Is there a spec for nested urlencoded params[]?

Question

At one point in history, server side languages started tweaking urlencoded parameters to add support for submitting data as arrays and key/value objects:

// key/value pairs
contact[name]=John
contact[phone]=800-555-1234

// arrays
foo[]=bar
foo[]=baz

I’m playing around with some edge cases in one library's nested parameter parsing, eg preservation of parameter order. Is there a spec that formalizes how a server should process this encoding? If not, which reference implementation introduced this syntax?

Answer 1

Square brackets in URIs

According to RFC-3986 "Uniform Resource Identifier (URI): Generic Syntax" using unencoded square brackets in URIs isn't allowed. Therefore it's not a HTTP standard.

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.

Many programming languages are using square brackets for arrays, therefore I guess it was a natural carry-over to use square brackets in URIs.

Is there a spec that formalizes how a server should process this encoding?

No, at least not language independent.

First Implementation

A lot of web application frameworks allow reuse of the same key in the query to create an array, for example http://example.org/?foobar=hello&foobar=world. These frameworks also allow to use square brackets in keys, but it makes no difference, they are just part of the name. Associative arrays are rarely supported. (Caveat: I'm not familiar with all this languages.)

• Perl, 1987: Numbered Arrays are supported, but not associative arrays.
• PHP, 1995: Supports numbered arrays as well as associative arrays.
• Active Server Pages (ASP), 1996: Numbered Arrays are supported, but not associative arrays.
• JavaServerPages (JSP), 1999: Numbered Arrays are supported, but not associative arrays.
• JAX-RS (Java), 2008: Numbered Arrays are supported, but not associative arrays.

So far PHP is the only language I've found, which supports associative arrays in URLs without custom code.