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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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156
src/backend/utils/adt/json.c
View File

@@ -23,6 +23,7 @@
#include "utils/builtins.h"
#include "utils/date.h"
#include "utils/datetime.h"
#include "utils/fmgroids.h"
#include "utils/json.h"
#include "utils/jsonfuncs.h"
#include "utils/lsyscache.h"
@@ -285,9 +286,16 @@ datum_to_json_internal(Datum val, bool is_null, StringInfo result,
pfree(jsontext);
break;
default:
outputstr = OidOutputFunctionCall(outfuncoid, val);
escape_json(result, outputstr);
pfree(outputstr);
/* special-case text types to save useless palloc/memcpy cycles */
if (outfuncoid == F_TEXTOUT || outfuncoid == F_VARCHAROUT ||
outfuncoid == F_BPCHAROUT)
escape_json_text(result, (text *) DatumGetPointer(val));
else
{
outputstr = OidOutputFunctionCall(outfuncoid, val);
escape_json(result, outputstr);
pfree(outputstr);
}
break;
}
}
@@ -1391,7 +1399,6 @@ json_object(PG_FUNCTION_ARGS)
count,
i;
text *rval;
char *v;
switch (ndims)
{
@@ -1434,19 +1441,16 @@ json_object(PG_FUNCTION_ARGS)
(errcode(ERRCODE_NULL_VALUE_NOT_ALLOWED),
errmsg("null value not allowed for object key")));
v = TextDatumGetCString(in_datums[i * 2]);
if (i > 0)
appendStringInfoString(&result, ", ");
escape_json(&result, v);
escape_json_text(&result, (text *) DatumGetPointer(in_datums[i * 2]));
appendStringInfoString(&result, " : ");
pfree(v);
if (in_nulls[i * 2 + 1])
appendStringInfoString(&result, "null");
else
{
v = TextDatumGetCString(in_datums[i * 2 + 1]);
escape_json(&result, v);
pfree(v);
escape_json_text(&result,
(text *) DatumGetPointer(in_datums[i * 2 + 1]));
}
}
@@ -1483,7 +1487,6 @@ json_object_two_arg(PG_FUNCTION_ARGS)
val_count,
i;
text *rval;
char *v;
if (nkdims > 1 || nkdims != nvdims)
ereport(ERROR,
@@ -1512,20 +1515,15 @@ json_object_two_arg(PG_FUNCTION_ARGS)
(errcode(ERRCODE_NULL_VALUE_NOT_ALLOWED),
errmsg("null value not allowed for object key")));
v = TextDatumGetCString(key_datums[i]);
if (i > 0)
appendStringInfoString(&result, ", ");
escape_json(&result, v);
escape_json_text(&result, (text *) DatumGetPointer(key_datums[i]));
appendStringInfoString(&result, " : ");
pfree(v);
if (val_nulls[i])
appendStringInfoString(&result, "null");
else
{
v = TextDatumGetCString(val_datums[i]);
escape_json(&result, v);
pfree(v);
}
escape_json_text(&result,
(text *) DatumGetPointer(val_datums[i]));
}
appendStringInfoChar(&result, '}');
@@ -1541,50 +1539,100 @@ json_object_two_arg(PG_FUNCTION_ARGS)
PG_RETURN_TEXT_P(rval);
}
/*
* escape_json_char
* Inline helper function for escape_json* functions
*/
static pg_attribute_always_inline void
escape_json_char(StringInfo buf, char c)
{
switch (c)
{
case '\b':
appendStringInfoString(buf, "\\b");
break;
case '\f':
appendStringInfoString(buf, "\\f");
break;
case '\n':
appendStringInfoString(buf, "\\n");
break;
case '\r':
appendStringInfoString(buf, "\\r");
break;
case '\t':
appendStringInfoString(buf, "\\t");
break;
case '"':
appendStringInfoString(buf, "\\\"");
break;
case '\\':
appendStringInfoString(buf, "\\\\");
break;
default:
if ((unsigned char) c < ' ')
appendStringInfo(buf, "\\u%04x", (int) c);
else
appendStringInfoCharMacro(buf, c);
break;
}
}
/*
* Produce a JSON string literal, properly escaping characters in the text.
* escape_json
* Produce a JSON string literal, properly escaping the NUL-terminated
* cstring.
*/
void
escape_json(StringInfo buf, const char *str)
{
const char *p;
appendStringInfoCharMacro(buf, '"');
for (; *str != '\0'; str++)
escape_json_char(buf, *str);
appendStringInfoCharMacro(buf, '"');
for (p = str; *p; p++)
{
switch (*p)
{
case '\b':
appendStringInfoString(buf, "\\b");
break;
case '\f':
appendStringInfoString(buf, "\\f");
break;
case '\n':
appendStringInfoString(buf, "\\n");
break;
case '\r':
appendStringInfoString(buf, "\\r");
break;
case '\t':
appendStringInfoString(buf, "\\t");
break;
case '"':
appendStringInfoString(buf, "\\\"");
break;
case '\\':
appendStringInfoString(buf, "\\\\");
break;
default:
if ((unsigned char) *p < ' ')
appendStringInfo(buf, "\\u%04x", (int) *p);
else
appendStringInfoCharMacro(buf, *p);
break;
}
}
}
/*
* escape_json_with_len
* Produce a JSON string literal, properly escaping the possibly not
* NUL-terminated characters in 'str'. 'len' defines the number of bytes
* from 'str' to process.
*/
void
escape_json_with_len(StringInfo buf, const char *str, int len)
{
appendStringInfoCharMacro(buf, '"');
for (int i = 0; i < len; i++)
escape_json_char(buf, str[i]);
appendStringInfoCharMacro(buf, '"');
}
/*
* escape_json_text
* Append 'txt' onto 'buf' and escape using escape_json_with_len.
*
* This is more efficient than calling text_to_cstring and appending the
* result as that could require an additional palloc and memcpy.
*/
void
escape_json_text(StringInfo buf, const text *txt)
{
/* must cast away the const, unfortunately */
text *tunpacked = pg_detoast_datum_packed(unconstify(text *, txt));
int len = VARSIZE_ANY_EXHDR(tunpacked);
char *str;
str = VARDATA_ANY(tunpacked);
escape_json_with_len(buf, str, len);
/* pfree any detoasted values */
if (tunpacked != txt)
pfree(tunpacked);
}
/* Semantic actions for key uniqueness check */