packages/s3ql: correctly determine buffer length when pre-seeked

patches/base/s3ql/s3c-accurate-length.patch

@@ -0,0 +1,26 @@
+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