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.
 *
 * 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) 1996-2026, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *  src/backend/libpq/pqcomm.c
 *
 *-------------------------------------------------------------------------
 */
 
/*------------------------
 * INTERFACE ROUTINES
 *
 * setup/teardown:
 *      ListenServerPort    - Open postmaster's server port
 *      AcceptConnection    - Accept new connection with client
 *      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>
#include <netinet/tcp.h>
#include <utime.h>
#ifdef WIN32
#include <mstcpip.h>
#endif
 
#include "common/ip.h"
#include "libpq/libpq.h"
#include "miscadmin.h"
#include "port/pg_bswap.h"
#include "postmaster/postmaster.h"
#include "storage/ipc.h"
#include "utils/guc_hooks.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 size_t PqSendPointer;    /* Next index to store a byte in PqSendBuffer */
static size_t 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 inline int internal_putbytes(const void *b, size_t len);
static inline int internal_flush(void);
static pg_noinline int internal_flush_buffer(const char *buf, size_t *start,
                                             size_t *end);
 
static int  Lock_AF_UNIX(const char *unixSocketDir, const char *unixSocketPath);
static int  Setup_AF_UNIX(const char *sock_path);
 
static const PQcommMethods PqCommSocketMethods = {
    .comm_reset = socket_comm_reset,
    .flush = socket_flush,
    .flush_if_writable = socket_flush_if_writable,
    .is_send_pending = socket_is_send_pending,
    .putmessage = socket_putmessage,
    .putmessage_noblock = socket_putmessage_noblock
};
 
const PQcommMethods *PqCommMethods = &PqCommSocketMethods;
 
WaitEventSet *FeBeWaitSet;
 
 
/* --------------------------------
 *      pq_init - initialize libpq at backend startup
 * --------------------------------
 */
Port *
pq_init(ClientSocket *client_sock)
{
    Port       *port;
    int         socket_pos PG_USED_FOR_ASSERTS_ONLY;
    int         latch_pos PG_USED_FOR_ASSERTS_ONLY;
 
    /* allocate the Port struct and copy the ClientSocket contents to it */
    port = palloc0_object(Port);
    port->sock = client_sock->sock;
    memcpy(&port->raddr.addr, &client_sock->raddr.addr, client_sock->raddr.salen);
    port->raddr.salen = client_sock->raddr.salen;
 
    /* 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(FATAL,
                (errmsg("%s() failed: %m", "getsockname")));
    }
 
    /* select NODELAY and KEEPALIVE options if it's a TCP connection */
    if (port->laddr.addr.ss_family != AF_UNIX)
    {
        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(FATAL,
                    (errmsg("%s(%s) failed: %m", "setsockopt", "TCP_NODELAY")));
        }
#endif
        on = 1;
        if (setsockopt(port->sock, SOL_SOCKET, SO_KEEPALIVE,
                       (char *) &on, sizeof(on)) < 0)
        {
            ereport(FATAL,
                    (errmsg("%s(%s) failed: %m", "setsockopt", "SO_KEEPALIVE")));
        }
 
#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(FATAL,
                    (errmsg("%s(%s) failed: %m", "getsockopt", "SO_SNDBUF")));
        }
        newopt = PQ_SEND_BUFFER_SIZE * 4;
        if (oldopt < newopt)
        {
            if (setsockopt(port->sock, SOL_SOCKET, SO_SNDBUF, (char *) &newopt,
                           sizeof(newopt)) < 0)
            {
                ereport(FATAL,
                        (errmsg("%s(%s) failed: %m", "setsockopt", "SO_SNDBUF")));
            }
        }
#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);
    }
 
    /* 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.
     */
#ifndef WIN32
    if (!pg_set_noblock(port->sock))
        ereport(FATAL,
                (errmsg("could not set socket to nonblocking mode: %m")));
#endif
 
#ifndef WIN32
 
    /* Don't give the socket to any subprograms we execute. */
    if (fcntl(port->sock, F_SETFD, FD_CLOEXEC) < 0)
        elog(FATAL, "fcntl(F_SETFD) failed on socket: %m");
#endif
 
    FeBeWaitSet = CreateWaitEventSet(NULL, FeBeWaitSetNEvents);
    socket_pos = AddWaitEventToSet(FeBeWaitSet, WL_SOCKET_WRITEABLE,
                                   port->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);
 
    return port;
}
 
/* --------------------------------
 *      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);
 
        /*
         * 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;
    }
}
 
 
 
/* --------------------------------
 * Postmaster functions to handle sockets.
 * --------------------------------
 */
 
/*
 * ListenServerPort -- 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 appended to the ListenSockets[] array.  On
 * entry, *NumListenSockets holds the number of elements currently in the
 * array, and it is updated to reflect the opened sockets.  MaxListen is the
 * allocated size of the array.
 *
 * RETURNS: STATUS_OK or STATUS_ERROR
 */
int
ListenServerPort(int family, const char *hostName, unsigned short portNumber,
                 const char *unixSocketDir,
                 pgsocket ListenSockets[], int *NumListenSockets, 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         added = 0;
    char        unixSocketPath[MAXPGPATH];
#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;
 
    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 %zu bytes)",
                            unixSocketPath,
                            (UNIXSOCK_PATH_BUFLEN - 1))));
            return STATUS_ERROR;
        }
        if (Lock_AF_UNIX(unixSocketDir, unixSocketPath) != STATUS_OK)
            return STATUS_ERROR;
        service = unixSocketPath;
    }
    else
    {
        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 (family != AF_UNIX && addr->ai_family == AF_UNIX)
        {
            /*
             * 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. */
        if (*NumListenSockets == 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;
            case AF_INET6:
                familyDesc = _("IPv6");
                break;
            case AF_UNIX:
                familyDesc = _("Unix");
                break;
            default:
                snprintf(familyDescBuf, sizeof(familyDescBuf),
                         _("unrecognized address family %d"),
                         addr->ai_family);
                familyDesc = familyDescBuf;
                break;
        }
 
        /* set up text form of address for log messages */
        if (addr->ai_family == AF_UNIX)
            addrDesc = unixSocketPath;
        else
        {
            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
        /* Don't give the listen socket to any subprograms we execute. */
        if (fcntl(fd, F_SETFD, FD_CLOEXEC) < 0)
            elog(FATAL, "fcntl(F_SETFD) failed on socket: %m");
 
        /*
         * 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 (addr->ai_family != AF_UNIX)
        {
            if ((setsockopt(fd, SOL_SOCKET, SO_REUSEADDR,
                            (char *) &one, sizeof(one))) == -1)
            {
                ereport(LOG,
                        (errcode_for_socket_access(),
                /* translator: third %s is IPv4 or IPv6 */
                         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 IPv6 */
                         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 ?
                     (addr->ai_family == AF_UNIX ?
                      errhint("Is another postmaster already running on port %d?",
                              portNumber) :
                      errhint("Is another postmaster already running on port %d?"
                              " If not, wait a few seconds and retry.",
                              portNumber)) : 0));
            closesocket(fd);
            continue;
        }
 
        if (addr->ai_family == AF_UNIX)
        {
            if (Setup_AF_UNIX(service) != STATUS_OK)
            {
                closesocket(fd);
                break;
            }
        }
 
        /*
         * Select appropriate accept-queue length limit.  It seems reasonable
         * to use a value similar to the maximum number of child processes
         * that the postmaster will permit.
         */
        maxconn = MaxConnections * 2;
 
        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;
        }
 
        if (addr->ai_family == AF_UNIX)
            ereport(LOG,
                    (errmsg("listening on Unix socket \"%s\"",
                            addrDesc)));
        else
            ereport(LOG,
            /* translator: first %s is IPv4 or IPv6 */
                    (errmsg("listening on %s address \"%s\", port %d",
                            familyDesc, addrDesc, portNumber)));
 
        ListenSockets[*NumListenSockets] = fd;
        (*NumListenSockets)++;
        added++;
    }
 
    pg_freeaddrinfo_all(hint.ai_family, addrs);
 
    if (!added)
        return STATUS_ERROR;
 
    return STATUS_OK;
}
 
 
/*
 * 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;
}
 
 
/*
 * AcceptConnection -- accept a new connection with client using
 *      server port.  Fills *client_sock with the FD and endpoint info
 *      of the new connection.
 *
 * ASSUME: that this doesn't need to be non-blocking because
 *      the Postmaster waits for the socket to be ready to accept().
 *
 * RETURNS: STATUS_OK or STATUS_ERROR
 */
int
AcceptConnection(pgsocket server_fd, ClientSocket *client_sock)
{
    /* accept connection and fill in the client (remote) address */
    client_sock->raddr.salen = sizeof(client_sock->raddr.addr);
    if ((client_sock->sock = accept(server_fd,
                                    (struct sockaddr *) &client_sock->raddr.addr,
                                    &client_sock->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;
    }
 
    return STATUS_OK;
}
 
/*
 * 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 */
}
 
 
/* --------------------------------
 * 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;
 
        errno = 0;
 
        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.
             *
             * If errno is zero, assume it's EOF and let the caller complain.
             */
            if (errno != 0)
                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);
 
    errno = 0;
 
    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.
             *
             * If errno is zero, assume it's EOF and let the caller complain.
             */
            if (errno != 0)
                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(void *b, size_t len)
{
    char       *s = b;
    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_remaining_data    - return number of bytes in receive buffer
 *
 * This will *not* attempt to read more data. And reading up to that number of
 * bytes should not cause reading any more data either.
 * --------------------------------
 */
ssize_t
pq_buffer_remaining_data(void)
{
    Assert(PqRecvLength >= PqRecvPointer);
    return (PqRecvLength - PqRecvPointer);
}
 
 
/* --------------------------------
 *      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(&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 inline int
internal_putbytes(const void *b, size_t len)
{
    const char *s = b;
 
    while (len > 0)
    {
        /* If buffer is full, then flush it out */
        if (PqSendPointer >= PqSendBufferSize)
        {
            socket_set_nonblocking(false);
            if (internal_flush())
                return EOF;
        }
 
        /*
         * If the buffer is empty and data length is larger than the buffer
         * size, send it without buffering.  Otherwise, copy as much data as
         * possible into the buffer.
         */
        if (len >= PqSendBufferSize && PqSendStart == PqSendPointer)
        {
            size_t      start = 0;
 
            socket_set_nonblocking(false);
            if (internal_flush_buffer(s, &start, &len))
                return EOF;
        }
        else
        {
            size_t      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 inline int
internal_flush(void)
{
    return internal_flush_buffer(PqSendBuffer, &PqSendStart, &PqSendPointer);
}
 
/* --------------------------------
 *      internal_flush_buffer - flush the given buffer content
 *
 * 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 pg_noinline int
internal_flush_buffer(const char *buf, size_t *start, size_t *end)
{
    static int  last_reported_send_errno = 0;
 
    const char *bufptr = buf + *start;
    const char *bufend = buf + *end;
 
    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.
             */
            *start = *end = 0;
            ClientConnectionLost = 1;
            InterruptPending = 1;
            return EOF;
        }
 
        last_reported_send_errno = 0;   /* reset after any successful send */
        bufptr += r;
        *start += r;
    }
 
    *start = *end = 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(&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 || port->laddr.addr.ss_family == AF_UNIX)
        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 || port->laddr.addr.ss_family == AF_UNIX)
        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 || port->laddr.addr.ss_family == AF_UNIX)
        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 || port->laddr.addr.ss_family == AF_UNIX)
        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 || port->laddr.addr.ss_family == AF_UNIX)
        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 || port->laddr.addr.ss_family == AF_UNIX)
        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 || port->laddr.addr.ss_family == AF_UNIX)
        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 || port->laddr.addr.ss_family == AF_UNIX)
        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;
}
 
