feat: serve an APPVERSIONS.json index file to clients via IMAP metadata

This is designed to help implement self-updating APKs (and later other clients),
see counterpart https://github.com/chatmail/core/pull/8557

chatmaild/src/chatmaild/config.py

@@ -63,6 +63,9 @@ class Config:
         self.turn_socket_path = params.pop(
             "turn_socket_path", "/run/chatmail-turn/turn.socket"
         )
+        self.appversions_path = Path(
+            params.pop("appversions_path", "/usr/local/lib/chatmaild/appversions.json")
+        )
         iroh_relay = params.pop("iroh_relay", None)
         if iroh_relay is None:
             self.iroh_relay = "https://" + raw_domain

chatmaild/src/chatmaild/metadata.py

@@ -1,3 +1,4 @@
+import json
 import logging
 import socket
 import sys
@@ -18,6 +19,18 @@ def turn_credentials(turn_socket_path):
             return file.readline().decode("utf-8").strip()
 
 
+def read_appversions(path):
+    try:
+        data = json.loads(path.read_bytes())
+    except FileNotFoundError:
+        return None
+    except (OSError, ValueError):
+        logging.exception(f"failed to read {path}")
+        return None
+    # the dict protocol is line-based, keep the value single-line
+    return json.dumps(data, separators=(",", ":"))
+
+
 def _is_valid_token_timestamp(timestamp, now):
     # Token if invalid after 90 days
     # or if the timestamp is in the future.
@@ -94,6 +107,7 @@ class MetadataDictProxy(DictProxy):
         iroh_relay=None,
         turn_hostname=None,
         turn_socket_path=None,
+        appversions_path=None,
     ):
         super().__init__()
         self.notifier = notifier
@@ -101,6 +115,7 @@ class MetadataDictProxy(DictProxy):
         self.iroh_relay = iroh_relay
         self.turn_hostname = turn_hostname
         self.turn_socket_path = turn_socket_path
+        self.appversions_path = appversions_path
 
     def handle_lookup(self, parts):
         # Lpriv/43f5f508a7ea0366dff30200c15250e3/devicetoken\tlkj123poi@c2.testrun.org
@@ -125,6 +140,9 @@ class MetadataDictProxy(DictProxy):
                         case "maxsmtprecipients":
                             # postfix default  (see "postconf smtpd_recipient_limit")
                             return "O1000\n"
+                        case "appversions" if self.appversions_path:
+                            value = read_appversions(self.appversions_path)
+                            return f"O{value}\n" if value else "N\n"
 
         logging.warning(f"lookup ignored: {parts!r}")
         return "N\n"
@@ -170,6 +188,7 @@ def main():
         iroh_relay=iroh_relay,
         turn_hostname=mail_domain,
         turn_socket_path=socket_path,
+        appversions_path=config.appversions_path,
     )
 
     dictproxy.serve_forever_from_socket(socket)

chatmaild/src/chatmaild/tests/test_config.py

@@ -47,6 +47,9 @@ def test_read_config_basic_using_defaults(tmp_path, maildomain):
     assert example_config.password_min_length == 9
     assert example_config.max_imap_connections == 10000
     assert example_config.max_smtp_connections == 1000
+    assert str(example_config.appversions_path) == (
+        "/usr/local/lib/chatmaild/appversions.json"
+    )
     assert example_config._unused_keys == []
 
 

chatmaild/src/chatmaild/tests/test_metadata.py

@@ -7,6 +7,7 @@ import requests
 from chatmaild.metadata import (
     Metadata,
     MetadataDictProxy,
+    read_appversions,
 )
 from chatmaild.notifier import (
     Notifier,
@@ -369,6 +370,17 @@ def test_iroh_relay(dictproxy):
     assert wfile.getvalue() == b"Ohttps://example.org/\n"
 
 
+def test_read_appversions(tmp_path):
+    path = tmp_path.joinpath("appversions.json")
+    assert read_appversions(path) is None
+
+    path.write_text('{\n  "clients": []\n}')
+    assert read_appversions(path) == '{"clients":[]}'
+
+    path.write_text("bad json")
+    assert read_appversions(path) is None
+
+
 def test_legacy_token_migration(metadata, testaddr):
     with metadata.get_metadata_dict(testaddr).modify() as data:
         data[metadata.DEVICETOKEN_KEY] = ["oldtoken1", "oldtoken2"]