ContentDisposition cannot parse encoded filename with leading space

[aaronols]

Affects:

• Tested with spring-web 5.2.1.RELEASE
• Affects probably all 5.0+ releases.

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The Content-Disposition parser supports filename encoding.
However, if there is a space in front of the encoding, it fails with an IllegalCharsetNameException:

Exception in thread "main" java.nio.charset.IllegalCharsetNameException:  UTF-8
	at java.nio.charset.Charset.checkName(Charset.java:315)
	at java.nio.charset.Charset.lookup2(Charset.java:484)
	at java.nio.charset.Charset.lookup(Charset.java:464)
	at java.nio.charset.Charset.forName(Charset.java:528)
	at org.springframework.http.ContentDisposition.parse(ContentDisposition.java:285)

Note the two spaces in front of the 'UTF-8'. One is from the exception string template, the other is from the parsed value from the response header.

We have an application running on the Undertow webserver. The exact header from an example response looks like this:
Content-Disposition: attachment; filename*= UTF-8''some-file.zip

This is a valid header format as per RFC 6266 Section 5 (Examples) where the following example is listed:

     Content-Disposition: attachment;
                          filename*= UTF-8''%e2%82%ac%20rates

My suggested fix is to trim() the charset before passing it to Java.