/*
 * getCopyStart - process CopyInResponse or CopyOutResponse message
 *
 * parseInput already read the message type and length.
 */
static int
getCopyStart(PGconn *conn, ExecStatusType copytype)
{
	PGresult   *result;
	int			nfields;
	int			i;

	result = PQmakeEmptyPGresult(conn, copytype);
	if (!result)
		goto failure;

	if (pqGetc(&conn->copy_is_binary, conn))
		goto failure;
	result->binary = conn->copy_is_binary;
	/* the next two bytes are the number of fields	*/
	if (pqGetInt(&(result->numAttributes), 2, conn))
		goto failure;
	nfields = result->numAttributes;

	/* allocate space for the attribute descriptors */
	if (nfields > 0)
	{
		result->attDescs = (PGresAttDesc *)
			pqResultAlloc(result, nfields * sizeof(PGresAttDesc), TRUE);
		if (!result->attDescs)
			goto failure;
		MemSet(result->attDescs, 0, nfields * sizeof(PGresAttDesc));
	}

	for (i = 0; i < nfields; i++)
	{
		int			format;

		if (pqGetInt(&format, 2, conn))
			goto failure;

		/*
		 * Since pqGetInt treats 2-byte integers as unsigned, we need to
		 * coerce these results to signed form.
		 */
		format = (int) ((int16) format);
		result->attDescs[i].format = format;
	}

	/* Success! */
	conn->result = result;
	return 0;

failure:
	PQclear(result);
	return EOF;
}

/*
 * getCopyDataMessage - fetch next CopyData message, process async messages
 *
 * Returns length word of CopyData message (> 0), or 0 if no complete
 * message available, -1 if end of copy, -2 if error.
 */
static int
getCopyDataMessage(PGconn *conn)
{
	char		id;
	int			msgLength;
	int			avail;

	for (;;)
	{
		/*
		 * Do we have the next input message?  To make life simpler for async
		 * callers, we keep returning 0 until the next message is fully
		 * available, even if it is not Copy Data.
		 */
		conn->inCursor = conn->inStart;
		if (pqGetc(&id, conn))
			return 0;
		if (pqGetInt(&msgLength, 4, conn))
			return 0;
		if (msgLength < 4)
		{
			handleSyncLoss(conn, id, msgLength);
			return -2;
		}
		avail = conn->inEnd - conn->inCursor;
		if (avail < msgLength - 4)
			return 0;

		/*
		 * If it's a legitimate async message type, process it.  (NOTIFY
		 * messages are not currently possible here, but we handle them for
		 * completeness.  NOTICE is definitely possible, and ParameterStatus
		 * could probably be made to happen.)  Otherwise, if it's anything
		 * except Copy Data, report end-of-copy.
		 */
		switch (id)
		{
			case 'A':			/* NOTIFY */
				if (getNotify(conn))
					return 0;
				break;
			case 'N':			/* NOTICE */
				if (pqGetErrorNotice3(conn, false))
					return 0;
				break;
			case 'S':			/* ParameterStatus */
				if (getParameterStatus(conn))
					return 0;
				break;
			case 'd':			/* Copy Data, pass it back to caller */
				return msgLength;
			default:			/* treat as end of copy */
				return -1;
		}

		/* Drop the processed message and loop around for another */
		conn->inStart = conn->inCursor;
	}
}

/*
 * parseInput subroutine to read a 't' (ParameterDescription) message.
 * We'll build a new PGresult structure containing the parameter data.
 * Returns: 0 if completed message, EOF if not enough data yet.
 *
 * Note that if we run out of data, we have to release the partially
 * constructed PGresult, and rebuild it again next time.  Fortunately,
 * that shouldn't happen often, since 't' messages usually fit in a packet.
 */
static int
getParamDescriptions(PGconn *conn)
{
	PGresult   *result;
	int			nparams;
	int			i;

	result = PQmakeEmptyPGresult(conn, PGRES_COMMAND_OK);
	if (!result)
		goto failure;

	/* parseInput already read the 't' label and message length. */
	/* the next two bytes are the number of parameters */
	if (pqGetInt(&(result->numParameters), 2, conn))
		goto failure;
	nparams = result->numParameters;

	/* allocate space for the parameter descriptors */
	if (nparams > 0)
	{
		result->paramDescs = (PGresParamDesc *)
			pqResultAlloc(result, nparams * sizeof(PGresParamDesc), TRUE);
		if (!result->paramDescs)
			goto failure;
		MemSet(result->paramDescs, 0, nparams * sizeof(PGresParamDesc));
	}

	/* get parameter info */
	for (i = 0; i < nparams; i++)
	{
		int			typid;

		if (pqGetInt(&typid, 4, conn))
			goto failure;
		result->paramDescs[i].typid = typid;
	}