/*
 * GUC assign_hook for tcp_keepalives_idle
 */
void
assign_tcp_keepalives_idle(int newval, void *extra)
{
    /*
     * The kernel API provides no way to test a value without setting it; and
     * once we set it we might fail to unset it.  So there seems little point
     * in fully implementing the check-then-assign GUC API for these
     * variables.  Instead we just do the assignment on demand.
     * pq_setkeepalivesidle reports any problems via ereport(LOG).
     *
     * This approach means that the GUC value might have little to do with the
     * actual kernel value, so we use a show_hook that retrieves the kernel
     * value rather than trusting GUC's copy.
     */
    (void) pq_setkeepalivesidle(newval, MyProcPort);
}
 
/*
 * GUC show_hook for tcp_keepalives_idle
 */
const char *
show_tcp_keepalives_idle(void)
{
    /* See comments in assign_tcp_keepalives_idle */
    static char nbuf[16];
 
    snprintf(nbuf, sizeof(nbuf), "%d", pq_getkeepalivesidle(MyProcPort));
    return nbuf;
}
 
/*
 * GUC assign_hook for tcp_keepalives_interval
 */
void
assign_tcp_keepalives_interval(int newval, void *extra)
{
    /* See comments in assign_tcp_keepalives_idle */
    (void) pq_setkeepalivesinterval(newval, MyProcPort);
}
 
/*
 * GUC show_hook for tcp_keepalives_interval
 */
const char *
show_tcp_keepalives_interval(void)
{
    /* See comments in assign_tcp_keepalives_idle */
    static char nbuf[16];
 
    snprintf(nbuf, sizeof(nbuf), "%d", pq_getkeepalivesinterval(MyProcPort));
    return nbuf;
}
 
/*
 * GUC assign_hook for tcp_keepalives_count
 */
void
assign_tcp_keepalives_count(int newval, void *extra)
{
    /* See comments in assign_tcp_keepalives_idle */
    (void) pq_setkeepalivescount(newval, MyProcPort);
}
 
/*
 * GUC show_hook for tcp_keepalives_count
 */
const char *
show_tcp_keepalives_count(void)
{
    /* See comments in assign_tcp_keepalives_idle */
    static char nbuf[16];
 
    snprintf(nbuf, sizeof(nbuf), "%d", pq_getkeepalivescount(MyProcPort));
    return nbuf;
}
 
/*
 * GUC assign_hook for tcp_user_timeout
 */
void
assign_tcp_user_timeout(int newval, void *extra)
{
    /* See comments in assign_tcp_keepalives_idle */
    (void) pq_settcpusertimeout(newval, MyProcPort);
}
 
/*
 * GUC show_hook for tcp_user_timeout
 */
const char *
show_tcp_user_timeout(void)
{
    /* See comments in assign_tcp_keepalives_idle */
    static char nbuf[16];
 
    snprintf(nbuf, sizeof(nbuf), "%d", pq_gettcpusertimeout(MyProcPort));
    return nbuf;
}
 
/*
 * Check if the client is still connected.
 */
bool
pq_check_connection(void)
{
    WaitEvent   events[FeBeWaitSetNEvents];
    int         rc;
 
    /*
     * It's OK to modify the socket event filter without restoring, because
     * all FeBeWaitSet socket wait sites do the same.
     */
    ModifyWaitEvent(FeBeWaitSet, FeBeWaitSetSocketPos, WL_SOCKET_CLOSED, NULL);
 
retry:
    rc = WaitEventSetWait(FeBeWaitSet, 0, events, lengthof(events), 0);
    for (int i = 0; i < rc; ++i)
    {
        if (events[i].events & WL_SOCKET_CLOSED)
            return false;
        if (events[i].events & WL_LATCH_SET)
        {
            /*
             * A latch event might be preventing other events from being
             * reported.  Reset it and poll again.  No need to restore it
             * because no code should expect latches to survive across
             * CHECK_FOR_INTERRUPTS().
             */
            ResetLatch(MyLatch);
            goto retry;
        }
    }
 
    return true;
}