niceSOFT/libssh | Gitverse

src/server.c
1 656 строк48 KB
Pavol Žáčik
Add a new API function ssh_session_kex_is_gss
28 июл 2026, 14:40
28 июл 2026, 14:40e9f81a5
/*
 * server.c - functions for creating a SSH server
 *
 * This file is part of the SSH Library
 *
 * Copyright (c) 2004-2013 by Aris Adamantiadis
 *
 * The SSH Library is free software; you can redistribute it and/or modify
 * it under the terms of the GNU Lesser General Public License as published by
 * the Free Software Foundation; either version 2.1 of the License, or (at your
 * option) any later version.
 *
 * The SSH Library is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
 * or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public
 * License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public License
 * along with the SSH Library; see the file COPYING.  If not, write to
 * the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
 * MA 02111-1307, USA.
 */

#include "config.h"

#include <errno.h>
#include <fcntl.h>
#include <stdio.h>
#include <string.h>
#include <stdlib.h>

#ifdef _WIN32
# include <winsock2.h>
# include <ws2tcpip.h>

  /*
   * <wspiapi.h> is necessary for getaddrinfo before Windows XP, but it isn't
   * available on some platforms like MinGW.
   */
# ifdef HAVE_WSPIAPI_H
#  include <wspiapi.h>
# endif
#else
# include <netinet/in.h>
#endif

#include "libssh/buffer.h"
#include "libssh/curve25519.h"
#include "libssh/dh.h"
#include "libssh/gssapi.h"
#include "libssh/kex.h"
#include "libssh/libssh.h"
#include "libssh/messages.h"
#include "libssh/misc.h"
#include "libssh/options.h"
#include "libssh/packet.h"
#include "libssh/pki.h"
#include "libssh/priv.h"
#include "libssh/server.h"
#include "libssh/session.h"
#include "libssh/socket.h"
#include "libssh/ssh2.h"
#include "libssh/token.h"

#define set_status(session, status) do {\
        if (session->common.callbacks && session->common.callbacks->connect_status_function) \
            session->common.callbacks->connect_status_function(session->common.callbacks->userdata, status); \
    } while (0)

/**
 * @addtogroup libssh_server
 *
 * @{
 */

/**
 * @internal
 * @brief Sets the server's key exchange, encryption, MAC, and compression
 * algorithms.
 *
 * Prepares the server key exchange (KEX) proposals by prioritizing the
 * available host keys (Ed25519, ECDSA, RSA)  based on their strength and fills
 * in the KEX method lists based on session options or defaults. This is
 * essential for negotiating secure communication parameters in the SSH
 * handshake.
 *
 * @param[in] session The SSH session to set up.
 *
 * @return `SSH_OK` on success, `SSH_ERROR` on failure (e.g., no host keys
 * available, random number generation error, or memory allocation failure).
 */
int server_set_kex(ssh_session session)
{
    struct ssh_kex_struct *server = &session->next_crypto->server_kex;
    int i, j, rc;
    const char *wanted = NULL, *allowed = NULL;
    char *kept = NULL;
    char hostkeys[128] = {0};
    enum ssh_keytypes_e keytype;
    size_t len;
    int ok;
#ifdef WITH_GSSAPI
    char *gssapi_algs = NULL;
#endif /* WITH_GSSAPI */

    /* Skip if already set, for example for the rekey or when we do the guessing
     * it could have been already used to make some protocol decisions. */
    if (server->methods[0] != NULL) {
        return SSH_OK;
    }

    ok = ssh_get_random(server->cookie, 16, 0);
    if (!ok) {
        ssh_set_error(session, SSH_FATAL, "PRNG error");
        return -1;
    }

    if (session->srv.ed25519_key != NULL) {
        snprintf(hostkeys,
                 sizeof(hostkeys),
                 "%s",
                 ssh_key_type_to_char(ssh_key_type(session->srv.ed25519_key)));
    }
#ifdef HAVE_ECC
    if (session->srv.ecdsa_key != NULL) {
        len = strlen(hostkeys);
        snprintf(hostkeys + len, sizeof(hostkeys) - len,
                 ",%s", session->srv.ecdsa_key->type_c);
    }
#endif
    if (session->srv.rsa_key != NULL) {
        /* We support also the SHA2 variants */
        len = strlen(hostkeys);
        snprintf(hostkeys + len, sizeof(hostkeys) - len,
                 ",rsa-sha2-512,rsa-sha2-256");

        len = strlen(hostkeys);
        keytype = ssh_key_type(session->srv.rsa_key);

        snprintf(hostkeys + len, sizeof(hostkeys) - len,
                 ",%s", ssh_key_type_to_char(keytype));
    }

    if (session->opts.wanted_methods[SSH_HOSTKEYS]) {
        allowed = session->opts.wanted_methods[SSH_HOSTKEYS];
    } else {
        if (ssh_fips_mode()) {
            allowed = ssh_kex_get_fips_methods(SSH_HOSTKEYS);
        } else {
            allowed = ssh_kex_get_default_methods(SSH_HOSTKEYS);
        }
    }

    if (strlen(hostkeys) != 0) {
        /* It is expected for the list of allowed hostkeys to be ordered by
         * preference */
        kept =
            ssh_find_all_matching(hostkeys[0] == ',' ? hostkeys + 1 : hostkeys,
                                  allowed);
        if (kept == NULL) {
            /* Nothing was allowed */
            return -1;
        }

        rc = ssh_options_set_algo(session,
                                  SSH_HOSTKEYS,
                                  kept,
                                  &session->opts.wanted_methods[SSH_HOSTKEYS]);
        SAFE_FREE(kept);
        if (rc < 0) {
            return -1;
        }
    }
#ifdef WITH_GSSAPI
    if (session->opts.gssapi_key_exchange) {
        ok = ssh_gssapi_init(session);
        if (ok != SSH_OK) {
            ssh_set_error_oom(session);
            return SSH_ERROR;
        }

        gssapi_algs = ssh_gssapi_kex_mechs(session);
        if (gssapi_algs == NULL) {
            return SSH_ERROR;
        }
        ssh_gssapi_free(session);

        /* Prefix the default algorithms with gsskex algs */
        session->opts.wanted_methods[SSH_KEX] =
            ssh_prefix_without_duplicates(ssh_kex_get_default_methods(SSH_KEX),
                                          gssapi_algs);

        if (strlen(hostkeys) == 0) {
            session->opts.wanted_methods[SSH_HOSTKEYS] = strdup("null");
        }

