Fix stream version and add basic readinto test

Author: tannewt

extmod/modujson.c

@@ -127,6 +127,8 @@ STATIC mp_obj_t _mod_ujson_load(mp_obj_t stream_obj, bool return_first_json) {
         stream_p = mp_get_stream_raise(stream_obj, MP_STREAM_OP_READ);
         s.stream_obj = stream_obj;
         s.read = stream_p->read;
+        s.errcode = 0;
+        s.cur = 0;
     }
 
     JSON_DEBUG("got JSON stream\n");

tests/extmod/ujson_load_readinto.py

@@ -0,0 +1,22 @@
+import ujson as json
+
+# Test that json can load from any object with readinto
+
+class Buffer:
+    def __init__(self, data):
+        self._data = data
+        self._i = 0
+
+    def readinto(self, buf):
+        end = self._i + len(buf)
+        remaining = len(self._data) - self._i
+        end = min(end, len(self._data))
+        l = min(len(buf), remaining)
+        buf[:l] = self._data[self._i:end]
+        self._i += l
+        return l
+
+print(json.load(Buffer(b'null')))
+print(json.load(Buffer(b'"abc\\u0064e"')))
+print(json.load(Buffer(b'[false, true, 1, -2]')))
+print(json.load(Buffer(b'{"a":true}')))

tests/extmod/ujson_load_readinto.py.exp

@@ -0,0 +1,4 @@
+None
+abcde
+[False, True, 1, -2]
+{'a': True}