Implemented pagelet initialization.

matemat/webserver/__init__.py

@@ -8,5 +8,5 @@ server will attempt to serve the request with a static resource in a previously
 
 from .requestargs import RequestArgument, RequestArguments
 from .responses import PageletResponse, RedirectResponse, TemplateResponse
-from .httpd import MatematWebserver, HttpHandler, pagelet
+from .httpd import MatematWebserver, HttpHandler, pagelet, pagelet_init
 from .config import parse_config_file

matemat/webserver/httpd.py

@@ -1,7 +1,8 @@
 
-from typing import Any, Callable, Dict, Tuple, Type, Union
+from typing import Any, Callable, Dict, List, Tuple, Type, Union
 
 import logging
+import sys
 import os
 import socket
 import mimetypes
@@ -38,6 +39,8 @@ _PAGELET_PATHS: Dict[str, Callable[[str,  # HTTP method (GET, POST, ...)
                                        bytes, str,  # Response body: will assign HTTP/1.0 200 OK
                                        PageletResponse,  # A generic response
                                    ]]] = dict()
+# The pagelet initialization functions, to be executed upon startup
+_PAGELET_INIT_FUNCTIONS: List[Callable[[Dict[str, str], logging.Logger], None]] = []
 
 # Inactivity timeout for client sessions
 _SESSION_TIMEOUT: int = 3600
@@ -94,6 +97,28 @@ def pagelet(path: str):
     return http_handler
 
 
+def pagelet_init(fun: Callable[[Dict[str, str], logging.Logger], None]):
+    """
+    Annotate a function to act as a pagelet initialization function.  The function will be called when the webserver is
+    started.  The function should set up everything required for pagelets to operate correctly, e.g. providing default
+    values for configuration items, or performing database schema migrations.
+
+    Any exception thrown by an initialization function will cause the web server to seize operation.  Multiple
+    initialization functions can be used.
+
+    The function must have the following signature:
+
+        (config: Dict[str, str], logger: logging.Logger) -> None
+
+        config:       The mutable dictionary of variables read from the [Pagelets] section of the configuration file.
+        logger:       The server's logger instance.
+        returns:      Nothing.
+
+    :param fun: The function to annotate
+    """
+    _PAGELET_INIT_FUNCTIONS.append(fun)
+
+
 class MatematHTTPServer(HTTPServer):
     """
     A http.server.HTTPServer subclass that acts as a container for data that must be persistent between requests.
@@ -184,8 +209,20 @@ class MatematWebserver(object):
 
     def start(self) -> None:
         """
-        Start the web server.  This call blocks while the server is running.
+        Call all pagelet initialization functions and start the web server.  This call blocks while the server is
+        running.  If any exception is raised in the initialization phase, the program is terminated with a non-zero
+        exit code.
         """
+        try:
+            # Run all pagelet initialization functions
+            for fun in _PAGELET_INIT_FUNCTIONS:
+                fun(self._httpd.pagelet_variables, self._httpd.logger)
+        except BaseException as e:
+            # If an error occurs, log it and terminate
+            self._httpd.logger.exception(e)
+            self._httpd.logger.critical('An initialization pagelet raised an error.  Stopping.')
+            sys.exit(1)
+        # If pagelet initialization went fine, start the HTTP server
         self._httpd.serve_forever()
 
 

matemat/webserver/pagelets/__init__.py

@@ -4,6 +4,7 @@ This package contains the pagelet functions served by the Matemat software.
 A new pagelet function must be imported here to be automatically loaded when the server is started.
 """
 
+from .initialization import initialization
 from .main import main_page
 from .login import login_page
 from .logout import logout

matemat/webserver/pagelets/initialization.py

@@ -0,0 +1,28 @@
+from typing import Dict
+
+import logging
+
+from matemat.webserver import pagelet_init
+from matemat.db import MatematDatabase
+
+
+@pagelet_init
+def initialization(config: Dict[str, str],
+                   logger: logging.Logger) -> None:
+    """
+    The pagelet initialization function.  Makes sure everything is ready for operation.  If anything fails here, the web
+    server won't resume operation.
+    """
+    # Set default values for missing config items
+    if 'InstanceName' not in config:
+        config['InstanceName'] = 'Matemat'
+        logger.warning('Property \'InstanceName\' not set, using \'Matemat\'')
+    if 'UploadDir' not in config:
+        config['UploadDir'] = './static/upload/'
+        logger.warning('Property \'UploadDir\' not set, using \'./static/upload/\'')
+    if 'DatabaseFile' not in config:
+        config['DatabaseFile'] = './matemat.db'
+        logger.warning('Property \'DatabaseFile\' not set, using \'./matemat.db\'')
+    with MatematDatabase(config['DatabaseFile']):
+        # Connect to the database to create it and perform any schema migrations
+        pass