Update copyright for 2022

[pgsql.git] / src / backend / libpq / pqcomm.c

/*-------------------------------------------------------------------------
 *
 * 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.
 *
 * To emit an outgoing message, use the routines in pqformat.c to construct
 * the message in a buffer and then emit it in one call to pq_putmessage.
 * There are no functions to send raw bytes or partial messages; this
 * ensures that the channel will not be clogged by an incomplete message if
 * execution is aborted by ereport(ERROR) partway through the message.
 *
 * 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) 1996-2022, 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
 *              socket_comm_reset       - reset libpq during error recovery
 *              socket_close            - shutdown libpq at backend exit
 *
 * low-level I/O:
 *              pq_getbytes             - get a known number of bytes 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_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
 *              pq_putmessage   - send a normal message (suppressed in COPY OUT mode)
 *              pq_putmessage_noblock - buffer a normal message (suppressed in COPY OUT)
 *
 *------------------------
 */
#include "postgres.h"

#ifdef HAVE_POLL_H
#include <poll.h>
#endif
#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 <utime.h>
#ifdef _MSC_VER                                 /* mstcpip.h is missing on mingw */
#include <mstcpip.h>
#endif

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

/*
 * Cope with the various platform-specific ways to spell TCP keepalive socket
 * options.  This doesn't cover Windows, which as usual does its own thing.
 */
#if defined(TCP_KEEPIDLE)
/* TCP_KEEPIDLE is the name of this option on Linux and *BSD */
#define PG_TCP_KEEPALIVE_IDLE TCP_KEEPIDLE
#define PG_TCP_KEEPALIVE_IDLE_STR "TCP_KEEPIDLE"
#elif defined(TCP_KEEPALIVE_THRESHOLD)
/* TCP_KEEPALIVE_THRESHOLD is the name of this option on Solaris >= 11 */
#define PG_TCP_KEEPALIVE_IDLE TCP_KEEPALIVE_THRESHOLD
#define PG_TCP_KEEPALIVE_IDLE_STR "TCP_KEEPALIVE_THRESHOLD"
#elif defined(TCP_KEEPALIVE) && defined(__darwin__)
/* TCP_KEEPALIVE is the name of this option on macOS */
/* Caution: Solaris has this symbol but it means something different */
#define PG_TCP_KEEPALIVE_IDLE TCP_KEEPALIVE
#define PG_TCP_KEEPALIVE_IDLE_STR "TCP_KEEPALIVE"
#endif

/*
 * 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;                 /* busy sending data to the client */
static bool PqCommReadingMsg;   /* in the middle of reading a message */


/* Internal functions */
static void socket_comm_reset(void);
static void socket_close(int code, Datum arg);
static void socket_set_nonblocking(bool nonblocking);
static int      socket_flush(void);
static int      socket_flush_if_writable(void);
static bool socket_is_send_pending(void);
static int      socket_putmessage(char msgtype, const char *s, size_t len);
static void socket_putmessage_noblock(char msgtype, const char *s, size_t len);
static int      internal_putbytes(const char *s, size_t len);
static int      internal_flush(void);

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

static const PQcommMethods PqCommSocketMethods = {
        socket_comm_reset,
        socket_flush,
        socket_flush_if_writable,
        socket_is_send_pending,
        socket_putmessage,
        socket_putmessage_noblock
};

const PQcommMethods *PqCommMethods = &PqCommSocketMethods;

WaitEventSet *FeBeWaitSet;


/* --------------------------------
 *              pq_init - initialize libpq at backend startup
 * --------------------------------
 */
void
pq_init(void)
{
        int                     socket_pos PG_USED_FOR_ASSERTS_ONLY;
        int                     latch_pos PG_USED_FOR_ASSERTS_ONLY;

        /* initialize state variables */
        PqSendBufferSize = PQ_SEND_BUFFER_SIZE;
        PqSendBuffer = MemoryContextAlloc(TopMemoryContext, PqSendBufferSize);
        PqSendPointer = PqSendStart = PqRecvPointer = PqRecvLength = 0;
        PqCommBusy = false;
        PqCommReadingMsg = false;

        /* set up process-exit hook to close the socket */
        on_proc_exit(socket_close, 0);

