Revise backend libpq interfaces so that messages to the frontend

can be generated in a buffer and then sent to the frontend in a single
libpq call.  This solves problems with NOTICE and ERROR messages generated
in the middle of a data message or COPY OUT operation.

src/include/lib/stringinfo.h

@@ -1,52 +1,108 @@
 /*-------------------------------------------------------------------------
  *
  * stringinfo.h
- *	  Declarations/definitons for "string" functions.
+ *	  Declarations/definitions for "StringInfo" functions.
  *
+ * StringInfo provides an indefinitely-extensible string data type.
+ * It can be used to buffer either ordinary C strings (null-terminated text)
+ * or arbitrary binary data.  All storage is allocated with palloc().
  *
  * Copyright (c) 1994, Regents of the University of California
  *
- * $Id: stringinfo.h,v 1.10 1999/02/13 23:21:32 momjian Exp $
+ * $Id: stringinfo.h,v 1.11 1999/04/25 03:19:27 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
 #ifndef STRINGINFO_H
 #define STRINGINFO_H
 
-
 /*-------------------------
- * StringInfoData holds information about a string.
- *		'data' is the string.
- *		'len' is the current string length (as returned by 'strlen')
- *		'maxlen' is the size in bytes of 'data', i.e. the maximum string
- *				size (including the terminating '\0' char) that we can
+ * StringInfoData holds information about an extensible string.
+ *		data	is the current buffer for the string (allocated with palloc).
+ *		len		is the current string length.  There is guaranteed to be
+ *				a terminating '\0' at data[len], although this is not very
+ *				useful when the string holds binary data rather than text.
+ *		maxlen	is the allocated size in bytes of 'data', i.e. the maximum
+ *				string size (including the terminating '\0' char) that we can
  *				currently store in 'data' without having to reallocate
- *				more space.
+ *				more space.  We must always have maxlen > len.
+ *-------------------------
  */
 typedef struct StringInfoData
 {
 	char	   *data;
-	int			maxlen;
 	int			len;
+	int			maxlen;
 } StringInfoData;
 
 typedef StringInfoData *StringInfo;
 
+
+/*------------------------
+ * There are two ways to create a StringInfo object initially:
+ *
+ * StringInfo stringptr = makeStringInfo();
+ *		Both the StringInfoData and the data buffer are palloc'd.
+ *
+ * StringInfoData string;
+ * initStringInfo(&string);
+ *		The data buffer is palloc'd but the StringInfoData is just local.
+ *		This is the easiest approach for a StringInfo object that will
+ *		only live as long as the current routine.
+ *
+ * To destroy a StringInfo, pfree() the data buffer, and then pfree() the
+ * StringInfoData if it was palloc'd.  There's no special support for this.
+ *
+ * NOTE: some routines build up a string using StringInfo, and then
+ * release the StringInfoData but return the data string itself to their
+ * caller.  At that point the data string looks like a plain palloc'd
+ * string.
+ *-------------------------
+ */
+
 /*------------------------
  * makeStringInfo
- * create a 'StringInfoData' & return a pointer to it.
+ * Create an empty 'StringInfoData' & return a pointer to it.
  */
 extern StringInfo makeStringInfo(void);
 
 /*------------------------
- * appendStringInfo
- * similar to 'strcat' but reallocates more space if necessary...
+ * initStringInfo
+ * Initialize a StringInfoData struct (with previously undefined contents)
+ * to describe an empty string.
  */
-extern void appendStringInfo(StringInfo str, const char *fmt,...);
+extern void initStringInfo(StringInfo str);
 
 /*------------------------
- * nullStringInfo
- * return the string itself or "<>" if it is NULL
+ * appendStringInfo
+ * Format text data under the control of fmt (an sprintf-like format string)
+ * and append it to whatever is already in str.  More space is allocated
+ * to str if necessary.  This is sort of like a combination of sprintf and
+ * strcat.
+ * CAUTION: the current implementation has a 1K limit on the amount of text
+ * generated in a single call (not on the total string length).
+ */
+extern void appendStringInfo(StringInfo str, const char *fmt, ...);
+
+/*------------------------
+ * appendStringInfoChar
+ * Append a single byte to str.
+ * Like appendStringInfo(str, "%c", ch) but much faster.
+ */
+extern void appendStringInfoChar(StringInfo str, char ch);
+
+/*------------------------
+ * appendBinaryStringInfo
+ * Append arbitrary binary data to a StringInfo, allocating more space
+ * if necessary.
+ */
+extern void appendBinaryStringInfo(StringInfo str,
+								   const char *data, int datalen);
+
+/*------------------------
+ * stringStringInfo
+ * Return the string itself or "<>" if it is NULL.
+ * This is just a convenience macro used by many callers of appendStringInfo.
  */
 #define stringStringInfo(s) (((s) == NULL) ? "<>" : (s))