IE7 won't display bmp files with encoded filenames

I have a test page that displays two images. One called hello.bmp and another called 徘吐驴欸觰.bmp (this is a rand开发者_如何学编程om collection of Chinese characters - apologies if it means something weird). For the latter image, I use an encoded format in the page's HTML.

The html is pretty straight forward:

<img src="%E5%BE%98%E5%90%90%E9%A9%B4%E6%AC%B8%E8%A7%B0.bmp" />
<img src="hello.bmp" />

In Internet explore 7, the encoded filepath does not display (Red x). All other browsers display it.

Does anyone know what would cause this? Can it be avoided?

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Character encoding of file:/// URLs works differently across browsers on Windows.

Windows filenames are natively Unicode-based, so when you use a URL, which is byte-based, it has to convert that sequence of bytes to Unicode characters using an encoding. What encoding? There is no standard to say, but there are two obvious possibilities:

• UTF-8, since it covers everything and is a popular default encoding, also used by the IRI standard for putting Unicode in URIs;

• the (misleadingly-named) “ANSI” code page, which is an arbitrary default that varies from system to system. On a Western European Windows install it will be code page 1252 (which is similar to ISO-8859-1); on a Chinese Windows install it will be code page 936 (similar to GB2312).

The ANSI code page is a pain because you never know what it's going to be, it's never UTF-8, and if your filename contains characters that don't exist in ANSI—which will certainly be the case if you have the filename 徘吐驴欸觰.bmp on a Western Windows install—you can't access the file at all.

So which do the browsers use?

• IE: ANSI code page
• Safari/Opera: UTF-8
• Chrome/Firefox: UTF-8, unless the bytes are not a valid UTF-8 sequence, in which case the ANSI code page is used instead.

So in conclusion, you can't reliably use non-ASCII characters in file:/// URLs at all.

This is in contrast to HTTP. The IIS web server, for example, has the same UTF-8-with-fallback-to-ANSI behaviour as Chrome and Firefox. Non-ASCII characters via IRI and a suitably-configured server are fine, but not the local filesystem.

(On non-Windows platforms filenames are natively bytes, usually representing UTF-8-encoded characters, but still bytes. Oo there is no ambiguity between the filesystem names and the byte-based URL %-sequences.)

_{die ANSI code page die. Why won't Microsoft kill you? You have long outstayed your welcome. You ruin everything.}