Relax check for return value from second call of pg_strnxfrm().

strxfrm() is not guaranteed to return the exact number of bytes needed
to store the result; it may return a higher value.

Discussion: https://postgr.es/m/32f85d88d1f64395abfe5a10dd97a62a4d3474ce.camel@j-davis.com
Reviewed-by: Heikki Linnakangas
Backpatch-through: 16

Author: jeff-davis

src/backend/access/hash/hashfunc.c

@@ -298,7 +298,9 @@ hashtext(PG_FUNCTION_ARGS)
 		buf = palloc(bsize + 1);
 
 		rsize = pg_strnxfrm(buf, bsize + 1, keydata, keylen, mylocale);
-		if (rsize != bsize)
+
+		/* the second call may return a smaller value than the first */
+		if (rsize > bsize)
 			elog(ERROR, "pg_strnxfrm() returned unexpected result");
 
 		/*
@@ -352,7 +354,9 @@ hashtextextended(PG_FUNCTION_ARGS)
 		buf = palloc(bsize + 1);
 
 		rsize = pg_strnxfrm(buf, bsize + 1, keydata, keylen, mylocale);
-		if (rsize != bsize)
+
+		/* the second call may return a smaller value than the first */
+		if (rsize > bsize)
 			elog(ERROR, "pg_strnxfrm() returned unexpected result");
 
 		/*

src/backend/utils/adt/pg_locale.c

@@ -2373,9 +2373,9 @@ pg_strxfrm_enabled(pg_locale_t locale)
  * The provided 'src' must be nul-terminated. If 'destsize' is zero, 'dest'
  * may be NULL.
  *
- * Returns the number of bytes needed to store the transformed string,
- * excluding the terminating nul byte. If the value returned is 'destsize' or
- * greater, the resulting contents of 'dest' are undefined.
+ * Returns the number of bytes needed (or more) to store the transformed
+ * string, excluding the terminating nul byte. If the value returned is
+ * 'destsize' or greater, the resulting contents of 'dest' are undefined.
  */
 size_t
 pg_strxfrm(char *dest, const char *src, size_t destsize, pg_locale_t locale)
@@ -2405,9 +2405,9 @@ pg_strxfrm(char *dest, const char *src, size_t destsize, pg_locale_t locale)
  * 'src' does not need to be nul-terminated. If 'destsize' is zero, 'dest' may
  * be NULL.
  *
- * Returns the number of bytes needed to store the transformed string,
- * excluding the terminating nul byte. If the value returned is 'destsize' or
- * greater, the resulting contents of 'dest' are undefined.
+ * Returns the number of bytes needed (or more) to store the transformed
+ * string, excluding the terminating nul byte. If the value returned is
+ * 'destsize' or greater, the resulting contents of 'dest' are undefined.
  *
  * This function may need to nul-terminate the argument for libc functions;
  * so if the caller already has a nul-terminated string, it should call

src/backend/utils/adt/varchar.c

@@ -1028,7 +1028,9 @@ hashbpchar(PG_FUNCTION_ARGS)
 		buf = palloc(bsize + 1);
 
 		rsize = pg_strnxfrm(buf, bsize + 1, keydata, keylen, mylocale);
-		if (rsize != bsize)
+
+		/* the second call may return a smaller value than the first */
+		if (rsize > bsize)
 			elog(ERROR, "pg_strnxfrm() returned unexpected result");
 
 		/*
@@ -1084,7 +1086,9 @@ hashbpcharextended(PG_FUNCTION_ARGS)
 		buf = palloc(bsize + 1);
 
 		rsize = pg_strnxfrm(buf, bsize + 1, keydata, keylen, mylocale);
-		if (rsize != bsize)
+
+		/* the second call may return a smaller value than the first */
+		if (rsize > bsize)
 			elog(ERROR, "pg_strnxfrm() returned unexpected result");
 
 		/*