remote.c

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/*
 * Copyright 2008-2021 the Pacemaker project contributors
 *
 * The version control history for this file may have further details.
 *
 * This source code is licensed under the GNU Lesser General Public License
 * version 2.1 or later (LGPLv2.1+) WITHOUT ANY WARRANTY.
 */

#include <crm_internal.h>
#include <crm/crm.h>

#include <sys/param.h>
#include <stdio.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <unistd.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#include <netinet/in.h>
#include <netinet/ip.h>
#include <netinet/tcp.h>
#include <netdb.h>
#include <stdlib.h>
#include <errno.h>
#include <inttypes.h>  /* X32T ~ PRIx32 */

#include <glib.h>
#include <bzlib.h>

#include <crm/common/ipc_internal.h>
#include <crm/common/xml.h>
#include <crm/common/mainloop.h>
#include <crm/common/remote_internal.h>

#ifdef HAVE_GNUTLS_GNUTLS_H
#  include <gnutls/gnutls.h>
#endif

/* Swab macros from linux/swab.h */
#ifdef HAVE_LINUX_SWAB_H
#  include <linux/swab.h>
#else
/*
 * casts are necessary for constants, because we never know how for sure
 * how U/UL/ULL map to __u16, __u32, __u64. At least not in a portable way.
 */
#define __swab16(x) ((uint16_t)(                                      \
        (((uint16_t)(x) & (uint16_t)0x00ffU) << 8) |                  \
        (((uint16_t)(x) & (uint16_t)0xff00U) >> 8)))

#define __swab32(x) ((uint32_t)(                                      \
        (((uint32_t)(x) & (uint32_t)0x000000ffUL) << 24) |            \
        (((uint32_t)(x) & (uint32_t)0x0000ff00UL) <<  8) |            \
        (((uint32_t)(x) & (uint32_t)0x00ff0000UL) >>  8) |            \
        (((uint32_t)(x) & (uint32_t)0xff000000UL) >> 24)))

#define __swab64(x) ((uint64_t)(                                      \
        (((uint64_t)(x) & (uint64_t)0x00000000000000ffULL) << 56) |   \
        (((uint64_t)(x) & (uint64_t)0x000000000000ff00ULL) << 40) |   \
        (((uint64_t)(x) & (uint64_t)0x0000000000ff0000ULL) << 24) |   \
        (((uint64_t)(x) & (uint64_t)0x00000000ff000000ULL) <<  8) |   \
        (((uint64_t)(x) & (uint64_t)0x000000ff00000000ULL) >>  8) |   \
        (((uint64_t)(x) & (uint64_t)0x0000ff0000000000ULL) >> 24) |   \
        (((uint64_t)(x) & (uint64_t)0x00ff000000000000ULL) >> 40) |   \
        (((uint64_t)(x) & (uint64_t)0xff00000000000000ULL) >> 56)))
#endif

#define REMOTE_MSG_VERSION 1
#define ENDIAN_LOCAL 0xBADADBBD

struct remote_header_v0 {
    uint32_t endian;    /* Detect messages from hosts with different endian-ness */
    uint32_t version;
    uint64_t id;
    uint64_t flags;
    uint32_t size_total;
    uint32_t payload_offset;
    uint32_t payload_compressed;
    uint32_t payload_uncompressed;

        /* New fields get added here */

} __attribute__ ((packed));

static struct remote_header_v0 *
localized_remote_header(pcmk__remote_t *remote)
{
    struct remote_header_v0 *header = (struct remote_header_v0 *)remote->buffer;
    if(remote->buffer_offset < sizeof(struct remote_header_v0)) {
        return NULL;

    } else if(header->endian != ENDIAN_LOCAL) {
        uint32_t endian = __swab32(header->endian);

        CRM_LOG_ASSERT(endian == ENDIAN_LOCAL);
        if(endian != ENDIAN_LOCAL) {
            crm_err("Invalid message detected, endian mismatch: %" X32T
                    " is neither %" X32T " nor the swab'd %" X32T,
                    ENDIAN_LOCAL, header->endian, endian);
            return NULL;
        }

        header->id = __swab64(header->id);
        header->flags = __swab64(header->flags);
        header->endian = __swab32(header->endian);

        header->version = __swab32(header->version);
        header->size_total = __swab32(header->size_total);
        header->payload_offset = __swab32(header->payload_offset);
        header->payload_compressed = __swab32(header->payload_compressed);
        header->payload_uncompressed = __swab32(header->payload_uncompressed);
    }

    return header;
}

#ifdef HAVE_GNUTLS_GNUTLS_H

int
pcmk__tls_client_handshake(pcmk__remote_t *remote, int timeout_ms)
{
    int rc = 0;
    int pollrc = 0;
    time_t time_limit = time(NULL) + timeout_ms / 1000;

