Прям совсем не подойдет, да? func неПодойдет(r *Request) (vs url.Values,

err error) {
if r.Body == nil {
err = errors.New("missing form body")
return
}
ct := r.Header.Get("Content-Type")
// RFC 7231, section 3.1.1.5 - empty type
// MAY be treated as application/octet-stream
if ct == "" {
ct = "application/octet-stream"
}
ct, _, err = mime.ParseMediaType(ct)
switch {
case ct == "application/x-www-form-urlencoded":
var reader io.Reader = r.Body
maxFormSize := int64(1<<63 - 1)
if _, ok := r.Body.(*maxBytesReader); !ok {
maxFormSize = int64(10 << 20) // 10 MB is a lot of text.
reader = io.LimitReader(r.Body, maxFormSize+1)
}
b, e := ioutil.ReadAll(reader)
if e != nil {
if err == nil {
err = e
}
break
}
if int64(len(b)) > maxFormSize {
err = errors.New("http: POST too large")
return
}
vs, e = url.ParseQuery(string(b))
if err == nil {
err = e
}
case ct == "multipart/form-data":
// handled by ParseMultipartForm (which is calling us, or should be)
// TODO(bradfitz): there are too many possible
// orders to call too many functions here.
// Clean this up and write more tests.
// request_test.go contains the start of this,
// in TestParseMultipartFormOrder and others.
}
return
}

не очень понял, зачем эта копипаста из стдлибы

Кидай уж на pastebin..