size_format(): Inconsistent behaviour when zero bytes are passed

[marian1]

The size_format() function returns false if zero is passed as a string and returns '0 B' if zero is passed as an integer.

The root cause is a strict comparison when checking against zero (if ( 0 === $bytes ) {). If the $bytes parameter is passed as a string ('0'), the condition fails.

Proposed Fix: if ( 0 === $bytes || '0' === $bytes ) {

This behaviour was introduced in WP 4.6.0. Before v4.6.0, both 0 and '0' resulted in size_format() returning false.

Trac ticket: https://core.trac.wordpress.org/ticket/61930

[narenin]

Hi @marian1

Welcome to the Core Trac!

Thanks for the detailed information.

I have added the patch for the same.

[devmooz]

This issue is indeed rooted in the strict comparison (===) used in the size_format() function. The strict comparison checks not only the value but also the type, so 0 === $bytes fails when $bytes is a string ('0').

Explanation:
Before WP 4.6.0: Both 0 (integer) and '0' (string) would cause size_format() to return false because the condition likely used a loose comparison (==), which checks only the value and not the type.

From WP 4.6.0 onwards: The strict comparison was introduced, so 0 === $bytes only returns true when $bytes is strictly an integer 0. If $bytes is a string '0', the condition fails, and the function continues processing, eventually returning '0 B' instead of false.

[devmooz]

To handle both cases (integer 0 and string '0'), the proposed fix checks for both explicitly:

if ( 0 === $bytes || '0' === $bytes ) {

<?php
if ( 0 === $bytes || '0' === $bytes ) {

Impact:
With the Fix: Both 0 (integer) and '0' (string) will result in the function returning false, restoring the behavior before WP 4.6.0.

Without the Fix: The function behaves inconsistently, depending on whether 0 is passed as an integer or a string.

This fix aligns with the intended behavior of the function, ensuring that both 0 and '0' are treated equivalently.

[hellofromTonya]

Hello @marian1,

Welcome to WordPress Core's Trac.

I'm doing triage today for bugs reported on 6.6.1 or 6.6.2 (i.e. via Version) and then updating ticket information.

The strict comparison was introduced in Version 4.6 via #36635 / [37962]. Updating the Version to 4.6.