path: root/vss.c

/* SPDX-License-Identifier: GPL-2.0 */

/** \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 <sys/socket.h>
#include <netinet/in.h>
#include <osl.h>
#include <sys/types.h>
#include <arpa/inet.h>
#include <sys/un.h>
#include <netdb.h>
#include <lopsub.h>

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

extern struct misc_meta_data *mmd;
extern const struct sender udp_sender, http_sender;
const struct sender * const senders[] = {
	&http_sender, &udp_sender, NULL};

/* The possible states of the afs socket. */
enum afs_socket_status {
	/* Socket is inactive. */
	AFS_SOCKET_READY,
	/* Socket fd was monitored for writing. */
	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 {
	/* 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 afs_socket. */
	enum afs_socket_status afsss;
	/* The memory mapped audio file. */
	void *map;
	/* The size of the memory mapping. */
	size_t mapsize;
	/* Used by the scheduler. */
	struct task *task;
	/* Pointer to the header of the mapped audio file. */
	char *header_buf;
	/* Length of the audio file header. */
	size_t header_len;
	/* Time between audio file headers are sent. */
	struct timeval header_interval;
	/* Only used if afh supports dynamic chunks. */
	void *afh_context;
};

/*
 * 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 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;
	/* Number of bytes per slice for this group. */
	uint16_t slice_bytes;
};

/* A FEC client is always in one of these states. */
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 */
};

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.  */
	unsigned char **src_data;
	/* Last time an audio  header was sent. */
	struct timeval next_header_time;
	/* Extra slices needed to store largest chunk + header. */
	int num_extra_slices;
	/* Contains the FEC-encoded data. */
	unsigned char *enc_buf;
	/* Maximal packet size. */
	int mps;
};

/* Write a fec header to the encoding buffer of a fec client. */
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_u8(buf + 19, 0); /* unused */
	write_u16(buf + 20, g->slice_bytes);
	write_u8(buf + 22, g->first_chunk? 0 : 1);
	write_u8(buf + 23, vsst->header_len? 1 : 0);
	memset(buf + 24, 0, 8);
}

static bool 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 false;
	}
	if (!vsst->header_buf)
		return false;
	if (vsst->header_len == 0)
		return false;
	if (fc->group.num > 0) {
		if (!fc->fcp->need_periodic_header)
			return false;
		if (tv_diff(&fc->next_header_time, now, NULL) > 0)
			return false;
	}
	tv_add(now, &vsst->header_interval, &fc->next_header_time);
	return true;
}

static bool need_data_slices(struct fec_client *fc, struct vss_task *vsst)
{
	if (fc->group.num > 0)
		return true;
	if (!vsst->header_buf)
		return true;
	if (vsst->header_len == 0)
		return true;
	if (fc->fcp->need_periodic_header)
		return true;
	return false;
}

static int fc_num_data_slices(const struct fec_client *fc)
{
	return fc->fcp->data_slices_per_group + fc->num_extra_slices;
}

static int fc_num_slices(const struct fec_client *fc)
{
	return fc->fcp->slices_per_group + fc->num_extra_slices;
}

static int num_slices(long unsigned bytes, int max_payload, int rs)
{
	int ret;

	assert(max_payload > 0);
	assert(rs > 0);
	ret = DIV_ROUND_UP(bytes, max_payload);
	if (ret + rs > 255)
		return -E_BAD_CT;
	return ret;
}

/* set group start and group duration */
static void set_group_timing(struct fec_client *fc, struct vss_task *vsst)
{
	struct fec_group *g = &fc->group;
	struct timeval *chunk_tv = &mmd->afd.afhi.chunk_tv;

	if (!need_data_slices(fc, vsst))
		ms2tv(200, &g->duration);
	else
		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 initialize_fec_client(struct fec_client *fc, struct vss_task *vsst)
{
	int i, k, n, ret;
	int hs, ds, rs; /* header/data/redundant slices */
	struct fec_client_parms *fcp = fc->fcp;

	/*
	 * Set the maximum slice size to the Maximum Packet Size if the
	 * transport protocol allows determination of this value. The user
	 * can specify a slice size up to this value.
	 */
	ret = fcp->init_fec(fc->sc);
	if (ret < 0)
		return ret;
	fc->mps = ret;
	if (fc->mps <= FEC_HEADER_SIZE)
		return -ERRNO_TO_PARA_ERROR(EINVAL);

