curve_server.cpp

/*
    Copyright (c) 2007-2015 Contributors as noted in the AUTHORS file

    This file is part of libzmq, the ZeroMQ core engine in C++.

    libzmq is free software; you can redistribute it and/or modify it under
    the terms of the GNU Lesser General Public License (LGPL) as published
    by the Free Software Foundation; either version 3 of the License, or
    (at your option) any later version.

    As a special exception, the Contributors give you permission to link
    this library with independent modules to produce an executable,
    regardless of the license terms of these independent modules, and to
    copy and distribute the resulting executable under terms of your choice,
    provided that you also meet, for each linked independent module, the
    terms and conditions of the license of that module. An independent
    module is a module which is not derived from or based on this library.
    If you modify this library, you must extend this exception to your
    version of the library.

    libzmq 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 this program.  If not, see <http://www.gnu.org/licenses/>.
*/

#include "platform.hpp"

#ifdef HAVE_LIBSODIUM

#ifdef ZMQ_HAVE_WINDOWS
#include "windows.hpp"
#endif

#include "msg.hpp"
#include "session_base.hpp"
#include "err.hpp"
#include "curve_server.hpp"
#include "wire.hpp"

zmq::curve_server_t::curve_server_t (session_base_t *session_,
                                     const std::string &peer_address_,
                                     const options_t &options_) :
    mechanism_t (options_),
    session (session_),
    peer_address (peer_address_),
    state (expect_hello),
    cn_nonce (1),
    cn_peer_nonce(1),
    sync()
{
    int rc;
    //  Fetch our secret key from socket options
    memcpy (secret_key, options_.curve_secret_key, crypto_box_SECRETKEYBYTES);
    scoped_lock_t lock (sync);
#if defined(HAVE_TWEETNACL)
    // allow opening of /dev/urandom
    unsigned char tmpbytes[4];
    randombytes(tmpbytes, 4);
#else
    rc = sodium_init ();
    zmq_assert (rc != -1);
#endif

    //  Generate short-term key pair
    rc = crypto_box_keypair (cn_public, cn_secret);
    zmq_assert (rc == 0);
}

zmq::curve_server_t::~curve_server_t ()
{
}

int zmq::curve_server_t::next_handshake_command (msg_t *msg_)
{
    int rc = 0;

    switch (state) {
        case send_welcome:
            rc = produce_welcome (msg_);
            if (rc == 0)
                state = expect_initiate;
            break;
        case send_ready:
            rc = produce_ready (msg_);
            if (rc == 0)
                state = connected;
            break;
        case send_error:
            rc = produce_error (msg_);
            if (rc == 0)
                state = error_sent;
            break;
        default:
            errno = EAGAIN;
            rc = -1;
            break;
    }
    return rc;
}

int zmq::curve_server_t::process_handshake_command (msg_t *msg_)
{
    int rc = 0;

    switch (state) {
        case expect_hello:
            rc = process_hello (msg_);
            break;
        case expect_initiate:
            rc = process_initiate (msg_);
            break;
        default:
            //  Temporary support for security debugging
            puts ("CURVE I: invalid handshake command");
            errno = EPROTO;
            rc = -1;
            break;
    }
    if (rc == 0) {
        rc = msg_->close ();
        errno_assert (rc == 0);
        rc = msg_->init ();
        errno_assert (rc == 0);
    }
    return rc;
}

int zmq::curve_server_t::encode (msg_t *msg_)
{
    zmq_assert (state == connected);

    const size_t mlen = crypto_box_ZEROBYTES + 1 + msg_->size ();

    uint8_t message_nonce [crypto_box_NONCEBYTES];
    memcpy (message_nonce, "CurveZMQMESSAGES", 16);
    put_uint64 (message_nonce + 16, cn_nonce);

    uint8_t flags = 0;
    if (msg_->flags () & msg_t::more)
        flags |= 0x01;
    if (msg_->flags () & msg_t::command)
        flags |= 0x02;

    uint8_t *message_plaintext = static_cast <uint8_t *> (malloc (mlen));
    alloc_assert (message_plaintext);

    memset (message_plaintext, 0, crypto_box_ZEROBYTES);
    message_plaintext [crypto_box_ZEROBYTES] = flags;
    memcpy (message_plaintext + crypto_box_ZEROBYTES + 1,
            msg_->data (), msg_->size ());

