server.c

Go to the documentation of this file.

// SPDX-License-Identifier: GPL-2.0-or-later
 
/***************************************************************************
 *   Copyright (C) 2005 by Dominic Rath                                    *
 *   Dominic.Rath@gmx.de                                                   *
 *                                                                         *
 *   Copyright (C) 2007-2010 Øyvind Harboe                                 *
 *   oyvind.harboe@zylin.com                                               *
 *                                                                         *
 *   Copyright (C) 2008 by Spencer Oliver                                  *
 *   spen@spen-soft.co.uk                                                  *
 ***************************************************************************/
 
#ifdef HAVE_CONFIG_H
#include "config.h"
#endif
 
#include "server.h"
#include <helper/time_support.h>
#include <target/target.h>
#include <target/target_request.h>
#include <target/openrisc/jsp_server.h>
#include "openocd.h"
#include "tcl_server.h"
#include "telnet_server.h"
#include "ipdbg.h"
 
#include <signal.h>
 
#ifdef HAVE_NETDB_H
#include <netdb.h>
#endif
 
#ifndef _WIN32
#include <netinet/tcp.h>
#endif
 
static struct service *services;
 
enum shutdown_reason {
    CONTINUE_MAIN_LOOP,         /* stay in main event loop */
    SHUTDOWN_REQUESTED,         /* set by shutdown command; exit the event loop and quit the debugger */
    SHUTDOWN_WITH_ERROR_CODE,   /* set by shutdown command; quit with non-zero return code */
    SHUTDOWN_WITH_SIGNAL_CODE   /* set by sig_handler; exec shutdown then exit with signal as return code */
};
 
static volatile sig_atomic_t shutdown_openocd = CONTINUE_MAIN_LOOP;
/* store received signal to exit application by killing ourselves */
static volatile sig_atomic_t last_signal;
 
/* set the polling period to 100ms */
static int polling_period = 100;
 
/* address by name on which to listen for incoming TCP/IP connections */
static char *bindto_name;
 
static int add_connection(struct service *service, struct command_context *cmd_ctx)
{
    socklen_t address_size;
    struct connection *c, **p;
    int retval;
    int flag = 1;
 
    c = malloc(sizeof(struct connection));
    c->fd = -1;
    c->fd_out = -1;
    memset(&c->sin, 0, sizeof(c->sin));
    c->cmd_ctx = copy_command_context(cmd_ctx);
    c->service = service;
    c->input_pending = false;
    c->priv = NULL;
    c->next = NULL;
 
    if (service->type == CONNECTION_TCP) {
        address_size = sizeof(c->sin);
 
        c->fd = accept(service->fd, (struct sockaddr *)&service->sin, &address_size);
        c->fd_out = c->fd;
 
        /* This increases performance dramatically for e.g. GDB load which
         * does not have a sliding window protocol.
         *
         * Ignore errors from this fn as it probably just means less performance
         */
        setsockopt(c->fd,   /* socket affected */
            IPPROTO_TCP,            /* set option at TCP level */
            TCP_NODELAY,            /* name of option */
            (char *)&flag,          /* the cast is historical cruft */
            sizeof(int));           /* length of option value */
 
        LOG_INFO("accepting '%s' connection on tcp/%s", service->name, service->port);
        retval = service->new_connection(c);
        if (retval != ERROR_OK) {
            close_socket(c->fd);
            LOG_ERROR("attempted '%s' connection rejected", service->name);
            command_done(c->cmd_ctx);
            free(c);
            return retval;
        }
    } else if (service->type == CONNECTION_STDINOUT) {
        c->fd = service->fd;
        c->fd_out = fileno(stdout);
 
#ifdef _WIN32
        /* we are using stdin/out so ignore ctrl-c under windoze */
        SetConsoleCtrlHandler(NULL, TRUE);
#endif
 
        /* do not check for new connections again on stdin */
        service->fd = -1;
 
        LOG_INFO("accepting '%s' connection from pipe", service->name);
        retval = service->new_connection(c);
        if (retval != ERROR_OK) {
            LOG_ERROR("attempted '%s' connection rejected", service->name);
            command_done(c->cmd_ctx);
            free(c);
            return retval;
        }
    } else if (service->type == CONNECTION_PIPE) {
        c->fd = service->fd;
        /* do not check for new connections again on stdin */
        service->fd = -1;
 
        char *out_file = alloc_printf("%so", service->port);
        c->fd_out = open(out_file, O_WRONLY);
        free(out_file);
        if (c->fd_out == -1) {
            LOG_ERROR("could not open %s", service->port);
            command_done(c->cmd_ctx);
            free(c);
            return ERROR_FAIL;
        }
 
        LOG_INFO("accepting '%s' connection from pipe %s", service->name, service->port);
        retval = service->new_connection(c);
        if (retval != ERROR_OK) {
            LOG_ERROR("attempted '%s' connection rejected", service->name);
            command_done(c->cmd_ctx);
            free(c);
            return retval;
        }
    }
 
    /* add to the end of linked list */
    for (p = &service->connections; *p; p = &(*p)->next)
        ;
    *p = c;
 
    if (service->max_connections != CONNECTION_LIMIT_UNLIMITED)
        service->max_connections--;
 
    return ERROR_OK;
}
 
static int remove_connection(struct service *service, struct connection *connection)
{
    struct connection **p = &service->connections;
    struct connection *c;
 
    /* find connection */
    while ((c = *p)) {
        if (c->fd == connection->fd) {
            service->connection_closed(c);
            if (service->type == CONNECTION_TCP)
                close_socket(c->fd);
            else if (service->type == CONNECTION_PIPE) {
                /* The service will listen to the pipe again */
                c->service->fd = c->fd;
            }
 
            command_done(c->cmd_ctx);
 
            /* delete connection */
            *p = c->next;
            free(c);
 
            if (service->max_connections != CONNECTION_LIMIT_UNLIMITED)
                service->max_connections++;
 
            break;
        }
 
        /* redirect p to next list pointer */
        p = &(*p)->next;
    }
 
    return ERROR_OK;
}
 
static void free_service(struct service *c)
{
    free(c->name);
    free(c->port);
    free(c);
}
 
int add_service(const struct service_driver *driver, const char *port,
        int max_connections, void *priv)
{
    struct service *c, **p;
    struct hostent *hp;
    int so_reuseaddr_option = 1;
 
    c = malloc(sizeof(struct service));
 
    c->name = strdup(driver->name);
    c->port = strdup(port);
    c->max_connections = 1; /* Only TCP/IP ports can support more than one connection */
    c->fd = -1;
    c->connections = NULL;
    c->new_connection_during_keep_alive = driver->new_connection_during_keep_alive_handler;
    c->new_connection = driver->new_connection_handler;
    c->input = driver->input_handler;
    c->connection_closed = driver->connection_closed_handler;
    c->keep_client_alive = driver->keep_client_alive_handler;
    c->priv = priv;
    c->next = NULL;
    long portnumber;
    if (strcmp(c->port, "pipe") == 0)
        c->type = CONNECTION_STDINOUT;
    else {
        char *end;
        portnumber = strtol(c->port, &end, 0);
        if (!*end && (parse_long(c->port, &portnumber) == ERROR_OK)) {
            c->portnumber = portnumber;
            c->type = CONNECTION_TCP;
        } else
            c->type = CONNECTION_PIPE;
    }
 
    if (c->type == CONNECTION_TCP) {
        c->max_connections = max_connections;
 
        c->fd = socket(AF_INET, SOCK_STREAM, 0);
        if (c->fd == -1) {
            LOG_ERROR("error creating socket: %s", strerror(errno));
            free_service(c);
            return ERROR_FAIL;
        }
 
        setsockopt(c->fd,
            SOL_SOCKET,
            SO_REUSEADDR,
            (void *)&so_reuseaddr_option,
            sizeof(int));
 
        socket_nonblock(c->fd);
 
        memset(&c->sin, 0, sizeof(c->sin));
        c->sin.sin_family = AF_INET;
 
        if (!bindto_name)
            c->sin.sin_addr.s_addr = htonl(INADDR_LOOPBACK);
        else {
            hp = gethostbyname(bindto_name);
            if (!hp) {
                LOG_ERROR("couldn't resolve bindto address: %s", bindto_name);
                close_socket(c->fd);
                free_service(c);
                return ERROR_FAIL;
            }
            memcpy(&c->sin.sin_addr, hp->h_addr_list[0], hp->h_length);
        }
        c->sin.sin_port = htons(c->portnumber);
 
        if (bind(c->fd, (struct sockaddr *)&c->sin, sizeof(c->sin)) == -1) {
            LOG_ERROR("couldn't bind %s to socket on port %d: %s", c->name, c->portnumber, strerror(errno));
            close_socket(c->fd);
            free_service(c);
            return ERROR_FAIL;
        }
 
