pqcomm.c

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/*-------------------------------------------------------------------------
 *
 * pqcomm.c
 *    Communication functions between the Frontend and the Backend
 *
 * These routines handle the low-level details of communication between
 * frontend and backend.  They just shove data across the communication
 * channel, and are ignorant of the semantics of the data --- or would be,
 * except for major brain damage in the design of the old COPY OUT protocol.
 * Unfortunately, COPY OUT was designed to commandeer the communication
 * channel (it just transfers data without wrapping it into messages).
 * No other messages can be sent while COPY OUT is in progress; and if the
 * copy is aborted by an ereport(ERROR), we need to close out the copy so that
 * the frontend gets back into sync.  Therefore, these routines have to be
 * aware of COPY OUT state.  (New COPY-OUT is message-based and does *not*
 * set the DoingCopyOut flag.)
 *
 * NOTE: generally, it's a bad idea to emit outgoing messages directly with
 * pq_putbytes(), especially if the message would require multiple calls
 * to send.  Instead, use the routines in pqformat.c to construct the message
 * in a buffer and then emit it in one call to pq_putmessage.  This ensures
 * that the channel will not be clogged by an incomplete message if execution
 * is aborted by ereport(ERROR) partway through the message.  The only
 * non-libpq code that should call pq_putbytes directly is old-style COPY OUT.
 *
 * At one time, libpq was shared between frontend and backend, but now
 * the backend's "backend/libpq" is quite separate from "interfaces/libpq".
 * All that remains is similarities of names to trap the unwary...
 *
 * Portions Copyright (c) 1996-2013, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *  src/backend/libpq/pqcomm.c
 *
 *-------------------------------------------------------------------------
 */

/*------------------------
 * INTERFACE ROUTINES
 *
 * setup/teardown:
 *      StreamServerPort    - Open postmaster's server port
 *      StreamConnection    - Create new connection with client
 *      StreamClose         - Close a client/backend connection
 *      TouchSocketFiles    - Protect socket files against /tmp cleaners
 *      pq_init         - initialize libpq at backend startup
 *      pq_comm_reset   - reset libpq during error recovery
 *      pq_close        - shutdown libpq at backend exit
 *
 * low-level I/O:
 *      pq_getbytes     - get a known number of bytes from connection
 *      pq_getstring    - get a null terminated string from connection
 *      pq_getmessage   - get a message with length word from connection
 *      pq_getbyte      - get next byte from connection
 *      pq_peekbyte     - peek at next byte from connection
 *      pq_putbytes     - send bytes to connection (not flushed until pq_flush)
 *      pq_flush        - flush pending output
 *      pq_flush_if_writable - flush pending output if writable without blocking
 *      pq_getbyte_if_available - get a byte if available without blocking
 *
 * message-level I/O (and old-style-COPY-OUT cruft):
 *      pq_putmessage   - send a normal message (suppressed in COPY OUT mode)
 *      pq_putmessage_noblock - buffer a normal message (suppressed in COPY OUT)
 *      pq_startcopyout - inform libpq that a COPY OUT transfer is beginning
 *      pq_endcopyout   - end a COPY OUT transfer
 *
 *------------------------
 */
#include "postgres.h"

#include <signal.h>
#include <fcntl.h>
#include <grp.h>
#include <unistd.h>
#include <sys/file.h>
#include <sys/socket.h>
#include <sys/stat.h>
#include <sys/time.h>
#include <netdb.h>
#include <netinet/in.h>
#ifdef HAVE_NETINET_TCP_H
#include <netinet/tcp.h>
#endif
#include <arpa/inet.h>
#ifdef HAVE_UTIME_H
#include <utime.h>
#endif
#ifdef WIN32_ONLY_COMPILER      /* mstcpip.h is missing on mingw */
#include <mstcpip.h>
#endif

#include "libpq/ip.h"
#include "libpq/libpq.h"
#include "miscadmin.h"
#include "storage/ipc.h"
#include "utils/guc.h"
#include "utils/memutils.h"

/*
 * Configuration options
 */
int         Unix_socket_permissions;
char       *Unix_socket_group;


/* Where the Unix socket files are (list of palloc'd strings) */
static List *sock_paths = NIL;


/*
 * Buffers for low-level I/O.
 *
 * The receive buffer is fixed size. Send buffer is usually 8k, but can be
 * enlarged by pq_putmessage_noblock() if the message doesn't fit otherwise.
 */

#define PQ_SEND_BUFFER_SIZE 8192
#define PQ_RECV_BUFFER_SIZE 8192

static char *PqSendBuffer;
static int  PqSendBufferSize;   /* Size send buffer */
static int  PqSendPointer;      /* Next index to store a byte in PqSendBuffer */
static int  PqSendStart;        /* Next index to send a byte in PqSendBuffer */

static char PqRecvBuffer[PQ_RECV_BUFFER_SIZE];
static int  PqRecvPointer;      /* Next index to read a byte from PqRecvBuffer */
static int  PqRecvLength;       /* End of data available in PqRecvBuffer */

/*
 * Message status
 */
static bool PqCommBusy;
static bool DoingCopyOut;


/* Internal functions */
static void pq_close(int code, Datum arg);
static int  internal_putbytes(const char *s, size_t len);
static int  internal_flush(void);
static void pq_set_nonblocking(bool nonblocking);

#ifdef HAVE_UNIX_SOCKETS
static int  Lock_AF_UNIX(char *unixSocketDir, char *unixSocketPath);
static int  Setup_AF_UNIX(char *sock_path);
#endif   /* HAVE_UNIX_SOCKETS */


/* --------------------------------
 *      pq_init - initialize libpq at backend startup
 * --------------------------------
 */
void
pq_init(void)
{
    PqSendBufferSize = PQ_SEND_BUFFER_SIZE;
    PqSendBuffer = MemoryContextAlloc(TopMemoryContext, PqSendBufferSize);
    PqSendPointer = PqSendStart = PqRecvPointer = PqRecvLength = 0;
    PqCommBusy = false;
    DoingCopyOut = false;
    on_proc_exit(pq_close, 0);
}

/* --------------------------------
 *      pq_comm_reset - reset libpq during error recovery
 *
 * This is called from error recovery at the outer idle loop.  It's
 * just to get us out of trouble if we somehow manage to elog() from
 * inside a pqcomm.c routine (which ideally will never happen, but...)
 * --------------------------------
 */
void
pq_comm_reset(void)
{
    /* Do not throw away pending data, but do reset the busy flag */
    PqCommBusy = false;
    /* We can abort any old-style COPY OUT, too */
    pq_endcopyout(true);
}

