AcceptHeaderLocaleResolver chooses wrong Locale for language match [SPR-16599]

[spring-projects-issues]

Naozumi Taromaru opened SPR-16599 and commented

Order of Locale in Accept-Language Header is slighted in AcceptHeaderLocaleResolver.

For example:

supportedLocales of AcceptHeaderLocaleResolver: ja, en_US, en
Accept-Language of Request: ja-JP,en-US;q=0.5
Expected: ja
Actual: en_US

"ja-JP,en-US;q=0.5" is meaning as "ja-JP ＞ ja ＞ en-US ＞ en".
(Reference: Last "For example" of https://tools.ietf.org/html/rfc4647#section-3.4.1)
And "ja" is supported.
So expected Locale is "ja".

Suggestion:

Change "languageMatch = candidate;"
at
https://github.com/spring-projects/spring-framework/blob/v5.0.4.RELEASE/spring-webmvc/src/main/java/org/springframework/web/servlet/i18n/AcceptHeaderLocaleResolver.java#L132
to "return candidate;".
And delete languageMatch(always null).

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Affects: 5.0.4

Reference URL: #21002

Issue Links:

• AcceptHeaderLocaleResolver should match country locales against supported language locales [SPR-16457] #21002 AcceptHeaderLocaleResolver should match country locales against supported language locales

Referenced from: commits 6e1cac9, f8588e3

Backported to: 4.3.15

[spring-projects-issues]

Juergen Hoeller commented

I've refined the algorithm slightly differently: We still check for full language+country match in the supported locales even for later Accept-Language entries... but only if their language part matches, i.e. only if they narrow the primary language to a specific country. This is necessary for backwards compatibility in always finding the most specific match possible: e.g. en-UK in case of en-US,en-UK in the accept header and Locale.ENGLISH, Locale UK as the supported locales.

[spring-projects-issues]

Naozumi Taromaru commented

Thanks!