Optimize escaping of JSON strings

There were quite a few places where we either had a non-NUL-terminated
string or a text Datum which we needed to call escape_json() on.  Many of
these places required that a temporary string was created due to the fact
that escape_json() needs a NUL-terminated cstring.  For text types, those
first had to be converted to cstring before calling escape_json() on them.

Here we introduce two new functions to make escaping JSON more optimal:

escape_json_text() can be given a text Datum to append onto the given
buffer.  This is more optimal as it foregoes the need to convert the text
Datum into a cstring.  A temporary allocation is only required if the text
Datum needs to be detoasted.

escape_json_with_len() can be used when the length of the cstring is
already known or the given string isn't NUL-terminated.  Having this
allows various places which were creating a temporary NUL-terminated
string to just call escape_json_with_len() without any temporary memory
allocations.

Discussion: https://postgr.es/m/CAApHDvpLXwMZvbCKcdGfU9XQjGCDm7tFpRdTXuB9PVgpNUYfEQ@mail.gmail.com
Reviewed-by: Melih Mutlu, Heikki Linnakangas

1 files changed, 17 insertions, 24 deletions

diff --git a/contrib/hstore/hstore_io.c b/contrib/hstore/hstore_io.c
index 999ddad76d9..2125436e40c 100644
--- a/contrib/hstore/hstore_io.c
+++ b/contrib/hstore/hstore_io.c
@@ -1343,23 +1343,20 @@ hstore_to_json_loose(PG_FUNCTION_ARGS)
 	int			count = HS_COUNT(in);
 	char	   *base = STRPTR(in);
 	HEntry	   *entries = ARRPTR(in);
-	StringInfoData tmp,
-				dst;
+	StringInfoData dst;
 
 	if (count == 0)
 		PG_RETURN_TEXT_P(cstring_to_text_with_len("{}", 2));
 
-	initStringInfo(&tmp);
 	initStringInfo(&dst);
 
 	appendStringInfoChar(&dst, '{');
 
 	for (i = 0; i < count; i++)
 	{
-		resetStringInfo(&tmp);
-		appendBinaryStringInfo(&tmp, HSTORE_KEY(entries, base, i),
-							   HSTORE_KEYLEN(entries, i));
-		escape_json(&dst, tmp.data);
+		escape_json_with_len(&dst,
+							 HSTORE_KEY(entries, base, i),
+							 HSTORE_KEYLEN(entries, i));
 		appendStringInfoString(&dst, ": ");
 		if (HSTORE_VALISNULL(entries, i))
 			appendStringInfoString(&dst, "null");
@@ -1372,13 +1369,13 @@ hstore_to_json_loose(PG_FUNCTION_ARGS)
 			appendStringInfoString(&dst, "false");
 		else
 		{
-			resetStringInfo(&tmp);
-			appendBinaryStringInfo(&tmp, HSTORE_VAL(entries, base, i),
-								   HSTORE_VALLEN(entries, i));
-			if (IsValidJsonNumber(tmp.data, tmp.len))
-				appendBinaryStringInfo(&dst, tmp.data, tmp.len);
+			char	   *str = HSTORE_VAL(entries, base, i);
+			int			len = HSTORE_VALLEN(entries, i);
+
+			if (IsValidJsonNumber(str, len))
+				appendBinaryStringInfo(&dst, str, len);
 			else
-				escape_json(&dst, tmp.data);
+				escape_json_with_len(&dst, str, len);
 		}
 
 		if (i + 1 != count)
@@ -1398,32 +1395,28 @@ hstore_to_json(PG_FUNCTION_ARGS)
 	int			count = HS_COUNT(in);
 	char	   *base = STRPTR(in);
 	HEntry	   *entries = ARRPTR(in);
-	StringInfoData tmp,
-				dst;
+	StringInfoData dst;
 
 	if (count == 0)
 		PG_RETURN_TEXT_P(cstring_to_text_with_len("{}", 2));
 
-	initStringInfo(&tmp);
 	initStringInfo(&dst);
 
 	appendStringInfoChar(&dst, '{');
 
 	for (i = 0; i < count; i++)
 	{
-		resetStringInfo(&tmp);
-		appendBinaryStringInfo(&tmp, HSTORE_KEY(entries, base, i),
-							   HSTORE_KEYLEN(entries, i));
-		escape_json(&dst, tmp.data);
+		escape_json_with_len(&dst,
+							 HSTORE_KEY(entries, base, i),
+							 HSTORE_KEYLEN(entries, i));
 		appendStringInfoString(&dst, ": ");
 		if (HSTORE_VALISNULL(entries, i))
 			appendStringInfoString(&dst, "null");
 		else
 		{
-			resetStringInfo(&tmp);
-			appendBinaryStringInfo(&tmp, HSTORE_VAL(entries, base, i),
-								   HSTORE_VALLEN(entries, i));
-			escape_json(&dst, tmp.data);
+			escape_json_with_len(&dst,
+								 HSTORE_VAL(entries, base, i),
+								 HSTORE_VALLEN(entries, i));
 		}
 
 		if (i + 1 != count)