feat: Add --enable-log-outputs flag for logging model generations (vllm-project#20707)

Signed-off-by: Adrian Garcia <[email protected]>

Author: mizadri

tests/test_logger.py

@@ -10,11 +10,12 @@
 from json.decoder import JSONDecodeError
 from tempfile import NamedTemporaryFile
 from typing import Any
-from unittest.mock import patch
+from unittest.mock import MagicMock, patch
 from uuid import uuid4
 
 import pytest
 
+from vllm.entrypoints.logger import RequestLogger
 from vllm.logger import (_DATE_FORMAT, _FORMAT, _configure_vllm_root_logger,
                          enable_trace_function_call, init_logger)
 from vllm.logging_utils import NewLineFormatter
@@ -228,9 +229,10 @@ def test_prepare_object_to_dump():
     list_obj = [1, 2, 3]
     assert prepare_object_to_dump(list_obj) == '[1, 2, 3]'
 
-    dict_obj = {'a': 1, 'b': 'b'}
+    dict_obj = {"a": 1, "b": "b"}
     assert prepare_object_to_dump(dict_obj) in [
-        "{a: 1, b: 'b'}", "{b: 'b', a: 1}"
+        "{a: 1, b: 'b'}",
+        "{b: 'b', a: 1}",
     ]
 
