Rework the JSON layer

Batch requests are now processed and encoded incrementally.
Their bandwidth usage is also incrementally added, and so overlarge
responses are rejected as soon as they become too large.
JSON text is also more memory efficient than the python data
structures they represent.

lib/jsonrpc.py

@@ -33,6 +33,9 @@ def json_request_payload(method, id_, params=None):
 def json_notification_payload(method, params=None):
     return json_request_payload(method, None, params)
 
+def json_payload_id(payload):
+    return payload.get('id') if isinstance(payload, dict) else None
+
 
 class JSONRPC(asyncio.Protocol, LoggedClass):
     '''Manages a JSONRPC connection.
@@ -179,16 +182,14 @@ class JSONRPC(asyncio.Protocol, LoggedClass):
             message = message.decode()
         except UnicodeDecodeError as e:
             msg = 'cannot decode binary bytes: {}'.format(e)
-            self.send_json_error(msg, self.PARSE_ERROR)
-            self.transport.close()
+            self.send_json_error(msg, self.INVALID_REQUEST)
             return
 
         try:
             message = json.loads(message)
         except json.JSONDecodeError as e:
             msg = 'cannot decode JSON: {}'.format(e)
-            self.send_json_error(msg, self.PARSE_ERROR)
-            self.transport.close()
+            self.send_json_error(msg, self.INVALID_REQUEST)
             return
 
         '''Queue the request for asynchronous handling.'''
@@ -196,55 +197,98 @@ class JSONRPC(asyncio.Protocol, LoggedClass):
         if self.log_me:
             self.log_info('queued {}'.format(message))
 
-    def send_json_notification(self, method, params):
-        '''Create a json notification.'''
-        self.send_json(json_notification_payload(method, params))
+    def encode_payload(self, payload):
+        try:
+            text = (json.dumps(payload) + '\n').encode()
+        except TypeError:
+            msg = 'JSON encoding failure: {}'.format(payload)
+            self.log_error(msg)
+            return self.json_error(msg, self.INTERNAL_ERROR,
+                                   json_payload_id(payload))
+
+        self.check_oversized_request(len(text))
+        if 'error' in payload:
+            self.error_count += 1
+        self.send_count += 1
+        self.send_size += len(text)
+        self.using_bandwidth(len(text))
+        return text
+
+    def send_text(self, text, close):
+        '''Send JSON text over the transport.  Close it if close is True.'''
+        # Confirmed this happens, sometimes a lot
+        if self.transport.is_closing():
+            return
+        self.transport.write(text)
+        if close:
+            self.transport.close()
 
-    def send_json_request(self, method, id_, params=None):
-        '''Send a JSON request.'''
-        self.send_json(json_request_payload(method, id_, params))
+    def send_json_error(self, message, code, id_=None, close=True):
+        '''Send a JSON error and close the connection by default.'''
+        self.send_text(self.json_error_text(message, code, id_), close)
 
-    def send_json_response(self, result, id_):
-        '''Send a JSON result.'''
-        self.send_json(json_response_payload(result, id_))
+    def encode_and_send_payload(self, payload):
+        '''Encode the payload and send it.'''
+        self.send_text(self.encode_payload(payload), False)
 
-    def send_json_error(self, message, code, id_=None):
-        '''Send a JSON error.'''
-        self.send_json(json_error_payload(message, code, id_))
-        self.error_count += 1
-        # Close abusive clients
-        if self.error_count >= 10:
-            self.transport.close()
+    def json_notification_text(self, method, params):
+        '''Return the text of a json notification.'''
+        return self.encode_payload(json_notification_payload(method, params))
 
-    def send_json(self, payload):
-        '''Send a JSON payload.'''
-        # Confirmed this happens, sometimes a lot
-        if self.transport.is_closing():
-            return
+    def json_request_text(self, method, id_, params=None):
+        '''Return the text of a JSON request.'''
+        return self.encode_payload(json_request_payload(method, params))
 
-        id_ = payload.get('id') if isinstance(payload, dict) else None
-        try:
-            data = (json.dumps(payload) + '\n').encode()
-        except TypeError:
-            msg = 'JSON encoding failure: {}'.format(payload)
-            self.log_error(msg)
-            self.send_json_error(msg, self.INTERNAL_ERROR, id_)
-        else:
-            if len(data) > max(1000, self.max_send):
-                self.send_json_error('request too large',
-                                     self.INVALID_REQUEST, id_)
-                raise self.LargeRequestError
-            else:
-                self.send_count += 1
-                self.send_size += len(data)
-                self.using_bandwidth(len(data))
-                self.transport.write(data)
+    def json_response_text(self, result, id_):
+        '''Return the text of a JSON response.'''
+        return self.encode_payload(json_response_payload(result, id_))
+
+    def json_error_text(self, message, code, id_=None):
+        '''Return the text of a JSON error.'''
+        return self.encode_payload(json_error_payload(message, code, id_))
 
-    async def handle_message(self, message):
+    async def handle_message(self, payload):
         '''Asynchronously handle a JSON request or response.
 
