🦀ADK-Rust

会话

ADK-Rust 中的会话提供了对话上下文管理，使 Agent 能够在多次交互中保持 State。会话存储对话历史 (Event) 和在整个对话中持久存在的任意 State 数据。

概述

一个会话代表用户和 Agent 之间的一次单独对话。每个会话：

  • 具有唯一的标识符
  • 属于一个应用程序 (app_name) 和用户 (user_id)
  • 包含一个 Event 列表（对话历史）
  • 维护 State 数据（键值对）
  • 跟踪最后更新时间

Session 特性

Session 特性定义了会话对象的接口：

use adk_session::{Events, State};
use chrono::{DateTime, Utc};

pub trait Session: Send + Sync {
    /// 唯一的会话标识符
    fn id(&self) -> &str;
    
    /// 此会话所属的应用程序名称
    fn app_name(&self) -> &str;
    
    /// 用户标识符
    fn user_id(&self) -> &str;
    
    /// 访问会话状态
    fn state(&self) -> &dyn State;
    
    /// 访问对话事件
    fn events(&self) -> &dyn Events;
    
    /// 会话最后更新时间
    fn last_update_time(&self) -> DateTime<Utc>;
}

SessionService 特性

SessionService 特性定义了管理会话的操作：

use adk_session::{CreateRequest, GetRequest, ListRequest, DeleteRequest, Event, Session};
use adk_core::Result;
use async_trait::async_trait;

#[async_trait]
pub trait SessionService: Send + Sync {
    /// 创建一个新会话
    async fn create(&self, req: CreateRequest) -> Result<Box<dyn Session>>;
    
    /// 获取一个现有会话
    async fn get(&self, req: GetRequest) -> Result<Box<dyn Session>>;
    
    /// 列出某个应用程序/用户的所有会话
    async fn list(&self, req: ListRequest) -> Result<Vec<Box<dyn Session>>>;
    
    /// 删除一个会话
    async fn delete(&self, req: DeleteRequest) -> Result<()>;
    
    /// 向会话追加一个事件
    async fn append_event(&self, session_id: &str, event: Event) -> Result<()>;
}

请求类型

CreateRequest

use adk_session::CreateRequest;
use std::collections::HashMap;

let request = CreateRequest {
    app_name: "my_app".to_string(),
    user_id: "user_123".to_string(),
    session_id: None,  // 如果为 None，则自动生成 UUID
    state: HashMap::new(),  // 初始状态
};

GetRequest

use adk_session::GetRequest;

let request = GetRequest {
    app_name: "my_app".to_string(),
    user_id: "user_123".to_string(),
    session_id: "session_abc".to_string(),
    num_recent_events: Some(10),  // 限制返回的事件数量
    after: None,  // 过滤特定时间戳后的事件
};

ListRequest

use adk_session::ListRequest;

let request = ListRequest {
    app_name: "my_app".to_string(),
    user_id: "user_123".to_string(),
};

DeleteRequest

use adk_session::DeleteRequest;

let request = DeleteRequest {
    app_name: "my_app".to_string(),
    user_id: "user_123".to_string(),
    session_id: "session_abc".to_string(),
};

SessionService 实现

ADK-Rust 提供了两种 SessionService 实现：

InMemorySessionService

将会话存储在内存中。适用于开发、测试和单实例部署。

use adk_session::{InMemorySessionService, SessionService, CreateRequest};
use std::collections::HashMap;

#[tokio::main]
async fn main() -> anyhow::Result<()> {
    // Create the service
    let session_service = InMemorySessionService::new();
    
    // Create a session
    let session = session_service.create(CreateRequest {
        app_name: "my_app".to_string(),
        user_id: "user_123".to_string(),
        session_id: None,
        state: HashMap::new(),
    }).await?;
    
    println!("Session ID: {}", session.id());
    println!("App: {}", session.app_name());
    println!("User: {}", session.user_id());
    
    Ok(())
}

DatabaseSessionService

将会话存储在 SQLite 数据库中。适用于需要持久化的生产部署。

use adk_session::{DatabaseSessionService, SessionService, CreateRequest};
use std::collections::HashMap;

#[tokio::main]
async fn main() -> anyhow::Result<()> {
    // Connect to database
    let session_service = DatabaseSessionService::new("sqlite:sessions.db").await?;
    
    // Run migrations to create tables
    session_service.migrate().await?;
    
