Fix content detection with libmagic when dealing with stdin... prefers using a dedicated file

archive.py

@@ -58,16 +58,17 @@ def hash_archive(cnt, dest=None, imposed_hash=None):
 
 
 def _guess_mime(data):
+    fd, path = tempfile.mkstemp()
+    with os.fdopen(fd, 'wb') as fp:
+        fp.write(data.encode() if isinstance(data, str) else data)
+
     with subprocess.Popen(["file",
                            "--brief",
                            "--mime-type",
-                           "-"], env={"LANG": 'C'}, stdin=subprocess.PIPE, stdout=subprocess.PIPE) as p:
+                           path], env={"LANG": 'C'}, stdout=subprocess.PIPE) as p:
-        try:
-            p.stdin.write(data.encode() if isinstance(data, str) else data)
-            p.stdin.close()
-        except BrokenPipeError:
-            pass
         p.wait()
+        os.unlink(path)
+
         if p.returncode == 0:
             return p.stdout.read().decode('utf-8', 'replace').strip()