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POHow to handle user input of invalid UTF-8 characters?
 

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  1. POHow to handle user input of invalid UTF-8 characters?
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    <p>I'm looking for general a strategy/advice on how to handle invalid UTF-8 input from users. </p> <p>Even though my webapp uses UTF-8, somehow some users enter invalid characters. This causes errors in PHP's <a href="http://us2.php.net/json_encode" rel="noreferrer">json_encode()</a> and overall seems like a bad idea to have around.</p> <p><a href="http://www.w3.org/International/questions/qa-forms-utf-8" rel="noreferrer">W3C I18N FAQ: Multilingual Forms</a> says "If non-UTF-8 data is received, an error message should be sent back.".</p> <ul> <li>How exactly should this be practically done, throughout a site with dozens of different places where data can be input?</li> <li>How do you present the error in a helpful way to the user?</li> <li>How do you temporarily store and display bad form data so the user doesn't lose all their text? Strip bad characters? Use a replacement character, and how?</li> <li>For existing data in the database, when invalid UTF-8 data is detected, should I try to convert it and save it back (how? <a href="http://us3.php.net/utf8_encode" rel="noreferrer">utf8_encode</a>()? <a href="http://php.net/manual/en/function.mb-convert-encoding.php" rel="noreferrer">mb_convert_encoding()</a>?), or leave as-is in the database but doing something (what?) before json_encode()?</li> </ul> <p><strong>EDIT: I'm very familiar with the mbstring extension and am not asking "how does UTF-8 work in PHP". I'd like advice from people with experience in real-world situations how they've handled this.</strong> </p> <p><strong>EDIT2: As part of the solution, I'd really like to see a <em>fast</em> method to convert invalid characters to U+FFFD</strong></p>
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    1. COIt doesn't follow the guidelines you linked, but I just replace invalid byte sequences with [U+FFFD](http://www.fileformat.info/info/unicode/char/fffd/index.htm) so I can be done with it.
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    2. CO@zildjohn01, What's the best way to do this (which PHP functions?). Could you leave a detailed answer with your approach?
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    3. COTo be honest, it's not very exciting. I just translated a UTF-8 parser from C to PHP. It scans the string byte by byte, and if an invalid byte sequence is found, it rewrites the string manually. Slow, but portable.
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