	/* free previous buffers, if any */
	if (fc->src_data) {
		k = fc_num_data_slices(fc);
		for (i = 0; i < k; i++)
			free(fc->src_data[i]);
		free(fc->src_data);
		fc->src_data = NULL;
	}
	free(fc->enc_buf);

	rs = fc->fcp->slices_per_group - fc->fcp->data_slices_per_group;
	ret = num_slices(vsst->header_len, fc->mps - FEC_HEADER_SIZE, rs);
	if (ret < 0)
		return ret;
	hs = ret;
	ret = num_slices(mmd->afd.afhi.max_chunk_size, fc->mps - FEC_HEADER_SIZE, rs);
	if (ret < 0)
		return ret;
	ds = ret;
	if (fc->fcp->need_periodic_header)
		k = hs + ds;
	else
		k = PARA_MAX(hs, ds);
	if (k < fc->fcp->data_slices_per_group)
		k = fc->fcp->data_slices_per_group;
	fc->num_extra_slices = k - fc->fcp->data_slices_per_group;
	n = fc_num_slices(fc);
	PARA_INFO_LOG("mps: %d, k: %d, n: %d, extra slices: %d\n",
		fc->mps, k, n, fc->num_extra_slices);

	fec_free(fc->parms);
	ret = fec_new(k, n, &fc->parms);
	if (ret < 0)
		return ret;
	fc->src_data = arr_alloc(k, sizeof(char *));
	for (i = 0; i < k; i++)
		fc->src_data[i] = alloc(fc->mps);
	fc->enc_buf = alloc(fc->mps);

	fc->state = FEC_STATE_READY_TO_RUN;
	fc->next_header_time.tv_sec = 0;
	fc->stream_start = *now;
	fc->first_stream_chunk = mmd->current_chunk;
	return 1;
}

static int vss_get_chunk(int chunk_num, struct vss_task *vsst,
		char **buf, uint32_t *len)
{
	int ret;

	/*
	 * Chunk zero is special for header streams: It is the first portion of
	 * the audio file which consists of the audio file header. It may be
	 * arbitrary large due to embedded meta data. Audio format handlers may
	 * replace the header by a stripped one with meta data omitted which is
	 * of bounded size. We always use the stripped header for streaming
	 * rather than the unmodified header (chunk zero).
	 */
	if (chunk_num == 0 && vsst->header_len > 0) {
		assert(vsst->header_buf);
		*buf = vsst->header_buf; /* stripped header */
		*len = vsst->header_len;
		return 0;
	}
	ret = afh_get_chunk(chunk_num, &mmd->afd.afhi,
		mmd->afd.audio_format_id, vsst->map, vsst->mapsize,
		(const char **)buf, len, &vsst->afh_context);
	if (ret < 0) {
		*buf = NULL;
		*len = 0;
	}
	return ret;
}

static int compute_group_size(struct vss_task *vsst, struct fec_group *g,
		int max_bytes)
{
	char *buf;
	uint32_t len;
	int ret, i, max_chunks;

	if (g->first_chunk == 0) {
		g->num_chunks = 1;
		ret = vss_get_chunk(0, vsst, &buf, &len);
		if (ret < 0)
			 return ret;
		g->bytes = len;
		return 0;
	}

	g->num_chunks = 0;
	g->bytes = 0;
	/*
	 * Include chunks into the group until the group duration is at least
	 * 150ms.  For ogg and wma, a single chunk's duration (ogg page/wma
	 * super frame) is already larger than 150ms, so a FEC group consists
	 * of exactly one chunk for these audio formats.
	 */
	max_chunks = PARA_MAX(1LU, 150 / tv2ms(&mmd->afd.afhi.chunk_tv));
	for (i = 0;; i++) {
		int chunk_num = g->first_chunk + i;

		if (g->bytes > 0 && i >= max_chunks) /* duration limit */
			break;
		if (chunk_num >= mmd->afd.afhi.chunks_total) /* eof */
			break;
		ret = vss_get_chunk(chunk_num, vsst, &buf, &len);
		if (ret < 0)
			 return ret;
		if (g->bytes + len > max_bytes)
			break;
		/* Include this chunk */
		g->bytes += len;
		g->num_chunks++;
	}
	if (g->num_chunks == 0)
		return -E_EOF;
	PARA_DEBUG_LOG("group #%u: %u chunks, %u bytes total\n", g->num,
		g->num_chunks, g->bytes);
	return 1;
}

