text: /*-------------------------------------------------------------------------
   *
   * 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) 1996-2021, PostgreSQL Global Development Group
   * Portions Copyright (c) 1994, Regents of the University of California
   *
   *	src/backend/libpq/pqcomm.c
   *
   *-------------------------------------------------------------------------
   */
  
  /*------------------------
   * INTERFACE ROUTINES
   *
   * setup/teardown:
   *		StreamServerPort	- Open postmaster's server port
   *		StreamConnection	- Create new connection with client
   *		StreamClose			- Close a client/backend connection
   *		TouchSocketFiles	- Protect socket files against /tmp cleaners
   *		pq_init			- initialize libpq at backend startup
   *		socket_comm_reset	- reset libpq during error recovery
   *		socket_close		- shutdown libpq at backend exit
   *
   * low-level I/O:
   *		pq_getbytes		- get a known number of bytes from connection
   *		pq_getmessage	- get a message with length word from connection
   *		pq_getbyte		- get next byte from connection
   *		pq_peekbyte		- peek at next byte from connection
   *		pq_flush		- flush pending output
   *		pq_flush_if_writable - flush pending output if writable without blocking
   *		pq_getbyte_if_available - get a byte if available without blocking
   *
   * message-level I/O
   *		pq_putmessage	- send a normal message (suppressed in COPY OUT mode)
   *		pq_putmessage_noblock - buffer a normal message (suppressed in COPY OUT)
   *
   *------------------------
   */
  #include "postgres.h"
  
  #ifdef HAVE_POLL_H
  #include <poll.h>
  #endif
  #include <signal.h>
  #include <fcntl.h>
  #include <grp.h>
  #include <unistd.h>
  #include <sys/file.h>
  #include <sys/socket.h>
  #include <sys/stat.h>
  #include <sys/time.h>
  #include <netdb.h>
  #include <netinet/in.h>
  #ifdef HAVE_NETINET_TCP_H
  #include <netinet/tcp.h>
  #endif
  #include <utime.h>
  #ifdef _MSC_VER					/* mstcpip.h is missing on mingw */
  #include <mstcpip.h>
  #endif
  
  #include "common/ip.h"
  #include "libpq/libpq.h"
  #include "miscadmin.h"
  #include "port/pg_bswap.h"
  #include "storage/ipc.h"
  #include "utils/guc.h"
  #include "utils/memutils.h"
  
  /*
   * Cope with the various platform-specific ways to spell TCP keepalive socket
   * options.  This doesn't cover Windows, which as usual does its own thing.
   */
  #if defined(TCP_KEEPIDLE)
  /* TCP_KEEPIDLE is the name of this option on Linux and *BSD */
  #define PG_TCP_KEEPALIVE_IDLE TCP_KEEPIDLE
  #define PG_TCP_KEEPALIVE_IDLE_STR "TCP_KEEPIDLE"
  #elif defined(TCP_KEEPALIVE_THRESHOLD)
  /* TCP_KEEPALIVE_THRESHOLD is the name of this option on Solaris >= 11 */
  #define PG_TCP_KEEPALIVE_IDLE TCP_KEEPALIVE_THRESHOLD
  #define PG_TCP_KEEPALIVE_IDLE_STR "TCP_KEEPALIVE_THRESHOLD"
  #elif defined(TCP_KEEPALIVE) && defined(__darwin__)
  /* TCP_KEEPALIVE is the name of this option on macOS */
  /* Caution: Solaris has this symbol but it means something different */
  #define PG_TCP_KEEPALIVE_IDLE TCP_KEEPALIVE
  #define PG_TCP_KEEPALIVE_IDLE_STR "TCP_KEEPALIVE"
  #endif
  
  /*
   * Configuration options
   */
  int			Unix_socket_permissions;
  char	   *Unix_socket_group;
  
  /* Where the Unix socket files are (list of palloc'd strings) */
  static List *sock_paths = NIL;
  
  /*
   * Buffers for low-level I/O.
   *
   * The receive buffer is fixed size. Send buffer is usually 8k, but can be
   * enlarged by pq_putmessage_noblock() if the message doesn't fit otherwise.
   */
  
  #define PQ_SEND_BUFFER_SIZE 8192
  #define PQ_RECV_BUFFER_SIZE 8192
  
  static char *PqSendBuffer;
  static int	PqSendBufferSize;	/* Size send buffer */
  static int	PqSendPointer;		/* Next index to store a byte in PqSendBuffer */
  static int	PqSendStart;		/* Next index to send a byte in PqSendBuffer */
  
  static char PqRecvBuffer[PQ_RECV_BUFFER_SIZE];
  static int	PqRecvPointer;		/* Next index to read a byte from PqRecvBuffer */
  static int	PqRecvLength;		/* End of data available in PqRecvBuffer */
  
  /*
   * Message status
   */
  static bool PqCommBusy;			/* busy sending data to the client */
  static bool PqCommReadingMsg;	/* in the middle of reading a message */
  
  
  /* Internal functions */
  static void socket_comm_reset(void);
  static void socket_close(int code, Datum arg);
  static void socket_set_nonblocking(bool nonblocking);
  static int	socket_flush(void);
  static int	socket_flush_if_writable(void);
  static bool socket_is_send_pending(void);
  static int	socket_putmessage(char msgtype, const char *s, size_t len);
  static void socket_putmessage_noblock(char msgtype, const char *s, size_t len);
  static int	internal_putbytes(const char *s, size_t len);
  static int	internal_flush(void);
  
  #ifdef HAVE_UNIX_SOCKETS
  static int	Lock_AF_UNIX(const char *unixSocketDir, const char *unixSocketPath);
  static int	Setup_AF_UNIX(const char *sock_path);
  #endif							/* HAVE_UNIX_SOCKETS */
  
  static const PQcommMethods PqCommSocketMethods = {
  	socket_comm_reset,
  	socket_flush,
  	socket_flush_if_writable,
  	socket_is_send_pending,
  	socket_putmessage,
  	socket_putmessage_noblock
  };
  
  const PQcommMethods *PqCommMethods = &PqCommSocketMethods;
  
  WaitEventSet *FeBeWaitSet;
  
  
  /* --------------------------------
   *		pq_init - initialize libpq at backend startup
   * --------------------------------
   */
  void
  pq_init(void)
  {
  	int			socket_pos PG_USED_FOR_ASSERTS_ONLY;
  	int			latch_pos PG_USED_FOR_ASSERTS_ONLY;
  
  	/* initialize state variables */
  	PqSendBufferSize = PQ_SEND_BUFFER_SIZE;
  	PqSendBuffer = MemoryContextAlloc(TopMemoryContext, PqSendBufferSize);
  	PqSendPointer = PqSendStart = PqRecvPointer = PqRecvLength = 0;
  	PqCommBusy = false;
  	PqCommReadingMsg = false;
  
  	/* set up process-exit hook to close the socket */
  	on_proc_exit(socket_close, 0);
  
  	/*
  	 * In backends (as soon as forked) we operate the underlying socket in
  	 * nonblocking mode and use latches to implement blocking semantics if
  	 * needed. That allows us to provide safely interruptible reads and
  	 * writes.
  	 *
  	 * Use COMMERROR on failure, because ERROR would try to send the error to
  	 * the client, which might require changing the mode again, leading to
  	 * infinite recursion.
  	 */
  #ifndef WIN32
  	if (!pg_set_noblock(MyProcPort->sock))
  		ereport(COMMERROR,
  				(errmsg("could not set socket to nonblocking mode: %m")));
  #endif
  
  	FeBeWaitSet = CreateWaitEventSet(TopMemoryContext, 3);
  	socket_pos = AddWaitEventToSet(FeBeWaitSet, WL_SOCKET_WRITEABLE,
  								   MyProcPort->sock, NULL, NULL);
  	latch_pos = AddWaitEventToSet(FeBeWaitSet, WL_LATCH_SET, PGINVALID_SOCKET,
  								  MyLatch, NULL);
  	AddWaitEventToSet(FeBeWaitSet, WL_POSTMASTER_DEATH, PGINVALID_SOCKET,
  					  NULL, NULL);
  
