Byte order mark in XML content causes a hard crash

[drmohundro]

It looks like NSXMLParser will crash if a byte order mark (BOM) is present in the file/content being parsed. I've been able to reproduce the error and I have a repro committed on the bom-crash branch (see https://github.com/drmohundro/SWXMLHash/blob/bom-crash/Tests/SWXMLHashSpecs.swift#L303-L320).

I can think of a few options for handling it:

• Leave it as is - it isn't strictly a bug in SWXMLHash, but instead is being thrown by NSXMLParser
  • I'm not fond of this idea because this crash has affected at least one app - it was privately reported to me. Their app on the AppStore was crashing because user-provided (I think?) XML content had BOM content in it.
  • It also reflects poorly on this library even though it was not directly caused by code in SWXMLHash.
• Strip BOM bytes from the content before parsing
  • This is doable, but I'm concerned about blindly stripping out bytes from content. Also, if performance is at all a concern, I wouldn't want to spin all of the XML to strip these characters out and then spin the content again for actual XML parsing
• Add a config option to strip optionally strip them out
  • This would be a really obscure setting - config.stripByteOrderMarkBytes = true or config.stripCrashingCharacters = true or something like that?
• Add a more friendly exception/error if BOM content is found in the XML
  • It would still likely crash, but it would at least tell the developer what is wrong.

I'm open to thoughts or ideas here. I'd also be curious if anyone else has run into this issue before related to the NSXMLParser.