From 2dab021d03750b56cb4eca5420603f5471054a6e Mon Sep 17 00:00:00 2001
From: Bob Halley <halley@dnspython.org>
Date: Tue, 18 May 2021 06:59:58 -0700
Subject: [PATCH] Eliminate the need for a serial parameter to inbound_xfr()

---
 dns/asyncquery.py |  5 +++--
 dns/query.py      |  4 +++-
 dns/xfr.py        | 19 +++++++++++++++++++
 tests/test_xfr.py | 15 +++++++++++++++
 4 files changed, 40 insertions(+), 3 deletions(-)

diff --git a/dns/asyncquery.py b/dns/asyncquery.py
index c02a4789..deeff274 100644
--- a/dns/asyncquery.py
+++ b/dns/asyncquery.py
@@ -356,8 +356,7 @@ async def tls(q, where, timeout=None, port=853, source=None, source_port=0,
 
 async def inbound_xfr(where, txn_manager, query=None,
                       port=53, timeout=None, lifetime=None, source=None,
-                      source_port=0, udp_mode=UDPMode.NEVER, serial=0,
-                      backend=None):
+                      source_port=0, udp_mode=UDPMode.NEVER, backend=None):
     """Conduct an inbound transfer and apply it via a transaction from the
     txn_manager.
 
@@ -369,6 +368,8 @@ async def inbound_xfr(where, txn_manager, query=None,
     """
     if query is None:
         (query, serial) = dns.xfr.make_query(txn_manager)
+    else:
+        serial = dns.xfr.extract_serial_from_query(query)
     rdtype = query.question[0].rdtype
     is_ixfr = rdtype == dns.rdatatype.IXFR
     origin = txn_manager.from_wire_origin()
diff --git a/dns/query.py b/dns/query.py
index 7cfa16c1..934bf410 100644
--- a/dns/query.py
+++ b/dns/query.py
@@ -997,7 +997,7 @@ class UDPMode(enum.IntEnum):
 
 def inbound_xfr(where, txn_manager, query=None,
                 port=53, timeout=None, lifetime=None, source=None,
-                source_port=0, udp_mode=UDPMode.NEVER, serial=0):
+                source_port=0, udp_mode=UDPMode.NEVER):
     """Conduct an inbound transfer and apply it via a transaction from the
     txn_manager.
 
@@ -1036,6 +1036,8 @@ def inbound_xfr(where, txn_manager, query=None,
     """
     if query is None:
         (query, serial) = dns.xfr.make_query(txn_manager)
+    else:
+        serial = dns.xfr.extract_serial_from_query(query)
     rdtype = query.question[0].rdtype
     is_ixfr = rdtype == dns.rdatatype.IXFR
     origin = txn_manager.from_wire_origin()
diff --git a/dns/xfr.py b/dns/xfr.py
index 84059a3a..5efa6991 100644
--- a/dns/xfr.py
+++ b/dns/xfr.py
@@ -295,3 +295,22 @@ def make_query(txn_manager, serial=0,
     if keyring is not None:
         q.use_tsig(keyring, keyname, algorithm=keyalgorithm)
     return (q, serial)
+
+def extract_serial_from_query(query):
+    """Extract the SOA serial number from query if it is an IXFR and return
+    it, otherwise return None.
+
+    *query* is a dns.message.QueryMessage that is an IXFR or AXFR request.
+
+    Raises if the query is not an IXFR or AXFR, or if an IXFR doesn't have
+    an appropriate SOA RRset in the authority section."""
+
+    question = query.question[0]
+    if question.rdtype == dns.rdatatype.AXFR:
+        return None
+    elif question.rdtype != dns.rdatatype.IXFR:
+        raise ValueError("query is not an AXFR or IXFR")
+    print(question.name, question.rdclass)
+    soa = query.find_rrset(query.authority, question.name, question.rdclass,
+                           dns.rdatatype.SOA)
+    return soa[0].serial
diff --git a/tests/test_xfr.py b/tests/test_xfr.py
index c1a011c6..7429fa35 100644
--- a/tests/test_xfr.py
+++ b/tests/test_xfr.py
@@ -593,6 +593,21 @@ def test_make_query_bad_serial():
     with pytest.raises(ValueError):
         dns.xfr.make_query(z, serial=4294967296)
 
+def test_extract_serial_from_query():
+    z = dns.versioned.Zone('example.')
+    (q, s) = dns.xfr.make_query(z)
+    xs = dns.xfr.extract_serial_from_query(q)
+    assert s is None
+    assert s == xs
+    (q, s) = dns.xfr.make_query(z, serial=10)
+    print(q)
+    xs = dns.xfr.extract_serial_from_query(q)
+    assert s == 10
+    assert s == xs
+    q = dns.message.make_query('example', 'a')
+    with pytest.raises(ValueError):
+        dns.xfr.extract_serial_from_query(q)
+
 
 class XFRNanoNameserver(Server):
 
-- 
2.47.3