Fix handling of large compressed packets

[nikic]

Fix for https://bugs.php.net/bug.php?id=80107. There's two layers of packet splitting going on. First, packets need to be split into having a payload of exactly 2^24-1 bytes or being the last packet. If the split packet has size between 2^24-5 and 2^24-1 bytes, the compressed packets also needs to be split, though the choice of split doesn't matter here. I'm splitting off the first 8192 bytes, as that's what I observe libmysqlclient to be doing.

If I may say so, the protocol is pretty ridiculous.

[cmb69]

The test fails on default configurations of MySQL 5.6 and 8.0 on Windows, because max_allowed_packet is only 4MB there. I suggest something like:

 ext/mysqli/tests/mysqli_real_connect_compression_error.phpt | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/ext/mysqli/tests/mysqli_real_connect_compression_error.phpt b/ext/mysqli/tests/mysqli_real_connect_compression_error.phpt
index 4ce0804bc8..fb876bf449 100644
--- a/ext/mysqli/tests/mysqli_real_connect_compression_error.phpt
+++ b/ext/mysqli/tests/mysqli_real_connect_compression_error.phpt
@@ -4,7 +4,15 @@ Bug #80107 mysqli_query() fails for ~16 MB long query when compression is enable
 <?php
 require_once('skipif.inc');
 require_once('skipifemb.inc');
-require_once('skipifconnectfailure.inc');
+require_once("connect.inc");
+$link = @my_mysqli_connect($host, $user, $passwd, $db, $port, $socket);
+if (!$link) {
+    die(sprintf("skip Can't connect to MySQL Server - [%d] %s", mysqli_connect_errno(), mysqli_connect_error()));
+}
+$result = $link->query("SHOW VARIABLES LIKE 'max_allowed_packet'");
+if ($result->fetch_assoc()['Value'] < 0xffffff) {
+    die('skip max_allowed_packet is less than 0xffffff');
+}
 ?>
 --INI--
 mysqli.allow_local_infile=1

[nikic]

@cmb69 I see a couple tests doing SET @@global.max_allowed_packet = or SET GLOBAL max_allowed_packet =. Would that work as well?

[cmb69]

That needs SUPER privilege, and fails otherwise. We could check for that, but given that the test apparently works in CI, I think just skipping is okay.

[nikic]

Merged into 7.3 up.