  	/*
  	 * The event positions match the order we added them, but let's sanity
  	 * check them to be sure.
  	 */
  	Assert(socket_pos == FeBeWaitSetSocketPos);
  	Assert(latch_pos == FeBeWaitSetLatchPos);
  }
  
  /* --------------------------------
   *		socket_comm_reset - reset libpq during error recovery
   *
   * This is called from error recovery at the outer idle loop.  It's
   * just to get us out of trouble if we somehow manage to elog() from
   * inside a pqcomm.c routine (which ideally will never happen, but...)
   * --------------------------------
   */
  static void
  socket_comm_reset(void)
  {
  	/* Do not throw away pending data, but do reset the busy flag */
  	PqCommBusy = false;
  }
  
  /* --------------------------------
   *		socket_close - shutdown libpq at backend exit
   *
   * This is the one pg_on_exit_callback in place during BackendInitialize().
   * That function's unusual signal handling constrains that this callback be
   * safe to run at any instant.
   * --------------------------------
   */
  static void
  socket_close(int code, Datum arg)
  {
  	/* Nothing to do in a standalone backend, where MyProcPort is NULL. */
  	if (MyProcPort != NULL)
  	{
  #ifdef ENABLE_GSS
  		/*
  		 * Shutdown GSSAPI layer.  This section does nothing when interrupting
  		 * BackendInitialize(), because pg_GSS_recvauth() makes first use of
  		 * "ctx" and "cred".
  		 *
  		 * Note that we don't bother to free MyProcPort->gss, since we're
  		 * about to exit anyway.
  		 */
  		if (MyProcPort->gss)
  		{
  			OM_uint32	min_s;
  
  			if (MyProcPort->gss->ctx != GSS_C_NO_CONTEXT)
  				gss_delete_sec_context(&min_s, &MyProcPort->gss->ctx, NULL);
  
  			if (MyProcPort->gss->cred != GSS_C_NO_CREDENTIAL)
  				gss_release_cred(&min_s, &MyProcPort->gss->cred);
  		}
  #endif							/* ENABLE_GSS */
  
  		/*
  		 * Cleanly shut down SSL layer.  Nowhere else does a postmaster child
  		 * call this, so this is safe when interrupting BackendInitialize().
  		 */
  		secure_close(MyProcPort);
  
  		/*
  		 * Formerly we did an explicit close() here, but it seems better to
  		 * leave the socket open until the process dies.  This allows clients
  		 * to perform a "synchronous close" if they care --- wait till the
  		 * transport layer reports connection closure, and you can be sure the
  		 * backend has exited.
  		 *
  		 * We do set sock to PGINVALID_SOCKET to prevent any further I/O,
  		 * though.
  		 */
  		MyProcPort->sock = PGINVALID_SOCKET;
  	}
  }
  
  
  
  /*
   * Streams -- wrapper around Unix socket system calls
   *
   *
   *		Stream functions are used for vanilla TCP connection protocol.
   */
  
  
  /*
   * StreamServerPort -- open a "listening" port to accept connections.
   *
   * family should be AF_UNIX or AF_UNSPEC; portNumber is the port number.
   * For AF_UNIX ports, hostName should be NULL and unixSocketDir must be
   * specified.  For TCP ports, hostName is either NULL for all interfaces or
   * the interface to listen on, and unixSocketDir is ignored (can be NULL).
   *
   * Successfully opened sockets are added to the ListenSocket[] array (of
   * length MaxListen), at the first position that isn't PGINVALID_SOCKET.
   *
   * RETURNS: STATUS_OK or STATUS_ERROR
   */
  
  int
  StreamServerPort(int family, const char *hostName, unsigned short portNumber,
  				 const char *unixSocketDir,
  				 pgsocket ListenSocket[], int MaxListen)
  {
  	pgsocket	fd;
  	int			err;
  	int			maxconn;
  	int			ret;
  	char		portNumberStr[32];
  	const char *familyDesc;
  	char		familyDescBuf[64];
  	const char *addrDesc;
  	char		addrBuf[NI_MAXHOST];
  	char	   *service;
  	struct addrinfo *addrs = NULL,
  			   *addr;
  	struct addrinfo hint;
  	int			listen_index = 0;
  	int			added = 0;
  
  #ifdef HAVE_UNIX_SOCKETS
  	char		unixSocketPath[MAXPGPATH];
  #endif
  #if !defined(WIN32) || defined(IPV6_V6ONLY)
  	int			one = 1;
  #endif
  
  	/* Initialize hint structure */
  	MemSet(&hint, 0, sizeof(hint));
  	hint.ai_family = family;
  	hint.ai_flags = AI_PASSIVE;
  	hint.ai_socktype = SOCK_STREAM;
  
  #ifdef HAVE_UNIX_SOCKETS
  	if (family == AF_UNIX)
  	{
  		/*
  		 * Create unixSocketPath from portNumber and unixSocketDir and lock
  		 * that file path
  		 */
  		UNIXSOCK_PATH(unixSocketPath, portNumber, unixSocketDir);
  		if (strlen(unixSocketPath) >= UNIXSOCK_PATH_BUFLEN)
  		{
  			ereport(LOG,
  					(errmsg("Unix-domain socket path \"%s\" is too long (maximum %d bytes)",
  							unixSocketPath,
  							(int) (UNIXSOCK_PATH_BUFLEN - 1))));
  			return STATUS_ERROR;
  		}
  		if (Lock_AF_UNIX(unixSocketDir, unixSocketPath) != STATUS_OK)
  			return STATUS_ERROR;
  		service = unixSocketPath;
  	}
  	else
  #endif							/* HAVE_UNIX_SOCKETS */
  	{
  		snprintf(portNumberStr, sizeof(portNumberStr), "%d", portNumber);
  		service = portNumberStr;
  	}
  
  	ret = pg_getaddrinfo_all(hostName, service, &hint, &addrs);
  	if (ret || !addrs)
  	{
  		if (hostName)
  			ereport(LOG,
  					(errmsg("could not translate host name \"%s\", service \"%s\" to address: %s",
  							hostName, service, gai_strerror(ret))));
  		else
  			ereport(LOG,
  					(errmsg("could not translate service \"%s\" to address: %s",
  							service, gai_strerror(ret))));
  		if (addrs)
  			pg_freeaddrinfo_all(hint.ai_family, addrs);
  		return STATUS_ERROR;
  	}
  
  	for (addr = addrs; addr; addr = addr->ai_next)
  	{
  		if (!IS_AF_UNIX(family) && IS_AF_UNIX(addr->ai_family))
  		{
  			/*
  			 * Only set up a unix domain socket when they really asked for it.
  			 * The service/port is different in that case.
  			 */
  			continue;
  		}
  
  		/* See if there is still room to add 1 more socket. */
  		for (; listen_index < MaxListen; listen_index++)
  		{
  			if (ListenSocket[listen_index] == PGINVALID_SOCKET)
  				break;
  		}
  		if (listen_index >= MaxListen)
  		{
  			ereport(LOG,
  					(errmsg("could not bind to all requested addresses: MAXLISTEN (%d) exceeded",
  							MaxListen)));
  			break;
  		}
  
  		/* set up address family name for log messages */
  		switch (addr->ai_family)
  		{
  			case AF_INET:
  				familyDesc = _("IPv4");
  				break;
  #ifdef HAVE_IPV6
  			case AF_INET6:
  				familyDesc = _("IPv6");
  				break;
  #endif
  #ifdef HAVE_UNIX_SOCKETS
  			case AF_UNIX:
  				familyDesc = _("Unix");
  				break;
  #endif
  			default:
  				snprintf(familyDescBuf, sizeof(familyDescBuf),
  						 _("unrecognized address family %d"),
  						 addr->ai_family);
  				familyDesc = familyDescBuf;
  				break;
  		}
  
