Doc #79965 [Com]: Why does the manual say fread/fwrite changed in PHP 7.4?
Edit report at https://bugs.php.net/bug.php?id=79965&edit=1
ID: 79965
Comment by: webmaster_php20201022 at cubiclesoft dot com
Reported by: thiemo dot kreuz at wikimedia dot de
Summary: Why does the manual say fread/fwrite changed in PHP
7.4?
Status: Verified
Type: Documentation Problem
Package: *Directory/Filesystem functions
PHP Version: 7.4.9
Block user comment: N
Private report: N
New Comment:
"Does this section refer to a bugfix?"
The change actually originally stemmed from a potential denial of service opportunity in PHP that I
ran into back in 2016 while building TCP socket servers that was impossible to work around without
incurring another denial of service opportunity. For the gory details (and some of the drama):
https://bugs.php.net/bug.php?id=73535
There was a formal CVE issued for this bug (CVE-2016-9321) but, as you can see, it was never applied
to the ticket nor mentioned anywhere in release notes. I believe the PHP devs ended up very quietly
deploying the fix because it took so long to fix the problem and tried to keep the messaging as
simple as possible in the release notes. Specifically, fixing it required a BC break, which only
happens in major version releases (e.g. 7.3 to 7.4) and those only happen once a year.
This particular bug exposes a significant weakness in the software release cycles of languages (not
just PHP): Discovered security vulnerabilities in a major language but requires a BC break in order
to fix the problem might take more than one year to fix. The issue was opened too late for
inclusion in 7.2 and was accidentally forgotten for 7.3. As a dev, what would *you* do in that
situation? Fixing the bug as quietly as possible for 7.4 and using a simple two sentence string in
the migration guide to minimize questions from userland devs seems like a decent strategy to me.
This is a perfect example of the fact that software is written by humans, humans are fallable and
can miss stuff, and that even perfectly good processes like a standard software release cycle could
even be exploited by malicious actors.
Some people who read the previous paragraph might be tempted to jump ship from PHP, but all formal
language development has the same problem if the devs of a language adhere to good software
development methodologies. In this particular instance, the documentation reflected good wishes
prior to 7.4 rather than how the software was actually written. The issue might have been noticed
and fixed a lot sooner if PHP userland documentation pages linked to the relevant C source code.
There's always a lot of inertia to go from documentation to actual source code. When was the
last time you cracked open and read the C source code to PHP itself? For 99% of PHP userland devs,
the answer is "never."
Personally, I'm just glad it got fixed because it's a low-level stream handling problem
that had significant negative repercussions throughout PHP userland beyond socket streams.
Regardless of how we got here, PHP 7.4 is a good upgrade because stream error handling is improved.
Previous Comments:
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[2020-08-12 22:28:11] thiemo dot kreuz at wikimedia dot de
Oh wow, that's a massive change. Thanks!
I guess the manual should say something like "fread/fwrite will now return false in all error
situations, as it was always documented. Before, an empty string or 0 was returned in many error
situations, e.g. when a gzip stream couldn't be decoded, or when writing to a file that was
opened in read mode."
Note it's not only fread/fwrite, but also fgetcsv/fputcsv.
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[2020-08-12 21:57:27] cmb@php.net
The relevant commit is d59aac5[1]; the PHPTs show that some, but
not all return values in case of failure have been changed from
int(0) to bool(false).
[1] <http://git.php.net/?p=php-src.git;a=commit;h=d59aac58b3e7da7ad01a194fe9840d89725ea229>
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[2020-08-12 17:03:19] thiemo dot kreuz at wikimedia dot de
Description:
------------
---
From manual page: https://php.net/migration74.incompatible
---
Quote: "fread() and fwrite() will now return FALSE if the operation failed. Previously an empty
string or 0 was returned."
This is not correct, or at least misleading. Both functions are documented to return false in case
of a failure ever since. What changed in PHP 7.4? I tried to find the related code change, but all I
found are bugfixes. Does this section refer to a bugfix? Maybe there was a very specific failure
situation that was not reported via false?
TL;DR: Please re-write or remove this misleading section from the migration manual.
https://www.php.net/manual/en/migration74.incompatible.php#migration74.incompatible.core.fread-fwrite
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