Add custom log handler for sending logs to UI

src/openflexure_microscope_server/logging.py

@@ -11,6 +11,7 @@ OFM_LOG_FILE = os.path.join(OFM_LOG_FOLDER, "openflexure_microscope.log")
 def configure_logging():
     root_logger = logging.getLogger()
     root_logger.setLevel(logging.INFO)
+
     try:
         if not os.path.exists(OFM_LOG_FOLDER):
             os.makedirs(OFM_LOG_FOLDER)
@@ -20,10 +21,13 @@ def configure_logging():
             maxBytes=1000000,
             backupCount=10,
         )
-        handler.setFormatter(
-            logging.Formatter("[%(asctime)s] [%(levelname)s] %(message)s")
-        )
+        format_str = "[%(asctime)s] [%(levelname)s] <%(name)s> %(message)s"
+        handler.setFormatter(logging.Formatter(format_str))
         root_logger.addHandler(handler)
+        ofm_format_str = "[%(asctime)s] [%(levelname)s] %(message)s"
+        OFM_HANDLER.setFormatter(logging.Formatter(ofm_format_str))
+        root_logger.addHandler(OFM_HANDLER)
+
     except PermissionError as e:
         logging.warning(f"Cannot create log file at {OFM_LOG_FILE}: {e}")
     logging.info("")
@@ -33,5 +37,65 @@ def configure_logging():
 
 
 def retrieve_log() -> PlainTextResponse:
-    """The most recent 1Mb of logs from the server"""
-    return FileResponse(OFM_LOG_FILE, media_type=PlainTextResponse.media_type)
+    """
+    Returns logs since we started running the server, up to a maxiumum of
+    250 messages. This log is the one shown in the UI and on the logging page.
+
+    It does not include any of the `uvicorn.access` logs as these are emmitted
+    every time any API route is called.
+
+    All logs, including `uvicorn.access` are logged to the OFM_LOG_FILE (see above)
+    ths is the best place to get logs about crashes.
+    """
+    return PlainTextResponse(OFM_HANDLER.log_history)
+
+
+class OFMHandler(logging.Handler):
+    """
+    A child class of logging.Handler. This class handles storing the most recent
+    logs for access by the server.
+    """
+
+    def __init__(self, level=logging.INFO, max_logs=250):
+        super().__init__(level=level)
+        self._log = []
+        self._max_logs = max_logs
+
+    def append_record(self, record):
+        """
+        Use the built in formatter to format the record, then save
+        it to an array. Pop any in excess of the mamimum number of logs
+        """
+        self._log.append(self.format(record))
+        while len(self._log) > self._max_logs:
+            self._log.pop(0)
+
+    def emit(self, record):
+        """
+        Emit will save the logged record to the log
+        """
+
+        # Basic filter for now that simply stops uvicorn.access logs
+        # These are the logs each time an API endpoint is accessed
+        # This is only the log for the UI.
+        if record.name.startswith("uvicorn.access"):
+            return
+        try:
+            if record.levelno >= self.level:
+                self.append_record(record)
+        except RecursionError as e:
+            raise e
+        except BaseException:
+            # Never let the logger crash unless there is somehow recursion.
+            # Use built in logging error handler
+            self.handleError(record)
+
+    @property
+    def log_history(self):
+        """
+        Return the log history up to the maximum number of logs
+        """
+        return "\n".join(self._log)
+
+
+OFM_HANDLER = OFMHandler()