/* --------------------------------
 *      pq_close - shutdown libpq at backend exit
 *
 * Note: in a standalone backend MyProcPort will be null,
 * don't crash during exit...
 * --------------------------------
 */
static void
pq_close(int code, Datum arg)
{
    if (MyProcPort != NULL)
    {
#if defined(ENABLE_GSS) || defined(ENABLE_SSPI)
#ifdef ENABLE_GSS
        OM_uint32   min_s;

        /* Shutdown GSSAPI layer */
        if (MyProcPort->gss->ctx != GSS_C_NO_CONTEXT)
            gss_delete_sec_context(&min_s, &MyProcPort->gss->ctx, NULL);

        if (MyProcPort->gss->cred != GSS_C_NO_CREDENTIAL)
            gss_release_cred(&min_s, &MyProcPort->gss->cred);
#endif   /* ENABLE_GSS */
        /* GSS and SSPI share the port->gss struct */

        free(MyProcPort->gss);
#endif   /* ENABLE_GSS || ENABLE_SSPI */

        /* Cleanly shut down SSL layer */
        secure_close(MyProcPort);

        /*
         * Formerly we did an explicit close() here, but it seems better to
         * leave the socket open until the process dies.  This allows clients
         * to perform a "synchronous close" if they care --- wait till the
         * transport layer reports connection closure, and you can be sure the
         * backend has exited.
         *
         * We do set sock to PGINVALID_SOCKET to prevent any further I/O,
         * though.
         */
        MyProcPort->sock = PGINVALID_SOCKET;
    }
}



/*
 * Streams -- wrapper around Unix socket system calls
 *
 *
 *      Stream functions are used for vanilla TCP connection protocol.
 */


/* StreamDoUnlink()
 * Shutdown routine for backend connection
 * If any Unix sockets are used for communication, explicitly close them.
 */
#ifdef HAVE_UNIX_SOCKETS
static void
StreamDoUnlink(int code, Datum arg)
{
    ListCell   *l;

    /* Loop through all created sockets... */
    foreach(l, sock_paths)
    {
        char       *sock_path = (char *) lfirst(l);

        unlink(sock_path);
    }
    /* Since we're about to exit, no need to reclaim storage */
    sock_paths = NIL;
}
#endif   /* HAVE_UNIX_SOCKETS */

/*
 * StreamServerPort -- open a "listening" port to accept connections.
 *
 * family should be AF_UNIX or AF_UNSPEC; portNumber is the port number.
 * For AF_UNIX ports, hostName should be NULL and unixSocketDir must be
 * specified.  For TCP ports, hostName is either NULL for all interfaces or
 * the interface to listen on, and unixSocketDir is ignored (can be NULL).
 *
 * Successfully opened sockets are added to the ListenSocket[] array (of
 * length MaxListen), at the first position that isn't PGINVALID_SOCKET.
 *
 * RETURNS: STATUS_OK or STATUS_ERROR
 */

int
StreamServerPort(int family, char *hostName, unsigned short portNumber,
                 char *unixSocketDir,
                 pgsocket ListenSocket[], int MaxListen)
{
    pgsocket    fd;
    int         err;
    int         maxconn;
    int         ret;
    char        portNumberStr[32];
    const char *familyDesc;
    char        familyDescBuf[64];
    char       *service;
    struct addrinfo *addrs = NULL,
               *addr;
    struct addrinfo hint;
    int         listen_index = 0;
    int         added = 0;

#ifdef HAVE_UNIX_SOCKETS
    char        unixSocketPath[MAXPGPATH];
#endif
#if !defined(WIN32) || defined(IPV6_V6ONLY)
    int         one = 1;
#endif

    /* Initialize hint structure */
    MemSet(&hint, 0, sizeof(hint));
    hint.ai_family = family;
    hint.ai_flags = AI_PASSIVE;
    hint.ai_socktype = SOCK_STREAM;

#ifdef HAVE_UNIX_SOCKETS
    if (family == AF_UNIX)
    {
        /*
         * Create unixSocketPath from portNumber and unixSocketDir and lock
         * that file path
         */
        UNIXSOCK_PATH(unixSocketPath, portNumber, unixSocketDir);
        if (strlen(unixSocketPath) >= UNIXSOCK_PATH_BUFLEN)
        {
            ereport(LOG,
                    (errmsg("Unix-domain socket path \"%s\" is too long (maximum %d bytes)",
                            unixSocketPath,
                            (int) (UNIXSOCK_PATH_BUFLEN - 1))));
            return STATUS_ERROR;
        }
        if (Lock_AF_UNIX(unixSocketDir, unixSocketPath) != STATUS_OK)
            return STATUS_ERROR;
        service = unixSocketPath;
    }
    else
#endif   /* HAVE_UNIX_SOCKETS */
    {
        snprintf(portNumberStr, sizeof(portNumberStr), "%d", portNumber);
        service = portNumberStr;
    }

    ret = pg_getaddrinfo_all(hostName, service, &hint, &addrs);
    if (ret || !addrs)
    {
        if (hostName)
            ereport(LOG,
                    (errmsg("could not translate host name \"%s\", service \"%s\" to address: %s",
                            hostName, service, gai_strerror(ret))));
        else
            ereport(LOG,
                 (errmsg("could not translate service \"%s\" to address: %s",
                         service, gai_strerror(ret))));
        if (addrs)
            pg_freeaddrinfo_all(hint.ai_family, addrs);
        return STATUS_ERROR;
    }

    for (addr = addrs; addr; addr = addr->ai_next)
    {
        if (!IS_AF_UNIX(family) && IS_AF_UNIX(addr->ai_family))
        {
            /*
             * Only set up a unix domain socket when they really asked for it.
             * The service/port is different in that case.
             */
            continue;
        }

        /* See if there is still room to add 1 more socket. */
        for (; listen_index < MaxListen; listen_index++)
        {
            if (ListenSocket[listen_index] == PGINVALID_SOCKET)
                break;
        }
        if (listen_index >= MaxListen)
        {
            ereport(LOG,
                    (errmsg("could not bind to all requested addresses: MAXLISTEN (%d) exceeded",
                            MaxListen)));
            break;
        }

        /* set up family name for possible error messages */
        switch (addr->ai_family)
        {
            case AF_INET:
                familyDesc = _("IPv4");
                break;
#ifdef HAVE_IPV6
            case AF_INET6:
                familyDesc = _("IPv6");
                break;
#endif
#ifdef HAVE_UNIX_SOCKETS
            case AF_UNIX:
                familyDesc = _("Unix");
                break;
#endif
            default:
                snprintf(familyDescBuf, sizeof(familyDescBuf),
                         _("unrecognized address family %d"),
                         addr->ai_family);
                familyDesc = familyDescBuf;
                break;
        }

        if ((fd = socket(addr->ai_family, SOCK_STREAM, 0)) < 0)
        {
            ereport(LOG,
                    (errcode_for_socket_access(),
            /* translator: %s is IPv4, IPv6, or Unix */
                     errmsg("could not create %s socket: %m",
                            familyDesc)));
            continue;
        }

