安全的PHP JSON日志记录

Question

I am using JSON as a data store and over time I foresee that several parties might be wanting to write to my JSON file like a chat log within a short space of time.

<?php
$foo = json_decode(file_get_contents("foo.json"), true);
if (! is_array($foo["bar"])) { $foo["bar"] = array(); }
array_push($foo["bar"], array("time" => time(), "who" => $_SERVER['REMOTE_ADDR'], msg => $_GET['m']));
file_put_contents("foo.json", json_encode($foo, JSON_PRETTY_PRINT));
?>

So the above code works, but I am worried what happens if the file is read before it's written out, or some case where they are writing out at the same time, leading to some data loss?

What's a better or safer design, preferably using flat file storage (i.e. not databases)?

As for a bonus I really don't want to return to my client who made the request this that were was some "lock". Ideally the request is made to wait until it's safe to return.

Answer 1

You can use the flock() function for this. What it does is it locks the file for all processes except the current one.

http://php.net/manual/en/function.flock.php

Basic usage:

<?php

$fp = fopen('path/to/data.json', 'r+');

if (flock($fp, LOCK_EX)) // locks the file
{
    // write to the file

    flock($fp, LOCK_UN); // remove the lock
}

fclose($fp);

flock() is blocking by default. That means a process is waiting until it gets permission to access the lock. Have a look at the docs on how to implement a nonblocking version.