Add flag --skipmerklecheck (#4957)

The --skipmerklecheck optional flag makes Electrum tolerate invalid
merkle proofs from the server. This is useful for building Electrum
servers that need a minimum amount of storage, though of course users
should only enable it if they completely trust the connected server.

electrum/commands.py

@@ -909,6 +909,7 @@ def add_network_options(parser):
     parser.add_argument("-s", "--server", dest="server", default=None, help="set server host:port:protocol, where protocol is either t (tcp) or s (ssl)")
     parser.add_argument("-p", "--proxy", dest="proxy", default=None, help="set proxy [type:]host[:port], where type is socks4,socks5 or http")
     parser.add_argument("--noonion", action="store_true", dest="noonion", default=None, help="do not try to connect to onion servers")
+    parser.add_argument("--skipmerklecheck", action="store_true", dest="skipmerklecheck", default=False, help="Tolerate invalid merkle proofs from server")
 
 def add_global_options(parser):
     group = parser.add_argument_group('global options')

electrum/verifier.py

@@ -116,8 +116,11 @@ class SPV(NetworkJobOnDefaultServer):
         try:
             verify_tx_is_in_block(tx_hash, merkle_branch, pos, header, tx_height)
         except MerkleVerificationFailure as e:
-            self.print_error(str(e))
-            raise GracefulDisconnect(e)
+            if self.network.config.get("skipmerklecheck"):
+                self.print_error("skipping merkle proof check %s" % tx_hash)
+            else:
+                self.print_error(str(e))
+                raise GracefulDisconnect(e)
         # we passed all the tests
         self.merkle_roots[tx_hash] = header.get('merkle_root')
         try: self.requested_merkle.remove(tx_hash)