--- a/weatherlog/http_writer.py	Sun Sep 29 01:18:58 2019 -0400
+++ b/weatherlog/http_writer.py	Sun Sep 29 11:52:23 2019 -0400
@@ -11,15 +11,16 @@
 
 class HTTPWriter(logger.RemoteWriter):
 
-    def __init__(self, url: str):
+    def __init__(self, url: str, preamble: t.Dict[str, t.Any]):
         self._url = url
         self._session = requests.Session()
         self._session.headers['User-Agent'] = 'weatherlogger/0.0.1'
+        self._preamble = bson.BSON.encode(preamble)
 
     def write(self, readings: t.Sequence[types.Reading]) -> None:
         try:
             data = b''.join(bson.BSON.encode(r.as_dict()) for r in readings)
-            response = self._session.post(self._url, data=data)
+            response = self._session.post(self._url, data=self._preamble + data)
             response.raise_for_status()
         except requests.exceptions.RequestException as rex:
             raise logger.RemoteWriteError("Coulndn't write values") from rex