server: Reduce scope of struct server_command.

[paraslash.git] / command.c

/*
 * Copyright (C) 1997 Andre Noll <maan@tuebingen.mpg.de>
 *
 * Licensed under the GPL v2. For licencing details see COPYING.
 */

/** \file command.c Client authentication and server commands. */

#include <netinet/in.h>
#include <sys/socket.h>
#include <regex.h>
#include <signal.h>
#include <sys/types.h>
#include <osl.h>
#include <arpa/inet.h>
#include <sys/un.h>
#include <netdb.h>

#include "para.h"
#include "error.h"
#include "crypt.h"
#include "sideband.h"
#include "command.h"
#include "server.cmdline.h"
#include "string.h"
#include "afh.h"
#include "afs.h"
#include "server.h"
#include "list.h"
#include "send.h"
#include "sched.h"
#include "vss.h"
#include "net.h"
#include "daemon.h"
#include "fd.h"
#include "ipc.h"
#include "user_list.h"
#include "server.command_list.h"
#include "afs.command_list.h"
#include "signal.h"
#include "version.h"

/* Defines one command of para_server. */
struct server_command {
        /* The name of the command. */
        const char *name;
        /* Pointer to the function that handles the command. */
        int (*handler)(struct command_context *);
        /* The privileges a user must have to execute this command. */
        unsigned int perms;
        /* One-line description of the command. */
        const char *description;
        /* Summary of the command line options. */
        const char *usage;
        /* The long help text. */
        const char *help;
};

static struct server_command afs_cmds[] = {DEFINE_AFS_CMD_ARRAY};
static struct server_command server_cmds[] = {DEFINE_SERVER_CMD_ARRAY};

/** Commands including options must be shorter than this. */
#define MAX_COMMAND_LEN 32768

extern int mmd_mutex;
extern struct misc_meta_data *mmd;
extern struct sender senders[];
int send_afs_status(struct command_context *cc, int parser_friendly);

static void dummy(__a_unused int s)
{
}

static void mmd_dup(struct misc_meta_data *new_mmd)
{
        mutex_lock(mmd_mutex);
        *new_mmd = *mmd;
        mutex_unlock(mmd_mutex);
}

/*
 * Compute human readable string containing vss status for given integer value.
 *
 * We don't want to use vss_playing() and friends here because we take a
 * snapshot of the mmd struct and use the copy for computing the state of the
 * vss. If the real data were used, we would take the mmd lock for a rather
 * long time or risk to get an inconsistent view.
 */
static char *vss_status_tohuman(unsigned int flags)
{
        if (flags & VSS_PLAYING)
                return para_strdup("playing");
        if (flags & VSS_NEXT)
                return para_strdup("stopped");
        return para_strdup("paused");
}

/*
 * return human readable permission string. Never returns NULL.
 */
static char *cmd_perms_itohuman(unsigned int perms)
{
        char *msg = para_malloc(5 * sizeof(char));

        msg[0] = perms & AFS_READ? 'a' : '-';
        msg[1] = perms & AFS_WRITE? 'A' : '-';
        msg[2] = perms & VSS_READ? 'v' : '-';
        msg[3] = perms & VSS_WRITE? 'V' : '-';
        msg[4] = '\0';
        return msg;
}

/*
 * Never returns NULL.
 */
static char *vss_get_status_flags(unsigned int flags)
{
        char *msg = para_malloc(5 * sizeof(char));

        msg[0] = (flags & VSS_PLAYING)? 'P' : '_';
        msg[1] = (flags & VSS_NOMORE)? 'O' : '_';
        msg[2] = (flags & VSS_NEXT)? 'N' : '_';
        msg[3] = (flags & VSS_REPOS)? 'R' : '_';
        msg[4] = '\0';
        return msg;
}

static unsigned get_status(struct misc_meta_data *nmmd, int parser_friendly,
                char **result)
{
        char *status, *flags; /* vss status info */
        /* nobody updates our version of "now" */
        long offset = (nmmd->offset + 500) / 1000;
        struct timeval current_time;
        struct para_buffer b = {.flags = parser_friendly? PBF_SIZE_PREFIX : 0};

        /* report real status */
        status = vss_status_tohuman(nmmd->vss_status_flags);
        flags = vss_get_status_flags(nmmd->vss_status_flags);
        clock_get_realtime(&current_time);
        /*
         * The calls to WRITE_STATUS_ITEM() below never fail because
         * b->max_size is zero (unlimited), see para_printf(). However, clang
         * is not smart enough to prove this and complains nevertheless.
         * Casting the return value to void silences clang.
         */
        (void)WRITE_STATUS_ITEM(&b, SI_STATUS, "%s\n", status);
        (void)WRITE_STATUS_ITEM(&b, SI_STATUS_FLAGS, "%s\n", flags);
        (void)WRITE_STATUS_ITEM(&b, SI_OFFSET, "%li\n", offset);
        (void)WRITE_STATUS_ITEM(&b, SI_AFS_MODE, "%s\n", mmd->afs_mode_string);
        (void)WRITE_STATUS_ITEM(&b, SI_STREAM_START, "%lu.%lu\n",
                (long unsigned)nmmd->stream_start.tv_sec,
                (long unsigned)nmmd->stream_start.tv_usec);
        (void)WRITE_STATUS_ITEM(&b, SI_CURRENT_TIME, "%lu.%lu\n",
                (long unsigned)current_time.tv_sec,
                (long unsigned)current_time.tv_usec);
        free(flags);
        free(status);
        *result = b.buf;
        return b.offset;
}

static int check_sender_args(int argc, char * const * argv, struct sender_command_data *scd)
{
        int i;
        /* this has to match sender.h */
        const char *subcmds[] = {"add", "delete", "allow", "deny", "on", "off", NULL};

        scd->sender_num = -1;
        if (argc < 2)
                return -E_COMMAND_SYNTAX;
        for (i = 0; senders[i].name; i++)
                if (!strcmp(senders[i].name, argv[1]))
                        break;
        PARA_DEBUG_LOG("%d:%s\n", argc, argv[1]);
        if (!senders[i].name)
                return -E_COMMAND_SYNTAX;
        scd->sender_num = i;
        for (i = 0; subcmds[i]; i++)
                if (!strcmp(subcmds[i], argv[2]))
                        break;
        if (!subcmds[i])
                return -E_COMMAND_SYNTAX;
        scd->cmd_num = i;
        if (!senders[scd->sender_num].client_cmds[scd->cmd_num])
                return -E_SENDER_CMD;
        switch (scd->cmd_num) {
        case SENDER_ON:
        case SENDER_OFF:
                if (argc != 3)
                        return -E_COMMAND_SYNTAX;
                break;
        case SENDER_DENY:
        case SENDER_ALLOW:
                if (argc != 4 || parse_cidr(argv[3], scd->host,
                                sizeof(scd->host), &scd->netmask) == NULL)
                        return -E_COMMAND_SYNTAX;
                break;
        case SENDER_ADD:
        case SENDER_DELETE:
                if (argc != 4)
                        return -E_COMMAND_SYNTAX;
                return parse_fec_url(argv[3], scd);
        default:
                return -E_COMMAND_SYNTAX;
        }
        return 1;
}

/**
 * Send a sideband packet through a blocking file descriptor.
 *
 * \param scc fd and crypto keys.
 * \param buf The buffer to send.
 * \param numbytes The size of \a buf.
 * \param band The sideband designator of this packet.
 * \param dont_free If true, never deallocate \a buf.
 *
 * The nonblock flag must be disabled for the file descriptor given by \a scc.
 *
 * Stream cipher encryption is automatically activated if necessary via the
 * sideband transformation, depending on the value of \a band.
 *
 * \return Standard.
 *
 * \sa \ref send_sb_va().
 */
int send_sb(struct stream_cipher_context *scc, void *buf, size_t numbytes,
                int band, bool dont_free)
{
        int ret;
        struct sb_context *sbc;
        struct iovec iov[2];
        sb_transformation trafo = band < SBD_PROCEED? NULL : sc_trafo;
        struct sb_buffer sbb = SBB_INIT(band, buf, numbytes);

        sbc = sb_new_send(&sbb, dont_free, trafo, scc->send);
        do {
                ret = sb_get_send_buffers(sbc, iov);
                ret = xwritev(scc->fd, iov, ret);
                if (ret < 0)
                        goto fail;
        } while (sb_sent(sbc, ret) == false);
        return 1;
fail:
        sb_free(sbc);
        return ret;
}

