);
        return fc;
}

/**
 * Remove one entry from the list of active fec clients.
 *
 * \param fc The client to be removed.
 */
void vss_del_fec_client(struct fec_client *fc)
{
        list_del(&fc->node);
        free(fc->src_data);
        free(fc->enc_buf);
        free(fc->extra_src_buf);
        fec_free(fc->parms);
        free(fc);
}

/*
 * Compute if/when next slice is due. If it isn't due yet and \a diff is
 * not \p Null, compute the time difference next - now, where
 *
 *      next = stream_start + (first_group_chunk - first_stream_chunk)
 *              * chunk_time + slice_num * slice_time
 */
static int next_slice_is_due(struct fec_client *fc, struct timeval *diff)
{
        struct timeval tmp, next;
        int ret;

        if (fc->first_stream_chunk < 0)
                return 1;
        tv_scale(fc->current_slice_num, &fc->group.slice_duration, &tmp);
        tv_add(&tmp, &fc->group.start, &next);
        ret = tv_diff(&next, now, diff);
        return ret < 0? 1 : 0;
}

static void compute_slice_timeout(struct timeval *timeout)
{
        struct fec_client *fc;

        list_for_each_entry(fc, &fec_client_list, node) {
                struct timeval diff;

                if (fc->state != FEC_STATE_READY_TO_RUN)
                        continue;
                if (next_slice_is_due(fc, &diff)) {
                        timeout->tv_sec = 0;
                        timeout->tv_usec = 0;
                        return;
                }
                /* timeout = min(timeout, diff) */
                if (tv_diff(&diff, timeout, NULL) < 0)
                        *timeout = diff;
        }
}

static void set_eof_barrier(struct vss_task *vsst)
{
        struct fec_client *fc;
        struct timeval timeout = {1, 0}, *chunk_tv = vss_chunk_time();

        if (!chunk_tv)
                goto out;
        list_for_each_entry(fc, &fec_client_list, node) {
                struct timeval group_duration;

                if (fc->state != FEC_STATE_READY_TO_RUN)
                        continue;
                tv_scale(fc->group.num_chunks, chunk_tv, &group_duration);
                if (tv_diff(&timeout, &group_duration, NULL) < 0)
                        timeout = group_duration;
        }
out:
        tv_add(now, &timeout, &vsst->eof_barrier);
}

/**
 * Check if vss status flag \a P (playing) is set.
 *
 * \return Greater than zero if playing, zero otherwise.
 *
 */
unsigned int vss_playing(void)
{
        return mmd->new_vss_status_flags & VSS_PLAYING;
}

/**
 * Check if the \a N (next) status flag is set.
 *
 * \return Greater than zero if set, zero if not.
 *
 */
unsigned int vss_next(void)
{
        return mmd->new_vss_status_flags & VSS_NEXT;
}

/**
 * Check if a reposition request is pending.
 *
 * \return Greater than zero if true, zero otherwise.
 *
 */
unsigned int vss_repos(void)
{
        return mmd->new_vss_status_flags & VSS_REPOS;
}

/**
 * Check if the vss is currently paused.
 *
 * \return Greater than zero if paused, zero otherwise.
 *
 */
unsigned int vss_paused(void)
{
        return !(mmd->new_vss_status_flags & VSS_NEXT)
                && !(mmd->new_vss_status_flags & VSS_PLAYING);
}

/**
 * Check if the vss is currently stopped.
 *
 * \return Greater than zero if paused, zero otherwise.
 *
 */
unsigned int vss_stopped(void)
{
        return (mmd->new_vss_status_flags & VSS_NEXT)
                && !(mmd->new_vss_status_flags & VSS_PLAYING);
}

static int chk_barrier(const char *bname, const struct timeval *barrier,
                struct timeval *diff, int print_log)
{
        long ms;

        if (tv_diff(now, barrier, diff) > 0)
                return 1;
        ms = tv2ms(diff);
        if (print_log && ms)
                PARA_DEBUG_LOG("%s barrier: %lims left\n", bname, ms);
        return -1;
}

