/*--------------------------------------------------------------------
 * Symbols referenced in this file:
 * - PqCommMethods
 *--------------------------------------------------------------------
 */

/*-------------------------------------------------------------------------
 *
 * 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) 1996-2020, 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_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
 *		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 (and old-style-COPY-OUT cruft):
 *		pq_putmessage	- send a normal message (suppressed in COPY OUT mode)
 *		pq_putmessage_noblock - buffer a normal message (suppressed in COPY OUT)
 *		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 <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
 */



/* Where the Unix socket files are (list of palloc'd strings) */


/*
 * 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


	/* Size send buffer */
		/* Next index to store a byte in PqSendBuffer */
		/* Next index to send a byte in PqSendBuffer */


		/* Next index to read a byte from PqRecvBuffer */
		/* End of data available in PqRecvBuffer */

/*
 * Message status
 */
			/* busy sending data to the client */
	/* in the middle of reading a message */
		/* in old-protocol COPY OUT processing */


/* 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 void socket_startcopyout(void);
static void socket_endcopyout(bool errorAbort);
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 */



const PQcommMethods *PqCommMethods = NULL;





/* --------------------------------
 *		pq_init - initialize libpq at backend startup
 * --------------------------------
 */
#ifndef WIN32
#endif

/* --------------------------------
 *		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...)
 * --------------------------------
 */


/* --------------------------------
 *		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.
 * --------------------------------
 */
#ifdef ENABLE_GSS
#endif							/* ENABLE_GSS */



/*
 * 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
 */

#ifdef HAVE_UNIX_SOCKETS
#endif
#if !defined(WIN32) || defined(IPV6_V6ONLY)
#endif
#ifdef HAVE_UNIX_SOCKETS
#endif							/* HAVE_UNIX_SOCKETS */
#ifdef HAVE_IPV6
#endif
#ifdef HAVE_UNIX_SOCKETS
#endif
#ifdef HAVE_UNIX_SOCKETS
#endif
#ifndef WIN32
#endif
#ifdef IPV6_V6ONLY
#endif
#ifdef HAVE_UNIX_SOCKETS
#endif
#ifdef HAVE_UNIX_SOCKETS
#endif


#ifdef HAVE_UNIX_SOCKETS

/*
 * Lock_AF_UNIX -- configure unix socket file path
 */



/*
 * Setup_AF_UNIX -- configure unix socket permissions
 */
#ifdef WIN32
#else
#endif
#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
 */
#ifdef WIN32
#endif
#ifdef	TCP_NODELAY
#endif
#ifdef WIN32
#endif

/*
 * 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.
 */


/*
 * 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...)
 */


/*
 * RemoveSocketFiles -- unlink socket files at postmaster shutdown
 */



/* --------------------------------
 * 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.
 * --------------------------------
 */


/* --------------------------------
 *		pq_recvbuf - load some bytes into the input buffer
 *
 *		returns 0 if OK, EOF if trouble
 * --------------------------------
 */


/* --------------------------------
 *		pq_getbyte	- get a single byte from connection, or return EOF
 * --------------------------------
 */


/* --------------------------------
 *		pq_peekbyte		- peek at next byte from connection
 *
 *	 Same as pq_getbyte() except we don't advance the pointer.
 * --------------------------------
 */


/* --------------------------------
 *		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.
 * --------------------------------
 */


/* --------------------------------
 *		pq_getbytes		- get a known number of bytes from connection
 *
 *		returns 0 if OK, EOF if trouble
 * --------------------------------
 */


/* --------------------------------
 *		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
 * --------------------------------
 */


/* --------------------------------
 *		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
 * --------------------------------
 */



/* --------------------------------
 *		pq_startmsgread - begin reading a message from the client.
 *
 *		This must be called before any of the pq_get* functions.
 * --------------------------------
 */



/* --------------------------------
 *		pq_endmsgread	- finish reading message.
 *
 *		This must be called after reading a V2 protocol message with
 *		pq_getstring() and friends, to indicate that we have read the whole
 *		message. In V3 protocol, pq_getmessage() does this implicitly.
 * --------------------------------
 */


/* --------------------------------
 *		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.
 * --------------------------------
 */


/* --------------------------------
 *		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
 * --------------------------------
 */



/* --------------------------------
 *		pq_putbytes		- send bytes to connection (not flushed until pq_flush)
 *
 *		returns 0 if OK, EOF if trouble
 * --------------------------------
 */




/* --------------------------------
 *		socket_flush		- flush pending output
 *
 *		returns 0 if OK, EOF if trouble
 * --------------------------------
 */


/* --------------------------------
 *		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.
 * --------------------------------
 */


/* --------------------------------
 *		pq_flush_if_writable - flush pending output if writable without blocking
 *
 * Returns 0 if OK, or EOF if trouble.
 * --------------------------------
 */


/* --------------------------------
 *	socket_is_send_pending	- is there any pending data in the output buffer?
 * --------------------------------
 */


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


/* --------------------------------
 *		socket_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
 * --------------------------------
 */


/* --------------------------------
 *		pq_putmessage_noblock	- like pq_putmessage, but never blocks
 *
 *		If the output buffer is too small to hold the message, the buffer
 *		is enlarged.
 */



/* --------------------------------
 *		socket_startcopyout - inform libpq that an old-style COPY OUT transfer
 *			is beginning
 * --------------------------------
 */


/* --------------------------------
 *		socket_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.
 * --------------------------------
 */


/*
 * 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)
	{
		elog(LOG, "WSAIoctl(SIO_KEEPALIVE_VALS) failed: %ui",
			 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

#if defined(PG_TCP_KEEPALIVE_IDLE) || defined(SIO_KEEPALIVE_VALS)
#ifndef WIN32
#else							/* WIN32 */
#endif							/* WIN32 */
#else
#endif

#if defined(PG_TCP_KEEPALIVE_IDLE) || defined(SIO_KEEPALIVE_VALS)
#ifndef WIN32
#else							/* WIN32 */
#endif
#else
#endif

#if defined(TCP_KEEPINTVL) || defined(SIO_KEEPALIVE_VALS)
#ifndef WIN32
#else
#endif							/* WIN32 */
#else
#endif

#if defined(TCP_KEEPINTVL) || defined(SIO_KEEPALIVE_VALS)
#ifndef WIN32
#else							/* WIN32 */
#endif
#else
#endif

#ifdef TCP_KEEPCNT
#else
#endif

#ifdef TCP_KEEPCNT
#else
#endif

#ifdef TCP_USER_TIMEOUT
#else
#endif

#ifdef TCP_USER_TIMEOUT
#else
#endif