$var is valid unix timestamp - php

Question

I need a function to validate if the content of a variable is a valid unix timestamp.
I've checked this thread: Check whether the string is a unix timestamp but the problem is that the function in the most voted answer still can cause some errors, for eg:
function is_timestamp($timestamp)
{
return ((string) (int) $timestamp === $timestamp)
&& ($timestamp <= PHP_INT_MAX)
&& ($timestamp >= ~PHP_INT_MAX);
}
// Some tests:
$timestamp = 1289216307;
var_dump(is_timestamp($timestamp));
var_dump(date('Y-m-d', $timestamp));
// result
bool(false)
string(10) "2010-11-08"
$timestamp = '20101108';
var_dump(is_timestamp($timestamp));
var_dump(date('Y-m-d', $timestamp));
// result
bool(true)
string(10) "1970-08-21"
Here, the first should be TRUE and the second should be FALSE so, what's the best way to test if a $var is a real valid unix timestamp?

Answer 1

Here, the first should be TRUE and the second should be FALSE
Why? 20101108 is a valid UNIX timestamp, - as you say, it's August 21, 1970. Could well be a person's birthday for example.
The only way to achieve what you want is to set a range of dates that mark a "sane" timestamp by the definition you are working with - e.g. anything after January 1st, 2000 - and do a check against that.

Answer 2

A workaround for this would be to check if strtotime recognises the string as a valid date string.
function is_timestamp($timestamp)
{
return ((string) (int) $timestamp === $timestamp)
&& ($timestamp <= PHP_INT_MAX)
&& ($timestamp >= ~PHP_INT_MAX)
&& (!strtotime($timestamp));
}
This will weed out strings that are probably date strings rather than timestamps. It is probably easier to code than writing your own sanity checks.

Answer 3

You can check unix timestamp format using regular expression when your timestamp is bigger than size of integer:
/**
* Check if timestamp is in unix format.
*
* #param string $timestamp
* Target timestamp that will be checked.
*
* #return bool
* TRUE if timestamp is in unix format. FALSE on failure.
*/
function is_unix_timestamp($timestamp) {
return preg_match('/^\d+$/', $timestamp);
}

Answer 4

Write your own ;)
Some things you could check:
Is the given parameter an int? if not => false
Is it negative or above max? => false
Everything else is true
This would work for your given tests.

Answer 5

Any number is potentially a timestamp. The only significant difference between your two examples is that the latter case is a string. In which case:
function is_timestamp($timestamp) {
return is_int($timestamp) || is_float($timestamp);
}
(is_numeric is no good as it also returns true for strings that can be parsed as numbers.)