    do {
        rc = gnutls_handshake(*remote->tls_session);
        if ((rc == GNUTLS_E_INTERRUPTED) || (rc == GNUTLS_E_AGAIN)) {
            pollrc = pcmk__remote_ready(remote, 1000);
            if ((pollrc != pcmk_rc_ok) && (pollrc != ETIME)) {
                /* poll returned error, there is no hope */
                crm_trace("TLS handshake poll failed: %s (%d)",
                          pcmk_strerror(pollrc), pollrc);
                return pcmk_legacy2rc(pollrc);
            }
        } else if (rc < 0) {
            crm_trace("TLS handshake failed: %s (%d)",
                      gnutls_strerror(rc), rc);
            return EPROTO;
        } else {
            return pcmk_rc_ok;
        }
    } while (time(NULL) < time_limit);
    return ETIME;
}

static void
set_minimum_dh_bits(gnutls_session_t *session)
{
    int dh_min_bits;

    pcmk__scan_min_int(getenv("PCMK_dh_min_bits"), &dh_min_bits, 0);

    /* This function is deprecated since GnuTLS 3.1.7, in favor of letting
     * the priority string imply the DH requirements, but this is the only
     * way to give the user control over compatibility with older servers.
     */
    if (dh_min_bits > 0) {
        crm_info("Requiring server use a Diffie-Hellman prime of at least %d bits",
                 dh_min_bits);
        gnutls_dh_set_prime_bits(*session, dh_min_bits);
    }
}

static unsigned int
get_bound_dh_bits(unsigned int dh_bits)
{
    int dh_min_bits;
    int dh_max_bits;

    pcmk__scan_min_int(getenv("PCMK_dh_min_bits"), &dh_min_bits, 0);
    pcmk__scan_min_int(getenv("PCMK_dh_max_bits"), &dh_max_bits, 0);
    if ((dh_max_bits > 0) && (dh_max_bits < dh_min_bits)) {
        crm_warn("Ignoring PCMK_dh_max_bits less than PCMK_dh_min_bits");
        dh_max_bits = 0;
    }
    if ((dh_min_bits > 0) && (dh_bits < dh_min_bits)) {
        return dh_min_bits;
    }
    if ((dh_max_bits > 0) && (dh_bits > dh_max_bits)) {
        return dh_max_bits;
    }
    return dh_bits;
}

gnutls_session_t *
pcmk__new_tls_session(int csock, unsigned int conn_type,
                      gnutls_credentials_type_t cred_type, void *credentials)
{
    int rc = GNUTLS_E_SUCCESS;
    const char *prio_base = NULL;
    char *prio = NULL;
    gnutls_session_t *session = NULL;

    /* Determine list of acceptable ciphers, etc. Pacemaker always adds the
     * values required for its functionality.
     *
     * For an example of anonymous authentication, see:
     * http://www.manpagez.com/info/gnutls/gnutls-2.10.4/gnutls_81.php#Echo-Server-with-anonymous-authentication
     */

    prio_base = getenv("PCMK_tls_priorities");
    if (prio_base == NULL) {
        prio_base = PCMK_GNUTLS_PRIORITIES;
    }
    prio = crm_strdup_printf("%s:%s", prio_base,
                             (cred_type == GNUTLS_CRD_ANON)? "+ANON-DH" : "+DHE-PSK:+PSK");

    session = gnutls_malloc(sizeof(gnutls_session_t));
    if (session == NULL) {
        rc = GNUTLS_E_MEMORY_ERROR;
        goto error;
    }

    rc = gnutls_init(session, conn_type);
    if (rc != GNUTLS_E_SUCCESS) {
        goto error;
    }

    /* @TODO On the server side, it would be more efficient to cache the
     * priority with gnutls_priority_init2() and set it with
     * gnutls_priority_set() for all sessions.
     */
    rc = gnutls_priority_set_direct(*session, prio, NULL);
    if (rc != GNUTLS_E_SUCCESS) {
        goto error;
    }
    if (conn_type == GNUTLS_CLIENT) {
        set_minimum_dh_bits(session);
    }

    gnutls_transport_set_ptr(*session,
                             (gnutls_transport_ptr_t) GINT_TO_POINTER(csock));

    rc = gnutls_credentials_set(*session, cred_type, credentials);
    if (rc != GNUTLS_E_SUCCESS) {
        goto error;
    }
    free(prio);
    return session;