        SAFE_FREE(gssapi_algs);
    }
#endif /* WITH_GSSAPI */

    for (i = 0; i < SSH_KEX_METHODS; i++) {
        wanted = session->opts.wanted_methods[i];
        if (wanted == NULL) {
            if (ssh_fips_mode()) {
                wanted = ssh_kex_get_fips_methods(i);
            } else {
                wanted = ssh_kex_get_default_methods(i);
            }
        }
        if (wanted == NULL) {
            for (j = 0; j < i; j++) {
                SAFE_FREE(server->methods[j]);
            }
            return -1;
        }

        server->methods[i] = strdup(wanted);
        if (server->methods[i] == NULL) {
            for (j = 0; j < i; j++) {
                SAFE_FREE(server->methods[j]);
            }
            return -1;
        }
    }

    /* Do not append the extensions during rekey */
    if (session->flags & SSH_SESSION_FLAG_AUTHENTICATED) {
        return SSH_OK;
    }

    rc = ssh_kex_append_extensions(session, server);
    return rc;
}

int ssh_server_init_kex(ssh_session session) {
    int i;

    if (session->session_state > SSH_SESSION_STATE_BANNER_RECEIVED) {
        return SSH_ERROR;
    }

    /* free any currently-set methods: server_set_kex will allocate new ones */
    for (i = 0; i < SSH_KEX_METHODS; i++) {
        SAFE_FREE(session->next_crypto->server_kex.methods[i]);
    }

    return server_set_kex(session);
}

/**
 * @internal
 *
 * @brief Sends SSH extension information from the server to client.
 *
 * A server may send this message (`SSH_MSG_EXT_INFO`) after its first
 * `SSH_MSG_NEWKEYS` message or just before sending `SSH_MSG_USERAUTH_SUCCESS`
 * to provide additional extensions support that are not meant for an
 * unauthenticated client.
 *
 * If any error occurs during the packing or sending of the packet, the function
 * aborts to avoid partial or corrupted sends.
 *
 * @param[in] session The SSH session.
 *
 * @return `SSH_OK` on success, `SSH_ERROR` on failure.
 */
static int ssh_server_send_extensions(ssh_session session)
{
    int rc;
    const char *hostkey_algorithms = NULL;

    SSH_LOG(SSH_LOG_PACKET, "Sending SSH_MSG_EXT_INFO");

    if (session->opts.pubkey_accepted_types) {
        hostkey_algorithms = session->opts.pubkey_accepted_types;
    } else {
        if (ssh_fips_mode()) {
            hostkey_algorithms = ssh_kex_get_fips_methods(SSH_HOSTKEYS);
        } else {
            /* There are no restrictions to the accepted public keys */
            hostkey_algorithms = ssh_kex_get_default_methods(SSH_HOSTKEYS);
        }
    }

    rc = ssh_buffer_pack(session->out_buffer,
                         "bdssss",
                         SSH2_MSG_EXT_INFO,
                         2, /* nr. of extensions */
                         "server-sig-algs",
                         hostkey_algorithms,
                         "publickey-hostbound@openssh.com",
                         "0");
    if (rc != SSH_OK) {
        goto error;
    }

    if (ssh_packet_send(session) == SSH_ERROR) {
        goto error;
    }

    return 0;
error:
    ssh_buffer_reinit(session->out_buffer);

    return -1;
}

SSH_PACKET_CALLBACK(ssh_packet_kexdh_init){
  (void)packet;
  (void)type;
  (void)user;

  SSH_LOG(SSH_LOG_PACKET,"Received SSH_MSG_KEXDH_INIT");
  if(session->dh_handshake_state != DH_STATE_INIT){
    SSH_LOG(SSH_LOG_RARE,"Invalid state for SSH_MSG_KEXDH_INIT");
    session->session_state = SSH_SESSION_STATE_ERROR;
    return SSH_PACKET_USED;
  }

  /* If first_kex_packet_follows guess was wrong, ignore this message. */
  if (session->first_kex_follows_guess_wrong != 0) {
    SSH_LOG(SSH_LOG_RARE, "first_kex_packet_follows guess was wrong, "
                          "ignoring first SSH_MSG_KEXDH_INIT message");
    session->first_kex_follows_guess_wrong = 0;

    return SSH_PACKET_USED;
  }
  SSH_LOG(SSH_LOG_DEBUG, "Calling next KEXDH handler");
  return SSH_PACKET_NOT_USED;
}

/**
 * @brief Prepares server host key parameters for the key exchange process.
 *
 * Selects the appropriate private host key (RSA, ECDSA, or Ed25519) based on
 * the session's configured host key type, sets the corresponding @p digest
 * algorithm, and imports the public key blob into the Diffie-Hellman key
 * exchange state.
 *
 * @param[in]  session  The SSH session to which we are preparing host key
 * parameters.
 * @param[out] privkey  Pointer to receive the selected private host key.
 * @param[out] digest   Pointer to receive the host key digest algorithm.
 *
 * @return `SSH_OK` on success; `SSH_ERROR` on failure (invalid key type, export
 * failure, or DH import error).
 */
int
ssh_get_key_params(ssh_session session,
                   ssh_key *privkey,
                   enum ssh_digest_e *digest)
{
    ssh_key pubkey = NULL;
    ssh_string pubkey_blob = NULL;
    int rc;

    switch(session->srv.hostkey) {
      case SSH_KEYTYPE_RSA:
        *privkey = session->srv.rsa_key;
        break;
      case SSH_KEYTYPE_ECDSA_P256:
      case SSH_KEYTYPE_ECDSA_P384:
      case SSH_KEYTYPE_ECDSA_P521:
        *privkey = session->srv.ecdsa_key;
        break;
      case SSH_KEYTYPE_ED25519:
        *privkey = session->srv.ed25519_key;
        break;
      case SSH_KEYTYPE_RSA1:
      case SSH_KEYTYPE_UNKNOWN:
      default:
        *privkey = NULL;
    }