#ifndef _WIN32
        int segsize = 65536;
        setsockopt(c->fd, IPPROTO_TCP, TCP_MAXSEG,  &segsize, sizeof(int));
#endif
        int window_size = 128 * 1024;
 
        /* These setsockopt()s must happen before the listen() */
 
        setsockopt(c->fd, SOL_SOCKET, SO_SNDBUF,
            (char *)&window_size, sizeof(window_size));
        setsockopt(c->fd, SOL_SOCKET, SO_RCVBUF,
            (char *)&window_size, sizeof(window_size));
 
        if (listen(c->fd, 1) == -1) {
            LOG_ERROR("couldn't listen on socket: %s", strerror(errno));
            close_socket(c->fd);
            free_service(c);
            return ERROR_FAIL;
        }
 
        struct sockaddr_in addr_in;
        addr_in.sin_port = 0;
        socklen_t addr_in_size = sizeof(addr_in);
        if (getsockname(c->fd, (struct sockaddr *)&addr_in, &addr_in_size) == 0)
            LOG_INFO("Listening on port %hu for %s connections",
                 ntohs(addr_in.sin_port), c->name);
    } else if (c->type == CONNECTION_STDINOUT) {
        c->fd = fileno(stdin);
 
#ifdef _WIN32
        /* for win32 set stdin/stdout to binary mode */
        if (_setmode(_fileno(stdout), _O_BINARY) < 0)
            LOG_WARNING("cannot change stdout mode to binary");
        if (_setmode(_fileno(stdin), _O_BINARY) < 0)
            LOG_WARNING("cannot change stdin mode to binary");
        if (_setmode(_fileno(stderr), _O_BINARY) < 0)
            LOG_WARNING("cannot change stderr mode to binary");
#else
        socket_nonblock(c->fd);
#endif
    } else if (c->type == CONNECTION_PIPE) {
#ifdef _WIN32
        /* we currently do not support named pipes under win32
         * so exit openocd for now */
        LOG_ERROR("Named pipes currently not supported under this os");
        free_service(c);
        return ERROR_FAIL;
#else
        /* Pipe we're reading from */
        c->fd = open(c->port, O_RDONLY | O_NONBLOCK);
        if (c->fd == -1) {
            LOG_ERROR("could not open %s", c->port);
            free_service(c);
            return ERROR_FAIL;
        }
#endif
    }
 
    /* add to the end of linked list */
    for (p = &services; *p; p = &(*p)->next)
        ;
    *p = c;
 
    return ERROR_OK;
}
 
static void remove_connections(struct service *service)
{
    struct connection *connection;
 
    connection = service->connections;
 
    while (connection) {
        struct connection *tmp;
 
        tmp = connection->next;
        remove_connection(service, connection);
        connection = tmp;
    }
}
 
int remove_service(const char *name, const char *port)
{
    struct service *tmp;
    struct service *prev;
 
    prev = services;
 
    for (tmp = services; tmp; prev = tmp, tmp = tmp->next) {
        if (!strcmp(tmp->name, name) && !strcmp(tmp->port, port)) {
            remove_connections(tmp);
 
            if (tmp == services)
                services = tmp->next;
            else
                prev->next = tmp->next;
 
            if (tmp->type != CONNECTION_STDINOUT)
                close_socket(tmp->fd);
 
            free(tmp->priv);
            free_service(tmp);
 
            return ERROR_OK;
        }
    }
 
    return ERROR_OK;
}
 
static int remove_services(void)
{
    struct service *c = services;
 
    /* loop service */
    while (c) {
        struct service *next = c->next;
 
        remove_connections(c);
 
        free(c->name);
 
        if (c->type == CONNECTION_PIPE) {
            if (c->fd != -1)
                close(c->fd);
        }
        free(c->port);
        free(c->priv);
        /* delete service */
        free(c);
 
        /* remember the last service for unlinking */
        c = next;
    }
 
    services = NULL;
 
    return ERROR_OK;
}
 
void server_keep_clients_alive(void)
{
    for (struct service *s = services; s; s = s->next)
        if (s->keep_client_alive)
            for (struct connection *c = s->connections; c; c = c->next)
                s->keep_client_alive(c);
}
 
int server_loop(struct command_context *command_context)
{
    struct service *service;
 
    bool poll_ok = true;
 
