Fix: no infinite loop on tx from unauthorized emitter (#480)

Problem: the Ethereum sync tx handler enters an infinite loop when the
last transaction from the sync smart contract comes from an
unauthorized emitter. The problem arises because the Ethereum height is
not stored when this occurs.

Solution: store the last height in all cases.

src/aleph/chains/ethereum.py

@@ -195,36 +195,36 @@ async def _request_transactions(
             publisher = event_data.args.addr
             timestamp = event_data.args.timestamp
 
-            if publisher not in config.ethereum.authorized_emitters.value:
-                LOGGER.info(
-                    "TX with unauthorized emitter %s in block %s"
-                    % (publisher, event_data.blockNumber)
-                )
-                continue
-
-            last_height = event_data.blockNumber
+            if publisher in config.ethereum.authorized_emitters.value:
+                message = event_data.args.message
+                try:
+                    jdata = json.loads(message)
+                    context = TxContext(
+                        chain=CHAIN_NAME,
+                        hash=event_data.transactionHash.hex(),
+                        time=timestamp,
+                        height=event_data.blockNumber,
+                        publisher=publisher,
+                    )
+                    yield jdata, context
 
-            message = event_data.args.message
-            try:
-                jdata = json.loads(message)
-                context = TxContext(
-                    chain=CHAIN_NAME,
-                    hash=event_data.transactionHash.hex(),
-                    time=timestamp,
-                    height=event_data.blockNumber,
-                    publisher=publisher,
-                )
-                yield jdata, context
+                except json.JSONDecodeError:
+                    # if it's not valid json, just ignore it...
+                    LOGGER.info("Incoming logic data is not JSON, ignoring. %r" % message)
 
-            except json.JSONDecodeError:
-                # if it's not valid json, just ignore it...
-                LOGGER.info("Incoming logic data is not JSON, ignoring. %r" % message)
+                except Exception:
+                    LOGGER.exception("Can't decode incoming logic data %r" % message)
 
-            except Exception:
-                LOGGER.exception("Can't decode incoming logic data %r" % message)
+            else:
+                LOGGER.info(
+                    "TX with unauthorized emitter %s in block %s",
+                    publisher,
+                    event_data.blockNumber,
+                )
 
             # Since we got no critical exception, save last received object
             # block height to do next requests from there.
+            last_height = event_data.blockNumber
             if last_height:
                 with self.session_factory() as session:
                     upsert_chain_sync_status(