/*
 * Compute the slice size of the next group.
 *
 * The FEC parameters n and k are fixed but the slice size varies per
 * FEC group.  We'd like to choose slices as small as possible to avoid
 * unnecessary FEC calculations but large enough to guarantee that the
 * k data slices suffice to encode the header (if needed) and the data
 * chunk(s).
 *
 * Once we know the payload of the next group, we define the number s
 * of bytes per slice for this group by
 *
 * 	s = ceil(payload / k)
 *
 * However, for header streams, computing s is more complicated since no
 * overlapping of header and data slices is possible. Hence we have k >=
 * 2 and s must satisfy
 *
 * (*)	ceil(h / s) + ceil(d / s) <= k
 *
 * where h and d are payload of the header and the data chunk(s)
 * respectively. In general there is no value for s such that (*)
 * becomes an equality, for example if h = 4000, d = 5000 and k = 10.
 *
 * We use the following approach for computing a suitable value for s:
 *
 * Let
 * 	k1 := ceil(k * min(h, d) / (h + d)),
 * 	k2 := k - k1.
 *
 * Note that k >= 2 implies k1 > 0 and k2 > 0, so
 *
 * 	s := max(ceil(min(h, d) / k1), ceil(max(h, d) / k2))
 *
 * is well-defined. Inequality (*) holds for this value of s since k1
 * slices suffice to store min(h, d) while k2 slices suffice to store
 * max(h, d), i.e. the first addent of (*) is bounded by k1 and the
 * second by k2.
 *
 * For the above example we obtain
 *
 * 	k1 = ceil(10 * 4000 / 9000) = 5, k2 = 5,
 * 	s = max(4000 / 5, 5000 / 5) = 1000,
 *
 * which is optimal since a slice size of 999 bytes would already require
 * 11 slices.
 */
static int compute_slice_size(struct fec_client *fc, struct vss_task *vsst)
{
	struct fec_group *g = &fc->group;
	int k = fc_num_data_slices(fc);
	int n = fc_num_slices(fc);
	int ret, k1, k2, h, d, min, max, sum;
	int max_slice_bytes = fc->mps - FEC_HEADER_SIZE;
	int max_group_bytes;

	if (!need_audio_header(fc, vsst)) {
		max_group_bytes = k * max_slice_bytes;
		g->num_header_slices = 0;
		ret = compute_group_size(vsst, g, max_group_bytes);
		if (ret < 0)
			return ret;
		g->slice_bytes = DIV_ROUND_UP(g->bytes, k);
		if (g->slice_bytes == 0)
			g->slice_bytes = 1;
		return 1;
	}
	if (!need_data_slices(fc, vsst)) {
		g->bytes = 0;
		g->num_chunks = 0;
		g->slice_bytes = DIV_ROUND_UP(vsst->header_len, k);
		g->num_header_slices = k;
		return 1;
	}
	h = vsst->header_len;
	max_group_bytes = (k - num_slices(h, max_slice_bytes, n - k))
		* max_slice_bytes;
	ret = compute_group_size(vsst, g, max_group_bytes);
	if (ret < 0)
		return ret;
	d = g->bytes;
	if (d == 0) {
		g->slice_bytes = DIV_ROUND_UP(h, k);
		ret = num_slices(vsst->header_len, g->slice_bytes, n - k);
		if (ret < 0)
			return ret;
		g->num_header_slices = ret;
		return 1;
	}
	min = PARA_MIN(h, d);
	max = PARA_MAX(h, d);
	sum = h + d;
	k1 = DIV_ROUND_UP(k * min, sum);
	k2 = k - k1;
	assert(k1 > 0);
	assert(k2 > 0);

	g->slice_bytes = PARA_MAX(DIV_ROUND_UP(min, k1), DIV_ROUND_UP(max, k2));
	/*
	 * This value of s := g->slice_bytes satisfies inequality (*) above,
	 * but it might be larger than max_slice_bytes. However, we know that
	 * max_slice_bytes are sufficient to store header and data, so:
	 */
	g->slice_bytes = PARA_MIN((int)g->slice_bytes, max_slice_bytes);

	ret = num_slices(vsst->header_len, g->slice_bytes, n - k);
	if (ret < 0)
		return ret;
	g->num_header_slices = ret;
	return 1;
}

static int setup_next_fec_group(struct fec_client *fc, struct vss_task *vsst)
{
	int ret, i, c;
	size_t copy, src_copied, slice_copied;
	struct fec_group *g = &fc->group;

