backend/libpq/pqformat.c

/*-------------------------------------------------------------------------
 *
 * pqformat.c
 *		Routines for formatting and parsing frontend/backend messages
 *
 * Outgoing messages are built up in a StringInfo buffer (which is expansible)
 * and then sent in a single call to pq_putmessage.  This module provides data
 * formatting/conversion routines that are needed to produce valid messages.
 * Note in particular the distinction between "raw data" and "text"; raw data
 * is message protocol characters and binary values that are not subject to
 * character set conversion, while text is converted by character encoding
 * rules.
 *
 * Incoming messages are similarly read into a StringInfo buffer, via
 * pq_getmessage, and then parsed and converted from that using the routines
 * in this module.
 *
 * These same routines support reading and writing of external binary formats
 * (typsend/typreceive routines).  The conversion routines for individual
 * data types are exactly the same, only initialization and completion
 * are different.
 *
 *
 * Portions Copyright (c) 1996-2021, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *	src/backend/libpq/pqformat.c
 *
 *-------------------------------------------------------------------------
 */
/*
 * INTERFACE ROUTINES
 * Message assembly and output:
 *		pq_beginmessage - initialize StringInfo buffer
 *		pq_sendbyte		- append a raw byte to a StringInfo buffer
 *		pq_sendint		- append a binary integer to a StringInfo buffer
 *		pq_sendint64	- append a binary 8-byte int to a StringInfo buffer
 *		pq_sendfloat4	- append a float4 to a StringInfo buffer
 *		pq_sendfloat8	- append a float8 to a StringInfo buffer
 *		pq_sendbytes	- append raw data to a StringInfo buffer
 *		pq_sendcountedtext - append a counted text string (with character set conversion)
 *		pq_sendtext		- append a text string (with conversion)
 *		pq_sendstring	- append a null-terminated text string (with conversion)
 *		pq_send_ascii_string - append a null-terminated text string (without conversion)
 *		pq_endmessage	- send the completed message to the frontend
 * Note: it is also possible to append data to the StringInfo buffer using
 * the regular StringInfo routines, but this is discouraged since required
 * character set conversion may not occur.
 *
 * typsend support (construct a bytea value containing external binary data):
 *		pq_begintypsend - initialize StringInfo buffer
 *		pq_endtypsend	- return the completed string as a "bytea*"
 *
 * Special-case message output:
 *		pq_puttextmessage - generate a character set-converted message in one step
 *		pq_putemptymessage - convenience routine for message with empty body
 *
 * Message parsing after input:
 *		pq_getmsgbyte	- get a raw byte from a message buffer
 *		pq_getmsgint	- get a binary integer from a message buffer
 *		pq_getmsgint64	- get a binary 8-byte int from a message buffer
 *		pq_getmsgfloat4 - get a float4 from a message buffer
 *		pq_getmsgfloat8 - get a float8 from a message buffer
 *		pq_getmsgbytes	- get raw data from a message buffer
 *		pq_copymsgbytes - copy raw data from a message buffer
 *		pq_getmsgtext	- get a counted text string (with conversion)
 *		pq_getmsgstring - get a null-terminated text string (with conversion)
 *		pq_getmsgrawstring - get a null-terminated text string - NO conversion
 *		pq_getmsgend	- verify message fully consumed
 */

#include "postgres.h"

#include <sys/param.h>

#include "libpq/libpq.h"
#include "libpq/pqformat.h"
#include "mb/pg_wchar.h"
#include "port/pg_bswap.h"


/* --------------------------------
 *		pq_beginmessage		- initialize for sending a message
 * --------------------------------
 */
void
pq_beginmessage(StringInfo buf, char msgtype)
{
	initStringInfo(buf);

	/*
	 * We stash the message type into the buffer's cursor field, expecting
	 * that the pq_sendXXX routines won't touch it.  We could alternatively
	 * make it the first byte of the buffer contents, but this seems easier.
	 */
	buf->cursor = msgtype;
}

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

 *		pq_beginmessage_reuse - initialize for sending a message, reuse buffer
 *
 * This requires the buffer to be allocated in a sufficiently long-lived
 * memory context.
 * --------------------------------
 */
void
pq_beginmessage_reuse(StringInfo buf, char msgtype)
{
	resetStringInfo(buf);

	/*
	 * We stash the message type into the buffer's cursor field, expecting
	 * that the pq_sendXXX routines won't touch it.  We could alternatively
	 * make it the first byte of the buffer contents, but this seems easier.
	 */
	buf->cursor = msgtype;
}

/* --------------------------------
 *		pq_sendbytes	- append raw data to a StringInfo buffer
 * --------------------------------
 */
void
pq_sendbytes(StringInfo buf, const char *data, int datalen)
{
	/* use variant that maintains a trailing null-byte, out of caution */
	appendBinaryStringInfo(buf, data, datalen);
}

/* --------------------------------
 *		pq_sendcountedtext - append a counted text string (with character set conversion)
 *
 * The data sent to the frontend by this routine is a 4-byte count field
 * followed by the string.  The count includes itself or not, as per the
 * countincludesself flag (pre-3.0 protocol requires it to include itself).
 * The passed text string need not be null-terminated, and the data sent
 * to the frontend isn't either.
 * --------------------------------
 */
void
pq_sendcountedtext(StringInfo buf, const char *str, int slen,
				   bool countincludesself)
{
	int			extra = countincludesself ? 4 : 0;
	char	   *p;

	p = pg_server_to_client(str, slen);
	if (p != str)				/* actual conversion has been done? */
	{
		slen = strlen(p);
		pq_sendint32(buf, slen + extra);
		appendBinaryStringInfoNT(buf, p, slen);
		pfree(p);
	}
	else
	{
		pq_sendint32(buf, slen + extra);
		appendBinaryStringInfoNT(buf, str, slen);
	}
}

/* --------------------------------
 *		pq_sendtext		- append a text string (with conversion)
 *
 * The passed text string need not be null-terminated, and the data sent
 * to the frontend isn't either.  Note that this is not actually useful
 * for direct frontend transmissions, since there'd be no way for the
 * frontend to determine the string length.  But it is useful for binary
 * format conversions.
 * --------------------------------
 */
void
pq_sendtext(StringInfo buf, const char *str, int slen)
{
	char	   *p;

	p = pg_server_to_client(str, slen);
	if (p != str)				/* actual conversion has been done? */
	{
		slen = strlen(p);
		appendBinaryStringInfo(buf, p, slen);
		pfree(p);
	}
	else
		appendBinaryStringInfo(buf, str, slen);
}

/* --------------------------------
 *		pq_sendstring	- append a null-terminated text string (with conversion)
 *
 * NB: passed text string must be null-terminated, and so is the data
 * sent to the frontend.
 * --------------------------------
 */
void
pq_sendstring(StringInfo buf, const char *str)
{
	int			slen = strlen(str);
	char	   *p;

	p = pg_server_to_client(str, slen);
	if (p != str)				/* actual conversion has been done? */
	{
		slen = strlen(p);
		appendBinaryStringInfoNT(buf, p, slen + 1);
		pfree(p);
	}
	else
		appendBinaryStringInfoNT(buf, str, slen + 1);
}

/* --------------------------------
 *		pq_send_ascii_string	- append a null-terminated text string (without conversion)
 *
 * This function intentionally bypasses encoding conversion, instead just
 * silently replacing any non-7-bit-ASCII characters with question marks.
 * It is used only when we are having trouble sending an error message to
 * the client with normal localization and encoding conversion.  The caller
 * should already have taken measures to ensure the string is just ASCII;
 * the extra work here is just to make certain we don't send a badly encoded
 * string to the client (which might or might not be robust about that).
 *
 * NB: passed text string must be null-terminated, and so is the data
 * sent to the frontend.
 * --------------------------------
 */
void
pq_send_ascii_string(StringInfo buf, const char *str)
{
	while (*str)
	{
		char		ch = *str++;

		if (IS_HIGHBIT_SET(ch))
			ch = '?';
		appendStringInfoCharMacro(buf, ch);
	}
	appendStringInfoChar(buf, '\0');
}

/* --------------------------------
 *		pq_sendfloat4	- append a float4 to a StringInfo buffer
 *
 * The point of this routine is to localize knowledge of the external binary
 * representation of float4, which is a component of several datatypes.
 *
 * We currently assume that float4 should be byte-swapped in the same way
 * as int4.  This rule is not perfect but it gives us portability across
 * most IEEE-float-using architectures.
 * --------------------------------
 */
void
pq_sendfloat4(StringInfo buf, float4 f)
{
	union
	{
		float4		f;
		uint32		i;
	}			swap;

	swap.f = f;
	pq_sendint32(buf, swap.i);
}

/* --------------------------------
 *		pq_sendfloat8	- append a float8 to a StringInfo buffer
 *
 * The point of this routine is to localize knowledge of the external binary
 * representation of float8, which is a component of several datatypes.
 *
 * We currently assume that float8 should be byte-swapped in the same way
 * as int8.  This rule is not perfect but it gives us portability across
 * most IEEE-float-using architectures.
 * --------------------------------
 */
void
pq_sendfloat8(StringInfo buf, float8 f)
{
	union
	{
		float8		f;
		int64		i;
	}			swap;

	swap.f = f;
	pq_sendint64(buf, swap.i);
}

/* --------------------------------
 *		pq_endmessage	- send the completed message to the frontend
 *
 * The data buffer is pfree()d, but if the StringInfo was allocated with
 * makeStringInfo then the caller must still pfree it.
 * --------------------------------
 */
void
pq_endmessage(StringInfo buf)
{
	/* msgtype was saved in cursor field */
	(void) pq_putmessage(buf->cursor, buf->data, buf->len);
	/* no need to complain about any failure, since pqcomm.c already did */
	pfree(buf->data);
	buf->data = NULL;
}

