Improved AJAX, XHTML, and RSS Safe Function for Converting Entities to ASCII in PHP

— Geekery

In March, I reported on a particular problem that may or may not have arisen for developers. In short: WebKit and, consequently, Google Chrome might have introduced some problems for developers who weren’t properly converting their variables to ensure they were safe for XHTML, RSS and AJAX by converting their characters to the proper ASCII format.

Here’s the solution that I came up with in March:

function clean_string_for_valid_xml($string) {
    $entities_array = array();
    foreach (get_html_translation_table(HTML_ENTITIES, ENT_QUOTES) as $character => $entity) {
        $entities_array[$entity] = '&#' . ord($character) . ';';
    }
    return str_replace(array_keys($entities_array), $entities_array, $string);
}

While this will take care of most special entities that may have to be commonly dealt with, get_html_translation_table, the built-in PHP function designated to handle these type of operations, doesn’t provide a comprehensive list of the entities or elements that one may encounter when dealing with the aforementioned standards where ASCII conversion is necessary. In fact, there are quite a few elements that are missed.

After doing a bit of searching on the internet, I feel I have compiled a fairly complete list of entities that do not appear in get_html_translation_table that may assist people relying on the PHP built-ins. This will handle characters ranging from “ to Ω and all of your ∗ and ≅ characters too.

So, here you go:

clean_string_for_xhtml($string) {
    $entities_array = array();
    foreach (get_html_translation_table(HTML_ENTITIES, ENT_QUOTES) as $character => $entity) {
        $entities_array[$entity] = '&#' . ord($character) . ';';
    }
    $entities_array += array ('''=>''', '−'=>'-', 'ˆ'=>'^', '˜'=>'~', 'Š'=>'Š', '‹'=>'‹', 'Œ'=>'Œ', '‘'=>'‘' , '’'=>'’', '“'=>'“', '”'=>'”', '•'=>'•', '–'=>'–', '—'=>'—', '˜'=>'˜', '™'=>'™', 'š'=>'š', '›'=>'›', 'œ'=>'œ', 'Ÿ'=>'Ÿ', 'ÿ'=>'ÿ', 'Œ'=>'Œ', 'œ'=>'œ', 'Š'=>'Š', 'š'=>'š', 'Ÿ'=>'Ÿ', 'ƒ'=>'ƒ', 'ˆ'=>'ˆ', '˜'=>'˜', 'Α'=>'Α', 'Β'=>'Β', 'Γ'=>'Γ', 'Δ'=>'Δ', 'Ε'=>'Ε', 'Ζ'=>'Ζ', 'Η'=>'Η', 'Θ'=>'Θ', 'Ι'=>'Ι', 'Κ'=>'Κ', 'Λ'=>'Λ', 'Μ'=>'Μ', 'Ν'=>'Ν', 'Ξ'=>'Ξ', 'Ο'=>'Ο', 'Π'=>'Π', 'Ρ'=>'Ρ', 'Σ'=>'Σ', 'Τ'=>'Τ', 'Υ'=>'Υ', 'Φ'=>'Φ', 'Χ'=>'Χ', 'Ψ'=>'Ψ', 'Ω'=>'Ω', 'α'=>'α', 'β'=>'β', 'γ'=>'γ', 'δ'=>'δ', 'ε'=>'ε', 'ζ'=>'ζ', 'η'=>'η', 'θ'=>'θ', 'ι'=>'ι', 'κ'=>'κ', 'λ'=>'λ', 'μ'=>'μ', 'ν'=>'ν', 'ξ'=>'ξ', 'ο'=>'ο', 'π'=>'π', 'ρ'=>'ρ', 'ς'=>'ς', 'σ'=>'σ', 'τ'=>'τ', 'υ'=>'υ', 'φ'=>'φ', 'χ' =>'χ', 'ψ'=>'ψ', 'ω'=>'ω', 'ϑ'=>'ϑ', 'ϒ'=>'ϒ', 'ϖ'=>'ϖ', ' '=>' ', ' '=>' ', ' '=>' ', '‌'=>'‌', '‍'=>'‍', '‎'=>'‎', '‏'=>'‏', '–'=>'–', '—'=>'—', '‘'=>'‘', '’'=>'’', '‚'=>'‚', '“'=>'“',     '”'=>'”', '„'=>'„', '†'=>'†', '‡'=>'‡', '•'=>'•', '…'=>'…', '‰'=>'‰', '′'=>'′', '″'=>'″', '‹'=>'‹', '›'=>'›', '‾'=>'‾', '⁄'=>'⁄', '€'=>'€', 'ℑ'=>'ℑ', '℘'=>'℘', 'ℜ'=>'ℜ', '™'=>'™', 'ℵ'=>'ℵ', '←'=>'←', '↑'=>'↑', '→'=>'→', '↓'=>'↓', '↔'=>'↔', '↵'=>'↵', '⇐'=>'⇐', '⇑'=>'⇑', '⇒'=>'⇒', '⇓'=>'⇓', '⇔'=>'⇔', '∀'=>'∀', '∂'=>'∂', '∃'=>'∃', '∅'=>'∅', '∇'=>'∇', '∈'=>'∈', '   ∉'=>'∉', '∋'=>'∋', '∏'=>'∏', '∑'=>'∑', '−'=>'−', '∗'=>'∗', '√'=>'√', '∝'=>'∝', '∞'=>'∞', '∠'=>'∠', '∧'=>'∧', '∨'=>'∨', '∩'=>'∩', '∪'=>'∪', '∫'=>'∫', '∴'=>'∴', '∼'=>'∼', '≅'=>'≅', '≈'=>'≈', '≠'=>'≠', '≡'=>'≡', '≤'=>'≤', '≥'=>'≥', '⊂'=>'⊂', '⊃'=>'⊃', '⊄'=>'⊄', '⊆'=>'⊆', '⊇'=>'⊇', '⊕'=>'&    #8853;', '⊗'=>'⊗', '⊥'=>'⊥', '⋅'=>'⋅', '⌈'=>'⌈', '⌉'=>'⌉', '⌊'=>'⌊', '⌋'=>'⌋', '⟨'=>'〈', '⟩'=>'〉', '◊'=>'◊', '♠'=>'♠', '♣'=>'♣', '♥'=>'♥', '♦'=>'♦');
 
    return str_replace(array_keys($entities_array), $entities_array, $string);
}

Hope that helps others. Any comments or fixes to the code? Please post them below.

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