Detect encoding and make everything UTF-8

You first have to detect what encoding has been used. As you’re parsing RSS feeds (probably via HTTP), you should read the encoding from the charset parameter of the Content-Type HTTP header field. If it is not present, read the encoding from the encoding attribute of the XML processing instruction. If that’s missing too, use UTF-8 as defined in the specification.

Here is what I probably would do:

I’d use cURL to send and fetch the response. That allows you to set specific header fields and fetch the response header as well. After fetching the response, you have to parse the HTTP response and split it into header and body. The header should then contain the Content-Type header field that contains the MIME type and (hopefully) the charset parameter with the encoding/charset too. If not, we’ll analyse the XML PI for the presence of the encoding attribute and get the encoding from there. If that’s also missing, the XML specs define to use UTF-8 as encoding.

$url = 'http://www.lr-online.de/storage/rss/rss/sport.xml';

$accept = array(
    'type' => array('application/rss+xml', 'application/xml', 'application/rdf+xml', 'text/xml'),
    'charset' => array_diff(mb_list_encodings(), array('pass', 'auto', 'wchar', 'byte2be', 'byte2le', 'byte4be', 'byte4le', 'BASE64', 'UUENCODE', 'HTML-ENTITIES', 'Quoted-Printable', '7bit', '8bit'))
);
$header = array(
    'Accept: '.implode(', ', $accept['type']),
    'Accept-Charset: '.implode(', ', $accept['charset']),
);
$encoding = null;
$curl = curl_init($url);
curl_setopt($curl, CURLOPT_RETURNTRANSFER, true);
curl_setopt($curl, CURLOPT_HEADER, true);
curl_setopt($curl, CURLOPT_HTTPHEADER, $header);
$response = curl_exec($curl);
if (!$response) {
    // error fetching the response
} else {
    $offset = strpos($response, "\r\n\r\n");
    $header = substr($response, 0, $offset);
    if (!$header || !preg_match('/^Content-Type:\s+([^;]+)(?:;\s*charset=(.*))?/im', $header, $match)) {
        // error parsing the response
    } else {
        if (!in_array(strtolower($match[1]), array_map('strtolower', $accept['type']))) {
            // type not accepted
        }
        $encoding = trim($match[2], '"\'');
    }
    if (!$encoding) {
        $body = substr($response, $offset + 4);
        if (preg_match('/^<\?xml\s+version=(?:"[^"]*"|\'[^\']*\')\s+encoding=("[^"]*"|\'[^\']*\')/s', $body, $match)) {
            $encoding = trim($match[1], '"\'');
        }
    }
    if (!$encoding) {
        $encoding = 'utf-8';
    } else {
        if (!in_array($encoding, array_map('strtolower', $accept['charset']))) {
            // encoding not accepted
        }
        if ($encoding != 'utf-8') {
            $body = mb_convert_encoding($body, 'utf-8', $encoding);
        }
    }
    $simpleXML = simplexml_load_string($body, null, LIBXML_NOERROR);
    if (!$simpleXML) {
        // parse error
    } else {
        echo $simpleXML->asXML();
    }
}

Detecting the encoding is hard.

mb_detect_encoding works by guessing, based on a number of candidates that you pass it. In some encodings, certain byte-sequences are invalid, an therefore it can distinguish between various candidates. Unfortunately, there are a lot of encodings, where the same bytes are valid (but different). In these cases, there is no way to determine the encoding; You can implement your own logic to make guesses in these cases. For example, data coming from a Japanese site might be more likely to have a Japanese encoding.

As long as you only deal with Western European languages, the three major encodings to consider are utf-8, iso-8859-1 and cp-1252. Since these are defaults for many platforms, they are also the most likely to be reported wrongly about. Eg. if people use different encodings, they are likely to be frank about it, since else their software would break very often. Therefore, a good strategy is to trust the provider, unless the encoding is reported as one of those three. You should still doublecheck that it is indeed valid, using mb_check_encoding (note that valid is not the same as being - the same input may be valid for many encodings). If it is one of those, you can then use mb_detect_encoding to distinguish between them. Luckily that is fairly deterministic; You just need to use the proper detect-sequence, which is UTF-8,ISO-8859-1,WINDOWS-1252.

