lightningd: refuse to create rune with empty fields.

These look like uniqueids, and so can confuse us (I discovered this by
making a typo in a test!)

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

lightningd/runes.c

@@ -419,6 +419,10 @@ static struct rune_altern *rune_altern_from_json(const tal_t *ctx,
 	alt->fieldname = tal_strndup(alt, unescape, condoff);
 	alt->condition = unescape[condoff];
 	alt->value = tal_strdup(alt, unescape + condoff + 1);
+
+	/* don't let them add empty fieldnames */
+	if (streq(alt->fieldname, ""))
+		return tal_free(alt);
 	return alt;
 }
 

tests/test_runes.py

@@ -514,6 +514,14 @@ def test_missing_method_or_nodeid(node_factory):
         l1.rpc.checkrune(rune=rune4, nodeid=l1.info['id'])
 
 
+def test_invalid_restrictions(node_factory):
+    # I meant "method!" not "!method"!
+    l1 = node_factory.get_node()
+    for cond in "!=/^$~<>{}#,":
+        with pytest.raises(RpcError, match='not a valid restriction'):
+            print(l1.rpc.createrune(restrictions=[[f"{cond}method"]]))
+
+
 def test_showrune_id(node_factory):
     l1 = node_factory.get_node()