[Bug fix] JSON logs - Ensure only 1 log is emitted (previously duplicate json logs were getting emitted) (#10580)

* fix logging with JSON logs

* test: test_initialize_loggers_with_handler_sets_propagate_false

litellm/_logging.py

@@ -103,31 +103,36 @@ verbose_proxy_logger = logging.getLogger("LiteLLM Proxy")
 verbose_router_logger = logging.getLogger("LiteLLM Router")
 verbose_logger = logging.getLogger("LiteLLM")
 
-# Add the handler to the logger
-verbose_router_logger.addHandler(handler)
-verbose_proxy_logger.addHandler(handler)
-verbose_logger.addHandler(handler)
+ALL_LOGGERS = [
+    logging.getLogger(),
+    verbose_logger,
+    verbose_router_logger,
+    verbose_proxy_logger,
+]
+
+
+def _initialize_loggers_with_handler(handler: logging.Handler):
+    """
+    Initialize all loggers with a handler
+
+    - Adds a handler to each logger
+    - Prevents bubbling to parent/root (critical to prevent duplicate JSON logs)
+    """
+    for lg in ALL_LOGGERS:
+        lg.handlers.clear()  # remove any existing handlers
+        lg.addHandler(handler)  # add JSON formatter handler
+        lg.propagate = False  # prevent bubbling to parent/root
 
 
 def _turn_on_json():
+    """
+    Turn on JSON logging
+
+    - Adds a JSON formatter to all loggers
+    """
     handler = logging.StreamHandler()
     handler.setFormatter(JsonFormatter())
-
-    # Define all loggers to update, including root logger
-    loggers = [logging.getLogger()] + [
-        verbose_router_logger,
-        verbose_proxy_logger,
-        verbose_logger,
-    ]
-
-    # Iterate through each logger and update its handlers
-    for logger in loggers:
-        # Remove all existing handlers
-        for h in logger.handlers[:]:
-            logger.removeHandler(h)
-        # Add the new handler
-        logger.addHandler(handler)
-
+    _initialize_loggers_with_handler(handler)
     # Set up exception handlers
     _setup_json_exception_handlers(JsonFormatter())
 

litellm/proxy/proxy_config.yaml

@@ -4,6 +4,6 @@ model_list:
       model: openai/gpt-4o
       api_key: os.environ/OPENAI_API_KEY
 
-litellm_settings:
-  success_callback: ["generic_api"]
 
+litellm_settings:
+    json_logs: true

tests/litellm/test_logging.py

@@ -0,0 +1,71 @@
+import datetime
+import json
+import os
+import sys
+import unittest
+from typing import List, Optional, Tuple
+from unittest.mock import ANY, MagicMock, Mock, patch
+
+import httpx
+import pytest
+
+sys.path.insert(
+    0, os.path.abspath("../../..")
+)  # Adds the parent directory to the system-path
+import io
+import logging
+import sys
+import unittest
+from contextlib import redirect_stdout
+
+import litellm
+from litellm._logging import (
+    ALL_LOGGERS,
+    _initialize_loggers_with_handler,
+    verbose_logger,
+    verbose_proxy_logger,
+    verbose_router_logger,
+)
+
+
+def test_json_mode_emits_one_record_per_logger(capfd):
+    # Turn on JSON logging
+    litellm._logging._turn_on_json()
+    # Make sure our loggers will emit INFO-level records
+    for lg in (verbose_logger, verbose_router_logger, verbose_proxy_logger):
+        lg.setLevel(logging.INFO)
+
+    # Log one message from each logger at different levels
+    verbose_logger.info("first info")
+    verbose_router_logger.info("second info from router")
+    verbose_proxy_logger.info("third info from proxy")
+
+    # Capture stdout
+    out, err = capfd.readouterr()
+    print("out", out)
+    print("err", err)
+    lines = [l for l in err.splitlines() if l.strip()]
+
+    # Expect exactly three JSON lines
+    assert len(lines) == 3, f"got {len(lines)} lines, want 3: {lines!r}"
+
+    # Each line must be valid JSON with the required fields
+    for line in lines:
+        obj = json.loads(line)
+        assert "message" in obj, "`message` key missing"
+        assert "level" in obj, "`level` key missing"
+        assert "timestamp" in obj, "`timestamp` key missing"
+
+
+def test_initialize_loggers_with_handler_sets_propagate_false():
+    """
+    Test that the initialize_loggers_with_handler function sets propagate to False for all loggers
+    """
+    # Initialize loggers with the test handler
+    _initialize_loggers_with_handler(logging.StreamHandler())
+
+    # Check that propagate is set to False for all loggers
+    for logger in ALL_LOGGERS:
+        assert (
+            logger.propagate is False
+        ), f"Logger {logger.name} has propagate set to {logger.propagate}, expected False"