the headers (up to, but not including, the trailing blank line)
length of str
#SoupMessageHeaders to store the header values in
if non-null, will be filled in with the request method
if non-null, will be filled in with the request path
if non-null, will be filled in with the HTTP version
soup.types.Status.Ok if the headers could be parsed, or an HTTP error to be returned to the client if they could not be.
Parses the headers of an HTTP request in str and stores the results in req_method, req_path, ver, and req_headers.
Beware that req_headers may be modified even on failure.