/* --------------------------------
 *		pq_endmessage_reuse	- send the completed message to the frontend
 *
 * The data buffer is *not* freed, allowing to reuse the buffer with
 * pq_beginmessage_reuse.
 --------------------------------
 */

void
pq_endmessage_reuse(StringInfo buf)
{
	/* msgtype was saved in cursor field */
	(void) pq_putmessage(buf->cursor, buf->data, buf->len);
}


/* --------------------------------
 *		pq_begintypsend		- initialize for constructing a bytea result
 * --------------------------------
 */
void
pq_begintypsend(StringInfo buf)
{
	initStringInfo(buf);
	/* Reserve four bytes for the bytea length word */
	appendStringInfoCharMacro(buf, '\0');
	appendStringInfoCharMacro(buf, '\0');
	appendStringInfoCharMacro(buf, '\0');
	appendStringInfoCharMacro(buf, '\0');
}

/* --------------------------------
 *		pq_endtypsend	- finish constructing a bytea result
 *
 * The data buffer is returned as the palloc'd bytea value.  (We expect
 * that it will be suitably aligned for this because it has been palloc'd.)
 * We assume the StringInfoData is just a local variable in the caller and
 * need not be pfree'd.
 * --------------------------------
 */
bytea *
pq_endtypsend(StringInfo buf)
{
	bytea	   *result = (bytea *) buf->data;

	/* Insert correct length into bytea length word */
	Assert(buf->len >= VARHDRSZ);
	SET_VARSIZE(result, buf->len);

	return result;
}


/* --------------------------------
 *		pq_puttextmessage - generate a character set-converted message in one step
 *
 *		This is the same as the pqcomm.c routine pq_putmessage, except that
 *		the message body is a null-terminated string to which encoding
 *		conversion applies.
 * --------------------------------
 */
void
pq_puttextmessage(char msgtype, const char *str)
{
	int			slen = strlen(str);
	char	   *p;

	p = pg_server_to_client(str, slen);
	if (p != str)				/* actual conversion has been done? */
	{
		(void) pq_putmessage(msgtype, p, strlen(p) + 1);
		pfree(p);
		return;
	}
	(void) pq_putmessage(msgtype, str, slen + 1);
}


/* --------------------------------
 *		pq_putemptymessage - convenience routine for message with empty body
 * --------------------------------
 */
void
pq_putemptymessage(char msgtype)
{
	(void) pq_putmessage(msgtype, NULL, 0);
}


/* --------------------------------
 *		pq_getmsgbyte	- get a raw byte from a message buffer
 * --------------------------------
 */
int
pq_getmsgbyte(StringInfo msg)
{
	if (msg->cursor >= msg->len)
		ereport(ERROR,
				(errcode(ERRCODE_PROTOCOL_VIOLATION),
				 errmsg("no data left in message")));
	return (unsigned char) msg->data[msg->cursor++];
}

/* --------------------------------
 *		pq_getmsgint	- get a binary integer from a message buffer
 *
 *		Values are treated as unsigned.
 * --------------------------------
 */
unsigned int
pq_getmsgint(StringInfo msg, int b)
{
	unsigned int result;
	unsigned char n8;
	uint16		n16;
	uint32		n32;

	switch (b)
	{
		case 1:
			pq_copymsgbytes(msg, (char *) &n8, 1);
			result = n8;
			break;
		case 2:
			pq_copymsgbytes(msg, (char *) &n16, 2);
			result = pg_ntoh16(n16);
			break;
		case 4:
			pq_copymsgbytes(msg, (char *) &n32, 4);
			result = pg_ntoh32(n32);
			break;
		default:
			elog(ERROR, "unsupported integer size %d", b);
			result = 0;			/* keep compiler quiet */
			break;
	}
	return result;
}

