Fix: SSE Stream parser expects additional space after colon "data:" (#559)

* Update api_requestor.py

* fix: SSE event for api_requestor.py

Author: michaelfeil

Diff for: openai/api_requestor.py

@@ -98,16 +98,18 @@ def _make_session() -> requests.Session:
 
 
 def parse_stream_helper(line: bytes) -> Optional[str]:
-    if line:
-        if line.strip() == b"data: [DONE]":
-            # return here will cause GeneratorExit exception in urllib3
-            # and it will close http connection with TCP Reset
-            return None
+    if line and line.startswith(b"data:"):
         if line.startswith(b"data: "):
+            # SSE event may be valid when it contain whitespace
             line = line[len(b"data: "):]
-            return line.decode("utf-8")
         else:
+            line = line[len(b"data:"):]
+        if line.strip() == b"[DONE]":
+            # return here will cause GeneratorExit exception in urllib3
+            # and it will close http connection with TCP Reset
             return None
+        else:
+            return line.decode("utf-8")
     return None