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 HTTP version
if non-null, will be filled in with the status code
if non-null, will be filled in with the reason phrase
success or failure.
Parses the headers of an HTTP response in str and stores the results in ver, status_code, reason_phrase, and headers.
Beware that headers may be modified even on failure.