Add support for adding callables as extra tags

README.md

@@ -88,3 +88,65 @@ logger = logging.getLogger("my-logger")
 logger.addHandler(handler)
 logger.error(...)
 ```
+
+Adding extra callable tags
+--------------------------
+
+Having a prior definition of:
+```python
+import logging
+import logging_loki
+from multiprocessing import Queue
+from myapp.tracing import tracer
+
+get_context = lambda: tracer.active_span.context
+add_trace_id = lambda: hex(get_context().trace_id)[
+                       2:] if tracer is not None and tracer.active_span is not None else None
+add_span_id = lambda: hex(get_context().span_id)[2:] if tracer is not None and tracer.active_span else None
+```
+
+If you want to add extra span IDs or trace IDs do the following:
+
+```python
+handler = logging_loki.LokiQueueHandler(
+    Queue(-1),
+    url="https://my-loki-instance/loki/api/v1/push", 
+    tags={"application": "my-app", 'span_id': add_span_id, 'trace_id': add_trace_id},
+    auth=("username", "password"),
+    version="1"
+)
+logger = logging.getLogger("my-logger")
+logger.addHandler(handler)
+logger.error(...)
+```
+
+Basically if your callable returns a non-None value, it will be added as a tag. No casting to string will be made.
+
+You can use also the blocking approach of:
+
+```python
+handler = logging_loki.LokiHandler(
+    url="https://my-loki-instance/loki/api/v1/push", 
+    tags={"application": "my-app", "trace_id": add_trace_id, "span_id": add_span_id},
+    auth=("username", "password"),
+    version="1",
+)
+
+logger = logging.getLogger("my-logger")
+logger.addHandler(handler)
+logger.error(
+    "Something happened", 
+    extra={"tags": {"service": "my-service"}},
+)
+```
+
+
+Supplying extra tags
+--------------------
+
+If you want to supply extra tags, you can do it twofold:
+
+```python
+logger.error('Something happened', extra={'test': 4})
+logger.error('Something happened', extra={'tags': {'test': 4}})
+```

logging_loki/emitter.py

@@ -20,6 +20,9 @@
 BasicAuth = Optional[Tuple[str, str]]
 
 
+KEYS_TO_SKIP = {'severity', 'logger', 'msg', 'message', 'tags', 'lineno'}
+
+
 class LokiEmitter(abc.ABC):
     """Base Loki emitter class."""
 
@@ -30,6 +33,17 @@ class LokiEmitter(abc.ABC):
     label_replace_with = const.label_replace_with
     session_class = requests.Session
 
+    @staticmethod
+    def get_entry_labels(record: logging.LogRecord, line: int) -> dict:
+        labels = {}
+        for key, value in record.__dict__.items():
+            if key in KEYS_TO_SKIP:
+                continue
+            if value:
+                labels[key] = value
+        labels['line_no'] = line
+        return labels
+
     def __init__(self, url: str, tags: Optional[dict] = None, auth: BasicAuth = None):
         """
         Create new Loki emitter.
@@ -89,7 +103,6 @@ def format_label(self, label: str) -> str:
     def build_tags(self, record: logging.LogRecord) -> Dict[str, Any]:
         """Return tags that must be send to Loki with a log record."""
         tags = dict(self.tags) if isinstance(self.tags, ConvertingDict) else self.tags
-        tags = copy.deepcopy(tags)
         tags[self.level_tag] = record.levelname.lower()
         tags[self.logger_tag] = record.name
 
@@ -99,9 +112,8 @@ def build_tags(self, record: logging.LogRecord) -> Dict[str, Any]:
 
         for tag_name, tag_value in extra_tags.items():
             cleared_name = self.format_label(tag_name)
-            if cleared_name:
+            if cleared_name and tag_value:
                 tags[cleared_name] = tag_value
-
         return tags
 
 
@@ -138,6 +150,6 @@ def build_payload(self, record: logging.LogRecord, line) -> dict:
         ts = str(int(time.time() * ns))
         stream = {
             "stream": labels,
-            "values": [[ts, line]],
+            "values": [[ts, line, LokiEmitter.get_entry_labels(record, line)]],
         }
         return {"streams": [stream]}

logging_loki/handlers.py

@@ -1,30 +1,60 @@
 # -*- coding: utf-8 -*-
-
+import copy
 import logging
 import warnings
 from logging.handlers import QueueHandler
 from logging.handlers import QueueListener
 from queue import Queue
-from typing import Dict
+from typing import Dict, Callable, Any, Union
 from typing import Optional
 from typing import Type
 
 from logging_loki import const
 from logging_loki import emitter
 
 
-class LokiQueueHandler(QueueHandler):
+class TagMixin:
+    """
+    A mixin class to support callable tags.
+
+    This is to be inherited from as a first class, eg
+    >>> class Handler(TagMixin, logging.Handler):
+    >>>     pass
+    """
+
+    def __init__(self, tags=None):
+        self.tags = tags or {}
+
+    def prepare(self, record):
+        # This is invoked in the same thread in which logging is invoked
+        # assume the second class has a proper solution for prepare()
+        try:
+            record = self.__class__.__bases__[1].prepare(self, record)
+        except AttributeError:      # logging.Handler has no prepare
+            pass
+        record.tags = getattr(record, 'tags', {})
+        for key, value in (self.tags | record.tags).items():
+            if callable(value):
+                value = value()
+            if value is None:
+                continue
+            record.__dict__[key] = value
+        return record
+
+
+class LokiQueueHandler(TagMixin, QueueHandler):
     """This handler automatically creates listener and `LokiHandler` to handle logs queue."""