  		/* set up text form of address for log messages */
  #ifdef HAVE_UNIX_SOCKETS
  		if (addr->ai_family == AF_UNIX)
  			addrDesc = unixSocketPath;
  		else
  #endif
  		{
  			pg_getnameinfo_all((const struct sockaddr_storage *) addr->ai_addr,
  							   addr->ai_addrlen,
  							   addrBuf, sizeof(addrBuf),
  							   NULL, 0,
  							   NI_NUMERICHOST);
  			addrDesc = addrBuf;
  		}
  
  		if ((fd = socket(addr->ai_family, SOCK_STREAM, 0)) == PGINVALID_SOCKET)
  		{
  			ereport(LOG,
  					(errcode_for_socket_access(),
  			/* translator: first %s is IPv4, IPv6, or Unix */
  					 errmsg("could not create %s socket for address \"%s\": %m",
  							familyDesc, addrDesc)));
  			continue;
  		}
  
  #ifndef WIN32
  
  		/*
  		 * Without the SO_REUSEADDR flag, a new postmaster can't be started
  		 * right away after a stop or crash, giving "address already in use"
  		 * error on TCP ports.
  		 *
  		 * On win32, however, this behavior only happens if the
  		 * SO_EXCLUSIVEADDRUSE is set. With SO_REUSEADDR, win32 allows
  		 * multiple servers to listen on the same address, resulting in
  		 * unpredictable behavior. With no flags at all, win32 behaves as Unix
  		 * with SO_REUSEADDR.
  		 */
  		if (!IS_AF_UNIX(addr->ai_family))
  		{
  			if ((setsockopt(fd, SOL_SOCKET, SO_REUSEADDR,
  							(char *) &one, sizeof(one))) == -1)
  			{
  				ereport(LOG,
  						(errcode_for_socket_access(),
  				/* translator: third %s is IPv4, IPv6, or Unix */
  						 errmsg("%s(%s) failed for %s address \"%s\": %m",
  								"setsockopt", "SO_REUSEADDR",
  								familyDesc, addrDesc)));
  				closesocket(fd);
  				continue;
  			}
  		}
  #endif
  
  #ifdef IPV6_V6ONLY
  		if (addr->ai_family == AF_INET6)
  		{
  			if (setsockopt(fd, IPPROTO_IPV6, IPV6_V6ONLY,
  						   (char *) &one, sizeof(one)) == -1)
  			{
  				ereport(LOG,
  						(errcode_for_socket_access(),
  				/* translator: third %s is IPv4, IPv6, or Unix */
  						 errmsg("%s(%s) failed for %s address \"%s\": %m",
  								"setsockopt", "IPV6_V6ONLY",
  								familyDesc, addrDesc)));
  				closesocket(fd);
  				continue;
  			}
  		}
  #endif
  
  		/*
  		 * Note: This might fail on some OS's, like Linux older than
  		 * 2.4.21-pre3, that don't have the IPV6_V6ONLY socket option, and map
  		 * ipv4 addresses to ipv6.  It will show ::ffff:ipv4 for all ipv4
  		 * connections.
  		 */
  		err = bind(fd, addr->ai_addr, addr->ai_addrlen);
  		if (err < 0)
  		{
  			int			saved_errno = errno;
  
  			ereport(LOG,
  					(errcode_for_socket_access(),
  			/* translator: first %s is IPv4, IPv6, or Unix */
  					 errmsg("could not bind %s address \"%s\": %m",
  							familyDesc, addrDesc),
  					 saved_errno == EADDRINUSE ?
  					 (IS_AF_UNIX(addr->ai_family) ?
  					  errhint("Is another postmaster already running on port %d?",
  							  (int) portNumber) :
  					  errhint("Is another postmaster already running on port %d?"
  							  " If not, wait a few seconds and retry.",
  							  (int) portNumber)) : 0));
  			closesocket(fd);
  			continue;
  		}
  
  #ifdef HAVE_UNIX_SOCKETS
  		if (addr->ai_family == AF_UNIX)
  		{
  			if (Setup_AF_UNIX(service) != STATUS_OK)
  			{
  				closesocket(fd);
  				break;
  			}
  		}
  #endif
  
  		/*
  		 * Select appropriate accept-queue length limit.  PG_SOMAXCONN is only
  		 * intended to provide a clamp on the request on platforms where an
  		 * overly large request provokes a kernel error (are there any?).
  		 */
  		maxconn = MaxBackends * 2;
  		if (maxconn > PG_SOMAXCONN)
  			maxconn = PG_SOMAXCONN;
  
  		err = listen(fd, maxconn);
  		if (err < 0)
  		{
  			ereport(LOG,
  					(errcode_for_socket_access(),
  			/* translator: first %s is IPv4, IPv6, or Unix */
  					 errmsg("could not listen on %s address \"%s\": %m",
  							familyDesc, addrDesc)));
  			closesocket(fd);
  			continue;
  		}
  
  #ifdef HAVE_UNIX_SOCKETS
  		if (addr->ai_family == AF_UNIX)
  			ereport(LOG,
  					(errmsg("listening on Unix socket \"%s\"",
  							addrDesc)));
  		else
  #endif
  			ereport(LOG,
  			/* translator: first %s is IPv4 or IPv6 */
  					(errmsg("listening on %s address \"%s\", port %d",
  							familyDesc, addrDesc, (int) portNumber)));
  
  		ListenSocket[listen_index] = fd;
  		added++;
  	}
  
  	pg_freeaddrinfo_all(hint.ai_family, addrs);
  
  	if (!added)
  		return STATUS_ERROR;
  
  	return STATUS_OK;
  }
  
  
  #ifdef HAVE_UNIX_SOCKETS
  
  /*
   * Lock_AF_UNIX -- configure unix socket file path
   */
  static int
  Lock_AF_UNIX(const char *unixSocketDir, const char *unixSocketPath)
  {
  	/* no lock file for abstract sockets */
  	if (unixSocketPath[0] == '@')
  		return STATUS_OK;
  
  	/*
  	 * Grab an interlock file associated with the socket file.
  	 *
  	 * Note: there are two reasons for using a socket lock file, rather than
  	 * trying to interlock directly on the socket itself.  First, it's a lot
  	 * more portable, and second, it lets us remove any pre-existing socket
  	 * file without race conditions.
  	 */
  	CreateSocketLockFile(unixSocketPath, true, unixSocketDir);
  
  	/*
  	 * Once we have the interlock, we can safely delete any pre-existing
  	 * socket file to avoid failure at bind() time.
  	 */
  	(void) unlink(unixSocketPath);
  
  	/*
  	 * Remember socket file pathnames for later maintenance.
  	 */
  	sock_paths = lappend(sock_paths, pstrdup(unixSocketPath));
  
  	return STATUS_OK;
  }
  
  
  /*
   * Setup_AF_UNIX -- configure unix socket permissions
   */
  static int
  Setup_AF_UNIX(const char *sock_path)
  {
  	/* no file system permissions for abstract sockets */
  	if (sock_path[0] == '@')
  		return STATUS_OK;
  
  	/*
  	 * Fix socket ownership/permission if requested.  Note we must do this
  	 * before we listen() to avoid a window where unwanted connections could
  	 * get accepted.
  	 */
  	Assert(Unix_socket_group);
  	if (Unix_socket_group[0] != '\0')
  	{
  #ifdef WIN32
  		elog(WARNING, "configuration item unix_socket_group is not supported on this platform");
  #else
  		char	   *endptr;
  		unsigned long val;
  		gid_t		gid;
  
  		val = strtoul(Unix_socket_group, &endptr, 10);
  		if (*endptr == '\0')
  		{						/* numeric group id */
  			gid = val;
  		}
  		else
  		{						/* convert group name to id */
  			struct group *gr;
  
  			gr = getgrnam(Unix_socket_group);
  			if (!gr)
  			{
  				ereport(LOG,
  						(errmsg("group \"%s\" does not exist",
  								Unix_socket_group)));
  				return STATUS_ERROR;
  			}
  			gid = gr->gr_gid;
  		}
  		if (chown(sock_path, -1, gid) == -1)
  		{
  			ereport(LOG,
  					(errcode_for_file_access(),
  					 errmsg("could not set group of file \"%s\": %m",
  							sock_path)));
  			return STATUS_ERROR;
  		}
  #endif
  	}
  
  	if (chmod(sock_path, Unix_socket_permissions) == -1)
  	{
  		ereport(LOG,
  				(errcode_for_file_access(),
  				 errmsg("could not set permissions of file \"%s\": %m",
  						sock_path)));
  		return STATUS_ERROR;
  	}
  	return STATUS_OK;
  }
  #endif							/* HAVE_UNIX_SOCKETS */
  
