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Add json_encode/json_decode micro-benchmarks and optimize JSON key writing #22492

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Add json_encode/json_decode micro-benchmarks and optimize JSON key writing #22492

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afc607e
Zend/micro_bench.php: add json_encode benchmarks
Jun 27, 2026
cca07d9
ext/json: single-alloc fast path for strings without special characters
Jun 27, 2026
a77ac43
ext/json: fast path for declared-property object keys
Jun 27, 2026
faef2b3
ext/json: factor out \uXXXX escape writing into php_json_append_unico…
Jun 27, 2026
6e114db
ext/json: flush clean ASCII prefix before slow path in escape_string …
Jun 27, 2026
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2 changes: 2 additions & 0 deletions UPGRADING
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Original file line number Diff line number Diff line change
Expand Up @@ -499,6 +499,8 @@ PHP 8.6 UPGRADE NOTES
. Improve performance of encoding arrays and objects.
. Improved performance of indentation generation in json_encode()
when using PHP_JSON_PRETTY_PRINT.
. Improved performance of json_encode() for strings without special
characters and for objects with declared properties.

- Phar:
. Reduced temporary allocations when iterating Phar directories.
Expand Down
28 changes: 28 additions & 0 deletions Zend/micro_bench.php
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Expand Up @@ -231,6 +231,30 @@ function ternary2($n) {
}
}

class JsonObj {
public function __construct(
public int $id,
public string $name,
public bool $active,
public string $category,
public int $score
) {}
}

function json_encode_obj($n) {
$obj = new JsonObj(1, 'test', true, 'category', 42);
for ($i = 0; $i < $n; $i++) {
json_encode($obj);
}
}

function json_encode_arr($n) {
$arr = ['id' => 1, 'name' => 'test', 'active' => true, 'category' => 'cat', 'score' => 42];
for ($i = 0; $i < $n; $i++) {
json_encode($arr);
}
}

/*****/

function empty_loop($n) {
Expand Down Expand Up @@ -355,4 +379,8 @@ function total()
$t = end_test($t, '$x = $f ? $f : $a', $overhead);
ternary2(N);
$t = end_test($t, '$x = $f ? $f : tmp', $overhead);
json_encode_obj(N/50);
$t = end_test($t, 'json_encode(obj)', $overhead);
json_encode_arr(N/50);
$t = end_test($t, 'json_encode(arr)', $overhead);
total($t0, "Total");
150 changes: 131 additions & 19 deletions ext/json/json_encoder.c
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Original file line number Diff line number Diff line change
Expand Up @@ -30,6 +30,25 @@

static const char digits[] = "0123456789abcdef";

static zend_always_inline void php_json_append_quoted(smart_str *buf, const char *s, size_t len)
{
char *dst = smart_str_extend(buf, len + 2);

ghost Oct 23, 2026 •
edited by cgsmith
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I tried the same string fast path independently on current master before finding your PR. Adding a gate is helpful too.

dst = smart_str_fextend_ex(buf, len + 2, false, /* fallible */ true);
if (UNEXPECTED(!dst)) {
     return FAILURE;
}

dst[0] = '"';
memcpy(dst + 1, s, len);
dst[len + 1] = '"';
}

static zend_always_inline void php_json_append_unicode_escape(smart_str *buf, unsigned int us)
{
char *dst = smart_str_extend(buf, 6);
dst[0] = '\\';
dst[1] = 'u';
dst[2] = digits[(us >> 12) & 0xf];
dst[3] = digits[(us >> 8) & 0xf];
dst[4] = digits[(us >> 4) & 0xf];
dst[5] = digits[us & 0xf];
}

static zend_always_inline bool php_json_check_stack_limit(void)
{
#ifdef ZEND_CHECK_STACK_LIMIT
Expand Down Expand Up @@ -105,6 +124,96 @@ static inline void php_json_encode_double(smart_str *buf, double d, int options)
} \
} while (0)

/* encode a PHP identifier (property name) as a JSON string key.
* PHP identifiers cannot contain ASCII characters that require JSON escaping,
* so the fast path only scans for multi-byte UTF-8 sequences (bytes >= 0x80). */
static zend_result php_json_encode_identifier(
smart_str *buf, const char *s, size_t len,
int options, php_json_encoder *encoder)
{
size_t pos, checkpoint;

/* fast path: no characters require escaping (PHP identifiers contain no JSON-special ASCII bytes) */
pos = 0;
while (pos < len && (unsigned char)s[pos] < 0x80) {
pos++;
}
if (EXPECTED(pos == len)) {
php_json_append_quoted(buf, s, len);
return SUCCESS;
}

checkpoint = buf->s ? ZSTR_LEN(buf->s) : 0;
smart_str_alloc(buf, len + 2, 0);
smart_str_appendc(buf, '"');