	if (fc->state == FEC_STATE_NONE) {
		ret = initialize_fec_client(fc, vsst);
		if (ret < 0)
			return ret;
		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);
		set_group_timing(fc, vsst);
		g->first_chunk += g->num_chunks;
		g->num++;
	}
	ret = compute_slice_size(fc, vsst);
	if (ret < 0)
		return ret;
	assert(g->slice_bytes > 0);
	fc->current_slice_num = 0;
	if (g->num == 0)
		set_group_timing(fc, vsst);
	/* setup header slices */
	for (i = 0, src_copied = 0; i < g->num_header_slices; i++) {
		copy = PARA_MIN((size_t)g->slice_bytes, vsst->header_len - src_copied);
		if (copy == 0)
			break;
		memcpy(fc->src_data[i], vsst->header_buf + src_copied, copy);
		if (copy < g->slice_bytes)
			memset(fc->src_data[i] + copy, 0, g->slice_bytes - copy);
		src_copied += copy;
	}
	/*
	 * There might be more than one header slice to fill although only the
	 * first one will be used. Zero out any remaining header slices.
	 */
	while (i < g->num_header_slices)
		memset(fc->src_data[i++], 0, g->slice_bytes);

	slice_copied = 0;
	for (c = g->first_chunk; c < g->first_chunk + g->num_chunks; c++) {
		char *buf;
		uint32_t src_len;
		ret = vss_get_chunk(c, vsst, &buf, &src_len);
		if (ret < 0)
			return ret;
		if (src_len == 0)
			continue;
		src_copied = 0;
		while (src_copied < src_len) {
			copy = PARA_MIN((size_t)g->slice_bytes - slice_copied,
				src_len - src_copied);
			memcpy(fc->src_data[i] + slice_copied,
				buf + src_copied, copy);
			src_copied += copy;
			slice_copied += copy;
			if (slice_copied == g->slice_bytes) {
				i++;
				slice_copied = 0;
			}
		}
	}
	if (i < fc_num_data_slices(fc) && slice_copied < g->slice_bytes)
		memset(fc->src_data[i] + slice_copied, 0,
			 g->slice_bytes - slice_copied);
	/* zero out remaining slices, if any */
	while (++i < fc_num_data_slices(fc))
		memset(fc->src_data[i], 0, g->slice_bytes);
	PARA_DEBUG_LOG("FEC group %u: %u chunks (%u - %u), %u bytes\n",
		g->num, g->num_chunks, g->first_chunk,
		g->first_chunk + g->num_chunks - 1, g->bytes
	);
	PARA_DEBUG_LOG("slice_bytes: %d, %d header slices, %d data slices\n",
		g->slice_bytes, g->num_header_slices, fc_num_data_slices(fc)
	);
	return 1;
}

static int compute_next_fec_slice(struct fec_client *fc, struct vss_task *vsst)
{
	if (fc->state == FEC_STATE_NONE || 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, (const unsigned char * const*)fc->src_data,
		fc->enc_buf + FEC_HEADER_SIZE, fc->current_slice_num,
		fc->group.slice_bytes);
	return 1;
}

/**
 * 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 = zalloc(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)
{
	int i;

	list_del(&fc->node);
	free(fc->enc_buf);
	if (fc->src_data) {
		for (i = 0; i < fc_num_data_slices(fc); i++)
			free(fc->src_data[i]);
		free(fc->src_data);
	}
	fec_free(fc->parms);
	free(fc);
}

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

	if (fc->state == FEC_STATE_NONE)
		return true;
	tv_scale(fc->current_slice_num, &fc->group.slice_duration, &tmp);
	tv_add(&tmp, &fc->group.start, &next);
	return tv_diff(&next, now, diff) < 0;
}

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

	if (!vsst->map)
		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, &mmd->afd.afhi.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 the "P" (playing) vss status flag is set.
 *
 * \return True if playing, false otherwise.
 */
bool vss_playing(void)
{
	return mmd->new_vss_status_flags & VSS_PLAYING;
}

/* Check whether the N (next) status flag is set. */
static bool vss_next(void)
{
	return mmd->new_vss_status_flags & VSS_NEXT;
}

/* Check whether a reposition request is pending. */
static bool vss_repos(void)
{
	return mmd->new_vss_status_flags & VSS_REPOS;
}

/**
 * Check if the virtual streaming system is currently paused.
 *
 * \return True if paused, false otherwise.
 */
bool vss_paused(void)
{
	return !(mmd->new_vss_status_flags & VSS_NEXT)
		&& !(mmd->new_vss_status_flags & VSS_PLAYING);
}

/**
 * Check if the virtual streaming system is currently stopped.
 *
 * \return True iff stopped.
 */
bool vss_stopped(void)
{
	return (mmd->new_vss_status_flags & VSS_NEXT)
		&& !(mmd->new_vss_status_flags & VSS_PLAYING);
}

static bool barrier_has_passed(const char *bname, const struct timeval *barrier)
{
	long unsigned ms;
	struct timeval diff;

	if (tv_diff(now, barrier, &diff) > 0)
		return true;
	ms = tv2ms(&diff);
	if (ms > 0)
		PARA_INFO_LOG("%s barrier: %lums left\n", bname, ms);
	return false;
}

static void vss_eof(struct vss_task *vsst)
{
	if (mmd->new_vss_status_flags & VSS_NOMORE)
		mmd->new_vss_status_flags = VSS_NEXT;
	afh_free_header(vsst->header_buf, mmd->afd.audio_format_id);
	vsst->header_buf = NULL;
	para_munmap(vsst->map, vsst->mapsize);
	vsst->map = NULL;
	mmd->afd.afhi.seconds_total = 0;
	mmd->afd.afhi.chunks_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;
	vsst->mapsize = 0;
	afh_close(vsst->afh_context, mmd->afd.audio_format_id);
	vsst->afh_context = NULL;
	mmd->events++;
}

static bool need_to_request_new_audio_file(struct vss_task *vsst)
{
	if (vsst->map) /* have audio file */
		return false;
	if (!vss_playing()) /* don't need one */
		return false;
	if (mmd->new_vss_status_flags & VSS_NOMORE)
		return false;
	if (vsst->afsss != AFS_SOCKET_READY) /* already requested one */
		return false;
	if (!barrier_has_passed("autoplay_delay", &vsst->autoplay_barrier))
		return false;
	return true;
}

static void vss_pre_monitor(struct sched *s, void *context)
{
	struct vss_task *vsst = context;
	int i;
	struct timeval tv;
	struct fec_client *fc;

	if (vsst->afsss == AFS_SOCKET_CHECK_FOR_WRITE) {
		sched_monitor_writefd(vsst->afs_socket, s);
	} else if (vsst->afsss == AFS_SOCKET_AFD_PENDING)
		sched_monitor_readfd(vsst->afs_socket, s);
	FOR_EACH_SENDER(i) {
		if (!senders[i]->pre_monitor)
			continue;
		senders[i]->pre_monitor(s);
	}
	if (!vss_playing() || !vsst->map)
		return;
	if (vss_next() && vsst->map)
		return sched_min_delay(s);

	/* Each of these barriers must have passed until we may proceed */
	if (sched_request_barrier(&vsst->autoplay_barrier, s) == 1)
		return;
	if (sched_request_barrier(&vsst->eof_barrier, s) == 1)
		return;
	if (sched_request_barrier(&vsst->data_send_barrier, s) == 1)
		return;
	/*
	 * Compute the I/O timeout as the minimal time until the next
	 * chunk/slice is due for any client.
	 */
	compute_chunk_time(mmd->chunks_sent, &mmd->afd.afhi.chunk_tv,
		&mmd->stream_start, &tv);
	if (sched_request_barrier_or_min_delay(&tv, s) == 0)
		return;
	list_for_each_entry(fc, &fec_client_list, node) {
		if (fc->state != FEC_STATE_READY_TO_RUN)
			continue;
		if (next_slice_is_due(fc, &tv))
			return sched_min_delay(s);
		sched_request_timeout(&tv, s);
	}
}

static int recv_afd(int afs_socket, int *fd, uint32_t *code, uint32_t *data)
{
	char control[255] __a_aligned(8), buf[8];
	struct iovec iov = {.iov_base = buf, .iov_len = sizeof(buf)};
	struct msghdr msg = {
		.msg_iov = &iov,
		.msg_iovlen = 1,
		.msg_control = control,
		.msg_controllen = sizeof(control),
	};
	struct cmsghdr *cmsg;

	*fd = -1;
	if (recvmsg(afs_socket, &msg, 0) < 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;
}

