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mysqlnd: Do not compress packets smaller than 512 bytes #24702

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mysqlnd: Do not compress packets smaller than 512 bytes #24702

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3e9a997
mysqlnd: Do not compress packets smaller than 512 bytes
lohmag Oct 25, 2026
3d3b1c9
Use incompressible data in the compression packet size test
lohmag Oct 26, 2026
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46 changes: 46 additions & 0 deletions ext/mysqli/tests/mysqli_compression_packet_sizes.phpt
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Original file line number Diff line number Diff line change
@@ -0,0 +1,46 @@
--TEST--
Compressed protocol: packets on both sides of the compression threshold
--EXTENSIONS--
mysqli
--SKIPIF--
<?php
require_once 'skipifconnectfailure.inc';
?>
--FILE--
<?php
require_once 'connect.inc';

$link = mysqli_init();
if (!my_mysqli_real_connect($link, $host, $user, $passwd, $db, $port, $socket, MYSQLI_CLIENT_COMPRESS)) {
printf("[001] Cannot connect: [%d] %s\n", mysqli_connect_errno(), mysqli_connect_error());
}
var_dump($link->query("SHOW SESSION STATUS LIKE 'Compression'")->fetch_row()[1]);

foreach ([1, 230, 235, 236, 237, 238, 240, 600, 4000, 100000, 3000000] as $length) {
$value = substr(str_repeat('compressed protocol packet ', intdiv($length, 27) + 1), 0, $length);
$row = $link->query("SELECT '$value' AS v, LENGTH('$value') AS l")->fetch_assoc();
if ($row['v'] !== $value || (int) $row['l'] !== $length) {
printf("[002] Round trip failed for %d bytes\n", $length);
}
}

$stmt = $link->prepare("SELECT HEX(?)");
for ($i = 0; $i < 200; $i++) {
$value = random_bytes(1 + $i * 37);
$stmt->bind_param('s', $value);
$stmt->execute();
$stmt->bind_result($hex);
$stmt->fetch();
$stmt->free_result();
if ($hex !== strtoupper(bin2hex($value))) {
printf("[003] Round trip failed for %d bytes\n", strlen($value));
}
}
$stmt->close();

$link->close();
print "done!";
?>
--EXPECT--
string(2) "ON"
done!
3 changes: 2 additions & 1 deletion ext/mysqlnd/mysqlnd_protocol_frame_codec.c
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Original file line number Diff line number Diff line change
Expand Up @@ -55,7 +55,8 @@ static ssize_t write_compressed_packet(
/* here we need to compress the data and then write it, first comes the compressed header */
size_t tmp_complen = to_be_sent;
size_t payload_size;
if (PASS == pfc->data->m.encode((compress_buf + COMPRESSED_HEADER_SIZE + MYSQLND_HEADER_SIZE), &tmp_complen,
if (to_be_sent >= MYSQLND_MIN_COMPRESS_LENGTH
&& PASS == pfc->data->m.encode((compress_buf + COMPRESSED_HEADER_SIZE + MYSQLND_HEADER_SIZE), &tmp_complen,
uncompressed_payload, to_be_sent))
{
int3store(compress_buf + MYSQLND_HEADER_SIZE, to_be_sent);
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2 changes: 2 additions & 0 deletions ext/mysqlnd/mysqlnd_wireprotocol.h
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Expand Up @@ -18,6 +18,8 @@

#define MYSQLND_HEADER_SIZE 4
#define COMPRESSED_HEADER_SIZE 3
/* Packets smaller than this are sent uncompressed: they barely shrink. */
#define MYSQLND_MIN_COMPRESS_LENGTH 512

#define MYSQLND_NULL_LENGTH (zend_ulong) ~0

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