        /*
         * In backends (as soon as forked) we operate the underlying socket in
         * nonblocking mode and use latches to implement blocking semantics if
         * needed. That allows us to provide safely interruptible reads and
         * writes.
         *
         * 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.
         */
#ifndef WIN32
        if (!pg_set_noblock(MyProcPort->sock))
                ereport(COMMERROR,
                                (errmsg("could not set socket to nonblocking mode: %m")));
#endif

        FeBeWaitSet = CreateWaitEventSet(TopMemoryContext, 3);
        socket_pos = AddWaitEventToSet(FeBeWaitSet, WL_SOCKET_WRITEABLE,
                                                                   MyProcPort->sock, NULL, NULL);
        latch_pos = AddWaitEventToSet(FeBeWaitSet, WL_LATCH_SET, PGINVALID_SOCKET,
                                                                  MyLatch, NULL);
        AddWaitEventToSet(FeBeWaitSet, WL_POSTMASTER_DEATH, PGINVALID_SOCKET,
                                          NULL, NULL);

        /*
         * The event positions match the order we added them, but let's sanity
         * check them to be sure.
         */
        Assert(socket_pos == FeBeWaitSetSocketPos);
        Assert(latch_pos == FeBeWaitSetLatchPos);
}

/* --------------------------------
 *              socket_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...)
 * --------------------------------
 */
static void
socket_comm_reset(void)
{
        /* Do not throw away pending data, but do reset the busy flag */
        PqCommBusy = false;
}

/* --------------------------------
 *              socket_close - shutdown libpq at backend exit
 *
 * This is the one pg_on_exit_callback in place during BackendInitialize().
 * That function's unusual signal handling constrains that this callback be
 * safe to run at any instant.
 * --------------------------------
 */
static void
socket_close(int code, Datum arg)
{
        /* Nothing to do in a standalone backend, where MyProcPort is NULL. */
        if (MyProcPort != NULL)
        {
#ifdef ENABLE_GSS
                /*
                 * Shutdown GSSAPI layer.  This section does nothing when interrupting
                 * BackendInitialize(), because pg_GSS_recvauth() makes first use of
                 * "ctx" and "cred".
                 *
                 * Note that we don't bother to free MyProcPort->gss, since we're
                 * about to exit anyway.
                 */
                if (MyProcPort->gss)
                {
                        OM_uint32       min_s;

                        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 */

                /*
                 * Cleanly shut down SSL layer.  Nowhere else does a postmaster child
                 * call this, so this is safe when interrupting BackendInitialize().
                 */
                secure_close(MyProcPort);

                /*
                 * On most platforms, we 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.  Saves a kernel call, too.
                 *
                 * However, that does not work on Windows: if the kernel closes the
                 * socket it will invoke an "abortive shutdown" that discards any data
                 * not yet sent to the client.  (This is a flat-out violation of the
                 * TCP RFCs, but count on Microsoft not to care about that.)  To get
                 * the spec-compliant "graceful shutdown" behavior, we must invoke
                 * closesocket() explicitly.  When using OpenSSL, it seems that clean
                 * shutdown also requires an explicit shutdown() call.
                 *
                 * This code runs late enough during process shutdown that we should
                 * have finished all externally-visible shutdown activities, so that
                 * in principle it's good enough to act as a synchronous close on
                 * Windows too.  But it's a lot more fragile than the other way.
                 */
#ifdef WIN32
                shutdown(MyProcPort->sock, SD_SEND);
                closesocket(MyProcPort->sock);
#endif

                /* In any case, set sock to PGINVALID_SOCKET to prevent further I/O */
                MyProcPort->sock = PGINVALID_SOCKET;
        }
}



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


/*
 * 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, const char *hostName, unsigned short portNumber,
                                 const char *unixSocketDir,
                                 pgsocket ListenSocket[], int MaxListen)
{
        pgsocket        fd;
        int                     err;
        int                     maxconn;
        int                     ret;
        char            portNumberStr[32];
        const char *familyDesc;
        char            familyDescBuf[64];
        const char *addrDesc;
        char            addrBuf[NI_MAXHOST];
        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 address family name for log 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;
                }