error:
    crm_err("Could not initialize %s TLS %s session: %s "
            CRM_XS " rc=%d priority='%s'",
            (cred_type == GNUTLS_CRD_ANON)? "anonymous" : "PSK",
            (conn_type == GNUTLS_SERVER)? "server" : "client",
            gnutls_strerror(rc), rc, prio);
    free(prio);
    if (session != NULL) {
        gnutls_free(session);
    }
    return NULL;
}

int
pcmk__init_tls_dh(gnutls_dh_params_t *dh_params)
{
    int rc = GNUTLS_E_SUCCESS;
    unsigned int dh_bits = 0;

    rc = gnutls_dh_params_init(dh_params);
    if (rc != GNUTLS_E_SUCCESS) {
        goto error;
    }

    dh_bits = gnutls_sec_param_to_pk_bits(GNUTLS_PK_DH,
                                          GNUTLS_SEC_PARAM_NORMAL);
    if (dh_bits == 0) {
        rc = GNUTLS_E_DH_PRIME_UNACCEPTABLE;
        goto error;
    }
    dh_bits = get_bound_dh_bits(dh_bits);

    crm_info("Generating Diffie-Hellman parameters with %u-bit prime for TLS",
             dh_bits);
    rc = gnutls_dh_params_generate2(*dh_params, dh_bits);
    if (rc != GNUTLS_E_SUCCESS) {
        goto error;
    }

    return pcmk_rc_ok;

error:
    crm_err("Could not initialize Diffie-Hellman parameters for TLS: %s "
            CRM_XS " rc=%d", gnutls_strerror(rc), rc);
    return EPROTO;
}

int
pcmk__read_handshake_data(pcmk__client_t *client)
{
    int rc = 0;

    CRM_ASSERT(client && client->remote && client->remote->tls_session);

    do {
        rc = gnutls_handshake(*client->remote->tls_session);
    } while (rc == GNUTLS_E_INTERRUPTED);

    if (rc == GNUTLS_E_AGAIN) {
        /* No more data is available at the moment. This function should be
         * invoked again once the client sends more.
         */
        return EAGAIN;
    } else if (rc != GNUTLS_E_SUCCESS) {
        crm_err("TLS handshake with remote client failed: %s "
                CRM_XS " rc=%d", gnutls_strerror(rc), rc);
        return EPROTO;
    }
    return pcmk_rc_ok;
}

// \return Standard Pacemaker return code
static int
send_tls(gnutls_session_t *session, struct iovec *iov)
{
    const char *unsent = iov->iov_base;
    size_t unsent_len = iov->iov_len;
    ssize_t gnutls_rc;

    if (unsent == NULL) {
        return EINVAL;
    }

    crm_trace("Sending TLS message of %llu bytes",
              (unsigned long long) unsent_len);
    while (true) {
        gnutls_rc = gnutls_record_send(*session, unsent, unsent_len);

        if (gnutls_rc == GNUTLS_E_INTERRUPTED || gnutls_rc == GNUTLS_E_AGAIN) {
            crm_trace("Retrying to send %llu bytes remaining",
                      (unsigned long long) unsent_len);

        } else if (gnutls_rc < 0) {
            // Caller can log as error if necessary
            crm_info("TLS connection terminated: %s " CRM_XS " rc=%lld",
                     gnutls_strerror((int) gnutls_rc),
                     (long long) gnutls_rc);
            return ECONNABORTED;

        } else if (gnutls_rc < unsent_len) {
            crm_trace("Sent %lld of %llu bytes remaining",
                      (long long) gnutls_rc, (unsigned long long) unsent_len);
            unsent_len -= gnutls_rc;
            unsent += gnutls_rc;
        } else {
            crm_trace("Sent all %lld bytes remaining", (long long) gnutls_rc);
            break;
        }
    }
    return pcmk_rc_ok;
}
#endif

// \return Standard Pacemaker return code
static int
send_plaintext(int sock, struct iovec *iov)
{
    const char *unsent = iov->iov_base;
    size_t unsent_len = iov->iov_len;
    ssize_t write_rc;

    if (unsent == NULL) {
        return EINVAL;
    }

    crm_debug("Sending plaintext message of %llu bytes to socket %d",
              (unsigned long long) unsent_len, sock);
    while (true) {
        write_rc = write(sock, unsent, unsent_len);
        if (write_rc < 0) {
            int rc = errno;

            if ((errno == EINTR) || (errno == EAGAIN)) {
                crm_trace("Retrying to send %llu bytes remaining to socket %d",
                          (unsigned long long) unsent_len, sock);
                continue;
            }

            // Caller can log as error if necessary
            crm_info("Could not send message: %s " CRM_XS " rc=%d socket=%d",
                     pcmk_rc_str(rc), rc, sock);
            return rc;