#ifndef WIN32

        /*
         * Without the SO_REUSEADDR flag, a new postmaster can't be started
         * right away after a stop or crash, giving "address already in use"
         * error on TCP ports.
         *
         * On win32, however, this behavior only happens if the
         * SO_EXLUSIVEADDRUSE is set. With SO_REUSEADDR, win32 allows multiple
         * servers to listen on the same address, resulting in unpredictable
         * behavior. With no flags at all, win32 behaves as Unix with
         * SO_REUSEADDR.
         */
        if (!IS_AF_UNIX(addr->ai_family))
        {
            if ((setsockopt(fd, SOL_SOCKET, SO_REUSEADDR,
                            (char *) &one, sizeof(one))) == -1)
            {
                ereport(LOG,
                        (errcode_for_socket_access(),
                         errmsg("setsockopt(SO_REUSEADDR) failed: %m")));
                closesocket(fd);
                continue;
            }
        }
#endif

#ifdef IPV6_V6ONLY
        if (addr->ai_family == AF_INET6)
        {
            if (setsockopt(fd, IPPROTO_IPV6, IPV6_V6ONLY,
                           (char *) &one, sizeof(one)) == -1)
            {
                ereport(LOG,
                        (errcode_for_socket_access(),
                         errmsg("setsockopt(IPV6_V6ONLY) failed: %m")));
                closesocket(fd);
                continue;
            }
        }
#endif

        /*
         * Note: This might fail on some OS's, like Linux older than
         * 2.4.21-pre3, that don't have the IPV6_V6ONLY socket option, and map
         * ipv4 addresses to ipv6.  It will show ::ffff:ipv4 for all ipv4
         * connections.
         */
        err = bind(fd, addr->ai_addr, addr->ai_addrlen);
        if (err < 0)
        {
            ereport(LOG,
                    (errcode_for_socket_access(),
            /* translator: %s is IPv4, IPv6, or Unix */
                     errmsg("could not bind %s socket: %m",
                            familyDesc),
                     (IS_AF_UNIX(addr->ai_family)) ?
                  errhint("Is another postmaster already running on port %d?"
                          " If not, remove socket file \"%s\" and retry.",
                          (int) portNumber, service) :
                  errhint("Is another postmaster already running on port %d?"
                          " If not, wait a few seconds and retry.",
                          (int) portNumber)));
            closesocket(fd);
            continue;
        }

#ifdef HAVE_UNIX_SOCKETS
        if (addr->ai_family == AF_UNIX)
        {
            if (Setup_AF_UNIX(service) != STATUS_OK)
            {
                closesocket(fd);
                break;
            }
        }
#endif

        /*
         * Select appropriate accept-queue length limit.  PG_SOMAXCONN is only
         * intended to provide a clamp on the request on platforms where an
         * overly large request provokes a kernel error (are there any?).
         */
        maxconn = MaxBackends * 2;
        if (maxconn > PG_SOMAXCONN)
            maxconn = PG_SOMAXCONN;

        err = listen(fd, maxconn);
        if (err < 0)
        {
            ereport(LOG,
                    (errcode_for_socket_access(),
            /* translator: %s is IPv4, IPv6, or Unix */
                     errmsg("could not listen on %s socket: %m",
                            familyDesc)));
            closesocket(fd);
            continue;
        }
        ListenSocket[listen_index] = fd;
        added++;
    }

    pg_freeaddrinfo_all(hint.ai_family, addrs);

    if (!added)
        return STATUS_ERROR;

    return STATUS_OK;
}


#ifdef HAVE_UNIX_SOCKETS

/*
 * Lock_AF_UNIX -- configure unix socket file path
 */
static int
Lock_AF_UNIX(char *unixSocketDir, char *unixSocketPath)
{
    /*
     * Grab an interlock file associated with the socket file.
     *
     * Note: there are two reasons for using a socket lock file, rather than
     * trying to interlock directly on the socket itself.  First, it's a lot
     * more portable, and second, it lets us remove any pre-existing socket
     * file without race conditions.
     */
    CreateSocketLockFile(unixSocketPath, true, unixSocketDir);

    /*
     * Once we have the interlock, we can safely delete any pre-existing
     * socket file to avoid failure at bind() time.
     */
    unlink(unixSocketPath);

    /*
     * Arrange to unlink the socket file(s) at proc_exit.  If this is the
     * first one, set up the on_proc_exit function to do it; then add this
     * socket file to the list of files to unlink.
     */
    if (sock_paths == NIL)
        on_proc_exit(StreamDoUnlink, 0);

    sock_paths = lappend(sock_paths, pstrdup(unixSocketPath));

    return STATUS_OK;
}


/*
 * Setup_AF_UNIX -- configure unix socket permissions
 */
static int
Setup_AF_UNIX(char *sock_path)
{
    /*
     * Fix socket ownership/permission if requested.  Note we must do this
     * before we listen() to avoid a window where unwanted connections could
     * get accepted.
     */
    Assert(Unix_socket_group);
    if (Unix_socket_group[0] != '\0')
    {
#ifdef WIN32
        elog(WARNING, "configuration item unix_socket_group is not supported on this platform");
#else
        char       *endptr;
        unsigned long val;
        gid_t       gid;

        val = strtoul(Unix_socket_group, &endptr, 10);
        if (*endptr == '\0')
        {                       /* numeric group id */
            gid = val;
        }
        else
        {                       /* convert group name to id */
            struct group *gr;

            gr = getgrnam(Unix_socket_group);
            if (!gr)
            {
                ereport(LOG,
                        (errmsg("group \"%s\" does not exist",
                                Unix_socket_group)));
                return STATUS_ERROR;
            }
            gid = gr->gr_gid;
        }
        if (chown(sock_path, -1, gid) == -1)
        {
            ereport(LOG,
                    (errcode_for_file_access(),
                     errmsg("could not set group of file \"%s\": %m",
                            sock_path)));
            return STATUS_ERROR;
        }
#endif
    }

    if (chmod(sock_path, Unix_socket_permissions) == -1)
    {
        ereport(LOG,
                (errcode_for_file_access(),
                 errmsg("could not set permissions of file \"%s\": %m",
                        sock_path)));
        return STATUS_ERROR;
    }
    return STATUS_OK;
}
#endif   /* HAVE_UNIX_SOCKETS */


