Make progress bar cursor draggable

spotify.py

@@ -90,7 +90,12 @@ class SpotifyClient:
         try:
             with urllib.request.urlopen(request, timeout=self.timeout) as response:
                 raw = response.read()
+            # A player command (seek, say) can answer 200 with a body that is
+            # not JSON at all -- it worked, there is just nothing to read.
+            try:
                 return json.loads(raw) if raw else {}
+            except ValueError:
+                return {}
         except urllib.error.HTTPError as exc:
             if exc.code == 401 and not retrying:
                 # The access token can go stale between calls even inside
@@ -135,6 +140,11 @@ class SpotifyClient:
         self._call("PUT", "/v1/me/player", body={"device_ids": [device["id"]], "play": True})
         return device
 
+    def seek(self, position_ms: int):
+        """Jump to position_ms in whatever the account is playing, on
+        whichever device is playing it."""
+        self._call("PUT", f"/v1/me/player/seek?position_ms={int(position_ms)}")
+
 
 def _error_detail(exc: urllib.error.HTTPError) -> str:
     try: