Add a LLMMessagesTransformFrame to facilitate programmatically editing context in a frame-based way.

The previous approach required the caller to directly grab a reference to the context object, grab a "snapshot" of its messages *at that point in time*, transform the messages, and then push an `LLMMessagesUpdateFrame` with the transformed messages. This approach can lead to problems: what if there had already been a change to the context queued in the pipeline? The transformed messages would simply overwrite it without consideration.

changelog/4231.added.md

@@ -0,0 +1,3 @@
+- Added `LLMMessagesTransformFrame` to facilitate programmatically editing context in a frame-based way.
+
+  The previous approach required the caller to directly grab a reference to the context object, grab a "snapshot" of its messages _at that point in time_, transform the messages, and then push an `LLMMessagesUpdateFrame` with the transformed messages. This approach can lead to problems: what if there had already been a change to the context queued in the pipeline? The transformed messages would simply overwrite it without consideration.

src/pipecat/frames/frames.py

@@ -38,7 +38,7 @@ from pipecat.utils.time import nanoseconds_to_str
 from pipecat.utils.utils import obj_count, obj_id
 
 if TYPE_CHECKING:
-    from pipecat.processors.aggregators.llm_context import LLMContext, NotGiven
+    from pipecat.processors.aggregators.llm_context import LLMContext, LLMContextMessage, NotGiven
     from pipecat.processors.frame_processor import FrameProcessor
     from pipecat.services.settings import ServiceSettings
     from pipecat.utils.context.llm_context_summarization import LLMContextSummaryConfig
@@ -587,6 +587,25 @@ class LLMMessagesUpdateFrame(DataFrame):
     run_llm: Optional[bool] = None
 
 
+@dataclass
+class LLMMessagesTransformFrame(DataFrame):
+    """Frame containing a transform function to modify the current context's LLM messages.
+
+    A frame containing a transform function that takes the context's current list
+    of LLM messages and returns a modified list.
+
+    Only compatible with LLMContext and not the deprecated OpenAILLMContext.
+
+    Parameters:
+        transform: A function that takes a list of messages and returns a
+            modified list.
+        run_llm: Whether the context update should be sent to the LLM.
+    """
+
+    transform: Callable[[List["LLMContextMessage"]], List["LLMContextMessage"]]
+    run_llm: Optional[bool] = None
+
+
 @dataclass
 class LLMSetToolsFrame(DataFrame):
     """Frame containing tools for LLM function calling.

src/pipecat/processors/aggregators/llm_context.py

@@ -19,7 +19,7 @@ import base64
 import io
 import wave
 from dataclasses import dataclass
-from typing import Any, List, Optional, TypeAlias, Union
+from typing import Any, Callable, List, Optional, TypeAlias, Union
 
 from loguru import logger
 from openai._types import NOT_GIVEN as OPEN_AI_NOT_GIVEN
@@ -266,6 +266,17 @@ class LLMContext:
         """
         self._messages[:] = messages
 
+    def transform_messages(
+        self, transform: Callable[[List[LLMContextMessage]], List[LLMContextMessage]]
+    ):
+        """Transform the current messages using the provided function.
+
+        Args:
+            transform: A function that takes the current list of messages and returns
+                a modified list of messages to set in the context.
+        """
+        self.set_messages(transform(self._messages))
+
     def set_tools(self, tools: ToolsSchema | NotGiven = NOT_GIVEN):
         """Set the available tools for the LLM.
 

src/pipecat/processors/aggregators/llm_response_universal.py

@@ -16,7 +16,7 @@ import json
 import warnings
 from abc import abstractmethod
 from dataclasses import dataclass, field
-from typing import Any, Dict, List, Literal, Optional, Set, Type
+from typing import Any, Callable, Dict, List, Literal, Optional, Set, Type
 
 from loguru import logger
 
@@ -42,6 +42,7 @@ from pipecat.frames.frames import (
     LLMFullResponseEndFrame,
     LLMFullResponseStartFrame,
     LLMMessagesAppendFrame,
+    LLMMessagesTransformFrame,
     LLMMessagesUpdateFrame,
     LLMRunFrame,
     LLMSetToolChoiceFrame,
@@ -315,6 +316,17 @@ class LLMContextAggregator(FrameProcessor):
         """
         self._context.set_messages(messages)
 
+    def transform_messages(
+        self, transform: Callable[[List[LLMContextMessage]], List[LLMContextMessage]]
+    ):
+        """Transform the context messages using a provided function.
+
+        Args:
+            transform: A function that takes the current list of messages and returns
+                a modified list of messages to set in the context.
+        """
+        self._context.transform_messages(transform)
+
     def set_tools(self, tools: ToolsSchema | NotGiven):
         """Set tools in the context.
 
