static ngx_int_t
ngx_http_lua_socket_udp_read(ngx_http_request_t *r,
    ngx_http_lua_socket_udp_upstream_t *u)
{
    ngx_connection_t            *c;
    ngx_event_t                 *rev;
    ssize_t                      n;

    c = u->udp_connection.connection;
    rev = c->read;

    ngx_log_debug1(NGX_LOG_DEBUG_HTTP, c->log, 0,
                   "lua udp socket read data: waiting: %d", (int) u->waiting);

    n = ngx_udp_recv(u->udp_connection.connection,
                     ngx_http_lua_socket_udp_buffer, u->recv_buf_size);

    ngx_log_debug1(NGX_LOG_DEBUG_HTTP, c->log, 0,
                   "lua udp recv returned %z", n);

    if (n >= 0) {
        u->received = n;
        ngx_http_lua_socket_udp_handle_success(r, u);
        return NGX_OK;
    }

    if (n == NGX_ERROR) {
        u->socket_errno = ngx_socket_errno;
        ngx_http_lua_socket_udp_handle_error(r, u,
                                             NGX_HTTP_LUA_SOCKET_FT_ERROR);
        return NGX_ERROR;
    }

    /* n == NGX_AGAIN */

#if 1
    if (ngx_handle_read_event(rev, 0) != NGX_OK) {
        ngx_http_lua_socket_udp_handle_error(r, u,
                                             NGX_HTTP_LUA_SOCKET_FT_ERROR);
        return NGX_ERROR;
    }
#endif

    if (rev->active) {
        ngx_add_timer(rev, u->read_timeout);

    } else if (rev->timer_set) {
        ngx_del_timer(rev);
    }

    return NGX_AGAIN;
}
static void
ngx_http_lua_socket_udp_read_handler(ngx_http_request_t *r,
    ngx_http_lua_socket_udp_upstream_t *u)
{
    ngx_connection_t            *c;
    ngx_http_lua_loc_conf_t     *llcf;

    c = u->udp_connection.connection;

    ngx_log_debug0(NGX_LOG_DEBUG_HTTP, r->connection->log, 0,
                   "lua udp socket read handler");

    if (c->read->timedout) {
        c->read->timedout = 0;

        llcf = ngx_http_get_module_loc_conf(r, ngx_http_lua_module);

        if (llcf->log_socket_errors) {
            ngx_log_error(NGX_LOG_ERR, r->connection->log, 0,
                          "lua udp socket read timed out");
        }

        ngx_http_lua_socket_udp_handle_error(r, u,
                                             NGX_HTTP_LUA_SOCKET_FT_TIMEOUT);
        return;
    }

#if 1
    if (c->read->timer_set) {
        ngx_del_timer(c->read);
    }
#endif

    (void) ngx_http_lua_socket_udp_read(r, u);
}
static void
ngx_http_lua_socket_resolve_handler(ngx_resolver_ctx_t *ctx)
{
    ngx_http_request_t                  *r;
    ngx_connection_t                    *c;
    ngx_http_upstream_resolved_t        *ur;
    ngx_http_lua_ctx_t                  *lctx;
    lua_State                           *L;
    ngx_http_lua_socket_udp_upstream_t  *u;
    u_char                              *p;
    size_t                               len;
    struct sockaddr_in                  *sin;
    ngx_uint_t                           i;
    unsigned                             waiting;

    u = ctx->data;
    r = u->request;
    c = r->connection;
    ur = u->resolved;

    ngx_log_debug0(NGX_LOG_DEBUG_HTTP, c->log, 0,
                   "lua udp socket resolve handler");

    lctx = ngx_http_get_module_ctx(r, ngx_http_lua_module);
    if (lctx == NULL) {
        return;
    }

    lctx->cur_co_ctx = u->co_ctx;

    u->co_ctx->cleanup = NULL;

    L = lctx->cur_co_ctx->co;

    dd("setting socket_ready to 1");

    waiting = u->waiting;

    if (ctx->state) {
        ngx_log_debug2(NGX_LOG_DEBUG_HTTP, c->log, 0,
                       "lua udp socket resolver error: %s (waiting: %d)",
                       ngx_resolver_strerror(ctx->state), (int) u->waiting);

        lua_pushnil(L);
        lua_pushlstring(L, (char *) ctx->name.data, ctx->name.len);
        lua_pushfstring(L, " could not be resolved (%d: %s)",
                        (int) ctx->state,
                        ngx_resolver_strerror(ctx->state));
        lua_concat(L, 2);

        u->prepare_retvals = ngx_http_lua_socket_error_retval_handler;
        ngx_http_lua_socket_udp_handle_error(r, u,
                                             NGX_HTTP_LUA_SOCKET_FT_RESOLVER);

        if (waiting) {
            ngx_http_run_posted_requests(c);
        }

        return;
    }

    ur->naddrs = ctx->naddrs;
    ur->addrs = ctx->addrs;

