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如何从你的 RAG 应用流式传输结果

本指南将介绍如何从 RAG 应用流式传输结果。它涵盖了从最终输出流式传输 token，以及链的中间步骤（例如，从查询重写）。

我们将基于 Lilian Weng 在 RAG 教程 中关于 LLM 驱动的自主代理 这篇博文所构建的、带有来源的问答应用。

设置​

依赖​

我们将使用以下包：

%pip install --upgrade --quiet  langchain langchain-community langchainhub beautifulsoup4

LangSmith​

你使用 LangChain 构建的许多应用程序将包含多个步骤和多次 LLM 调用。随着这些应用程序变得越来越复杂，能够检查链或代理内部究竟发生了什么变得至关重要。做到这一点最好的方法是使用 LangSmith。

请注意，LangSmith并非必需品，但它很有帮助。如果你确实想使用 LangSmith，在上面的链接注册后，请确保设置你的环境变量以开始记录追踪：

os.environ["LANGSMITH_TRACING"] = "true"
os.environ["LANGSMITH_API_KEY"] = getpass.getpass()

组件​

我们需要从 LangChain 的集成套件中选择三个组件。

一个 聊天模型：

pip install -qU "langchain[google-genai]"
import getpass
import os

if not os.environ.get("GOOGLE_API_KEY"):
  os.environ["GOOGLE_API_KEY"] = getpass.getpass("Enter API key for Google Gemini: ")

from langchain.chat_models import init_chat_model

llm = init_chat_model("gemini-2.0-flash", model_provider="google_genai")

一个嵌入模型：

pip install -qU langchain-openai
import getpass
import os

if not os.environ.get("OPENAI_API_KEY"):
  os.environ["OPENAI_API_KEY"] = getpass.getpass("Enter API key for OpenAI: ")

from langchain_openai import OpenAIEmbeddings

embeddings = OpenAIEmbeddings(model="text-embedding-3-large")

以及一个 向量存储：

pip install -qU langchain-core
from langchain_core.vectorstores import InMemoryVectorStore

vector_store = InMemoryVectorStore(embeddings)

RAG 应用​

让我们回顾一下在 Lilian Weng 的 LLM 驱动的自主代理 博客文章中构建的、并在 RAG 教程 中实现的 Q&A 应用。

首先，我们索引文档：

import bs4
from langchain import hub
from langchain_community.document_loaders import WebBaseLoader
from langchain_core.documents import Document
from langchain_text_splitters import RecursiveCharacterTextSplitter
from typing_extensions import List, TypedDict

# Load and chunk contents of the blog
loader = WebBaseLoader(
    web_paths=("https://lilianweng.github.io/posts/2023-06-23-agent/",),
    bs_kwargs=dict(
        parse_only=bs4.SoupStrainer(
            class_=("post-content", "post-title", "post-header")
        )
    ),
)
docs = loader.load()

text_splitter = RecursiveCharacterTextSplitter(chunk_size=1000, chunk_overlap=200)
all_splits = text_splitter.split_documents(docs)
# Index chunks
_ = vector_store.add_documents(documents=all_splits)

接下来我们构建应用程序：

from langchain import hub
from langchain_core.documents import Document
from langgraph.graph import START, StateGraph
from typing_extensions import List, TypedDict

# Define prompt for question-answering
prompt = hub.pull("rlm/rag-prompt")


# Define state for application
class State(TypedDict):
    question: str
    context: List[Document]
    answer: str


# Define application steps
def retrieve(state: State):
    retrieved_docs = vector_store.similarity_search(state["question"])
    return {"context": retrieved_docs}


def generate(state: State):
    docs_content = "\n\n".join(doc.page_content for doc in state["context"])
    messages = prompt.invoke({"question": state["question"], "context": docs_content})
    response = llm.invoke(messages)
    return {"answer": response.content}


# Compile application and test
graph_builder = StateGraph(State).add_sequence([retrieve, generate])
graph_builder.add_edge(START, "retrieve")
graph = graph_builder.compile()
API Reference:hub | Document | StateGraph
from IPython.display import Image, display

display(Image(graph.get_graph().draw_mermaid_png()))

流式输出最终结果​

LangGraph 支持多种 流式模式，可以通过指定 stream_mode 参数来控制。将 stream_mode 设置为 "messages" 可以让我们从聊天模型调用中流式传输 token。

通常，一个应用中可能存在多个聊天模型调用（尽管这里只有一个）。下面，我们通过节点名称来筛选，只选择最后一个步骤：

input_message = "What is Task Decomposition?"