/*
 * != NULL: timeout for next chunk
 * NULL: nothing to do
 */
static struct timeval *vss_compute_timeout(struct vss_task *vsst)
{
        static struct timeval the_timeout;
        struct timeval next_chunk;

        if (vss_next() && vsst->map) {
                /* only sleep a bit, nec*/
                the_timeout.tv_sec = 0;
                the_timeout.tv_usec = 100;
                return &the_timeout;
        }
        if (chk_barrier("autoplay_delay", &vsst->autoplay_barrier,
                        &the_timeout, 1) < 0)
                return &the_timeout;
        if (chk_barrier("eof", &vsst->eof_barrier, &the_timeout, 1) < 0)
                return &the_timeout;
        if (chk_barrier("data send", &vsst->data_send_barrier,
                        &the_timeout, 1) < 0)
                return &the_timeout;
        if (!vss_playing() || !vsst->map)
                return NULL;
        compute_chunk_time(mmd->chunks_sent, &mmd->afd.afhi.chunk_tv,
                &mmd->stream_start, &next_chunk);
        if (chk_barrier("chunk", &next_chunk, &the_timeout, 0) >= 0) {
                /* chunk is due or bof */
                the_timeout.tv_sec = 0;
                the_timeout.tv_usec = 0;
                return &the_timeout;
        }
        /* compute min of current timeout and next slice time */
        compute_slice_timeout(&the_timeout);
        return &the_timeout;
}

static void vss_eof(struct vss_task *vsst)
{

        if (!vsst->map)
                return;
        if (mmd->new_vss_status_flags & VSS_NOMORE)
                mmd->new_vss_status_flags = VSS_NEXT;
        set_eof_barrier(vsst);
        para_munmap(vsst->map, mmd->size);
        vsst->map = NULL;
        mmd->chunks_sent = 0;
        //mmd->offset = 0;
        mmd->afd.afhi.seconds_total = 0;
        mmd->afd.afhi.chunk_tv.tv_sec = 0;
        mmd->afd.afhi.chunk_tv.tv_usec = 0;
        free(mmd->afd.afhi.chunk_table);
        mmd->afd.afhi.chunk_table = NULL;
        mmd->mtime = 0;
        mmd->size = 0;
        mmd->events++;
}

/**
 * Get the list of all supported audio formats.
 *
 * \return Aa space separated list of all supported audio formats
 * It is not allocated at runtime, i.e. there is no need to free
 * the returned string in the caller.
 */
const char *supported_audio_formats(void)
{
        return SUPPORTED_AUDIO_FORMATS;
}

static int need_to_request_new_audio_file(struct vss_task *vsst)
{
        struct timeval diff;

        if (vsst->map) /* have audio file */
                return 0;
        if (!vss_playing()) /* don't need one */
                return 0;
        if (mmd->new_vss_status_flags & VSS_NOMORE)
                return 0;
        if (vsst->afsss == AFS_SOCKET_AFD_PENDING) /* already requested one */
                return 0;
        if (chk_barrier("autoplay_delay", &vsst->autoplay_barrier,
                        &diff, 1) < 0)
                return 0;
        return 1;
}

static void set_mmd_offset(void)
{
        struct timeval offset;
        tv_scale(mmd->current_chunk, &mmd->afd.afhi.chunk_tv, &offset);
        mmd->offset = tv2ms(&offset);
}

/**
 * Compute the timeout for the main select-loop of the scheduler.
 *
 * \param s Pointer to the server scheduler.
 * \param t Pointer to the vss task structure.
 *
 * Before the timeout is computed, the current vss status flags are evaluated
 * and acted upon by calling appropriate functions from the lower layers.
 * Possible actions include
 *
 *      - request a new audio file from afs,
 *      - shutdown of all senders (stop/pause command),
 *      - reposition the stream (ff/jmp command).
 */
static void vss_pre_select(struct sched *s, struct task *t)
{
        int i;
        struct timeval *tv, diff;
        struct vss_task *vsst = container_of(t, struct vss_task, task);

