Disallow empty passwords in LDAP authentication, the same way

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

/*-------------------------------------------------------------------------
 *
 * pqcomm.c
 *        Communication functions between the Frontend and the Backend
 *
 * These routines handle the low-level details of communication between
 * frontend and backend.  They just shove data across the communication
 * channel, and are ignorant of the semantics of the data --- or would be,
 * except for major brain damage in the design of the old COPY OUT protocol.
 * Unfortunately, COPY OUT was designed to commandeer the communication
 * channel (it just transfers data without wrapping it into messages).
 * No other messages can be sent while COPY OUT is in progress; and if the
 * copy is aborted by an ereport(ERROR), we need to close out the copy so that
 * the frontend gets back into sync.  Therefore, these routines have to be
 * aware of COPY OUT state.  (New COPY-OUT is message-based and does *not*
 * set the DoingCopyOut flag.)
 *
 * NOTE: generally, it's a bad idea to emit outgoing messages directly with
 * pq_putbytes(), especially if the message would require multiple calls
 * to send.  Instead, use the routines in pqformat.c to construct the message
 * in a buffer and then emit it in one call to pq_putmessage.  This ensures
 * that the channel will not be clogged by an incomplete message if execution
 * is aborted by ereport(ERROR) partway through the message.  The only
 * non-libpq code that should call pq_putbytes directly is old-style COPY OUT.
 *
 * At one time, libpq was shared between frontend and backend, but now
 * the backend's "backend/libpq" is quite separate from "interfaces/libpq".
 * All that remains is similarities of names to trap the unwary...
 *
 * Portions Copyright (c) 1996-2009, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *      $PostgreSQL$
 *
 *-------------------------------------------------------------------------
 */

/*------------------------
 * INTERFACE ROUTINES
 *
 * setup/teardown:
 *              StreamServerPort        - Open postmaster's server port
 *              StreamConnection        - Create new connection with client
 *              StreamClose                     - Close a client/backend connection
 *              TouchSocketFile         - Protect socket file against /tmp cleaners
 *              pq_init                 - initialize libpq at backend startup
 *              pq_comm_reset   - reset libpq during error recovery
 *              pq_close                - shutdown libpq at backend exit
 *
 * low-level I/O:
 *              pq_getbytes             - get a known number of bytes from connection
 *              pq_getstring    - get a null terminated string from connection
 *              pq_getmessage   - get a message with length word from connection
 *              pq_getbyte              - get next byte from connection
 *              pq_peekbyte             - peek at next byte from connection
 *              pq_putbytes             - send bytes to connection (not flushed until pq_flush)
 *              pq_flush                - flush pending output
 *
 * message-level I/O (and old-style-COPY-OUT cruft):
 *              pq_putmessage   - send a normal message (suppressed in COPY OUT mode)
 *              pq_startcopyout - inform libpq that a COPY OUT transfer is beginning
 *              pq_endcopyout   - end a COPY OUT transfer
 *
 *------------------------
 */
#include "postgres.h"

#include <signal.h>
#include <fcntl.h>
#include <grp.h>
#include <unistd.h>
#include <sys/file.h>
#include <sys/socket.h>
#include <sys/stat.h>
#include <sys/time.h>
#include <netdb.h>
#include <netinet/in.h>
#ifdef HAVE_NETINET_TCP_H
#include <netinet/tcp.h>
#endif
#include <arpa/inet.h>
#ifdef HAVE_UTIME_H
#include <utime.h>
#endif

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

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


/* Where the Unix socket file is */
static char sock_path[MAXPGPATH];


/*
 * Buffers for low-level I/O
 */

#define PQ_BUFFER_SIZE 8192

static char PqSendBuffer[PQ_BUFFER_SIZE];
static int      PqSendPointer;          /* Next index to store a byte in PqSendBuffer */

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

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


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

#ifdef HAVE_UNIX_SOCKETS
static int      Lock_AF_UNIX(unsigned short portNumber, char *unixSocketName);
static int      Setup_AF_UNIX(void);
#endif   /* HAVE_UNIX_SOCKETS */


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

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

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

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

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

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

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

                /*
                 * Formerly we did an explicit close() here, but it seems better to
                 * leave the socket open until the process dies.  This allows clients
                 * to perform a "synchronous close" if they care --- wait till the
                 * transport layer reports connection closure, and you can be sure the
                 * backend has exited.
                 *
                 * We do set sock to -1 to prevent any further I/O, though.
                 */
                MyProcPort->sock = -1;
        }
}



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


/* StreamDoUnlink()
 * Shutdown routine for backend connection
 * If a Unix socket is used for communication, explicitly close it.
 */
#ifdef HAVE_UNIX_SOCKETS
static void
StreamDoUnlink(int code, Datum arg)
{
        Assert(sock_path[0]);
        unlink(sock_path);
}
#endif   /* HAVE_UNIX_SOCKETS */

