feat: automatic oldest-first message removal from mailboxes to (almost) always stay under max_mailbox_size

Both dovecot-quota-threshold triggers and the daily expiry routine
will now expunge oldest messages from mailboxes automatically
when the mailbox reaches 75% of max_mailbox_size.
Delta Chat users should not see any warnings (at 80/95 percent) or bounce messages,
and existing over-quota mailboxes should start receiving mails again.

chatmaild/src/chatmaild/tests/test_expire.py

@@ -1,5 +1,7 @@
+import itertools
 import os
 import random
+import time
 from datetime import datetime
 from fnmatch import fnmatch
 from pathlib import Path
@@ -9,13 +11,19 @@ import pytest
 from chatmaild.expire import (
     FileEntry,
     MailboxStat,
+    expire_to_target,
     get_file_entry,
     iter_mailboxes,
     os_listdir_if_exists,
+    parse_dovecot_filename,
+    quota_expire_main,
+    scan_mailbox_messages,
 )
-from chatmaild.expire import main as expiry_main
+from chatmaild.expire import daily_expire_main as expiry_main
 from chatmaild.fsreport import main as report_main
 
+MB = 1024 * 1024
+
 
 def fill_mbox(folderdir):
     password = folderdir.joinpath("password")
@@ -196,3 +204,51 @@ def test_os_listdir_if_exists(tmp_path):
     tmp_path.joinpath("x").write_text("hello")
     assert len(os_listdir_if_exists(str(tmp_path))) == 1
     assert len(os_listdir_if_exists(str(tmp_path.joinpath("123123")))) == 0
+
+
+# --- quota expire tests ---
+
+_msg_counter = itertools.count(1)
+
+
+def _create_message(basedir, sub, size, days_old=0, disk_size=None):
+    seq = next(_msg_counter)
+    mtime = int(time.time() - days_old * 86400)
+    name = f"{mtime}.M1P1Q{seq}.hostname,S={size},W={size}:2,S"
+    path = basedir / sub / name
+    path.parent.mkdir(parents=True, exist_ok=True)
+    path.write_bytes(b"x" * (disk_size if disk_size is not None else size))
+    os.utime(path, (mtime, mtime))
+    return path
+
+
+def test_parse_dovecot_filename():
+    e = parse_dovecot_filename("cur/1775324677.M448978P3029757.exam,S=3235,W=3305:2,S")
+    assert e.path == "cur/1775324677.M448978P3029757.exam,S=3235,W=3305:2,S"
+    assert e.mtime == 1775324677
+    assert e.quota_size == 3235
+    assert parse_dovecot_filename("cur/msg_without_structure") is None
+
+
+def test_expire_to_target(tmp_path):
+    _create_message(tmp_path, "cur", MB, days_old=10, disk_size=100)
+    _create_message(tmp_path, "new", MB, days_old=5)
+    _create_message(tmp_path, "cur", MB, days_old=0)  # undeletable (<1 hour)
+    assert len(scan_mailbox_messages(tmp_path)) == 3
+    # removes oldest first, uses S= size not disk size
+    removed = expire_to_target(tmp_path, MB)
+    assert removed == 2
+    msgs = scan_mailbox_messages(tmp_path)
+    assert len(msgs) == 1
+    # the surviving message is the fresh undeletable one
+    assert msgs[0].mtime > time.time() - 3600
+
+
+def test_quota_expire_main(tmp_path, capsys):
+    mbox = tmp_path / "user@example.org"
+    _create_message(mbox, "cur", 2 * MB, days_old=5)
+    (mbox / "maildirsize").write_text("x")
+    quota_expire_main([str(1), str(mbox)])
+    _, err = capsys.readouterr()
+    assert "quota-expire: removed 1 message(s) from user@example.org" in err
+    assert not (mbox / "maildirsize").exists()