                /* set up text form of address for log messages */
#ifdef HAVE_UNIX_SOCKETS
                if (addr->ai_family == AF_UNIX)
                        addrDesc = unixSocketPath;
                else
#endif
                {
                        pg_getnameinfo_all((const struct sockaddr_storage *) addr->ai_addr,
                                                           addr->ai_addrlen,
                                                           addrBuf, sizeof(addrBuf),
                                                           NULL, 0,
                                                           NI_NUMERICHOST);
                        addrDesc = addrBuf;
                }

                if ((fd = socket(addr->ai_family, SOCK_STREAM, 0)) == PGINVALID_SOCKET)
                {
                        ereport(LOG,
                                        (errcode_for_socket_access(),
                        /* translator: first %s is IPv4, IPv6, or Unix */
                                         errmsg("could not create %s socket for address \"%s\": %m",
                                                        familyDesc, addrDesc)));
                        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_EXCLUSIVEADDRUSE 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(),
                                /* translator: third %s is IPv4, IPv6, or Unix */
                                                 errmsg("%s(%s) failed for %s address \"%s\": %m",
                                                                "setsockopt", "SO_REUSEADDR",
                                                                familyDesc, addrDesc)));
                                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(),
                                /* translator: third %s is IPv4, IPv6, or Unix */
                                                 errmsg("%s(%s) failed for %s address \"%s\": %m",
                                                                "setsockopt", "IPV6_V6ONLY",
                                                                familyDesc, addrDesc)));
                                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)
                {
                        int                     saved_errno = errno;

                        ereport(LOG,
                                        (errcode_for_socket_access(),
                        /* translator: first %s is IPv4, IPv6, or Unix */
                                         errmsg("could not bind %s address \"%s\": %m",
                                                        familyDesc, addrDesc),
                                         saved_errno == EADDRINUSE ?
                                         (IS_AF_UNIX(addr->ai_family) ?
                                          errhint("Is another postmaster already running on port %d?",
                                                          (int) portNumber) :
                                          errhint("Is another postmaster already running on port %d?"
                                                          " If not, wait a few seconds and retry.",
                                                          (int) portNumber)) : 0));
                        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: first %s is IPv4, IPv6, or Unix */
                                         errmsg("could not listen on %s address \"%s\": %m",
                                                        familyDesc, addrDesc)));
                        closesocket(fd);
                        continue;
                }

#ifdef HAVE_UNIX_SOCKETS
                if (addr->ai_family == AF_UNIX)
                        ereport(LOG,
                                        (errmsg("listening on Unix socket \"%s\"",
                                                        addrDesc)));
                else
#endif
                        ereport(LOG,
                        /* translator: first %s is IPv4 or IPv6 */
                                        (errmsg("listening on %s address \"%s\", port %d",
                                                        familyDesc, addrDesc, (int) portNumber)));

                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(const char *unixSocketDir, const char *unixSocketPath)
{
        /* no lock file for abstract sockets */
        if (unixSocketPath[0] == '@')
                return STATUS_OK;

        /*
         * 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.
         */
        (void) unlink(unixSocketPath);

        /*
         * Remember socket file pathnames for later maintenance.
         */
        sock_paths = lappend(sock_paths, pstrdup(unixSocketPath));

        return STATUS_OK;
}


/*
 * Setup_AF_UNIX -- configure unix socket permissions
 */
static int
Setup_AF_UNIX(const char *sock_path)
{
        /* no file system permissions for abstract sockets */
        if (sock_path[0] == '@')
                return STATUS_OK;

        /*
         * 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 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)) == PGINVALID_SOCKET)
        {
                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;
        }

        /* 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)
        {
                ereport(LOG,
                                (errmsg("%s() failed: %m", "getsockname")));
                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 WIN32
                int                     oldopt;
                int                     optlen;
                int                     newopt;
#endif

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

#ifdef WIN32

                /*
                 * This is a Win32 socket optimization.  The OS send buffer should be
                 * large enough to send the whole Postgres send buffer in one go, or
                 * performance suffers.  The Postgres send buffer can be enlarged if a
                 * very large message needs to be sent, but we won't attempt to
                 * enlarge the OS buffer if that happens, so somewhat arbitrarily
                 * ensure that the OS buffer is at least PQ_SEND_BUFFER_SIZE * 4.
                 * (That's 32kB with the current default).
                 *
                 * The default OS buffer size used to be 8kB in earlier Windows
                 * versions, but was raised to 64kB in Windows 2012.  So it shouldn't
                 * be necessary to change it in later versions anymore.  Changing it
                 * unnecessarily can even reduce performance, because setting
                 * SO_SNDBUF in the application disables the "dynamic send buffering"
                 * feature that was introduced in Windows 7.  So before fiddling with
                 * SO_SNDBUF, check if the current buffer size is already large enough
                 * and only increase it if necessary.
                 *
                 * See https://support.microsoft.com/kb/823764/EN-US/ and
                 * https://msdn.microsoft.com/en-us/library/bb736549%28v=vs.85%29.aspx
                 */
                optlen = sizeof(oldopt);
                if (getsockopt(port->sock, SOL_SOCKET, SO_SNDBUF, (char *) &oldopt,
                                           &optlen) < 0)
                {
                        ereport(LOG,
                                        (errmsg("%s(%s) failed: %m", "getsockopt", "SO_SNDBUF")));
                        return STATUS_ERROR;
                }
                newopt = PQ_SEND_BUFFER_SIZE * 4;
                if (oldopt < newopt)
                {
                        if (setsockopt(port->sock, SOL_SOCKET, SO_SNDBUF, (char *) &newopt,
                                                   sizeof(newopt)) < 0)
                        {
                                ereport(LOG,
                                                (errmsg("%s(%s) failed: %m", "setsockopt", "SO_SNDBUF")));
                                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);
                (void) pq_settcpusertimeout(tcp_user_timeout, 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);

                /* Ignore errors; there's no point in complaining */
                (void) utime(sock_path, NULL);
        }
}

/*
 * RemoveSocketFiles -- unlink socket files at postmaster shutdown
 */
void
RemoveSocketFiles(void)
{
        ListCell   *l;

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

                /* Ignore any error. */
                (void) unlink(sock_path);
        }
        /* Since we're about to exit, no need to reclaim storage */
        sock_paths = NIL;
}


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

/* --------------------------------
 *                        socket_set_nonblocking - set socket blocking/non-blocking
 *
 * Sets the socket non-blocking if nonblocking is true, or sets it
 * blocking otherwise.
 * --------------------------------
 */
static void
socket_set_nonblocking(bool nonblocking)
{
        if (MyProcPort == NULL)
                ereport(ERROR,
                                (errcode(ERRCODE_CONNECTION_DOES_NOT_EXIST),
                                 errmsg("there is no client connection")));

        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 */
        socket_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)
{
        Assert(PqCommReadingMsg);

        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)
{
        Assert(PqCommReadingMsg);

        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;

        Assert(PqCommReadingMsg);

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

        /* Put the socket into non-blocking mode */
        socket_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;

        Assert(PqCommReadingMsg);

        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;

        Assert(PqCommReadingMsg);

        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_buffer_has_data              - is any buffered data available to read?
 *
 * This will *not* attempt to read more data.
 * --------------------------------
 */
bool
pq_buffer_has_data(void)
{
        return (PqRecvPointer < PqRecvLength);
}


/* --------------------------------
 *              pq_startmsgread - begin reading a message from the client.
 *
 *              This must be called before any of the pq_get* functions.
 * --------------------------------
 */
void
pq_startmsgread(void)
{
        /*
         * There shouldn't be a read active already, but let's check just to be
         * sure.
         */
        if (PqCommReadingMsg)
                ereport(FATAL,
                                (errcode(ERRCODE_PROTOCOL_VIOLATION),
                                 errmsg("terminating connection because protocol synchronization was lost")));

        PqCommReadingMsg = true;
}


/* --------------------------------
 *              pq_endmsgread   - finish reading message.
 *
 *              This must be called after reading a message with pq_getbytes()
 *              and friends, to indicate that we have read the whole message.
 *              pq_getmessage() does this implicitly.
 * --------------------------------
 */
void
pq_endmsgread(void)
{
        Assert(PqCommReadingMsg);

