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mysqlnd: Do not compress packets smaller than 100 bytes #24702

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mysqlnd: Do not compress packets smaller than 100 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
c25b7e8
Drop the closing calls from the compression packet size test
lohmag Oct 29, 2026
814d625
Lower the compression threshold to 170 and test it on the wire
lohmag Oct 29, 2026
04664b0
Lower the compression threshold to 100
lohmag Oct 30, 2026
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22 changes: 22 additions & 0 deletions ext/mysqli/tests/fake_server.inc
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Original file line number Diff line number Diff line change
Expand Up @@ -630,6 +630,15 @@ class my_mysqli_fake_server_conn
fprintf(STDERR, "[*] Received: %s\n", bin2hex($data));
}

public function read_compressed_packet(): void
{
$header = $this->read_bytes(7);
$compressed_length = ord($header[0]) | (ord($header[1]) << 8) | (ord($header[2]) << 16);
$uncompressed_length = ord($header[4]) | (ord($header[5]) << 8) | (ord($header[6]) << 16);
$this->read_bytes($compressed_length);
fprintf(STDERR, "[*] Received compressed packet: %d bytes, uncompressed length %d\n", $compressed_length, $uncompressed_length);
}

public function close()
{
fclose($this->conn);
Expand Down Expand Up @@ -1445,6 +1454,19 @@ function my_mysqli_test_stmt_response_field_len_premature(my_mysqli_fake_server_
$conn->read(65536);
}

function my_mysqli_test_compressed_queries(my_mysqli_fake_server_conn $conn): void
{
$conn->send_server_greetings();
$conn->read();
$conn->send_server_ok();
for ($i = 0; $i < 2; $i++) {
$conn->read_compressed_packet();
$ok = $conn->packet_generator->server_ok("01")->to_bytes();
$conn->send(substr(pack('V', strlen($ok)), 0, 3) . "\x01\x00\x00\x00" . $ok, "Compressed Server OK");
}
$conn->read_compressed_packet();
}

function run_fake_server(string $test_function, int|string $port = 0): void
{
$host = '127.0.0.1';
Expand Down
43 changes: 43 additions & 0 deletions ext/mysqli/tests/mysqli_compression_threshold.phpt
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Original file line number Diff line number Diff line change
@@ -0,0 +1,43 @@
--TEST--
Compressed protocol: packets below the threshold are sent uncompressed
--EXTENSIONS--
mysqli
--SKIPIF--
<?php
ob_start();
if (extension_loaded('mysqlnd')) {
(new ReflectionExtension('mysqlnd'))->info();
}
if (!str_contains(ob_get_clean(), 'Compression => supported')) {
die('skip mysqlnd is built without compression support');
}
?>
--FILE--
<?php
require_once 'fake_server.inc';

$process = run_fake_server_in_background('compressed_queries');
$process->wait();

$link = mysqli_init();
$link->real_connect('127.0.0.1', 'root', '', '', $process->getPort(), null, MYSQLI_CLIENT_COMPRESS);
var_dump($link->query("SELECT '" . str_repeat('a', 80) . "'"));
var_dump($link->query("SELECT '" . str_repeat('a', 1000) . "'"));
$link->close();

$process->terminate(true);
?>
--EXPECTF--
[*] Server started on 127.0.0.1:%d
[*] Connection established
[*] Sending - Server Greeting: 580000000a352e352e352d31302e352e31382d4d6172696144420003000000473e3f6047257c6700fef7080200ff81150000000000000f0000006c6b55463f49335f686c6431006d7973716c5f6e61746976655f70617373776f7264
[*] Received: %s
[*] Sending - Server OK: 0700000200000002000000
[*] Received compressed packet: 94 bytes, uncompressed length 0
[*] Sending - Compressed Server OK: 0b0000010000000700000100000002000000
bool(true)
[*] Received compressed packet: %d bytes, uncompressed length 1014
[*] Sending - Compressed Server OK: 0b0000010000000700000100000002000000
bool(true)
[*] Received compressed packet: 5 bytes, uncompressed length 0
[*] Server finished
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);
Expand Down
2 changes: 2 additions & 0 deletions ext/mysqlnd/mysqlnd_wireprotocol.h
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Original file line number Diff line number Diff line change
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 100

#define MYSQLND_NULL_LENGTH (zend_ulong) ~0

Expand Down
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