Check to determine if userA has access to fileB (PHP) - php

Question

PHP has a is_readable function which checks to see if the file is readable by the owner of the script. Is there a corresponding script to see if a file is readable by a specified user, for example
is_readable('Gavrilo Princip', 'black_hand.srj')

Answer 1

Not built in. I don't even think there is a command line utility to check if a certain user has read permissions to a file.
You can write your own function to do the checking though. Look into the fileperms(), fileowner(), filegroup(), and posix_getpwuid() functions.

Answer 2

Check this question
Check file permissions
PHP fileperms http://php.net/manual/en/function.fileperms.php
PHP stat http://www.php.net/manual/en/function.stat.php
The examples in there are for *nix systems. I don't know if it will operate the same on Windows hosts. With these you could get the GID and UID of the file.
I don't know if there is a PHP equivalent that would let you get the UID and/or GID of the particular system user. You may need to get that manually and search against those values. You can find the value typically in the /etc/passwd file

Answer 3

Thanks to the help of Chris and AndrewR I have come up with a, as of yet untested, solution. This solution is implemented in shell, and waits for input from standard in (designed to work with Apache RewriteMap). However, it can easily be modified to be called from either the command line or from a PHP script. It is a little bit more complicated than it has to be because we are piping the input of a function (getfacl) to a while loop. When we do this, it starts a new suprocess, so any variables declared or updated inside this loop (ie. result) will not be available to the outside world. Furthermore, I used getfacl as I can later expand it to also work with ACL permissions as well. Finally, for implementation reasons, I already know the owner of the file (user) before calling this script, however, if this is not the case, one can easily find this from the getfacl command.
#!/bin/bash
#USAGE: STDIN viewer:user:file
while read line
do
viewer=`echo $4 | cut -d ':' -f 1`
user=`echo $4 | cut -d ':' -f 2`
file=`echo $4 | cut -d ':' -f 3`
result=$(
getfacl $file 2>/dev/null | while read line
do
if [[ $user == $viewer ]] && [[ $line =~ ^user: ]]
then
permissions=`echo $line | cut -d ':' -f 3`
if [[ $permissions =~ r ]]
then
echo true
break
fi
elif [[ $user == $viewer ]] && [ $line =~ ^group: ]]
then
#NOTE: I take advantage of the fact that each user has one single group and that group has the same name as the user's name
permissions=`echo $line | cut -d ':' -f 3`
if [[ $permissions =~ r ]]
then
echo true
break
fi
elif [[ $line =~ ^other: ]]
then
permissions=`echo $line | cut -d ':' -f 3`
if [[ $permissions =~ r ]]
then
echo true
break
fi
fi
done
)
if [[ $result == "true" ]]
then
echo true
else
echo false
fi
done