  
  /*
   * StreamConnection -- create a new connection with client using
   *		server port.  Set port->sock to the FD of the new connection.
   *
   * ASSUME: that this doesn't need to be non-blocking because
   *		the Postmaster uses select() to tell when the socket is ready for
   *		accept().
   *
   * RETURNS: STATUS_OK or STATUS_ERROR
   */
  int
  StreamConnection(pgsocket server_fd, Port *port)
  {
  	/* accept connection and fill in the client (remote) address */
  	port->raddr.salen = sizeof(port->raddr.addr);
  	if ((port->sock = accept(server_fd,
  							 (struct sockaddr *) &port->raddr.addr,
  							 &port->raddr.salen)) == PGINVALID_SOCKET)
  	{
  		ereport(LOG,
  				(errcode_for_socket_access(),
  				 errmsg("could not accept new connection: %m")));
  
  		/*
  		 * If accept() fails then postmaster.c will still see the server
  		 * socket as read-ready, and will immediately try again.  To avoid
  		 * uselessly sucking lots of CPU, delay a bit before trying again.
  		 * (The most likely reason for failure is being out of kernel file
  		 * table slots; we can do little except hope some will get freed up.)
  		 */
  		pg_usleep(100000L);		/* wait 0.1 sec */
  		return STATUS_ERROR;
  	}
  
  	/* fill in the server (local) address */
  	port->laddr.salen = sizeof(port->laddr.addr);
  	if (getsockname(port->sock,
  					(struct sockaddr *) &port->laddr.addr,
  					&port->laddr.salen) < 0)
  	{
  		ereport(LOG,
  				(errmsg("%s() failed: %m", "getsockname")));
  		return STATUS_ERROR;
  	}
  
  	/* select NODELAY and KEEPALIVE options if it's a TCP connection */
  	if (!IS_AF_UNIX(port->laddr.addr.ss_family))
  	{
  		int			on;
  #ifdef WIN32
  		int			oldopt;
  		int			optlen;
  		int			newopt;
  #endif
  
  #ifdef	TCP_NODELAY
  		on = 1;
  		if (setsockopt(port->sock, IPPROTO_TCP, TCP_NODELAY,
  					   (char *) &on, sizeof(on)) < 0)
  		{
  			ereport(LOG,
  					(errmsg("%s(%s) failed: %m", "setsockopt", "TCP_NODELAY")));
  			return STATUS_ERROR;
  		}
  #endif
  		on = 1;
  		if (setsockopt(port->sock, SOL_SOCKET, SO_KEEPALIVE,
  					   (char *) &on, sizeof(on)) < 0)
  		{
  			ereport(LOG,
  					(errmsg("%s(%s) failed: %m", "setsockopt", "SO_KEEPALIVE")));
  			return STATUS_ERROR;
  		}
  
  #ifdef WIN32
  
  		/*
  		 * This is a Win32 socket optimization.  The OS send buffer should be
  		 * large enough to send the whole Postgres send buffer in one go, or
  		 * performance suffers.  The Postgres send buffer can be enlarged if a
  		 * very large message needs to be sent, but we won't attempt to
  		 * enlarge the OS buffer if that happens, so somewhat arbitrarily
  		 * ensure that the OS buffer is at least PQ_SEND_BUFFER_SIZE * 4.
  		 * (That's 32kB with the current default).
  		 *
  		 * The default OS buffer size used to be 8kB in earlier Windows
  		 * versions, but was raised to 64kB in Windows 2012.  So it shouldn't
  		 * be necessary to change it in later versions anymore.  Changing it
  		 * unnecessarily can even reduce performance, because setting
  		 * SO_SNDBUF in the application disables the "dynamic send buffering"
  		 * feature that was introduced in Windows 7.  So before fiddling with
  		 * SO_SNDBUF, check if the current buffer size is already large enough
  		 * and only increase it if necessary.
  		 *
  		 * See https://support.microsoft.com/kb/823764/EN-US/ and
  		 * https://msdn.microsoft.com/en-us/library/bb736549%28v=vs.85%29.aspx
  		 */
  		optlen = sizeof(oldopt);
  		if (getsockopt(port->sock, SOL_SOCKET, SO_SNDBUF, (char *) &oldopt,
  					   &optlen) < 0)
  		{
  			ereport(LOG,
  					(errmsg("%s(%s) failed: %m", "getsockopt", "SO_SNDBUF")));
  			return STATUS_ERROR;
  		}
  		newopt = PQ_SEND_BUFFER_SIZE * 4;
  		if (oldopt < newopt)
  		{
  			if (setsockopt(port->sock, SOL_SOCKET, SO_SNDBUF, (char *) &newopt,
  						   sizeof(newopt)) < 0)
  			{
  				ereport(LOG,
  						(errmsg("%s(%s) failed: %m", "setsockopt", "SO_SNDBUF")));
  				return STATUS_ERROR;
  			}
  		}
  #endif
  
  		/*
  		 * Also apply the current keepalive parameters.  If we fail to set a
  		 * parameter, don't error out, because these aren't universally
  		 * supported.  (Note: you might think we need to reset the GUC
  		 * variables to 0 in such a case, but it's not necessary because the
  		 * show hooks for these variables report the truth anyway.)
  		 */
  		(void) pq_setkeepalivesidle(tcp_keepalives_idle, port);
  		(void) pq_setkeepalivesinterval(tcp_keepalives_interval, port);
  		(void) pq_setkeepalivescount(tcp_keepalives_count, port);
  		(void) pq_settcpusertimeout(tcp_user_timeout, port);
  	}
  
  	return STATUS_OK;
  }
  
  /*
   * StreamClose -- close a client/backend connection
   *
   * NOTE: this is NOT used to terminate a session; it is just used to release
   * the file descriptor in a process that should no longer have the socket
   * open.  (For example, the postmaster calls this after passing ownership
   * of the connection to a child process.)  It is expected that someone else
   * still has the socket open.  So, we only want to close the descriptor,
   * we do NOT want to send anything to the far end.
   */
  void
  StreamClose(pgsocket sock)
  {
  	closesocket(sock);
  }
  
  /*
   * TouchSocketFiles -- mark socket files as recently accessed
   *
   * This routine should be called every so often to ensure that the socket
   * files have a recent mod date (ordinary operations on sockets usually won't
   * change the mod date).  That saves them from being removed by
   * overenthusiastic /tmp-directory-cleaner daemons.  (Another reason we should
   * never have put the socket file in /tmp...)
   */
  void
  TouchSocketFiles(void)
  {
  	ListCell   *l;
  
  	/* Loop through all created sockets... */
  	foreach(l, sock_paths)
  	{
  		char	   *sock_path = (char *) lfirst(l);
  
  		/* Ignore errors; there's no point in complaining */
  		(void) utime(sock_path, NULL);
  	}
  }
  
  /*
   * RemoveSocketFiles -- unlink socket files at postmaster shutdown
   */
  void
  RemoveSocketFiles(void)
  {
  	ListCell   *l;
  
  	/* Loop through all created sockets... */
  	foreach(l, sock_paths)
  	{
  		char	   *sock_path = (char *) lfirst(l);
  
  		/* Ignore any error. */
  		(void) unlink(sock_path);
  	}
  	/* Since we're about to exit, no need to reclaim storage */
  	sock_paths = NIL;
  }
  
  
  /* --------------------------------
   * Low-level I/O routines begin here.
   *
   * These routines communicate with a frontend client across a connection
   * already established by the preceding routines.
   * --------------------------------
   */
  
