commit 1edbbcf08d5701ea38f13fca7491418318aebca9
Author: Max <max@privatevoid.net>
Date:   Fri Jun 7 23:31:08 2024 +0200

    accurate length

diff --git a/src/s3ql/backends/s3c.py b/src/s3ql/backends/s3c.py
index 2995ca4f..3c3c79ab 100644
--- a/src/s3ql/backends/s3c.py
+++ b/src/s3ql/backends/s3c.py
@@ -387,9 +387,13 @@ class Backend(AbstractBackend):
         '''
 
         off = fh.tell()
+        fh.seek(0, os.SEEK_END)
+        actual_len = fh.tell() - off
+        fh.seek(off, os.SEEK_SET)
         if len_ is None:
-            fh.seek(0, os.SEEK_END)
-            len_ = fh.tell()
+            len_ = actual_len
+        else:
+            len_ = min(len_, actual_len)
         return self._write_fh(key, fh, off, len_, metadata or {})
 
     @retry