/*
 * StreamServerPort -- open a "listening" port to accept connections.
 *
 * Successfully opened sockets are added to the ListenSocket[] array,
 * at the first position that isn't -1.
 *
 * RETURNS: STATUS_OK or STATUS_ERROR
 */

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

#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)
        {
                /* Lock_AF_UNIX will also fill in sock_path. */
                if (Lock_AF_UNIX(portNumber, unixSocketName) != STATUS_OK)
                        return STATUS_ERROR;
                service = sock_path;
        }
        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] == -1)
                                break;
                }
                if (listen_index >= MaxListen)
                {
                        ereport(LOG,
                                        (errmsg("could not bind to all requested addresses: MAXLISTEN (%d) exceeded",
                                                        MaxListen)));
                        break;
                }

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

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

#ifndef WIN32

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

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

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

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

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

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

        pg_freeaddrinfo_all(hint.ai_family, addrs);

        if (!added)
                return STATUS_ERROR;

        return STATUS_OK;
}


#ifdef HAVE_UNIX_SOCKETS

/*
 * Lock_AF_UNIX -- configure unix socket file path
 */
static int
Lock_AF_UNIX(unsigned short portNumber, char *unixSocketName)
{
        UNIXSOCK_PATH(sock_path, portNumber, unixSocketName);

        /*
         * Grab an interlock file associated with the socket file.
         */
        CreateSocketLockFile(sock_path, true);

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

        return STATUS_OK;
}


/*
 * Setup_AF_UNIX -- configure unix socket permissions
 */
static int
Setup_AF_UNIX(void)
{
        /* Arrange to unlink the socket file at exit */
        on_proc_exit(StreamDoUnlink, 0);

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

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

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

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


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

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

#ifdef SCO_ACCEPT_BUG

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

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

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

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

#ifdef WIN32

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

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

        return STATUS_OK;
}

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

/*
 * TouchSocketFile -- mark socket file as recently accessed
 *
 * This routine should be called every so often to ensure that the socket
 * file has a recent mod date (ordinary operations on sockets usually won't
 * change the mod date).  That saves it from being removed by
 * overenthusiastic /tmp-directory-cleaner daemons.  (Another reason we should
 * never have put the socket file in /tmp...)
 */
void
TouchSocketFile(void)
{
        /* Do nothing if we did not create a socket... */
        if (sock_path[0] != '\0')
        {
                /*
                 * utime() is POSIX standard, utimes() is a common alternative. If we
                 * have neither, there's no way to affect the mod or access time of
                 * the socket :-(
                 *
                 * In either path, we ignore errors; there's no point in complaining.
                 */
#ifdef HAVE_UTIME
                utime(sock_path, NULL);
#else                                                   /* !HAVE_UTIME */
#ifdef HAVE_UTIMES
                utimes(sock_path, NULL);
#endif   /* HAVE_UTIMES */
#endif   /* HAVE_UTIME */
        }
}


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


/* --------------------------------
 *              pq_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;
        }

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

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

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

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

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

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

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

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

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

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

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

        resetStringInfo(s);

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

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

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


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

        resetStringInfo(s);

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

        len = ntohl(len);

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

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

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

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

        return 0;
}


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

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

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

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

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

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

static int
internal_flush(void)
{
        static int      last_reported_send_errno = 0;

        char       *bufptr = PqSendBuffer;
        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 */

                        /*
                         * 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.
                         */
                        PqSendPointer = 0;
                        return EOF;
                }

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

        PqSendPointer = 0;
        return 0;
}


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


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

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

fail:
        PqCommBusy = false;
        return EOF;
}

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

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


/*
 * Support for TCP Keepalive parameters
 */

int
pq_getkeepalivesidle(Port *port)
{
#ifdef TCP_KEEPIDLE
        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)
        {
                ACCEPT_TYPE_ARG3 size = sizeof(port->default_keepalives_idle);

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

        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;

#ifdef TCP_KEEPIDLE
        if (idle == port->keepalives_idle)
                return STATUS_OK;

        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, TCP_KEEPIDLE,
                                   (char *) &idle, sizeof(idle)) < 0)
        {
                elog(LOG, "setsockopt(TCP_KEEPIDLE) failed: %m");
                return STATUS_ERROR;
        }

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

        return STATUS_OK;
}

int
pq_getkeepalivesinterval(Port *port)
{
#ifdef TCP_KEEPINTVL
        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)
        {
                ACCEPT_TYPE_ARG3 size = sizeof(port->default_keepalives_interval);

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

        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;

#ifdef TCP_KEEPINTVL
        if (interval == port->keepalives_interval)
                return STATUS_OK;

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

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

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

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

        return STATUS_OK;
}

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

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

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

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

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

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

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

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

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

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

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

        return STATUS_OK;
}