	/* Success! */
	conn->result = result;
	return 0;

failure:
	PQclear(result);
	return EOF;
}

/*
 * Attempt to read a Notify response message.
 * This is possible in several places, so we break it out as a subroutine.
 * Entry: 'A' message type and length have already been consumed.
 * Exit: returns 0 if successfully consumed Notify message.
 *		 returns EOF if not enough data.
 */
static int
getNotify(PGconn *conn)
{
	int			be_pid;
	char	   *svname;
	int			nmlen;
	int			extralen;
	PGnotify   *newNotify;

	if (pqGetInt(&be_pid, 4, conn))
		return EOF;
	if (pqGets(&conn->workBuffer, conn))
		return EOF;
	/* must save name while getting extra string */
	svname = strdup(conn->workBuffer.data);
	if (!svname)
		return EOF;
	if (pqGets(&conn->workBuffer, conn))
	{
		free(svname);
		return EOF;
	}

	/*
	 * Store the strings right after the PQnotify structure so it can all be
	 * freed at once.  We don't use NAMEDATALEN because we don't want to tie
	 * this interface to a specific server name length.
	 */
	nmlen = strlen(svname);
	extralen = strlen(conn->workBuffer.data);
	newNotify = (PGnotify *) malloc(sizeof(PGnotify) + nmlen + extralen + 2);
	if (newNotify)
	{
		newNotify->relname = (char *) newNotify + sizeof(PGnotify);
		strcpy(newNotify->relname, svname);
		newNotify->extra = newNotify->relname + nmlen + 1;
		strcpy(newNotify->extra, conn->workBuffer.data);
		newNotify->be_pid = be_pid;
		newNotify->next = NULL;
		if (conn->notifyTail)
			conn->notifyTail->next = newNotify;
		else
			conn->notifyHead = newNotify;
		conn->notifyTail = newNotify;
	}

	free(svname);
	return 0;
}

/*
 * Attempt to read a Notify response message.
 * This is possible in several places, so we break it out as a subroutine.
 * Entry: 'A' message type and length have already been consumed.
 * Exit: returns 0 if successfully consumed Notify message.
 *		 returns EOF if not enough data.
 */
static int
getNotify(PGconn *conn)
{
	int			be_pid;
	int			nmlen;
	PGnotify   *newNotify;

	if (pqGetInt(&be_pid, 4, conn))
		return EOF;
	if (pqGets(&conn->workBuffer, conn))
		return EOF;

	/*
	 * Store the relation name right after the PQnotify structure so it can
	 * all be freed at once.  We don't use NAMEDATALEN because we don't want
	 * to tie this interface to a specific server name length.
	 */
	nmlen = strlen(conn->workBuffer.data);
	newNotify = (PGnotify *) malloc(sizeof(PGnotify) + nmlen + 1);
	if (newNotify)
	{
		newNotify->relname = (char *) newNotify + sizeof(PGnotify);
		strcpy(newNotify->relname, conn->workBuffer.data);
		/* fake up an empty-string extra field */
		newNotify->extra = newNotify->relname + nmlen;
		newNotify->be_pid = be_pid;
		newNotify->next = NULL;
		if (conn->notifyTail)
			conn->notifyTail->next = newNotify;
		else
			conn->notifyHead = newNotify;
		conn->notifyTail = newNotify;
	}

	return 0;
}

/*
 * parseInput subroutine to read a 'B' or 'D' (row data) message.
 * We fill rowbuf with column pointers and then call the row processor.
 * Returns: 0 if completed message, EOF if error or not enough data
 * received yet.
 *
 * Note that if we run out of data, we have to suspend and reprocess
 * the message after more data is received.  Otherwise, conn->inStart
 * must get advanced past the processed data.
 */
static int
getAnotherTuple(PGconn *conn, bool binary)
{
	PGresult   *result = conn->result;
	int			nfields = result->numAttributes;
	const char *errmsg;
	PGdataValue *rowbuf;

	/* the backend sends us a bitmap of which attributes are null */
	char		std_bitmap[64]; /* used unless it doesn't fit */
	char	   *bitmap = std_bitmap;
	int			i;
	size_t		nbytes;			/* the number of bytes in bitmap  */
	char		bmap;			/* One byte of the bitmap */
	int			bitmap_index;	/* Its index */
	int			bitcnt;			/* number of bits examined in current byte */
	int			vlen;			/* length of the current field value */

	/* Resize row buffer if needed */
	rowbuf = conn->rowBuf;
	if (nfields > conn->rowBufLen)
	{
		rowbuf = (PGdataValue *) realloc(rowbuf,
										 nfields * sizeof(PGdataValue));
		if (!rowbuf)
		{
			errmsg = NULL;		/* means "out of memory", see below */
			goto advance_and_error;
		}
		conn->rowBuf = rowbuf;
		conn->rowBufLen = nfields;
	}

	/* Save format specifier */
	result->binary = binary;

	/*
	 * If it's binary, fix the column format indicators.  We assume the
	 * backend will consistently send either B or D, not a mix.
	 */
	if (binary)
	{
		for (i = 0; i < nfields; i++)
			result->attDescs[i].format = 1;
	}

	/* Get the null-value bitmap */
	nbytes = (nfields + BITS_PER_BYTE - 1) / BITS_PER_BYTE;
	/* malloc() only for unusually large field counts... */
	if (nbytes > sizeof(std_bitmap))
	{
		bitmap = (char *) malloc(nbytes);
		if (!bitmap)
		{
			errmsg = NULL;		/* means "out of memory", see below */
			goto advance_and_error;
		}
	}

	if (pqGetnchar(bitmap, nbytes, conn))
		goto EOFexit;

	/* Scan the fields */
	bitmap_index = 0;
	bmap = bitmap[bitmap_index];
	bitcnt = 0;

	for (i = 0; i < nfields; i++)
	{
		/* get the value length */
		if (!(bmap & 0200))
			vlen = NULL_LEN;
		else if (pqGetInt(&vlen, 4, conn))
			goto EOFexit;
		else
		{
			if (!binary)
				vlen = vlen - 4;
			if (vlen < 0)
				vlen = 0;
		}
		rowbuf[i].len = vlen;

		/*
		 * rowbuf[i].value always points to the next address in the data
		 * buffer even if the value is NULL.  This allows row processors to
		 * estimate data sizes more easily.
		 */
		rowbuf[i].value = conn->inBuffer + conn->inCursor;

//.........这里部分代码省略.........

/*
 * parseInput subroutine to read a 'T' (row descriptions) message.
 * We build a PGresult structure containing the attribute data.
 * Returns: 0 if completed message, EOF if error or not enough data
 * received yet.
 *
 * Note that if we run out of data, we have to suspend and reprocess
 * the message after more data is received.  Otherwise, conn->inStart
 * must get advanced past the processed data.
 */
static int
getRowDescriptions(PGconn *conn)
{
	PGresult   *result;
	int			nfields;
	const char *errmsg;
	int			i;

	result = PQmakeEmptyPGresult(conn, PGRES_TUPLES_OK);
	if (!result)
	{
		errmsg = NULL;			/* means "out of memory", see below */
		goto advance_and_error;
	}

	/* parseInput already read the 'T' label. */
	/* the next two bytes are the number of fields	*/
	if (pqGetInt(&(result->numAttributes), 2, conn))
		goto EOFexit;
	nfields = result->numAttributes;

	/* allocate space for the attribute descriptors */
	if (nfields > 0)
	{
		result->attDescs = (PGresAttDesc *)
			pqResultAlloc(result, nfields * sizeof(PGresAttDesc), TRUE);
		if (!result->attDescs)
		{
			errmsg = NULL;		/* means "out of memory", see below */
			goto advance_and_error;
		}
		MemSet(result->attDescs, 0, nfields * sizeof(PGresAttDesc));
	}

	/* get type info */
	for (i = 0; i < nfields; i++)
	{
		int			typid;
		int			typlen;
		int			atttypmod;

		if (pqGets(&conn->workBuffer, conn) ||
			pqGetInt(&typid, 4, conn) ||
			pqGetInt(&typlen, 2, conn) ||
			pqGetInt(&atttypmod, 4, conn))
			goto EOFexit;

		/*
		 * Since pqGetInt treats 2-byte integers as unsigned, we need to
		 * coerce the result to signed form.
		 */
		typlen = (int) ((int16) typlen);

		result->attDescs[i].name = pqResultStrdup(result,
												  conn->workBuffer.data);
		if (!result->attDescs[i].name)
		{
			errmsg = NULL;		/* means "out of memory", see below */
			goto advance_and_error;
		}
		result->attDescs[i].tableid = 0;
		result->attDescs[i].columnid = 0;
		result->attDescs[i].format = 0;
		result->attDescs[i].typid = typid;
		result->attDescs[i].typlen = typlen;
		result->attDescs[i].atttypmod = atttypmod;
	}

	/* Success! */
	conn->result = result;

	/* Advance inStart to show that the "T" message has been processed. */
	conn->inStart = conn->inCursor;

	/*
	 * We could perform additional setup for the new result set here, but for
	 * now there's nothing else to do.
	 */

	/* And we're done. */
	return 0;

advance_and_error:

	/*
	 * Discard the failed message.  Unfortunately we don't know for sure where
	 * the end is, so just throw away everything in the input buffer. This is
	 * not very desirable but it's the best we can do in protocol v2.
	 */
	conn->inStart = conn->inEnd;
//.........这里部分代码省略.........

//.........这里部分代码省略.........
					conn->asyncStatus = PGASYNC_READY;
					break;
				case 'Z':		/* backend is ready for new query */
					conn->asyncStatus = PGASYNC_IDLE;
					break;
				case 'I':		/* empty query */
					/* read and throw away the closing '\0' */
					if (pqGetc(&id, conn))
						return;
					if (id != '\0')
						pqInternalNotice(&conn->noticeHooks,
										 "unexpected character %c following empty query response (\"I\" message)",
										 id);
					if (conn->result == NULL)
					{
						conn->result = PQmakeEmptyPGresult(conn,
														   PGRES_EMPTY_QUERY);
						if (!conn->result)
						{
							printfPQExpBuffer(&conn->errorMessage,
											  libpq_gettext("out of memory"));
							pqSaveErrorResult(conn);
						}
					}
					conn->asyncStatus = PGASYNC_READY;
					break;
				case 'K':		/* secret key data from the backend */

					/*
					 * This is expected only during backend startup, but it's
					 * just as easy to handle it as part of the main loop.
					 * Save the data and continue processing.
					 */
					if (pqGetInt(&(conn->be_pid), 4, conn))
						return;
					if (pqGetInt(&(conn->be_key), 4, conn))
						return;
					break;
				case 'P':		/* synchronous (normal) portal */
					if (pqGets(&conn->workBuffer, conn))
						return;
					/* We pretty much ignore this message type... */
					break;
				case 'T':		/* row descriptions (start of query results) */
					if (conn->result == NULL)
					{
						/* First 'T' in a query sequence */
						if (getRowDescriptions(conn))
							return;
						/* getRowDescriptions() moves inStart itself */
						continue;
					}
					else
					{
						/*
						 * A new 'T' message is treated as the start of
						 * another PGresult.  (It is not clear that this is
						 * really possible with the current backend.) We stop
						 * parsing until the application accepts the current
						 * result.
						 */
						conn->asyncStatus = PGASYNC_READY;
						return;
					}
					break;
				case 'D':		/* ASCII data tuple */

/*
 * PQfn - Send a function call to the POSTGRES backend.
 *
 * See fe-exec.c for documentation.
 */
PGresult *
pqFunctionCall2(PGconn *conn, Oid fnid,
				int *result_buf, int *actual_result_len,
				int result_is_int,
				const PQArgBlock *args, int nargs)
{
	bool		needInput = false;
	ExecStatusType status = PGRES_FATAL_ERROR;
	char		id;
	int			i;

	/* PQfn already validated connection state */

	if (pqPutMsgStart('F', false, conn) < 0 ||	/* function call msg */
		pqPuts(" ", conn) < 0 ||	/* dummy string */
		pqPutInt(fnid, 4, conn) != 0 || /* function id */
		pqPutInt(nargs, 4, conn) != 0)	/* # of args */
	{
		pqHandleSendFailure(conn);
		return NULL;
	}

	for (i = 0; i < nargs; ++i)
	{							/* len.int4 + contents	   */
		if (pqPutInt(args[i].len, 4, conn))
		{
			pqHandleSendFailure(conn);
			return NULL;
		}

		if (args[i].isint)
		{
			if (pqPutInt(args[i].u.integer, 4, conn))
			{
				pqHandleSendFailure(conn);
				return NULL;
			}
		}
		else
		{
			if (pqPutnchar((char *) args[i].u.ptr, args[i].len, conn))
			{
				pqHandleSendFailure(conn);
				return NULL;
			}
		}
	}

	if (pqPutMsgEnd(conn) < 0 ||
		pqFlush(conn))
	{
		pqHandleSendFailure(conn);
		return NULL;
	}

	for (;;)
	{
		if (needInput)
		{
			/* Wait for some data to arrive (or for the channel to close) */
			if (pqWait(TRUE, FALSE, conn) ||
				pqReadData(conn) < 0)
				break;
		}

		/*
		 * Scan the message. If we run out of data, loop around to try again.
		 */
		conn->inCursor = conn->inStart;
		needInput = true;

		if (pqGetc(&id, conn))
			continue;

		/*
		 * We should see V or E response to the command, but might get N
		 * and/or A notices first. We also need to swallow the final Z before
		 * returning.
		 */
		switch (id)
		{
			case 'V':			/* function result */
				if (pqGetc(&id, conn))
					continue;
				if (id == 'G')
				{
					/* function returned nonempty value */
					if (pqGetInt(actual_result_len, 4, conn))
						continue;
					if (result_is_int)
					{
						if (pqGetInt(result_buf, 4, conn))
							continue;
					}
					else
//.........这里部分代码省略.........

