rpc: checkmessage return an error if pubkey is not found

Returning an warning message when the pub key is not specified and there is no node in the graph.

We try to help people that use core lightning as a signer and nothings else.

Changelog-Deprecated: rpc: checkmessage return an error when the pubkey is not specified and it is unknown in the network graph.

tests/test_misc.py

@@ -1850,7 +1850,8 @@ def test_relative_config_dir(node_factory):
 
 
 def test_signmessage(node_factory):
-    l1, l2 = node_factory.line_graph(2, wait_for_announce=True)
+    l1, l2 = node_factory.line_graph(2, wait_for_announce=True,
+                                     opts={'allow-deprecated-apis': True})
 
     corpus = [[None,
                "this is a test!",
@@ -2712,3 +2713,18 @@ def test_torv2_in_db(node_factory):
     l1.stop()
     l1.db_manip("UPDATE peers SET address='3fyb44wdhnd2ghhl.onion:1234';")
     l1.start()
+
+
+def test_checkmessage_pubkey_not_found(node_factory):
+    l1 = node_factory.get_node()
+
+    msg = "testcase to check new rpc error"
+    pubkey = "03be3b0e9992153b1d5a6e1623670b6c3663f72ce6cf2e0dd39c0a373a7de5a3b7"
+    zbase = "d66bqz3qsku5fxtqsi37j11pci47ydxa95iusphutggz9ezaxt56neh77kxe5hyr41kwgkncgiu94p9ecxiexgpgsz8daoq4tw8kj8yx"
+
+    with pytest.raises(RpcError, match="not found in the graph, expected pubkey is {}".format(pubkey)):
+        l1.rpc.checkmessage(msg, zbase)
+
+    check_result = l1.rpc.checkmessage(msg, zbase, pubkey=pubkey)
+    assert check_result["pubkey"] == pubkey
+    assert check_result["verified"] is True