        } else if (write_rc < unsent_len) {
            crm_trace("Sent %lld of %llu bytes remaining",
                      (long long) write_rc, (unsigned long long) unsent_len);
            unsent += write_rc;
            unsent_len -= write_rc;
            continue;

        } else {
            crm_trace("Sent all %lld bytes remaining: %.100s",
                      (long long) write_rc, (char *) (iov->iov_base));
            break;
        }
    }
    return pcmk_rc_ok;
}

// \return Standard Pacemaker return code
static int
remote_send_iovs(pcmk__remote_t *remote, struct iovec *iov, int iovs)
{
    int rc = pcmk_rc_ok;

    for (int lpc = 0; (lpc < iovs) && (rc == pcmk_rc_ok); lpc++) {
#ifdef HAVE_GNUTLS_GNUTLS_H
        if (remote->tls_session) {
            rc = send_tls(remote->tls_session, &(iov[lpc]));
            continue;
        }
#endif
        if (remote->tcp_socket) {
            rc = send_plaintext(remote->tcp_socket, &(iov[lpc]));
        } else {
            rc = ESOCKTNOSUPPORT;
        }
    }
    return rc;
}

int
pcmk__remote_send_xml(pcmk__remote_t *remote, xmlNode *msg)
{
    int rc = pcmk_rc_ok;
    static uint64_t id = 0;
    char *xml_text = NULL;

    struct iovec iov[2];
    struct remote_header_v0 *header;

    CRM_CHECK((remote != NULL) && (msg != NULL), return EINVAL);

    xml_text = dump_xml_unformatted(msg);
    CRM_CHECK(xml_text != NULL, return EINVAL);

    header = calloc(1, sizeof(struct remote_header_v0));
    CRM_ASSERT(header != NULL);

    iov[0].iov_base = header;
    iov[0].iov_len = sizeof(struct remote_header_v0);

    iov[1].iov_base = xml_text;
    iov[1].iov_len = 1 + strlen(xml_text);

    id++;
    header->id = id;
    header->endian = ENDIAN_LOCAL;
    header->version = REMOTE_MSG_VERSION;
    header->payload_offset = iov[0].iov_len;
    header->payload_uncompressed = iov[1].iov_len;
    header->size_total = iov[0].iov_len + iov[1].iov_len;

    rc = remote_send_iovs(remote, iov, 2);
    if (rc != pcmk_rc_ok) {
        crm_err("Could not send remote message: %s " CRM_XS " rc=%d",
                pcmk_rc_str(rc), rc);
    }

    free(iov[0].iov_base);
    free(iov[1].iov_base);
    return rc;
}

xmlNode *
pcmk__remote_message_xml(pcmk__remote_t *remote)
{
    xmlNode *xml = NULL;
    struct remote_header_v0 *header = localized_remote_header(remote);

    if (header == NULL) {
        return NULL;
    }

    /* Support compression on the receiving end now, in case we ever want to add it later */
    if (header->payload_compressed) {
        int rc = 0;
        unsigned int size_u = 1 + header->payload_uncompressed;
        char *uncompressed = calloc(1, header->payload_offset + size_u);

        crm_trace("Decompressing message data %d bytes into %d bytes",
                 header->payload_compressed, size_u);

        rc = BZ2_bzBuffToBuffDecompress(uncompressed + header->payload_offset, &size_u,
                                        remote->buffer + header->payload_offset,
                                        header->payload_compressed, 1, 0);

        if (rc != BZ_OK && header->version > REMOTE_MSG_VERSION) {
            crm_warn("Couldn't decompress v%d message, we only understand v%d",
                     header->version, REMOTE_MSG_VERSION);
            free(uncompressed);
            return NULL;

        } else if (rc != BZ_OK) {
            crm_err("Decompression failed: %s " CRM_XS " bzerror=%d",
                    bz2_strerror(rc), rc);
            free(uncompressed);
            return NULL;
        }

        CRM_ASSERT(size_u == header->payload_uncompressed);

        memcpy(uncompressed, remote->buffer, header->payload_offset);       /* Preserve the header */
        remote->buffer_size = header->payload_offset + size_u;

        free(remote->buffer);
        remote->buffer = uncompressed;
        header = localized_remote_header(remote);
    }

    /* take ownership of the buffer */
    remote->buffer_offset = 0;

    CRM_LOG_ASSERT(remote->buffer[sizeof(struct remote_header_v0) + header->payload_uncompressed - 1] == 0);

    xml = string2xml(remote->buffer + header->payload_offset);
    if (xml == NULL && header->version > REMOTE_MSG_VERSION) {
        crm_warn("Couldn't parse v%d message, we only understand v%d",
                 header->version, REMOTE_MSG_VERSION);

