Is it possible to reliably auto-decode user files to Unicode? [C#]
- by NVRAM
I have a web application that allows users to upload their content for processing. The processing engine expects UTF8 (and I'm composing XML from multiple users' files), so I need to ensure that I can properly decode the uploaded files.
Since I'd be surprised if any of my users knew their files even were encoded, I have very little hope they'd be able to correctly specify the encoding (decoder) to use. And so, my application is left with task of detecting before decoding.
This seems like such a universal problem, I'm surprised not to find either a framework capability or general recipe for the solution. Can it be I'm not searching with meaningful search terms?
I've implemented BOM-aware detection (http://en.wikipedia.org/wiki/Byte_order_mark) but I'm not sure how often files will be uploaded w/o a BOM to indicate encoding, and this isn't useful for most non-UTF files.
My questions boil down to:
Is BOM-aware detection sufficient for the vast majority of files?
In the case where BOM-detection fails, is it possible to try different decoders and determine if they are "valid"? (My attempts indicate the answer is "no.")
Under what circumstances will a "valid" file fail with the C# encoder/decoder framework?
Is there a repository anywhere that has a multitude of files with various encodings to use for testing?
While I'm specifically asking about C#/.NET, I'd like to know the answer for Java, Python and other languages for the next time I have to do this.
So far I've found:
A "valid" UTF-16 file with Ctrl-S characters has caused encoding to UTF-8 to throw an exception (Illegal character?) (That was an XML encoding exception.)
Decoding a valid UTF-16 file with UTF-8 succeeds but gives text with null characters. Huh?
Currently, I only expect UTF-8, UTF-16 and probably ISO-8859-1 files, but I want the solution to be extensible if possible.
My existing set of input files isn't nearly broad enough to uncover all the problems that will occur with live files.
Although the files I'm trying to decode are "text" I think they are often created w/methods that leave garbage characters in the files. Hence "valid" files may not be "pure". Oh joy.
Thanks.
