interface: implement support for protocol 1.6

diff --git a/electrum/interface.py b/electrum/interface.py
index a092e35..1e19b8d 100644
--- a/electrum/interface.py
+++ b/electrum/interface.py
@@ -868,13 +868,25 @@ class Interface(Logger):
         res = await self.session.send_request('blockchain.block.headers', [start_height, count], timeout=timeout)
         # check response
         assert_dict_contains_field(res, field_name='count')
-        assert_dict_contains_field(res, field_name='hex')
         assert_dict_contains_field(res, field_name='max')
         assert_non_negative_integer(res['count'])
         assert_non_negative_integer(res['max'])
-        assert_hex_str(res['hex'])
-        if len(res['hex']) != HEADER_SIZE * 2 * res['count']:
-            raise RequestCorrupted('inconsistent chunk hex and count')
+        if self.active_protocol_tuple >= (1, 6):
+            hex_headers_list = assert_dict_contains_field(res, field_name='headers')
+            assert_list_or_tuple(hex_headers_list)
+            for item in hex_headers_list:
+                assert_hex_str(item)
+                if len(item) != HEADER_SIZE * 2:
+                    raise RequestCorrupted(f"invalid header size. got {len(item)//2}, expected {HEADER_SIZE}")
+            if len(hex_headers_list) != res['count']:
+                raise RequestCorrupted(f"{len(hex_headers_list)=} != {res['count']=}")
+            headers = list(bfh(hex_header) for hex_header in hex_headers_list)
+        else: # proto 1.4
+            hex_headers_concat = assert_dict_contains_field(res, field_name='hex')
+            assert_hex_str(hex_headers_concat)
+            if len(hex_headers_concat) != HEADER_SIZE * 2 * res['count']:
+                raise RequestCorrupted('inconsistent chunk hex and count')
+            headers = list(util.chunks(bfh(hex_headers_concat), size=HEADER_SIZE))
         # we never request more than MAX_NUM_HEADERS_IN_REQUEST headers, but we enforce those fit in a single response
         if res['max'] < MAX_NUM_HEADERS_PER_REQUEST:
             raise RequestCorrupted(f"server uses too low 'max' count for block.headers: {res['max']} < {MAX_NUM_HEADERS_PER_REQUEST}")
@@ -887,7 +899,6 @@ class Interface(Logger):
                 raise RequestCorrupted(
                     f"asked for {count} headers but got fewer: {res['count']}. ({start_height=}, {self.tip=})")
         # checks done.
-        headers = list(util.chunks(bfh(res['hex']), size=HEADER_SIZE))
         return headers
 
     async def request_chunk_below_max_checkpoint(
@@ -1405,6 +1416,33 @@ class Interface(Logger):
         # the status of a scripthash we are subscribed to. Caching here will save a future get_transaction RPC.
         self._rawtx_cache[txid_calc] = bytes.fromhex(rawtx)
 
+    async def broadcast_txpackage(self, txs: Sequence['Transaction']) -> bool:
+        assert self.active_protocol_tuple >= (1, 6), f"server using old protocol: {self.active_protocol_tuple}"
+        rawtxs = [tx.serialize() for tx in txs]
+        assert all(is_hex_str(rawtx) for rawtx in rawtxs)
+        assert all(tx.txid() is not None for tx in txs)
+        timeout = self.network.get_network_timeout_seconds(NetworkTimeout.Urgent)
+        for tx in txs:
+            if any(DummyAddress.is_dummy_address(txout.address) for txout in tx.outputs()):
+                raise DummyAddressUsedInTxException("tried to broadcast tx with dummy address!")
+        try:
+            res = await self.session.send_request('blockchain.transaction.broadcast_package', [rawtxs], timeout=timeout)
+        except aiorpcx.jsonrpc.CodeMessageError as e:
+            self.logger.info(f"broadcast_txpackage error [DO NOT TRUST THIS MESSAGE]: {error_text_str_to_safe_str(repr(e))}. {rawtxs=}")
+            return False
+        success = assert_dict_contains_field(res, field_name='success')
+        if not success:
+            errors = assert_dict_contains_field(res, field_name='errors')
+            self.logger.info(f"broadcast_txpackage error [DO NOT TRUST THIS MESSAGE]: {error_text_str_to_safe_str(repr(errors))}. {rawtxs=}")
+            return False
+        assert success
+        # broadcast succeeded.
+        # We now cache the rawtx, for *this interface only*. The tx likely touches some ismine addresses, affecting
+        # the status of a scripthash we are subscribed to. Caching here will save a future get_transaction RPC.
+        for tx, rawtx in zip(txs, rawtxs):
+            self._rawtx_cache[tx.txid()] = bytes.fromhex(rawtx)
+        return True
+
     async def get_history_for_scripthash(self, sh: str) -> List[dict]:
         if not is_hash256_str(sh):
             raise Exception(f"{repr(sh)} is not a scripthash")
@@ -1525,10 +1563,14 @@ class Interface(Logger):
     async def get_relay_fee(self) -> int:
         """Returns the min relay feerate in sat/kbyte."""
         # do request
-        res = await self.session.send_request('blockchain.relayfee')
+        if self.active_protocol_tuple >= (1, 6):
+            res = await self.session.send_request('mempool.get_info')
+            minrelaytxfee = assert_dict_contains_field(res, field_name='minrelaytxfee')
+        else:
+            minrelaytxfee = await self.session.send_request('blockchain.relayfee')
         # check response
-        assert_non_negative_int_or_float(res)
-        relayfee = int(res * bitcoin.COIN)
+        assert_non_negative_int_or_float(minrelaytxfee)
+        relayfee = int(minrelaytxfee * bitcoin.COIN)
         relayfee = max(0, relayfee)
         return relayfee
 
diff --git a/electrum/version.py b/electrum/version.py
index 49ad233..18ee702 100644
--- a/electrum/version.py
+++ b/electrum/version.py
@@ -1,7 +1,7 @@
 ELECTRUM_VERSION = '4.6.2'       # version of the client package
 
 PROTOCOL_VERSION_MIN = '1.4'     # electrum protocol
-PROTOCOL_VERSION_MAX = '1.4'
+PROTOCOL_VERSION_MAX = '1.6'
 
 # The hash of the mnemonic seed must begin with this
 SEED_PREFIX        = '01'      # Standard wallet
diff --git a/tests/test_interface.py b/tests/test_interface.py
index 0f9a0e2..3e39c74 100644
--- a/tests/test_interface.py
+++ b/tests/test_interface.py
@@ -157,6 +157,7 @@ class ToyServerSession(aiorpcx.RPCSession, Logger):
             'blockchain.transaction.get': self._handle_transaction_get,
             'blockchain.transaction.broadcast': self._handle_transaction_broadcast,
             'blockchain.transaction.get_merkle': self._handle_transaction_get_merkle,
+            'mempool.get_info': self._handle_mempool_get_info,
             'server.ping': self._handle_ping,
         }
         handler = handlers.get(request.method)
@@ -164,15 +165,15 @@ class ToyServerSession(aiorpcx.RPCSession, Logger):
         coro = aiorpcx.handler_invocation(handler, request)()
         return await coro
 
-    async def _handle_server_version(self, client_name='', protocol_version=None):
-        return ['best_server_impl/0.1', '1.4']
+    async def _handle_server_version(self, client_name='', protocol_version=None, *args, **kwargs):
+        return ['toy_server/0.1', '1.6']
 
     async def _handle_server_features(self) -> dict:
         return {
             'genesis_hash': constants.net.GENESIS,
             'hosts': {"14.3.140.101": {"tcp_port": 51001, "ssl_port": 51002}},
-            'protocol_max': '1.7.0',
-            'protocol_min': '1.4.3',
+            'protocol_max': '1.6',
+            'protocol_min': '1.6',
             'pruning': None,
             'server_version': 'ElectrumX 1.19.0',
             'hash_function': 'sha256',
@@ -181,6 +182,13 @@ class ToyServerSession(aiorpcx.RPCSession, Logger):
     async def _handle_estimatefee(self, number, mode=None):
         return 0.00001000
 
+    async def _handle_mempool_get_info(self):
+        return {
+            "mempoolminfee": 0.00001000,
+            "minrelaytxfee": 0.00001000,
+            "incrementalrelayfee": 0.00001000,
+        }
+
     def _get_headersub_result(self):
         return {'hex': BLOCK_HEADERS[self.cur_height].hex(), 'height': self.cur_height}
 
@@ -195,8 +203,8 @@ class ToyServerSession(aiorpcx.RPCSession, Logger):
         assert start_height <= self.cur_height, (start_height, self.cur_height)
         last_height = min(start_height+count-1, self.cur_height)  # [start_height, last_height]
         count = last_height - start_height + 1
-        headers = b"".join(BLOCK_HEADERS[idx] for idx in range(start_height, last_height+1))
-        return {'hex': headers.hex(), 'count': count, 'max': 2016}
+        headers = list(BLOCK_HEADERS[idx].hex() for idx in range(start_height, last_height+1))
+        return {'headers': headers, 'count': count, 'max': 2016}
 
     async def _handle_ping(self):
         return None