 
     def __init__(self, queue: Queue, **kwargs):
         """Create new logger handler with the specified queue and kwargs for the `LokiHandler`."""
-        super().__init__(queue)
+        QueueHandler.__init__(self, queue)
+        TagMixin.__init__(self, kwargs.get("tags"))
         self.handler = LokiHandler(**kwargs)  # noqa: WPS110
         self.listener = QueueListener(self.queue, self.handler)
         self.listener.start()
 
 
-class LokiHandler(logging.Handler):
+class LokiHandler(TagMixin, logging.Handler):
     """
     Log handler that sends log records to Loki.
 
@@ -39,7 +69,7 @@ class LokiHandler(logging.Handler):
     def __init__(
         self,
         url: str,
-        tags: Optional[dict] = None,
+        tags: Optional[Dict[str, Union[Any, Callable]]] = None,
         auth: Optional[emitter.BasicAuth] = None,
         version: Optional[str] = None,
     ):
@@ -53,7 +83,8 @@ def __init__(
             version: Version of Loki emitter to use.
 
         """
-        super().__init__()
+        logging.Handler.__init__(self)
+        TagMixin.__init__(self, tags)
 
         if version is None and const.emitter_ver == "0":
             msg = (
@@ -65,9 +96,10 @@ def __init__(
             warnings.warn(" ".join(msg), DeprecationWarning)
 
         version = version or const.emitter_ver
-        if version not in self.emitters:
-            raise ValueError("Unknown emitter version: {0}".format(version))
-        self.emitter = self.emitters[version](url, tags, auth)
+        try:
+            self.emitter = self.emitters[version](url, tags, auth)
+        except KeyError as exc:
+            raise ValueError("Unknown emitter version: {0}".format(version)) from exc
 
     def handleError(self, record):  # noqa: N802
         """Close emitter and let default handler take actions on error."""
@@ -76,8 +108,9 @@ def handleError(self, record):  # noqa: N802
 
     def emit(self, record: logging.LogRecord):
         """Send log record to Loki."""
+        record = self.prepare(record)
         # noinspection PyBroadException
         try:
-            self.emitter(record, self.format(record))
+            self.emitter(record, record.lineno)
         except Exception:
             self.handleError(record)

tests/test_emitter_v1.py

@@ -176,3 +176,4 @@ def test_can_build_tags_from_converting_dict(emitter_v1):
     logger = logging.getLogger(logger_name)
     emitter: LokiEmitterV1 = logger.handlers[0].handler.emitter
     emitter.build_tags(create_record())
+    payload = emitter.build_payload(create_record(), 10)

tests/test_real_logs.py

@@ -0,0 +1,76 @@
+def test_callable_tags():
+    class MyEmitter(LokiEmitterV1):
+
+        def build_payload(self, record, line) -> dict:
+            labels = self.build_tags(record)
+            ns = 1e9
+            ts = str(int(time.time() * ns))
+            stream = {
+                "stream": labels,
+                "values": [[ts, line, self.get_entry_labels(record, line)]],
+            }
+            return {"streams": [stream]}
+
+        def __call__(self, record, line_no):
+            payload = self.build_payload(record, line_no)
+            stream = payload['streams'][0]['values'][0][2]
+            assert 'application' in stream
+            assert stream['value'] == 5
+            assert stream['device'] == 'test'
+            assert stream['levelname'] == 'WARNING'
+
+    # Register a mock emitter
+    logging_loki.LokiHandler.emitters['mock_emitter'] = MyEmitter
+
+    handler = logging_loki.LokiHandler(
+        url="https://example.com/loki/api/v1/push",
+        tags={"application": "my-app", 'value': lambda: 5},
+        auth=("username", "password"),
+        version="mock_emitter"
+    )
+    logger = logging.getLogger("my-logger")
+    logger.addHandler(handler)
+    logger.warning('Error occurred', extra={'device': 'test'})
+
+
+import logging
+import time
+
+import logging_loki
+from logging_loki.emitter import LokiEmitterV1
+
+
+def test_callable_tags():
+    class MyEmitter(LokiEmitterV1):
+
+        def build_payload(self, record, line) -> dict:
+            labels = self.build_tags(record)
+            ns = 1e9
+            ts = str(int(time.time() * ns))
+            stream = {
+                "stream": labels,
+                "values": [[ts, line, self.get_entry_labels(record, line)]],
+            }
+            return {"streams": [stream]}
+
+        def __call__(self, record, line_no):
+            payload = self.build_payload(record, line_no)
+            stream = payload['streams'][0]['values'][0][2]
+            assert 'application' in stream
+            assert stream['value'] == 5
+            assert stream['device'] == 'test'
+            assert stream['levelname'] == 'WARNING'
+
+    # Register a mock emitter
+    logging_loki.LokiHandler.emitters['mock_emitter'] = MyEmitter
+
+    handler = logging_loki.LokiHandler(
+        url="https://example.com/loki/api/v1/push",
+        tags={"application": "my-app", 'value': lambda: 5},
+        auth=("username", "password"),
+        version="mock_emitter"
+    )
+    logger = logging.getLogger("my-logger")
+    logger.addHandler(handler)
+    logger.warning('Error occurred', extra={'tags': {'device': 'test'}})
+    logger.warning('Error occurred', extra={'device': 'test'})