    } else if (xml == NULL) {
        crm_err("Couldn't parse: '%.120s'", remote->buffer + header->payload_offset);
    }

    return xml;
}

static int
get_remote_socket(pcmk__remote_t *remote)
{
#ifdef HAVE_GNUTLS_GNUTLS_H
    if (remote->tls_session) {
        void *sock_ptr = gnutls_transport_get_ptr(*remote->tls_session);

        return GPOINTER_TO_INT(sock_ptr);
    }
#endif

    if (remote->tcp_socket) {
        return remote->tcp_socket;
    }

    crm_err("Remote connection type undetermined (bug?)");
    return -1;
}

int
pcmk__remote_ready(pcmk__remote_t *remote, int timeout_ms)
{
    struct pollfd fds = { 0, };
    int sock = 0;
    int rc = 0;
    time_t start;
    int timeout = timeout_ms;

    sock = get_remote_socket(remote);
    if (sock <= 0) {
        crm_trace("No longer connected");
        return ENOTCONN;
    }

    start = time(NULL);
    errno = 0;
    do {
        fds.fd = sock;
        fds.events = POLLIN;

        /* If we got an EINTR while polling, and we have a
         * specific timeout we are trying to honor, attempt
         * to adjust the timeout to the closest second. */
        if (errno == EINTR && (timeout > 0)) {
            timeout = timeout_ms - ((time(NULL) - start) * 1000);
            if (timeout < 1000) {
                timeout = 1000;
            }
        }

        rc = poll(&fds, 1, timeout);
    } while (rc < 0 && errno == EINTR);

    if (rc < 0) {
        return errno;
    }
    return (rc == 0)? ETIME : pcmk_rc_ok;
}

static int
read_available_remote_data(pcmk__remote_t *remote)
{
    int rc = pcmk_rc_ok;
    size_t read_len = sizeof(struct remote_header_v0);
    struct remote_header_v0 *header = localized_remote_header(remote);
    bool received = false;
    ssize_t read_rc;

    if(header) {
        /* Stop at the end of the current message */
        read_len = header->size_total;
    }

    /* automatically grow the buffer when needed */
    if(remote->buffer_size < read_len) {
        remote->buffer_size = 2 * read_len;
        crm_trace("Expanding buffer to %llu bytes",
                  (unsigned long long) remote->buffer_size);
        remote->buffer = pcmk__realloc(remote->buffer, remote->buffer_size + 1);
    }

#ifdef HAVE_GNUTLS_GNUTLS_H
    if (!received && remote->tls_session) {
        read_rc = gnutls_record_recv(*(remote->tls_session),
                                     remote->buffer + remote->buffer_offset,
                                     remote->buffer_size - remote->buffer_offset);
        if (read_rc == GNUTLS_E_INTERRUPTED) {
            rc = EINTR;
        } else if (read_rc == GNUTLS_E_AGAIN) {
            rc = EAGAIN;
        } else if (read_rc < 0) {
            crm_debug("TLS receive failed: %s (%lld)",
                      gnutls_strerror(read_rc), (long long) read_rc);
            rc = EIO;
        }
        received = true;
    }
#endif

    if (!received && remote->tcp_socket) {
        read_rc = read(remote->tcp_socket,
                       remote->buffer + remote->buffer_offset,
                       remote->buffer_size - remote->buffer_offset);
        if (read_rc < 0) {
            rc = errno;
        }
        received = true;
    }

    if (!received) {
        crm_err("Remote connection type undetermined (bug?)");
        return ESOCKTNOSUPPORT;
    }

    /* process any errors. */
    if (read_rc > 0) {
        remote->buffer_offset += read_rc;
        /* always null terminate buffer, the +1 to alloc always allows for this. */
        remote->buffer[remote->buffer_offset] = '\0';
        crm_trace("Received %lld more bytes (%llu total)",
                  (long long) read_rc,
                  (unsigned long long) remote->buffer_offset);

    } else if ((rc == EINTR) || (rc == EAGAIN)) {
        crm_trace("No data available for non-blocking remote read: %s (%d)",
                  pcmk_rc_str(rc), rc);

    } else if (read_rc == 0) {
        crm_debug("End of remote data encountered after %llu bytes",
                  (unsigned long long) remote->buffer_offset);
        return ENOTCONN;