#if (NGX_DEBUG)
    {
    in_addr_t   addr;
    ngx_uint_t  i;

    for (i = 0; i < ctx->naddrs; i++) {
        dd("addr i: %d %p", (int) i,  &ctx->addrs[i]);

        addr = ntohl(ctx->addrs[i]);

        ngx_log_debug4(NGX_LOG_DEBUG_HTTP, c->log, 0,
                       "name was resolved to %ud.%ud.%ud.%ud",
                       (addr >> 24) & 0xff, (addr >> 16) & 0xff,
                       (addr >> 8) & 0xff, addr & 0xff);
    }
    }
#endif

    if (ur->naddrs == 0) {
        ngx_resolve_name_done(ctx);
        u->ft_type |= NGX_HTTP_LUA_SOCKET_FT_RESOLVER;

        lua_pushnil(L);
        lua_pushliteral(L, "name cannot be resolved to a address");

        if (waiting) {
            ngx_http_run_posted_requests(c);
        }

        return;
    }

    if (ur->naddrs == 1) {
        i = 0;

    } else {
        i = ngx_random() % ur->naddrs;
    }

    dd("selected addr index: %d", (int) i);

    len = NGX_INET_ADDRSTRLEN + sizeof(":65536") - 1;

    p = ngx_pnalloc(r->pool, len + sizeof(struct sockaddr_in));
    if (p == NULL) {
        ngx_resolve_name_done(ctx);
        u->ft_type |= NGX_HTTP_LUA_SOCKET_FT_RESOLVER;

        lua_pushnil(L);
        lua_pushliteral(L, "out of memory");

        if (waiting) {
            ngx_http_run_posted_requests(c);
        }

        return;
    }

    sin = (struct sockaddr_in *) &p[len];
    ngx_memzero(sin, sizeof(struct sockaddr_in));

    len = ngx_inet_ntop(AF_INET, &ur->addrs[i], p, NGX_INET_ADDRSTRLEN);
    len = ngx_sprintf(&p[len], ":%d", ur->port) - p;

    sin->sin_family = AF_INET;
    sin->sin_port = htons(ur->port);
    sin->sin_addr.s_addr = ur->addrs[i];

    ur->sockaddr = (struct sockaddr *) sin;
    ur->socklen = sizeof(struct sockaddr_in);

    ur->host.data = p;
    ur->host.len = len;
    ur->naddrs = 1;

    ur->ctx = NULL;

    ngx_resolve_name_done(ctx);

    u->waiting = 0;

    if (waiting) {
        lctx->resume_handler = ngx_http_lua_socket_udp_resume;
        r->write_event_handler(r);
        ngx_http_run_posted_requests(c);

    } else {
        (void) ngx_http_lua_socket_resolve_retval_handler(r, u, L);
    }
}
static void
ngx_http_lua_socket_resolve_handler(ngx_resolver_ctx_t *ctx)
{
    ngx_http_request_t                  *r;
    ngx_connection_t                    *c;
    ngx_http_upstream_resolved_t        *ur;
    ngx_http_lua_ctx_t                  *lctx;
    lua_State                           *L;
    ngx_http_lua_socket_udp_upstream_t  *u;
    u_char                              *p;
    size_t                               len;
#if defined(nginx_version) && nginx_version >= 1005008
    socklen_t                            socklen;
    struct sockaddr                     *sockaddr;
#else
    struct sockaddr_in                  *sin;
#endif
    ngx_uint_t                           i;
    unsigned                             waiting;

    u = ctx->data;
    r = u->request;
    c = r->connection;
    ur = u->resolved;

    ngx_log_debug0(NGX_LOG_DEBUG_HTTP, c->log, 0,
                   "lua udp socket resolve handler");

    lctx = ngx_http_get_module_ctx(r, ngx_http_lua_module);
    if (lctx == NULL) {
        return;
    }

    lctx->cur_co_ctx = u->co_ctx;

    u->co_ctx->cleanup = NULL;

    L = lctx->cur_co_ctx->co;

    dd("setting socket_ready to 1");

    waiting = u->waiting;

    if (ctx->state) {
        ngx_log_debug2(NGX_LOG_DEBUG_HTTP, c->log, 0,
                       "lua udp socket resolver error: %s (waiting: %d)",
                       ngx_resolver_strerror(ctx->state), (int) u->waiting);

        lua_pushnil(L);
        lua_pushlstring(L, (char *) ctx->name.data, ctx->name.len);
        lua_pushfstring(L, " could not be resolved (%d: %s)",
                        (int) ctx->state,
                        ngx_resolver_strerror(ctx->state));
        lua_concat(L, 2);

