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

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

The entry points are SplFileObject::isReadable(), SplFileObject::isWriteable(), and the read/write methods demonstrated in the example. Start by tracing how these methods evaluate filesystem permissions versus the resource mode. Add regression coverage for the r+, write-only, and append cases, then verify the reported and expected outputs.