        if (!vsst->map || vss_next() || vss_paused() || vss_repos()) {
                struct fec_client *fc, *tmp;
                for (i = 0; senders[i].name; i++)
                        if (senders[i].shutdown_clients)
                                senders[i].shutdown_clients();
                list_for_each_entry_safe(fc, tmp, &fec_client_list, node) {
                        fc->first_stream_chunk = -1;
                        fc->state = FEC_STATE_NONE;
                }
                mmd->stream_start.tv_sec = 0;
                mmd->stream_start.tv_usec = 0;
        }
        if (vss_next())
                vss_eof(vsst);
        else if (vss_paused()) {
                if (mmd->chunks_sent)
                        set_eof_barrier(vsst);
                mmd->chunks_sent = 0;
        } else if (vss_repos()) {
                tv_add(now, &vsst->announce_tv, &vsst->data_send_barrier);
                set_eof_barrier(vsst);
                mmd->chunks_sent = 0;
                mmd->current_chunk = mmd->repos_request;
                mmd->new_vss_status_flags &= ~VSS_REPOS;
                set_mmd_offset();
        }
        if (need_to_request_new_audio_file(vsst)) {
                PARA_DEBUG_LOG("ready and playing, but no audio file\n");
                para_fd_set(vsst->afs_socket, &s->wfds, &s->max_fileno);
                vsst->afsss = AFS_SOCKET_CHECK_FOR_WRITE;
        } else
                para_fd_set(vsst->afs_socket, &s->rfds, &s->max_fileno);
        for (i = 0; senders[i].name; i++) {
                if (!senders[i].pre_select)
                        continue;
                senders[i].pre_select(&s->max_fileno, &s->rfds, &s->wfds);
        }
        tv = vss_compute_timeout(vsst);
        if (tv && tv_diff(tv, &s->timeout, &diff) < 0)
                s->timeout = *tv;
}

static int recv_afs_msg(int afs_socket, int *fd, uint32_t *code, uint32_t *data)
{
        char control[255], buf[8];
        struct msghdr msg = {.msg_iov = NULL};
        struct cmsghdr *cmsg;
        struct iovec iov;
        int ret = 0;

        *fd = -1;
        iov.iov_base = buf;
        iov.iov_len = sizeof(buf);
        msg.msg_iov = &iov;
        msg.msg_iovlen = 1;
        msg.msg_control = control;
        msg.msg_controllen = sizeof(control);
        memset(buf, 0, sizeof(buf));
        ret = recvmsg(afs_socket, &msg, 0);
        if (ret < 0)
                return -ERRNO_TO_PARA_ERROR(errno);
        if (iov.iov_len != sizeof(buf))
                return -E_AFS_SHORT_READ;
        *code = *(uint32_t*)buf;
        *data =  *(uint32_t*)(buf + 4);
        for (cmsg = CMSG_FIRSTHDR(&msg); cmsg; cmsg = CMSG_NXTHDR(&msg, cmsg)) {
                if (cmsg->cmsg_level != SOL_SOCKET
                        || cmsg->cmsg_type != SCM_RIGHTS)
                        continue;
                if ((cmsg->cmsg_len - CMSG_LEN(0)) / sizeof(int) != 1)
                        continue;
                *fd = *(int *)CMSG_DATA(cmsg);
        }
        return 1;
}

static void recv_afs_result(struct vss_task *vsst, fd_set *rfds)
{
        int ret, passed_fd, shmid;
        uint32_t afs_code = 0, afs_data = 0;
        struct stat statbuf;

        if (!FD_ISSET(vsst->afs_socket, rfds))
                return;
        ret = recv_afs_msg(vsst->afs_socket, &passed_fd, &afs_code, &afs_data);
        if (ret == -ERRNO_TO_PARA_ERROR(EAGAIN))
                return;
        if (ret < 0)
                goto err;
        vsst->afsss = AFS_SOCKET_READY;
        PARA_DEBUG_LOG("fd: %d, code: %u, shmid: %u\n", passed_fd, afs_code,
                afs_data);
        ret = -E_NOFD;
        if (afs_code != NEXT_AUDIO_FILE)
                goto err;
        if (passed_fd < 0)
                goto err;
        shmid = afs_data;
        ret = load_afd(shmid, &mmd->afd);
        if (ret < 0)
                goto err;
        shm_destroy(shmid);
        ret = fstat(passed_fd, &statbuf);
        if (ret < 0) {
                PARA_ERROR_LOG("fstat error:\n");
                ret = -ERRNO_TO_PARA_ERROR(errno);
                goto err;
        }
        mmd->size = statbuf.st_size;
        mmd->mtime = statbuf.st_mtime;
        ret = para_mmap(mmd->size, PROT_READ, MAP_PRIVATE, passed_fd,
                0, &vsst->map);
        if (ret < 0)
                goto err;
        close(passed_fd);
        mmd->chunks_sent = 0;
        mmd->current_chunk = 0;
        mmd->offset = 0;
        mmd->events++;
        mmd->num_played++;
        mmd->new_vss_status_flags &= (~VSS_NEXT);
        afh_get_header(&mmd->afd.afhi, vsst->map, &vsst->header_buf,
                &vsst->header_len);
        return;
err:
        free(mmd->afd.afhi.chunk_table);
        if (passed_fd >= 0)
                close(passed_fd);
        PARA_ERROR_LOG("%s\n", para_strerror(-ret));
        mmd->new_vss_status_flags = VSS_NEXT;
}

