[swift-corelibs-dev] Foundation: NSString init detect encoding

Tony Parker anthony.parker at apple.com
Wed Jun 21 11:43:58 CDT 2017

Hi Andy,

> On Jun 21, 2017, at 7:39 AM, Andy Best via swift-corelibs-dev <swift-corelibs-dev at swift.org> wrote:
> Hey,
> I've been looking at the init(contentsOfFile, usedEncoding) initializer for NSString in corelibs-foundation.
> Am I right in thinking that this method should use some method to attempt to detect the character encoding of the file before returning a decoded String?

In this case, the Foundation implementation just looks at an extended attribute of the file to see if it contains the encoding. If it doesn’t have the xattr then we don’t attempt to guess (name of xattr is “com.apple.TextEncoding”).

Foundation has another API which attempts to guess the encoding of a data blob, but I think we left it out of the swift-corelibs stubs:

+ (NSStringEncoding)stringEncodingForData:(NSData *)data
                          encodingOptions:(nullable NSDictionary<NSStringEncodingDetectionOptionsKey, id> *)opts
                          convertedString:(NSString * _Nullable * _Nullable)string
                      usedLossyConversion:(nullable BOOL *)usedLossyConversion API_AVAILABLE(macos(10.10), ios(8.0), watchos(2.0), tvos(9.0));

- Tony

> If so, I've been working on a pure Swift library to detect string encodings, and wondered if continued work on it might be useful for implementing this missing method?
> Andy
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