Allow more characters in header values

docs/source/changes.rst

@@ -10,6 +10,11 @@ Bug fixes:
 
 * Always return headers as ``bytes`` objects (`#60
   <https://github.com/python-hyper/h11/issues/60>`__)
+* Allow a broader range of characters in header values. This violates
+  the RFC, but is apparently required for compatibility with
+  real-world code, like Google Analytics cookies (`#57
+  <https://github.com/python-hyper/h11/issues/57>`__, `#58
+  <https://github.com/python-hyper/h11/issues/58>`__)
 
 Other changes:
 

h11/_abnf.py

@@ -44,7 +44,14 @@
 # See: https://www.rfc-editor.org/errata_search.php?rfc=7230&eid=4189
 #
 # So our definition of field_content attempts to fix it up...
-vchar_or_obs_text = r"[\x21-\xff]"
+#
+# Also, we allow lots of control characters, because apparently people assume
+# that they're legal in practice (e.g., google analytics makes cookies with
+# \x01 in them!):
+#   https://github.com/python-hyper/h11/issues/57
+# We still don't allow NUL or whitespace, because those are often treated as
+# meta-characters and letting them through can lead to nasty issues like SSRF.
+vchar_or_obs_text = r"[^\x00\s]"
 field_vchar = vchar_or_obs_text
 field_content = r"{field_vchar}+(?:[ \t]+{field_vchar}+)*".format(**globals())
 

h11/tests/test_events.py

@@ -82,10 +82,17 @@ def test_events():
                       http_version="1.0")
 
     # Header values are validated
-    with pytest.raises(LocalProtocolError):
-        req = Request(method="GET", target="/",
-                      headers=[("Host", "a"), ("Foo", "  asd\x00")],
-                      http_version="1.0")
+    for bad_char in "\x00\r\n\f\v":
+        with pytest.raises(LocalProtocolError):
+            req = Request(method="GET", target="/",
+                          headers=[("Host", "a"), ("Foo", "asd" + bad_char)],
+                          http_version="1.0")
+
+    # But for compatibility we allow non-whitespace control characters, even
+    # though they're forbidden by the spec.
+    Request(method="GET", target="/",
+            headers=[("Host", "a"), ("Foo", "asd\x01\x02\x7f")],
+            http_version="1.0")
 
     ir = InformationalResponse(status_code=100, headers=[("Host", "a")])
     assert ir.status_code == 100

h11/tests/test_headers.py

@@ -18,6 +18,12 @@ def test_normalize_and_validate():
     assert "foo bar" in str(excinfo.value)
     with pytest.raises(LocalProtocolError):
         normalize_and_validate([(b"foo\x00bar", b"baz")])
+    # Not even 8-bit characters:
+    with pytest.raises(LocalProtocolError):
+        normalize_and_validate([(b"foo\xffbar", b"baz")])
+    # And not even the control characters we allow in values:
+    with pytest.raises(LocalProtocolError):
+        normalize_and_validate([(b"foo\x01bar", b"baz")])
 
     # no return or NUL characters in values
     with pytest.raises(LocalProtocolError) as excinfo:
@@ -29,7 +35,13 @@ def test_normalize_and_validate():
         normalize_and_validate([("foo", "bar\x00baz")])
     # no leading/trailing whitespace
     with pytest.raises(LocalProtocolError):
-        normalize_and_validate([("foo", "  barbaz  ")])
+        normalize_and_validate([("foo", "barbaz  ")])
+    with pytest.raises(LocalProtocolError):
+        normalize_and_validate([("foo", "  barbaz")])
+    with pytest.raises(LocalProtocolError):
+        normalize_and_validate([("foo", "barbaz\t")])
+    with pytest.raises(LocalProtocolError):
+        normalize_and_validate([("foo", "\tbarbaz")])
 
     # content-length
     assert (normalize_and_validate([("Content-Length", "1")])

h11/tests/test_io.py

@@ -388,6 +388,19 @@ def test_reject_garbage_in_header_line():
            b"Host: foo\x00bar\r\n\r\n",
            None)
 
+# https://github.com/python-hyper/h11/issues/57
+def test_allow_some_garbage_in_cookies():
+    tr(READERS[CLIENT, IDLE],
+       b"HEAD /foo HTTP/1.1\r\n"
+       b"Host: foo\r\n"
+       b"Set-Cookie: ___utmvafIumyLc=kUd\x01UpAt; path=/; Max-Age=900\r\n"
+       b"\r\n",
+       Request(method="HEAD", target="/foo",
+               headers=[
+                   ("Host", "foo"),
+                   ("Set-Cookie", "___utmvafIumyLc=kUd\x01UpAt; path=/; Max-Age=900"),
+               ]))
+
 def test_host_comes_first():
     tw(write_headers,
        normalize_and_validate([("foo", "bar"), ("Host", "example.com")]),