Question

I recently had a problem when comparing two NSURLs and compare one NSURL with an NSString(which is a URL address), the situation is I got an NSURLRequest from somewhere, I may or may not know the URL address it points to, and I have an URL NSString, say “http://m.google.com”, now I need to check if the URL in that NSURLRequest is the same as the URL string I had:

[[request.URL.absoluteString lowercaseString] isEqualToString: [self.myAddress lowercaseString]];

this returns NO as the absoluteString gives me “http://m.google.com/” whereas my string is “http://m.google.com” without a slash in the end, even if I create the NSURLRequest using

[NSURLRequest requestWithURL:[NSURL URLWithString:@"http://m.google.com"]]

it still gives me “http://m.google.com/” for absoluteString, I wonder is there any reliable way to compare to NSURL or one NSURL and one NSString?

1. check if one ‘contains’ another, but this is not reliable as ‘http://m.google.com/blabla’ contains ‘http://m.google.com’.

2. convert the NSString to NSURL and use the isEqual method to compare two NSURL and hopefully NSURL’s implementation of isEqual can figure it out?

3. based on step 2, but convert each NSURL to a standard URL using standardizedURL?

Thanks a lot!

Answer 1

If you care only about the trailing slash ambiguity, you can dispense with this question quickly by knowing that NSURL path trims the trailing slash.

But I like the idea of a category method on NSURL that implements some standards-based equivalence (“equivalence” is probably a better term than equality in this case).

@RobNapier refers to a related question with a good answer that points to RFC2616. Another relevant standard for url syntax is RFC1808.

The tough part is deciding what we mean by equivalence, for example, what about differing queries or fragments (anchor links)? The code below errs on the side of permissiveness for most of these ambiguities…

// in NSURL+uriEquivalence.m

- (BOOL)isEquivalent:(NSURL *)aURL {

    if ([self isEqual:aURL]) return YES;
    if ([[self scheme] caseInsensitiveCompare:[aURL scheme]] != NSOrderedSame) return NO;
    if ([[self host] caseInsensitiveCompare:[aURL host]] != NSOrderedSame) return NO;

    // NSURL path is smart about trimming trailing slashes
    // note case-sensitivty here
    if ([[self path] compare:[aURL path]] != NSOrderedSame) return NO;

    // at this point, we've established that the urls are equivalent according to the rfc
    // insofar as scheme, host, and paths match

    // according to rfc2616, port's can weakly match if one is missing and the
    // other is default for the scheme, but for now, let's insist on an explicit match
    if ([self port] || [aURL port]) {
        if (![[self port] isEqual:[aURL port]]) return NO;
        if (![[self query] isEqual:[aURL query]]) return NO;
    }

    // for things like user/pw, fragment, etc., seems sensible to be
    // permissive about these.
    return YES;
}