    } else {
        crm_debug("Error receiving remote data after %llu bytes: %s (%d)",
                  (unsigned long long) remote->buffer_offset,
                  pcmk_rc_str(rc), rc);
        return ENOTCONN;
    }

    header = localized_remote_header(remote);
    if(header) {
        if(remote->buffer_offset < header->size_total) {
            crm_trace("Read partial remote message (%llu of %u bytes)",
                      (unsigned long long) remote->buffer_offset,
                      header->size_total);
        } else {
            crm_trace("Read full remote message of %llu bytes",
                      (unsigned long long) remote->buffer_offset);
            return pcmk_rc_ok;
        }
    }

    return EAGAIN;
}

int
pcmk__read_remote_message(pcmk__remote_t *remote, int timeout_ms)
{
    int rc = pcmk_rc_ok;
    time_t start = time(NULL);
    int remaining_timeout = 0;

    if (timeout_ms == 0) {
        timeout_ms = 10000;
    } else if (timeout_ms < 0) {
        timeout_ms = 60000;
    }

    remaining_timeout = timeout_ms;
    while (remaining_timeout > 0) {

        crm_trace("Waiting for remote data (%d ms of %d ms timeout remaining)",
                  remaining_timeout, timeout_ms);
        rc = pcmk__remote_ready(remote, remaining_timeout);

        if (rc == ETIME) {
            crm_err("Timed out (%d ms) while waiting for remote data",
                    remaining_timeout);
            return rc;

        } else if (rc != pcmk_rc_ok) {
            crm_debug("Wait for remote data aborted (will retry): %s "
                      CRM_XS " rc=%d", pcmk_rc_str(rc), rc);

        } else {
            rc = read_available_remote_data(remote);
            if (rc == pcmk_rc_ok) {
                return rc;
            } else if (rc == EAGAIN) {
                crm_trace("Waiting for more remote data");
            } else {
                crm_debug("Could not receive remote data: %s " CRM_XS " rc=%d",
                          pcmk_rc_str(rc), rc);
            }
        }

        // Don't waste time retrying after fatal errors
        if ((rc == ENOTCONN) || (rc == ESOCKTNOSUPPORT)) {
            return rc;
        }

        remaining_timeout = timeout_ms - ((time(NULL) - start) * 1000);
    }
    return ETIME;
}

struct tcp_async_cb_data {
    int sock;
    int timeout_ms;
    time_t start;
    void *userdata;
    void (*callback) (void *userdata, int rc, int sock);
};

// \return TRUE if timer should be rescheduled, FALSE otherwise
static gboolean
check_connect_finished(gpointer userdata)
{
    struct tcp_async_cb_data *cb_data = userdata;
    int rc;

    fd_set rset, wset;
    struct timeval ts = { 0, };

    if (cb_data->start == 0) {
        // Last connect() returned success immediately
        rc = pcmk_rc_ok;
        goto dispatch_done;
    }

    // If the socket is ready for reading or writing, the connect succeeded
    FD_ZERO(&rset);
    FD_SET(cb_data->sock, &rset);
    wset = rset;
    rc = select(cb_data->sock + 1, &rset, &wset, NULL, &ts);

    if (rc < 0) { // select() error
        rc = errno;
        if ((rc == EINPROGRESS) || (rc == EAGAIN)) {
            if ((time(NULL) - cb_data->start) < (cb_data->timeout_ms / 1000)) {
                return TRUE; // There is time left, so reschedule timer
            } else {
                rc = ETIMEDOUT;
            }
        }
        crm_trace("Could not check socket %d for connection success: %s (%d)",
                  cb_data->sock, pcmk_rc_str(rc), rc);

    } else if (rc == 0) { // select() timeout
        if ((time(NULL) - cb_data->start) < (cb_data->timeout_ms / 1000)) {
            return TRUE; // There is time left, so reschedule timer
        }
        crm_debug("Timed out while waiting for socket %d connection success",
                  cb_data->sock);
        rc = ETIMEDOUT;

    // select() returned number of file descriptors that are ready

    } else if (FD_ISSET(cb_data->sock, &rset)
               || FD_ISSET(cb_data->sock, &wset)) {

        // The socket is ready; check it for connection errors
        int error = 0;
        socklen_t len = sizeof(error);

        if (getsockopt(cb_data->sock, SOL_SOCKET, SO_ERROR, &error, &len) < 0) {
            rc = errno;
            crm_trace("Couldn't check socket %d for connection errors: %s (%d)",
                      cb_data->sock, pcmk_rc_str(rc), rc);
        } else if (error != 0) {
            rc = error;
            crm_trace("Socket %d connected with error: %s (%d)",
                      cb_data->sock, pcmk_rc_str(rc), rc);
        } else {
            rc = pcmk_rc_ok;
        }

