parse auth headers using pyparsing instead of regexp

Fixes CPU burn DoS by cubic complexity of whitespace matching in
WWW_AUTH_RELAXED (default) regexp.

python2/httplib2/auth.py

@@ -0,0 +1,61 @@
+import base64
+import re
+
+import pyparsing as pp
+
+from .error import *
+
+UNQUOTE_PAIRS = re.compile(r"\\(.)")
+unquote = lambda s, l, t: UNQUOTE_PAIRS.sub(r"\1", t[0][1:-1])
+
+# https://tools.ietf.org/html/rfc7235#section-1.2
+# https://tools.ietf.org/html/rfc7235#appendix-B
+tchar = "!#$%&'*+-.^_`|~" + pp.nums + pp.alphas
+token = pp.Word(tchar).setName("token")
+token68 = pp.Combine(pp.Word("-._~+/" + pp.nums + pp.alphas) + pp.ZeroOrMore("=")).setName("token68")
+
+quoted_string = pp.dblQuotedString.copy().setName("quoted-string").setParseAction(unquote)
+auth_param_name = token.copy().setName("auth-param-name").addParseAction(pp.downcaseTokens)
+auth_param = auth_param_name + pp.Suppress("=") + (token ^ quoted_string)
+params = pp.Dict(pp.delimitedList(pp.Group(auth_param)))
+
+scheme = token("scheme")
+challenge = scheme + (token68("token") ^ params("params"))
+
+authentication_info = params.copy()
+www_authenticate = pp.delimitedList(pp.Group(challenge))
+
+
+def _parse_authentication_info(headers, headername="authentication-info"):
+    """https://tools.ietf.org/html/rfc7615
+    """
+    header = headers.get(headername, "").strip()
+    if not header:
+        return {}
+    try:
+        parsed = authentication_info.parseString(header)
+    except pp.ParseException as ex:
+        # print(ex.explain(ex))
+        raise MalformedHeader(headername)
+
+    return parsed.asDict()
+
+
+def _parse_www_authenticate(headers, headername="www-authenticate"):
+    """Returns a dictionary of dictionaries, one dict per auth_scheme."""
+    header = headers.get(headername, "").strip()
+    if not header:
+        return {}
+    try:
+        parsed = www_authenticate.parseString(header)
+    except pp.ParseException as ex:
+        # print(ex.explain(ex))
+        raise MalformedHeader(headername)
+
+    retval = {
+        challenge["scheme"].lower(): challenge["params"].asDict()
+        if "params" in challenge
+        else {"token": challenge.get("token")}
+        for challenge in parsed
+    }
+    return retval

python2/httplib2/error.py

@@ -0,0 +1,48 @@
+# All exceptions raised here derive from HttpLib2Error
+class HttpLib2Error(Exception):
+    pass
+
+
+# Some exceptions can be caught and optionally
+# be turned back into responses.
+class HttpLib2ErrorWithResponse(HttpLib2Error):
+    def __init__(self, desc, response, content):
+        self.response = response
+        self.content = content
+        HttpLib2Error.__init__(self, desc)
+
+
+class RedirectMissingLocation(HttpLib2ErrorWithResponse):
+    pass
+
+
+class RedirectLimit(HttpLib2ErrorWithResponse):
+    pass
+
+
+class FailedToDecompressContent(HttpLib2ErrorWithResponse):
+    pass
+
+
+class UnimplementedDigestAuthOptionError(HttpLib2ErrorWithResponse):
+    pass
+
+
+class UnimplementedHmacDigestAuthOptionError(HttpLib2ErrorWithResponse):
+    pass
+
+
+class MalformedHeader(HttpLib2Error):
+    pass
+
+
+class RelativeURIError(HttpLib2Error):
+    pass
+
+
+class ServerNotFoundError(HttpLib2Error):
+    pass
+
+
+class ProxiesUnavailableError(HttpLib2Error):
+    pass