/*
 * StreamConnection -- create a new connection with client using
 *      server port.  Set port->sock to the FD of the new connection.
 *
 * ASSUME: that this doesn't need to be non-blocking because
 *      the Postmaster uses select() to tell when the server master
 *      socket is ready for accept().
 *
 * RETURNS: STATUS_OK or STATUS_ERROR
 */
int
StreamConnection(pgsocket server_fd, Port *port)
{
    /* accept connection and fill in the client (remote) address */
    port->raddr.salen = sizeof(port->raddr.addr);
    if ((port->sock = accept(server_fd,
                             (struct sockaddr *) & port->raddr.addr,
                             &port->raddr.salen)) < 0)
    {
        ereport(LOG,
                (errcode_for_socket_access(),
                 errmsg("could not accept new connection: %m")));

        /*
         * If accept() fails then postmaster.c will still see the server
         * socket as read-ready, and will immediately try again.  To avoid
         * uselessly sucking lots of CPU, delay a bit before trying again.
         * (The most likely reason for failure is being out of kernel file
         * table slots; we can do little except hope some will get freed up.)
         */
        pg_usleep(100000L);     /* wait 0.1 sec */
        return STATUS_ERROR;
    }

#ifdef SCO_ACCEPT_BUG

    /*
     * UnixWare 7+ and OpenServer 5.0.4 are known to have this bug, but it
     * shouldn't hurt to catch it for all versions of those platforms.
     */
    if (port->raddr.addr.ss_family == 0)
        port->raddr.addr.ss_family = AF_UNIX;
#endif

    /* fill in the server (local) address */
    port->laddr.salen = sizeof(port->laddr.addr);
    if (getsockname(port->sock,
                    (struct sockaddr *) & port->laddr.addr,
                    &port->laddr.salen) < 0)
    {
        elog(LOG, "getsockname() failed: %m");
        return STATUS_ERROR;
    }

    /* select NODELAY and KEEPALIVE options if it's a TCP connection */
    if (!IS_AF_UNIX(port->laddr.addr.ss_family))
    {
        int         on;

#ifdef  TCP_NODELAY
        on = 1;
        if (setsockopt(port->sock, IPPROTO_TCP, TCP_NODELAY,
                       (char *) &on, sizeof(on)) < 0)
        {
            elog(LOG, "setsockopt(TCP_NODELAY) failed: %m");
            return STATUS_ERROR;
        }
#endif
        on = 1;
        if (setsockopt(port->sock, SOL_SOCKET, SO_KEEPALIVE,
                       (char *) &on, sizeof(on)) < 0)
        {
            elog(LOG, "setsockopt(SO_KEEPALIVE) failed: %m");
            return STATUS_ERROR;
        }

#ifdef WIN32

        /*
         * This is a Win32 socket optimization.  The ideal size is 32k.
         * http://support.microsoft.com/kb/823764/EN-US/
         */
        on = PQ_SEND_BUFFER_SIZE * 4;
        if (setsockopt(port->sock, SOL_SOCKET, SO_SNDBUF, (char *) &on,
                       sizeof(on)) < 0)
        {
            elog(LOG, "setsockopt(SO_SNDBUF) failed: %m");
            return STATUS_ERROR;
        }
#endif

        /*
         * Also apply the current keepalive parameters.  If we fail to set a
         * parameter, don't error out, because these aren't universally
         * supported.  (Note: you might think we need to reset the GUC
         * variables to 0 in such a case, but it's not necessary because the
         * show hooks for these variables report the truth anyway.)
         */
        (void) pq_setkeepalivesidle(tcp_keepalives_idle, port);
        (void) pq_setkeepalivesinterval(tcp_keepalives_interval, port);
        (void) pq_setkeepalivescount(tcp_keepalives_count, port);
    }

    return STATUS_OK;
}

/*
 * StreamClose -- close a client/backend connection
 *
 * NOTE: this is NOT used to terminate a session; it is just used to release
 * the file descriptor in a process that should no longer have the socket
 * open.  (For example, the postmaster calls this after passing ownership
 * of the connection to a child process.)  It is expected that someone else
 * still has the socket open.  So, we only want to close the descriptor,
 * we do NOT want to send anything to the far end.
 */
void
StreamClose(pgsocket sock)
{
    closesocket(sock);
}

/*
 * TouchSocketFiles -- mark socket files as recently accessed
 *
 * This routine should be called every so often to ensure that the socket
 * files have a recent mod date (ordinary operations on sockets usually won't
 * change the mod date).  That saves them from being removed by
 * overenthusiastic /tmp-directory-cleaner daemons.  (Another reason we should
 * never have put the socket file in /tmp...)
 */
void
TouchSocketFiles(void)
{
    ListCell   *l;

    /* Loop through all created sockets... */
    foreach(l, sock_paths)
    {
        char       *sock_path = (char *) lfirst(l);

        /*
         * utime() is POSIX standard, utimes() is a common alternative. If we
         * have neither, there's no way to affect the mod or access time of
         * the socket :-(
         *
         * In either path, we ignore errors; there's no point in complaining.
         */
#ifdef HAVE_UTIME
        utime(sock_path, NULL);
#else                           /* !HAVE_UTIME */
#ifdef HAVE_UTIMES
        utimes(sock_path, NULL);
#endif   /* HAVE_UTIMES */
#endif   /* HAVE_UTIME */
    }
}


/* --------------------------------
 * Low-level I/O routines begin here.
 *
 * These routines communicate with a frontend client across a connection
 * already established by the preceding routines.
 * --------------------------------
 */

/* --------------------------------
 *            pq_set_nonblocking - set socket blocking/non-blocking
 *
 * Sets the socket non-blocking if nonblocking is TRUE, or sets it
 * blocking otherwise.
 * --------------------------------
 */
static void
pq_set_nonblocking(bool nonblocking)
{
    if (MyProcPort->noblock == nonblocking)
        return;

#ifdef WIN32
    pgwin32_noblock = nonblocking ? 1 : 0;
#else

    /*
     * Use COMMERROR on failure, because ERROR would try to send the error to
     * the client, which might require changing the mode again, leading to
     * infinite recursion.
     */
    if (nonblocking)
    {
        if (!pg_set_noblock(MyProcPort->sock))
            ereport(COMMERROR,
                  (errmsg("could not set socket to nonblocking mode: %m")));
    }
    else
    {
        if (!pg_set_block(MyProcPort->sock))
            ereport(COMMERROR,
                    (errmsg("could not set socket to blocking mode: %m")));
    }
#endif
    MyProcPort->noblock = nonblocking;
}

