Edit report at http://bugs.php.net/bug.php?id=51056&edit=1
ID: 51056
Updated by: lbarnaud@php.net
Reported by: magicaltux@php.net
Summary: fread() on blocking stream will block even if data is
available
-Status: Open
+Status: Feedback
Type: Bug
Package: Streams related
Operating System: Linux Gentoo 2.6.32
PHP Version: 5.3.1
New Comment:
> When data is already available in buffer, an information should be
passed to the lower-level read() to let it know it should not block.
This will block anyway when the buffer is empty and you won't be able to
known when it is empty, so you can't rely on this (sometimes it will
block, sometimes not).
Also, some applications may rely on the blocking and will break if it is
changed. This behavior exists since at least PHP 5.1.
> Considering any application handling data from network should handle
cases when received data is not complete
As this is not the normal case I would suggest to introduce some timeout
handling (this is what applications like e.g. Apache does, I guess), or
fixing what prevents you from using non blocking i/o with SSL streams
instead.
Previous Comments:
------------------------------------------------------------------------
[2010-03-11 02:21:59] magicaltux@php.net
Hi,
I know about fread() returning less data than asked for, however I could
not
modify this behaviour without passing some kind of value to lower-level
read
operation, which will call poll() if socket is blocking.
When data is already available in buffer, an information should be
passed to the
lower-level read() to let it know it should not block.
The only non-intrusive solution to fix this would be to temporarly pass
socket
in non-blocking mode if data was found in PHP buffer.
Considering any application handling data from network should handle
cases when
received data is not complete, I believe it was best to return
immediatly if
data is found and let the application call fread() again rather than
trying to
workaround this problem with a dirty solution like passing temporarly in
non-
blocking mode.
Another solution would be to add an argument to the internal read call
("do not
block") however it would change the API for the internal stream api, and
would
require the argument to be handled into each stream wrapper.
------------------------------------------------------------------------
[2010-03-11 02:05:59] lbarnaud@php.net
Hi,
I made a test case for this ( 51056.phpt.txt )
fread() in C has exactly the same behavior, it will block if you try to
read more bytes than available.
Your patch correctly avoids this, however it introduces an other issue:
fread() will return less data than asked for, even if enough data is
available ( 51056-2.phpt.txt ).
------------------------------------------------------------------------
[2010-02-17 16:00:07] jani@php.net
btw. If you really want someone to do something about this, post the
patch to internals@lists.php.net as well. :)
------------------------------------------------------------------------
[2010-02-17 05:39:56] magicaltux@php.net
While for file sockets it makes sense when reading data to make sure a
buffer gets completly filled until EOF is reached, this is not true
for sockets.
There is already a condition for "greedy read", but it does not apply
when we first restore data from the read buffer.
Here is a diff (PHP_5_3) that solves the issue:
Index: main/streams/streams.c
===================================================================
--- main/streams/streams.c (révision 295152)
+++ main/streams/streams.c (copie de travail)
@@ -592,6 +592,10 @@
size -= toread;
buf += toread;
didread += toread;
+
+ /* avoid trying to read if we already have
data to pass */
+ if (stream->wrapper !=
&php_plain_files_wrapper)
+ break;
}
/* ignore eof here; the underlying state might have
changed */
Test script output:
Testing PHP version: 5.3.3-dev
fread took 0.07ms to read 8 bytes
fread took 5.07ms to read 256 bytes
fread took 0.00ms to read 45 bytes
fread took 1000.11ms to read 8 bytes
fread took 5.02ms to read 256 bytes
fread took 0.00ms to read 45 bytes
fread took 1000.13ms to read 8 bytes
fread took 5.04ms to read 256 bytes
------------------------------------------------------------------------
[2010-02-16 13:06:45] magicaltux@php.net
I tried to switch to non-blocking mode. This solves this issue with
most sockets, except for SSL sockets when transmitting a lot of data.
This bug is blocking in my case (socket communication transmitting a
lot of data).
------------------------------------------------------------------------
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the rest of the comments, please view the bug report online at
http://bugs.php.net/bug.php?id=51056
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