/*
 * parseInput: if appropriate, parse input data from backend
 * until input is exhausted or a stopping state is reached.
 * Note that this function will NOT attempt to read more data from the backend.
 */
void
pqParseInput3(PGconn *conn)
{
	char		id;
	int			msgLength;
	int			avail;

	/*
	 * Loop to parse successive complete messages available in the buffer.
	 */
	for (;;)
	{
		/*
		 * Try to read a message.  First get the type code and length. Return
		 * if not enough data.
		 */
		conn->inCursor = conn->inStart;
		if (pqGetc(&id, conn))
			return;
		if (pqGetInt(&msgLength, 4, conn))
			return;

		/*
		 * Try to validate message type/length here.  A length less than 4 is
		 * definitely broken.  Large lengths should only be believed for a few
		 * message types.
		 */
		if (msgLength < 4)
		{
			handleSyncLoss(conn, id, msgLength);
			return;
		}
		if (msgLength > 30000 && !VALID_LONG_MESSAGE_TYPE(id))
		{
			handleSyncLoss(conn, id, msgLength);
			return;
		}

		/*
		 * Can't process if message body isn't all here yet.
		 */
		msgLength -= 4;
		avail = conn->inEnd - conn->inCursor;
		if (avail < msgLength)
		{
			/*
			 * Before returning, enlarge the input buffer if needed to hold
			 * the whole message.  This is better than leaving it to
			 * pqReadData because we can avoid multiple cycles of realloc()
			 * when the message is large; also, we can implement a reasonable
			 * recovery strategy if we are unable to make the buffer big
			 * enough.
			 */
			if (pqCheckInBufferSpace(conn->inCursor + msgLength, conn))
			{
				/*
				 * XXX add some better recovery code... plan is to skip over
				 * the message using its length, then report an error. For the
				 * moment, just treat this like loss of sync (which indeed it
				 * might be!)
				 */
				handleSyncLoss(conn, id, msgLength);
			}
			return;
		}

		/*
		 * NOTIFY and NOTICE messages can happen in any state; always process
		 * them right away.
		 *
		 * Most other messages should only be processed while in BUSY state.
		 * (In particular, in READY state we hold off further parsing until
		 * the application collects the current PGresult.)
		 *
		 * However, if the state is IDLE then we got trouble; we need to deal
		 * with the unexpected message somehow.
		 *
		 * ParameterStatus ('S') messages are a special case: in IDLE state we
		 * must process 'em (this case could happen if a new value was adopted
		 * from config file due to SIGHUP), but otherwise we hold off until
		 * BUSY state.
		 */
		if (id == 'A')
		{
			if (getNotify(conn))
				return;
		}
		else if (id == 'N')
		{
			if (pqGetErrorNotice3(conn, false))
				return;
		}
		else if (conn->asyncStatus != PGASYNC_BUSY)
		{
			/* If not IDLE state, just wait ... */
//.........这里部分代码省略.........

/*
 * parseInput subroutine to read a 'D' (row data) message.
 * We add another tuple to the existing PGresult structure.
 * Returns: 0 if completed message, EOF if error or not enough data yet.
 *
 * Note that if we run out of data, we have to suspend and reprocess
 * the message after more data is received.  We keep a partially constructed
 * tuple in conn->curTuple, and avoid reallocating already-allocated storage.
 */
static int
getAnotherTuple(PGconn *conn, int msgLength)
{
	PGresult   *result = conn->result;
	int			nfields = result->numAttributes;
	PGresAttValue *tup;
	int			tupnfields;		/* # fields from tuple */
	int			vlen;			/* length of the current field value */
	int			i;

	/* Allocate tuple space if first time for this data message */
	if (conn->curTuple == NULL)
	{
		conn->curTuple = (PGresAttValue *)
			pqResultAlloc(result, nfields * sizeof(PGresAttValue), TRUE);
		if (conn->curTuple == NULL)
			goto outOfMemory;
		MemSet(conn->curTuple, 0, nfields * sizeof(PGresAttValue));
	}
	tup = conn->curTuple;

	/* Get the field count and make sure it's what we expect */
	if (pqGetInt(&tupnfields, 2, conn))
		return EOF;

	if (tupnfields != nfields)
	{
		/* Replace partially constructed result with an error result */
		printfPQExpBuffer(&conn->errorMessage,
				 libpq_gettext("unexpected field count in \"D\" message\n"));
		pqSaveErrorResult(conn);
		/* Discard the failed message by pretending we read it */
		conn->inCursor = conn->inStart + 5 + msgLength;
		return 0;
	}

	/* Scan the fields */
	for (i = 0; i < nfields; i++)
	{
		/* get the value length */
		if (pqGetInt(&vlen, 4, conn))
			return EOF;
		if (vlen == -1)
		{
			/* null field */
			tup[i].value = result->null_field;
			tup[i].len = NULL_LEN;
			continue;
		}
		if (vlen < 0)
			vlen = 0;
		if (tup[i].value == NULL)
		{
			bool		isbinary = (result->attDescs[i].format != 0);

			tup[i].value = (char *) pqResultAlloc(result, vlen + 1, isbinary);
			if (tup[i].value == NULL)
				goto outOfMemory;
		}
		tup[i].len = vlen;
		/* read in the value */
		if (vlen > 0)
			if (pqGetnchar((char *) (tup[i].value), vlen, conn))
				return EOF;
		/* we have to terminate this ourselves */
		tup[i].value[vlen] = '\0';
	}

	/* Success!  Store the completed tuple in the result */
	if (!pqAddTuple(result, tup))
		goto outOfMemory;
	/* and reset for a new message */
	conn->curTuple = NULL;

	return 0;

outOfMemory:

	/*
	 * Replace partially constructed result with an error result. First
	 * discard the old result to try to win back some memory.
	 */
	pqClearAsyncResult(conn);
	printfPQExpBuffer(&conn->errorMessage,
					  libpq_gettext("out of memory for query result\n"));
	pqSaveErrorResult(conn);

	/* Discard the failed message by pretending we read it */
	conn->inCursor = conn->inStart + 5 + msgLength;
	return 0;
}

/*
 * parseInput subroutine to read a 'T' (row descriptions) message.
 * We'll build a new PGresult structure (unless called for a Describe
 * command for a prepared statement) containing the attribute data.
 * Returns: 0 if completed message, EOF if not enough data yet.
 *
 * Note that if we run out of data, we have to release the partially
 * constructed PGresult, and rebuild it again next time.  Fortunately,
 * that shouldn't happen often, since 'T' messages usually fit in a packet.
 */
static int
getRowDescriptions(PGconn *conn)
{
	PGresult   *result;
	int			nfields;
	int			i;

	/*
	 * When doing Describe for a prepared statement, there'll already be a
	 * PGresult created by getParamDescriptions, and we should fill data into
	 * that.  Otherwise, create a new, empty PGresult.
	 */
	if (conn->queryclass == PGQUERY_DESCRIBE)
	{
		if (conn->result)
			result = conn->result;
		else
			result = PQmakeEmptyPGresult(conn, PGRES_COMMAND_OK);
	}
	else
		result = PQmakeEmptyPGresult(conn, PGRES_TUPLES_OK);
	if (!result)
		goto failure;

	/* parseInput already read the 'T' label and message length. */
	/* the next two bytes are the number of fields */
	if (pqGetInt(&(result->numAttributes), 2, conn))
		goto failure;
	nfields = result->numAttributes;

	/* allocate space for the attribute descriptors */
	if (nfields > 0)
	{
		result->attDescs = (PGresAttDesc *)
			pqResultAlloc(result, nfields * sizeof(PGresAttDesc), TRUE);
		if (!result->attDescs)
			goto failure;
		MemSet(result->attDescs, 0, nfields * sizeof(PGresAttDesc));
	}

	/* result->binary is true only if ALL columns are binary */
	result->binary = (nfields > 0) ? 1 : 0;

	/* get type info */
	for (i = 0; i < nfields; i++)
	{
		int			tableid;
		int			columnid;
		int			typid;
		int			typlen;
		int			atttypmod;
		int			format;

		if (pqGets(&conn->workBuffer, conn) ||
			pqGetInt(&tableid, 4, conn) ||
			pqGetInt(&columnid, 2, conn) ||
			pqGetInt(&typid, 4, conn) ||
			pqGetInt(&typlen, 2, conn) ||
			pqGetInt(&atttypmod, 4, conn) ||
			pqGetInt(&format, 2, conn))
		{
			goto failure;
		}

		/*
		 * Since pqGetInt treats 2-byte integers as unsigned, we need to
		 * coerce these results to signed form.
		 */
		columnid = (int) ((int16) columnid);
		typlen = (int) ((int16) typlen);
		format = (int) ((int16) format);

		result->attDescs[i].name = pqResultStrdup(result,
												  conn->workBuffer.data);
		if (!result->attDescs[i].name)
			goto failure;
		result->attDescs[i].tableid = tableid;
		result->attDescs[i].columnid = columnid;
		result->attDescs[i].format = format;
		result->attDescs[i].typid = typid;
		result->attDescs[i].typlen = typlen;
		result->attDescs[i].atttypmod = atttypmod;

		if (format != 1)
			result->binary = 0;
	}

	/* Success! */
	conn->result = result;
	return 0;
//.........这里部分代码省略.........

/*
 * PQfn - Send a function call to the POSTGRES backend.
 *
 * See fe-exec.c for documentation.
 */
PGresult *
pqFunctionCall3(PGconn *conn, Oid fnid,
				int *result_buf, int *actual_result_len,
				int result_is_int,
				const PQArgBlock *args, int nargs)
{
	bool		needInput = false;
	ExecStatusType status = PGRES_FATAL_ERROR;
	char		id;
	int			msgLength;
	int			avail;
	int			i;

	/* PQfn already validated connection state */

	if (pqPutMsgStart('F', false, conn) < 0 ||	/* function call msg */
		pqPutInt(fnid, 4, conn) < 0 ||	/* function id */
		pqPutInt(1, 2, conn) < 0 ||		/* # of format codes */
		pqPutInt(1, 2, conn) < 0 ||		/* format code: BINARY */
		pqPutInt(nargs, 2, conn) < 0)	/* # of args */
	{
		pqHandleSendFailure(conn);
		return NULL;
	}

	for (i = 0; i < nargs; ++i)
	{							/* len.int4 + contents	   */
		if (pqPutInt(args[i].len, 4, conn))
		{
			pqHandleSendFailure(conn);
			return NULL;
		}
		if (args[i].len == -1)
			continue;			/* it's NULL */

		if (args[i].isint)
		{
			if (pqPutInt(args[i].u.integer, args[i].len, conn))
			{
				pqHandleSendFailure(conn);
				return NULL;
			}
		}
		else
		{
			if (pqPutnchar((char *) args[i].u.ptr, args[i].len, conn))
			{
				pqHandleSendFailure(conn);
				return NULL;
			}
		}
	}

	if (pqPutInt(1, 2, conn) < 0)		/* result format code: BINARY */
	{
		pqHandleSendFailure(conn);
		return NULL;
	}

	if (pqPutMsgEnd(conn) < 0 ||
		pqFlush(conn))
	{
		pqHandleSendFailure(conn);
		return NULL;
	}

	for (;;)
	{
		if (needInput)
		{
			/* Wait for some data to arrive (or for the channel to close) */
			if (pqWait(TRUE, FALSE, conn) ||
				pqReadData(conn) < 0)
				break;
		}

		/*
		 * Scan the message. If we run out of data, loop around to try again.
		 */
		needInput = true;

		conn->inCursor = conn->inStart;
		if (pqGetc(&id, conn))
			continue;
		if (pqGetInt(&msgLength, 4, conn))
			continue;

		/*
		 * Try to validate message type/length here.  A length less than 4 is
		 * definitely broken.  Large lengths should only be believed for a few
		 * message types.
		 */
		if (msgLength < 4)
		{
			handleSyncLoss(conn, id, msgLength);
//.........这里部分代码省略.........

/*
 * parseInput subroutine to read a 'B' or 'D' (row data) message.
 * We add another tuple to the existing PGresult structure.
 * Returns: 0 if completed message, EOF if error or not enough data yet.
 *
 * Note that if we run out of data, we have to suspend and reprocess
 * the message after more data is received.  We keep a partially constructed
 * tuple in conn->curTuple, and avoid reallocating already-allocated storage.
 */
static int
getAnotherTuple(PGconn *conn, bool binary)
{
	PGresult   *result = conn->result;
	int			nfields = result->numAttributes;
	PGresAttValue *tup;

	/* the backend sends us a bitmap of which attributes are null */
	char		std_bitmap[64]; /* used unless it doesn't fit */
	char	   *bitmap = std_bitmap;
	int			i;
	size_t		nbytes;			/* the number of bytes in bitmap  */
	char		bmap;			/* One byte of the bitmap */
	int			bitmap_index;	/* Its index */
	int			bitcnt;			/* number of bits examined in current byte */
	int			vlen;			/* length of the current field value */

	result->binary = binary;

	/* Allocate tuple space if first time for this data message */
	if (conn->curTuple == NULL)
	{
		conn->curTuple = (PGresAttValue *)
			pqResultAlloc(result, nfields * sizeof(PGresAttValue), TRUE);
		if (conn->curTuple == NULL)
			goto outOfMemory;
		MemSet(conn->curTuple, 0, nfields * sizeof(PGresAttValue));

		/*
		 * If it's binary, fix the column format indicators.  We assume the
		 * backend will consistently send either B or D, not a mix.
		 */
		if (binary)
		{
			for (i = 0; i < nfields; i++)
				result->attDescs[i].format = 1;
		}
	}
	tup = conn->curTuple;

	/* Get the null-value bitmap */
	nbytes = (nfields + BITS_PER_BYTE - 1) / BITS_PER_BYTE;
	/* malloc() only for unusually large field counts... */
	if (nbytes > sizeof(std_bitmap))
	{
		bitmap = (char *) malloc(nbytes);
		if (!bitmap)
			goto outOfMemory;
	}

	if (pqGetnchar(bitmap, nbytes, conn))
		goto EOFexit;

	/* Scan the fields */
	bitmap_index = 0;
	bmap = bitmap[bitmap_index];
	bitcnt = 0;

	for (i = 0; i < nfields; i++)
	{
		if (!(bmap & 0200))
		{
			/* if the field value is absent, make it a null string */
			tup[i].value = result->null_field;
			tup[i].len = NULL_LEN;
		}
		else
		{
			/* get the value length (the first four bytes are for length) */
			if (pqGetInt(&vlen, 4, conn))
				goto EOFexit;
			if (!binary)
				vlen = vlen - 4;
			if (vlen < 0)
				vlen = 0;
			if (tup[i].value == NULL)
			{
				tup[i].value = (char *) pqResultAlloc(result, vlen + 1, binary);
				if (tup[i].value == NULL)
					goto outOfMemory;
			}
			tup[i].len = vlen;
			/* read in the value */
			if (vlen > 0)
				if (pqGetnchar((char *) (tup[i].value), vlen, conn))
					goto EOFexit;
			/* we have to terminate this ourselves */
			tup[i].value[vlen] = '\0';
		}
		/* advance the bitmap stuff */
		bitcnt++;
//.........这里部分代码省略.........