/* --------------------------------
 *      pq_recvbuf - load some bytes into the input buffer
 *
 *      returns 0 if OK, EOF if trouble
 * --------------------------------
 */
static int
pq_recvbuf(void)
{
    if (PqRecvPointer > 0)
    {
        if (PqRecvLength > PqRecvPointer)
        {
            /* still some unread data, left-justify it in the buffer */
            memmove(PqRecvBuffer, PqRecvBuffer + PqRecvPointer,
                    PqRecvLength - PqRecvPointer);
            PqRecvLength -= PqRecvPointer;
            PqRecvPointer = 0;
        }
        else
            PqRecvLength = PqRecvPointer = 0;
    }

    /* Ensure that we're in blocking mode */
    pq_set_nonblocking(false);

    /* Can fill buffer from PqRecvLength and upwards */
    for (;;)
    {
        int         r;

        r = secure_read(MyProcPort, PqRecvBuffer + PqRecvLength,
                        PQ_RECV_BUFFER_SIZE - PqRecvLength);

        if (r < 0)
        {
            if (errno == EINTR)
                continue;       /* Ok if interrupted */

            /*
             * Careful: an ereport() that tries to write to the client would
             * cause recursion to here, leading to stack overflow and core
             * dump!  This message must go *only* to the postmaster log.
             */
            ereport(COMMERROR,
                    (errcode_for_socket_access(),
                     errmsg("could not receive data from client: %m")));
            return EOF;
        }
        if (r == 0)
        {
            /*
             * EOF detected.  We used to write a log message here, but it's
             * better to expect the ultimate caller to do that.
             */
            return EOF;
        }
        /* r contains number of bytes read, so just incr length */
        PqRecvLength += r;
        return 0;
    }
}

/* --------------------------------
 *      pq_getbyte  - get a single byte from connection, or return EOF
 * --------------------------------
 */
int
pq_getbyte(void)
{
    while (PqRecvPointer >= PqRecvLength)
    {
        if (pq_recvbuf())       /* If nothing in buffer, then recv some */
            return EOF;         /* Failed to recv data */
    }
    return (unsigned char) PqRecvBuffer[PqRecvPointer++];
}

/* --------------------------------
 *      pq_peekbyte     - peek at next byte from connection
 *
 *   Same as pq_getbyte() except we don't advance the pointer.
 * --------------------------------
 */
int
pq_peekbyte(void)
{
    while (PqRecvPointer >= PqRecvLength)
    {
        if (pq_recvbuf())       /* If nothing in buffer, then recv some */
            return EOF;         /* Failed to recv data */
    }
    return (unsigned char) PqRecvBuffer[PqRecvPointer];
}

/* --------------------------------
 *      pq_getbyte_if_available - get a single byte from connection,
 *          if available
 *
 * The received byte is stored in *c. Returns 1 if a byte was read,
 * 0 if no data was available, or EOF if trouble.
 * --------------------------------
 */
int
pq_getbyte_if_available(unsigned char *c)
{
    int         r;

    if (PqRecvPointer < PqRecvLength)
    {
        *c = PqRecvBuffer[PqRecvPointer++];
        return 1;
    }

    /* Put the socket into non-blocking mode */
    pq_set_nonblocking(true);

    r = secure_read(MyProcPort, c, 1);
    if (r < 0)
    {
        /*
         * Ok if no data available without blocking or interrupted (though
         * EINTR really shouldn't happen with a non-blocking socket). Report
         * other errors.
         */
        if (errno == EAGAIN || errno == EWOULDBLOCK || errno == EINTR)
            r = 0;
        else
        {
            /*
             * Careful: an ereport() that tries to write to the client would
             * cause recursion to here, leading to stack overflow and core
             * dump!  This message must go *only* to the postmaster log.
             */
            ereport(COMMERROR,
                    (errcode_for_socket_access(),
                     errmsg("could not receive data from client: %m")));
            r = EOF;
        }
    }
    else if (r == 0)
    {
        /* EOF detected */
        r = EOF;
    }

    return r;
}

/* --------------------------------
 *      pq_getbytes     - get a known number of bytes from connection
 *
 *      returns 0 if OK, EOF if trouble
 * --------------------------------
 */
int
pq_getbytes(char *s, size_t len)
{
    size_t      amount;

    while (len > 0)
    {
        while (PqRecvPointer >= PqRecvLength)
        {
            if (pq_recvbuf())   /* If nothing in buffer, then recv some */
                return EOF;     /* Failed to recv data */
        }
        amount = PqRecvLength - PqRecvPointer;
        if (amount > len)
            amount = len;
        memcpy(s, PqRecvBuffer + PqRecvPointer, amount);
        PqRecvPointer += amount;
        s += amount;
        len -= amount;
    }
    return 0;
}

/* --------------------------------
 *      pq_discardbytes     - throw away a known number of bytes
 *
 *      same as pq_getbytes except we do not copy the data to anyplace.
 *      this is used for resynchronizing after read errors.
 *
 *      returns 0 if OK, EOF if trouble
 * --------------------------------
 */
static int
pq_discardbytes(size_t len)
{
    size_t      amount;

    while (len > 0)
    {
        while (PqRecvPointer >= PqRecvLength)
        {
            if (pq_recvbuf())   /* If nothing in buffer, then recv some */
                return EOF;     /* Failed to recv data */
        }
        amount = PqRecvLength - PqRecvPointer;
        if (amount > len)
            amount = len;
        PqRecvPointer += amount;
        len -= amount;
    }
    return 0;
}

/* --------------------------------
 *      pq_getstring    - get a null terminated string from connection
 *
 *      The return value is placed in an expansible StringInfo, which has
 *      already been initialized by the caller.
 *
 *      This is used only for dealing with old-protocol clients.  The idea
 *      is to produce a StringInfo that looks the same as we would get from
 *      pq_getmessage() with a newer client; we will then process it with
 *      pq_getmsgstring.  Therefore, no character set conversion is done here,
 *      even though this is presumably useful only for text.
 *
 *      returns 0 if OK, EOF if trouble
 * --------------------------------
 */
int
pq_getstring(StringInfo s)
{
    int         i;

    resetStringInfo(s);

    /* Read until we get the terminating '\0' */
    for (;;)
    {
        while (PqRecvPointer >= PqRecvLength)
        {
            if (pq_recvbuf())   /* If nothing in buffer, then recv some */
                return EOF;     /* Failed to recv data */
        }

        for (i = PqRecvPointer; i < PqRecvLength; i++)
        {
            if (PqRecvBuffer[i] == '\0')
            {
                /* include the '\0' in the copy */
                appendBinaryStringInfo(s, PqRecvBuffer + PqRecvPointer,
                                       i - PqRecvPointer + 1);
                PqRecvPointer = i + 1;  /* advance past \0 */
                return 0;
            }
        }

