Add forward error correction code to the udp sender/receiver.

[paraslash.git] / vss.c

/*
 * Copyright (C) 1997-2009 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 <dirent.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 "vss.h"
#include "send.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;
};

static struct list_head fec_client_list;

struct fec_slice {
        uint8_t num;
        uint16_t bytes;
};

struct fec_group {
        uint32_t num;
        uint32_t bytes;
        uint32_t first_chunk;
        uint32_t num_chunks;
        struct timeval duration;
        struct timeval start;
        struct timeval slice_duration;
};

struct fec_client {
        struct fec_client_parms *fcp;
        struct fec_parms *parms;
        struct list_head node;
        struct timeval stream_start;
        int first_stream_chunk;
        struct fec_group group;
        struct fec_slice slice;
        const unsigned char **src_data;
        unsigned char *extra_src_buf;
        size_t extra_src_buf_size;
        unsigned char *enc_buf;
        size_t enc_buf_size;
};

/**
 * 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;
}

static void setup_fec_group(struct fec_client *fc, struct vss_task *vsst)
{
        uint32_t num_bytes = 0, chunk_num, max_group_size, last_payload_size;
        int i, k = fc->fcp->data_slices_per_group;
        const unsigned char *start_buf = NULL;
        struct timeval tmp, *chunk_tv = vss_chunk_time();

        assert(chunk_tv);
        max_group_size = (fc->fcp->max_slice_bytes - FEC_HEADER_SIZE) * k;
        chunk_num = fc->group.first_chunk;
        for (;;) {
                const unsigned char *buf;
                size_t len;

                if (chunk_num >= mmd->afd.afhi.chunks_total)
                        break;
                afh_get_chunk(chunk_num, &mmd->afd.afhi, vsst->map, (const char **)&buf, &len);
                if (!start_buf)
                        start_buf = buf;
                if (num_bytes + len > max_group_size)
                        break;
                chunk_num++;
                num_bytes += len;
        }
        assert(start_buf);
        fc->group.num_chunks = chunk_num - fc->group.first_chunk;
        fc->group.num++;
        fc->group.bytes = num_bytes;
        fc->slice.num = 0;
        fc->slice.bytes = ROUND_UP(num_bytes, k) / k;

        /* The last slice will not be fully used */
        last_payload_size = num_bytes % fc->slice.bytes;
        if (!last_payload_size)
                last_payload_size = fc->slice.bytes;

        tv_scale(fc->group.num_chunks, chunk_tv, &fc->group.duration);
        tv_scale(fc->group.first_chunk - fc->first_stream_chunk, chunk_tv,
                &tmp);
        tv_add(&fc->stream_start, &tmp, &fc->group.start);
        tv_divide(fc->fcp->slices_per_group, &fc->group.duration,
                &fc->group.slice_duration);

        for (i = 0; i < k; i++)
                fc->src_data[i] = start_buf + i * fc->slice.bytes;

        if ((char *)start_buf + k * fc->slice.bytes > vsst->map + mmd->size) {
                /* can not use last slice as it goes beyond the map */
                if (fc->extra_src_buf_size < fc->slice.bytes)
                        fc->extra_src_buf = para_realloc(fc->extra_src_buf, fc->slice.bytes);
                memcpy(fc->extra_src_buf, start_buf + (k - 1) * fc->slice.bytes,
                        last_payload_size);
                memset(fc->extra_src_buf + last_payload_size, 0,
                        fc->slice.bytes - last_payload_size);
                fc->src_data[k - 1] = fc->extra_src_buf;
        }

}

/**
 * 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)
{
        char *buf = (char *)fc->enc_buf;

        write_u32(buf, FEC_MAGIC);

        write_u8(buf + 4, fc->fcp->slices_per_group);
        write_u8(buf + 5, fc->fcp->data_slices_per_group);
        write_u32(buf + 6, (uint32_t)0); /* audio header len */

        write_u32(buf + 10, fc->group.num);
        write_u32(buf + 14, fc->group.bytes);

        write_u8(buf + 18, fc->slice.num);
        write_u16(buf + 20, fc->slice.bytes);
        memset(buf + 22, 0, 11);
}

/**
 * Return a buffer that marks the end of the stream.
 *
 * \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] =
        "\xec\x0d\xcc\xfe\0\0\0\0"
        "\0\0\0\0\0\0\0\0"
        "\0\0\0\0\0\0\0\0"
        "\0\0\0\0\0\0\0\0";
        *buf = fec_eof_packet;
        return FEC_HEADER_SIZE;
}

static void compute_next_fec_slice(struct fec_client *fc, struct vss_task *vsst)
{
        if (fc->first_stream_chunk < 0) {
                fc->stream_start = *now;
                fc->first_stream_chunk = mmd->current_chunk;
                fc->group.first_chunk = mmd->current_chunk;
                fc->group.num = 0;
                setup_fec_group(fc, vsst);
        } else if (fc->slice.num == fc->fcp->slices_per_group) {
                fc->group.first_chunk += fc->group.num_chunks;
                setup_fec_group(fc, vsst);

        }
        if (fc->enc_buf_size < fc->slice.bytes + FEC_HEADER_SIZE) {
                fc->enc_buf_size = fc->slice.bytes + FEC_HEADER_SIZE;
                fc->enc_buf = para_realloc(fc->enc_buf, fc->enc_buf_size);
        }
        write_fec_header(fc);
        fec_encode(fc->parms, fc->src_data, fc->enc_buf + FEC_HEADER_SIZE,
                fc->slice.num, fc->slice.bytes);
}

