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[ticket/10188] Prevent semi-compressed output

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When a non-fatal error occurs at the beginning of the script before any custom
error handler is set one of two situations can be encountered:

1) if the ini option output buffer is disabled:
      - headers are sent to the http client
      - the error message is output
2) if the ini option output_buffer is enabled or the script
   is run within an ob_start()/ob_end() wrapper:
      - the error message is written to the output buffer

Once the script reaches page_header() phpbb starts gzip compression if enabled.
This is done through ob_start with a ob_gzhandler as a callback. The
compression is skipped if headers have already been sent. In situation 1) the
error message sent in plain text comes with headers and this gzip compression
is skipped. The client receives a plaintext version of the page. However in
situation 2) headers have not been sent yet and the rest of the page will be
compressed. The result is a plaintext error message followed by compressed
output. The client does not understand this output resulting in either an
error message or simply a blank page in the browser.

In addition to the above situation this problem occurs with errors that are
triggered after the custom error handler is loaded. The problem has been
noticed before, and a workaround was found. The error handler would call
ob_flush() for particular configuration settings before outputting the error
message. This resulted in headers being sent when output buffering was enabled
thus disabling gzip compression for the rest of the page. The constraints under
which ob_flush() was called were lessened over time whenever a new case was
found that would trigger this problem. Eventually ob_flush() would be called
even when code causing an E_NOTICE was simply run within an ob_start/ob_end.
This makes it impossible to use output buffering to retrieve the content of an
error message without prohibiting the page from setting headers afterwards.

This commit removes all flushing in msg_handler completely and instead fixes
the problem for both errors before and after the error handler is registered.
GZIP compression is only enabled if there is at most one level of output
buffering (e.g. the output_buffer php.ini option is enabled) and if there has
not yet been any output in this buffer. This should avoid any partial output
compression.

PHPBB3-10188
This commit is contained in:
Nils Adermann 2011-06-26 11:01:46 +02:00
parent fc5a68c2cf
commit a5ef6c3b20
1 changed files with 15 additions and 16 deletions
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31
phpBB/includes/functions.php
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@ -3758,21 +3758,6 @@ function msg_handler($errno, $msg_text, $errfile, $errline)
if (strpos($errfile, 'cache') === false && strpos($errfile, 'template.') === false)
{
// flush the content, else we get a white page if output buffering is on
if (ob_get_level() > 0)
{
@ob_flush();
}
// Another quick fix for those having gzip compression enabled, but do not flush if the coder wants to catch "something". ;)
if (!empty($config['gzip_compress']))
{
if (@extension_loaded('zlib') && !headers_sent() && !ob_get_level())
{
@ob_flush();
}
}
// remove complete path to installation, with the risk of changing backslashes meant to be there
$errfile = str_replace(array(phpbb_realpath($phpbb_root_path), '\\'), array('', '/'), $errfile);
$msg_text = str_replace(array(phpbb_realpath($phpbb_root_path), '\\'), array('', '/'), $msg_text);
@ -4332,7 +4317,21 @@ function page_header($page_title = '', $display_online_list = true, $item_id = 0
// gzip_compression
if ($config['gzip_compress'])
{
if (@extension_loaded('zlib') && !headers_sent())
// to avoid partially compressed output resulting in blank pages in
// the browser or error messages, compression is disabled in a few cases:
//
// 1) if headers have already been sent, this indicates plaintext output
// has been started so further content must not be compressed
// 2) the length of the current output buffer is non-zero. This means
// there is already some uncompressed content in this output buffer
// so further output must not be compressed
// 3) if more than one level of output buffering is used because we
// cannot test all output buffer level content lengths. One level
// could be caused by php.ini output_buffering. Anything
// beyond that is manual, so the code wrapping phpBB in output buffering
// can easily compress the output itself.
//
if (@extension_loaded('zlib') && !headers_sent() && ob_get_level() <= 1 && ob_get_length() == 0)
{
ob_start('ob_gzhandler');
}