Re: How to handle unicode escaped params?

[Tobias Bielohlawek | SoundCloud <tobi@soundcloud.com>]

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Hey John

thank you very much for you comprehensive answer. Good you pointed me to ISO-8859-1, stupid I didn't thought of that - that confused me most. So the request params we are seeing are indeed ISO-8859-1 encoded but without any  "accept-charset" param given. For those cases we don't wont to fail, but be smart and try to encode ISO-8859-1:

So on error I try decode again, but with Encoding::ISO8859_1, followed , by iconv to get it to UTF-8
 
str = URI.decode_www_form_component("%E9", Encoding::ISO8859_1)
Iconv.conv("utf-8", "ISO-8859-1", str)

That seams to do the trick. Thanks!

Tobi



On 25.07.2011, at 20:48, John Firebaugh wrote:

> Hi Tobi,
> 
> Both %c3%a9 and %e9 could be valid -- it depends on the content of the page and what the server is prepared to accept. In short, a standards-conforming browser will choose which encoding to use based (mainly) on the form's accept-charset attribute. You can read the details here:
> 
> http://www.w3.org/TR/html5/association-of-controls-and-forms.html#url-encoded-form-data
> 
> Also, note that while UTF-8 is indeed a character encoding, "Unicode" is a standard, not a character encoding itself. As such, it doesn't make sense to talk about é being "encoded in Unicode". It is true that é is the Unicode code point U+00E9, but code points are independent of encodings (they are just an abstract numeric identifiers for a particular characters). You can say that é is encoded in ISO-8859-1 (and other common encodings) as hex E9, however. (See here for more: http://www.joelonsoftware.com/articles/Unicode.html)
> 
> So, with a form that specifies accept-charset="utf-8", é would be escaped as %c3%a9. With a form that specifies accept-charset="iso-8859-1", it would be escaped as %e9. Leaving it unescaped is technically invalid.
> 
> In order to process the data correctly, the server must know what encoding the incoming URL parameters are encoded in, typically either by convention or via HTTP headers. Rack has a deficiency here, in that Rack::Utils.unescape does not allow you to specify the encoding -- only UTF-8 is supported. The underlying API used by Rack,


> URI.decode_www_form_component, does allow you to specify the encoding, so if that matters to you, you might have to use that directly. (Though as was discovered recently, it has a rexexp that is vulnerable to catastrophic backtracking.)
> 
> John
> 
> On Mon, Jul 25, 2011 at 7:22 AM, Tobias Bielohlawek <tobi@soundcloud.com> wrote:
> I have a question on correct behavior of handling unicode encoded
> query params.
> 
> Let's take character 'é', in UTF-8 that's encoded '%c3%a9 ' in unicode
> '%e9'. As an real life example, we're seeing those URLs:
> 
> 1. not escaped: -> http://soundcloud.com/search?q%5Bfulltext%5D=café
> 2. UTF8 escaped -> http://soundcloud.com/search?q%5Bfulltext%5D=caf%c3%a9
> 3. or Unicode escaped -> http://soundcloud.com/search?q%5Bfulltext%5D=caf%E9
> 
> Using rack 1.3.1, the first two cases are processed correct, but the
> latter fails with error 'incorrect UTF-8 byte sequence'. Which is
> correct behavior at first place as it's
> not UTF-8 but the unicode.
> 
> I'm no wondering what's best solution here? Why not be smart and give
> it another run to unescape the URL assuming it's unicode encoded?
> 
> I checked other players, e.g. Twitter has same error (but fails
> silently)
> http://twitter.com/search/é
> http://twitter.com/search/%c3%a9
> http://twitter.com/search/%E9
> 
> but not Google, it does it this way:
> http://www.google.de/search?q=é
> http://www.google.de/search?q=%c3%a9
> http://www.google.de/search?q=%E9
> 
> 
> Any advice is very much appreciated. Patch is comming..
> 
> Thx - Tobi
> 
> 
> 


Cheers,
  Tobi

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