/**
 * Create a variable sized buffer and send it as a sideband packet.
 *
 * \param scc Passed to \ref send_sb.
 * \param band See \ref send_sb.
 * \param fmt The format string.
 *
 * \return The return value of the underlying call to \ref send_sb.
 */
__printf_3_4 int send_sb_va(struct stream_cipher_context *scc, int band,
                const char *fmt, ...)
{
        va_list ap;
        char *msg;
        int ret;

        va_start(ap, fmt);
        ret = xvasprintf(&msg, fmt, ap);
        va_end(ap);
        return send_sb(scc, msg, ret, band, false);
}

/**
 * Send an error message to a client.
 *
 * \param cc Client info.
 * \param err The (positive) error code.
 *
 * \return The return value of the underlying call to send_sb_va().
 */
int send_strerror(struct command_context *cc, int err)
{
        return send_sb_va(&cc->scc, SBD_ERROR_LOG, "%s\n", para_strerror(err));
}

/**
 * Send a sideband packet through a blocking file descriptor.
 *
 * \param scc fd and crypto keys.
 * \param expected_band The expected band designator.
 * \param max_size Passed to \ref sb_new_recv().
 * \param result Body of the sideband packet is returned here.
 *
 * If \a expected_band is not \p SBD_ANY, the band designator of the received
 * sideband packet is compared to \a expected_band and a mismatch is considered
 * an error.
 *
 * \return Standard.
 */
int recv_sb(struct stream_cipher_context *scc,
                enum sb_designator expected_band,
                size_t max_size, struct iovec *result)
{
        int ret;
        struct sb_context *sbc;
        struct iovec iov;
        struct sb_buffer sbb;
        sb_transformation trafo;

        trafo = expected_band != SBD_ANY && expected_band < SBD_PROCEED?
                NULL : sc_trafo;
        sbc = sb_new_recv(max_size, trafo, scc->recv);
        for (;;) {
                sb_get_recv_buffer(sbc, &iov);
                ret = recv_bin_buffer(scc->fd, iov.iov_base, iov.iov_len);
                if (ret == 0)
                        ret = -E_EOF;
                if (ret < 0)
                        goto fail;
                ret = sb_received(sbc, ret, &sbb);
                if (ret < 0)
                        goto fail;
                if (ret > 0)
                        break;
        }
        ret = -E_BAD_BAND;
        if (expected_band != SBD_ANY && sbb.band != expected_band)
                goto fail;
        *result = sbb.iov;
        return 1;
fail:
        sb_free(sbc);
        return ret;
}

static int com_sender(struct command_context *cc)
{
        int i, ret = 0;
        char *msg = NULL;
        struct sender_command_data scd;

        if (cc->argc < 2) {
                for (i = 0; senders[i].name; i++) {
                        char *tmp;
                        ret = xasprintf(&tmp, "%s%s\n", msg? msg : "",
                                senders[i].name);
                        free(msg);
                        msg = tmp;
                }
                return send_sb(&cc->scc, msg, ret, SBD_OUTPUT, false);
        }
        ret = check_sender_args(cc->argc, cc->argv, &scd);
        if (ret < 0) {
                if (scd.sender_num < 0)
                        return ret;
                if (strcmp(cc->argv[2], "status") == 0)
                        msg = senders[scd.sender_num].status();
                else
                        msg = senders[scd.sender_num].help();
                return send_sb(&cc->scc, msg, strlen(msg), SBD_OUTPUT, false);
        }

        switch (scd.cmd_num) {
        case SENDER_ADD:
        case SENDER_DELETE:
                assert(senders[scd.sender_num].resolve_target);
                ret = senders[scd.sender_num].resolve_target(cc->argv[3], &scd);
                if (ret < 0)
                        return ret;
        }

        for (i = 0; i < 10; i++) {
                mutex_lock(mmd_mutex);
                if (mmd->sender_cmd_data.cmd_num >= 0) {
                        /* another sender command is active, retry in 100ms */
                        struct timespec ts = {.tv_nsec = 100 * 1000 * 1000};
                        mutex_unlock(mmd_mutex);
                        nanosleep(&ts, NULL);
                        continue;
                }
                mmd->sender_cmd_data = scd;
                mutex_unlock(mmd_mutex);
                break;
        }
        return (i < 10)? 1 : -E_LOCK;
}