     set_obj = {1, 2, 3}
@@ -252,4 +254,246 @@ class CustomClass:
         b: str
 
     assert (prepare_object_to_dump(CustomClass(
-        1, 'b')) == "CustomClass(a=1, b='b')")
+        1, "b")) == "CustomClass(a=1, b='b')")
+
+
+def test_request_logger_log_outputs():
+    """Test the new log_outputs functionality."""
+    # Create a mock logger to capture log calls
+    mock_logger = MagicMock()
+
+    with patch("vllm.entrypoints.logger.logger", mock_logger):
+        request_logger = RequestLogger(max_log_len=None)
+
+        # Test basic output logging
+        request_logger.log_outputs(
+            request_id="test-123",
+            outputs="Hello, world!",
+            output_token_ids=[1, 2, 3, 4],
+            finish_reason="stop",
+            is_streaming=False,
+            delta=False,
+        )
+
+        mock_logger.info.assert_called_once()
+        call_args = mock_logger.info.call_args.args
+        assert "Generated response %s%s" in call_args[0]
+        assert call_args[1] == "test-123"
+        assert call_args[3] == "Hello, world!"
+        assert call_args[4] == [1, 2, 3, 4]
+        assert call_args[5] == "stop"
+
+
+def test_request_logger_log_outputs_streaming_delta():
+    """Test log_outputs with streaming delta mode."""
+    mock_logger = MagicMock()
+
+    with patch("vllm.entrypoints.logger.logger", mock_logger):
+        request_logger = RequestLogger(max_log_len=None)
+
+        # Test streaming delta logging
+        request_logger.log_outputs(
+            request_id="test-456",
+            outputs="Hello",
+            output_token_ids=[1],
+            finish_reason=None,
+            is_streaming=True,
+            delta=True,
+        )
+
+        mock_logger.info.assert_called_once()
+        call_args = mock_logger.info.call_args.args
+        assert "Generated response %s%s" in call_args[0]
+        assert call_args[1] == "test-456"
+        assert call_args[2] == " (streaming delta)"
+        assert call_args[3] == "Hello"
+        assert call_args[4] == [1]
+        assert call_args[5] is None
+
+
+def test_request_logger_log_outputs_streaming_complete():
+    """Test log_outputs with streaming complete mode."""
+    mock_logger = MagicMock()
+
+    with patch("vllm.entrypoints.logger.logger", mock_logger):
+        request_logger = RequestLogger(max_log_len=None)
+
+        # Test streaming complete logging
+        request_logger.log_outputs(
+            request_id="test-789",
+            outputs="Complete response",
+            output_token_ids=[1, 2, 3],
+            finish_reason="length",
+            is_streaming=True,
+            delta=False,
+        )
+
+        mock_logger.info.assert_called_once()
+        call_args = mock_logger.info.call_args.args
+        assert "Generated response %s%s" in call_args[0]
+        assert call_args[1] == "test-789"
+        assert call_args[2] == " (streaming complete)"
+        assert call_args[3] == "Complete response"
+        assert call_args[4] == [1, 2, 3]
+        assert call_args[5] == "length"
+
+
+def test_request_logger_log_outputs_with_truncation():
+    """Test log_outputs respects max_log_len setting."""
+    mock_logger = MagicMock()
+
+    with patch("vllm.entrypoints.logger.logger", mock_logger):
+        # Set max_log_len to 10
+        request_logger = RequestLogger(max_log_len=10)
+
+        # Test output truncation
+        long_output = "This is a very long output that should be truncated"
+        long_token_ids = list(range(20))  # 20 tokens
+
+        request_logger.log_outputs(
+            request_id="test-truncate",
+            outputs=long_output,
+            output_token_ids=long_token_ids,
+            finish_reason="stop",
+            is_streaming=False,
+            delta=False,
+        )
+
+        mock_logger.info.assert_called_once()
+        call_args = mock_logger.info.call_args
+
+        # Check that output was truncated to first 10 characters
+        logged_output = call_args[0][3]
+        assert logged_output == "This is a "
+        assert len(logged_output) == 10
+
+        # Check that token IDs were truncated to first 10 tokens
+        logged_token_ids = call_args[0][4]
+        assert logged_token_ids == list(range(10))
+        assert len(logged_token_ids) == 10
+
+
+def test_request_logger_log_outputs_none_values():
+    """Test log_outputs handles None values correctly."""
+    mock_logger = MagicMock()
+
+    with patch("vllm.entrypoints.logger.logger", mock_logger):
+        request_logger = RequestLogger(max_log_len=None)
+
+        # Test with None output_token_ids
+        request_logger.log_outputs(
+            request_id="test-none",
+            outputs="Test output",
+            output_token_ids=None,
+            finish_reason="stop",
+            is_streaming=False,
+            delta=False,
+        )
+
+        mock_logger.info.assert_called_once()
+        call_args = mock_logger.info.call_args.args
+        assert "Generated response %s%s" in call_args[0]
+        assert call_args[1] == "test-none"
+        assert call_args[3] == "Test output"
+        assert call_args[4] is None
+        assert call_args[5] == "stop"
+
+
+def test_request_logger_log_outputs_empty_output():
+    """Test log_outputs handles empty output correctly."""
+    mock_logger = MagicMock()
+
+    with patch("vllm.entrypoints.logger.logger", mock_logger):
+        request_logger = RequestLogger(max_log_len=5)
+
+        # Test with empty output
+        request_logger.log_outputs(
+            request_id="test-empty",
+            outputs="",
+            output_token_ids=[],
+            finish_reason="stop",
+            is_streaming=False,
+            delta=False,
+        )
+
+        mock_logger.info.assert_called_once()
+        call_args = mock_logger.info.call_args.args
+        assert "Generated response %s%s" in call_args[0]
+        assert call_args[1] == "test-empty"
+        assert call_args[3] == ""
+        assert call_args[4] == []
+        assert call_args[5] == "stop"
+
+
+def test_request_logger_log_outputs_integration():
+    """Test that log_outputs can be called alongside log_inputs."""
+    mock_logger = MagicMock()
+
+    with patch("vllm.entrypoints.logger.logger", mock_logger):
+        request_logger = RequestLogger(max_log_len=None)
+
+        # Test that both methods can be called without interference
+        request_logger.log_inputs(
+            request_id="test-integration",
+            prompt="Test prompt",
+            prompt_token_ids=[1, 2, 3],
+            prompt_embeds=None,
+            params=None,
+            lora_request=None,
+        )
+
+        request_logger.log_outputs(
+            request_id="test-integration",
+            outputs="Test output",
+            output_token_ids=[4, 5, 6],
+            finish_reason="stop",
+            is_streaming=False,
+            delta=False,
+        )
+
+        # Should have been called twice - once for inputs, once for outputs
+        assert mock_logger.info.call_count == 2
+
+        # Check that the calls were made with correct patterns
+        input_call = mock_logger.info.call_args_list[0][0]
+        output_call = mock_logger.info.call_args_list[1][0]
+
+        assert "Received request %s" in input_call[0]
+        assert input_call[1] == "test-integration"
+
+        assert "Generated response %s%s" in output_call[0]
+        assert output_call[1] == "test-integration"
+
+
+def test_streaming_complete_logs_full_text_content():
+    """Test that streaming complete logging includes
+      full accumulated text, not just token count."""
+    mock_logger = MagicMock()
+
+    with patch("vllm.entrypoints.logger.logger", mock_logger):
+        request_logger = RequestLogger(max_log_len=None)
+
+        # Test with actual content instead of token count format
+        full_response = "This is a complete response from streaming"
+        request_logger.log_outputs(
+            request_id="test-streaming-full-text",
+            outputs=full_response,
+            output_token_ids=None,
+            finish_reason="streaming_complete",
+            is_streaming=True,
+            delta=False,
+        )
+
+        mock_logger.info.assert_called_once()
+        call_args = mock_logger.info.call_args.args
+
+        # Verify the logged output is the full text, not a token count format
+        logged_output = call_args[3]
+        assert logged_output == full_response
+        assert "tokens>" not in logged_output
+        assert "streaming_complete" not in logged_output
+
+        # Verify other parameters
+        assert call_args[1] == "test-streaming-full-text"
+        assert call_args[2] == " (streaming complete)"
+        assert call_args[5] == "streaming_complete"

