writeonce/docs/examples/writeonce-serve/http/form.wo

-- http/form.wo — the public body-inspection surface: what media type a
-- request carries, and form-encoded bodies as decoded pairs.
--
-- PUBLIC by design (iteration 17). It sits here rather than in
-- `internal/parse.wo` with the rest of the parsing code because these two
-- functions are exactly what a consuming app calls; the decoders they lean on
-- stay behind the privacy line. `use internal` is legal INSIDE the library —
-- the boundary is consumer-only.
use internal

-- The request's media type: the content-type header lowercased with any
-- parameters ("; charset=...") stripped; "" when the header is absent.
pub fn media_type(req: Req) -> Text {
  let ct = req.headers["content-type"];
  if ct == nil { return ""; }
  let semi = index_of(ct, ";");
  if semi >= 0 { return to_lower(trim(substr(ct, 0, semi))); }
  return to_lower(trim("${ct}"));
}

-- Form-encoded body -> decoded pairs ('+' as space, %XX), the body-parsing
-- hook for application/x-www-form-urlencoded. nil when the content-type
-- says the body is something else — a JSON body is not silently misread
-- as one giant form key.
pub fn form_values(req: Req) -> ?map<Text, Text> {
  if media_type(req) != "application/x-www-form-urlencoded" { return nil; }
  return parse_query(req.body);
}