    uint8_t *message_box = static_cast <uint8_t *> (malloc (mlen));
    alloc_assert (message_box);

    int rc = crypto_box_afternm (message_box, message_plaintext,
                                 mlen, message_nonce, cn_precom);
    zmq_assert (rc == 0);

    rc = msg_->close ();
    zmq_assert (rc == 0);

    rc = msg_->init_size (16 + mlen - crypto_box_BOXZEROBYTES);
    zmq_assert (rc == 0);

    uint8_t *message = static_cast <uint8_t *> (msg_->data ());

    memcpy (message, "\x07MESSAGE", 8);
    memcpy (message + 8, message_nonce + 16, 8);
    memcpy (message + 16, message_box + crypto_box_BOXZEROBYTES,
            mlen - crypto_box_BOXZEROBYTES);

    free (message_plaintext);
    free (message_box);

    cn_nonce++;

    return 0;
}

int zmq::curve_server_t::decode (msg_t *msg_)
{
    zmq_assert (state == connected);

    if (msg_->size () < 33) {
        //  Temporary support for security debugging
        puts ("CURVE I: invalid CURVE client, sent malformed command");
        errno = EPROTO;
        return -1;
    }

    const uint8_t *message = static_cast <uint8_t *> (msg_->data ());
    if (memcmp (message, "\x07MESSAGE", 8)) {
        //  Temporary support for security debugging
        puts ("CURVE I: invalid CURVE client, did not send MESSAGE");
        errno = EPROTO;
        return -1;
    }

    uint8_t message_nonce [crypto_box_NONCEBYTES];
    memcpy (message_nonce, "CurveZMQMESSAGEC", 16);
    memcpy (message_nonce + 16, message + 8, 8);
    uint64_t nonce = get_uint64(message + 8);
    if (nonce <= cn_peer_nonce) {
        errno = EPROTO;
        return -1;
    }
    cn_peer_nonce = nonce;

    const size_t clen = crypto_box_BOXZEROBYTES + msg_->size () - 16;

    uint8_t *message_plaintext = static_cast <uint8_t *> (malloc (clen));
    alloc_assert (message_plaintext);

    uint8_t *message_box = static_cast <uint8_t *> (malloc (clen));
    alloc_assert (message_box);

    memset (message_box, 0, crypto_box_BOXZEROBYTES);
    memcpy (message_box + crypto_box_BOXZEROBYTES,
            message + 16, msg_->size () - 16);

    int rc = crypto_box_open_afternm (message_plaintext, message_box,
                                      clen, message_nonce, cn_precom);
    if (rc == 0) {
        rc = msg_->close ();
        zmq_assert (rc == 0);

        rc = msg_->init_size (clen - 1 - crypto_box_ZEROBYTES);
        zmq_assert (rc == 0);

        const uint8_t flags = message_plaintext [crypto_box_ZEROBYTES];
        if (flags & 0x01)
            msg_->set_flags (msg_t::more);
        if (flags & 0x02)
            msg_->set_flags (msg_t::command);

        memcpy (msg_->data (),
                message_plaintext + crypto_box_ZEROBYTES + 1,
                msg_->size ());
    }
    else {
        //  Temporary support for security debugging
        puts ("CURVE I: connection key used for MESSAGE is wrong");
        errno = EPROTO;
    }
    free (message_plaintext);
    free (message_box);

    return rc;
}

int zmq::curve_server_t::zap_msg_available ()
{
    if (state != expect_zap_reply) {
        errno = EFSM;
        return -1;
    }
    const int rc = receive_and_process_zap_reply ();
    if (rc == 0)
        state = status_code == "200"
            ? send_ready
            : send_error;
    return rc;
}

zmq::mechanism_t::status_t zmq::curve_server_t::status () const
{
    if (state == connected)
        return mechanism_t::ready;
    else
    if (state == error_sent)
        return mechanism_t::error;
    else
        return mechanism_t::handshaking;
}

int zmq::curve_server_t::process_hello (msg_t *msg_)
{
    if (msg_->size () != 200) {
        //  Temporary support for security debugging
        puts ("CURVE I: client HELLO is not correct size");
        errno = EPROTO;
        return -1;
    }

    const uint8_t * const hello = static_cast <uint8_t *> (msg_->data ());
    if (memcmp (hello, "\x05HELLO", 6)) {
        //  Temporary support for security debugging
        puts ("CURVE I: client HELLO has invalid command name");
        errno = EPROTO;
        return -1;
    }

    const uint8_t major = hello [6];
    const uint8_t minor = hello [7];

    if (major != 1 || minor != 0) {
        //  Temporary support for security debugging
        puts ("CURVE I: client HELLO has unknown version number");
        errno = EPROTO;
        return -1;
    }

    //  Save client's short-term public key (C')
    memcpy (cn_client, hello + 80, 32);

    uint8_t hello_nonce [crypto_box_NONCEBYTES];
    uint8_t hello_plaintext [crypto_box_ZEROBYTES + 64];
    uint8_t hello_box [crypto_box_BOXZEROBYTES + 80];

    memcpy (hello_nonce, "CurveZMQHELLO---", 16);
    memcpy (hello_nonce + 16, hello + 112, 8);
    cn_peer_nonce = get_uint64(hello + 112);

    memset (hello_box, 0, crypto_box_BOXZEROBYTES);
    memcpy (hello_box + crypto_box_BOXZEROBYTES, hello + 120, 80);

    //  Open Box [64 * %x0](C'->S)
    int rc = crypto_box_open (hello_plaintext, hello_box,
                              sizeof hello_box,
                              hello_nonce, cn_client, secret_key);
    if (rc != 0) {
        //  Temporary support for security debugging
        puts ("CURVE I: cannot open client HELLO -- wrong server key?");
        errno = EPROTO;
        return -1;
    }

    state = send_welcome;
    return rc;
}

int zmq::curve_server_t::produce_welcome (msg_t *msg_)
{
    uint8_t cookie_nonce [crypto_secretbox_NONCEBYTES];
    uint8_t cookie_plaintext [crypto_secretbox_ZEROBYTES + 64];
    uint8_t cookie_ciphertext [crypto_secretbox_BOXZEROBYTES + 80];

    //  Create full nonce for encryption
    //  8-byte prefix plus 16-byte random nonce
    memcpy (cookie_nonce, "COOKIE--", 8);
    randombytes (cookie_nonce + 8, 16);

    //  Generate cookie = Box [C' + s'](t)
    memset (cookie_plaintext, 0, crypto_secretbox_ZEROBYTES);
    memcpy (cookie_plaintext + crypto_secretbox_ZEROBYTES,
            cn_client, 32);
    memcpy (cookie_plaintext + crypto_secretbox_ZEROBYTES + 32,
            cn_secret, 32);

    //  Generate fresh cookie key
    randombytes (cookie_key, crypto_secretbox_KEYBYTES);

    //  Encrypt using symmetric cookie key
    int rc = crypto_secretbox (cookie_ciphertext, cookie_plaintext,
                               sizeof cookie_plaintext,
                               cookie_nonce, cookie_key);
    zmq_assert (rc == 0);

    uint8_t welcome_nonce [crypto_box_NONCEBYTES];
    uint8_t welcome_plaintext [crypto_box_ZEROBYTES + 128];
    uint8_t welcome_ciphertext [crypto_box_BOXZEROBYTES + 144];

    //  Create full nonce for encryption
    //  8-byte prefix plus 16-byte random nonce
    memcpy (welcome_nonce, "WELCOME-", 8);
    randombytes (welcome_nonce + 8, crypto_box_NONCEBYTES - 8);

    //  Create 144-byte Box [S' + cookie](S->C')
    memset (welcome_plaintext, 0, crypto_box_ZEROBYTES);
    memcpy (welcome_plaintext + crypto_box_ZEROBYTES, cn_public, 32);
    memcpy (welcome_plaintext + crypto_box_ZEROBYTES + 32,
            cookie_nonce + 8, 16);
    memcpy (welcome_plaintext + crypto_box_ZEROBYTES + 48,
            cookie_ciphertext + crypto_secretbox_BOXZEROBYTES, 80);

    rc = crypto_box (welcome_ciphertext, welcome_plaintext,
                     sizeof welcome_plaintext,
                     welcome_nonce, cn_client, secret_key);
    zmq_assert (rc == 0);

    rc = msg_->init_size (168);
    errno_assert (rc == 0);

    uint8_t * const welcome = static_cast <uint8_t *> (msg_->data ());
    memcpy (welcome, "\x07WELCOME", 8);
    memcpy (welcome + 8, welcome_nonce + 8, 16);
    memcpy (welcome + 24, welcome_ciphertext + crypto_box_BOXZEROBYTES, 144);

    return 0;
}

int zmq::curve_server_t::process_initiate (msg_t *msg_)
{
    if (msg_->size () < 257) {
        //  Temporary support for security debugging
        puts ("CURVE I: client INITIATE is not correct size");
        errno = EPROTO;
        return -1;
    }

    const uint8_t *initiate = static_cast <uint8_t *> (msg_->data ());
    if (memcmp (initiate, "\x08INITIATE", 9)) {
        //  Temporary support for security debugging
        puts ("CURVE I: client INITIATE has invalid command name");
        errno = EPROTO;
        return -1;
    }

    uint8_t cookie_nonce [crypto_secretbox_NONCEBYTES];
    uint8_t cookie_plaintext [crypto_secretbox_ZEROBYTES + 64];
    uint8_t cookie_box [crypto_secretbox_BOXZEROBYTES + 80];

    //  Open Box [C' + s'](t)
    memset (cookie_box, 0, crypto_secretbox_BOXZEROBYTES);
    memcpy (cookie_box + crypto_secretbox_BOXZEROBYTES, initiate + 25, 80);

    memcpy (cookie_nonce, "COOKIE--", 8);
    memcpy (cookie_nonce + 8, initiate + 9, 16);

    int rc = crypto_secretbox_open (cookie_plaintext, cookie_box,
                                    sizeof cookie_box,
                                    cookie_nonce, cookie_key);
    if (rc != 0) {
        //  Temporary support for security debugging
        puts ("CURVE I: cannot open client INITIATE cookie");
        errno = EPROTO;
        return -1;
    }

    //  Check cookie plain text is as expected [C' + s']
    if (memcmp (cookie_plaintext + crypto_secretbox_ZEROBYTES, cn_client, 32)
    ||  memcmp (cookie_plaintext + crypto_secretbox_ZEROBYTES + 32, cn_secret, 32)) {
        //  Temporary support for security debugging
        puts ("CURVE I: client INITIATE cookie is not valid");
        errno = EPROTO;
        return -1;
    }

    const size_t clen = (msg_->size () - 113) + crypto_box_BOXZEROBYTES;

    uint8_t initiate_nonce [crypto_box_NONCEBYTES];
    uint8_t initiate_plaintext [crypto_box_ZEROBYTES + 128 + 256];
    uint8_t initiate_box [crypto_box_BOXZEROBYTES + 144 + 256];

    //  Open Box [C + vouch + metadata](C'->S')
    memset (initiate_box, 0, crypto_box_BOXZEROBYTES);
    memcpy (initiate_box + crypto_box_BOXZEROBYTES,
            initiate + 113, clen - crypto_box_BOXZEROBYTES);

    memcpy (initiate_nonce, "CurveZMQINITIATE", 16);
    memcpy (initiate_nonce + 16, initiate + 105, 8);
    cn_peer_nonce = get_uint64(initiate + 105);

    rc = crypto_box_open (initiate_plaintext, initiate_box,
                          clen, initiate_nonce, cn_client, cn_secret);
    if (rc != 0) {
        //  Temporary support for security debugging
        puts ("CURVE I: cannot open client INITIATE");
        errno = EPROTO;
        return -1;
    }

    const uint8_t *client_key = initiate_plaintext + crypto_box_ZEROBYTES;

    uint8_t vouch_nonce [crypto_box_NONCEBYTES];
    uint8_t vouch_plaintext [crypto_box_ZEROBYTES + 64];
    uint8_t vouch_box [crypto_box_BOXZEROBYTES + 80];

    //  Open Box Box [C',S](C->S') and check contents
    memset (vouch_box, 0, crypto_box_BOXZEROBYTES);
    memcpy (vouch_box + crypto_box_BOXZEROBYTES,
            initiate_plaintext + crypto_box_ZEROBYTES + 48, 80);

    memcpy (vouch_nonce, "VOUCH---", 8);
    memcpy (vouch_nonce + 8,
            initiate_plaintext + crypto_box_ZEROBYTES + 32, 16);

    rc = crypto_box_open (vouch_plaintext, vouch_box,
                          sizeof vouch_box,
                          vouch_nonce, client_key, cn_secret);
    if (rc != 0) {
        //  Temporary support for security debugging
        puts ("CURVE I: cannot open client INITIATE vouch");
        errno = EPROTO;
        return -1;
    }

