pytest: add schema support for JSON responses.

This adds our first (basic) schema, and sews support into pyln-testing
so it will load schemas for any method for doc/schemas/{method}.schema.json.

All JSON responses in a test run are checked against the schema (if any).

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

contrib/pyln-testing/pyln/testing/utils.py

@@ -601,7 +601,17 @@ class PrettyPrintingLightningRpc(LightningRpc):
     eyes. It has some overhead since we re-serialize the request and
     result to json in order to pretty print it.
 
+    Also validates (optional) schemas for us.
     """
+    def __init__(self, socket_path, executor=None, logger=logging,
+                 patch_json=True, jsonschemas={}):
+        super().__init__(
+            socket_path,
+            executor,
+            logger,
+            patch_json,
+        )
+        self.jsonschemas = jsonschemas
 
     def call(self, method, payload=None):
         id = self.next_id
@@ -615,6 +625,10 @@ class PrettyPrintingLightningRpc(LightningRpc):
             "id": id,
             "result": res
         }, indent=2))
+
+        if method in self.jsonschemas:
+            self.jsonschemas[method].validate(res)
+
         return res
 
 
@@ -625,6 +639,7 @@ class LightningNode(object):
                  allow_warning=False,
                  allow_bad_gossip=False,
                  db=None, port=None, disconnect=None, random_hsm=None, options=None,
+                 jsonschemas={},
                  **kwargs):
         self.bitcoin = bitcoind
         self.executor = executor
@@ -639,7 +654,7 @@ class LightningNode(object):
         self.rc = 0
 
         socket_path = os.path.join(lightning_dir, TEST_NETWORK, "lightning-rpc").format(node_id)
-        self.rpc = PrettyPrintingLightningRpc(socket_path, self.executor)
+        self.rpc = PrettyPrintingLightningRpc(socket_path, self.executor, jsonschemas=jsonschemas)
 
         self.daemon = LightningD(
             lightning_dir, bitcoindproxy=bitcoind.get_proxy(),
@@ -1196,7 +1211,7 @@ class NodeFactory(object):
     """A factory to setup and start `lightningd` daemons.
     """
     def __init__(self, request, testname, bitcoind, executor, directory,
-                 db_provider, node_cls, throttler):
+                 db_provider, node_cls, throttler, jsonschemas):
         if request.node.get_closest_marker("slow_test") and SLOW_MACHINE:
             self.valgrind = False
         else:
@@ -1211,6 +1226,7 @@ class NodeFactory(object):
         self.db_provider = db_provider
         self.node_cls = node_cls
         self.throttler = throttler
+        self.jsonschemas = jsonschemas
 
     def split_options(self, opts):
         """Split node options from cli options
@@ -1289,6 +1305,7 @@ class NodeFactory(object):
         node = self.node_cls(
             node_id, lightning_dir, self.bitcoind, self.executor, self.valgrind, db=db,
             port=port, options=options, may_fail=may_fail or expect_fail,
+            jsonschemas=self.jsonschemas,
             **kwargs
         )