/* server info */
static int com_si(struct command_context *cc)
{
        int ret;
        char *msg, *ut;

        if (cc->argc != 1)
                return -E_COMMAND_SYNTAX;
        mutex_lock(mmd_mutex);
        ut = daemon_get_uptime_str(now);
        ret = xasprintf(&msg,
                "up: %s\nplayed: %u\n"
                "server_pid: %d\n"
                "afs_pid: %d\n"
                "connections (active/accepted/total): %u/%u/%u\n"
                "current loglevel: %s\n"
                "supported audio formats: %s\n",
                ut, mmd->num_played,
                (int)getppid(),
                (int)mmd->afs_pid,
                mmd->active_connections,
                mmd->num_commands,
                mmd->num_connects,
                conf.loglevel_arg,
                AUDIO_FORMAT_HANDLERS
        );
        mutex_unlock(mmd_mutex);
        free(ut);
        return send_sb(&cc->scc, msg, ret, SBD_OUTPUT, false);
}

/* version */
static int com_version(struct command_context *cc)
{
        char *msg;
        size_t len;

        if (cc->argc != 1)
                return -E_COMMAND_SYNTAX;
        len = xasprintf(&msg, "%s", version_text("server"));
        return send_sb(&cc->scc, msg, len, SBD_OUTPUT, false);
}

/** These status items are cleared if no audio file is currently open. */
#define EMPTY_STATUS_ITEMS \
        ITEM(PATH) \
        ITEM(DIRECTORY) \
        ITEM(BASENAME) \
        ITEM(SCORE) \
        ITEM(ATTRIBUTES_BITMAP) \
        ITEM(ATTRIBUTES_TXT) \
        ITEM(HASH) \
        ITEM(IMAGE_ID) \
        ITEM(IMAGE_NAME) \
        ITEM(LYRICS_ID) \
        ITEM(LYRICS_NAME) \
        ITEM(BITRATE) \
        ITEM(FORMAT) \
        ITEM(FREQUENCY) \
        ITEM(CHANNELS) \
        ITEM(DURATION) \
        ITEM(SECONDS_TOTAL) \
        ITEM(NUM_PLAYED) \
        ITEM(LAST_PLAYED) \
        ITEM(TECHINFO) \
        ITEM(ARTIST) \
        ITEM(TITLE) \
        ITEM(YEAR) \
        ITEM(ALBUM) \
        ITEM(COMMENT) \
        ITEM(MTIME) \
        ITEM(FILE_SIZE) \
        ITEM(CHUNK_TIME) \
        ITEM(NUM_CHUNKS) \
        ITEM(AMPLIFICATION) \

/**
 * Write a list of audio-file related status items with empty values.
 *
 * This is used by vss when currently no audio file is open.
 */
static unsigned empty_status_items(int parser_friendly, char **result)
{
        char *esi;
        unsigned len;

        if (parser_friendly)
                len = xasprintf(&esi,
                        #define ITEM(x) "0004 %02x:\n"
                        EMPTY_STATUS_ITEMS
                        #undef ITEM
                        #define ITEM(x) , SI_ ## x
                        EMPTY_STATUS_ITEMS
                        #undef ITEM
                );
        else
                len = xasprintf(&esi,
                        #define ITEM(x) "%s:\n"
                        EMPTY_STATUS_ITEMS
                        #undef ITEM
                        #define ITEM(x) ,status_item_list[SI_ ## x]
                        EMPTY_STATUS_ITEMS
                        #undef ITEM
                );
        *result = esi;
        return len;
}
#undef EMPTY_STATUS_ITEMS

/* stat */
static int com_stat(struct command_context *cc)
{
        int i, ret;
        struct misc_meta_data tmp, *nmmd = &tmp;
        char *s;
        int32_t num = 0;
        int parser_friendly = 0;

        para_sigaction(SIGUSR1, dummy);

        for (i = 1; i < cc->argc; i++) {
                const char *arg = cc->argv[i];
                if (arg[0] != '-')
                        break;
                if (!strcmp(arg, "--")) {
                        i++;
                        break;
                }
                if (!strncmp(arg, "-n=", 3)) {
                        ret = para_atoi32(arg + 3, &num);
                        if (ret < 0)
                                return ret;
                        continue;
                }
                if (!strcmp(arg, "-p")) {
                        parser_friendly = 1;
                        continue;
                }
                return -E_COMMAND_SYNTAX;
        }
        if (i != cc->argc)
                return -E_COMMAND_SYNTAX;
        for (;;) {
                mmd_dup(nmmd);
                ret = get_status(nmmd, parser_friendly, &s);
                ret = send_sb(&cc->scc, s, ret, SBD_OUTPUT, false);
                if (ret < 0)
                        goto out;
                if (nmmd->vss_status_flags & VSS_NEXT) {
                        char *esi;
                        ret = empty_status_items(parser_friendly, &esi);
                        ret = send_sb(&cc->scc, esi, ret, SBD_OUTPUT, false);
                        if (ret < 0)
                                goto out;
                } else
                        send_afs_status(cc, parser_friendly);
                ret = 1;
                if (num > 0 && !--num)
                        goto out;
                sleep(50);
                ret = -E_SERVER_CRASH;
                if (getppid() == 1)
                        goto out;
        }
out:
        return ret;
}

static int send_list_of_commands(struct command_context *cc, struct server_command *cmd,
                const char *handler)
{
        char *msg = NULL;

        for (; cmd->name; cmd++) {
                char *tmp, *perms = cmd_perms_itohuman(cmd->perms);
                tmp = make_message("%s\t%s\t%s\t%s\n", cmd->name, handler,
                        perms, cmd->description);
                free(perms);
                msg = para_strcat(msg, tmp);
                free(tmp);
        }
        assert(msg);
        return send_sb(&cc->scc, msg, strlen(msg), SBD_OUTPUT, false);
}

/* returns string that must be freed by the caller */
static struct server_command *get_cmd_ptr(const char *name, char **handler)
{
        struct server_command *cmd;

        for (cmd = server_cmds; cmd->name; cmd++)
                if (!strcmp(cmd->name, name)) {
                        if (handler)
                                *handler = para_strdup("server"); /* server commands */
                        return cmd;
                }
        /* not found, look for commands supported by afs */
        for (cmd = afs_cmds; cmd->name; cmd++)
                if (!strcmp(cmd->name, name)) {
                        if (handler)
                                *handler = para_strdup("afs");
                        return cmd;
                }
        return NULL;
}

/* help */
static int com_help(struct command_context *cc)
{
        struct server_command *cmd;
        char *perms, *handler, *buf;
        int ret;

        if (cc->argc < 2) {
                /* no argument given, print list of commands */
                if ((ret = send_list_of_commands(cc, server_cmds, "server")) < 0)
                        return ret;
                return send_list_of_commands(cc, afs_cmds, "afs");
        }
        /* argument given for help */
        cmd = get_cmd_ptr(cc->argv[1], &handler);
        if (!cmd)
                return -E_BAD_CMD;
        perms = cmd_perms_itohuman(cmd->perms);
        ret = xasprintf(&buf, "%s - %s\n\n"
                "handler: %s\n"
                "permissions: %s\n"
                "usage: %s\n\n"
                "%s\n",
                cc->argv[1],
                cmd->description,
                handler,
                perms,
                cmd->usage,
                cmd->help
        );
        free(perms);
        free(handler);
        return send_sb(&cc->scc, buf, ret, SBD_OUTPUT, false);
}

/* hup */
static int com_hup(struct command_context *cc)
{
        if (cc->argc != 1)
                return -E_COMMAND_SYNTAX;
        kill(getppid(), SIGHUP);
        return 1;
}

/* term */
static int com_term(struct command_context *cc)
{
        if (cc->argc != 1)
                return -E_COMMAND_SYNTAX;
        kill(getppid(), SIGTERM);
        return 1;
}

static int com_play(struct command_context *cc)
{
        if (cc->argc != 1)
                return -E_COMMAND_SYNTAX;
        mutex_lock(mmd_mutex);
        mmd->new_vss_status_flags |= VSS_PLAYING;
        mmd->new_vss_status_flags &= ~VSS_NOMORE;
        mutex_unlock(mmd_mutex);
        return 1;
}

/* stop */
static int com_stop(struct command_context *cc)
{
        if (cc->argc != 1)
                return -E_COMMAND_SYNTAX;
        mutex_lock(mmd_mutex);
        mmd->new_vss_status_flags &= ~VSS_PLAYING;
        mmd->new_vss_status_flags &= ~VSS_REPOS;
        mmd->new_vss_status_flags |= VSS_NEXT;
        mutex_unlock(mmd_mutex);
        return 1;
}

/* pause */
static int com_pause(struct command_context *cc)
{
        if (cc->argc != 1)
                return -E_COMMAND_SYNTAX;
        mutex_lock(mmd_mutex);
        if (!vss_paused() && !vss_stopped()) {
                mmd->events++;
                mmd->new_vss_status_flags &= ~VSS_PLAYING;
                mmd->new_vss_status_flags &= ~VSS_NEXT;
        }
        mutex_unlock(mmd_mutex);
        return 1;
}