    } else { // Should not be possible
        crm_trace("select() succeeded, but socket %d not in resulting "
                  "read/write sets", cb_data->sock);
        rc = EAGAIN;
    }

  dispatch_done:
    if (rc == pcmk_rc_ok) {
        crm_trace("Socket %d is connected", cb_data->sock);
    } else {
        close(cb_data->sock);
        cb_data->sock = -1;
    }

    if (cb_data->callback) {
        cb_data->callback(cb_data->userdata, rc, cb_data->sock);
    }
    free(cb_data);
    return FALSE; // Do not reschedule timer
}

static int
connect_socket_retry(int sock, const struct sockaddr *addr, socklen_t addrlen,
                     int timeout_ms, int *timer_id, void *userdata,
                     void (*callback) (void *userdata, int rc, int sock))
{
    int rc = 0;
    int interval = 500;
    int timer;
    struct tcp_async_cb_data *cb_data = NULL;

    rc = pcmk__set_nonblocking(sock);
    if (rc != pcmk_rc_ok) {
        crm_warn("Could not set socket non-blocking: %s " CRM_XS " rc=%d",
                 pcmk_rc_str(rc), rc);
        return rc;
    }

    rc = connect(sock, addr, addrlen);
    if (rc < 0 && (errno != EINPROGRESS) && (errno != EAGAIN)) {
        rc = errno;
        crm_warn("Could not connect socket: %s " CRM_XS " rc=%d",
                 pcmk_rc_str(rc), rc);
        return rc;
    }

    cb_data = calloc(1, sizeof(struct tcp_async_cb_data));
    cb_data->userdata = userdata;
    cb_data->callback = callback;
    cb_data->sock = sock;
    cb_data->timeout_ms = timeout_ms;

    if (rc == 0) {
        /* The connect was successful immediately, we still return to mainloop
         * and let this callback get called later. This avoids the user of this api
         * to have to account for the fact the callback could be invoked within this
         * function before returning. */
        cb_data->start = 0;
        interval = 1;
    } else {
        cb_data->start = time(NULL);
    }

    /* This timer function does a non-blocking poll on the socket to see if we
     * can use it. Once we can, the connect has completed. This method allows us
     * to connect without blocking the mainloop.
     *
     * @TODO Use a mainloop fd callback for this instead of polling. Something
     *       about the way mainloop is currently polling prevents this from
     *       working at the moment though. (See connect(2) regarding EINPROGRESS
     *       for possible new handling needed.)
     */
    crm_trace("Scheduling check in %dms for whether connect to fd %d finished",
              interval, sock);
    timer = g_timeout_add(interval, check_connect_finished, cb_data);
    if (timer_id) {
        *timer_id = timer;
    }

    // timer callback should be taking care of cb_data
    // cppcheck-suppress memleak
    return pcmk_rc_ok;
}

static int
connect_socket_once(int sock, const struct sockaddr *addr, socklen_t addrlen)
{
    int rc = connect(sock, addr, addrlen);

    if (rc < 0) {
        rc = errno;
        crm_warn("Could not connect socket: %s " CRM_XS " rc=%d",
                 pcmk_rc_str(rc), rc);
        return rc;
    }

    rc = pcmk__set_nonblocking(sock);
    if (rc != pcmk_rc_ok) {
        crm_warn("Could not set socket non-blocking: %s " CRM_XS " rc=%d",
                 pcmk_rc_str(rc), rc);
        return rc;
    }

    return pcmk_ok;
}

int
pcmk__connect_remote(const char *host, int port, int timeout, int *timer_id,
                     int *sock_fd, void *userdata,
                     void (*callback) (void *userdata, int rc, int sock))
{
    char buffer[INET6_ADDRSTRLEN];
    struct addrinfo *res = NULL;
    struct addrinfo *rp = NULL;
    struct addrinfo hints;
    const char *server = host;
    int rc;
    int sock = -1;

    CRM_CHECK((host != NULL) && (sock_fd != NULL), return EINVAL);

    // Get host's IP address(es)
    memset(&hints, 0, sizeof(struct addrinfo));
    hints.ai_family = AF_UNSPEC;        /* Allow IPv4 or IPv6 */
    hints.ai_socktype = SOCK_STREAM;
    hints.ai_flags = AI_CANONNAME;
    rc = getaddrinfo(server, NULL, &hints, &res);
    if (rc != 0) {
        crm_err("Unable to get IP address info for %s: %s",
                server, gai_strerror(rc));
        rc = ENOTCONN;
        goto async_cleanup;
    }
    if (!res || !res->ai_addr) {
        crm_err("Unable to get IP address info for %s: no result", server);
        rc = ENOTCONN;
        goto async_cleanup;
    }

