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, 17 deletions

diff --git a/src/backend/utils/adt/jsonfuncs.c b/src/backend/utils/adt/jsonfuncs.c
index 1b681eff5f1..7076b344b7b 100644
--- a/src/backend/utils/adt/jsonfuncs.c
+++ b/src/backend/utils/adt/jsonfuncs.c
@@ -3133,18 +3133,6 @@ populate_scalar(ScalarIOData *io, Oid typid, int32 typmod, JsValue *jsv,
 
 		json = jsv->val.json.str;
 		Assert(json);
-		if (len >= 0)
-		{
-			/* Need to copy non-null-terminated string */
-			str = palloc(len + 1 * sizeof(char));
-			memcpy(str, json, len);
-			str[len] = '\0';
-		}
-		else
-		{
-			/* string is already null-terminated */
-			str = unconstify(char *, json);
-		}
 
 		/* If converting to json/jsonb, make string into valid JSON literal */
 		if ((typid == JSONOID || typid == JSONBOID) &&
@@ -3153,12 +3141,24 @@ populate_scalar(ScalarIOData *io, Oid typid, int32 typmod, JsValue *jsv,
 			StringInfoData buf;
 
 			initStringInfo(&buf);
-			escape_json(&buf, str);
-			/* free temporary buffer */
-			if (str != json)
-				pfree(str);
+			if (len >= 0)
+				escape_json_with_len(&buf, json, len);
+			else
+				escape_json(&buf, json);
 			str = buf.data;
 		}
+		else if (len >= 0)
+		{
+			/* create a NUL-terminated version */
+			str = palloc(len + 1);
+			memcpy(str, json, len);
+			str[len] = '\0';
+		}
+		else
+		{
+			/* string is already NUL-terminated */
+			str = unconstify(char *, json);
+		}
 	}
 	else
 	{
@@ -5936,7 +5936,7 @@ transform_string_values_scalar(void *state, char *token, JsonTokenType tokentype
 	{
 		text	   *out = _state->action(_state->action_state, token, strlen(token));
 
-		escape_json(_state->strval, text_to_cstring(out));
+		escape_json_text(_state->strval, out);
 	}
 	else
 		appendStringInfoString(_state->strval, token);