form

Overview ¶

Package form implements application/x-www-form-urlencoded as a codec.Codec — the encoding every HTML form POSTs and every query string carries. It is stdlib-only: net/url supplies the decode half.

The wire format is a flat, ordered list of key=value pairs joined by '&', with keys and values percent-escaped and space written as '+'. It has no types, no nesting, and no array syntax: the ONLY way to carry more than one value under a key is to repeat the key. This codec models that literally, so its native Go shape is url.Values (== map[string][]string). Marshal accepts url.Values, map[string][]string and — for the common single-valued form — map[string]string, plus non-nil pointers to any of the three; Unmarshal writes into a pointer to any of the three.

Repeated keys: "a=1&a=2" decodes to {"a": ["1","2"]}, in wire order. No bracket dialect (a[]=, a[0]=) is invented and no value is dropped — see the package CLAUDE.md for the full round-trip contract and the two documented places where Marshal ∘ Unmarshal is not byte-for-byte identity.