Need to check utf8_encode() is available before use.

[gitlost]

The DOM/XML extension isn't necessarily installed on some distros so use of utf8_encode() should be checked for availability first. It's not checked in wp_read_image_metadata() in "wp-admin/includes/image.php" (where I encountered its lack on a Ubuntu 16.04 PHP 7 server), introduced in [36429] and [36430], nor in wxr_cdata() in "wp-admin/includes/export.php", introduced in the distant past.

(Also it does ISO-8859-1 not Windows-1252 so more than likely not that good in the image situation anyway.)

[desrosj]

@gitlost are you interested in making a patch for this?

[gitlost]

Hi @desrosj yes, I'll give it a blast.

Trac Ticket: Core-38479

## Overview

• This pull request addresses the issue of handling the utf8_encode() function in WordPress, particularly when the DOM/XML extension is not available or utf8_encode() itself is not present. This function has been deprecated and is not guaranteed to be available on all server configurations. This change ensures compatibility and avoids potential errors related to its use in the functions wp_read_image_metadata() and wxr_cdata().

## Problem Statement

• The use of utf8_encode() in the following functions may lead to compatibility issues:

• wp_read_image_metadata() in wp-admin/includes/image.php

• wxr_cdata() in wp-admin/includes/export.php

• On servers where the DOM/XML extension is not installed or where utf8_encode() is not available, the current implementation may fail. Furthermore, utf8_encode() is deprecated and should be replaced with a more reliable approach.

## Solution

• Check for Function Availability: Before using utf8_encode(), check if it is available using the function_exists() function. This prevents errors on servers where utf8_encode() is not defined.

• Deprecation Handling: Replace utf8_encode() with the recommended mb_convert_encoding() function, which provides better support for different character encodings and is not deprecated.

## Benefits

• Improved Compatibility: Ensures that WordPress functions do not fail on servers where utf8_encode() is not available or where the DOM/XML extension is not installed.

• Future-Proof: By replacing utf8_encode() with mb_convert_encoding(), we align with modern standards and avoid issues related to deprecated functions.

• Enhanced Reliability: The use of mb_convert_encoding() provides more robust handling of different character encodings.

## Notes

• This change is backward-compatible and ensures that existing functionality remains unaffected while improving overall reliability.

[SergeyBiryukov]

Related: #55603