    *digest = session->srv.hostkey_digest;
    rc = ssh_pki_export_privkey_to_pubkey(*privkey, &pubkey);
    if (rc < 0) {
      ssh_set_error(session, SSH_FATAL,
          "Could not get the public key from the private key");

      return -1;
    }

    rc = ssh_pki_export_pubkey_blob(pubkey, &pubkey_blob);
    ssh_key_free(pubkey);
    if (rc < 0) {
      ssh_set_error_oom(session);
      return -1;
    }

    rc = ssh_dh_import_next_pubkey_blob(session, pubkey_blob);
    SSH_STRING_FREE(pubkey_blob);
    if (rc != 0) {
        ssh_set_error(session,
                      SSH_FATAL,
                      "Could not import server public key");
        return -1;
    }

    return SSH_OK;
}

/**
 * @internal
 *
 * @brief A function to be called each time a step has been done in the
 * connection.
 */
static void ssh_server_connection_callback(ssh_session session)
{
    int rc;

    switch (session->session_state) {
    case SSH_SESSION_STATE_NONE:
    case SSH_SESSION_STATE_CONNECTING:
    case SSH_SESSION_STATE_SOCKET_CONNECTED:
        break;
    case SSH_SESSION_STATE_BANNER_RECEIVED:
        if (session->clientbanner == NULL) {
            goto error;
        }
        set_status(session, 0.4f);
        SSH_LOG(SSH_LOG_DEBUG,
                "SSH client banner: %s", session->clientbanner);

        /* Here we analyze the different protocols the server allows. */
        rc = ssh_analyze_banner(session, 1);
        if (rc < 0) {
            ssh_set_error(session, SSH_FATAL,
                    "No version of SSH protocol usable (banner: %s)",
                    session->clientbanner);
            goto error;
        }

        /* from now, the packet layer is handling incoming packets */
        ssh_packet_register_socket_callback(session, session->socket);

        ssh_packet_set_default_callbacks(session);
        set_status(session, 0.5f);
        session->session_state = SSH_SESSION_STATE_INITIAL_KEX;
        rc = ssh_send_kex(session);
        if (rc < 0) {
            goto error;
        }
        break;
    case SSH_SESSION_STATE_INITIAL_KEX:
        /* TODO: This state should disappear in favor of get_key handle */
        break;
    case SSH_SESSION_STATE_KEXINIT_RECEIVED:
        set_status(session, 0.6f);
        if ((session->flags & SSH_SESSION_FLAG_KEXINIT_SENT) == 0) {
            rc = server_set_kex(session);
            if (rc == SSH_ERROR) {
                goto error;
            }
            /* We are in a rekeying, so we need to send the server kex */
            rc = ssh_send_kex(session);
            if (rc < 0) {
                goto error;
            }
        }
        ssh_list_kex(&session->next_crypto->client_kex); // log client kex
        rc = ssh_kex_select_methods(session);
        if (rc < 0) {
            goto error;
        }
        rc = crypt_set_algorithms_server(session);
        if (rc == SSH_ERROR) {
            goto error;
        }
        set_status(session, 0.8f);
        session->session_state = SSH_SESSION_STATE_DH;
        break;
    case SSH_SESSION_STATE_DH:
        if (session->dh_handshake_state == DH_STATE_FINISHED) {

            rc = ssh_packet_set_newkeys(session, SSH_DIRECTION_IN);
            if (rc != SSH_OK) {
                goto error;
            }

            /*
             * If the client supports extension negotiation, we will send
             * our supported extensions now. This is the first message after
             * sending NEWKEYS message and after turning on crypto.
             */
            if (session->extensions & SSH_EXT_NEGOTIATION &&
                session->session_state != SSH_SESSION_STATE_AUTHENTICATED) {
                /*
                 * Only send an SSH_MSG_EXT_INFO message the first time the
                 * client undergoes NEWKEYS.  It is unexpected for this message
                 * to be sent upon rekey, and may cause clients to log error
                 * messages.
                 *
                 * The session_state can not be used for this purpose because it
                 * is re-set to SSH_SESSION_STATE_KEXINIT_RECEIVED during rekey.
                 * So, use the connected flag which transitions from non-zero
                 * below.
                 *
                 * See also:
                 * - https://bugzilla.mindrot.org/show_bug.cgi?id=2929
                 */
                if (session->connected == 0) {
                    ssh_server_send_extensions(session);
                }
            }

            set_status(session, 1.0f);
            session->connected = 1;
            session->session_state = SSH_SESSION_STATE_AUTHENTICATING;
            if (session->flags & SSH_SESSION_FLAG_AUTHENTICATED)
                session->session_state = SSH_SESSION_STATE_AUTHENTICATED;

        }
        break;
    case SSH_SESSION_STATE_AUTHENTICATING:
        break;
    case SSH_SESSION_STATE_ERROR:
        goto error;
    default:
        ssh_set_error(session, SSH_FATAL, "Invalid state %d",
                      session->session_state);
    }

    return;
error:
    ssh_socket_close(session->socket);
    session->alive = 0;
    session->session_state = SSH_SESSION_STATE_ERROR;
}

/**
 * @internal
 *
 * @brief Gets the banner from socket and saves it in session.
 * Updates the session state
 *
 * @param  data pointer to the beginning of header
 * @param  len size of the banner
 * @param  user is a pointer to session
 * @returns Number of bytes processed, or zero if the banner is not complete.
 */
static size_t callback_receive_banner(const void *data, size_t len, void *user)
{
    char *buffer = (char *)data;
    ssh_session session = (ssh_session)user;
    char *str = NULL;
    size_t i;
    size_t processed = 0;

    for (i = 0; i < len; i++) {
#ifdef WITH_PCAP
        if (session->pcap_ctx && buffer[i] == '\n') {
            ssh_pcap_context_write(session->pcap_ctx,
                                   SSH_PCAP_DIR_IN,
                                   buffer,
                                   (uint32_t)(i + 1),
                                   (uint32_t)(i + 1));
        }
#endif
        if (buffer[i] == '\r') {
            buffer[i] = '\0';
        }

        if (buffer[i] == '\n') {
            buffer[i] = '\0';

            str = strdup(buffer);
            if (str == NULL) {
                session->session_state = SSH_SESSION_STATE_ERROR;
                ssh_set_error_oom(session);
                return 0;
            }
            /* number of bytes read */
            processed = i + 1;
            session->clientbanner = str;
            session->session_state = SSH_SESSION_STATE_BANNER_RECEIVED;
            SSH_LOG(SSH_LOG_PACKET, "Received banner: %s", str);
            session->ssh_connection_callback(session);

            return processed;
        }

        if (i > 127) {
            /* Too big banner */
            session->session_state = SSH_SESSION_STATE_ERROR;
            ssh_set_error(session, SSH_FATAL,
                          "Receiving banner: too large banner");

            return 0;
        }
    }

    return processed;
}

/* returns 0 until the key exchange is not finished */
static int ssh_server_kex_termination(void *s){
  ssh_session session = s;
  if (session->session_state != SSH_SESSION_STATE_ERROR &&
      session->session_state != SSH_SESSION_STATE_AUTHENTICATING &&
      session->session_state != SSH_SESSION_STATE_AUTHENTICATED &&
      session->session_state != SSH_SESSION_STATE_DISCONNECTED)
    return 0;
  else
    return 1;
}

