Question

Came across something odd today, which perhaps has a simple explanation.

If I create an NSURLRequest using an NSURL that was originally constructed relative to a base URL that is a subdirectory, NSURLRequest removes the subdirectory.

This is much easier to explain with code:

// create a base URL to work with
NSURL *baseUrl = [NSURL URLWithString:@"http://www.google.com/sub"];

// create a URL relative to the base URL
NSURL *url1 = [NSURL URLWithString:@"/foo/bar" relativeToURL:baseUrl];

// create a NSURLRequest using this first URL
NSURLRequest *mangled_req = [[NSURLRequest alloc] initWithURL:url1];
NSLog(@"url1: %@", url1);
NSLog(@"mangled_req: %@", mangled_req);

// now create another URL that puts the base URL together with the relative path
NSURL *url2 = [NSURL URLWithString:@"http://www.google.com/sub/foo/bar"];

// and create a NSURLRequest, which should be the same as above
NSURLRequest *correct_req = [[NSURLRequest alloc] initWithURL:url2];
NSLog(@"url2: %@", url2);
NSLog(@"correct_req: %@", correct_req);

The output demonstrates the point:

2013-01-25 11:55:37.386 url1: /foo/bar -- http://www.google.com/sub
2013-01-25 11:55:37.408 mangled_req: <NSURLRequest http://www.google.com/foo/bar>
2013-01-25 11:55:37.409 url2: http://www.google.com/sub/foo/bar
2013-01-25 11:55:37.409 correct_req: <NSURLRequest http://www.google.com/sub/foo/bar>

Note that the “mangled_req” omits /sub.

This is annoying me right now, because I’m using AFNetworking and want to switch between localhost for testing (which naturally has my web application in a subdirectory) and the remote server (which doesn’t).

Certainly there are workarounds, but this seems odd enough to me that I must be doing something wrong.

Answer 1

NSURL is behaving correctly and your assumptions about how URLs work are wrong. A “relative” URL that starts with a slash, as /foo/bar does, always means relative to the host, not relative to the existing path. So if I add /foo/bar as a relative URL to any url scheme://host/path/1/2/3/whatever I will always get back scheme://host/foo/bar. A prefix / on the path means the path is absolute.

Of course, if you fix this such that your relative URL is foo/bar, you’ll find that you still have a problem, because your original URL did not have a trailing slash. Just as how if I click a link that points to somefile.html while visiting http://host.com/foo/index.html I end up at http://host.com/foo/somefile.html instead of http://host.com/foo/index.html/somefile.html, NSURL will remove the last path component if it does not have a trailing slash.