SplFileObject::isReadable and SplFileObject::isWriteable provide an untrustworthy interface

[neclimdul]

Description

isReadable and isWriteable only consider the file system permissions but that isn't actually reflective of the state of the object because read and write methods also consider the resource mode so if you trust them you can can run into unexpected bugs as demonstrated in the example below.

Specifically
1 . Streams don't look readable?
2. Resources that are opened write only look readable.

The following code:

<?php

function showFile(\SplFileObject $file) {
    var_dump($file->isReadable());
    if ($file->isReadable()) {
      var_dump($file->fread($file->getSize()));
    }
    echo str_repeat('=', 80) . PHP_EOL;
}

showFile(new SplFileObject(__FILE__));
$f = new SplFileObject('php://temp', 'r+');
$f->fwrite('content');
showFile($f);
showFile(new SplFileObject(__FILE__, 'a'));

Resulted in this output:

bool(true)
string(376) "<?php

function showFile(\SplFileObject $file) {
    var_dump($file->isReadable());
    if ($file->isReadable()) {
      var_dump($file->fread($file->getSize()));
    }
    echo str_repeat('=', 80) . PHP_EOL;
}

showFile(new SplFileObject(__FILE__));
$f = new SplFileObject('php://temp', 'r+');
$f->fwrite('content');
showFile($f);
showFile(new SplFileObject(__FILE__, 'a'));
"
================================================================================
bool(false)
================================================================================
bool(true)
PHP Notice:  SplFileObject::fread(): Read of 8192 bytes failed with errno=9 Bad file descriptor in /tmp/tmp.php on line 6
bool(false)
================================================================================

But I expected this output instead:

bool(true)
string(376) "<?php

function showFile(\SplFileObject $file) {
    var_dump($file->isReadable());
    if ($file->isReadable()) {
      var_dump($file->fread($file->getSize()));
    }
    echo str_repeat('=', 80) . PHP_EOL;
}

showFile(new SplFileObject(__FILE__));
$f = new SplFileObject('php://temp', 'r+');
$f->fwrite('content');
showFile($f);
showFile(new SplFileObject(__FILE__, 'a'));
"
================================================================================
bool(true)
string(7) "content"
================================================================================
bool(false)

PHP Version

all

Operating System

No response

[damianwadley]

This makes sense when you consider that isReadable and isWritable are being inherited from SplFileInfo, and the methods are documented like "Check if the file is readable" or "Check if the current entry is writable". Says nothing about streams...

[neclimdul]

Ah that does explain a lot. Seems like FileObjects should then either override the logic to better meet expectations(admittedly probably a BC break but this is pretty broken) or maybe provide an additional method to expose the file mode.

Looking at the streams documentation, the readability check seems like it would be a problem so that's probably a deeper problem. Frustrating when using the temp stream but understandably more complicated.

[cmb69]

admittedly probably a BC break

That. As such it might be better to introduce a new feature.

maybe provide an additional method to expose the file mode

This is theoretically already possible by using stream_get_meta_data(), but requires get_resources() which shouldn't be used in production, especially not wrt. SplFileObject. It seems to me that introducing SplFileObject::get_meta_data() would be reasonable.