Add isctest.check.ede() helper for pytest

Add a utility function to check for EDE options present in the DNS
message. The primary benefit of this helper function is that it
handles the compatibility issues with different dnspython versions
and the actual test code doesn't have to deal with that any more.

Rather than using the convenience .extended_errors() method
introduced in dnspython 2.7.0, iterate over the options and find
EDEOption types, which is supported from 2.2.0 onwards.

To work around the issue of using dns.edns.EDECode to specify EDE codes
in our tests, create an isctest.compat.EDECode wrapper. This can be used
even with dnspython versions prior to 2.2.0 and will simply result in
no-op, since EDE isn't supported in the older dnspython anyway.

bin/tests/system/isctest/check.py

@@ -12,15 +12,16 @@
 import difflib
 import shutil
 import os
-from typing import Optional
+from typing import cast, List, Optional
 
+import dns.edns
 import dns.flags
 import dns.message
 import dns.rcode
 import dns.zone
 
 import isctest.log
-from isctest.compat import dns_rcode
+from isctest.compat import dns_rcode, EDECode, EDEOption
 
 
 def rcode(message: dns.message.Message, expected_rcode) -> None:
@@ -67,6 +68,54 @@ def noraflag(message: dns.message.Message) -> None:
     assert (message.flags & dns.flags.RA) == 0, str(message)
 
 
+def _extract_ede_options(
+    message: dns.message.Message,
+) -> List[EDEOption]:
+    """Extract EDE options from the DNS message."""
+    return cast(
+        List[EDEOption],
+        [
+            option
+            for option in message.options
+            if option.otype == dns.edns.OptionType.EDE
+        ],
+    )
+
+
+def noede(message: dns.message.Message) -> None:
+    """Check that message contains no EDE option."""
+    if not hasattr(dns.edns, "EDECode"):
+        # dnspython<2.2.0 doesn't support EDE, skip check
+        return
+
+    ede_options = _extract_ede_options(message)
+    assert not ede_options, f"unexpected EDE options {ede_options} in {message}"
+
+
+def ede(
+    message: dns.message.Message, code: EDECode, text: Optional[str] = None
+) -> None:
+    """Check if message contains expected EDE code (and its text)."""
+    if not hasattr(dns.edns, "EDECode"):
+        # dnspython<2.2.0 doesn't support EDE, skip check
+        return
+
+    msg_opts = _extract_ede_options(message)
+    matching_opts = [opt for opt in msg_opts if opt.code == code]
+
+    assert matching_opts, f"missing EDE code {code} in {message}"
+
+    if text is None:
+        return
+
+    # check at least one matching EDE option has the required text
+    for opt in matching_opts:
+        if opt.text == text:
+            return
+    opt_str = ", ".join([opt.to_text() for opt in matching_opts])
+    assert False, f'EDE text "{text}" not found in [{opt_str}]'
+
+
 def section_equal(first_section: list, second_section: list) -> None:
     for rrset in first_section:
         assert (

bin/tests/system/isctest/compat.py

@@ -9,8 +9,9 @@
 # See the COPYRIGHT file distributed with this work for additional
 # information regarding copyright ownership.
 
-from typing import Any
+from typing import Any, TYPE_CHECKING
 
+import dns.edns
 import dns.rcode
 
 # compatiblity with dnspython<2.0.0
@@ -22,3 +23,34 @@ except AttributeError:
     # In dnspython<2.0.0, selected rcodes are available as integers directly
     # from dns.rcode
     dns_rcode = dns.rcode
+
+
+if TYPE_CHECKING:
+    EDECode = dns.edns.EDECode
+    EDEOption = dns.edns.EDEOption
+else:
+    try:  # compatiblity with dnspython<2.2.0
+        EDECode = dns.edns.EDECode
+    except AttributeError:
+        # In dnspython<2.2.0, the dns.edns.EDECode doesn't exist.
+        #
+        # The primary use-case is for us to use existing EDECode objects from the
+        # class, e.g. EDECode.FILTERED. To mimick this behavior, use a string
+        # factory that just turns the attribute name into a string.
+        #
+        # The used compatibility hack doesn't really matter (as long as EDECode.xxx
+        # doesn't raise exception), as with dnspython versions prior to 2.2.0, any
+        # EDE checking will be skipped anyway.
+        class _CompatEDECode:
+            def __getattr__(self, name: str) -> str:
+                return name
+
+        EDECode = _CompatEDECode()
+    try:
+        EDEOption = dns.edns.EDEOption
+    except AttributeError:
+        # In dnspython<2.2.0, the dns.edns.EDEOption doesn't exist, so we stub it to be
+        # able to use it in type annotations.
+        class EDEOption:
+            def __new__(cls, *args, **kwargs):
+                raise RuntimeError("Using EDEOption requires dnspython>=2.2.0")