/* next */
static int com_next(struct command_context *cc)
{
        if (cc->argc != 1)
                return -E_COMMAND_SYNTAX;
        mutex_lock(mmd_mutex);
        mmd->events++;
        mmd->new_vss_status_flags |= VSS_NEXT;
        mutex_unlock(mmd_mutex);
        return 1;
}

/* nomore */
static int com_nomore(struct command_context *cc)
{
        if (cc->argc != 1)
                return -E_COMMAND_SYNTAX;
        mutex_lock(mmd_mutex);
        if (vss_playing() || vss_paused())
                mmd->new_vss_status_flags |= VSS_NOMORE;
        mutex_unlock(mmd_mutex);
        return 1;
}

/* ff */
static int com_ff(struct command_context *cc)
{
        long promille;
        int ret, backwards = 0;
        unsigned i;
        char c;

        if (cc->argc != 2)
                return -E_COMMAND_SYNTAX;
        if (!(ret = sscanf(cc->argv[1], "%u%c", &i, &c)))
                return -E_COMMAND_SYNTAX;
        if (ret > 1 && c == '-')
                backwards = 1; /* jmp backwards */
        mutex_lock(mmd_mutex);
        ret = -E_NO_AUDIO_FILE;
        if (!mmd->afd.afhi.chunks_total || !mmd->afd.afhi.seconds_total)
                goto out;
        promille = (1000 * mmd->current_chunk) / mmd->afd.afhi.chunks_total;
        if (backwards)
                promille -= 1000 * i / mmd->afd.afhi.seconds_total;
        else
                promille += 1000 * i / mmd->afd.afhi.seconds_total;
        if (promille < 0)
                promille = 0;
        if (promille > 1000) {
                mmd->new_vss_status_flags |= VSS_NEXT;
                goto out;
        }
        mmd->repos_request = (mmd->afd.afhi.chunks_total * promille) / 1000;
        mmd->new_vss_status_flags |= VSS_REPOS;
        mmd->new_vss_status_flags &= ~VSS_NEXT;
        mmd->events++;
        ret = 1;
out:
        mutex_unlock(mmd_mutex);
        return ret;
}

/* jmp */
static int com_jmp(struct command_context *cc)
{
        long unsigned int i;
        int ret;

        if (cc->argc != 2)
                return -E_COMMAND_SYNTAX;
        if (sscanf(cc->argv[1], "%lu", &i) <= 0)
                return -E_COMMAND_SYNTAX;
        mutex_lock(mmd_mutex);
        ret = -E_NO_AUDIO_FILE;
        if (!mmd->afd.afhi.chunks_total)
                goto out;
        if (i > 100)
                i = 100;
        PARA_INFO_LOG("jumping to %lu%%\n", i);
        mmd->repos_request = (mmd->afd.afhi.chunks_total * i + 50) / 100;
        PARA_INFO_LOG("sent: %lu, offset before jmp: %lu\n",
                mmd->chunks_sent, mmd->offset);
        mmd->new_vss_status_flags |= VSS_REPOS;
        mmd->new_vss_status_flags &= ~VSS_NEXT;
        ret = 1;
        mmd->events++;
out:
        mutex_unlock(mmd_mutex);
        return ret;
}

static int com_tasks(struct command_context *cc)
{
        char *tl = server_get_tasks();
        int ret = 1;

        if (tl)
                ret = send_sb(&cc->scc, tl, strlen(tl), SBD_OUTPUT, false);
        return ret;
}

/*
 * check if perms are sufficient to exec a command having perms cmd_perms.
 * Returns 0 if perms are sufficient, -E_PERM otherwise.
 */
static int check_perms(unsigned int perms, const struct server_command *cmd_ptr)
{
        PARA_DEBUG_LOG("checking permissions\n");
        return (cmd_ptr->perms & perms) < cmd_ptr->perms ? -E_PERM : 0;
}

static void reset_signals(void)
{
        para_sigaction(SIGCHLD, SIG_IGN);
        para_sigaction(SIGINT, SIG_DFL);
        para_sigaction(SIGTERM, SIG_DFL);
        para_sigaction(SIGHUP, SIG_DFL);
}

struct connection_features {
        bool sideband_requested;
        bool aes_ctr128_requested;
};

static int parse_auth_request(char *buf, int len, struct user **u,
                struct connection_features *cf)
{
        int ret;
        char *p, *username, **features = NULL;
        size_t auth_rq_len = strlen(AUTH_REQUEST_MSG);

        *u = NULL;
        memset(cf, 0, sizeof(*cf));
        if (len < auth_rq_len + 2)
                return -E_AUTH_REQUEST;
        if (strncmp(buf, AUTH_REQUEST_MSG, auth_rq_len) != 0)
                return -E_AUTH_REQUEST;
        username = buf + auth_rq_len;
        p = strchr(username, ' ');
        if (p) {
                int i;
                if (p == username)
                        return -E_AUTH_REQUEST;
                *p = '\0';
                p++;
                create_argv(p, ",", &features);
                for (i = 0; features[i]; i++) {
                        if (strcmp(features[i], "sideband") == 0)
                                cf->sideband_requested = true;
                        else if (strcmp(features[i], "aes_ctr128") == 0)
                                cf->aes_ctr128_requested = true;
                        else {
                                ret = -E_BAD_FEATURE;
                                goto out;
                        }
                }
        }
        PARA_DEBUG_LOG("received auth request for user %s\n", username);
        *u = lookup_user(username);
        ret = 1;
out:
        free_argv(features);
        return ret;
}

#define HANDSHAKE_BUFSIZE 4096

static int parse_sb_command(struct command_context *cc, struct iovec *iov)
{
        int ret, i;
        char *p, *end;

        ret = -E_BAD_CMD;
        if (iov->iov_base == NULL || iov->iov_len == 0)
                goto out;
        p = iov->iov_base;
        p[iov->iov_len - 1] = '\0'; /* just to be sure */
        cc->cmd = get_cmd_ptr(p, NULL);
        if (!cc->cmd)
                goto out;
        ret = check_perms(cc->u->perms, cc->cmd);
        if (ret < 0)
                goto out;
        end = iov->iov_base + iov->iov_len;
        for (i = 0; p < end; i++)
                p += strlen(p) + 1;
        cc->argc = i;
        cc->argv = para_malloc((cc->argc + 1) * sizeof(char *));
        for (i = 0, p = iov->iov_base; p < end; i++) {
                cc->argv[i] = para_strdup(p);
                p += strlen(p) + 1;
        }
        cc->argv[cc->argc] = NULL;
        ret = cc->argc;
out:
        free(iov->iov_base);
        return ret;
}

/**
 * Perform user authentication and execute a command.
 *
 * \param fd The file descriptor to send output to.
 * \param peername Identifies the connecting peer.
 *
 * Whenever para_server accepts an incoming tcp connection on the port it
 * listens on, it forks and the resulting child calls this function.
 *
 * An RSA-based challenge/response is used to authenticate the peer. It that
 * authentication succeeds, a random session key is generated and sent back to
 * the peer, encrypted with its RSA public key. From this point on, all
 * transfers are crypted with this session key.
 *
 * Next it is checked if the peer supplied a valid server command or a command
 * for the audio file selector. If yes, and if the user has sufficient
 * permissions to execute that command, the function calls the corresponding
 * command handler which does argument checking and further processing.
 *
 * In order to cope with a DOS attacks, a timeout is set up which terminates
 * the function if the connection was not authenticated when the timeout
 * expires.
 *
 * \sa alarm(2), crypt.c, crypt.h
 */
__noreturn void handle_connect(int fd, const char *peername)
{
        int ret;
        unsigned char rand_buf[CHALLENGE_SIZE + 2 * SESSION_KEY_LEN];
        unsigned char challenge_hash[HASH_SIZE];
        char *command = NULL, *buf = para_malloc(HANDSHAKE_BUFSIZE) /* must be on the heap */;
        size_t numbytes;
        struct command_context cc_struct = {.peer = peername}, *cc = &cc_struct;
        struct iovec iov;
        struct connection_features cf;

