postgresql/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, FeBeWaitSetNEvents);
	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;
	int			max_backends = GetMaxBackends();

#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 (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. */
		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 (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, 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 ?
					 (addr->ai_family == AF_UNIX ?
					  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 = max_backends * 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 (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(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 || 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;
}

/*
 * 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;
}