/* FIXME: auth_methods should be unsigned */
void ssh_set_auth_methods(ssh_session session, int auth_methods)
{
    /* accept only methods in range */
    session->auth.supported_methods = (uint32_t)auth_methods & 0x3fU;
}

int ssh_send_issue_banner(ssh_session session, const ssh_string banner)
{
    int rc = SSH_ERROR;

    if (session == NULL) {
        return SSH_ERROR;
    }

    SSH_LOG(SSH_LOG_PACKET,
            "Sending a server issue banner");

    rc = ssh_buffer_pack(session->out_buffer,
                         "bSs",
                         SSH2_MSG_USERAUTH_BANNER,
                         banner,
                         "");
    if (rc != SSH_OK) {
        ssh_set_error_oom(session);
        return SSH_ERROR;
    }

    rc = ssh_packet_send(session);
    return rc;
}

/* Do the banner and key exchange */
int ssh_handle_key_exchange(ssh_session session)
{
    int rc;

    if (session->session_state != SSH_SESSION_STATE_NONE) {
        goto pending;
    }

    rc = ssh_send_banner(session, 1);
    if (rc < 0) {
        return SSH_ERROR;
    }

    session->alive = 1;

    session->ssh_connection_callback = ssh_server_connection_callback;
    session->session_state = SSH_SESSION_STATE_SOCKET_CONNECTED;
    ssh_socket_set_callbacks(session->socket,&session->socket_callbacks);
    session->socket_callbacks.data = callback_receive_banner;
    session->socket_callbacks.exception = ssh_socket_exception_callback;
    session->socket_callbacks.userdata = session;

    rc = server_set_kex(session);
    if (rc < 0) {
        return SSH_ERROR;
    }
pending:
    rc = ssh_handle_packets_termination(session, SSH_TIMEOUT_USER,
                                        ssh_server_kex_termination,session);
    SSH_LOG(SSH_LOG_PACKET, "ssh_handle_key_exchange: current state : %d",
            session->session_state);
    if (rc != SSH_OK) {
        return rc;
    }
    if (session->session_state == SSH_SESSION_STATE_ERROR ||
        session->session_state == SSH_SESSION_STATE_DISCONNECTED) {
        return SSH_ERROR;
    }

    return SSH_OK;
}

/* messages */

/** @internal
 * replies to an SSH_AUTH packet with a default (denied) response.
 */
int ssh_auth_reply_default(ssh_session session,int partial) {
  char methods_c[128] = {0};
  int rc = SSH_ERROR;


  if (session->auth.supported_methods == 0) {
    session->auth.supported_methods = SSH_AUTH_METHOD_PUBLICKEY | SSH_AUTH_METHOD_PASSWORD;
  }
  if (session->auth.supported_methods & SSH_AUTH_METHOD_PUBLICKEY) {
    strncat(methods_c, "publickey,",
            sizeof(methods_c) - strlen(methods_c) - 1);
  }
  if (session->auth.supported_methods & SSH_AUTH_METHOD_GSSAPI_MIC){
	  strncat(methods_c,"gssapi-with-mic,",
			  sizeof(methods_c) - strlen(methods_c) - 1);
  }
  /* Check if GSSAPI Key exchange was performed */
  if (session->auth.supported_methods & SSH_AUTH_METHOD_GSSAPI_KEYEX) {
      if (ssh_session_kex_is_gss(session)) {
          strncat(methods_c,
                  "gssapi-keyex,",
                  sizeof(methods_c) - strlen(methods_c) - 1);
      }
  }
  if (session->auth.supported_methods & SSH_AUTH_METHOD_INTERACTIVE) {
    strncat(methods_c, "keyboard-interactive,",
            sizeof(methods_c) - strlen(methods_c) - 1);
  }
  if (session->auth.supported_methods & SSH_AUTH_METHOD_PASSWORD) {
    strncat(methods_c, "password,",
            sizeof(methods_c) - strlen(methods_c) - 1);
  }
  if (session->auth.supported_methods & SSH_AUTH_METHOD_HOSTBASED) {
    strncat(methods_c, "hostbased,",
            sizeof(methods_c) - strlen(methods_c) - 1);
  }

  if (methods_c[0] == '\0' || methods_c[strlen(methods_c)-1] != ',') {
      return SSH_ERROR;
  }

  /* Strip the comma. */
  methods_c[strlen(methods_c) - 1] = '\0'; // strip the comma. We are sure there is at

  SSH_LOG(SSH_LOG_PACKET,
      "Sending a auth failure. methods that can continue: %s", methods_c);

  rc = ssh_buffer_pack(session->out_buffer,
                       "bsb",
                       SSH2_MSG_USERAUTH_FAILURE,
                       methods_c,
                       partial ? 1 : 0);
  if (rc != SSH_OK){
      ssh_set_error_oom(session);
      return SSH_ERROR;
  }
  rc = ssh_packet_send(session);
  return rc;
}

/**
 * @internal
 *
 * @brief Sends default refusal for a channel open request.
 *
 * Default handler that rejects incoming SSH channel open requests by sending
 * a `SSH2_MSG_CHANNEL_OPEN_FAILURE` packet with "administratively prohibited"
 * reason code. Used when no custom channel open handler is registered.
 *
 * @param[in] msg The SSH message containing the channel open request details.
 *
 * @return `SSH_OK` on successful packet send; `SSH_ERROR` on buffer allocation
 *         or packet send failure.
 */
static int ssh_message_channel_request_open_reply_default(ssh_message msg) {
    int rc;

    SSH_LOG(SSH_LOG_FUNCTIONS, "Refusing a channel");

    rc = ssh_buffer_pack(msg->session->out_buffer,
                         "bdddd",
                         SSH2_MSG_CHANNEL_OPEN_FAILURE,
                         msg->channel_request_open.sender,
                         SSH2_OPEN_ADMINISTRATIVELY_PROHIBITED,
                         0,    /* reason is empty string */
                         0);   /* language string */
    if (rc != SSH_OK){
        ssh_set_error_oom(msg->session);
        return SSH_ERROR;
    }

    rc = ssh_packet_send(msg->session);
    return rc;
}

/**
 * @internal
 *
 * @brief Sends default refusal for a channel request.
 *
 * Default handler that rejects incoming SSH channel requests. If the client
 * requested a reply (`want_reply`), sends `SSH2_MSG_CHANNEL_FAILURE` to the
 * specific channel. If no reply requested, logs the refusal and returns
 * success.
 *
 * @param[in] msg The SSH message containing the channel request details.
 *
 * @return `SSH_OK` on success; `SSH_ERROR` if buffer allocation or packet send
 * fails.
 */
static int ssh_message_channel_request_reply_default(ssh_message msg) {
  uint32_t channel;
  int rc;

  if (msg->channel_request.want_reply) {
    channel = msg->channel_request.channel->remote_channel;

    SSH_LOG(SSH_LOG_PACKET,
        "Sending a default channel_request denied to channel %" PRIu32, channel);

    rc = ssh_buffer_pack(msg->session->out_buffer,
                         "bd",
                         SSH2_MSG_CHANNEL_FAILURE,
                         channel);
    if (rc != SSH_OK){
        ssh_set_error_oom(msg->session);
        return SSH_ERROR;
    }
    return ssh_packet_send(msg->session);
  }

  SSH_LOG(SSH_LOG_PACKET,
      "The client doesn't want to know the request failed!");

  return SSH_OK;
}

static int ssh_message_service_request_reply_default(ssh_message msg) {
  /* The only return code accepted by specifications are success or disconnect */
  return ssh_message_service_reply_success(msg);
}

/**
 * @brief   Sends `SSH2_MSG_SERVICE_ACCEPT` to the client
 *
 * @param msg The message to reply to
 *
 * @returns `SSH_OK` when success otherwise `SSH_ERROR`
 */
int ssh_message_service_reply_success(ssh_message msg)
{
    ssh_session session = NULL;
    int rc;

    if (msg == NULL) {
        return SSH_ERROR;
    }
    session = msg->session;

    SSH_LOG(SSH_LOG_PACKET,
            "Sending a SERVICE_ACCEPT for service %s", msg->service_request.service);

    rc = ssh_buffer_pack(session->out_buffer,
                         "bs",
                         SSH2_MSG_SERVICE_ACCEPT,
                         msg->service_request.service);
    if (rc != SSH_OK){
        ssh_set_error_oom(session);
        return SSH_ERROR;
    }
    rc = ssh_packet_send(msg->session);
    return rc;
}

/**
 * @brief Send a global request success message
 *
 * @param msg The message
 *
 * @param bound_port The remote bind port
 *
 * @returns `SSH_OK` on success, otherwise `SSH_ERROR`
 */
int ssh_message_global_request_reply_success(ssh_message msg, uint16_t bound_port) {
    int rc;

    SSH_LOG(SSH_LOG_FUNCTIONS, "Accepting a global request");

    if (msg->global_request.want_reply) {
        if (ssh_buffer_add_u8(msg->session->out_buffer
                    , SSH2_MSG_REQUEST_SUCCESS) < 0) {
            goto error;
        }

        if(msg->global_request.type == SSH_GLOBAL_REQUEST_TCPIP_FORWARD
                                && msg->global_request.bind_port == 0) {
            rc = ssh_buffer_pack(msg->session->out_buffer, "d", bound_port);
            if (rc != SSH_OK) {
                ssh_set_error_oom(msg->session);
                goto error;
            }
        }

        return ssh_packet_send(msg->session);
    }

    if(msg->global_request.type == SSH_GLOBAL_REQUEST_TCPIP_FORWARD
                                && msg->global_request.bind_port == 0) {
        SSH_LOG(SSH_LOG_PACKET,
                "The client doesn't want to know the remote port!");
    }

    return SSH_OK;
error:
    return SSH_ERROR;
}

/**
 * @internal
 *
 * @brief Sends default refusal for a global request.
 *
 * Default handler that rejects incoming SSH global requests. If the client
 * requested a reply (`want_reply`), sends `SSH2_MSG_REQUEST_FAILURE`. If no
 * reply requested, logs the refusal and returns success immediately.
 *
 * @param[in] msg The SSH message containing the global request details.
 *
 * @return `SSH_OK` on success; `SSH_ERROR` if buffer allocation or packet send
 * fails.
 */
static int ssh_message_global_request_reply_default(ssh_message msg) {
    SSH_LOG(SSH_LOG_FUNCTIONS, "Refusing a global request");

    if (msg->global_request.want_reply) {
        if (ssh_buffer_add_u8(msg->session->out_buffer
                    , SSH2_MSG_REQUEST_FAILURE) < 0) {
            goto error;
        }
        return ssh_packet_send(msg->session);
    }
    SSH_LOG(SSH_LOG_PACKET,
            "The client doesn't want to know the request failed!");

    return SSH_OK;
error:
    return SSH_ERROR;
}

int ssh_message_reply_default(ssh_message msg) {
  if (msg == NULL) {
    return -1;
  }

  switch(msg->type) {
    case SSH_REQUEST_AUTH:
      return ssh_auth_reply_default(msg->session, 0);
    case SSH_REQUEST_CHANNEL_OPEN:
      return ssh_message_channel_request_open_reply_default(msg);
    case SSH_REQUEST_CHANNEL:
      return ssh_message_channel_request_reply_default(msg);
    case SSH_REQUEST_SERVICE:
      return ssh_message_service_request_reply_default(msg);
    case SSH_REQUEST_GLOBAL:
      return ssh_message_global_request_reply_default(msg);
    default:
      SSH_LOG(SSH_LOG_PACKET,
          "Don't know what to default reply to %d type",
          msg->type);
      break;
  }

  return -1;
}

/**
 * @brief Gets the service name from the service request message
 *
 * @param msg The service request message
 *
 * @returns the service name from the message
 */
const char *ssh_message_service_service(ssh_message msg){
  if (msg == NULL) {
    return NULL;
  }
  return msg->service_request.service;
}

const char *ssh_message_auth_user(ssh_message msg) {
  if (msg == NULL) {
    return NULL;
  }

  return msg->auth_request.username;
}

const char *ssh_message_auth_password(ssh_message msg){
  if (msg == NULL) {
    return NULL;
  }

  return msg->auth_request.password;
}

ssh_key ssh_message_auth_pubkey(ssh_message msg) {
  if (msg == NULL) {
    return NULL;
  }

  return msg->auth_request.pubkey;
}

ssh_public_key ssh_message_auth_publickey(ssh_message msg){
  if (msg == NULL) {
    return NULL;
  }

  return ssh_pki_convert_key_to_publickey(msg->auth_request.pubkey);
}

enum ssh_publickey_state_e ssh_message_auth_publickey_state(ssh_message msg){
	if (msg == NULL) {
	    return -1;
	  }
	  return msg->auth_request.signature_state;
}

/**
 *  @brief Check if the message is a keyboard-interactive response
 *
 *  @param msg The message to check
 *
 *  @returns 1 if the message is a response, otherwise 0
 */
int ssh_message_auth_kbdint_is_response(ssh_message msg) {
  if (msg == NULL) {
    return -1;
  }

  return msg->auth_request.kbdint_response != 0;
}

/* FIXME: methods should be unsigned */
/**
 * @brief Sets the supported authentication methods to a message
 *
 * @param msg The message
 *
 * @param methods Methods to set to the message.
 * The supported methods are listed in ssh_set_auth_methods
 * @see ssh_set_auth_methods
 *
 * @returns 0 on success, otherwise -1
 */
int ssh_message_auth_set_methods(ssh_message msg, int methods) {
  if (msg == NULL || msg->session == NULL) {
    return -1;
  }

  if (methods < 0) {
      return -1;
  }

  msg->session->auth.supported_methods = (uint32_t)methods;

  return 0;
}

/**
 * @brief Sends an interactive authentication request message.
 *
 * Builds and sends an `SSH2_MSG_USERAUTH_INFO_REQUEST` packet containing the
 * given name and @p instruction, followed by a number of @p prompts with
 * associated @p echo flags to control whether user input is echoed.
 * It initializes the keyboard-interactive state in the session.
 *
 * @param[in]  msg          The SSH message representing the client
 *                          authentication request.
 * @param[in]  name         The name of the authentication request.
 * @param[in]  instruction  Instruction string with information for the user.
 * @param[in]  num_prompts  Number of prompts to send. The arrays prompts and
 *                          echo must both have num_prompts elements.
 * @param[in]  prompts      Array of @p num_prompts prompt strings to display.
 * @param[in]  echo         Array of num_prompts boolean values (0 or 1). A
 *                          non-zero value means the user input for that prompt
 *                          is echoed (visible); 0 means the input is hidden
 *                          (typically for passwords).
 *
 * @return `SSH_OK` on successful send; `SSH_ERROR` on failure.
 */
int ssh_message_auth_interactive_request(ssh_message msg, const char *name,
                            const char *instruction, unsigned int num_prompts,
                            const char **prompts, char *echo) {
  int rc;
  unsigned int i = 0;

  if(name == NULL || instruction == NULL) {
    return SSH_ERROR;
  }
  if(num_prompts > 0 && (prompts == NULL || echo == NULL)) {
    return SSH_ERROR;
  }

  rc = ssh_buffer_pack(msg->session->out_buffer,
                       "bsssd",
                       SSH2_MSG_USERAUTH_INFO_REQUEST,
                       name,
                       instruction,
                       "",           /* language tag */
                       num_prompts);
  if (rc != SSH_OK){
    ssh_set_error_oom(msg->session);
    return SSH_ERROR;
  }

  for(i = 0; i < num_prompts; i++) {
    rc = ssh_buffer_pack(msg->session->out_buffer,
                         "sb",
                         prompts[i],
                         echo[i] ? 1 : 0);
    if (rc != SSH_OK){
        ssh_set_error_oom(msg->session);
        return SSH_ERROR;
    }
  }

  rc = ssh_packet_send(msg->session);

  /* fill in the kbdint structure */
  if (msg->session->kbdint == NULL) {
    SSH_LOG(SSH_LOG_DEBUG, "Warning: Got a keyboard-interactive response "
                           "but it seems we didn't send the request.");

    msg->session->kbdint = ssh_kbdint_new();
    if (msg->session->kbdint == NULL) {
      ssh_set_error_oom(msg->session);

      return SSH_ERROR;
    }
  } else {
    ssh_kbdint_clean(msg->session->kbdint);
  }

  msg->session->kbdint->name = strdup(name);
  if(msg->session->kbdint->name == NULL) {
      ssh_set_error_oom(msg->session);
      ssh_kbdint_free(msg->session->kbdint);
      msg->session->kbdint = NULL;
      return SSH_PACKET_USED;
  }
  msg->session->kbdint->instruction = strdup(instruction);
  if(msg->session->kbdint->instruction == NULL) {
      ssh_set_error_oom(msg->session);
      ssh_kbdint_free(msg->session->kbdint);
      msg->session->kbdint = NULL;
      return SSH_PACKET_USED;
  }

  msg->session->kbdint->nprompts = num_prompts;
  if(num_prompts > 0) {
    msg->session->kbdint->prompts = calloc(num_prompts, sizeof(char *));
    if (msg->session->kbdint->prompts == NULL) {
      msg->session->kbdint->nprompts = 0;
      ssh_set_error_oom(msg->session);
      ssh_kbdint_free(msg->session->kbdint);
      msg->session->kbdint = NULL;
      return SSH_ERROR;
    }
    msg->session->kbdint->echo = calloc(num_prompts, sizeof(unsigned char));
    if (msg->session->kbdint->echo == NULL) {
      ssh_set_error_oom(msg->session);
      ssh_kbdint_free(msg->session->kbdint);
      msg->session->kbdint = NULL;
      return SSH_ERROR;
    }
    for (i = 0; i < num_prompts; i++) {
      msg->session->kbdint->echo[i] = echo[i];
      msg->session->kbdint->prompts[i] = strdup(prompts[i]);
      if (msg->session->kbdint->prompts[i] == NULL) {
        ssh_set_error_oom(msg->session);
        msg->session->kbdint->nprompts = i;
        ssh_kbdint_free(msg->session->kbdint);
        msg->session->kbdint = NULL;
        return SSH_PACKET_USED;
      }
    }
  } else {
    msg->session->kbdint->prompts = NULL;
    msg->session->kbdint->echo = NULL;
  }
  msg->session->auth.state = SSH_AUTH_STATE_INFO;

  return rc;
}

/**
 * @brief Sends `SSH2_MSG_USERAUTH_SUCCESS` or `SSH2_MSG_USERAUTH_FAILURE`
 * message depending on the success of the authentication method
 *
 * @param session The session to reply to
 *
 * @param partial Denotes if the authentication process was partially completed
 * (unsuccessful)
 *
 * @returns `SSH_OK` on success, otherwise `SSH_ERROR`
 */
int ssh_auth_reply_success(ssh_session session, int partial)
{
    struct ssh_crypto_struct *crypto = NULL;
    int r;

    if (session == NULL) {
        return SSH_ERROR;
    }

    if (partial) {
        return ssh_auth_reply_default(session, partial);
    }

    r = ssh_buffer_add_u8(session->out_buffer,SSH2_MSG_USERAUTH_SUCCESS);
    if (r < 0) {
        return SSH_ERROR;
    }

    r = ssh_packet_send(session);