  /* --------------------------------
   *			  socket_set_nonblocking - set socket blocking/non-blocking
   *
   * Sets the socket non-blocking if nonblocking is true, or sets it
   * blocking otherwise.
   * --------------------------------
   */
  static void
  socket_set_nonblocking(bool nonblocking)
  {
  	if (MyProcPort == NULL)
  		ereport(ERROR,
  				(errcode(ERRCODE_CONNECTION_DOES_NOT_EXIST),
  				 errmsg("there is no client connection")));
  
  	MyProcPort->noblock = nonblocking;
  }
  
  /* --------------------------------
   *		pq_recvbuf - load some bytes into the input buffer
   *
   *		returns 0 if OK, EOF if trouble
   * --------------------------------
   */
  static int
  pq_recvbuf(void)
  {
  	if (PqRecvPointer > 0)
  	{
  		if (PqRecvLength > PqRecvPointer)
  		{
  			/* still some unread data, left-justify it in the buffer */
  			memmove(PqRecvBuffer, PqRecvBuffer + PqRecvPointer,
  					PqRecvLength - PqRecvPointer);
  			PqRecvLength -= PqRecvPointer;
  			PqRecvPointer = 0;
  		}
  		else
  			PqRecvLength = PqRecvPointer = 0;
  	}
  
  	/* Ensure that we're in blocking mode */
  	socket_set_nonblocking(false);
  
  	/* Can fill buffer from PqRecvLength and upwards */
  	for (;;)
  	{
  		int			r;
  
  		r = secure_read(MyProcPort, PqRecvBuffer + PqRecvLength,
  						PQ_RECV_BUFFER_SIZE - PqRecvLength);
  
  		if (r < 0)
  		{
  			if (errno == EINTR)
  				continue;		/* Ok if interrupted */
  
  			/*
  			 * Careful: an ereport() that tries to write to the client would
  			 * cause recursion to here, leading to stack overflow and core
  			 * dump!  This message must go *only* to the postmaster log.
  			 */
  			ereport(COMMERROR,
  					(errcode_for_socket_access(),
  					 errmsg("could not receive data from client: %m")));
  			return EOF;
  		}
  		if (r == 0)
  		{
  			/*
  			 * EOF detected.  We used to write a log message here, but it's
  			 * better to expect the ultimate caller to do that.
  			 */
  			return EOF;
  		}
  		/* r contains number of bytes read, so just incr length */
  		PqRecvLength += r;
  		return 0;
  	}
  }
  
  /* --------------------------------
   *		pq_getbyte	- get a single byte from connection, or return EOF
   * --------------------------------
   */
  int
  pq_getbyte(void)
  {
  	Assert(PqCommReadingMsg);
  
  	while (PqRecvPointer >= PqRecvLength)
  	{
  		if (pq_recvbuf())		/* If nothing in buffer, then recv some */
  			return EOF;			/* Failed to recv data */
  	}
  	return (unsigned char) PqRecvBuffer[PqRecvPointer++];
  }
  
  /* --------------------------------
   *		pq_peekbyte		- peek at next byte from connection
   *
   *	 Same as pq_getbyte() except we don't advance the pointer.
   * --------------------------------
   */
  int
  pq_peekbyte(void)
  {
  	Assert(PqCommReadingMsg);
  
  	while (PqRecvPointer >= PqRecvLength)
  	{
  		if (pq_recvbuf())		/* If nothing in buffer, then recv some */
  			return EOF;			/* Failed to recv data */
  	}
  	return (unsigned char) PqRecvBuffer[PqRecvPointer];
  }
  
  /* --------------------------------
   *		pq_getbyte_if_available - get a single byte from connection,
   *			if available
   *
   * The received byte is stored in *c. Returns 1 if a byte was read,
   * 0 if no data was available, or EOF if trouble.
   * --------------------------------
   */
  int
  pq_getbyte_if_available(unsigned char *c)
  {
  	int			r;
  
  	Assert(PqCommReadingMsg);
  
  	if (PqRecvPointer < PqRecvLength)
  	{
  		*c = PqRecvBuffer[PqRecvPointer++];
  		return 1;
  	}
  
  	/* Put the socket into non-blocking mode */
  	socket_set_nonblocking(true);
  
  	r = secure_read(MyProcPort, c, 1);
  	if (r < 0)
  	{
  		/*
  		 * Ok if no data available without blocking or interrupted (though
  		 * EINTR really shouldn't happen with a non-blocking socket). Report
  		 * other errors.
  		 */
  		if (errno == EAGAIN || errno == EWOULDBLOCK || errno == EINTR)
  			r = 0;
  		else
  		{
  			/*
  			 * Careful: an ereport() that tries to write to the client would
  			 * cause recursion to here, leading to stack overflow and core
  			 * dump!  This message must go *only* to the postmaster log.
  			 */
  			ereport(COMMERROR,
  					(errcode_for_socket_access(),
  					 errmsg("could not receive data from client: %m")));
  			r = EOF;
  		}
  	}
  	else if (r == 0)
  	{
  		/* EOF detected */
  		r = EOF;
  	}
  
  	return r;
  }
  
  /* --------------------------------
   *		pq_getbytes		- get a known number of bytes from connection
   *
   *		returns 0 if OK, EOF if trouble
   * --------------------------------
   */
  int
  pq_getbytes(char *s, size_t len)
  {
  	size_t		amount;
  
  	Assert(PqCommReadingMsg);
  
  	while (len > 0)
  	{
  		while (PqRecvPointer >= PqRecvLength)
  		{
  			if (pq_recvbuf())	/* If nothing in buffer, then recv some */
  				return EOF;		/* Failed to recv data */
  		}
  		amount = PqRecvLength - PqRecvPointer;
  		if (amount > len)
  			amount = len;
  		memcpy(s, PqRecvBuffer + PqRecvPointer, amount);
  		PqRecvPointer += amount;
  		s += amount;
  		len -= amount;
  	}
  	return 0;
  }
  
  /* --------------------------------
   *		pq_discardbytes		- throw away a known number of bytes
   *
   *		same as pq_getbytes except we do not copy the data to anyplace.
   *		this is used for resynchronizing after read errors.
   *
   *		returns 0 if OK, EOF if trouble
   * --------------------------------
   */
  static int
  pq_discardbytes(size_t len)
  {
  	size_t		amount;
  
  	Assert(PqCommReadingMsg);
  
  	while (len > 0)
  	{
  		while (PqRecvPointer >= PqRecvLength)
  		{
  			if (pq_recvbuf())	/* If nothing in buffer, then recv some */
  				return EOF;		/* Failed to recv data */
  		}
  		amount = PqRecvLength - PqRecvPointer;
  		if (amount > len)
  			amount = len;
  		PqRecvPointer += amount;
  		len -= amount;
  	}
  	return 0;
  }
  
  /* --------------------------------
   *		pq_buffer_has_data		- is any buffered data available to read?
   *
   * This will *not* attempt to read more data.
   * --------------------------------
   */
  bool
  pq_buffer_has_data(void)
  {
  	return (PqRecvPointer < PqRecvLength);
  }
  
  
  /* --------------------------------
   *		pq_startmsgread - begin reading a message from the client.
   *
   *		This must be called before any of the pq_get* functions.
   * --------------------------------
   */
  void
  pq_startmsgread(void)
  {
  	/*
  	 * There shouldn't be a read active already, but let's check just to be
  	 * sure.
  	 */
  	if (PqCommReadingMsg)
  		ereport(FATAL,
  				(errcode(ERRCODE_PROTOCOL_VIOLATION),
  				 errmsg("terminating connection because protocol synchronization was lost")));
  
  	PqCommReadingMsg = true;
  }
  
  
  /* --------------------------------
   *		pq_endmsgread	- finish reading message.
   *
   *		This must be called after reading a message with pq_getbytes()
   *		and friends, to indicate that we have read the whole message.
   *		pq_getmessage() does this implicitly.
   * --------------------------------
   */
  void
  pq_endmsgread(void)
  {
  	Assert(PqCommReadingMsg);
  
  	PqCommReadingMsg = false;
  }
  
  /* --------------------------------
   *		pq_is_reading_msg - are we currently reading a message?
   *
   * This is used in error recovery at the outer idle loop to detect if we have
   * lost protocol sync, and need to terminate the connection. pq_startmsgread()
   * will check for that too, but it's nicer to detect it earlier.
   * --------------------------------
   */
  bool
  pq_is_reading_msg(void)
  {
  	return PqCommReadingMsg;
  }
  
  /* --------------------------------
   *		pq_getmessage	- get a message with length word from connection
   *
   *		The return value is placed in an expansible StringInfo, which has
   *		already been initialized by the caller.
   *		Only the message body is placed in the StringInfo; the length word
   *		is removed.  Also, s->cursor is initialized to zero for convenience
   *		in scanning the message contents.
   *
   *		maxlen is the upper limit on the length of the
   *		message we are willing to accept.  We abort the connection (by
   *		returning EOF) if client tries to send more than that.
   *
   *		returns 0 if OK, EOF if trouble
   * --------------------------------
   */
  int
  pq_getmessage(StringInfo s, int maxlen)
  {
  	int32		len;
  
  	Assert(PqCommReadingMsg);
  
  	resetStringInfo(s);
  
  	/* Read message length word */
  	if (pq_getbytes((char *) &len, 4) == EOF)
  	{
  		ereport(COMMERROR,
  				(errcode(ERRCODE_PROTOCOL_VIOLATION),
  				 errmsg("unexpected EOF within message length word")));
  		return EOF;
  	}
  
  	len = pg_ntoh32(len);
  
  	if (len < 4 || len > maxlen)
  	{
  		ereport(COMMERROR,
  				(errcode(ERRCODE_PROTOCOL_VIOLATION),
  				 errmsg("invalid message length")));
  		return EOF;
  	}
  
  	len -= 4;					/* discount length itself */
  
  	if (len > 0)
  	{
  		/*
  		 * Allocate space for message.  If we run out of room (ridiculously
  		 * large message), we will elog(ERROR), but we want to discard the
  		 * message body so as not to lose communication sync.
  		 */
  		PG_TRY();
  		{
  			enlargeStringInfo(s, len);
  		}
  		PG_CATCH();
  		{
  			if (pq_discardbytes(len) == EOF)
  				ereport(COMMERROR,
  						(errcode(ERRCODE_PROTOCOL_VIOLATION),
  						 errmsg("incomplete message from client")));
  
  			/* we discarded the rest of the message so we're back in sync. */
  			PqCommReadingMsg = false;
  			PG_RE_THROW();
  		}
  		PG_END_TRY();
  
  		/* And grab the message */
  		if (pq_getbytes(s->data, len) == EOF)
  		{
  			ereport(COMMERROR,
  					(errcode(ERRCODE_PROTOCOL_VIOLATION),
  					 errmsg("incomplete message from client")));
  			return EOF;
  		}
  		s->len = len;
  		/* Place a trailing null per StringInfo convention */
  		s->data[len] = '\0';
  	}
  
  	/* finished reading the message. */
  	PqCommReadingMsg = false;
  
  	return 0;
  }
  
  
  static int
  internal_putbytes(const char *s, size_t len)
  {
  	size_t		amount;
  
  	while (len > 0)
  	{
  		/* If buffer is full, then flush it out */
  		if (PqSendPointer >= PqSendBufferSize)
  		{
  			socket_set_nonblocking(false);
  			if (internal_flush())
  				return EOF;
  		}
  		amount = PqSendBufferSize - PqSendPointer;
  		if (amount > len)
  			amount = len;
  		memcpy(PqSendBuffer + PqSendPointer, s, amount);
  		PqSendPointer += amount;
  		s += amount;
  		len -= amount;
  	}
  	return 0;
  }
  
  /* --------------------------------
   *		socket_flush		- flush pending output
   *
   *		returns 0 if OK, EOF if trouble
   * --------------------------------
   */
  static int
  socket_flush(void)
  {
  	int			res;
  
  	/* No-op if reentrant call */
  	if (PqCommBusy)
  		return 0;
  	PqCommBusy = true;
  	socket_set_nonblocking(false);
  	res = internal_flush();
  	PqCommBusy = false;
  	return res;
  }
  
  /* --------------------------------
   *		internal_flush - flush pending output
   *
   * Returns 0 if OK (meaning everything was sent, or operation would block
   * and the socket is in non-blocking mode), or EOF if trouble.
   * --------------------------------
   */
  static int
  internal_flush(void)
  {
  	static int	last_reported_send_errno = 0;
  
  	char	   *bufptr = PqSendBuffer + PqSendStart;
  	char	   *bufend = PqSendBuffer + PqSendPointer;
  
  	while (bufptr < bufend)
  	{
  		int			r;
  
  		r = secure_write(MyProcPort, bufptr, bufend - bufptr);
  
  		if (r <= 0)
  		{
  			if (errno == EINTR)
  				continue;		/* Ok if we were interrupted */
  
  			/*
  			 * Ok if no data writable without blocking, and the socket is in
  			 * non-blocking mode.
  			 */
  			if (errno == EAGAIN ||
  				errno == EWOULDBLOCK)
  			{
  				return 0;
  			}
  
  			/*
  			 * Careful: an ereport() that tries to write to the client would
  			 * cause recursion to here, leading to stack overflow and core
  			 * dump!  This message must go *only* to the postmaster log.
  			 *
  			 * If a client disconnects while we're in the midst of output, we
  			 * might write quite a bit of data before we get to a safe query
  			 * abort point.  So, suppress duplicate log messages.
  			 */
  			if (errno != last_reported_send_errno)
  			{
  				last_reported_send_errno = errno;
  				ereport(COMMERROR,
  						(errcode_for_socket_access(),
  						 errmsg("could not send data to client: %m")));
  			}
  
  			/*
  			 * We drop the buffered data anyway so that processing can
  			 * continue, even though we'll probably quit soon. We also set a
  			 * flag that'll cause the next CHECK_FOR_INTERRUPTS to terminate
  			 * the connection.
  			 */
  			PqSendStart = PqSendPointer = 0;
  			ClientConnectionLost = 1;
  			InterruptPending = 1;
  			return EOF;
  		}
  
  		last_reported_send_errno = 0;	/* reset after any successful send */
  		bufptr += r;
  		PqSendStart += r;
  	}
  
  	PqSendStart = PqSendPointer = 0;
  	return 0;
  }
  
  /* --------------------------------
   *		pq_flush_if_writable - flush pending output if writable without blocking
   *
   * Returns 0 if OK, or EOF if trouble.
   * --------------------------------
   */
  static int
  socket_flush_if_writable(void)
  {
  	int			res;
  
  	/* Quick exit if nothing to do */
  	if (PqSendPointer == PqSendStart)
  		return 0;
  
  	/* No-op if reentrant call */
  	if (PqCommBusy)
  		return 0;
  
  	/* Temporarily put the socket into non-blocking mode */
  	socket_set_nonblocking(true);
  
  	PqCommBusy = true;
  	res = internal_flush();
  	PqCommBusy = false;
  	return res;
  }
  
  /* --------------------------------
   *	socket_is_send_pending	- is there any pending data in the output buffer?
   * --------------------------------
   */
  static bool
  socket_is_send_pending(void)
  {
  	return (PqSendStart < PqSendPointer);
  }
  
  /* --------------------------------
   * Message-level I/O routines begin here.
   * --------------------------------
   */
  
  
  /* --------------------------------
   *		socket_putmessage - send a normal message (suppressed in COPY OUT mode)
   *
   *		msgtype is a message type code to place before the message body.
   *
   *		len is the length of the message body data at *s.  A message length
   *		word (equal to len+4 because it counts itself too) is inserted by this
   *		routine.
   *
   *		We suppress messages generated while pqcomm.c is busy.  This
   *		avoids any possibility of messages being inserted within other
   *		messages.  The only known trouble case arises if SIGQUIT occurs
   *		during a pqcomm.c routine --- quickdie() will try to send a warning
   *		message, and the most reasonable approach seems to be to drop it.
   *
   *		returns 0 if OK, EOF if trouble
   * --------------------------------
   */
  static int
  socket_putmessage(char msgtype, const char *s, size_t len)
  {
  	uint32		n32;
  