vllm/entrypoints/logger.py

@@ -1,6 +1,7 @@
 # SPDX-License-Identifier: Apache-2.0
 # SPDX-FileCopyrightText: Copyright contributors to the vLLM project
 
+from collections.abc import Sequence
 from typing import Optional, Union
 
 import torch
@@ -16,8 +17,6 @@
 class RequestLogger:
 
     def __init__(self, *, max_log_len: Optional[int]) -> None:
-        super().__init__()
-
         self.max_log_len = max_log_len
 
     def log_inputs(
@@ -45,3 +44,36 @@ def log_inputs(
             "lora_request: %s.", request_id, prompt, params, prompt_token_ids,
             prompt_embeds.shape if prompt_embeds is not None else None,
             lora_request)
+
+    def log_outputs(
+        self,
+        request_id: str,
+        outputs: str,
+        output_token_ids: Optional[Sequence[int]],
+        finish_reason: Optional[str] = None,
+        is_streaming: bool = False,
+        delta: bool = False,
+    ) -> None:
+        max_log_len = self.max_log_len
+        if max_log_len is not None:
+            if outputs is not None:
+                outputs = outputs[:max_log_len]
+
+            if output_token_ids is not None:
+                # Convert to list and apply truncation
+                output_token_ids = list(output_token_ids)[:max_log_len]
+
+        stream_info = ""
+        if is_streaming:
+            stream_info = (" (streaming delta)"
+                           if delta else " (streaming complete)")
+
+        logger.info(
+            "Generated response %s%s: output: %r, "
+            "output_token_ids: %s, finish_reason: %s",
+            request_id,
+            stream_info,
+            outputs,
+            output_token_ids,
+            finish_reason,
+        )

vllm/entrypoints/openai/cli_args.py

@@ -44,10 +44,10 @@ def __call__(
 
         lora_list: list[LoRAModulePath] = []
         for item in values:
-            if item in [None, '']:  # Skip if item is None or empty string
+            if item in [None, ""]:  # Skip if item is None or empty string
                 continue
-            if '=' in item and ',' not in item:  # Old format: name=path
-                name, path = item.split('=')
+            if "=" in item and "," not in item:  # Old format: name=path
+                name, path = item.split("=")
                 lora_list.append(LoRAModulePath(name, path))
             else:  # Assume JSON format
                 try:
@@ -167,6 +167,9 @@ class FrontendArgs:
     enable_tokenizer_info_endpoint: bool = False
     """Enable the /get_tokenizer_info endpoint. May expose chat
     templates and other tokenizer configuration."""
+    enable_log_outputs: bool = False
+    """If set to True, enable logging of model outputs (generations) 
+    in addition to the input logging that is enabled by default."""
 
     @staticmethod
     def add_cli_args(parser: FlexibleArgumentParser) -> FlexibleArgumentParser: