inline handshake parsing and explain MAX_LENGTH for transit server

src/wormhole_transit_relay/transit_server.py

@@ -26,6 +26,10 @@ def blur_size(size):
 
 class TransitConnection(LineReceiver):
     delimiter = b'\n'
+    # maximum length of a line we will accept before the handshake is complete.
+    # This must be >= to the longest possible handshake message.
+
+    MAX_LENGTH = 1024
 
     def __init__(self):
         self._got_token = False
@@ -51,14 +55,17 @@ class TransitConnection(LineReceiver):
         self.transport.setTcpKeepAlive(True)
 
     def lineReceived(self, line):
-        old = self._check_old_handshake(line)
-        if old is not None:
-            token = old
+        # old: "please relay {64}\n"
+        old = re.fullmatch(br"please relay (\w{64})", line)
+        if old:
+            token = old.group(1)
             return self._got_handshake(token, None)
 
-        new = self._check_new_handshake(line)
-        if new is not None:
-            token, side = new
+        # new: "please relay {64} for side {16}\n"
+        new = re.fullmatch(br"please relay (\w{64}) for side (\w{16})", line)
+        if new:
+            token = new.group(1)
+            side = new.group(2)
             return self._got_handshake(token, side)
 
         self.sendLine(b"bad handshake")
@@ -76,27 +83,6 @@ class TransitConnection(LineReceiver):
         if self._log_requests:
             log.msg("transit impatience failure")
 
-    def _check_old_handshake(self, buf):
-        # old: "please relay {64}\n"
-        # return token if buf contains an old-style handshake
-        # return None if buf does not contain one
-        mo = re.search(br"^please relay (\w{64})$", buf, re.M)
-        if mo:
-            token = mo.group(1)
-            return token
-        return None
-
-    def _check_new_handshake(self, buf):
-        # new: "please relay {64} for side {16}\n"
-        # return (token, side) if but contains a new-style handshake
-        # return None if buf does not contain one
-        mo = re.search(br"^please relay (\w{64}) for side (\w{16})$", buf, re.M)
-        if mo:
-            token = mo.group(1)
-            side = mo.group(2)
-            return (token, side)
-        return None
-    
     def _got_handshake(self, token, side):
         self._got_token = token
         self._got_side = side