#if 1
        ngx_resolve_name_done(ctx);
        ur->ctx = NULL;
#endif

        u->prepare_retvals = ngx_http_lua_socket_error_retval_handler;
        ngx_http_lua_socket_udp_handle_error(r, u,
                                             NGX_HTTP_LUA_SOCKET_FT_RESOLVER);

        if (waiting) {
            ngx_http_run_posted_requests(c);
        }

        return;
    }

    ur->naddrs = ctx->naddrs;
    ur->addrs = ctx->addrs;

#if (NGX_DEBUG)
    {
#   if defined(nginx_version) && nginx_version >= 1005008
    u_char      text[NGX_SOCKADDR_STRLEN];
    ngx_str_t   addr;
#   else
    in_addr_t   addr;
#   endif
    ngx_uint_t  i;

#   if defined(nginx_version) && nginx_version >= 1005008
    addr.data = text;

    for (i = 0; i < ctx->naddrs; i++) {
        addr.len = ngx_sock_ntop(ur->addrs[i].sockaddr, ur->addrs[i].socklen,
                                 text, NGX_SOCKADDR_STRLEN, 0);

        ngx_log_debug1(NGX_LOG_DEBUG_HTTP, r->connection->log, 0,
                       "name was resolved to %V", &addr);
    }
#   else
    for (i = 0; i < ctx->naddrs; i++) {
        dd("addr i: %d %p", (int) i,  &ctx->addrs[i]);

        addr = ntohl(ctx->addrs[i]);

        ngx_log_debug4(NGX_LOG_DEBUG_HTTP, c->log, 0,
                       "name was resolved to %ud.%ud.%ud.%ud",
                       (addr >> 24) & 0xff, (addr >> 16) & 0xff,
                       (addr >> 8) & 0xff, addr & 0xff);
    }
#   endif
    }
#endif

    ngx_http_lua_assert(ur->naddrs > 0);

    if (ur->naddrs == 1) {
        i = 0;

    } else {
        i = ngx_random() % ur->naddrs;
    }

    dd("selected addr index: %d", (int) i);

#if defined(nginx_version) && nginx_version >= 1005008
    socklen = ur->addrs[i].socklen;

    sockaddr = ngx_palloc(r->pool, socklen);
    if (sockaddr == NULL) {
        goto nomem;
    }

    ngx_memcpy(sockaddr, ur->addrs[i].sockaddr, socklen);

    switch (sockaddr->sa_family) {
#if (NGX_HAVE_INET6)
    case AF_INET6:
        ((struct sockaddr_in6 *) sockaddr)->sin6_port = htons(ur->port);
        break;
#endif
    default: /* AF_INET */
        ((struct sockaddr_in *) sockaddr)->sin_port = htons(ur->port);
    }

    p = ngx_pnalloc(r->pool, NGX_SOCKADDR_STRLEN);
    if (p == NULL) {
        goto nomem;
    }

    len = ngx_sock_ntop(sockaddr, socklen, p, NGX_SOCKADDR_STRLEN, 1);
    ur->sockaddr = sockaddr;
    ur->socklen = socklen;

#else
    /* for nginx older than 1.5.8 */

    len = NGX_INET_ADDRSTRLEN + sizeof(":65536") - 1;

    p = ngx_pnalloc(r->pool, len + sizeof(struct sockaddr_in));
    if (p == NULL) {
        goto nomem;
    }

    sin = (struct sockaddr_in *) &p[len];
    ngx_memzero(sin, sizeof(struct sockaddr_in));

    len = ngx_inet_ntop(AF_INET, &ur->addrs[i], p, NGX_INET_ADDRSTRLEN);
    len = ngx_sprintf(&p[len], ":%d", ur->port) - p;

    sin->sin_family = AF_INET;
    sin->sin_port = htons(ur->port);
    sin->sin_addr.s_addr = ur->addrs[i];

    ur->sockaddr = (struct sockaddr *) sin;
    ur->socklen = sizeof(struct sockaddr_in);
#endif

    ur->host.data = p;
    ur->host.len = len;
    ur->naddrs = 1;

    ngx_resolve_name_done(ctx);
    ur->ctx = NULL;

    u->waiting = 0;

    if (waiting) {
        lctx->resume_handler = ngx_http_lua_socket_udp_resume;
        r->write_event_handler(r);
        ngx_http_run_posted_requests(c);

    } else {
        (void) ngx_http_lua_socket_resolve_retval_handler(r, u, L);
    }

    return;

nomem:

    if (ur->ctx) {
        ngx_resolve_name_done(ctx);
        ur->ctx = NULL;
    }

    u->prepare_retvals = ngx_http_lua_socket_error_retval_handler;
    ngx_http_lua_socket_udp_handle_error(r, u,
                                         NGX_HTTP_LUA_SOCKET_FT_NOMEM);

    if (waiting) {
        ngx_http_run_posted_requests(c);

    } else {
        lua_pushnil(L);
        lua_pushliteral(L, "no memory");
    }
}