Same name in other branches

1. 8.9.x core/lib/Drupal/Component/Utility/UserAgent.php \Drupal\Component\Utility\UserAgent::getBestMatchingLangcode()
2. 10 core/lib/Drupal/Component/Utility/UserAgent.php \Drupal\Component\Utility\UserAgent::getBestMatchingLangcode()
3. 11.x core/lib/Drupal/Component/Utility/UserAgent.php \Drupal\Component\Utility\UserAgent::getBestMatchingLangcode()

Identifies user agent language from the Accept-language HTTP header.

The algorithm works as follows:

• map user agent language codes to available language codes.
• order all user agent language codes by qvalue from high to low.
• add generic user agent language codes if they aren't already specified but with a slightly lower qvalue.
• find the most specific available language code with the highest qvalue.
• if 2 or more languages are having the same qvalue, respect the order of them inside the $languages array.

We perform user agent accept-language parsing only if page cache is disabled, otherwise we would cache a user-specific preference.

Parameters

string $http_accept_language: The value of the "Accept-Language" HTTP header.

array $langcodes: An array of available language codes to pick from.

array $mappings: (optional) Custom mappings to support user agents that are sending non standard language codes. No mapping is assumed by default.

Return value

string The selected language code or FALSE if no valid language can be identified.

3 calls to UserAgent::getBestMatchingLangcode()

LanguageNegotiationBrowser::getLangcode in core/modules/language/src/Plugin/LanguageNegotiation/LanguageNegotiationBrowser.php

Performs language negotiation.

SelectLanguageForm::buildForm in core/lib/Drupal/Core/Installer/Form/SelectLanguageForm.php

Form constructor.

UserAgentTest::testGetBestMatchingLangcode in core/tests/Drupal/Tests/Component/Utility/UserAgentTest.php

Tests matching language from user agent.

File

core/lib/Drupal/Component/Utility/UserAgent.php, line 39

Class

UserAgent

Provides user agent related utility functions.

Namespace

Drupal\Component\Utility

Code

public static function getBestMatchingLangcode($http_accept_language, $langcodes, $mappings = []) {
    // The Accept-Language header contains information about the language
    // preferences configured in the user's user agent / operating system.
    // RFC 2616 (section 14.4) defines the Accept-Language header as follows:
    // @code
    //   Accept-Language = "Accept-Language" ":"
    //                  1#( language-range [ ";" "q" "=" qvalue ] )
    //   language-range  = ( ( 1*8ALPHA *( "-" 1*8ALPHA ) ) | "*" )
    // @endcode
    // Samples: "hu, en-us;q=0.66, en;q=0.33", "hu,en-us;q=0.5"
    $ua_langcodes = [];
    if (preg_match_all('@(?<=[, ]|^)([a-zA-Z-]+|\\*)(?:;q=([0-9.]+))?(?:$|\\s*,\\s*)@', trim($http_accept_language), $matches, PREG_SET_ORDER)) {
        foreach ($matches as $match) {
            if ($mappings) {
                $langcode = strtolower($match[1]);
                foreach ($mappings as $ua_langcode => $standard_langcode) {
                    if ($langcode == $ua_langcode) {
                        $match[1] = $standard_langcode;
                    }
                }
            }
            // We can safely use strtolower() here, tags are ASCII.
            // RFC2616 mandates that the decimal part is no more than three digits,
            // so we multiply the qvalue by 1000 to avoid floating point
            // comparisons.
            $langcode = strtolower($match[1]);
            $qvalue = isset($match[2]) ? (double) $match[2] : 1;
            // Take the highest qvalue for this langcode. Although the request
            // supposedly contains unique langcodes, our mapping possibly resolves
            // to the same langcode for different qvalues. Keep the highest.
            $ua_langcodes[$langcode] = max((int) ($qvalue * 1000), $ua_langcodes[$langcode] ?? 0);
        }
    }
    // We should take pristine values from the HTTP headers, but Internet
    // Explorer from version 7 sends only specific language tags (eg. fr-CA)
    // without the corresponding generic tag (fr) unless explicitly configured.
    // In that case, we assume that the lowest value of the specific tags is the
    // value of the generic language to be as close to the HTTP 1.1 spec as
    // possible.
    // See http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.4 and
    // http://blogs.msdn.com/b/ie/archive/2006/10/17/accept-language-header-for-internet-explorer-7.aspx
    asort($ua_langcodes);
    foreach ($ua_langcodes as $langcode => $qvalue) {
        // For Chinese languages the generic tag is either zh-hans or zh-hant, so
        // we need to handle this separately, we can not split $langcode on the
        // first occurrence of '-' otherwise we get a non-existing language zh.
        // All other languages use a langcode without a '-', so we can safely
        // split on the first occurrence of it.
        if (strlen($langcode) > 7 && (substr($langcode, 0, 7) == 'zh-hant' || substr($langcode, 0, 7) == 'zh-hans')) {
            $generic_tag = substr($langcode, 0, 7);
        }
        else {
            $generic_tag = strtok($langcode, '-');
        }
        if (!empty($generic_tag) && !isset($ua_langcodes[$generic_tag])) {
            // Add the generic langcode, but make sure it has a lower qvalue as the
            // more specific one, so the more specific one gets selected if it's
            // defined by both the user agent and us.
            $ua_langcodes[$generic_tag] = $qvalue - 0.1;
        }
    }
    // Find the added language with the greatest qvalue, following the rules
    // of RFC 2616 (section 14.4). If several languages have the same qvalue,
    // prefer the one with the greatest weight.
    $best_match_langcode = FALSE;
    $max_qvalue = 0;
    foreach ($langcodes as $langcode_case_sensitive) {
        // Language tags are case insensitive (RFC2616, sec 3.10).
        $langcode = strtolower($langcode_case_sensitive);
        // If nothing matches below, the default qvalue is the one of the wildcard
        // language, if set, or is 0 (which will never match).
        $qvalue = $ua_langcodes['*'] ?? 0;
        // Find the longest possible prefix of the user agent supplied language
        // ('the language-range') that matches this site language ('the language
        // tag').
        $prefix = $langcode;
        do {
            if (isset($ua_langcodes[$prefix])) {
                $qvalue = $ua_langcodes[$prefix];
                break;
            }
        } while ($prefix = substr($prefix, 0, strrpos($prefix, '-')));
        // Find the best match.
        if ($qvalue > $max_qvalue) {
            $best_match_langcode = $langcode_case_sensitive;
            $max_qvalue = $qvalue;
        }
    }
    return $best_match_langcode;
}

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