Determine MIME Type of NSData Loaded From a File

问题:

For various reasons I am intercepting http requests and loading content from files in my app's document directory using NSURLProtocol. Part of the process involves loading an NSData object, which could be anything from an html file to a jpeg image. NSURLProtocol requires setting a mimetype.

Is there an API in the iPhone-SDK to determine the mimetype of the file or NSData content?

回答1:

Perhaps you could download the file and use this to get the file's MIME type.

+ (NSString*) mimeTypeForFileAtPath: (NSString *) path {
    if (![[NSFileManager defaultManager] fileExistsAtPath:path]) {
        return nil;
    }
    // Borrowed from https://stackoverflow.com/questions/5996797/determine-mime-type-of-nsdata-loaded-from-a-file
    // itself, derived from  https://stackoverflow.com/questions/2439020/wheres-the-iphone-mime-type-database
    CFStringRef UTI = UTTypeCreatePreferredIdentifierForTag(kUTTagClassFilenameExtension, (CFStringRef)[path pathExtension], NULL);
    CFStringRef mimeType = UTTypeCopyPreferredTagWithClass (UTI, kUTTagClassMIMEType);
    CFRelease(UTI);
    if (!mimeType) {
        return @"application/octet-stream";
    }
    return [NSMakeCollectable((NSString *)mimeType) autorelease];
}

回答2:

I'm not familiar with such API in the SDK. However, if there no way to save the mime-type, then you can use MagicKit.

回答3:

can you not see anything in the HTTP accept headers, if you are intercepting requests i would expect the accept header to be set to the mime of the expected type in most cases