UrlByAppendingPathComponent vs UrlByAppendingPathExtension - objective-c

Question

I've read the documentation, and it looks like some edge cases might be different (trailing slashes, etc.), but it's not clear to me what the main difference between these two method is. Do the terms Component and Extension have special meaning in the URL world that people other than me understand?

Answer 1

The path extension is for adding things like .html to the URL, and the path component is for adding things like /news/local. The documentation for path extension:
If the original URL ends with one or more forward slashes, these are removed from the returned URL. A period is inserted between the two parts of the new URL.
So http://hello.com/news/ would become http://hello.com/news.html
The docs for path component:
If the original URL does not end with a forward slash and pathComponent does not begin with a forward slash, a forward slash is inserted between the two parts of the returned URL, unless the original URL is the empty string.
So http://hello.com/news/ would become http://hello.com/news/html
Here's a quick test:
NSURL *originalURL = [NSURL URLWithString:#"http://hello.com/news"];
NSLog(#"%#", [originalURL URLByAppendingPathComponent:#"local"]);
NSLog(#"%#", [originalURL URLByAppendingPathExtension:#"local"]);
Output:
http://hello.com/news/local
http://hello.com/news.local

Answer 2

Whenever I have questions about things like this, and the documentation is not helping, I just test it in a logic test.
NSURL *baseURL = [NSURL URLWithString:#"http://foo.com/bar/baz"];
NSURL *appendExtension = [baseURL URLByAppendingPathExtension:#"qux"];
NSURL *appendComponent = [baseURL URLByAppendingPathComponent:#"qux"];
STAssertEqualObjects([appendExtension absoluteString], #"http://foo.com/bar/baz.qux", nil);
STAssertEqualObjects([appendComponent absoluteString], #"http://foo.com/bar/baz/qux", nil);
So there it is, an extension is the .(file-type) there component is /(directory).