/* --------------------------------
 *		pq_getmsgint64	- get a binary 8-byte int from a message buffer
 *
 * It is tempting to merge this with pq_getmsgint, but we'd have to make the
 * result int64 for all data widths --- that could be a big performance
 * hit on machines where int64 isn't efficient.
 * --------------------------------
 */
int64
pq_getmsgint64(StringInfo msg)
{
	uint64		n64;

	pq_copymsgbytes(msg, (char *) &n64, sizeof(n64));

	return pg_ntoh64(n64);
}

/* --------------------------------
 *		pq_getmsgfloat4 - get a float4 from a message buffer
 *
 * See notes for pq_sendfloat4.
 * --------------------------------
 */
float4
pq_getmsgfloat4(StringInfo msg)
{
	union
	{
		float4		f;
		uint32		i;
	}			swap;

	swap.i = pq_getmsgint(msg, 4);
	return swap.f;
}

/* --------------------------------
 *		pq_getmsgfloat8 - get a float8 from a message buffer
 *
 * See notes for pq_sendfloat8.
 * --------------------------------
 */
float8
pq_getmsgfloat8(StringInfo msg)
{
	union
	{
		float8		f;
		int64		i;
	}			swap;

	swap.i = pq_getmsgint64(msg);
	return swap.f;
}

/* --------------------------------
 *		pq_getmsgbytes	- get raw data from a message buffer
 *
 *		Returns a pointer directly into the message buffer; note this
 *		may not have any particular alignment.
 * --------------------------------
 */
const char *
pq_getmsgbytes(StringInfo msg, int datalen)
{
	const char *result;

	if (datalen < 0 || datalen > (msg->len - msg->cursor))
		ereport(ERROR,
				(errcode(ERRCODE_PROTOCOL_VIOLATION),
				 errmsg("insufficient data left in message")));
	result = &msg->data[msg->cursor];
	msg->cursor += datalen;
	return result;
}

/* --------------------------------
 *		pq_copymsgbytes - copy raw data from a message buffer
 *
 *		Same as above, except data is copied to caller's buffer.
 * --------------------------------
 */
void
pq_copymsgbytes(StringInfo msg, char *buf, int datalen)
{
	if (datalen < 0 || datalen > (msg->len - msg->cursor))
		ereport(ERROR,
				(errcode(ERRCODE_PROTOCOL_VIOLATION),
				 errmsg("insufficient data left in message")));
	memcpy(buf, &msg->data[msg->cursor], datalen);
	msg->cursor += datalen;
}

/* --------------------------------
 *		pq_getmsgtext	- get a counted text string (with conversion)
 *
 *		Always returns a pointer to a freshly palloc'd result.
 *		The result has a trailing null, *and* we return its strlen in *nbytes.
 * --------------------------------
 */
char *
pq_getmsgtext(StringInfo msg, int rawbytes, int *nbytes)
{
	char	   *str;
	char	   *p;

	if (rawbytes < 0 || rawbytes > (msg->len - msg->cursor))
		ereport(ERROR,
				(errcode(ERRCODE_PROTOCOL_VIOLATION),
				 errmsg("insufficient data left in message")));
	str = &msg->data[msg->cursor];
	msg->cursor += rawbytes;

	p = pg_client_to_server(str, rawbytes);
	if (p != str)				/* actual conversion has been done? */
		*nbytes = strlen(p);
	else
	{
		p = (char *) palloc(rawbytes + 1);
		memcpy(p, str, rawbytes);
		p[rawbytes] = '\0';
		*nbytes = rawbytes;
	}
	return p;
}

/* --------------------------------
 *		pq_getmsgstring - get a null-terminated text string (with conversion)
 *
 *		May return a pointer directly into the message buffer, or a pointer
 *		to a palloc'd conversion result.
 * --------------------------------
 */
const char *
pq_getmsgstring(StringInfo msg)
{
	char	   *str;
	int			slen;

	str = &msg->data[msg->cursor];

	/*
	 * It's safe to use strlen() here because a StringInfo is guaranteed to
	 * have a trailing null byte.  But check we found a null inside the
	 * message.
	 */
	slen = strlen(str);
	if (msg->cursor + slen >= msg->len)
		ereport(ERROR,
				(errcode(ERRCODE_PROTOCOL_VIOLATION),
				 errmsg("invalid string in message")));
	msg->cursor += slen + 1;

	return pg_client_to_server(str, slen);
}

/* --------------------------------
 *		pq_getmsgrawstring - get a null-terminated text string - NO conversion
 *
 *		Returns a pointer directly into the message buffer.
 * --------------------------------
 */
const char *
pq_getmsgrawstring(StringInfo msg)
{
	char	   *str;
	int			slen;

	str = &msg->data[msg->cursor];

	/*
	 * It's safe to use strlen() here because a StringInfo is guaranteed to
	 * have a trailing null byte.  But check we found a null inside the
	 * message.
	 */
	slen = strlen(str);
	if (msg->cursor + slen >= msg->len)
		ereport(ERROR,
				(errcode(ERRCODE_PROTOCOL_VIOLATION),
				 errmsg("invalid string in message")));
	msg->cursor += slen + 1;

	return str;
}

/* --------------------------------
 *		pq_getmsgend	- verify message fully consumed
 * --------------------------------
 */
void
pq_getmsgend(StringInfo msg)
{
	if (msg->cursor != msg->len)
		ereport(ERROR,
				(errcode(ERRCODE_PROTOCOL_VIOLATION),
				 errmsg("invalid message format")));
}