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From Konstantin Preißer <>
Subject RE: Tomcat 8.5.19 corrupts static text files encoded with UTF-8
Date Sun, 30 Jul 2017 08:59:29 GMT
Hi Mark,

> -----Original Message-----
> From: Mark Thomas []
> Sent: Saturday, July 29, 2017 2:56 PM
>> (...)
> >Why would Tomcat want to modify static files, instead of just serving
> >them as-is?
> Because Tomcat now checks the response encoding and the file encoding
> and converts if necessary.
> You probably want to set the fileEncoding init param of the Default servlet to
> UTF-8.

Thanks. So I set the following parameter in web.xml:

The result now is, that Tomcat converts the static file without a BOM from UTF-8 to ISO-8859-1,
which means my JavaScript files included by the HTML page will still be broken, as the brower
expects them to be UTF-8-encoded ...

I honestly don't understand that change. As a web developer, I expect a web server to serve
static files exactly as-is, without trying to convert the files into another charset and without
trying to detect the charset of the file (unless the server is configured to do so).

Bug 49464 [1] mentions that "As per spec the encoding of the page is asssumed to be iso-8859-1.".
Do I understand correctly that this refers to the following section "3.7.1 Canonicalization
and Text Defaults" of RFC2616?

   The "charset" parameter is used with some media types to define the
   character set (section 3.4) of the data. When no explicit charset
   parameter is provided by the sender, media subtypes of the "text"
   type are defined to have a default charset value of "ISO-8859-1" when
   received via HTTP.

But not that RFC7231 says in "Appendix B.  Changes from RFC 2616":

   The default charset of ISO-8859-1 for text media types has been
   removed; the default is now whatever the media type definition says.
   Likewise, special treatment of ISO-8859-1 has been removed from the
   Accept-Charset header field.  (Section and Section 5.3.3)

I found a following page that talks about this change [2] and mentions RFC6657 [3] that describes
text/* media registrations with charset handling.

While RFC6657 seems to indicate that the default charset of text/plain is US-ASCII (which
is not what browsers do), it doesn't seem to indicate a default charset for other types like
text/html, text/javascript, application/javascript etc.

Browsers (I tested with IE, Firefox and Chrome) already handle the encoding of text-based
files where the Content-Type doesn't specify a charset as the user would expect:
- For example, with text/html files that don't contain a BOM, they will respect the <meta
charset=...> element. If a UTF-8 BOM is present, they will interpret it as UTF-8.
- If you directly open text/plain, text/css, application/javascript files in a browser, they
will check if the file has an UTF-8 BOM, and interpret it as UTF-8 in that case; otherwise,
they seem to interpret it as ISO-8859-1/Windows-1252 (or maybe using the default system encoding,
I'm not exactly sure about that).
- However, if such files (.css and .js) are referenced by a HTML file, browsers will interpret
them in the same encoding that the HTML file (if they don't have a BOM), which means if the
HTML uses UTF-8, they will interpret .js and .css also as UTF-8 (unless the HTML element uses
a charset parameter, e.g. <script src="script.js" charset="windows-1252"></script>).

Therefore, I don't see why Tomcat would want to convert static resources to other encodings.
(I think it should also not try to detect the charset of files and then include a "; charset=..."
parameter in the Content-Type, as this may override the browser's behavior and thus also lead
to incorrect decoding of JavaScript files that are encoded with UTF-8 without a BOM).

Further, as an system administrator, I would expect that I can update Tomcat from x.y.z to
x.y.(z+n), without static JavaScript files suddenly getting broken (which isn't immediately
obvious as mostly the script per se will work, only that some special string characters outside
of ASCII are displayed incorrectly to the user).
Shouldn't such behavior changes be reserved for the next major/minor version which is not
yet stable, in this case Tomcat 9.0.0?


Konstantin Preißer


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