Fix netlib.utils.is_valid_host

- Don't crash when passed an empty string. This translated into an actual core
crash, discovered while fuzzing with afl.
- Taking a slice of length one out of bytes returns an integer, so the check
for trailing period in this function never worked on Python3.
- Add unit tests.

netlib/utils.py

@@ -82,7 +82,7 @@ _label_valid = re.compile(b"(?!-)[A-Z\d-]{1,63}(?<!-)$", re.IGNORECASE)
 def is_valid_host(host):
     # type: (bytes) -> bool
     """
-    Checks if a hostname is valid.
+        Checks if a hostname is valid.
     """
     try:
         host.decode("idna")
@@ -90,7 +90,7 @@ def is_valid_host(host):
         return False
     if len(host) > 255:
         return False
-    if host[-1] == b".":
+    if host and host[-1:] == b".":
         host = host[:-1]
     return all(_label_valid.match(x) for x in host.split(b"."))
 

test/netlib/http/http1/test_read.py

@@ -13,6 +13,7 @@ from netlib.http.http1.read import (
     _read_headers, _read_chunked, get_header_tokens
 )
 from netlib.tutils import treq, tresp, raises
+from netlib import exceptions
 
 
 def test_get_header_tokens():
@@ -42,6 +43,14 @@ def test_read_request(input):
     assert rfile.read() == b"skip"
 
 
+@pytest.mark.parametrize("input", [
+    b"CONNECT :0 0",
+])
+def test_read_request_error(input):
+    rfile = BytesIO(input)
+    raises(exceptions.HttpException, read_request, rfile)
+
+
 def test_read_request_head():
     rfile = BytesIO(
         b"GET / HTTP/1.1\r\n"

test/netlib/test_utils.py

@@ -3,6 +3,13 @@
 from netlib import utils, tutils
 
 
+def test_is_valid_host():
+    assert not utils.is_valid_host(b"")
+    assert utils.is_valid_host(b"one.two")
+    assert not utils.is_valid_host(b"one"*255)
+    assert utils.is_valid_host(b"one.two.")
+
+
 def test_bidi():
     b = utils.BiDi(a=1, b=2)
     assert b.a == 1