feat: add Momento as a standard cache and chat message history provider (#5221)

# Add Momento as a standard cache and chat message history provider

This PR adds Momento as a standard caching provider. Implements the
interface, adds integration tests, and documentation. We also add
Momento as a chat history message provider along with integration tests,
and documentation.

[Momento](https://www.gomomento.com/) is a fully serverless cache.
Similar to S3 or DynamoDB, it requires zero configuration,
infrastructure management, and is instantly available. Users sign up for
free and get 50GB of data in/out for free every month.

## Before submitting

✅ We have added documentation, notebooks, and integration tests
demonstrating usage.

Co-authored-by: Dev 2049 <dev.dev2049@gmail.com>

tests/integration_tests/cache/test_momento_cache.py

@@ -0,0 +1,94 @@
+"""Test Momento cache functionality.
+
+To run tests, set the environment variable MOMENTO_AUTH_TOKEN to a valid
+Momento auth token. This can be obtained by signing up for a free
+Momento account at https://gomomento.com/.
+"""
+from __future__ import annotations
+
+import uuid
+from datetime import timedelta
+from typing import Iterator
+
+import pytest
+from momento import CacheClient, Configurations, CredentialProvider
+
+import langchain
+from langchain.cache import MomentoCache
+from langchain.schema import Generation, LLMResult
+from tests.unit_tests.llms.fake_llm import FakeLLM
+
+
+def random_string() -> str:
+    return str(uuid.uuid4())
+
+
+@pytest.fixture(scope="module")
+def momento_cache() -> Iterator[MomentoCache]:
+    cache_name = f"langchain-test-cache-{random_string()}"
+    client = CacheClient(
+        Configurations.Laptop.v1(),
+        CredentialProvider.from_environment_variable("MOMENTO_AUTH_TOKEN"),
+        default_ttl=timedelta(seconds=30),
+    )
+    try:
+        llm_cache = MomentoCache(client, cache_name)
+        langchain.llm_cache = llm_cache
+        yield llm_cache
+    finally:
+        client.delete_cache(cache_name)
+
+
+def test_invalid_ttl() -> None:
+    client = CacheClient(
+        Configurations.Laptop.v1(),
+        CredentialProvider.from_environment_variable("MOMENTO_AUTH_TOKEN"),
+        default_ttl=timedelta(seconds=30),
+    )
+    with pytest.raises(ValueError):
+        MomentoCache(client, cache_name=random_string(), ttl=timedelta(seconds=-1))
+
+
+def test_momento_cache_miss(momento_cache: MomentoCache) -> None:
+    llm = FakeLLM()
+    stub_llm_output = LLMResult(generations=[[Generation(text="foo")]])
+    assert llm.generate([random_string()]) == stub_llm_output
+
+
+@pytest.mark.parametrize(
+    "prompts,  generations",
+    [
+        # Single prompt, single generation
+        ([random_string()], [[random_string()]]),
+        # Single prompt, multiple generations
+        ([random_string()], [[random_string(), random_string()]]),
+        # Single prompt, multiple generations
+        ([random_string()], [[random_string(), random_string(), random_string()]]),
+        # Multiple prompts, multiple generations
+        (
+            [random_string(), random_string()],
+            [[random_string()], [random_string(), random_string()]],
+        ),
+    ],
+)
+def test_momento_cache_hit(
+    momento_cache: MomentoCache, prompts: list[str], generations: list[list[str]]
+) -> None:
+    llm = FakeLLM()
+    params = llm.dict()
+    params["stop"] = None
+    llm_string = str(sorted([(k, v) for k, v in params.items()]))
+
+    llm_generations = [
+        [
+            Generation(text=generation, generation_info=params)
+            for generation in prompt_i_generations
+        ]
+        for prompt_i_generations in generations
+    ]
+    for prompt_i, llm_generations_i in zip(prompts, llm_generations):
+        momento_cache.update(prompt_i, llm_string, llm_generations_i)
+
+    assert llm.generate(prompts) == LLMResult(
+        generations=llm_generations, llm_output={}
+    )

tests/integration_tests/memory/test_momento.py

@@ -0,0 +1,70 @@
+"""Test Momento chat message history functionality.
+
+To run tests, set the environment variable MOMENTO_AUTH_TOKEN to a valid
+Momento auth token. This can be obtained by signing up for a free
+Momento account at https://gomomento.com/.
+"""
+import json
+import uuid
+from datetime import timedelta
+from typing import Iterator
+
+import pytest
+from momento import CacheClient, Configurations, CredentialProvider
+
+from langchain.memory import ConversationBufferMemory
+from langchain.memory.chat_message_histories import MomentoChatMessageHistory
+from langchain.schema import _message_to_dict
+
+
+def random_string() -> str:
+    return str(uuid.uuid4())
+
+
+@pytest.fixture(scope="function")
+def message_history() -> Iterator[MomentoChatMessageHistory]:
+    cache_name = f"langchain-test-cache-{random_string()}"
+    client = CacheClient(
+        Configurations.Laptop.v1(),
+        CredentialProvider.from_environment_variable("MOMENTO_AUTH_TOKEN"),
+        default_ttl=timedelta(seconds=30),
+    )
+    try:
+        chat_message_history = MomentoChatMessageHistory(
+            session_id="my-test-session",
+            cache_client=client,
+            cache_name=cache_name,
+        )
+        yield chat_message_history
+    finally:
+        client.delete_cache(cache_name)
+
+
+def test_memory_empty_on_new_session(
+    message_history: MomentoChatMessageHistory,
+) -> None:
+    memory = ConversationBufferMemory(
+        memory_key="foo", chat_memory=message_history, return_messages=True
+    )
+    assert memory.chat_memory.messages == []
+
+
+def test_memory_with_message_store(message_history: MomentoChatMessageHistory) -> None:
+    memory = ConversationBufferMemory(
+        memory_key="baz", chat_memory=message_history, return_messages=True
+    )
+
+    # Add some messages to the memory store
+    memory.chat_memory.add_ai_message("This is me, the AI")
+    memory.chat_memory.add_user_message("This is me, the human")
+
+    # Verify that the messages are in the store
+    messages = memory.chat_memory.messages
+    messages_json = json.dumps([_message_to_dict(msg) for msg in messages])
+
+    assert "This is me, the AI" in messages_json
+    assert "This is me, the human" in messages_json
+
+    # Verify clearing the store
+    memory.chat_memory.clear()
+    assert memory.chat_memory.messages == []