@@ -512,6 +524,8 @@ class LLMUserAggregator(LLMContextAggregator):
             await self._handle_llm_messages_append(frame)
         elif isinstance(frame, LLMMessagesUpdateFrame):
             await self._handle_llm_messages_update(frame)
+        elif isinstance(frame, LLMMessagesTransformFrame):
+            await self._handle_llm_messages_transform(frame)
         elif isinstance(frame, LLMSetToolsFrame):
             self.set_tools(frame.tools)
             # Push the LLMSetToolsFrame as well, since speech-to-speech LLM
@@ -635,6 +649,11 @@ class LLMUserAggregator(LLMContextAggregator):
         if frame.run_llm:
             await self.push_context_frame()
 
+    async def _handle_llm_messages_transform(self, frame: LLMMessagesTransformFrame):
+        self.transform_messages(frame.transform)
+        if frame.run_llm:
+            await self.push_context_frame()
+
     async def _handle_transcription(self, frame: TranscriptionFrame):
         text = frame.text
 
@@ -923,6 +942,8 @@ class LLMAssistantAggregator(LLMContextAggregator):
             await self._handle_llm_messages_append(frame)
         elif isinstance(frame, LLMMessagesUpdateFrame):
             await self._handle_llm_messages_update(frame)
+        elif isinstance(frame, LLMMessagesTransformFrame):
+            await self._handle_llm_messages_transform(frame)
         elif isinstance(frame, LLMSetToolsFrame):
             self.set_tools(frame.tools)
         elif isinstance(frame, LLMSetToolChoiceFrame):
@@ -982,6 +1003,11 @@ class LLMAssistantAggregator(LLMContextAggregator):
         if frame.run_llm:
             await self.push_context_frame(FrameDirection.UPSTREAM)
 
+    async def _handle_llm_messages_transform(self, frame: LLMMessagesTransformFrame):
+        self.transform_messages(frame.transform)
+        if frame.run_llm:
+            await self.push_context_frame(FrameDirection.UPSTREAM)
+
     async def _handle_interruptions(self, frame: InterruptionFrame):
         await self._trigger_assistant_turn_stopped()
         await self.reset()

tests/test_context_aggregators_universal.py

@@ -22,6 +22,7 @@ from pipecat.frames.frames import (
     LLMFullResponseEndFrame,
     LLMFullResponseStartFrame,
     LLMMessagesAppendFrame,
+    LLMMessagesTransformFrame,
     LLMMessagesUpdateFrame,
     LLMRunFrame,
     LLMTextFrame,
@@ -180,6 +181,56 @@ class TestLLMUserAggregator(unittest.IsolatedAsyncioTestCase):
         assert context.messages[0]["content"] == "You are a helpful assistant."
         assert context.messages[1]["content"] == "Hello!"
 
+    async def test_llm_messages_transform(self):
+        context = LLMContext()
+        # Set up initial messages
+        context.set_messages(
+            [
+                {"role": "user", "content": "Hello"},
+                {"role": "assistant", "content": "Hi there!"},
+                {"role": "user", "content": "How are you?"},
+            ]
+        )
+
+        pipeline = Pipeline([LLMUserAggregator(context)])
+
+        # Transform that keeps only user messages
+        def keep_user_messages(messages):
+            return [m for m in messages if m["role"] == "user"]
+
+        frames_to_send = [LLMMessagesTransformFrame(transform=keep_user_messages)]
+        expected_down_frames = [
+            SpeechControlParamsFrame  # no LLMContextFrame expected, run_llm defaults to False
+        ]
+        await run_test(
+            pipeline,
+            frames_to_send=frames_to_send,
+            expected_down_frames=expected_down_frames,
+        )
+        assert len(context.messages) == 2
+        assert context.messages[0]["content"] == "Hello"
+        assert context.messages[1]["content"] == "How are you?"
+
+    async def test_llm_messages_transform_run(self):
+        context = LLMContext()
+        # Set up initial messages
+        context.set_messages([{"role": "user", "content": "Hello"}])
+
+        pipeline = Pipeline([LLMUserAggregator(context)])
+
+        # Transform that modifies the content
+        def uppercase_content(messages):
+            return [{"role": m["role"], "content": m["content"].upper()} for m in messages]
+
+        frames_to_send = [LLMMessagesTransformFrame(transform=uppercase_content, run_llm=True)]
+        expected_down_frames = [SpeechControlParamsFrame, LLMContextFrame]
+        await run_test(
+            pipeline,
+            frames_to_send=frames_to_send,
+            expected_down_frames=expected_down_frames,
+        )
+        assert context.messages[0]["content"] == "HELLO"
+
     async def test_default_user_turn_strategies(self):
         context = LLMContext()
         user_aggregator = LLMUserAggregator(