    //  What we decrypted must be the client's short-term public key
    if (memcmp (vouch_plaintext + crypto_box_ZEROBYTES, cn_client, 32)) {
        //  Temporary support for security debugging
        puts ("CURVE I: invalid handshake from client (public key)");
        errno = EPROTO;
        return -1;
    }

    //  Precompute connection secret from client key
    rc = crypto_box_beforenm (cn_precom, cn_client, cn_secret);
    zmq_assert (rc == 0);

    //  Use ZAP protocol (RFC 27) to authenticate the user.
    rc = session->zap_connect ();
    if (rc == 0) {
        send_zap_request (client_key);
        rc = receive_and_process_zap_reply ();
        if (rc == 0)
            state = status_code == "200"
                ? send_ready
                : send_error;
        else
        if (errno == EAGAIN)
            state = expect_zap_reply;
        else
            return -1;
    }
    else
        state = send_ready;

    return parse_metadata (initiate_plaintext + crypto_box_ZEROBYTES + 128,
                           clen - crypto_box_ZEROBYTES - 128);
}

int zmq::curve_server_t::produce_ready (msg_t *msg_)
{
    uint8_t ready_nonce [crypto_box_NONCEBYTES];
    uint8_t ready_plaintext [crypto_box_ZEROBYTES + 256];
    uint8_t ready_box [crypto_box_BOXZEROBYTES + 16 + 256];

    //  Create Box [metadata](S'->C')
    memset (ready_plaintext, 0, crypto_box_ZEROBYTES);
    uint8_t *ptr = ready_plaintext + crypto_box_ZEROBYTES;

    //  Add socket type property
    const char *socket_type = socket_type_string (options.type);
    ptr += add_property (ptr, "Socket-Type", socket_type, strlen (socket_type));

    //  Add identity property
    if (options.type == ZMQ_REQ
    ||  options.type == ZMQ_DEALER
    ||  options.type == ZMQ_ROUTER)
        ptr += add_property (ptr, "Identity", options.identity, options.identity_size);

    const size_t mlen = ptr - ready_plaintext;

    memcpy (ready_nonce, "CurveZMQREADY---", 16);
    put_uint64 (ready_nonce + 16, cn_nonce);

    int rc = crypto_box_afternm (ready_box, ready_plaintext,
                                 mlen, ready_nonce, cn_precom);
    zmq_assert (rc == 0);

    rc = msg_->init_size (14 + mlen - crypto_box_BOXZEROBYTES);
    errno_assert (rc == 0);

    uint8_t *ready = static_cast <uint8_t *> (msg_->data ());

    memcpy (ready, "\x05READY", 6);
    //  Short nonce, prefixed by "CurveZMQREADY---"
    memcpy (ready + 6, ready_nonce + 16, 8);
    //  Box [metadata](S'->C')
    memcpy (ready + 14, ready_box + crypto_box_BOXZEROBYTES,
            mlen - crypto_box_BOXZEROBYTES);

    cn_nonce++;

    return 0;
}

int zmq::curve_server_t::produce_error (msg_t *msg_) const
{
    zmq_assert (status_code.length () == 3);
    const int rc = msg_->init_size (6 + 1 + status_code.length ());
    zmq_assert (rc == 0);
    char *msg_data = static_cast <char *> (msg_->data ());
    memcpy (msg_data, "\5ERROR", 6);
    msg_data [6] = sizeof status_code;
    memcpy (msg_data + 7, status_code.c_str (), status_code.length ());
    return 0;
}

void zmq::curve_server_t::send_zap_request (const uint8_t *key)
{
    int rc;
    msg_t msg;

    //  Address delimiter frame
    rc = msg.init ();
    errno_assert (rc == 0);
    msg.set_flags (msg_t::more);
    rc = session->write_zap_msg (&msg);
    errno_assert (rc == 0);