/* As of 2025, neither FreeBSD-13.5 nor NetBSD-10.0 have MAP_POPULATE. */
#ifndef MAP_POPULATE
#define MAP_POPULATE 0
#endif

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

	if (!sched_read_ok(vsst->afs_socket, s))
		return;
	ret = recv_afd(vsst->afs_socket, &passed_fd, &afs_code, &afs_data);
	if (ret == -ERRNO_TO_PARA_ERROR(EAGAIN))
		return;
	vsst->afsss = AFS_SOCKET_READY;
	if (ret < 0)
		goto err;
	if (afs_code == NO_ADMISSIBLE_FILES) {
		PARA_NOTICE_LOG("no admissible files\n");
		ret = 0;
		goto err;
	}
	ret = -E_NOFD;
	if (afs_code != NEXT_AUDIO_FILE) {
		PARA_ERROR_LOG("afs code: %u, expected: %d\n", 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;
	}
	ret = para_mmap(statbuf.st_size, PROT_READ, MAP_PRIVATE | MAP_POPULATE,
		passed_fd, &vsst->map);
	if (ret < 0)
		goto err;
	vsst->mapsize = statbuf.st_size;
	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, mmd->afd.audio_format_id,
		vsst->map, vsst->mapsize, &vsst->header_buf, &vsst->header_len);
	return;
err:
	free(mmd->afd.afhi.chunk_table);
	mmd->afd.afhi.chunk_table = NULL;
	if (passed_fd >= 0)
		close(passed_fd);
	if (ret < 0)
		PARA_ERROR_LOG("%s\n", para_strerror(-ret));
	mmd->new_vss_status_flags = VSS_NEXT;
}

/*
 * If the next chunk needs to be sent, pass a pointer to the chunk data to all
 * registered fec clients and to each sender's ->send() method.
 */
static void vss_send(struct vss_task *vsst)
{
	int i, ret;
	bool fec_active = false;
	struct timeval due;
	struct fec_client *fc, *tmp_fc;
	char *buf;
	uint32_t len;

	if (!vsst->map || !vss_playing())
		return;
	if (!barrier_has_passed("eof", &vsst->eof_barrier))
		return;
	if (!barrier_has_passed("data send", &vsst->data_send_barrier))
		return;
	list_for_each_entry_safe(fc, tmp_fc, &fec_client_list, node) {
		if (fc->state == FEC_STATE_DISABLED)
			continue;
		if (!next_slice_is_due(fc, NULL)) {
			fec_active = true;
			continue;
		}
		if (compute_next_fec_slice(fc, vsst) <= 0)
			continue;
		PARA_DEBUG_LOG("sending %u:%u (%u bytes)\n", fc->group.num,
			fc->current_slice_num, fc->group.slice_bytes);
		fc->current_slice_num++;
		fc->fcp->send_fec(fc->sc, (char *)fc->enc_buf,
			fc->group.slice_bytes + FEC_HEADER_SIZE);
		fec_active = true;
	}
	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)
		return;
	if (!mmd->chunks_sent) {
		mmd->stream_start = *now;
		mmd->events++;
	}
	ret = vss_get_chunk(mmd->current_chunk, vsst, &buf, &len);
	if (ret < 0) {
		PARA_ERROR_LOG("could not get chunk %lu: %s\n",
			mmd->current_chunk, para_strerror(-ret));
	} else {
		/*
		 * We call ->send() even if len is zero because senders might
		 * have data queued which can be sent now.
		 */
		FOR_EACH_SENDER(i) {
			if (!senders[i]->send)
				continue;
			senders[i]->send(mmd->current_chunk, buf, len,
				vsst->header_buf, vsst->header_len);
		}
	}
	mmd->chunks_sent++;
	mmd->current_chunk++;
}

static int vss_post_monitor(struct sched *s, void *context)
{
	int ret, i;
	struct vss_task *vsst = context;
	bool about2pause, next_flag_flipped;