    /* used in select() */
    fd_set read_fds;
    int fd_max;
 
    /* used in accept() */
    int retval;
 
    int64_t next_event = timeval_ms() + polling_period;
 
#ifndef _WIN32
    if (signal(SIGPIPE, SIG_IGN) == SIG_ERR)
        LOG_ERROR("couldn't set SIGPIPE to SIG_IGN");
#endif
 
    while (shutdown_openocd == CONTINUE_MAIN_LOOP) {
        /* monitor sockets for activity */
        fd_max = 0;
        FD_ZERO(&read_fds);
 
        /* add service and connection fds to read_fds */
        for (service = services; service; service = service->next) {
            if (service->fd != -1) {
                /* listen for new connections */
                FD_SET(service->fd, &read_fds);
 
                if (service->fd > fd_max)
                    fd_max = service->fd;
            }
 
            if (service->connections) {
                struct connection *c;
 
                for (c = service->connections; c; c = c->next) {
                    /* check for activity on the connection */
                    FD_SET(c->fd, &read_fds);
                    if (c->fd > fd_max)
                        fd_max = c->fd;
                }
            }
        }
 
        struct timeval tv;
        tv.tv_sec = 0;
        if (poll_ok) {
            /* we're just polling this iteration, this is faster on embedded
             * hosts */
            tv.tv_usec = 0;
            retval = socket_select(fd_max + 1, &read_fds, NULL, NULL, &tv);
        } else {
            /* Timeout socket_select() when a target timer expires or every polling_period */
            int timeout_ms = next_event - timeval_ms();
            if (timeout_ms < 0)
                timeout_ms = 0;
            else if (timeout_ms > polling_period)
                timeout_ms = polling_period;
            tv.tv_usec = timeout_ms * 1000;
            /* Only while we're sleeping we'll let others run */
            retval = socket_select(fd_max + 1, &read_fds, NULL, NULL, &tv);
        }
 
        if (retval == -1) {
#ifdef _WIN32
 
            errno = WSAGetLastError();
 
            if (errno == WSAEINTR)
                FD_ZERO(&read_fds);
            else {
                LOG_ERROR("error during select: %s", strerror(errno));
                return ERROR_FAIL;
            }
#else
 
            if (errno == EINTR)
                FD_ZERO(&read_fds);
            else {
                LOG_ERROR("error during select: %s", strerror(errno));
                return ERROR_FAIL;
            }
#endif
        }
 
        if (retval == 0) {
            /* Execute callbacks of expired timers when
             * - there was nothing to do if poll_ok was true
             * - socket_select() timed out if poll_ok was false, now one or more
             *   timers expired or the polling period elapsed
             */
            target_call_timer_callbacks();
            next_event = target_timer_next_event();
            process_jim_events(command_context);
 
            FD_ZERO(&read_fds); /* eCos leaves read_fds unchanged in this case!  */
 
            /* We timed out/there was nothing to do, timeout rather than poll next time
             **/
            poll_ok = false;
        } else {
            /* There was something to do, next time we'll just poll */
            poll_ok = true;
        }
 
        /* This is a simple back-off algorithm where we immediately
         * re-poll if we did something this time around.
         *
         * This greatly improves performance of DCC.
         */
        poll_ok = poll_ok || target_got_message();
 
        for (service = services; service; service = service->next) {
            /* handle new connections on listeners */
            if ((service->fd != -1)
                && (FD_ISSET(service->fd, &read_fds))) {
                if (service->max_connections != 0)
                    add_connection(service, command_context);
                else {
                    if (service->type == CONNECTION_TCP) {
                        struct sockaddr_in sin;
                        socklen_t address_size = sizeof(sin);
                        int tmp_fd;
                        tmp_fd = accept(service->fd,
                                (struct sockaddr *)&service->sin,
                                &address_size);
                        close_socket(tmp_fd);
                    }
                    LOG_INFO(
                        "rejected '%s' connection, no more connections allowed",
                        service->name);
                }
            }
 