/*
 * parseInput subroutine to read a 'T' (row descriptions) message.
 * We build a PGresult structure containing the attribute data.
 * Returns: 0 if completed message, EOF if not enough data yet.
 *
 * Note that if we run out of data, we have to release the partially
 * constructed PGresult, and rebuild it again next time.  Fortunately,
 * that shouldn't happen often, since 'T' messages usually fit in a packet.
 */
static int
getRowDescriptions(PGconn *conn)
{
	PGresult   *result = NULL;
	int			nfields;
	int			i;

	result = PQmakeEmptyPGresult(conn, PGRES_TUPLES_OK);
	if (!result)
		goto failure;

	/* parseInput already read the 'T' label. */
	/* the next two bytes are the number of fields	*/
	if (pqGetInt(&(result->numAttributes), 2, conn))
		goto failure;
	nfields = result->numAttributes;

	/* allocate space for the attribute descriptors */
	if (nfields > 0)
	{
		result->attDescs = (PGresAttDesc *)
			pqResultAlloc(result, nfields * sizeof(PGresAttDesc), TRUE);
		if (!result->attDescs)
			goto failure;
		MemSet(result->attDescs, 0, nfields * sizeof(PGresAttDesc));
	}

	/* get type info */
	for (i = 0; i < nfields; i++)
	{
		int			typid;
		int			typlen;
		int			atttypmod;

		if (pqGets(&conn->workBuffer, conn) ||
			pqGetInt(&typid, 4, conn) ||
			pqGetInt(&typlen, 2, conn) ||
			pqGetInt(&atttypmod, 4, conn))
			goto failure;

		/*
		 * Since pqGetInt treats 2-byte integers as unsigned, we need to
		 * coerce the result to signed form.
		 */
		typlen = (int) ((int16) typlen);

		result->attDescs[i].name = pqResultStrdup(result,
												  conn->workBuffer.data);
		if (!result->attDescs[i].name)
			goto failure;
		result->attDescs[i].tableid = 0;
		result->attDescs[i].columnid = 0;
		result->attDescs[i].format = 0;
		result->attDescs[i].typid = typid;
		result->attDescs[i].typlen = typlen;
		result->attDescs[i].atttypmod = atttypmod;
	}

	/* Success! */
	conn->result = result;
	return 0;

failure:
	if (result)
		PQclear(result);
	return EOF;
}

/*
 * getCopyDataMessage - fetch next CopyData message, process async messages
 *
 * Returns length word of CopyData message (> 0), or 0 if no complete
 * message available, -1 if end of copy, -2 if error.
 */
static int
getCopyDataMessage(PGconn *conn)
{
	char		id;
	int			msgLength;
	int			avail;

	for (;;)
	{
		/*
		 * Do we have the next input message?  To make life simpler for async
		 * callers, we keep returning 0 until the next message is fully
		 * available, even if it is not Copy Data.
		 */
		conn->inCursor = conn->inStart;
		if (pqGetc(&id, conn))
			return 0;
		if (pqGetInt(&msgLength, 4, conn))
			return 0;
		if (msgLength < 4)
		{
			handleSyncLoss(conn, id, msgLength);
			return -2;
		}
		avail = conn->inEnd - conn->inCursor;
		if (avail < msgLength - 4)
		{
			/*
			 * Before returning, enlarge the input buffer if needed to hold
			 * the whole message.  See notes in parseInput.
			 */
			if (pqCheckInBufferSpace(conn->inCursor + (size_t) msgLength - 4,
									 conn))
			{
				/*
				 * XXX add some better recovery code... plan is to skip over
				 * the message using its length, then report an error. For the
				 * moment, just treat this like loss of sync (which indeed it
				 * might be!)
				 */
				handleSyncLoss(conn, id, msgLength);
				return -2;
			}
			return 0;
		}

		/*
		 * If it's a legitimate async message type, process it.  (NOTIFY
		 * messages are not currently possible here, but we handle them for
		 * completeness.)  Otherwise, if it's anything except Copy Data,
		 * report end-of-copy.
		 */
		switch (id)
		{
			case 'A':			/* NOTIFY */
				if (getNotify(conn))
					return 0;
				break;
			case 'N':			/* NOTICE */
				if (pqGetErrorNotice3(conn, false))
					return 0;
				break;
			case 'S':			/* ParameterStatus */
				if (getParameterStatus(conn))
					return 0;
				break;
			case 'd':			/* Copy Data, pass it back to caller */
				return msgLength;
			default:			/* treat as end of copy */
				return -1;
		}

		/* Drop the processed message and loop around for another */
		conn->inStart = conn->inCursor;
	}
}