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Optimize escaping of JSON strings

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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
This commit is contained in:
David Rowley
2024-07-27 23:46:07 +12:00
parent 67427f1009
commit 17a5871d9d
7 changed files with 151 additions and 101 deletions
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34
src/backend/utils/adt/jsonfuncs.c
View File

@@ -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);