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diff --git a/src/include/lib/stringinfo.h b/src/include/lib/stringinfo.h
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+/*-------------------------------------------------------------------------
+ *
+ * stringinfo.h
+ *	  Declarations/definitions for "StringInfo" functions.
+ *
+ * StringInfo provides an extensible string data type (currently limited to a
+ * length of 1GB).  It can be used to buffer either ordinary C strings
+ * (null-terminated text) or arbitrary binary data.  All storage is allocated
+ * with palloc() (falling back to malloc in frontend code).
+ *
+ * Portions Copyright (c) 1996-2021, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ * src/include/lib/stringinfo.h
+ *
+ *-------------------------------------------------------------------------
+ */
+#ifndef STRINGINFO_H
+#define STRINGINFO_H
+
+/*-------------------------
+ * 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.  We must always have maxlen > len.
+ *		cursor	is initialized to zero by makeStringInfo or initStringInfo,
+ *				but is not otherwise touched by the stringinfo.c routines.
+ *				Some routines use it to scan through a StringInfo.
+ *-------------------------
+ */
+typedef struct StringInfoData
+{
+	char	   *data;
+	int			len;
+	int			maxlen;
+	int			cursor;
+} 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 an empty 'StringInfoData' & return a pointer to it.
+ */
+extern StringInfo makeStringInfo(void);
+
+/*------------------------
+ * initStringInfo
+ * Initialize a StringInfoData struct (with previously undefined contents)
+ * to describe an empty string.
+ */
+extern void initStringInfo(StringInfo str);
+
+/*------------------------
+ * resetStringInfo
+ * Clears the current content of the StringInfo, if any. The
+ * StringInfo remains valid.
+ */
+extern void resetStringInfo(StringInfo str);
+
+/*------------------------
+ * appendStringInfo
+ * Format text data under the control of fmt (an sprintf-style 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.
+ */
+extern void appendStringInfo(StringInfo str, const char *fmt,...) pg_attribute_printf(2, 3);
+
+/*------------------------
+ * appendStringInfoVA
+ * Attempt to format text data under the control of fmt (an sprintf-style
+ * format string) and append it to whatever is already in str.  If successful
+ * return zero; if not (because there's not enough space), return an estimate
+ * of the space needed, without modifying str.  Typically the caller should
+ * pass the return value to enlargeStringInfo() before trying again; see
+ * appendStringInfo for standard usage pattern.
+ */
+extern int	appendStringInfoVA(StringInfo str, const char *fmt, va_list args) pg_attribute_printf(2, 0);
+
+/*------------------------
+ * appendStringInfoString
+ * Append a null-terminated string to str.
+ * Like appendStringInfo(str, "%s", s) but faster.
+ */
+extern void appendStringInfoString(StringInfo str, const char *s);
+
+/*------------------------
+ * appendStringInfoChar
+ * Append a single byte to str.
+ * Like appendStringInfo(str, "%c", ch) but much faster.
+ */
+extern void appendStringInfoChar(StringInfo str, char ch);
+
+/*------------------------
+ * appendStringInfoCharMacro
+ * As above, but a macro for even more speed where it matters.
+ * Caution: str argument will be evaluated multiple times.
+ */
+#define appendStringInfoCharMacro(str,ch) \
+	(((str)->len + 1 >= (str)->maxlen) ? \
+	 appendStringInfoChar(str, ch) : \
+	 (void)((str)->data[(str)->len] = (ch), (str)->data[++(str)->len] = '\0'))
+
+/*------------------------
+ * appendStringInfoSpaces
+ * Append a given number of spaces to str.
+ */
+extern void appendStringInfoSpaces(StringInfo str, int count);
+
+/*------------------------
+ * appendBinaryStringInfo
+ * Append arbitrary binary data to a StringInfo, allocating more space
+ * if necessary.
+ */
+extern void appendBinaryStringInfo(StringInfo str,
+								   const char *data, int datalen);
+
+/*------------------------
+ * appendBinaryStringInfoNT
+ * Append arbitrary binary data to a StringInfo, allocating more space
+ * if necessary. Does not ensure a trailing null-byte exists.
+ */
+extern void appendBinaryStringInfoNT(StringInfo str,
+									 const char *data, int datalen);
+
+/*------------------------
+ * enlargeStringInfo
+ * Make sure a StringInfo's buffer can hold at least 'needed' more bytes.
+ */
+extern void enlargeStringInfo(StringInfo str, int needed);
+
+#endif							/* STRINGINFO_H */