Question

We are developing a simple usenet reader for iOS5 implementing the NNTP protocol.

Unfortunately we have some problem with the encoding: A header may look like:

Subject: Re: [GA] =?ISO-8859-15?Q?Pr=FCfungsmodus?= 
Date: 22 Apr 2012 22:50:38 +0200

Is there some simple way in Objective-C to convert a NSString containing =?ISO-8859-15?Q?Pr=FCfungsmodus?= to “Prüfungsmodus“?

Thanks

EDIT:

Hm. I’m not sure if I got this right:
You meant something like:

NSRange range = [input rangeOfString:@"=?"];
NSRange range2 = [input rangeOfString:@"?="];

NSString *string_to_decode = [input substringWithRange:NSMakeRange(range.location, range2.location-(range.location-2))];


NSData *data = [string_to_decode dataUsingEncoding:NSISOLatin1StringEncoding allowLossyConversion:YES];

NSString *converted = [[NSString alloc] initWithData:data encoding:(NSISOLatin1StringEncoding)];

Because that’s not working..

EDIT2
Trying to convert the raw bytes:

uint8_t buffer[1024];
iStream read:buffer maxLength:sizeof(buffer)
NSString *output = [[NSString alloc] initWithBytes:buffer length:len encoding:NSISOLatin1StringEncoding];

No matter which encoding I choose here the Subject: Field will always look the same (except for japanese etc encoding…)

Answer 1

If you are doing this yourself from first principles then in outline:

• Read the bytes from the network
• Determine the ranges of each run in a particular encoding – in your example you’re looking for =?…?= sections [this looks like MIME word encoding] – for each range you need byte pointer, length, encoding [which may be both a character set and a separate encoding style, here it looks like ISO-8859-15 with Q-encoding]

• create an NSString for each using - (id)initWithBytes:(const void *)bytes length:(NSUInteger)length encoding:(NSStringEncoding)encoding

• concatenate

• you also need to deal with other escape sequences in the input, e.g. when the input contains a literal =?

For details on MIME look at Wikipedia.

[Edit: added notes on MIME.]