            /* handle activity on connections */
            if (service->connections) {
                struct connection *c;
 
                for (c = service->connections; c; ) {
                    if ((c->fd >= 0 && FD_ISSET(c->fd, &read_fds)) || c->input_pending) {
                        retval = service->input(c);
                        if (retval != ERROR_OK) {
                            struct connection *next = c->next;
                            if (service->type == CONNECTION_PIPE ||
                                    service->type == CONNECTION_STDINOUT) {
                                /* if connection uses a pipe then
                                 * shutdown openocd on error */
                                shutdown_openocd = SHUTDOWN_REQUESTED;
                            }
                            remove_connection(service, c);
                            LOG_INFO("dropped '%s' connection",
                                service->name);
                            c = next;
                            continue;
                        }
                    }
                    c = c->next;
                }
            }
        }
 
#ifdef _WIN32
        MSG msg;
        while (PeekMessage(&msg, NULL, 0, 0, PM_REMOVE)) {
            if (msg.message == WM_QUIT)
                shutdown_openocd = SHUTDOWN_WITH_SIGNAL_CODE;
        }
#endif
    }
 
    /* when quit for signal or CTRL-C, run (eventually user implemented) "shutdown" */
    if (shutdown_openocd == SHUTDOWN_WITH_SIGNAL_CODE)
        command_run_line(command_context, "shutdown");
 
    return shutdown_openocd == SHUTDOWN_WITH_ERROR_CODE ? ERROR_FAIL : ERROR_OK;
}
 
static void sig_handler(int sig)
{
    /* store only first signal that hits us */
    if (shutdown_openocd == CONTINUE_MAIN_LOOP) {
        shutdown_openocd = SHUTDOWN_WITH_SIGNAL_CODE;
        assert(sig >= SIG_ATOMIC_MIN && sig <= SIG_ATOMIC_MAX);
        last_signal = sig;
        LOG_DEBUG("Terminating on Signal %d", sig);
    } else
        LOG_DEBUG("Ignored extra Signal %d", sig);
}
 
 
#ifdef _WIN32
BOOL WINAPI control_handler(DWORD ctrl_type)
{
    shutdown_openocd = SHUTDOWN_WITH_SIGNAL_CODE;
    return TRUE;
}
#else
static void sigkey_handler(int sig)
{
    /* ignore keystroke generated signals if not in foreground process group */
 
    if (tcgetpgrp(STDIN_FILENO) > 0)
        sig_handler(sig);
    else
        LOG_DEBUG("Ignored Signal %d", sig);
}
#endif
 
 
int server_host_os_entry(void)
{
    /* this currently only calls WSAStartup on native win32 systems
     * before any socket operations are performed.
     * This is an issue if you call init in your config script */
 
#ifdef _WIN32
    WORD version_requested;
    WSADATA wsadata;
 
    version_requested = MAKEWORD(2, 2);
 
    if (WSAStartup(version_requested, &wsadata) != 0) {
        LOG_ERROR("Failed to Open Winsock");
        return ERROR_FAIL;
    }
#endif
    return ERROR_OK;
}
 
int server_host_os_close(void)
{
#ifdef _WIN32
    WSACleanup();
#endif
    return ERROR_OK;
}
 
int server_preinit(void)
{
#ifdef _WIN32
    /* register ctrl-c handler */
    SetConsoleCtrlHandler(control_handler, TRUE);
 
    signal(SIGBREAK, sig_handler);
    signal(SIGINT, sig_handler);
#else
    signal(SIGHUP, sig_handler);
    signal(SIGPIPE, sig_handler);
    signal(SIGQUIT, sigkey_handler);
    signal(SIGINT, sigkey_handler);
#endif
    signal(SIGTERM, sig_handler);
    signal(SIGABRT, sig_handler);
 
    return ERROR_OK;
}
 
int server_init(struct command_context *cmd_ctx)
{
    int ret = tcl_init();
 
    if (ret != ERROR_OK)
        return ret;
 
    ret = telnet_init("Open On-Chip Debugger");
 
    if (ret != ERROR_OK) {
        remove_services();
        return ret;
    }
 
    return ERROR_OK;
}
 
int server_quit(void)
{
    remove_services();
    target_quit();
 
