server: do not serialize python nan in rpc protocol.

This causes protocol failure and plugin to be killed. Javascript behavior is to convert NaN to null.
Mimicing this behavior ensures stability though all JSON dicts are recursively inspected.

server/python/rpc_reader.py

@@ -12,7 +12,23 @@ import multiprocessing.connection
 import rpc
 import concurrent.futures
 import json
+import math
 
+def convert_nan_inf_to_none(obj):
+    if isinstance(obj, dict):
+        return {key: convert_nan_inf_to_none(value) for key, value in obj.items()}
+    elif isinstance(obj, list):
+        return [convert_nan_inf_to_none(item) for item in obj]
+    elif isinstance(obj, float):
+        if math.isnan(obj):
+            return None
+        if math.isinf(obj):
+            return None
+    return obj
+
+def json_dumps_clean(obj, **kwargs):
+    cleaned_obj = convert_nan_inf_to_none(obj)
+    return json.dumps(cleaned_obj, **kwargs)
 
 class BufferSerializer(rpc.RpcSerializer):
     def serialize(self, value, serializationContext):
@@ -94,7 +110,7 @@ class RpcFileTransport(RpcTransport):
                 reject(e)
 
     def writeJSON(self, j, reject):
-        return self.writeMessage(0, bytes(json.dumps(j), 'utf8'), reject)
+        return self.writeMessage(0, bytes(json_dumps_clean(j), 'utf8'), reject)
 
     def writeBuffer(self, buffer, reject):
         return self.writeMessage(1, buffer, reject)
@@ -128,7 +144,7 @@ class RpcStreamTransport(RpcTransport):
                 reject(e)
 
     def writeJSON(self, j, reject):
-        return self.writeMessage(0, bytes(json.dumps(j), 'utf8'), reject)
+        return self.writeMessage(0, bytes(json_dumps_clean(j), 'utf8'), reject)
 
     def writeBuffer(self, buffer, reject):
         return self.writeMessage(1, buffer, reject)