for message, metadata in graph.stream(
    {"question": "What is Task Decomposition?"},
    stream_mode="messages",
):
    if metadata["langgraph_node"] == "generate":
        print(message.content, end="|")
|Task| De|composition| is| a| technique| used| to| break| down| complex| tasks| into| smaller|,| more| manageable| steps|.| It| often| involves| prompting| models| to| "|think| step| by| step|,"| allowing| for| clearer| reasoning| and| better| performance| on| intricate| problems|.| This| can| be| achieved| through| various| methods|,| including| simple| prompts|,| task|-specific| instructions|,| or| human| input|.||

流式传输中间步骤​

其他流式传输模式通常会从我们的调用中流式传输步骤——即，各个节点的更新状态。在这种情况下，每个节点只是向状态追加一个新键：

for step in graph.stream(
    {"question": "What is Task Decomposition?"},
    stream_mode="updates",
):
    print(f"{step}\n\n----------------\n")
{'retrieve': {'context': [Document(id='5bf5e308-6ccb-4f09-94d2-d0c36b8c9980', metadata={'source': 'https://lilianweng.github.io/posts/2023-06-23-agent/'}, page_content='Fig. 1. Overview of a LLM-powered autonomous agent system.\nComponent One: Planning#\nA complicated task usually involves many steps. An agent needs to know what they are and plan ahead.\nTask Decomposition#\nChain of thought (CoT; Wei et al. 2022) has become a standard prompting technique for enhancing model performance on complex tasks. The model is instructed to “think step by step” to utilize more test-time computation to decompose hard tasks into smaller and simpler steps. CoT transforms big tasks into multiple manageable tasks and shed lights into an interpretation of the model’s thinking process.'), Document(id='d8aed221-7943-414d-8ed7-63c2b0e7523b', metadata={'source': 'https://lilianweng.github.io/posts/2023-06-23-agent/'}, page_content='Tree of Thoughts (Yao et al. 2023) extends CoT by exploring multiple reasoning possibilities at each step. It first decomposes the problem into multiple thought steps and generates multiple thoughts per step, creating a tree structure. The search process can be BFS (breadth-first search) or DFS (depth-first search) with each state evaluated by a classifier (via a prompt) or majority vote.\nTask decomposition can be done (1) by LLM with simple prompting like "Steps for XYZ.\\n1.", "What are the subgoals for achieving XYZ?", (2) by using task-specific instructions; e.g. "Write a story outline." for writing a novel, or (3) with human inputs.'), Document(id='bfa87007-02ef-4f81-a008-4522ecea1025', metadata={'source': 'https://lilianweng.github.io/posts/2023-06-23-agent/'}, page_content='Resources:\n1. Internet access for searches and information gathering.\n2. Long Term memory management.\n3. GPT-3.5 powered Agents for delegation of simple tasks.\n4. File output.\n\nPerformance Evaluation:\n1. Continuously review and analyze your actions to ensure you are performing to the best of your abilities.\n2. Constructively self-criticize your big-picture behavior constantly.\n3. Reflect on past decisions and strategies to refine your approach.\n4. Every command has a cost, so be smart and efficient. Aim to complete tasks in the least number of steps.'), Document(id='6aff7fc0-5c21-4986-9f1e-91e89715d934', metadata={'source': 'https://lilianweng.github.io/posts/2023-06-23-agent/'}, page_content="(3) Task execution: Expert models execute on the specific tasks and log results.\nInstruction:\n\nWith the input and the inference results, the AI assistant needs to describe the process and results. The previous stages can be formed as - User Input: {{ User Input }}, Task Planning: {{ Tasks }}, Model Selection: {{ Model Assignment }}, Task Execution: {{ Predictions }}. You must first answer the user's request in a straightforward manner. Then describe the task process and show your analysis and model inference results to the user in the first person. If inference results contain a file path, must tell the user the complete file path.")]}}

----------------

{'generate': {'answer': 'Task Decomposition is the process of breaking down a complex task into smaller, manageable steps to enhance understanding and execution. Techniques like Chain of Thought (CoT) and Tree of Thoughts (ToT) guide models to think through steps systematically, allowing for better problem-solving. It can be achieved through simple prompting, task-specific instructions, or human input.'}}

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有关 LangGraph 的流式处理，请参阅其流式处理文档。有关流式处理单个 LangChain Runnables 的更多信息，请参阅本指南。