handle non-standard RPC responses

Sometimes there is a need to issue RPC commands to the services
that just pretend to be bitcoind, by emulating some of its commands.
These services might not follow the same protocol for error reporting
as bitcoind does. An example of such service would be feesim
(https://github.com/bitcoinfees/feesim, Model-based Bitcoin fee estimation)

With these changes, we can handle non-standard error responses
gracefully.

Author: dgpv

bitcoin/rpc.py

@@ -227,8 +227,13 @@ def _call(self, service_name, *args):
         self.__conn.request('POST', self.__url.path, postdata, headers)
 
         response = self._get_response()
-        if response['error'] is not None:
-            raise JSONRPCError(response['error'])
+        err = response.get('error')
+        if err is not None:
+            if isinstance(err, dict):
+                raise JSONRPCError(
+                    {'code': err.get('code', -345),
+                     'message': err.get('message', 'error message not specified')})
+            raise JSONRPCError({'code': -344, 'message': str(err)})
         elif 'result' not in response:
             raise JSONRPCError({
                 'code': -343, 'message': 'missing JSON-RPC result'})
@@ -256,8 +261,15 @@ def _get_response(self):
             raise JSONRPCError({
                 'code': -342, 'message': 'missing HTTP response from server'})
 
-        return json.loads(http_response.read().decode('utf8'),
-                          parse_float=decimal.Decimal)
+        rdata = http_response.read().decode('utf8')
+        try:
+            return json.loads(rdata, parse_float=decimal.Decimal)
+        except Exception:
+            raise JSONRPCError({
+                'code': -342,
+                'message': ('non-JSON HTTP response with \'%i %s\' from server: \'%.20s%s\''
+                            % (http_response.status, http_response.reason,
+                               rdata, '...' if len(rdata) > 20 else ''))})
 
     def close(self):
         if self.__conn is not None: