Simplify the internal definition of processors (#36)

This removes the weird "extend(class().setup())" pattern in favor of a more
straightforward approach:

* Some processors are simply functions: let's define them as such
* Some processors need other processors to run in the big picture: they are
  connected by specific "setup" functions

structlog_gcp/base.py

@@ -1,21 +1,35 @@
 import structlog.processors
 from structlog.typing import Processor
 
-from . import errors, processors
+from . import error_reporting, processors
 
 
 def build_processors(
     service: str | None = None,
     version: str | None = None,
 ) -> list[Processor]:
-    procs = []
-
-    procs.extend(processors.CoreCloudLogging().setup())
-    procs.extend(processors.LogSeverity().setup())
-    procs.extend(processors.CodeLocation().setup())
-    procs.extend(errors.ReportException().setup())
-    procs.extend(errors.ReportError(["CRITICAL"]).setup())
-    procs.extend(errors.ServiceContext(service, version).setup())
-    procs.extend(processors.FormatAsCloudLogging().setup())
+    procs: list[Processor] = []
+
+    # Add a timestamp in ISO 8601 format.
+    procs.append(structlog.processors.TimeStamper(fmt="iso"))
+    procs.append(processors.init_cloud_logging)
+
+    procs.extend(processors.setup_log_severity())
+    procs.extend(processors.setup_code_location())
+
+    # Errors: log exceptions
+    procs.extend(error_reporting.setup_exceptions())
+
+    # Errors: formatter for Error Reporting
+    procs.append(error_reporting.ReportError(["CRITICAL"]))
+
+    # Errors: add service context
+    procs.append(error_reporting.ServiceContext(service, version))
+
+    # Finally: Cloud Logging formatter
+    procs.append(processors.finalize_cloud_logging)
+
+    # Format as JSON
     procs.append(structlog.processors.JSONRenderer())
+
     return procs

structlog_gcp/errors.py → structlog_gcp/error_reporting.py

@@ -1,41 +1,13 @@
 import os
 
-import structlog
+import structlog.processors
 from structlog.typing import EventDict, Processor, WrappedLogger
 
 from .types import CLOUD_LOGGING_KEY, ERROR_EVENT_TYPE, SOURCE_LOCATION_KEY
 
 
-class ServiceContext:
-    def __init__(self, service: str | None = None, version: str | None = None) -> None:
-        # https://cloud.google.com/functions/docs/configuring/env-var#runtime_environment_variables_set_automatically
-        if service is None:
-            service = os.environ.get("K_SERVICE", "unknown service")
-
-        if version is None:
-            version = os.environ.get("K_REVISION", "unknown version")
-
-        self.service_context = {"service": service, "version": version}
-
-    def setup(self) -> list[Processor]:
-        return [self]
-
-    def __call__(
-        self, logger: WrappedLogger, method_name: str, event_dict: EventDict
-    ) -> EventDict:
-        """Add a service context in which an error has occurred.
-
-        This is part of the Error Reporting API, so it's only added when an error happens.
-        """
-
-        event_type = event_dict[CLOUD_LOGGING_KEY].get("@type")
-        if event_type != ERROR_EVENT_TYPE:
-            return event_dict
-
-        # https://cloud.google.com/error-reporting/reference/rest/v1beta1/ServiceContext
-        event_dict[CLOUD_LOGGING_KEY]["serviceContext"] = self.service_context
-
-        return event_dict
+def setup_exceptions(log_level: str = "CRITICAL") -> list[Processor]:
+    return [structlog.processors.format_exc_info, ReportException(log_level)]
 
 
 class ReportException:
@@ -47,9 +19,6 @@ class ReportException:
     def __init__(self, log_level: str = "CRITICAL") -> None:
         self.log_level = log_level
 
-    def setup(self) -> list[Processor]:
-        return [structlog.processors.format_exc_info, self]
-
     def __call__(
         self, logger: WrappedLogger, method_name: str, event_dict: EventDict
     ) -> EventDict:
@@ -80,19 +49,6 @@ class ReportError:
     def __init__(self, severities: list[str]) -> None:
         self.severities = severities
 
-    def setup(self) -> list[Processor]:
-        return [self]
-
-    def _build_service_context(self) -> dict[str, str]:
-        # https://cloud.google.com/error-reporting/reference/rest/v1beta1/ServiceContext
-        service_context = {
-            # https://cloud.google.com/functions/docs/configuring/env-var#runtime_environment_variables_set_automatically
-            "service": os.environ.get("K_SERVICE", "unknown service"),
-            "version": os.environ.get("K_REVISION", "unknown version"),
-        }
-
-        return service_context
-
     def __call__(
         self, logger: WrappedLogger, method_name: str, event_dict: EventDict
     ) -> EventDict:
@@ -108,6 +64,37 @@ def __call__(
 
         event_dict[CLOUD_LOGGING_KEY]["@type"] = ERROR_EVENT_TYPE
         event_dict[CLOUD_LOGGING_KEY]["context"] = error_context
-        event_dict[CLOUD_LOGGING_KEY]["serviceContext"] = self._build_service_context()
+
+        # "serviceContext" should be added by the ServiceContext processor.
+        # event_dict[CLOUD_LOGGING_KEY]["serviceContext"]
+
+        return event_dict
+
+
+class ServiceContext:
+    def __init__(self, service: str | None = None, version: str | None = None) -> None:
+        # https://cloud.google.com/functions/docs/configuring/env-var#runtime_environment_variables_set_automatically
+        if service is None:
+            service = os.environ.get("K_SERVICE", "unknown service")
+
+        if version is None:
+            version = os.environ.get("K_REVISION", "unknown version")
+
+        self.service_context = {"service": service, "version": version}
+
+    def __call__(
+        self, logger: WrappedLogger, method_name: str, event_dict: EventDict
+    ) -> EventDict:
+        """Add a service context in which an error has occurred.
+
+        This is part of the Error Reporting API, so it's only added when an error happens.
+        """
+
+        event_type = event_dict[CLOUD_LOGGING_KEY].get("@type")
+        if event_type != ERROR_EVENT_TYPE:
+            return event_dict
+
+        # https://cloud.google.com/error-reporting/reference/rest/v1beta1/ServiceContext
+        event_dict[CLOUD_LOGGING_KEY]["serviceContext"] = self.service_context
 
         return event_dict

structlog_gcp/processors.py

@@ -9,31 +9,40 @@
 from .types import CLOUD_LOGGING_KEY, SOURCE_LOCATION_KEY
 
 
-class CoreCloudLogging:
-    """Initialize the Google Cloud Logging event message"""
+def setup_log_severity() -> list[Processor]:
+    return [structlog.processors.add_log_level, LogSeverity()]
+
 
-    def setup(self) -> list[Processor]:
-        return [
-            # If some value is in bytes, decode it to a unicode str.
-            structlog.processors.UnicodeDecoder(),
-            # Add a timestamp in ISO 8601 format.
-            structlog.processors.TimeStamper(fmt="iso"),
-            self,
+def setup_code_location() -> list[Processor]:
+    call_site_processors = structlog.processors.CallsiteParameterAdder(
+        parameters=[
+            structlog.processors.CallsiteParameter.PATHNAME,
+            structlog.processors.CallsiteParameter.MODULE,
+            structlog.processors.CallsiteParameter.FUNC_NAME,
+            structlog.processors.CallsiteParameter.LINENO,
         ]
+    )
 
-    def __call__(
-        self, logger: WrappedLogger, method_name: str, event_dict: EventDict
-    ) -> EventDict:
-        value = {
-            "message": event_dict.pop("event"),
-            "time": event_dict.pop("timestamp"),
-        }
+    return [call_site_processors, code_location]
 
-        event_dict[CLOUD_LOGGING_KEY] = value
-        return event_dict
+
+def init_cloud_logging(
+    logger: WrappedLogger, method_name: str, event_dict: EventDict
+) -> EventDict:
+    """Initialize the Google Cloud Logging event message"""
+
+    value = {
+        "message": event_dict.pop("event"),
+        "time": event_dict.pop("timestamp"),
+    }
+
+    event_dict[CLOUD_LOGGING_KEY] = value
+    return event_dict
 
 
-class FormatAsCloudLogging:
+def finalize_cloud_logging(
+    logger: WrappedLogger, method_name: str, event_dict: EventDict
+) -> EventDict:
     """Finalize the Google Cloud Logging event message and replace the logging event.
 
     This is not exactly the format the Cloud Logging directly ingests, but
@@ -43,29 +52,28 @@ class FormatAsCloudLogging:
     See: https://cloud.google.com/logging/docs/structured-logging#special-payload-fields
     """
 
-    def setup(self) -> list[Processor]:
-        return [self]
+    # Take out the Google Cloud Logging set of fields from the event dict
+    gcp_event: EventDict = event_dict.pop(CLOUD_LOGGING_KEY)
 
-    def __call__(
-        self, logger: WrappedLogger, method_name: str, event_dict: EventDict
-    ) -> EventDict:
-        # Take out the Google Cloud Logging set of fields from the event dict
-        gcp_event: EventDict = event_dict.pop(CLOUD_LOGGING_KEY)
+    # Override whatever is left from the event dict with the content of all
+    # the Google Cloud Logging-formatted fields.
+    event_dict.update(gcp_event)
 
-        # Override whatever is left from the event dict with the content of all
-        # the Google Cloud Logging-formatted fields.
-        event_dict.update(gcp_event)
+    # Fields which are not known by Google Cloud Logging will be added to
+    # the `jsonPayload` field.
+    #
+    # See the `message` field documentation in:
+    # https://cloud.google.com/logging/docs/structured-logging#special-payload-fields
 
-        # Fields which are not known by Google Cloud Logging will be added to
-        # the `jsonPayload` field.
-        # See the `message` field documentation in:
-        # https://cloud.google.com/logging/docs/structured-logging#special-payload-fields
-
-        return event_dict
+    return event_dict
 
 
 class LogSeverity:
-    """Set the severity using the Google Cloud Logging severities"""
+    """Set the severity using the Google Cloud Logging severities.
+
+
+    See: https://cloud.google.com/logging/docs/reference/v2/rest/v2/LogEntry#LogSeverity
+    """
 
     def __init__(self) -> None:
         self.default = "notset"
@@ -84,17 +92,10 @@ def __init__(self) -> None:
             # "emergency": "EMERGENCY", #	One or more systems are unusable.
         }
 
-    def setup(self) -> list[Processor]:
-        # Add log level to event dict.
-        return [structlog.processors.add_log_level, self]
-
     def __call__(
         self, logger: WrappedLogger, method_name: str, event_dict: EventDict
     ) -> EventDict:
-        """Format a Python log level value as a GCP log severity.
-
-        See: https://cloud.google.com/logging/docs/reference/v2/rest/v2/LogEntry#LogSeverity
-        """
+        """Format a Python log level value as a GCP log severity."""
 
         log_level = event_dict.pop("level")
         severity = self.mapping.get(log_level, self.default)
@@ -103,30 +104,17 @@ def __call__(
         return event_dict
 
 
-class CodeLocation:
+def code_location(
+    logger: WrappedLogger, method_name: str, event_dict: EventDict
+) -> EventDict:
     """Inject the location of the logging message into the logs"""
 
-    def setup(self) -> list[Processor]:
-        # Add callsite parameters.
-        call_site_proc = structlog.processors.CallsiteParameterAdder(
-            parameters=[
-                structlog.processors.CallsiteParameter.PATHNAME,
-                structlog.processors.CallsiteParameter.MODULE,
-                structlog.processors.CallsiteParameter.FUNC_NAME,
-                structlog.processors.CallsiteParameter.LINENO,
-            ]
-        )
-        return [call_site_proc, self]
+    location = {
+        "file": event_dict.pop("pathname"),
+        "line": str(event_dict.pop("lineno")),
+        "function": f"{event_dict.pop('module')}:{event_dict.pop('func_name')}",
+    }
 
-    def __call__(
-        self, logger: WrappedLogger, method_name: str, event_dict: EventDict
-    ) -> EventDict:
-        location = {
-            "file": event_dict.pop("pathname"),
-            "line": str(event_dict.pop("lineno")),
-            "function": f"{event_dict.pop('module')}:{event_dict.pop('func_name')}",
-        }
-
-        event_dict[CLOUD_LOGGING_KEY][SOURCE_LOCATION_KEY] = location
+    event_dict[CLOUD_LOGGING_KEY][SOURCE_LOCATION_KEY] = location
 
-        return event_dict
+    return event_dict

tests/conftest.py

@@ -22,6 +22,7 @@ def mock_logger_env():
     ):
         yield
 
+
 @pytest.fixture
 def logger(mock_logger_env):
     """Setup a logger for testing and return it"""

tests/test_log.py

@@ -22,7 +22,7 @@ def test_normal(stdout, logger):
         "severity": "INFO",
         "time": "2023-04-01T08:00:00.000000Z",
     }
-    assert expected == msg
+    assert msg == expected
 
 
 def test_error(stdout, logger):
@@ -57,7 +57,7 @@ def test_error(stdout, logger):
         "stack_trace": "oh noes\nTraceback blabla",
         "time": "2023-04-01T08:00:00.000000Z",
     }
-    assert expected == msg
+    assert msg == expected
 
 
 def test_service_context_default(stdout, logger):
@@ -144,4 +144,4 @@ def test_extra_labels(stdout, logger):
         "test4": {"foo": "bar"},
         "test5": {"date": "datetime.date(2023, 1, 1)"},
     }
-    assert expected == msg
+    assert msg == expected