        /* If we're here we haven't got the \0 in the buffer yet. */
        appendBinaryStringInfo(s, PqRecvBuffer + PqRecvPointer,
                               PqRecvLength - PqRecvPointer);
        PqRecvPointer = PqRecvLength;
    }
}


/* --------------------------------
 *      pq_getmessage   - get a message with length word from connection
 *
 *      The return value is placed in an expansible StringInfo, which has
 *      already been initialized by the caller.
 *      Only the message body is placed in the StringInfo; the length word
 *      is removed.  Also, s->cursor is initialized to zero for convenience
 *      in scanning the message contents.
 *
 *      If maxlen is not zero, it is an upper limit on the length of the
 *      message we are willing to accept.  We abort the connection (by
 *      returning EOF) if client tries to send more than that.
 *
 *      returns 0 if OK, EOF if trouble
 * --------------------------------
 */
int
pq_getmessage(StringInfo s, int maxlen)
{
    int32       len;

    resetStringInfo(s);

    /* Read message length word */
    if (pq_getbytes((char *) &len, 4) == EOF)
    {
        ereport(COMMERROR,
                (errcode(ERRCODE_PROTOCOL_VIOLATION),
                 errmsg("unexpected EOF within message length word")));
        return EOF;
    }

    len = ntohl(len);

    if (len < 4 ||
        (maxlen > 0 && len > maxlen))
    {
        ereport(COMMERROR,
                (errcode(ERRCODE_PROTOCOL_VIOLATION),
                 errmsg("invalid message length")));
        return EOF;
    }

    len -= 4;                   /* discount length itself */

    if (len > 0)
    {
        /*
         * Allocate space for message.  If we run out of room (ridiculously
         * large message), we will elog(ERROR), but we want to discard the
         * message body so as not to lose communication sync.
         */
        PG_TRY();
        {
            enlargeStringInfo(s, len);
        }
        PG_CATCH();
        {
            if (pq_discardbytes(len) == EOF)
                ereport(COMMERROR,
                        (errcode(ERRCODE_PROTOCOL_VIOLATION),
                         errmsg("incomplete message from client")));
            PG_RE_THROW();
        }
        PG_END_TRY();

        /* And grab the message */
        if (pq_getbytes(s->data, len) == EOF)
        {
            ereport(COMMERROR,
                    (errcode(ERRCODE_PROTOCOL_VIOLATION),
                     errmsg("incomplete message from client")));
            return EOF;
        }
        s->len = len;
        /* Place a trailing null per StringInfo convention */
        s->data[len] = '\0';
    }

    return 0;
}


/* --------------------------------
 *      pq_putbytes     - send bytes to connection (not flushed until pq_flush)
 *
 *      returns 0 if OK, EOF if trouble
 * --------------------------------
 */
int
pq_putbytes(const char *s, size_t len)
{
    int         res;

    /* Should only be called by old-style COPY OUT */
    Assert(DoingCopyOut);
    /* No-op if reentrant call */
    if (PqCommBusy)
        return 0;
    PqCommBusy = true;
    res = internal_putbytes(s, len);
    PqCommBusy = false;
    return res;
}

static int
internal_putbytes(const char *s, size_t len)
{
    size_t      amount;

    while (len > 0)
    {
        /* If buffer is full, then flush it out */
        if (PqSendPointer >= PqSendBufferSize)
        {
            pq_set_nonblocking(false);
            if (internal_flush())
                return EOF;
        }
        amount = PqSendBufferSize - PqSendPointer;
        if (amount > len)
            amount = len;
        memcpy(PqSendBuffer + PqSendPointer, s, amount);
        PqSendPointer += amount;
        s += amount;
        len -= amount;
    }
    return 0;
}

/* --------------------------------
 *      pq_flush        - flush pending output
 *
 *      returns 0 if OK, EOF if trouble
 * --------------------------------
 */
int
pq_flush(void)
{
    int         res;

    /* No-op if reentrant call */
    if (PqCommBusy)
        return 0;
    PqCommBusy = true;
    pq_set_nonblocking(false);
    res = internal_flush();
    PqCommBusy = false;
    return res;
}

/* --------------------------------
 *      internal_flush - flush pending output
 *
 * Returns 0 if OK (meaning everything was sent, or operation would block
 * and the socket is in non-blocking mode), or EOF if trouble.
 * --------------------------------
 */
static int
internal_flush(void)
{
    static int  last_reported_send_errno = 0;

    char       *bufptr = PqSendBuffer + PqSendStart;
    char       *bufend = PqSendBuffer + PqSendPointer;

    while (bufptr < bufend)
    {
        int         r;

        r = secure_write(MyProcPort, bufptr, bufend - bufptr);

        if (r <= 0)
        {
            if (errno == EINTR)
                continue;       /* Ok if we were interrupted */

            /*
             * Ok if no data writable without blocking, and the socket is in
             * non-blocking mode.
             */
            if (errno == EAGAIN ||
                errno == EWOULDBLOCK)
            {
                return 0;
            }

            /*
             * Careful: an ereport() that tries to write to the client would
             * cause recursion to here, leading to stack overflow and core
             * dump!  This message must go *only* to the postmaster log.
             *
             * If a client disconnects while we're in the midst of output, we
             * might write quite a bit of data before we get to a safe query
             * abort point.  So, suppress duplicate log messages.
             */
            if (errno != last_reported_send_errno)
            {
                last_reported_send_errno = errno;
                ereport(COMMERROR,
                        (errcode_for_socket_access(),
                         errmsg("could not send data to client: %m")));
            }

            /*
             * We drop the buffered data anyway so that processing can
             * continue, even though we'll probably quit soon. We also set a
             * flag that'll cause the next CHECK_FOR_INTERRUPTS to terminate
             * the connection.
             */
            PqSendStart = PqSendPointer = 0;
            ClientConnectionLost = 1;
            InterruptPending = 1;
            return EOF;
        }

        last_reported_send_errno = 0;   /* reset after any successful send */
        bufptr += r;
        PqSendStart += r;
    }

    PqSendStart = PqSendPointer = 0;
    return 0;
}

/* --------------------------------
 *      pq_flush_if_writable - flush pending output if writable without blocking
 *
 * Returns 0 if OK, or EOF if trouble.
 * --------------------------------
 */
int
pq_flush_if_writable(void)
{
    int         res;

    /* Quick exit if nothing to do */
    if (PqSendPointer == PqSendStart)
        return 0;

    /* No-op if reentrant call */
    if (PqCommBusy)
        return 0;

    /* Temporarily put the socket into non-blocking mode */
    pq_set_nonblocking(true);

    PqCommBusy = true;
    res = internal_flush();
    PqCommBusy = false;
    return res;
}

/* --------------------------------
 *      pq_is_send_pending  - is there any pending data in the output buffer?
 * --------------------------------
 */
bool
pq_is_send_pending(void)
{
    return (PqSendStart < PqSendPointer);
}

/* --------------------------------
 * Message-level I/O routines begin here.
 *
 * These routines understand about the old-style COPY OUT protocol.
 * --------------------------------
 */


/* --------------------------------
 *      pq_putmessage   - send a normal message (suppressed in COPY OUT mode)
 *
 *      If msgtype is not '\0', it is a message type code to place before
 *      the message body.  If msgtype is '\0', then the message has no type
 *      code (this is only valid in pre-3.0 protocols).
 *
 *      len is the length of the message body data at *s.  In protocol 3.0
 *      and later, a message length word (equal to len+4 because it counts
 *      itself too) is inserted by this routine.
 *
 *      All normal messages are suppressed while old-style COPY OUT is in
 *      progress.  (In practice only a few notice messages might get emitted
 *      then; dropping them is annoying, but at least they will still appear
 *      in the postmaster log.)
 *
 *      We also suppress messages generated while pqcomm.c is busy.  This
 *      avoids any possibility of messages being inserted within other
 *      messages.  The only known trouble case arises if SIGQUIT occurs
 *      during a pqcomm.c routine --- quickdie() will try to send a warning
 *      message, and the most reasonable approach seems to be to drop it.
 *
 *      returns 0 if OK, EOF if trouble
 * --------------------------------
 */
int
pq_putmessage(char msgtype, const char *s, size_t len)
{
    if (DoingCopyOut || PqCommBusy)
        return 0;
    PqCommBusy = true;
    if (msgtype)
        if (internal_putbytes(&msgtype, 1))
            goto fail;
    if (PG_PROTOCOL_MAJOR(FrontendProtocol) >= 3)
    {
        uint32      n32;

        n32 = htonl((uint32) (len + 4));
        if (internal_putbytes((char *) &n32, 4))
            goto fail;
    }
    if (internal_putbytes(s, len))
        goto fail;
    PqCommBusy = false;
    return 0;

fail:
    PqCommBusy = false;
    return EOF;
}

/* --------------------------------
 *      pq_putmessage_noblock   - like pq_putmessage, but never blocks
 *
 *      If the output buffer is too small to hold the message, the buffer
 *      is enlarged.
 */
void
pq_putmessage_noblock(char msgtype, const char *s, size_t len)
{
    int res     PG_USED_FOR_ASSERTS_ONLY;
    int         required;

    /*
     * Ensure we have enough space in the output buffer for the message header
     * as well as the message itself.
     */
    required = PqSendPointer + 1 + 4 + len;
    if (required > PqSendBufferSize)
    {
        PqSendBuffer = repalloc(PqSendBuffer, required);
        PqSendBufferSize = required;
    }
    res = pq_putmessage(msgtype, s, len);
    Assert(res == 0);           /* should not fail when the message fits in
                                 * buffer */
}


/* --------------------------------
 *      pq_startcopyout - inform libpq that an old-style COPY OUT transfer
 *          is beginning
 * --------------------------------
 */
void
pq_startcopyout(void)
{
    DoingCopyOut = true;
}

/* --------------------------------
 *      pq_endcopyout   - end an old-style COPY OUT transfer
 *
 *      If errorAbort is indicated, we are aborting a COPY OUT due to an error,
 *      and must send a terminator line.  Since a partial data line might have
 *      been emitted, send a couple of newlines first (the first one could
 *      get absorbed by a backslash...)  Note that old-style COPY OUT does
 *      not allow binary transfers, so a textual terminator is always correct.
 * --------------------------------
 */
void
pq_endcopyout(bool errorAbort)
{
    if (!DoingCopyOut)
        return;
    if (errorAbort)
        pq_putbytes("\n\n\\.\n", 5);
    /* in non-error case, copy.c will have emitted the terminator line */
    DoingCopyOut = false;
}


/*
 * Support for TCP Keepalive parameters
 */

/*
 * On Windows, we need to set both idle and interval at the same time.
 * We also cannot reset them to the default (setting to zero will
 * actually set them to zero, not default), therefor we fallback to
 * the out-of-the-box default instead.
 */
#if defined(WIN32) && defined(SIO_KEEPALIVE_VALS)
static int
pq_setkeepaliveswin32(Port *port, int idle, int interval)
{
    struct tcp_keepalive ka;
    DWORD       retsize;

    if (idle <= 0)
        idle = 2 * 60 * 60;     /* default = 2 hours */
    if (interval <= 0)
        interval = 1;           /* default = 1 second */

    ka.onoff = 1;
    ka.keepalivetime = idle * 1000;
    ka.keepaliveinterval = interval * 1000;

    if (WSAIoctl(port->sock,
                 SIO_KEEPALIVE_VALS,
                 (LPVOID) &ka,
                 sizeof(ka),
                 NULL,
                 0,
                 &retsize,
                 NULL,
                 NULL)
        != 0)
    {
        elog(LOG, "WSAIoctl(SIO_KEEPALIVE_VALS) failed: %ui",
             WSAGetLastError());
        return STATUS_ERROR;
    }
    if (port->keepalives_idle != idle)
        port->keepalives_idle = idle;
    if (port->keepalives_interval != interval)
        port->keepalives_interval = interval;
    return STATUS_OK;
}
#endif

int
pq_getkeepalivesidle(Port *port)
{
#if defined(TCP_KEEPIDLE) || defined(TCP_KEEPALIVE) || defined(WIN32)
    if (port == NULL || IS_AF_UNIX(port->laddr.addr.ss_family))
        return 0;

    if (port->keepalives_idle != 0)
        return port->keepalives_idle;

    if (port->default_keepalives_idle == 0)
    {
#ifndef WIN32
        ACCEPT_TYPE_ARG3 size = sizeof(port->default_keepalives_idle);