        PqCommReadingMsg = false;
}

/* --------------------------------
 *              pq_is_reading_msg - are we currently reading a message?
 *
 * This is used in error recovery at the outer idle loop to detect if we have
 * lost protocol sync, and need to terminate the connection. pq_startmsgread()
 * will check for that too, but it's nicer to detect it earlier.
 * --------------------------------
 */
bool
pq_is_reading_msg(void)
{
        return PqCommReadingMsg;
}

/* --------------------------------
 *              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.
 *
 *              maxlen is the 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;

        Assert(PqCommReadingMsg);

        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 = pg_ntoh32(len);

        if (len < 4 || 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")));

                        /* we discarded the rest of the message so we're back in sync. */
                        PqCommReadingMsg = false;
                        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';
        }

        /* finished reading the message. */
        PqCommReadingMsg = false;

        return 0;
}


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)
                {
                        socket_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;
}

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

        /* No-op if reentrant call */
        if (PqCommBusy)
                return 0;
        PqCommBusy = true;
        socket_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.
 * --------------------------------
 */
static int
socket_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 */
        socket_set_nonblocking(true);

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

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

/* --------------------------------
 * Message-level I/O routines begin here.
 * --------------------------------
 */


/* --------------------------------
 *              socket_putmessage - send a normal message (suppressed in COPY OUT mode)
 *
 *              msgtype is a message type code to place before the message body.
 *
 *              len is the length of the message body data at *s.  A message length
 *              word (equal to len+4 because it counts itself too) is inserted by this
 *              routine.
 *
 *              We 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
 * --------------------------------
 */
static int
socket_putmessage(char msgtype, const char *s, size_t len)
{
        uint32          n32;

        Assert(msgtype != 0);

        if (PqCommBusy)
                return 0;
        PqCommBusy = true;
        if (internal_putbytes(&msgtype, 1))
                goto fail;

        n32 = pg_hton32((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.
 */
static void
socket_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_putmessage_v2 - send a message in protocol version 2
 *
 *              msgtype is a message type code to place before the message body.
 *
 *              We no longer support protocol version 2, but we have kept this
 *              function so that if a client tries to connect with protocol version 2,
 *              as a courtesy we can still send the "unsupported protocol version"
 *              error to the client in the old format.
 *
 *              Like in pq_putmessage(), we suppress messages generated while
 *              pqcomm.c is busy.
 *
 *              returns 0 if OK, EOF if trouble
 * --------------------------------
 */
int
pq_putmessage_v2(char msgtype, const char *s, size_t len)
{
        Assert(msgtype != 0);

        if (PqCommBusy)
                return 0;
        PqCommBusy = true;
        if (internal_putbytes(&msgtype, 1))
                goto fail;

        if (internal_putbytes(s, len))
                goto fail;
        PqCommBusy = false;
        return 0;

fail:
        PqCommBusy = false;
        return EOF;
}

/*
 * 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), therefore 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)
        {
                ereport(LOG,
                                (errmsg("%s(%s) failed: error code %d",
                                                "WSAIoctl", "SIO_KEEPALIVE_VALS", 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(PG_TCP_KEEPALIVE_IDLE) || defined(SIO_KEEPALIVE_VALS)
        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
                socklen_t       size = sizeof(port->default_keepalives_idle);

                if (getsockopt(port->sock, IPPROTO_TCP, PG_TCP_KEEPALIVE_IDLE,
                                           (char *) &port->default_keepalives_idle,
                                           &size) < 0)
                {
                        ereport(LOG,
                                        (errmsg("%s(%s) failed: %m", "getsockopt", PG_TCP_KEEPALIVE_IDLE_STR)));
                        port->default_keepalives_idle = -1; /* don't know */
                }
#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;

/* check SIO_KEEPALIVE_VALS here, not just WIN32, as some toolchains lack it */
#if defined(PG_TCP_KEEPALIVE_IDLE) || 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;

        if (setsockopt(port->sock, IPPROTO_TCP, PG_TCP_KEEPALIVE_IDLE,
                                   (char *) &idle, sizeof(idle)) < 0)
        {
                ereport(LOG,
                                (errmsg("%s(%s) failed: %m", "setsockopt", PG_TCP_KEEPALIVE_IDLE_STR)));
                return STATUS_ERROR;
        }

        port->keepalives_idle = idle;
#else                                                   /* WIN32 */
        return pq_setkeepaliveswin32(port, idle, port->keepalives_interval);
#endif
#else
        if (idle != 0)
        {
                ereport(LOG,
                                (errmsg("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
                socklen_t       size = sizeof(port->default_keepalives_interval);

                if (getsockopt(port->sock, IPPROTO_TCP, TCP_KEEPINTVL,
                                           (char *) &port->default_keepalives_interval,
                                           &size) < 0)
                {
                        ereport(LOG,
                                        (errmsg("%s(%s) failed: %m", "getsockopt", "TCP_KEEPINTVL")));
                        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)
        {
                ereport(LOG,
                                (errmsg("%s(%s) failed: %m", "setsockopt", "TCP_KEEPINTVL")));
                return STATUS_ERROR;
        }

        port->keepalives_interval = interval;
#else                                                   /* WIN32 */
        return pq_setkeepaliveswin32(port, port->keepalives_idle, interval);
#endif
#else
        if (interval != 0)
        {
                ereport(LOG,
                                (errmsg("%s(%s) not supported", "setsockopt", "TCP_KEEPINTVL")));
                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)
        {
                socklen_t       size = sizeof(port->default_keepalives_count);

                if (getsockopt(port->sock, IPPROTO_TCP, TCP_KEEPCNT,
                                           (char *) &port->default_keepalives_count,
                                           &size) < 0)
                {
                        ereport(LOG,
                                        (errmsg("%s(%s) failed: %m", "getsockopt", "TCP_KEEPCNT")));
                        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)
        {
                ereport(LOG,
                                (errmsg("%s(%s) failed: %m", "setsockopt", "TCP_KEEPCNT")));
                return STATUS_ERROR;
        }

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

        return STATUS_OK;
}

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

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

        if (port->default_tcp_user_timeout == 0)
        {
                socklen_t       size = sizeof(port->default_tcp_user_timeout);

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

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

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

#ifdef TCP_USER_TIMEOUT
        if (timeout == port->tcp_user_timeout)
                return STATUS_OK;

        if (port->default_tcp_user_timeout <= 0)
        {
                if (pq_gettcpusertimeout(port) < 0)
                {
                        if (timeout == 0)
                                return STATUS_OK;       /* default is set but unknown */
                        else
                                return STATUS_ERROR;
                }
        }

        if (timeout == 0)
                timeout = port->default_tcp_user_timeout;

        if (setsockopt(port->sock, IPPROTO_TCP, TCP_USER_TIMEOUT,
                                   (char *) &timeout, sizeof(timeout)) < 0)
        {
                ereport(LOG,
                                (errmsg("%s(%s) failed: %m", "setsockopt", "TCP_USER_TIMEOUT")));
                return STATUS_ERROR;
        }

        port->tcp_user_timeout = timeout;
#else
        if (timeout != 0)
        {
                ereport(LOG,
                                (errmsg("%s(%s) not supported", "setsockopt", "TCP_USER_TIMEOUT")));
                return STATUS_ERROR;
        }
#endif

        return STATUS_OK;
}

/*
 * Check if the client is still connected.
 */
bool
pq_check_connection(void)
{
#if defined(POLLRDHUP)
        /*
         * POLLRDHUP is a Linux extension to poll(2) to detect sockets closed by
         * the other end.  We don't have a portable way to do that without
         * actually trying to read or write data on other systems.  We don't want
         * to read because that would be confused by pipelined queries and COPY
         * data. Perhaps in future we'll try to write a heartbeat message instead.
         */
        struct pollfd pollfd;
        int                     rc;

        pollfd.fd = MyProcPort->sock;
        pollfd.events = POLLOUT | POLLIN | POLLRDHUP;
        pollfd.revents = 0;

        rc = poll(&pollfd, 1, 0);

        if (rc < 0)
        {
                ereport(COMMERROR,
                                (errcode_for_socket_access(),
                                 errmsg("could not poll socket: %m")));
                return false;
        }
        else if (rc == 1 && (pollfd.revents & (POLLHUP | POLLRDHUP)))
                return false;
#endif

        return true;
}