/**
 * Add one entry to the list of active fec clients.
 *
 * \param fcp Describes the fec parameters to be used for this client.
 * \param result An opaque pointer that must be used by remove the client later.
 *
 * \return Standard.
 */
int vss_add_fec_client(struct fec_client_parms *fcp, struct fec_client **result)
{
        int ret;
        struct fec_client *fc;

        if (fcp->max_slice_bytes < FEC_HEADER_SIZE + fcp->data_slices_per_group)
                return -ERRNO_TO_PARA_ERROR(EINVAL);
        fc = para_calloc(sizeof(*fc));
        fc->fcp = fcp;
        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 *));
        para_list_add(&fc->node, &fec_client_list);
        *result = fc;
        return 1;
err:
        fec_free(fc->parms);
        free(fc);
        *result = NULL;
        return ret;
}

/**
 * Remove one entry from the list of active fec clients.
 *
 * \param result 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->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;

        assert(vss_playing());
        list_for_each_entry(fc, &fec_client_list, node) {
                struct timeval diff;
                int ret = next_slice_is_due(fc, &diff);

                // PARA_NOTICE_LOG("diff: %lu, ret: %d\n", tv2ms(&diff), ret);
                if (ret) {
                        timeout->tv_sec = 0;
                        timeout->tv_usec = 0;
                        goto out;
                }
                /* timeout = min(timeout, diff) */
                if (tv_diff(&diff, timeout, NULL) < 0)
                        *timeout = diff;
        }
out:
        return;
        PARA_NOTICE_LOG("slice timeout: %lu:%lu\n", (long unsigned)timeout->tv_sec, (long unsigned)timeout->tv_usec);
}

/**
 * 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)
{

        mmd->stream_start = *now;
        if (!vsst->map)
                return;
        if (mmd->new_vss_status_flags & VSS_NOMORE)
                mmd->new_vss_status_flags = VSS_NEXT;
        tv_add(&mmd->afd.afhi.eof_tv, now, &vsst->eof_barrier);
        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;
        free(mmd->afd.afhi.info_string);
        mmd->afd.afhi.info_string = make_message("%s:\n%s:\n%s:\n", status_item_list[SI_AUDIO_FILE_INFO],
                status_item_list[SI_TAGINFO1], status_item_list[SI_TAGINFO2]);
        make_empty_status_items(mmd->afd.verbose_ls_output);
        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;
}



/**
 * Compute the timeout for para_server's main select-loop.
 *
 * This function gets called from para_server to determine the timeout value
 * for its main select loop.
 *
 * \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;
        }
        if (vss_next())
                vss_eof(vsst);
        else if (vss_paused()) {
                if (mmd->chunks_sent)
                        tv_add(&mmd->afd.afhi.eof_tv, now, &vsst->eof_barrier);
                mmd->chunks_sent = 0;
        } else if (vss_repos()) {
                tv_add(now, &vsst->announce_tv, &vsst->data_send_barrier);
                tv_add(&mmd->afd.afhi.eof_tv, now, &vsst->eof_barrier);
                mmd->chunks_sent = 0;
                mmd->current_chunk = mmd->repos_request;
                mmd->new_vss_status_flags &= ~VSS_REPOS;
        }
        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)
{
        int ret, passed_fd, shmid;
        uint32_t afs_code = 0, afs_data = 0;
        struct stat statbuf;

        vsst->afsss = AFS_SOCKET_READY;
        mmd->afd.afhi.chunk_table = NULL;
        ret = recv_afs_msg(vsst->afs_socket, &passed_fd, &afs_code, &afs_data);
        if (ret < 0)
                goto err;
        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;
}

/**
 * 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 i;
        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;
        if (mmd->current_chunk >= mmd->afd.afhi.chunks_total) { /* eof */
                mmd->new_vss_status_flags |= VSS_NEXT;
                return;
        }
        if (!mmd->chunks_sent) {
                struct timeval tmp;
                mmd->stream_start = *now;
                tv_scale(mmd->current_chunk, &mmd->afd.afhi.chunk_tv, &tmp);
                mmd->offset = tv2ms(&tmp);
                mmd->events++;
        }
        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;
                /*
                 * 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);
                }
        }
        list_for_each_entry_safe(fc, tmp_fc, &fec_client_list, node) {
                if (!next_slice_is_due(fc, NULL))
                        continue;
                compute_next_fec_slice(fc, vsst);
                PARA_DEBUG_LOG("sending %d:%d (%zu bytes)\n", fc->group.num,
                        fc->slice.num, fc->slice.bytes);
                fc->fcp->send((char *)fc->enc_buf,
                        fc->slice.bytes + FEC_HEADER_SIZE,
                        fc->fcp->private_data);
                fc->slice.num++;
        }
        mmd->new_vss_status_flags |= VSS_PLAYING;
        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])
                        senders[sender_num].client_cmds[num](&mmd->sender_cmd_data);
                mmd->sender_cmd_data.cmd_num = -1;
        }
        if (vsst->afsss != AFS_SOCKET_CHECK_FOR_WRITE) {
                if (FD_ISSET(vsst->afs_socket, &s->rfds))
                        recv_afs_result(vsst);
        } 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");
                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->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));
        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;
        make_empty_status_items(mmd->afd.verbose_ls_output);
        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);
        }
        INIT_LIST_HEAD(&fec_client_list);
        register_task(&vsst->task);
}