[rest] allow users to pass file descriptors to json without raising

sdk/core/azure-core/azure/core/rest/_helpers.py

@@ -157,11 +157,14 @@ def set_content_body(content):
 
 def set_json_body(json):
     # type: (Any) -> Tuple[Dict[str, str], Any]
-    body = dumps(json, cls=AzureJSONEncoder)
-    return {
-        "Content-Type": "application/json",
-        "Content-Length": str(len(body))
-    }, body
+    headers = {"Content-Type": "application/json"}
+    if hasattr(json, "read"):
+        content_headers, body = set_content_body(json)
+        headers.update(content_headers)
+    else:
+        body = dumps(json, cls=AzureJSONEncoder)
+        headers.update({"Content-Length": str(len(body))})
+    return headers, body
 
 def lookup_encoding(encoding):
     # type: (str) -> bool

sdk/core/azure-core/tests/test_rest_http_request.py

@@ -417,6 +417,32 @@ def on_request(self, pipeline_request):
     # work
     assert "I entered the policies!" in str(ex.value)
 
+def test_json_file_valid():
+    json_bytes = bytearray('{"more": "cowbell"}', encoding='utf-8')
+    with io.BytesIO(json_bytes) as json_file:
+        request = HttpRequest("PUT", "/fake", json=json_file)
+        assert request.headers == {"Content-Type": "application/json"}
+        assert request.content == json_file
+        assert not request.content.closed
+        assert request.content.read() == b'{"more": "cowbell"}'
+
+def test_json_file_invalid():
+    json_bytes = bytearray('{"more": "cowbell" i am not valid', encoding='utf-8')
+    with io.BytesIO(json_bytes) as json_file:
+        request = HttpRequest("PUT", "/fake", json=json_file)
+        assert request.headers == {"Content-Type": "application/json"}
+        assert request.content == json_file
+        assert not request.content.closed
+        assert request.content.read() == b'{"more": "cowbell" i am not valid'
+
+def test_json_file_content_type_input():
+    json_bytes = bytearray('{"more": "cowbell"}', encoding='utf-8')
+    with io.BytesIO(json_bytes) as json_file:
+        request = HttpRequest("PUT", "/fake", json=json_file, headers={"Content-Type": "application/json-special"})
+        assert request.headers == {"Content-Type": "application/json-special"}
+        assert request.content == json_file
+        assert not request.content.closed
+        assert request.content.read() == b'{"more": "cowbell"}'
 
 # NOTE: For files, we don't allow list of tuples yet, just dict. Will uncomment when we add this capability
 # def test_multipart_multiple_files_single_input_content():