        cc->scc.fd = fd;
        reset_signals();
        /* we need a blocking fd here as recv() might return EAGAIN otherwise. */
        ret = mark_fd_blocking(fd);
        if (ret < 0)
                goto net_err;
        /* send Welcome message */
        ret = write_va_buffer(fd, "This is para_server, version "
                PACKAGE_VERSION ".\n"
                "Features: sideband,aes_ctr128\n"
        );
        if (ret < 0)
                goto net_err;
        /* recv auth request line */
        ret = recv_buffer(fd, buf, HANDSHAKE_BUFSIZE);
        if (ret < 0)
                goto net_err;
        ret = parse_auth_request(buf, ret, &cc->u, &cf);
        if (ret < 0)
                goto net_err;
        if (!cf.sideband_requested) { /* sideband is mandatory */
                PARA_ERROR_LOG("client did not request sideband\n");
                ret = -E_BAD_FEATURE;
                goto net_err;
        }
        if (cc->u) {
                get_random_bytes_or_die(rand_buf, sizeof(rand_buf));
                ret = pub_encrypt(cc->u->pubkey, rand_buf, sizeof(rand_buf),
                        (unsigned char *)buf);
                if (ret < 0)
                        goto net_err;
                numbytes = ret;
        } else {
                /*
                 * We don't want to reveal our user names, so we send a
                 * challenge to the client even if the user does not exist, and
                 * fail the authentication later.
                 */
                numbytes = 256;
                get_random_bytes_or_die((unsigned char *)buf, numbytes);
        }
        PARA_DEBUG_LOG("sending %u byte challenge + session key (%zu bytes)\n",
                CHALLENGE_SIZE, numbytes);
        ret = send_sb(&cc->scc, buf, numbytes, SBD_CHALLENGE, false);
        buf = NULL;
        if (ret < 0)
                goto net_err;
        ret = recv_sb(&cc->scc, SBD_CHALLENGE_RESPONSE,
                HANDSHAKE_BUFSIZE, &iov);
        if (ret < 0)
                goto net_err;
        buf = iov.iov_base;
        numbytes = iov.iov_len;
        PARA_DEBUG_LOG("received %zu bytes challenge response\n", numbytes);
        ret = -E_BAD_USER;
        if (!cc->u)
                goto net_err;
        /*
         * The correct response is the hash of the first CHALLENGE_SIZE bytes
         * of the random data.
         */
        ret = -E_BAD_AUTH;
        if (numbytes != HASH_SIZE)
                goto net_err;
        hash_function((char *)rand_buf, CHALLENGE_SIZE, challenge_hash);
        if (memcmp(challenge_hash, buf, HASH_SIZE))
                goto net_err;
        /* auth successful */
        alarm(0);
        PARA_INFO_LOG("good auth for %s\n", cc->u->name);
        /* init stream cipher keys with the second part of the random buffer */
        cc->scc.recv = sc_new(rand_buf + CHALLENGE_SIZE, SESSION_KEY_LEN,
                cf.aes_ctr128_requested);
        cc->scc.send = sc_new(rand_buf + CHALLENGE_SIZE + SESSION_KEY_LEN,
                SESSION_KEY_LEN, cf.aes_ctr128_requested);
        ret = send_sb(&cc->scc, NULL, 0, SBD_PROCEED, false);
        if (ret < 0)
                goto net_err;
        ret = recv_sb(&cc->scc, SBD_COMMAND, MAX_COMMAND_LEN, &iov);
        if (ret < 0)
                goto net_err;
        ret = parse_sb_command(cc, &iov);
        if (ret < 0)
                goto err_out;
        cc->argc = ret;
        PARA_NOTICE_LOG("calling com_%s() for %s@%s\n", cc->cmd->name,
                cc->u->name, peername);
        ret = cc->cmd->handler(cc);
        free_argv(cc->argv);
        mutex_lock(mmd_mutex);
        mmd->num_commands++;
        mutex_unlock(mmd_mutex);
        if (ret >= 0)
                goto out;
err_out:
        if (send_strerror(cc, -ret) >= 0)
                send_sb(&cc->scc, NULL, 0, SBD_EXIT__FAILURE, true);
net_err:
        PARA_NOTICE_LOG("%s\n", para_strerror(-ret));
out:
        free(buf);
        free(command);
        mutex_lock(mmd_mutex);
        if (cc->cmd && (cc->cmd->perms & AFS_WRITE) && ret >= 0)
                mmd->events++;
        mmd->active_connections--;
        mutex_unlock(mmd_mutex);
        if (ret >= 0) {
                ret = send_sb(&cc->scc, NULL, 0, SBD_EXIT__SUCCESS, true);
                if (ret < 0)
                        PARA_NOTICE_LOG("%s\n", para_strerror(-ret));
        }
        sc_free(cc->scc.recv);
        sc_free(cc->scc.send);
        exit(ret < 0? EXIT_FAILURE : EXIT_SUCCESS);
}