    //  Version frame
    rc = msg.init_size (3);
    errno_assert (rc == 0);
    memcpy (msg.data (), "1.0", 3);
    msg.set_flags (msg_t::more);
    rc = session->write_zap_msg (&msg);
    errno_assert (rc == 0);

    //  Request ID frame
    rc = msg.init_size (1);
    errno_assert (rc == 0);
    memcpy (msg.data (), "1", 1);
    msg.set_flags (msg_t::more);
    rc = session->write_zap_msg (&msg);
    errno_assert (rc == 0);

    //  Domain frame
    rc = msg.init_size (options.zap_domain.length ());
    errno_assert (rc == 0);
    memcpy (msg.data (), options.zap_domain.c_str (), options.zap_domain.length ());
    msg.set_flags (msg_t::more);
    rc = session->write_zap_msg (&msg);
    errno_assert (rc == 0);

    //  Address frame
    rc = msg.init_size (peer_address.length ());
    errno_assert (rc == 0);
    memcpy (msg.data (), peer_address.c_str (), peer_address.length ());
    msg.set_flags (msg_t::more);
    rc = session->write_zap_msg (&msg);
    errno_assert (rc == 0);

    //  Identity frame
    rc = msg.init_size (options.identity_size);
    errno_assert (rc == 0);
    memcpy (msg.data (), options.identity, options.identity_size);
    msg.set_flags (msg_t::more);
    rc = session->write_zap_msg (&msg);
    errno_assert (rc == 0);

    //  Mechanism frame
    rc = msg.init_size (5);
    errno_assert (rc == 0);
    memcpy (msg.data (), "CURVE", 5);
    msg.set_flags (msg_t::more);
    rc = session->write_zap_msg (&msg);
    errno_assert (rc == 0);

    //  Credentials frame
    rc = msg.init_size (crypto_box_PUBLICKEYBYTES);
    errno_assert (rc == 0);
    memcpy (msg.data (), key, crypto_box_PUBLICKEYBYTES);
    rc = session->write_zap_msg (&msg);
    errno_assert (rc == 0);
}

int zmq::curve_server_t::receive_and_process_zap_reply ()
{
    int rc = 0;
    msg_t msg [7];  //  ZAP reply consists of 7 frames

    //  Initialize all reply frames
    for (int i = 0; i < 7; i++) {
        rc = msg [i].init ();
        errno_assert (rc == 0);
    }

    for (int i = 0; i < 7; i++) {
        rc = session->read_zap_msg (&msg [i]);
        if (rc == -1)
            break;
        if ((msg [i].flags () & msg_t::more) == (i < 6? 0: msg_t::more)) {
            //  Temporary support for security debugging
            puts ("CURVE I: ZAP handler sent incomplete reply message");
            errno = EPROTO;
            rc = -1;
            break;
        }
    }

    if (rc != 0)
        goto error;

    //  Address delimiter frame
    if (msg [0].size () > 0) {
        //  Temporary support for security debugging
        puts ("CURVE I: ZAP handler sent malformed reply message");
        errno = EPROTO;
        rc = -1;
        goto error;
    }

    //  Version frame
    if (msg [1].size () != 3 || memcmp (msg [1].data (), "1.0", 3)) {
        //  Temporary support for security debugging
        puts ("CURVE I: ZAP handler sent bad version number");
        errno = EPROTO;
        rc = -1;
        goto error;
    }

    //  Request id frame
    if (msg [2].size () != 1 || memcmp (msg [2].data (), "1", 1)) {
        //  Temporary support for security debugging
        puts ("CURVE I: ZAP handler sent bad request ID");
        errno = EPROTO;
        rc = -1;
        goto error;
    }

    //  Status code frame
    if (msg [3].size () != 3) {
        //  Temporary support for security debugging
        puts ("CURVE I: ZAP handler rejected client authentication");
        errno = EACCES;
        rc = -1;
        goto error;
    }

    //  Save status code
    status_code.assign (static_cast <char *> (msg [3].data ()), 3);

    //  Save user id
    set_user_id (msg [5].data (), msg [5].size ());

    //  Process metadata frame
    rc = parse_metadata (static_cast <const unsigned char*> (msg [6].data ()),
                         msg [6].size (), true);

error:
    for (int i = 0; i < 7; i++) {
        const int rc2 = msg [i].close ();
        errno_assert (rc2 == 0);
    }

    return rc;
}

#endif