	ret = task_get_notification(vsst->task);
	if (ret < 0) {
		afh_free_header(vsst->header_buf, mmd->afd.audio_format_id);
		afh_close(vsst->afh_context, mmd->afd.audio_format_id);
		return ret;
	}
	/* If a sender command is pending, run it. */
	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;
	}
	vss_send(vsst); /* might change vss status flags */
	about2pause = vss_paused() && (mmd->vss_status_flags & VSS_PLAYING);
	next_flag_flipped = vss_next() && !(mmd->vss_status_flags & VSS_NEXT);
	if (next_flag_flipped || about2pause || vss_repos()) { /* eos */
		struct fec_client *fc, *tmp;
		/* shut down senders and fec clients */
		FOR_EACH_SENDER(i)
			if (senders[i]->shutdown_clients)
				senders[i]->shutdown_clients();
		list_for_each_entry_safe(fc, tmp, &fec_client_list, node)
			fc->state = FEC_STATE_NONE;
		mmd->stream_start.tv_sec = 0;
		mmd->stream_start.tv_usec = 0;
		mmd->chunks_sent = 0;
		set_eof_barrier(vsst);
	}
	if (vss_repos()) /* set current chunk as requested */
		mmd->current_chunk = afh_get_start_chunk(
			mmd->repos_request, &mmd->afd.afhi,
			mmd->afd.audio_format_id);
	if (about2pause || vss_repos()) { /* set offset for the next stream */
		struct timeval offset;
		tv_scale(mmd->current_chunk, &mmd->afd.afhi.chunk_tv,
			&offset);
		mmd->offset = tv2ms(&offset);
		mmd->new_vss_status_flags &= ~VSS_REPOS;
	}
	if (next_flag_flipped)
		vss_eof(vsst);
	if (need_to_request_new_audio_file(vsst)) {
		PARA_DEBUG_LOG("ready and playing, but no audio file\n");
		vsst->afsss = AFS_SOCKET_CHECK_FOR_WRITE;
	} else if (vsst->afsss == AFS_SOCKET_CHECK_FOR_WRITE) {
		if (sched_write_ok(vsst->afs_socket, s)) {
			PARA_INFO_LOG("requesting new fd from afs\n");
			ret = write_buffer(vsst->afs_socket, "new");
			if (ret < 0)
				return ret;
			vsst->afsss = AFS_SOCKET_AFD_PENDING;
		}
	} else if (vsst->afsss == AFS_SOCKET_AFD_PENDING)
		recv_afs_result(vsst, s);
	FOR_EACH_SENDER(i)
		if (senders[i]->post_monitor)
			senders[i]->post_monitor();
	if ((vss_playing() && !(mmd->vss_status_flags & VSS_PLAYING)) ||
			(vss_next() && vss_playing()))
		tv_add(now, &announce_tv, &vsst->data_send_barrier);
	return 0;
}

/**
 * Initialize the virtual streaming system.
 *
 * This initializes all supported senders and registers the vss task to the
 * scheduler. If the autoplay command line option was given, the VSS_PLAYING
 * status flag is set to start streaming.
 *
 * \param afs_socket Used for communication with the audio file selector.
 * \param s The scheduler instance to register the vss task.
 */
void vss_init(int afs_socket, struct sched *s)
{
	static struct vss_task vss_task_struct, *vsst = &vss_task_struct;
	int i;

	vsst->header_interval.tv_sec = 5; /* should this be configurable? */
	vsst->afs_socket = afs_socket;
	init_list_head(&fec_client_list);
	FOR_EACH_SENDER(i) {
		PARA_INFO_LOG("initializing %s sender\n", senders[i]->name);
		senders[i]->init();
	}
	mmd->sender_cmd_data.cmd_num = -1;
	if (OPT_GIVEN(AUTOPLAY)) {
		struct timeval tmp;
		mmd->vss_status_flags |= VSS_PLAYING;
		mmd->new_vss_status_flags |= VSS_PLAYING;
		ms2tv(OPT_UINT32_VAL(AUTOPLAY_DELAY), &tmp);
		tv_add(clock_get_realtime(NULL), &tmp, &vsst->autoplay_barrier);
		tv_add(&vsst->autoplay_barrier, &announce_tv,
			&vsst->data_send_barrier);
	}
	vsst->task = task_register(&(struct task_info) {
		.name = "vss",
		.pre_monitor = vss_pre_monitor,
		.post_monitor = vss_post_monitor,
		.context = vsst,
	}, s);
}

/**
 * Turn off the virtual streaming system.
 *
 * This is only executed on exit. It calls the ->shutdown method of all senders.
 */
void vss_shutdown(void)
{
	int i;
	bool is_command_handler = process_is_command_handler();

	FOR_EACH_SENDER(i) {
		if (!senders[i]->shutdown)
			continue;
		if (!is_command_handler)
			PARA_NOTICE_LOG("shutting down %s sender\n",
				senders[i]->name);
		senders[i]->shutdown();
	}
}