    /*
     * Consider the session as having been authenticated only after sending
     * the `USERAUTH_SUCCESS` message.  Setting these flags after
     * ssh_packet_send ensures that a rekey is not triggered prematurely,
     * causing the message to be queued.
     */
    session->session_state = SSH_SESSION_STATE_AUTHENTICATED;
    session->flags |= SSH_SESSION_FLAG_AUTHENTICATED;

    crypto = ssh_packet_get_current_crypto(session, SSH_DIRECTION_OUT);
    if (crypto != NULL && crypto->delayed_compress_out) {
        SSH_LOG(SSH_LOG_DEBUG, "Enabling delayed compression OUT");
        crypto->do_compress_out = 1;
    }

    crypto = ssh_packet_get_current_crypto(session, SSH_DIRECTION_IN);
    if (crypto != NULL && crypto->delayed_compress_in) {
        SSH_LOG(SSH_LOG_DEBUG, "Enabling delayed compression IN");
        crypto->do_compress_in = 1;
    }
    return r;
}

/**
 * @brief Replies to an authentication request with success.
 *
 * Sends an authentication success message (`SSH2_MSG_USERAUTH_SUCCESS`) to the
 * client, or a partial success if further authentication steps are required.
 *
 * @param[in] msg     The SSH authentication message being handled.
 * @param[in] partial Set to nonzero if partial success (more auth needed), zero
 * for full success.
 *
 * @return `SSH_OK` on success, `SSH_ERROR` if msg is NULL or on send failure.
 */
int ssh_message_auth_reply_success(ssh_message msg, int partial) {
	if(msg == NULL)
		return SSH_ERROR;
	return ssh_auth_reply_success(msg->session, partial);
}

/**
 * @brief Answer `SSH2_MSG_USERAUTH_PK_OK` to a pubkey authentication request
 *
 * @param msg The message
 *
 * @param algo The algorithm of the accepted public key
 *
 * @param pubkey The accepted public key
 *
 * @returns `SSH_OK` on success, otherwise `SSH_ERROR`
 */
int ssh_message_auth_reply_pk_ok(ssh_message msg, ssh_string algo, ssh_string pubkey) {
    int rc;
    if (msg == NULL) {
        return SSH_ERROR;
    }

    rc = ssh_buffer_pack(msg->session->out_buffer,
                         "bSS",
                         SSH2_MSG_USERAUTH_PK_OK,
                         algo,
                         pubkey);
    if(rc != SSH_OK){
        ssh_set_error_oom(msg->session);
        return SSH_ERROR;
    }

    rc = ssh_packet_send(msg->session);
    return rc;
}

/**
 * @brief Answer `SSH2_MSG_USERAUTH_PK_OK` to a pubkey authentication request
 *
 * @param msg The message
 *
 * @returns `SSH_OK` on success, otherwise `SSH_ERROR`
 */
int ssh_message_auth_reply_pk_ok_simple(ssh_message msg)
{
    ssh_string algo = NULL;
    ssh_string pubkey_blob = NULL;
    int ret;

    algo = ssh_string_from_char(msg->auth_request.sigtype);
    if (algo == NULL) {
        return SSH_ERROR;
    }

    ret = ssh_pki_export_pubkey_blob(msg->auth_request.pubkey, &pubkey_blob);
    if (ret < 0) {
        SSH_STRING_FREE(algo);
        return SSH_ERROR;
    }

    ret = ssh_message_auth_reply_pk_ok(msg, algo, pubkey_blob);

    SSH_STRING_FREE(algo);
    SSH_STRING_FREE(pubkey_blob);

    return ret;
}

/**
 * @brief Get the originator address from the channel open message.
 *
 * @param[in] msg        The message.
 *
 * @return               The originator address, or NULL.
 */
const char *ssh_message_channel_request_open_originator(ssh_message msg){
    return msg->channel_request_open.originator;
}

/**
 * @brief Get the originator port from the channel open message.
 *
 * @param[in] msg        The message.
 *
 * @return               The originator port.
 */
int ssh_message_channel_request_open_originator_port(ssh_message msg){
    return msg->channel_request_open.originator_port;
}

/**
 * @brief Get the destination address from the channel open message.
 *
 * @param[in] msg        The message.
 *
 * @return               The destination address, or NULL.
 */
const char *ssh_message_channel_request_open_destination(ssh_message msg){
    return msg->channel_request_open.destination;
}

/**
 * @brief Get the destination port from the channel open message.
 *
 * @param[in] msg        The message.
 *
 * @return               The destination port.
 */
int ssh_message_channel_request_open_destination_port(ssh_message msg){
    return msg->channel_request_open.destination_port;
}

/**
 * @brief Get the channel associated with the message.
 *
 * @param[in] msg        The message.
 *
 * @return               The channel associated with the message.
 */
ssh_channel ssh_message_channel_request_channel(ssh_message msg){
    return msg->channel_request.channel;
}

/**
 * @brief Get the terminal type from the message.
 *
 * @param[in] msg        The message.
 *
 * @return               The terminal type (e.g. "xterm"), or NULL.
 *
 * @deprecated This function should not be used anymore as there is a
 * callback based server implementation function channel_pty_request_function.
 *
 * @see channel_pty_request_function.
 */
const char *ssh_message_channel_request_pty_term(ssh_message msg){
    return msg->channel_request.TERM;
}

/**
 * @brief Get the terminal width from the message.
 *
 * @param[in] msg        The message.
 *
 * @return               The terminal width in characters.
 *
 * @deprecated This function should not be used anymore as there is a
 * callback based server implementation function channel_pty_request_function.
 *
 * @see channel_pty_request_function.
 */
int ssh_message_channel_request_pty_width(ssh_message msg){
    return msg->channel_request.width;
}

/**
 * @brief Get the terminal height from the message.
 *
 * @param[in] msg        The message.
 *
 * @return               The terminal height in characters.
 *
 * @deprecated This function should not be used anymore as there is a
 * callback based server implementation function channel_pty_request_function.
 *
 * @see channel_pty_request_function.
 */
int ssh_message_channel_request_pty_height(ssh_message msg){
    return msg->channel_request.height;
}

/**
 * @brief Get the terminal pixel width from the message.
 *
 * @param[in] msg        The message.
 *
 * @return               The pixel width.
 *
 * @deprecated This function should not be used anymore as there is a
 * callback based server implementation function channel_pty_request_function.
 *
 * @see channel_pty_request_function.
 */
int ssh_message_channel_request_pty_pxwidth(ssh_message msg){
    return msg->channel_request.pxwidth;
}

/**
 * @brief Get the terminal pixel height from the message.
 *
 * @param[in] msg        The message.
 *
 * @return               The pixel height.
 *
 * @deprecated This function should not be used anymore as there is a
 * callback based server implementation function channel_pty_request_function.
 *
 * @see channel_pty_request_function.
 */
int ssh_message_channel_request_pty_pxheight(ssh_message msg){
    return msg->channel_request.pxheight;
}

/**
 * @brief Get the name of the environment variable from the message.
 *
 * @param[in] msg        The message.
 *
 * @return               The variable name, or NULL.
 */
const char *ssh_message_channel_request_env_name(ssh_message msg){
    return msg->channel_request.var_name;
}

/**
 * @brief Get the value of the environment variable from the message.
 *
 * @param[in] msg        The message.
 *
 * @return               The variable value, or NULL.
 */
const char *ssh_message_channel_request_env_value(ssh_message msg){
    return msg->channel_request.var_value;
}

/**
 * @brief Get the command from a channel request message.
 *
 * @param[in] msg        The message.
 *
 * @return               The command, or NULL.
 */
const char *ssh_message_channel_request_command(ssh_message msg){
    return msg->channel_request.command;
}

/**
 * @brief Get the subsystem from a channel request message.
 *
 * @param[in] msg        The message.
 *
 * @return               The subsystem, or NULL.
 */
const char *ssh_message_channel_request_subsystem(ssh_message msg){
    return msg->channel_request.subsystem;
}

/**
 * @brief Check if the X11 request is for a single connection.
 *
 * @param[in] msg        The message.
 *
 * @return               1 if single connection, 0 otherwise.
 *
 * @deprecated This function should not be used anymore as there is a
 * callback based server implementation function
 * channel_open_request_x11_function.
 *
 * @see channel_open_request_x11_function.
 */
int ssh_message_channel_request_x11_single_connection(ssh_message msg){
    return msg->channel_request.x11_single_connection ? 1 : 0;
}

/**
 * @brief Get the X11 authentication protocol from the message.
 *
 * @param[in] msg        The message.
 *
 * @return               The authentication protocol, or NULL.
 *
 * @deprecated This function should not be used anymore as there is a
 * callback based server implementation function
 * channel_open_request_x11_function.
 *
 * @see channel_open_request_x11_function.
 */
const char *ssh_message_channel_request_x11_auth_protocol(ssh_message msg){
    return msg->channel_request.x11_auth_protocol;
}

/**
 * @brief Get the X11 authentication cookie from the message.
 *
 * @param[in] msg        The message.
 *
 * @return               The authentication cookie, or NULL.
 *
 * @deprecated This function should not be used anymore as there is a
 * callback based server implementation function
 * channel_open_request_x11_function.
 *
 * @see channel_open_request_x11_function.
 */
const char *ssh_message_channel_request_x11_auth_cookie(ssh_message msg){
    return msg->channel_request.x11_auth_cookie;
}

/**
 * @brief Get the X11 screen number from the message.
 *
 * @param[in] msg        The message.
 *
 * @return               The screen number.
 *
 * @deprecated This function should not be used anymore as there is a
 * callback based server implementation function
 * channel_open_request_x11_function.
 *
 * @see channel_open_request_x11_function.
 */
int ssh_message_channel_request_x11_screen_number(ssh_message msg){
    return msg->channel_request.x11_screen_number;
}

/**
 * @brief Get the bind address from the global request message.
 *
 * @param[in] msg        The message.
 *
 * @return               The bind address, or NULL.
 */
const char *ssh_message_global_request_address(ssh_message msg){
    return msg->global_request.bind_address;
}

/**
 * @brief Get the bind port from the global request message.
 *
 * @param[in] msg        The message.
 *
 * @return               The bind port.
 */
int ssh_message_global_request_port(ssh_message msg){
    return msg->global_request.bind_port;
}

/** @brief defines the ssh_message callback
 * @param session the current ssh session
 * @param[in] ssh_bind_message_callback a function pointer to a callback taking the
 * current ssh session and received message as parameters. the function returns
 * 0 if the message has been parsed and treated successfully, 1 otherwise (libssh
 * must take care of the response).
 * @param[in] data void pointer to be passed to callback functions
 */
void ssh_set_message_callback(ssh_session session,
        int(*ssh_bind_message_callback)(ssh_session session, ssh_message msg, void *data),
        void *data) {
  session->ssh_message_callback = ssh_bind_message_callback;
  session->ssh_message_callback_data = data;
}

/**
 * @brief Execute callbacks for the messages in the queue.
 *
 * @param[in] session    The session.
 *
 * @return               `SSH_OK` on success, `SSH_ERROR` on error.
 */
int ssh_execute_message_callbacks(ssh_session session){
  ssh_message msg=NULL;
  int ret;
  ssh_handle_packets(session, SSH_TIMEOUT_NONBLOCKING);
  if(!session->ssh_message_list)
    return SSH_OK;
  if(session->ssh_message_callback){
    while((msg=ssh_message_pop_head(session)) != NULL) {
      ret=session->ssh_message_callback(session,msg,
                                        session->ssh_message_callback_data);
      if(ret==1){
        ret = ssh_message_reply_default(msg);
        ssh_message_free(msg);
        if(ret != SSH_OK)
          return ret;
      } else {
        ssh_message_free(msg);
      }
    }
  } else {
    while((msg=ssh_message_pop_head(session)) != NULL) {
      ret = ssh_message_reply_default(msg);
      ssh_message_free(msg);
      if(ret != SSH_OK)
        return ret;
    }
  }
  return SSH_OK;
}

/**
 * @brief Sends a keepalive message to the session
 *
 * @param session   The session to send the message to
 *
 * @returns `SSH_OK`
 */
int ssh_send_keepalive(ssh_session session)
{
    /* Client denies the request, so the error code is not meaningful */
    (void)ssh_global_request(session, "keepalive@openssh.com", NULL, 1);

    return SSH_OK;
}

/** @} */