    // getaddrinfo() returns a list of host's addresses, try them in order
    for (rp = res; rp != NULL; rp = rp->ai_next) {
        struct sockaddr *addr = rp->ai_addr;

        if (!addr) {
            continue;
        }

        if (rp->ai_canonname) {
            server = res->ai_canonname;
        }
        crm_debug("Got canonical name %s for %s", server, host);

        sock = socket(rp->ai_family, SOCK_STREAM, IPPROTO_TCP);
        if (sock == -1) {
            rc = errno;
            crm_warn("Could not create socket for remote connection to %s:%d: "
                     "%s " CRM_XS " rc=%d", server, port, pcmk_rc_str(rc), rc);
            continue;
        }

        /* Set port appropriately for address family */
        /* (void*) casts avoid false-positive compiler alignment warnings */
        if (addr->sa_family == AF_INET6) {
            ((struct sockaddr_in6 *)(void*)addr)->sin6_port = htons(port);
        } else {
            ((struct sockaddr_in *)(void*)addr)->sin_port = htons(port);
        }

        memset(buffer, 0, PCMK__NELEM(buffer));
        pcmk__sockaddr2str(addr, buffer);
        crm_info("Attempting remote connection to %s:%d", buffer, port);

        if (callback) {
            if (connect_socket_retry(sock, rp->ai_addr, rp->ai_addrlen, timeout,
                                     timer_id, userdata, callback) == pcmk_rc_ok) {
                goto async_cleanup; /* Success for now, we'll hear back later in the callback */
            }

        } else if (connect_socket_once(sock, rp->ai_addr,
                                       rp->ai_addrlen) == pcmk_rc_ok) {
            break;          /* Success */
        }

        // Connect failed
        close(sock);
        sock = -1;
        rc = ENOTCONN;
    }

async_cleanup:

    if (res) {
        freeaddrinfo(res);
    }
    *sock_fd = sock;
    return rc;
}

void
pcmk__sockaddr2str(void *sa, char *s)
{
    switch (((struct sockaddr*)sa)->sa_family) {
        case AF_INET:
            inet_ntop(AF_INET, &(((struct sockaddr_in *)sa)->sin_addr),
                      s, INET6_ADDRSTRLEN);
            break;

        case AF_INET6:
            inet_ntop(AF_INET6, &(((struct sockaddr_in6 *)sa)->sin6_addr),
                      s, INET6_ADDRSTRLEN);
            break;

        default:
            strcpy(s, "<invalid>");
    }
}

int
pcmk__accept_remote_connection(int ssock, int *csock)
{
    int rc;
    struct sockaddr_storage addr;
    socklen_t laddr = sizeof(addr);
    char addr_str[INET6_ADDRSTRLEN];

    /* accept the connection */
    memset(&addr, 0, sizeof(addr));
    *csock = accept(ssock, (struct sockaddr *)&addr, &laddr);
    if (*csock == -1) {
        rc = errno;
        crm_err("Could not accept remote client connection: %s "
                CRM_XS " rc=%d", pcmk_rc_str(rc), rc);
        return rc;
    }
    pcmk__sockaddr2str(&addr, addr_str);
    crm_info("Accepted new remote client connection from %s", addr_str);

    rc = pcmk__set_nonblocking(*csock);
    if (rc != pcmk_rc_ok) {
        crm_err("Could not set socket non-blocking: %s " CRM_XS " rc=%d",
                pcmk_rc_str(rc), rc);
        close(*csock);
        *csock = -1;
        return rc;
    }

#ifdef TCP_USER_TIMEOUT
    if (pcmk__get_sbd_timeout() > 0) {
        // Time to fail and retry before watchdog
        unsigned int optval = (unsigned int) pcmk__get_sbd_timeout() / 2;

        rc = setsockopt(*csock, SOL_TCP, TCP_USER_TIMEOUT,
                        &optval, sizeof(optval));
        if (rc < 0) {
            rc = errno;
            crm_err("Could not set TCP timeout to %d ms on remote connection: "
                    "%s " CRM_XS " rc=%d", optval, pcmk_rc_str(rc), rc);
            close(*csock);
            *csock = -1;
            return rc;
        }
    }
#endif

    return rc;
}

int
crm_default_remote_port()
{
    static int port = 0;

    if (port == 0) {
        const char *env = getenv("PCMK_remote_port");

        if (env) {
            errno = 0;
            port = strtol(env, NULL, 10);
            if (errno || (port < 1) || (port > 65535)) {
                crm_warn("Environment variable PCMK_remote_port has invalid value '%s', using %d instead",
                         env, DEFAULT_REMOTE_PORT);
                port = DEFAULT_REMOTE_PORT;
            }
        } else {
            port = DEFAULT_REMOTE_PORT;
        }
    }
    return port;
}