#ifdef TCP_KEEPIDLE
        if (getsockopt(port->sock, IPPROTO_TCP, TCP_KEEPIDLE,
                       (char *) &port->default_keepalives_idle,
                       &size) < 0)
        {
            elog(LOG, "getsockopt(TCP_KEEPIDLE) failed: %m");
            port->default_keepalives_idle = -1; /* don't know */
        }
#else
        if (getsockopt(port->sock, IPPROTO_TCP, TCP_KEEPALIVE,
                       (char *) &port->default_keepalives_idle,
                       &size) < 0)
        {
            elog(LOG, "getsockopt(TCP_KEEPALIVE) failed: %m");
            port->default_keepalives_idle = -1; /* don't know */
        }
#endif   /* TCP_KEEPIDLE */
#else                           /* WIN32 */
        /* We can't get the defaults on Windows, so return "don't know" */
        port->default_keepalives_idle = -1;
#endif   /* WIN32 */
    }

    return port->default_keepalives_idle;
#else
    return 0;
#endif
}

int
pq_setkeepalivesidle(int idle, Port *port)
{
    if (port == NULL || IS_AF_UNIX(port->laddr.addr.ss_family))
        return STATUS_OK;

#if defined(TCP_KEEPIDLE) || defined(TCP_KEEPALIVE) || defined(SIO_KEEPALIVE_VALS)
    if (idle == port->keepalives_idle)
        return STATUS_OK;

#ifndef WIN32
    if (port->default_keepalives_idle <= 0)
    {
        if (pq_getkeepalivesidle(port) < 0)
        {
            if (idle == 0)
                return STATUS_OK;       /* default is set but unknown */
            else
                return STATUS_ERROR;
        }
    }

    if (idle == 0)
        idle = port->default_keepalives_idle;

#ifdef TCP_KEEPIDLE
    if (setsockopt(port->sock, IPPROTO_TCP, TCP_KEEPIDLE,
                   (char *) &idle, sizeof(idle)) < 0)
    {
        elog(LOG, "setsockopt(TCP_KEEPIDLE) failed: %m");
        return STATUS_ERROR;
    }
#else
    if (setsockopt(port->sock, IPPROTO_TCP, TCP_KEEPALIVE,
                   (char *) &idle, sizeof(idle)) < 0)
    {
        elog(LOG, "setsockopt(TCP_KEEPALIVE) failed: %m");
        return STATUS_ERROR;
    }
#endif

    port->keepalives_idle = idle;
#else                           /* WIN32 */
    return pq_setkeepaliveswin32(port, idle, port->keepalives_interval);
#endif
#else                           /* TCP_KEEPIDLE || SIO_KEEPALIVE_VALS */
    if (idle != 0)
    {
        elog(LOG, "setting the keepalive idle time is not supported");
        return STATUS_ERROR;
    }
#endif
    return STATUS_OK;
}

int
pq_getkeepalivesinterval(Port *port)
{
#if defined(TCP_KEEPINTVL) || defined(SIO_KEEPALIVE_VALS)
    if (port == NULL || IS_AF_UNIX(port->laddr.addr.ss_family))
        return 0;

    if (port->keepalives_interval != 0)
        return port->keepalives_interval;

    if (port->default_keepalives_interval == 0)
    {
#ifndef WIN32
        ACCEPT_TYPE_ARG3 size = sizeof(port->default_keepalives_interval);

        if (getsockopt(port->sock, IPPROTO_TCP, TCP_KEEPINTVL,
                       (char *) &port->default_keepalives_interval,
                       &size) < 0)
        {
            elog(LOG, "getsockopt(TCP_KEEPINTVL) failed: %m");
            port->default_keepalives_interval = -1;     /* don't know */
        }
#else
        /* We can't get the defaults on Windows, so return "don't know" */
        port->default_keepalives_interval = -1;
#endif   /* WIN32 */
    }

    return port->default_keepalives_interval;
#else
    return 0;
#endif
}

int
pq_setkeepalivesinterval(int interval, Port *port)
{
    if (port == NULL || IS_AF_UNIX(port->laddr.addr.ss_family))
        return STATUS_OK;

#if defined(TCP_KEEPINTVL) || defined (SIO_KEEPALIVE_VALS)
    if (interval == port->keepalives_interval)
        return STATUS_OK;

#ifndef WIN32
    if (port->default_keepalives_interval <= 0)
    {
        if (pq_getkeepalivesinterval(port) < 0)
        {
            if (interval == 0)
                return STATUS_OK;       /* default is set but unknown */
            else
                return STATUS_ERROR;
        }
    }

    if (interval == 0)
        interval = port->default_keepalives_interval;

    if (setsockopt(port->sock, IPPROTO_TCP, TCP_KEEPINTVL,
                   (char *) &interval, sizeof(interval)) < 0)
    {
        elog(LOG, "setsockopt(TCP_KEEPINTVL) failed: %m");
        return STATUS_ERROR;
    }

    port->keepalives_interval = interval;
#else                           /* WIN32 */
    return pq_setkeepaliveswin32(port, port->keepalives_idle, interval);
#endif
#else
    if (interval != 0)
    {
        elog(LOG, "setsockopt(TCP_KEEPINTVL) not supported");
        return STATUS_ERROR;
    }
#endif

    return STATUS_OK;
}

int
pq_getkeepalivescount(Port *port)
{
#ifdef TCP_KEEPCNT
    if (port == NULL || IS_AF_UNIX(port->laddr.addr.ss_family))
        return 0;

    if (port->keepalives_count != 0)
        return port->keepalives_count;

    if (port->default_keepalives_count == 0)
    {
        ACCEPT_TYPE_ARG3 size = sizeof(port->default_keepalives_count);

        if (getsockopt(port->sock, IPPROTO_TCP, TCP_KEEPCNT,
                       (char *) &port->default_keepalives_count,
                       &size) < 0)
        {
            elog(LOG, "getsockopt(TCP_KEEPCNT) failed: %m");
            port->default_keepalives_count = -1;        /* don't know */
        }
    }

    return port->default_keepalives_count;
#else
    return 0;
#endif
}

int
pq_setkeepalivescount(int count, Port *port)
{
    if (port == NULL || IS_AF_UNIX(port->laddr.addr.ss_family))
        return STATUS_OK;

#ifdef TCP_KEEPCNT
    if (count == port->keepalives_count)
        return STATUS_OK;

    if (port->default_keepalives_count <= 0)
    {
        if (pq_getkeepalivescount(port) < 0)
        {
            if (count == 0)
                return STATUS_OK;       /* default is set but unknown */
            else
                return STATUS_ERROR;
        }
    }

    if (count == 0)
        count = port->default_keepalives_count;

    if (setsockopt(port->sock, IPPROTO_TCP, TCP_KEEPCNT,
                   (char *) &count, sizeof(count)) < 0)
    {
        elog(LOG, "setsockopt(TCP_KEEPCNT) failed: %m");
        return STATUS_ERROR;
    }

    port->keepalives_count = count;
#else
    if (count != 0)
    {
        elog(LOG, "setsockopt(TCP_KEEPCNT) not supported");
        return STATUS_ERROR;
    }
#endif

    return STATUS_OK;
}