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[2003-09-24 20:12 UTC] lew at mailduct dot com
Description:
------------
The behavior of "feof" has changed with the newer versions of PHP (4.1.1 exhibited different behavior). I believe 4.3.X has a problem with how it handles "feof" under FreeBSD.
For example, suppose I want to "tail" a logfile that keeps growing, such as "maillog" or even "httpd-access.log". In the old PHP, once I reached the end of file, "feof" would become true. If a process *added* to the file, then "feof" would become false until I read to the end of the file again. This is consistent with "tail" behavior. Under the new PHP (4.3.X), once "feof" becomes true, it *never* goes false again. Thus, it is *impossible* to "tail" a file!!
Reproduce code:
---------------
<?php
$fh = fopen( '/var/log/maillog' );
// Endless loop, for testing purposes
while( TRUE ) {
// Perform a "tail" on a growing logfile
while( !feof($fh) ) {
$log = fgets( $fh,512 );
print( $log );
}
// We've hit the end, until more data ready
print( "EOF detected... sleeping\n" );
sleep( 1 );
}
?>
Expected result:
----------------
I expect to see all the lines contained in maillog until we hit the EOF. Then I expect to see the "EOF detected" until more lines are added to maillog via another process. At that point, I expect to see the new lines of data until we hit the new EOF point again.
If I replace "fopen" with "popen" like this:
$fh = popen( 'tail -f /var/log/maillog','r' );
then it works. But I shouldn't have to spawn off a tail to do what the older 4.1.X version of PHP used to do. Someone has changed something in how EOF is detected (and reset).
Can you please see if you can find the cause of this.
Thank you for listening.
Actual result:
--------------
test line 1
test line 2
test line 3
EOF detected... sleeping
EOF detected... sleeping
EOF detected... sleeping
... forever ...
EOF detected... sleeping
(even though maillog continues to have more lines appended to it, either through a daemon or a simple "cat more.txt >> /var/log/maillog" ).
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Last updated: Thu Nov 21 13:01:29 2024 UTC |
As stated by sniper, your script is technically incorrect, although you did highlight a problem with feof(). The background on this bug is that prior to the introduction of the streams API, PHP feof() would simply call the libc feof() function. The docs for feof() under linux state that once the EOF indicator has been set, it can only be reset by calling clearerr() or by seeking the file pointer. From what you have described, it sounds like the BSD version of feof() does a little more than that. The PHP streams implementation uses the following logic for determining the EOF status: - after a read attempt, if no bytes were read OR (a read error occurred and the error != EWOULDBLOCK) --> set the EOF indicator otherwise, clear the EOF indicator [1] - after a successful fseek(), clear the EOF indicator. [1] - this step was missing and has just been comitted to the CVS. The feof() function call works like this: - if stream buffer has data, return false - otherwise, return the EOF indicator flag. Hopefully you will agree that the current behaviour is somewhat more portable than before. In terms of your script, the correct way to implement tail is something like this (untested!): $fp = fopen($file, 'r'); while (true) { $r = array($fp); $n = stream_select($r, $w = null, $e = null, 30); if ($n) { echo fgets($fp); } }