Once you've detected the encoding you need to convert it to your internal representation (UTF-8 is the only sane choice). The function utf8_encode transforms ISO-8859-1 to UTF-8, so it can only used for that particular input type. For other encodings, use mb_convert_encoding.

This cheatsheet lists some common caveats related to UTF-8 handling in PHP: http://developer.loftdigital.com/blog/php-utf-8-cheatsheet

This function detecting multibyte characters in a string might also prove helpful (source):

function detectUTF8($string)
{
    return preg_match('%(?:
        [\xC2-\xDF][\x80-\xBF]             # non-overlong 2-byte
        |\xE0[\xA0-\xBF][\x80-\xBF]        # excluding overlongs
        |[\xE1-\xEC\xEE\xEF][\x80-\xBF]{2} # straight 3-byte
        |\xED[\x80-\x9F][\x80-\xBF]        # excluding surrogates
        |\xF0[\x90-\xBF][\x80-\xBF]{2}     # planes 1-3
        |[\xF1-\xF3][\x80-\xBF]{3}         # planes 4-15
        |\xF4[\x80-\x8F][\x80-\xBF]{2}     # plane 16
        )+%xs', 
    $string);
}

Your encoding looks like you encoded into UTF-8 twice; that is, from some other encoding, into UTF-8, and again into UTF-8. As if you had ISO 8859-1, converted from ISO 8859-1 to UTF-8, and treated the new string as ISO 8859-1 for another conversion into UTF-8.

Here's some pseudocode of what you did:

$inputstring = getFromUser();
$utf8string = iconv($current_encoding, 'utf-8', $inputstring);
$flawedstring = iconv($current_encoding, 'utf-8', $utf8string);

You should try:

1. detect encoding using mb_detect_encoding() or whatever you like to use
2. if it's UTF-8, convert into ISO 8859-1, and repeat step 1
3. finally, convert back into UTF-8

That is presuming that in the "middle" conversion you used ISO 8859-1. If you used Windows-1252, then convert into Windows-1252 (latin1). The original source encoding is not important; the one you used in flawed, second conversion is.

This is my guess at what happened; there's very little else you could have done to get four bytes in place of one extended ASCII byte.

The German language also uses ISO 8859-2 and Windows-1250 (Latin-2).

The interesting thing about mb_detect_encoding and mb_convert_encoding is that the order of the encodings you suggest does matter:

// $input is actually UTF-8

mb_detect_encoding($input, "UTF-8", "ISO-8859-9, UTF-8");
// ISO-8859-9 (WRONG!)

mb_detect_encoding($input, "UTF-8", "UTF-8, ISO-8859-9");
// UTF-8 (OK)

So you might want to use a specific order when specifying expected encodings. Still, keep in mind that this is not foolproof.

Working out the character encoding of RSS feeds seems to be complicated. Even normal web pages often omit, or lie about, their encoding.

So you could try to use the correct way to detect the encoding and then fall back to some form of auto-detection (guessing).

mb_detect_encoding:

echo mb_detect_encoding($str, "auto");

Or

echo mb_detect_encoding($str, "UTF-8, ASCII, ISO-8859-1");

I really don't know what the results are, but I'd suggest you just take some of your feeds with different encodings and try if mb_detect_encoding works or not.

auto is short for "ASCII,JIS,UTF-8,EUC-JP,SJIS". It returns the detected charset, which you can use to convert the string to UTF-8 with iconv.

<?php
function convertToUTF8($str) {
    $enc = mb_detect_encoding($str);

    if ($enc && $enc != 'UTF-8') {
        return iconv($enc, 'UTF-8', $str);
    } else {
        return $str;
    }
}
?>

I haven't tested it, so no guarantee. And maybe there's a simpler way.

It's simple: when you get something that's not UTF-8, you must encode that into UTF-8.

So, when you're fetching a certain feed that's ISO 8859-1 parse it through utf8_encode.

However, if you're fetching an UTF-8 feed, you don't need to do anything.

Try to use this... every text that is not UTF-8 will be translated.

function is_utf8($str) {
    return (bool) preg_match('//u', $str);
}

$myString = "Fußball";

if(!is_utf8($myString)){
    $myString = utf8_encode($myString);
}

// or 1 line version ;) 
$myString = !is_utf8($myString) ? utf8_encode($myString) : trim($myString);