apache - Are square brackets permitted in URLs?

Question

Are square brackets in URLs allowed?

I noticed that Apache commons HttpClient (3.0.1) throws an IOException, wget and Firefox however accept square brackets.

URL example:

http://example.com/path/to/file[3].html

My HTTP client encounters such URLs but I'm not sure whether to patch the code or to throw an exception (as it actually should be).

Answer 1

RFC 3986 states

A host identified by an Internet Protocol literal address, version 6 [RFC3513] or later, is distinguished by enclosing the IP literal within square brackets ("[" and "]"). This is the only place where square bracket characters are allowed in the URI syntax.

So you should not be seeing such URI's in the wild in theory, as they should arrive encoded.