/* flush the clean ASCII prefix found by the fast path scan */
if (pos) {
smart_str_appendl(buf, s, pos);
s += pos;
len -= pos;
}
pos = 0;
do {
unsigned int us = (unsigned char)s[pos];
if (EXPECTED(us < 0x80)) {
pos++;
len--;
if (len == 0) {
smart_str_appendl(buf, s, pos);
break;
}
} else {
if (pos) {
smart_str_appendl(buf, s, pos);
s += pos;
pos = 0;
}
zend_result status;
us = php_next_utf8_char((unsigned char *)s, len, &pos, &status);

if (UNEXPECTED(status != SUCCESS)) {
if (options & PHP_JSON_INVALID_UTF8_IGNORE) {
/* ignore invalid UTF-8 byte */
} else if (options & PHP_JSON_INVALID_UTF8_SUBSTITUTE) {
if (options & PHP_JSON_UNESCAPED_UNICODE) {
smart_str_appendl(buf, "\xef\xbf\xbd", 3);
} else {
smart_str_appendl(buf, "\\ufffd", 6);
}
} else {
ZSTR_LEN(buf->s) = checkpoint;
encoder->error_code = PHP_JSON_ERROR_UTF8;
if (options & PHP_JSON_PARTIAL_OUTPUT_ON_ERROR) {
smart_str_appendl(buf, "null", 4);
}
return FAILURE;
}
} else if ((options & PHP_JSON_UNESCAPED_UNICODE)
&& ((options & PHP_JSON_UNESCAPED_LINE_TERMINATORS)
|| us < 0x2028 || us > 0x2029)) {
smart_str_appendl(buf, s, pos);
} else {
if (us >= 0x10000) {
unsigned int next_us;
us -= 0x10000;
next_us = (unsigned short)((us & 0x3ff) | 0xdc00);
us = (unsigned short)((us >> 10) | 0xd800);
php_json_append_unicode_escape(buf, us);
us = next_us;
}
php_json_append_unicode_escape(buf, us);
}
s += pos;
len -= pos;
pos = 0;
}
} while (len);
Comment on lines +166 to +211

ghost Jul 6, 2026

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This is very similar to the code in php_json_escape_string, stripped of the unreachable paths.


smart_str_appendc(buf, '"');
return SUCCESS;
}

static zend_result php_json_encode_array(smart_str *buf, zval *val, int options, php_json_encoder *encoder) /* {{{ */
{
bool encode_as_object = options & PHP_JSON_FORCE_OBJECT;
Expand Down Expand Up @@ -162,7 +271,7 @@ static zend_result php_json_encode_array(smart_str *buf, zval *val, int options,
php_json_pretty_print_char(buf, options, '\n');
php_json_pretty_print_indent(buf, options, encoder);

if (php_json_escape_string(buf, ZSTR_VAL(prop_info->name), ZSTR_LEN(prop_info->name),
if (php_json_encode_identifier(buf, ZSTR_VAL(prop_info->name), ZSTR_LEN(prop_info->name),
options & ~PHP_JSON_NUMERIC_CHECK, encoder) == FAILURE &&
(options & PHP_JSON_PARTIAL_OUTPUT_ON_ERROR) &&
buf->s) {
Expand Down Expand Up @@ -350,6 +459,9 @@ zend_result php_json_escape_string(
smart_str *buf, const char *s, size_t len,
int options, php_json_encoder *encoder) /* {{{ */
{
static const uint32_t charmap[8] = {
0xffffffff, 0x500080c4, 0x10000000, 0x00000000,
0xffffffff, 0xffffffff, 0xffffffff, 0xffffffff};
size_t pos, checkpoint;
char *dst;

Expand All @@ -374,19 +486,31 @@ zend_result php_json_escape_string(
}

}
/* fast path: no characters in the string require escaping allows us to single alloc and memcpy */
pos = 0;
while (pos < len && !ZEND_BIT_TEST(charmap, (unsigned char)s[pos])) {
pos++;
}
if (EXPECTED(pos == len)) {
php_json_append_quoted(buf, s, len);
return SUCCESS;
}

checkpoint = buf->s ? ZSTR_LEN(buf->s) : 0;

/* pre-allocate for string length plus 2 quotes */
smart_str_alloc(buf, len+2, 0);
smart_str_appendc(buf, '"');

/* flush the clean ASCII prefix found by the fast path scan */
if (pos) {
smart_str_appendl(buf, s, pos);
s += pos;
len -= pos;
}
pos = 0;

do {
static const uint32_t charmap[8] = {
0xffffffff, 0x500080c4, 0x10000000, 0x00000000,
0xffffffff, 0xffffffff, 0xffffffff, 0xffffffff};

unsigned int us = (unsigned char)s[pos];
if (EXPECTED(!ZEND_BIT_TEST(charmap, us))) {
pos++;
Expand Down Expand Up @@ -441,22 +565,10 @@ zend_result php_json_escape_string(
us -= 0x10000;
next_us = (unsigned short)((us & 0x3ff) | 0xdc00);
us = (unsigned short)((us >> 10) | 0xd800);
dst = smart_str_extend(buf, 6);
dst[0] = '\\';
dst[1] = 'u';
dst[2] = digits[(us >> 12) & 0xf];
dst[3] = digits[(us >> 8) & 0xf];
dst[4] = digits[(us >> 4) & 0xf];
dst[5] = digits[us & 0xf];
php_json_append_unicode_escape(buf, us);
us = next_us;
}
dst = smart_str_extend(buf, 6);
dst[0] = '\\';
dst[1] = 'u';
dst[2] = digits[(us >> 12) & 0xf];
dst[3] = digits[(us >> 8) & 0xf];
dst[4] = digits[(us >> 4) & 0xf];
dst[5] = digits[us & 0xf];
php_json_append_unicode_escape(buf, us);
}
s += pos;
len -= pos;
Expand Down