fix: recover interrupted settings saves

micro/app_main.py

@@ -76,7 +76,14 @@ def IRQ_button_press(pin):
     status_led=None,
     timeout_seconds=config["wifi"]["timeout_seconds"],
 )
-network.connect_with_fallback(watchdog_feed=watchdog.feed)
+printer_api_ready = config_loader.is_runtime_config_ready(config)
+if printer_api_ready:
+    network.connect_with_fallback(watchdog_feed=watchdog.feed)
+else:
+    # Keep the setup UI reachable until a complete, explicit printer
+    # configuration has been saved. In particular, do not poll or clear the
+    # baked-in/default printer ID while settings are incomplete.
+    network.start_access_point()
 if network.is_ap_mode():
     print("Wi-Fi unavailable; connect to the setup access point to update settings")
     flasher.on()
@@ -117,6 +124,10 @@ def handle_pending_button_press():
     global PENDING_BUTTON_PRESS
     global PRINTER_STATUS_UPDATE_REQUIRED
 
+    if not printer_api_ready:
+        PENDING_BUTTON_PRESS = False
+        return
+
     try:
         with_network_connection(
             lambda: api.clear_plate(config["printer"]["id"])
@@ -133,6 +144,10 @@ def handle_printer_status_update():
     global PRINTER_AWAITING_PLATE_CLEAR, PRINTER_STATUS_UPDATE_REQUIRED
     global CHAMBER_LIGHT_IS_ON
 
+    if not printer_api_ready:
+        PRINTER_STATUS_UPDATE_REQUIRED = False
+        return
+
     try:
         response = with_network_connection(
             lambda: api.get_printer_status(config["printer"]["id"])

micro/config_loader.py

@@ -3,6 +3,7 @@
 except ImportError:
     import json
 
+import os
 import random
 
 
@@ -36,7 +37,9 @@ def generate_hostname():
         "request_timeout_seconds": 3,
     },
     "printer": {
-        "id": 3,
+        # A printer must be selected in setup. Never guess a device ID: a
+        # default ID can send a button press to an unrelated printer.
+        "id": None,
         "poll_interval_seconds": 5,
     },
     "led": {
@@ -55,20 +58,175 @@ def generate_hostname():
 }
 
 
+_STRING_FIELDS = {
+    "wifi": ("ssid", "password", "hostname", "ap_password"),
+    "api": ("base_url", "key"),
+    "button": ("pull", "trigger"),
+    "web": ("password",),
+}
+_NUMBER_FIELDS = {
+    "wifi": ("timeout_seconds",),
+    "api": ("request_timeout_seconds",),
+    "printer": ("poll_interval_seconds",),
+    "led": ("pin", "flash_interval_ms"),
+    "button": ("pin", "debounce_ms"),
+}
+_KNOWN_SECTIONS = tuple(DEFAULT_CONFIG.keys())
+
+
 def load_config(path="config.json"):
     config = _copy_dict(DEFAULT_CONFIG)
 
-    try:
-        with open(path) as config_file:
-            loaded_config = json.load(config_file)
-    except OSError:
-        print("Config file not found, using defaults:", path)
+    path = str(path)
+    loaded_config = _load_config_file(path)
+    source_path = path
+    if loaded_config is None:
+        backup_path = path + ".bak"
+        loaded_config = _load_config_file(backup_path)
+        if loaded_config is not None:
+            source_path = backup_path
+
+    if loaded_config is None:
+        print("Config file missing or invalid, using defaults:", path)
         return config
 
     _deep_update(config, loaded_config)
+    if source_path != path:
+        print("Recovered configuration from backup:", source_path)
     return config
 
 
+def is_runtime_config_ready(config):
+    """Return whether the settings can safely address a printer API."""
+    if not isinstance(config, dict):
+        return False
+
+    wifi = config.get("wifi")
+    api = config.get("api")
+    printer = config.get("printer")
+    if not isinstance(wifi, dict) or not isinstance(api, dict):
+        return False
+    if not isinstance(printer, dict):
+        return False
+
+    printer_id = printer.get("id")
+    return bool(
+        wifi.get("ssid")
+        and api.get("base_url")
+        and api.get("key")
+        and isinstance(printer_id, int)
+        and not isinstance(printer_id, bool)
+        and printer_id >= 0
+    )
+
+
+def save_config(path, config):
+    """Replace a config atomically, retaining the previous copy until verified."""
+    path = str(path)
+    if not isinstance(config, dict):
+        raise ValueError("Configuration must be an object")
+
+    temporary_path = path + ".tmp"
+    backup_path = path + ".bak"
+    serialized = json.dumps(config)
+    with open(temporary_path, "w") as config_file:
+        config_file.write(serialized)
+        config_file.write("\n")
+    sync = getattr(os, "sync", None)
+    if sync is not None:
+        sync()
+
+    staged_config = _load_config_file(temporary_path)
+    if staged_config != config:
+        _remove_file(temporary_path)
+        raise ValueError("Could not verify saved configuration")
+
+    if _load_config_file(path) is not None:
+        _remove_file(backup_path)
+        os.rename(path, backup_path)
+    else:
+        # Keep any valid prior backup until the new config is installed.
+        _remove_file(path)
+
+    try:
+        os.rename(temporary_path, path)
+    except OSError:
+        # Restore a known-good config when the replacement could not be made.
+        if (
+            _load_config_file(path) is None
+            and _load_config_file(backup_path) is not None
+        ):
+            try:
+                os.rename(backup_path, path)
+            except OSError:
+                pass
+        _remove_file(temporary_path)
+        raise
+
+    if _load_config_file(path) != config:
+        _remove_file(path)
+        if _load_config_file(backup_path) is not None:
+            try:
+                os.rename(backup_path, path)
+            except OSError:
+                pass
+        raise ValueError("Could not verify active configuration")
+    _remove_file(backup_path)
+
+
+def _load_config_file(path):
+    try:
+        with open(path) as config_file:
+            loaded_config = json.load(config_file)
+    except (OSError, ValueError, TypeError):
+        return None
+    if not _is_valid_config_shape(loaded_config):
+        return None
+    return loaded_config
+
+
+def _is_valid_config_shape(config):
+    if not isinstance(config, dict):
+        return False
+
+    for section in _KNOWN_SECTIONS:
+        if section in config and not isinstance(config[section], dict):
+            return False
+
+    for section, fields in _STRING_FIELDS.items():
+        values = config.get(section, {})
+        for field in fields:
+            if field in values and not isinstance(values[field], str):
+                return False
+
+    for section, fields in _NUMBER_FIELDS.items():
+        values = config.get(section, {})
+        for field in fields:
+            value = values.get(field)
+            if field in values and (
+                not isinstance(value, (int, float)) or isinstance(value, bool)
+            ):
+                return False
+
+    if "id" in config.get("printer", {}):
+        printer_id = config["printer"]["id"]
+        if printer_id is not None and (
+            not isinstance(printer_id, int)
+            or isinstance(printer_id, bool)
+            or printer_id < 0
+        ):
+            return False
+
+    return True
+
+
+def _remove_file(path):
+    try:
+        os.remove(path)
+    except OSError:
+        pass
+
+
 def _copy_dict(source):
     result = {}
 

micro/web_config.py

@@ -12,8 +12,11 @@
 
 try:
     import ota_manager
+    import config_loader
 except ImportError:
-    from micro import ota_manager
+    from micro import ota_manager, config_loader
+
+save_config = config_loader.save_config
 
 
 CONFIG_PATH = "config.json"
@@ -292,13 +295,6 @@ def build_config(form, current_config):
     return config
 
 
-def save_config(path, config):
-    serialized = _json_dumps(config)
-    with open(path, "w") as config_file:
-        config_file.write(serialized)
-        config_file.write("\n")
-
-
 def render_config_page(config, message="", update_status=None):
     wifi = config.get("wifi", {})
     api = config.get("api", {})

tests/test_config_loader.py

@@ -8,10 +8,83 @@ def test_web_setup_default_hostname_has_four_character_suffix():
     assert re.fullmatch(r"bambutton-[A-Z0-9]{4}", config_loader.DEFAULT_HOSTNAME)
 
 
-def test_explicit_hostname_is_preserved_when_loading_config(tmp_path):
+def test_partial_config_keeps_explicit_settings_and_fills_defaults(tmp_path):
     config_path = tmp_path / "config.json"
     config_path.write_text(json.dumps({"wifi": {"hostname": "shop-button"}}))
 
     config = config_loader.load_config(config_path)
 
     assert config["wifi"]["hostname"] == "shop-button"
+    assert config["wifi"]["ssid"] == ""
+    assert config["api"]["base_url"] == ""
+    assert config["printer"]["id"] is None
+    assert not config_loader.is_runtime_config_ready(config)
+
+
+def test_malformed_config_recovers_from_valid_backup(tmp_path):
+    config_path = tmp_path / "config.json"
+    backup_path = tmp_path / "config.json.bak"
+    config_path.write_text('{"wifi":')
+    backup_path.write_text(json.dumps({
+        "wifi": {"ssid": "shop"},
+        "api": {"base_url": "http://bambuddy/api/v1"},
+        "printer": {"id": 7},
+    }))
+
+    config = config_loader.load_config(config_path)
+
+    assert config["wifi"]["ssid"] == "shop"
+    assert config["printer"]["id"] == 7
+
+
+def test_malformed_config_without_backup_uses_bootable_defaults(tmp_path):
+    config_path = tmp_path / "config.json"
+    config_path.write_text('{"wifi":')
+
+    config = config_loader.load_config(config_path)
+
+    assert config["wifi"]["ssid"] == ""
+    assert config["api"]["base_url"] == ""
+    assert config["printer"]["id"] is None
+    assert config["web"]["password"]
+    assert not config_loader.is_runtime_config_ready(config)
+
+
+def test_nested_invalid_active_config_recovers_from_valid_backup(tmp_path):
+    config_path = tmp_path / "config.json"
+    backup_path = tmp_path / "config.json.bak"
+    config_path.write_text(json.dumps({"wifi": None}))
+    backup_path.write_text(json.dumps({
+        "wifi": {"ssid": "shop"},
+        "api": {"base_url": "http://bambuddy/api/v1", "key": "secret"},
+        "printer": {"id": 7},
+    }))
+
+    config = config_loader.load_config(config_path)
+
+    assert config["wifi"]["ssid"] == "shop"
+    assert config["printer"]["id"] == 7
+    assert config_loader.is_runtime_config_ready(config)
+
+
+def test_incomplete_config_never_inherits_a_printer_id(tmp_path):
+    config_path = tmp_path / "config.json"
+    config_path.write_text(json.dumps({
+        "wifi": {"ssid": "shop"},
+        "api": {"base_url": "http://bambuddy/api/v1", "key": "secret"},
+    }))
+
+    config = config_loader.load_config(config_path)
+
+    assert config["printer"]["id"] is None
+    assert not config_loader.is_runtime_config_ready(config)
+
+
+def test_non_numeric_printer_id_is_rejected_and_uses_safe_defaults(tmp_path):
+    config_path = tmp_path / "config.json"
+    config_path.write_text(json.dumps({"printer": {"id": "3"}}))
+
+    config = config_loader.load_config(config_path)
+
+    assert config["printer"]["id"] is None
+    assert not config_loader.is_runtime_config_ready(config)