         Handles batches according to the JSON 2.0 spec.
         '''
+        try:
+            if isinstance(payload, list):
+                text = await self.process_json_batch(payload)
+            else:
+                text = await self.process_single_json(payload)
+        except self.RPCError as e:
+            text = self.json_error_text(e.msg, e.code,
+                                        json_payload_id(payload))
+
+        if text:
+            self.send_text(text, self.error_count > 10)
+
+    async def process_json_batch(self, batch):
+        '''Return the text response to a JSON batch request.'''
+        # Batches must have at least one request.
+        if not batch:
+            return self.json_error_text('empty batch', self.INVALID_REQUEST)
+
+        # PYTHON 3.6: use asynchronous comprehensions when supported
+        parts = []
+        total_len = 0
+        for item in batch:
+            part = await self.process_single_json(item)
+            if part:
+                parts.append(part)
+                total_len += len(part) + 2
+                self.check_oversized_request(total_len)
+        if parts:
+            return '{' + ', '.join(parts) + '}'
+        return ''
+
+    async def process_single_json(self, payload):
+        '''Return the JSON result of a single JSON request, response or
+        notification.
+
+        Return None if the request is a notification or a response.
+        '''
         # Throttle high-bandwidth connections by delaying processing
         # their requests.  Delay more the higher the excessive usage.
         excess = self.bandwidth_used - self.bandwidth_limit
@@ -255,59 +299,27 @@ class JSONRPC(asyncio.Protocol, LoggedClass):
                              .format(self.bandwidth_used, secs))
             await asyncio.sleep(secs)
 
-        if isinstance(message, list):
-            payload = await self.batch_payload(message)
-        else:
-            payload = await self.single_payload(message)
-
-        if payload:
-            try:
-                self.send_json(payload)
-            except self.LargeRequestError:
-                self.log_warning('blocked large request {}'.format(message))
-
-    async def batch_payload(self, batch):
-        '''Return the JSON payload corresponding to a batch JSON request.'''
-        # Batches must have at least one request.
-        if not batch:
-            return json_error_payload('empty request list',
-                                      self.INVALID_REQUEST)
-
-        # PYTHON 3.6: use asynchronous comprehensions when supported
-        payload = []
-        for message in batch:
-            message_payload = await self.single_payload(message)
-            if message_payload:
-                payload.append(message_payload)
-        return payload
-
-    async def single_payload(self, message):
-        '''Return the JSON payload corresponding to a single JSON request,
-        response or notification.
-
-        Return None if the request is a notification or a response.
-        '''
-        if not isinstance(message, dict):
-            return json_error_payload('request must be a dict',
-                                      self.INVALID_REQUEST)
+        if not isinstance(payload, dict):
+            return self.json_error_text('request must be a dict',
+                                        self.INVALID_REQUEST)
 
-        if not 'id' in message:
-            return await self.json_notification(message)
+        if not 'id' in payload:
+            return await self.process_json_notification(payload)
 
-        id_ = message['id']
+        id_ = payload['id']
         if not isinstance(id_, self.ID_TYPES):
-            return json_error_payload('invalid id: {}'.format(id_),
-                                      self.INVALID_REQUEST)
+            return self.json_error_text('invalid id: {}'.format(id_),
+                                        self.INVALID_REQUEST)
 
-        if 'method' in message:
-            return await self.json_request(message)
+        if 'method' in payload:
+            return await self.process_json_request(payload)
 
-        return await self.json_response(message)
+        return await self.process_json_response(payload)
 
     @classmethod
-    def method_and_params(cls, message):
-        method = message.get('method')
-        params = message.get('params', [])
+    def method_and_params(cls, payload):
+        method = payload.get('method')
+        params = payload.get('params', [])
 
         if not isinstance(method, str):
             raise cls.RPCError('invalid method: {}'.format(method),
@@ -319,31 +331,32 @@ class JSONRPC(asyncio.Protocol, LoggedClass):
 
         return method, params
 
-    async def json_notification(self, message):
+    async def process_json_notification(self, payload):
         try:
-            method, params = self.method_and_params(message)
+            method, params = self.method_and_params(payload)
         except self.RPCError:
             pass
         else:
             await self.handle_notification(method, params)
-        return None
+        return ''
 
-    async def json_request(self, message):
-        try:
-            method, params = self.method_and_params(message)
-            result = await self.handle_request(method, params)
-            return json_response_payload(result, message['id'])
-        except self.RPCError as e:
-            return json_error_payload(e.msg, e.code, message['id'])
+    async def process_json_request(self, payload):
+        method, params = self.method_and_params(payload)
+        result = await self.handle_request(method, params)
+        return self.json_response_text(result, payload['id'])
 
-    async def json_response(self, message):
+    async def process_json_response(self, payload):
         # Only one of result and error should exist; we go with 'error'
         # if both are supplied.
-        if 'error' in message:
-            await self.handle_response(None, message['error'], message['id'])
-        elif 'result' in message:
-            await self.handle_response(message['result'], None, message['id'])
-        return None
+        if 'error' in payload:
+            await self.handle_response(None, payload['error'], payload['id'])
+        elif 'result' in payload:
+            await self.handle_response(payload['result'], None, payload['id'])
+        return ''
+
+    def check_oversized_request(self, total_len):
+        if total_len > max(1000, self.max_send):
+            raise self.RPCError('request too large', self.INVALID_REQUEST)
 
     def raise_unknown_method(self, method):
         '''Respond to a request with an unknown method.'''

server/protocol.py

@@ -692,14 +692,14 @@ class ElectrumX(Session):
                         'blockchain.headers.subscribe',
                         (self.electrum_header(height), ),
                     )
-                self.send_json(cache[key])
+                self.encode_and_send_payload(cache[key])
 
             if self.subscribe_height:
                 payload = json_notification_payload(
                     'blockchain.numblocks.subscribe',
                     (height, ),
                 )
-                self.send_json(payload)
+                self.encode_and_send_payload(payload)
 
         hash168_to_address = self.coin.hash168_to_address
         matches = self.hash168s.intersection(touched)
@@ -708,7 +708,7 @@ class ElectrumX(Session):
             status = await self.address_status(hash168)
             payload = json_notification_payload(
                 'blockchain.address.subscribe', (address, status))
-            self.send_json(payload)
+            self.encode_and_send_payload(payload)
 
         if matches:
             self.log_info('notified of {:,d} addresses'.format(len(matches)))