  	Assert(msgtype != 0);
  
  	if (PqCommBusy)
  		return 0;
  	PqCommBusy = true;
  	if (internal_putbytes(&msgtype, 1))
  		goto fail;
  
  	n32 = pg_hton32((uint32) (len + 4));
  	if (internal_putbytes((char *) &n32, 4))
  		goto fail;
  
  	if (internal_putbytes(s, len))
  		goto fail;
  	PqCommBusy = false;
  	return 0;
  
  fail:
  	PqCommBusy = false;
  	return EOF;
  }
  
  /* --------------------------------
   *		pq_putmessage_noblock	- like pq_putmessage, but never blocks
   *
   *		If the output buffer is too small to hold the message, the buffer
   *		is enlarged.
   */
  static void
  socket_putmessage_noblock(char msgtype, const char *s, size_t len)
  {
  	int			res PG_USED_FOR_ASSERTS_ONLY;
  	int			required;
  
  	/*
  	 * Ensure we have enough space in the output buffer for the message header
  	 * as well as the message itself.
  	 */
  	required = PqSendPointer + 1 + 4 + len;
  	if (required > PqSendBufferSize)
  	{
  		PqSendBuffer = repalloc(PqSendBuffer, required);
  		PqSendBufferSize = required;
  	}
  	res = pq_putmessage(msgtype, s, len);
  	Assert(res == 0);			/* should not fail when the message fits in
  								 * buffer */
  }
  
  /* --------------------------------
   *		pq_putmessage_v2 - send a message in protocol version 2
   *
   *		msgtype is a message type code to place before the message body.
   *
   *		We no longer support protocol version 2, but we have kept this
   *		function so that if a client tries to connect with protocol version 2,
   *		as a courtesy we can still send the "unsupported protocol version"
   *		error to the client in the old format.
   *
   *		Like in pq_putmessage(), we suppress messages generated while
   *		pqcomm.c is busy.
   *
   *		returns 0 if OK, EOF if trouble
   * --------------------------------
   */
  int
  pq_putmessage_v2(char msgtype, const char *s, size_t len)
  {
  	Assert(msgtype != 0);
  
  	if (PqCommBusy)
  		return 0;
  	PqCommBusy = true;
  	if (internal_putbytes(&msgtype, 1))
  		goto fail;
  
  	if (internal_putbytes(s, len))
  		goto fail;
  	PqCommBusy = false;
  	return 0;
  
  fail:
  	PqCommBusy = false;
  	return EOF;
  }
  
  /*
   * Support for TCP Keepalive parameters
   */
  
  /*
   * On Windows, we need to set both idle and interval at the same time.
   * We also cannot reset them to the default (setting to zero will
   * actually set them to zero, not default), therefore we fallback to
   * the out-of-the-box default instead.
   */
  #if defined(WIN32) && defined(SIO_KEEPALIVE_VALS)
  static int
  pq_setkeepaliveswin32(Port *port, int idle, int interval)
  {
  	struct tcp_keepalive ka;
  	DWORD		retsize;
  
  	if (idle <= 0)
  		idle = 2 * 60 * 60;		/* default = 2 hours */
  	if (interval <= 0)
  		interval = 1;			/* default = 1 second */
  
  	ka.onoff = 1;
  	ka.keepalivetime = idle * 1000;
  	ka.keepaliveinterval = interval * 1000;
  
  	if (WSAIoctl(port->sock,
  				 SIO_KEEPALIVE_VALS,
  				 (LPVOID) &ka,
  				 sizeof(ka),
  				 NULL,
  				 0,
  				 &retsize,
  				 NULL,
  				 NULL)
  		!= 0)
  	{
  		ereport(LOG,
  				(errmsg("%s(%s) failed: error code %d",
  						"WSAIoctl", "SIO_KEEPALIVE_VALS", WSAGetLastError())));
  		return STATUS_ERROR;
  	}
  	if (port->keepalives_idle != idle)
  		port->keepalives_idle = idle;
  	if (port->keepalives_interval != interval)
  		port->keepalives_interval = interval;
  	return STATUS_OK;
  }
  #endif
  
  int
  pq_getkeepalivesidle(Port *port)
  {
  #if defined(PG_TCP_KEEPALIVE_IDLE) || defined(SIO_KEEPALIVE_VALS)
  	if (port == NULL || IS_AF_UNIX(port->laddr.addr.ss_family))
  		return 0;
  
  	if (port->keepalives_idle != 0)
  		return port->keepalives_idle;
  
  	if (port->default_keepalives_idle == 0)
  	{
  #ifndef WIN32
  		ACCEPT_TYPE_ARG3 size = sizeof(port->default_keepalives_idle);
  
  		if (getsockopt(port->sock, IPPROTO_TCP, PG_TCP_KEEPALIVE_IDLE,
  					   (char *) &port->default_keepalives_idle,
  					   &size) < 0)
  		{
  			ereport(LOG,
  					(errmsg("%s(%s) failed: %m", "getsockopt", PG_TCP_KEEPALIVE_IDLE_STR)));
  			port->default_keepalives_idle = -1; /* don't know */
  		}
  #else							/* WIN32 */
  		/* We can't get the defaults on Windows, so return "don't know" */
  		port->default_keepalives_idle = -1;
  #endif							/* WIN32 */
  	}
  
  	return port->default_keepalives_idle;
  #else
  	return 0;
  #endif
  }
  
  int
  pq_setkeepalivesidle(int idle, Port *port)
  {
  	if (port == NULL || IS_AF_UNIX(port->laddr.addr.ss_family))
  		return STATUS_OK;
  
  /* check SIO_KEEPALIVE_VALS here, not just WIN32, as some toolchains lack it */
  #if defined(PG_TCP_KEEPALIVE_IDLE) || defined(SIO_KEEPALIVE_VALS)
  	if (idle == port->keepalives_idle)
  		return STATUS_OK;
  
  #ifndef WIN32
  	if (port->default_keepalives_idle <= 0)
  	{
  		if (pq_getkeepalivesidle(port) < 0)
  		{
  			if (idle == 0)
  				return STATUS_OK;	/* default is set but unknown */
  			else
  				return STATUS_ERROR;
  		}
  	}
  
  	if (idle == 0)
  		idle = port->default_keepalives_idle;
  
  	if (setsockopt(port->sock, IPPROTO_TCP, PG_TCP_KEEPALIVE_IDLE,
  				   (char *) &idle, sizeof(idle)) < 0)
  	{
  		ereport(LOG,
  				(errmsg("%s(%s) failed: %m", "setsockopt", PG_TCP_KEEPALIVE_IDLE_STR)));
  		return STATUS_ERROR;
  	}
  
  	port->keepalives_idle = idle;
  #else							/* WIN32 */
  	return pq_setkeepaliveswin32(port, idle, port->keepalives_interval);
  #endif
  #else
  	if (idle != 0)
  	{
  		ereport(LOG,
  				(errmsg("setting the keepalive idle time is not supported")));
  		return STATUS_ERROR;
  	}
  #endif
  
  	return STATUS_OK;
  }
  
  int
  pq_getkeepalivesinterval(Port *port)
  {
  #if defined(TCP_KEEPINTVL) || defined(SIO_KEEPALIVE_VALS)
  	if (port == NULL || IS_AF_UNIX(port->laddr.addr.ss_family))
  		return 0;
  
  	if (port->keepalives_interval != 0)
  		return port->keepalives_interval;
  
  	if (port->default_keepalives_interval == 0)
  	{
  #ifndef WIN32
  		ACCEPT_TYPE_ARG3 size = sizeof(port->default_keepalives_interval);
  
  		if (getsockopt(port->sock, IPPROTO_TCP, TCP_KEEPINTVL,
  					   (char *) &port->default_keepalives_interval,
  					   &size) < 0)
  		{
  			ereport(LOG,
  					(errmsg("%s(%s) failed: %m", "getsockopt", "TCP_KEEPINTVL")));
  			port->default_keepalives_interval = -1; /* don't know */
  		}
  #else
  		/* We can't get the defaults on Windows, so return "don't know" */
  		port->default_keepalives_interval = -1;
  #endif							/* WIN32 */
  	}
  
  	return port->default_keepalives_interval;
  #else
  	return 0;
  #endif
  }
  
  int
  pq_setkeepalivesinterval(int interval, Port *port)
  {
  	if (port == NULL || IS_AF_UNIX(port->laddr.addr.ss_family))
  		return STATUS_OK;
  
  #if defined(TCP_KEEPINTVL) || defined(SIO_KEEPALIVE_VALS)
  	if (interval == port->keepalives_interval)
  		return STATUS_OK;
  
  #ifndef WIN32
  	if (port->default_keepalives_interval <= 0)
  	{
  		if (pq_getkeepalivesinterval(port) < 0)
  		{
  			if (interval == 0)
  				return STATUS_OK;	/* default is set but unknown */
  			else
  				return STATUS_ERROR;
  		}
  	}
  
  	if (interval == 0)
  		interval = port->default_keepalives_interval;
  
  	if (setsockopt(port->sock, IPPROTO_TCP, TCP_KEEPINTVL,
  				   (char *) &interval, sizeof(interval)) < 0)
  	{
  		ereport(LOG,
  				(errmsg("%s(%s) failed: %m", "setsockopt", "TCP_KEEPINTVL")));
  		return STATUS_ERROR;
  	}
  
  	port->keepalives_interval = interval;
  #else							/* WIN32 */
  	return pq_setkeepaliveswin32(port, port->keepalives_idle, interval);
  #endif
  #else
  	if (interval != 0)
  	{
  		ereport(LOG,
  				(errmsg("%s(%s) not supported", "setsockopt", "TCP_KEEPINTVL")));
  		return STATUS_ERROR;
  	}
  #endif
  
  	return STATUS_OK;
  }
  
  int
  pq_getkeepalivescount(Port *port)
  {
  #ifdef TCP_KEEPCNT
  	if (port == NULL || IS_AF_UNIX(port->laddr.addr.ss_family))
  		return 0;
  
  	if (port->keepalives_count != 0)
  		return port->keepalives_count;
  
  	if (port->default_keepalives_count == 0)
  	{
  		ACCEPT_TYPE_ARG3 size = sizeof(port->default_keepalives_count);
  
  		if (getsockopt(port->sock, IPPROTO_TCP, TCP_KEEPCNT,
  					   (char *) &port->default_keepalives_count,
  					   &size) < 0)
  		{
  			ereport(LOG,
  					(errmsg("%s(%s) failed: %m", "getsockopt", "TCP_KEEPCNT")));
  			port->default_keepalives_count = -1;	/* don't know */
  		}
  	}
  
  	return port->default_keepalives_count;
  #else
  	return 0;
  #endif
  }
  
  int
  pq_setkeepalivescount(int count, Port *port)
  {
  	if (port == NULL || IS_AF_UNIX(port->laddr.addr.ss_family))
  		return STATUS_OK;
  
  #ifdef TCP_KEEPCNT
  	if (count == port->keepalives_count)
  		return STATUS_OK;
  
  	if (port->default_keepalives_count <= 0)
  	{
  		if (pq_getkeepalivescount(port) < 0)
  		{
  			if (count == 0)
  				return STATUS_OK;	/* default is set but unknown */
  			else
  				return STATUS_ERROR;
  		}
  	}
  
  	if (count == 0)
  		count = port->default_keepalives_count;
  
  	if (setsockopt(port->sock, IPPROTO_TCP, TCP_KEEPCNT,
  				   (char *) &count, sizeof(count)) < 0)
  	{
  		ereport(LOG,
  				(errmsg("%s(%s) failed: %m", "setsockopt", "TCP_KEEPCNT")));
  		return STATUS_ERROR;
  	}
  
  	port->keepalives_count = count;
  #else
  	if (count != 0)
  	{
  		ereport(LOG,
  				(errmsg("%s(%s) not supported", "setsockopt", "TCP_KEEPCNT")));
  		return STATUS_ERROR;
  	}
  #endif
  
  	return STATUS_OK;
  }
  
  int
  pq_gettcpusertimeout(Port *port)
  {
  #ifdef TCP_USER_TIMEOUT
  	if (port == NULL || IS_AF_UNIX(port->laddr.addr.ss_family))
  		return 0;
  
  	if (port->tcp_user_timeout != 0)
  		return port->tcp_user_timeout;
  
  	if (port->default_tcp_user_timeout == 0)
  	{
  		ACCEPT_TYPE_ARG3 size = sizeof(port->default_tcp_user_timeout);
  
  		if (getsockopt(port->sock, IPPROTO_TCP, TCP_USER_TIMEOUT,
  					   (char *) &port->default_tcp_user_timeout,
  					   &size) < 0)
  		{
  			ereport(LOG,
  					(errmsg("%s(%s) failed: %m", "getsockopt", "TCP_USER_TIMEOUT")));
  			port->default_tcp_user_timeout = -1;	/* don't know */
  		}
  	}
  
  	return port->default_tcp_user_timeout;
  #else
  	return 0;
  #endif
  }
  
  int
  pq_settcpusertimeout(int timeout, Port *port)
  {
  	if (port == NULL || IS_AF_UNIX(port->laddr.addr.ss_family))
  		return STATUS_OK;
  
  #ifdef TCP_USER_TIMEOUT
  	if (timeout == port->tcp_user_timeout)
  		return STATUS_OK;
  
  	if (port->default_tcp_user_timeout <= 0)
  	{
  		if (pq_gettcpusertimeout(port) < 0)
  		{
  			if (timeout == 0)
  				return STATUS_OK;	/* default is set but unknown */
  			else
  				return STATUS_ERROR;
  		}
  	}
  
  	if (timeout == 0)
  		timeout = port->default_tcp_user_timeout;
  
  	if (setsockopt(port->sock, IPPROTO_TCP, TCP_USER_TIMEOUT,
  				   (char *) &timeout, sizeof(timeout)) < 0)
  	{
  		ereport(LOG,
  				(errmsg("%s(%s) failed: %m", "setsockopt", "TCP_USER_TIMEOUT")));
  		return STATUS_ERROR;
  	}
  
  	port->tcp_user_timeout = timeout;
  #else
  	if (timeout != 0)
  	{
  		ereport(LOG,
  				(errmsg("%s(%s) not supported", "setsockopt", "TCP_USER_TIMEOUT")));
  		return STATUS_ERROR;
  	}
  #endif
  
  	return STATUS_OK;
  }
  
  /*
   * Check if the client is still connected.
   */
  bool
  pq_check_connection(void)
  {
  #if defined(POLLRDHUP)
  	/*
  	 * POLLRDHUP is a Linux extension to poll(2) to detect sockets closed by
  	 * the other end.  We don't have a portable way to do that without
  	 * actually trying to read or write data on other systems.  We don't want
  	 * to read because that would be confused by pipelined queries and COPY
  	 * data. Perhaps in future we'll try to write a heartbeat message instead.
  	 */
  	struct pollfd pollfd;
  	int			rc;
  
  	pollfd.fd = MyProcPort->sock;
  	pollfd.events = POLLOUT | POLLIN | POLLRDHUP;
  	pollfd.revents = 0;
  
  	rc = poll(&pollfd, 1, 0);
  
  	if (rc < 0)
  	{
  		ereport(COMMERROR,
  				(errcode_for_socket_access(),
  				 errmsg("could not poll socket: %m")));
  		return false;
  	}
  	else if (rc == 1 && (pollfd.revents & (POLLHUP | POLLRDHUP)))
  		return false;
  #endif
  
  	return true;
  }
  