#ifdef _WIN32
    SetConsoleCtrlHandler(control_handler, FALSE);
 
    return ERROR_OK;
#endif
 
    /* return signal number so we can kill ourselves */
    return last_signal;
}
 
void server_free(void)
{
    tcl_service_free();
    telnet_service_free();
    jsp_service_free();
    ipdbg_server_free();
 
    free(bindto_name);
}
 
void exit_on_signal(int sig)
{
#ifndef _WIN32
    /* bring back default system handler and kill yourself */
    signal(sig, SIG_DFL);
    kill(getpid(), sig);
#endif
}
 
int connection_write(struct connection *connection, const void *data, int len)
{
    if (len == 0) {
        /* successful no-op. Sockets and pipes behave differently here... */
        return 0;
    }
    if (connection->service->type == CONNECTION_TCP)
        return write_socket(connection->fd_out, data, len);
    else
        return write(connection->fd_out, data, len);
}
 
int connection_read(struct connection *connection, void *data, int len)
{
    if (connection->service->type == CONNECTION_TCP)
        return read_socket(connection->fd, data, len);
    else
        return read(connection->fd, data, len);
}
 
bool openocd_is_shutdown_pending(void)
{
    return shutdown_openocd != CONTINUE_MAIN_LOOP;
}
 
/* tell the server we want to shut down */
COMMAND_HANDLER(handle_shutdown_command)
{
    LOG_USER("shutdown command invoked");
 
    shutdown_openocd = SHUTDOWN_REQUESTED;
 
    command_run_line(CMD_CTX, "_run_pre_shutdown_commands");
 
    if (CMD_ARGC == 1) {
        if (!strcmp(CMD_ARGV[0], "error")) {
            shutdown_openocd = SHUTDOWN_WITH_ERROR_CODE;
            return ERROR_FAIL;
        }
    }
 
    return ERROR_COMMAND_CLOSE_CONNECTION;
}
 
COMMAND_HANDLER(handle_poll_period_command)
{
    if (CMD_ARGC == 0)
        LOG_WARNING("You need to set a period value");
    else
        COMMAND_PARSE_NUMBER(int, CMD_ARGV[0], polling_period);
 
    LOG_INFO("set servers polling period to %ums", polling_period);
 
    return ERROR_OK;
}
 
COMMAND_HANDLER(handle_bindto_command)
{
    switch (CMD_ARGC) {
        case 0:
            command_print(CMD, "bindto name: %s", bindto_name);
            break;
        case 1:
            free(bindto_name);
            bindto_name = strdup(CMD_ARGV[0]);
            break;
        default:
            return ERROR_COMMAND_SYNTAX_ERROR;
    }
    return ERROR_OK;
}
 
static const struct command_registration server_command_handlers[] = {
    {
        .name = "shutdown",
        .handler = &handle_shutdown_command,
        .mode = COMMAND_ANY,
        .usage = "",
        .help = "shut the server down",
    },
    {
        .name = "poll_period",
        .handler = &handle_poll_period_command,
        .mode = COMMAND_ANY,
        .usage = "",
        .help = "set the servers polling period",
    },
    {
        .name = "bindto",
        .handler = &handle_bindto_command,
        .mode = COMMAND_CONFIG,
        .usage = "[name]",
        .help = "Specify address by name on which to listen for "
            "incoming TCP/IP connections",
    },
    COMMAND_REGISTRATION_DONE
};
 
int server_register_commands(struct command_context *cmd_ctx)
{
    int retval = telnet_register_commands(cmd_ctx);
    if (retval != ERROR_OK)
        return retval;
 
    retval = tcl_register_commands(cmd_ctx);
    if (retval != ERROR_OK)
        return retval;
 
    retval = jsp_register_commands(cmd_ctx);
    if (retval != ERROR_OK)
        return retval;
 
    return register_commands(cmd_ctx, NULL, server_command_handlers);
}
 
COMMAND_HELPER(server_port_command, unsigned short *out)
{
    switch (CMD_ARGC) {
        case 0:
            command_print(CMD, "%d", *out);
            break;
        case 1:
        {
            uint16_t port;
            COMMAND_PARSE_NUMBER(u16, CMD_ARGV[0], port);
            *out = port;
            break;
        }
        default:
            return ERROR_COMMAND_SYNTAX_ERROR;
    }
    return ERROR_OK;
}
 
COMMAND_HELPER(server_pipe_command, char **out)
{
    switch (CMD_ARGC) {
        case 0:
            command_print(CMD, "%s", *out);
            break;
        case 1:
        {
            if (CMD_CTX->mode == COMMAND_EXEC) {
                LOG_WARNING("unable to change server port after init");
                return ERROR_COMMAND_ARGUMENT_INVALID;
            }
            free(*out);
            *out = strdup(CMD_ARGV[0]);
            break;
        }
        default:
            return ERROR_COMMAND_SYNTAX_ERROR;
    }
    return ERROR_OK;
}