udnspkt: Make the module work again.

micropython/udnspkt/example_resolve.py

@@ -9,19 +9,17 @@
 
 
 def resolve(domain, is_ipv6):
-    buf = io.BytesIO(48)
-    udnspkt.make_req(buf, "google.com", is_ipv6)
-    v = buf.getvalue()
-    print("query: ", v)
-    s.sendto(v, dns_addr)
-
+    with io.BytesIO() as buf:
+        udnspkt.make_req(buf, domain, is_ipv6)
+        v = buf.getvalue()
+        print("query: ", v)
+        s.sendto(v, dns_addr)
     resp = s.recv(1024)
     print("resp:", resp)
-    buf = io.BytesIO(resp)
-
-    addr = udnspkt.parse_resp(buf, is_ipv6)
-    print("bin addr:", addr)
-    print("addr:", socket.inet_ntop(socket.AF_INET6 if is_ipv6 else socket.AF_INET, addr))
+    with io.BytesIO(resp) as buf:
+        addr = udnspkt.parse_resp(buf, is_ipv6)
+        print("bin addr:", addr)
+        print("addr:", socket.inet_ntop(socket.AF_INET6 if is_ipv6 else socket.AF_INET, addr))
 
 
 resolve("google.com", False)

micropython/udnspkt/manifest.py

@@ -1,4 +1,4 @@
-metadata(description="Make and parse DNS packets (Sans I/O approach).", version="0.1.0")
+metadata(description="Make and parse DNS packets (Sans I/O approach).", version="0.2.0")
 
 # Originally written by Paul Sokolovsky.
 

micropython/udnspkt/udnspkt.py

@@ -1,67 +1,50 @@
+import struct
+
+
 def write_fqdn(buf, name):
-    parts = name.split(".")
-    for p in parts:
-        buf.writebin("B", len(p))
-        buf.write(p)
-    buf.writebin("B", 0)
+    data = bytearray()
+    for part in name.split("."):
+        data.append(len(part))
+        data.extend(part.encode("ascii"))
+    data.append(0)
+    buf.write(data)
 
 
 def skip_fqdn(buf):
     while True:
-        sz = buf.readbin("B")
-        if not sz:
-            break
-        if sz >= 0xC0:
-            buf.readbin("B")
-            break
-        buf.read(sz)
+        # Label size
+        size = (buf.read(1) or b"\x00")[0]
+        if not size:
+            # Truncated packet or last label
+            return
+        # Ignore compressed response pointer
+        if size >= 0xC0:
+            buf.read(1)
+            return
+        # Skip label
+        buf.read(size)
 
 
 def make_req(buf, fqdn, is_ipv6):
-    typ = 1  # A
-    if is_ipv6:
-        typ = 28  # AAAA
-
-    buf.writebin(">H", 0)
-    buf.writebin(">H", 0x100)
-    # q count
-    buf.writebin(">H", 1)
-    buf.writebin(">H", 0)
-    # squashed together
-    buf.writebin(">I", 0)
-
+    # As per RFC1035, §4.1.1
+    # ID 0, Standard query, just one question entry
+    buf.write(b"\x00\x00\x00\x00\x00\x01\x00\x00\x00\x00\x00\x00")
+    # §4.1.3
     write_fqdn(buf, fqdn)
-    buf.writebin(">H", typ)
-    buf.writebin(">H", 1)  # Class
+    buf.write(b"\x00\x1c\x00\x01" if is_ipv6 else b"\x00\x01\x00\x01")
 
 
 def parse_resp(buf, is_ipv6):
-    typ = 1  # A
-    if is_ipv6:
-        typ = 28  # AAAA
-
-    buf.readbin(">H")  # id
-    flags = buf.readbin(">H")
-    assert flags & 0x8000
-    buf.readbin(">H")  # qcnt
-    acnt = buf.readbin(">H")
-    buf.readbin(">H")  # nscnt
-    buf.readbin(">H")  # addcnt
-
+    # As per RFC1035, §4.1.1
+    _, flags, _, acnt, _, _ = struct.unpack(">6H", buf.read(6 * 2))
+    # Bit 15 indicates it's a response, and bits 3..0 is the response code.
+    if flags & 0x800F != 0x8000:
+        raise ValueError(flags)
     skip_fqdn(buf)
-    buf.readbin(">H")
-    buf.readbin(">H")
-
-    for i in range(acnt):
-        # print("Resp #%d" % i)
-        # v = read_fqdn(buf)
-        # print(v)
+    buf.read(4)
+    for _ in range(acnt):
         skip_fqdn(buf)
-        t = buf.readbin(">H")  # Type
-        buf.readbin(">H")  # Class
-        buf.readbin(">I")  # TTL
-        rlen = buf.readbin(">H")
+        t, _, _, rlen = struct.unpack(">HHIH", buf.read(4 + (3 * 2)))
         rval = buf.read(rlen)
-
-        if t == typ:
+        if t == (0x1C if is_ipv6 else 0x01):
             return rval