pylightning: provide a class for Lightning JSONDecoder.

Some JSON functions want a *class*, not just a hook, so provide one.
To make it clear that we want an encoding *class* and a decoding *object*,
rename the UnixDomainSocketRpc encode parameter to encode_cls.

Signed-off-by: Rusty Russell <[email protected]>

contrib/pylightning/lightning/lightning.py

@@ -121,9 +121,9 @@ def __mod__(self, other):
 
 
 class UnixDomainSocketRpc(object):
-    def __init__(self, socket_path, executor=None, logger=logging, encoder=json.JSONEncoder, decoder=json.JSONDecoder):
+    def __init__(self, socket_path, executor=None, logger=logging, encoder_cls=json.JSONEncoder, decoder=json.JSONDecoder()):
         self.socket_path = socket_path
-        self.encoder = encoder
+        self.encoder_cls = encoder_cls
         self.decoder = decoder
         self.executor = executor
         self.logger = logger
@@ -133,7 +133,7 @@ def __init__(self, socket_path, executor=None, logger=logging, encoder=json.JSON
         self.next_id = 0
 
     def _writeobj(self, sock, obj):
-        s = json.dumps(obj, cls=self.encoder)
+        s = json.dumps(obj, cls=self.encoder_cls)
         sock.sendall(bytearray(s, 'UTF-8'))
 
     def _readobj_compat(self, sock, buff=b''):
@@ -245,32 +245,39 @@ def default(self, o):
                 pass
             return json.JSONEncoder.default(self, o)
 
-    @staticmethod
-    def lightning_json_hook(json_object):
-        return json_object
-
-    @staticmethod
-    def replace_amounts(obj):
-        """
-        Recursively replace _msat fields with appropriate values with Millisatoshi.
-        """
-        if isinstance(obj, dict):
-            for k, v in obj.items():
-                if k.endswith('msat'):
-                    if isinstance(v, str) and v.endswith('msat'):
-                        obj[k] = Millisatoshi(v)
-                    # Special case for array of msat values
-                    elif isinstance(v, list) and all(isinstance(e, str) and e.endswith('msat') for e in v):
-                        obj[k] = [Millisatoshi(e) for e in v]
-                else:
-                    obj[k] = LightningRpc.replace_amounts(v)
-        elif isinstance(obj, list):
-            obj = [LightningRpc.replace_amounts(e) for e in obj]
-
-        return obj
+    class LightningJSONDecoder(json.JSONDecoder):
+        def __init__(self, *, object_hook=None, parse_float=None, parse_int=None, parse_constant=None, strict=True, object_pairs_hook=None):
+            self.object_hook_next = object_hook
+            super().__init__(object_hook=self.millisatoshi_hook, parse_float=parse_float, parse_int=parse_int, parse_constant=parse_constant, strict=strict, object_pairs_hook=object_pairs_hook)
+
+        @staticmethod
+        def replace_amounts(obj):
+            """
+            Recursively replace _msat fields with appropriate values with Millisatoshi.
+            """
+            if isinstance(obj, dict):
+                for k, v in obj.items():
+                    if k.endswith('msat'):
+                        if isinstance(v, str) and v.endswith('msat'):
+                            obj[k] = Millisatoshi(v)
+                        # Special case for array of msat values
+                        elif isinstance(v, list) and all(isinstance(e, str) and e.endswith('msat') for e in v):
+                            obj[k] = [Millisatoshi(e) for e in v]
+                    else:
+                        obj[k] = LightningRpc.LightningJSONDecoder.replace_amounts(v)
+            elif isinstance(obj, list):
+                obj = [LightningRpc.LightningJSONDecoder.replace_amounts(e) for e in obj]
+
+            return obj
+
+        def millisatoshi_hook(self, obj):
+            obj = LightningRpc.LightningJSONDecoder.replace_amounts(obj)
+            if self.object_hook_next:
+                obj = self.object_hook_next(obj)
+            return obj
 
     def __init__(self, socket_path, executor=None, logger=logging):
-        super().__init__(socket_path, executor, logging, self.LightningJSONEncoder, json.JSONDecoder(object_hook=self.replace_amounts))
+        super().__init__(socket_path, executor, logging, self.LightningJSONEncoder, self.LightningJSONDecoder())
 
     def getpeer(self, peer_id, level=None):
         """