Empty URI query string parameters: "a=&b=" versus "a&b"

Question

Should the following URLs be considered functionally equivalent?

http://example.com/foo?a=&b=

http://example.com/foo?a&b

This came about when a user of a Drupal module I wrote which parses apart and then rewrites URIs noticed that the code sometimes causes the query string parts to change in unexpected ways due to how some of the underlying PHP functions behave. For example:

parse_str("a&b", $values); print http_build_query($values);

a=&b=

Is this something I should bother worrying about?

Edit so SO stops complaining that this question is similar to another one: The question is whether it's safe to assume that "no value for X" and "empty value for X" are equivalent, not whether the "no value" style is syntactically correct (which it is).

Answer 1

RFC 3986 Uniform Resource Identifier (URI): Generic Syntax doesn't have anything to say about the structure of the query string aside from how characters like ? should be dealt with. So strictly speaking, your two example URLs are different. Of course, the application which receives those query strings may treat them as functionally equivalent, but this isn't something you can determine from the URL alone.