static int initialize_fec_client(struct fec_client *fc)
{
        int ret;
        struct fec_client_parms *fcp = fc->fcp;

        if (fcp->init_fec) {
                /*
                 * Set the maximum slice size to the Maximum Packet Size if the
                 * transport protocol allows to determine this value. The user
                 * can specify a slice size up to this value.
                 */
                ret = fcp->init_fec(fc->sc);
                if (ret < 0)
                        return ret;
                if (!fcp->max_slice_bytes || fcp->max_slice_bytes > ret)
                        fcp->max_slice_bytes = ret;
        }
        if (fcp->max_slice_bytes < FEC_HEADER_SIZE + fcp->data_slices_per_group)
                return -ERRNO_TO_PARA_ERROR(EINVAL);
        ret = fec_new(fcp->data_slices_per_group, fcp->slices_per_group,
                &fc->parms);
        if (ret < 0)
                goto err;
        fc->first_stream_chunk = -1; /* stream not yet started */
        fc->src_data = para_malloc(fc->fcp->slices_per_group * sizeof(char *));
        fc->enc_buf = para_calloc(fc->fcp->max_slice_bytes);
        fc->num_extra_slices = 0;
        fc->extra_src_buf = para_calloc(fc->fcp->max_slice_bytes);
        fc->next_header_time.tv_sec = 0;
        fc->state = FEC_STATE_READY_TO_RUN;
        return 1;
err:
        fec_free(fc->parms);
        return ret;
}

/**
 * Main sending function.
 *
 * This function gets called from vss_post_select(). It checks whether the next
 * chunk of data should be pushed out. It obtains a pointer to the data to be
 * sent out as well as its length from mmd->afd.afhi. This information is then
 * passed to each supported sender's send() function as well as to the send()
 * functions of each registered fec client.
 */
static void vss_send(struct vss_task *vsst)
{
        int ret, i, fec_active = 0;
        struct timeval due;
        struct fec_client *fc, *tmp_fc;

        if (!vsst->map || !vss_playing())
                return;
        if (chk_barrier("eof", &vsst->eof_barrier, &due, 1) < 0)
                return;
        if (chk_barrier("data send", &vsst->data_send_barrier,
                        &due, 1) < 0)
                return;
        list_for_each_entry_safe(fc, tmp_fc, &fec_client_list, node) {
                switch (fc->state) {
                case FEC_STATE_DISABLED:
                        continue;
                case FEC_STATE_NONE:
                        ret = initialize_fec_client(fc);
                        if (ret < 0) {
                                PARA_ERROR_LOG("%s\n", para_strerror(-ret));
                                continue;
                        }
                        /* fall through */
                case FEC_STATE_READY_TO_RUN:
                        break;
                }
                if (!next_slice_is_due(fc, NULL)) {
                        fec_active = 1;
                        continue;
                }
                if (compute_next_fec_slice(fc, vsst) <= 0)
                        continue;
                PARA_DEBUG_LOG("sending %d:%d (%u bytes)\n", fc->group.num,
                        fc->current_slice_num, fc->fcp->max_slice_bytes);
                fc->fcp->send_fec(fc->sc, (char *)fc->enc_buf,
                                  fc->fcp->max_slice_bytes);
                fc->current_slice_num++;
                fec_active = 1;
        }
        if (mmd->current_chunk >= mmd->afd.afhi.chunks_total) { /* eof */
                if (!fec_active)
                        mmd->new_vss_status_flags |= VSS_NEXT;
                return;
        }
        compute_chunk_time(mmd->chunks_sent, &mmd->afd.afhi.chunk_tv,
                &mmd->stream_start, &due);
        if (tv_diff(&due, now, NULL) <= 0) {
                const char *buf;
                size_t len;

                if (!mmd->chunks_sent) {
                        mmd->stream_start = *now;
                        mmd->events++;
                        set_mmd_offset();
                }
                /*
                 * We call the send function also in case of empty chunks as
                 * they might have still some data queued which can be sent in
                 * this case.
                 */
                afh_get_chunk(mmd->current_chunk, &mmd->afd.afhi, vsst->map,
                        &buf, &len);
                for (i = 0; senders[i].name; i++) {
                        if (!senders[i].send)
                                continue;
                        senders[i].send(mmd->current_chunk, mmd->chunks_sent,
                                buf, len, vsst->header_buf, vsst->header_len);
                }
                mmd->chunks_sent++;
                mmd->current_chunk++;
        }
}

static void vss_post_select(struct sched *s, struct task *t)
{
        int ret, i;
        struct vss_task *vsst = container_of(t, struct vss_task, task);


        if (mmd->sender_cmd_data.cmd_num >= 0) {
                int num = mmd->sender_cmd_data.cmd_num,
                        sender_num = mmd->sender_cmd_data.sender_num;

                if (senders[sender_num].client_cmds[num]) {
                        ret = senders[sender_num].client_cmds[num]
                                (&mmd->sender_cmd_data);
                        if (ret < 0)
                                PARA_ERROR_LOG("%s\n", para_strerror(-ret));
                }
                mmd->sender_cmd_data.cmd_num = -1;
        }
        if (vsst->afsss != AFS_SOCKET_CHECK_FOR_WRITE)
                recv_afs_result(vsst, &s->rfds);
        else if (FD_ISSET(vsst->afs_socket, &s->wfds)) {
                PARA_NOTICE_LOG("requesting new fd from afs\n");
                ret = send_buffer(vsst->afs_socket, "new");
                if (ret < 0)
                        PARA_CRIT_LOG("%s\n", para_strerror(-ret));
                else
                        vsst->afsss = AFS_SOCKET_AFD_PENDING;
        }
        for (i = 0; senders[i].name; i++) {
                if (!senders[i].post_select)
                        continue;
                senders[i].post_select(&s->rfds, &s->wfds);
        }
        if ((vss_playing() && !(mmd->vss_status_flags & VSS_PLAYING)) ||
                        (vss_next() && vss_playing()))
                tv_add(now, &vsst->announce_tv, &vsst->data_send_barrier);
        vss_send(vsst);
}

/**
 * Initialize the virtual streaming system task.
 *
 * \param afs_socket The fd for communication with afs.
 *
 * This also initializes all supported senders and starts streaming
 * if the --autoplay command line flag was given.
 */
void init_vss_task(int afs_socket)
{
        static struct vss_task vss_task_struct, *vsst = &vss_task_struct;
        int i;
        char *hn = para_hostname(), *home = para_homedir();
        long unsigned announce_time = conf.announce_time_arg > 0?
                        conf.announce_time_arg : 300,
                autoplay_delay = conf.autoplay_delay_arg > 0?
                        conf.autoplay_delay_arg : 0;
        vsst->header_interval.tv_sec = 5; /* should this be configurable? */
        vsst->afs_socket = afs_socket;
        vsst->task.pre_select = vss_pre_select;
        vsst->task.post_select = vss_post_select;
        ms2tv(announce_time, &vsst->announce_tv);
        PARA_INFO_LOG("announce timeval: %lums\n", tv2ms(&vsst->announce_tv));
        INIT_LIST_HEAD(&fec_client_list);
        for (i = 0; senders[i].name; i++) {
                PARA_NOTICE_LOG("initializing %s sender\n", senders[i].name);
                senders[i].init(&senders[i]);
        }
        free(hn);
        free(home);
        mmd->sender_cmd_data.cmd_num = -1;
        if (conf.autoplay_given) {
                struct timeval tmp;
                mmd->vss_status_flags |= VSS_PLAYING;
                mmd->new_vss_status_flags |= VSS_PLAYING;
                ms2tv(autoplay_delay, &tmp);
                tv_add(now, &tmp, &vsst->autoplay_barrier);
                tv_add(&vsst->autoplay_barrier, &vsst->announce_tv,
                        &vsst->data_send_barrier);
        }
        register_task(&vsst->task);
}