    // Create a session
    let session = session_service.create(CreateRequest {
        app_name: "my_app".to_string(),
        user_id: "user_123".to_string(),
        session_id: None,
        state: HashMap::new(),
    }).await?;
    
    println!("Session persisted: {}", session.id());
    
    Ok(())
}

注意： DatabaseSessionService 需要 database 功能标志：

adk-session = { version = "0.2", features = ["database"] }

会话生命周期

1. 创建

会话使用 CreateRequest 创建。如果未提供 session_id，则会自动生成一个 UUID。

use adk_session::{InMemorySessionService, SessionService, CreateRequest};
use std::collections::HashMap;

let service = InMemorySessionService::new();

// Create with auto-generated ID
let session = service.create(CreateRequest {
    app_name: "my_app".to_string(),
    user_id: "user_123".to_string(),
    session_id: None,
    state: HashMap::new(),
}).await?;

// Create with specific ID
let session = service.create(CreateRequest {
    app_name: "my_app".to_string(),
    user_id: "user_123".to_string(),
    session_id: Some("my-custom-id".to_string()),
    state: HashMap::new(),
}).await?;

2. 检索

通过其标识符检索会话：

use adk_session::GetRequest;

let session = service.get(GetRequest {
    app_name: "my_app".to_string(),
    user_id: "user_123".to_string(),
    session_id: "session_abc".to_string(),
    num_recent_events: None,
    after: None,
}).await?;

println!("Retrieved session: {}", session.id());
println!("Events: {}", session.events().len());

3. 事件附加

随着对话的进行，事件会附加到会话中。这通常由 Runner 处理，但也可以手动完成：

use adk_session::Event;

let event = Event::new("invocation_123");
service.append_event(session.id(), event).await?;

4. 列表

列出用户的所有会话：

use adk_session::ListRequest;

let sessions = service.list(ListRequest {
    app_name: "my_app".to_string(),
    user_id: "user_123".to_string(),
}).await?;

for session in sessions {
    println!("Session: {} (updated: {})", 
        session.id(), 
        session.last_update_time()
    );
}

5. 删除

当不再需要会话时，将其删除：

use adk_session::DeleteRequest;

service.delete(DeleteRequest {
    app_name: "my_app".to_string(),
    user_id: "user_123".to_string(),
    session_id: "session_abc".to_string(),
}).await?;

结合 Runner 使用 Session

在执行 agents 时，Runner 通常会管理 Session。Runner 会执行以下操作：

  1. 创建或检索一个 Session
  2. 将 Session 上下文传递给 Agent
  3. 随着对话的进行追加事件
  4. 根据 Agent 的操作更新 Session 状态
use adk_rust::prelude::*;
use adk_runner::{Runner, RunnerConfig};
use adk_session::InMemorySessionService;
use std::sync::Arc;

#[tokio::main]
async fn main() -> anyhow::Result<()> {
    dotenvy::dotenv().ok();
    let api_key = std::env::var("GOOGLE_API_KEY")?;
    let model = Arc::new(GeminiModel::new(&api_key, "gemini-2.0-flash")?);

    let agent = LlmAgentBuilder::new("assistant")
        .model(model)
        .instruction("You are a helpful assistant.")
        .build()?;

    let session_service = Arc::new(InMemorySessionService::new());

    // Create runner with session service
    let runner = Runner::new(RunnerConfig {
        app_name: "my_app".to_string(),
        agent: Arc::new(agent),
        session_service,
        artifact_service: None,
        memory_service: None,
        run_config: None,
    })?;

    // Run with user and session IDs
    let user_content = Content::new("user").with_text("Hello!");
    let stream = runner.run(
        "user_123".to_string(),
        "session_abc".to_string(),
        user_content,
    ).await?;

    Ok(())
}

事件

Events trait 提供了对对话历史的访问：

pub trait Events: Send + Sync {
    /// Get all events
    fn all(&self) -> Vec<Event>;
    
    /// Get number of events
    fn len(&self) -> usize;
    
    /// Get event at index
    fn at(&self, index: usize) -> Option<&Event>;
    
    /// Check if empty
    fn is_empty(&self) -> bool;
}

从 Session 访问事件：

let events = session.events();
println!("Total events: {}", events.len());

for event in events.all() {
    println!("Event {} by {} at {}", 
        event.id, 
        event.author, 
        event.timestamp
    );
}

完整示例

use adk_session::{
    InMemorySessionService, SessionService, 
    CreateRequest, GetRequest, ListRequest, DeleteRequest,
    Event, KEY_PREFIX_USER,
};
use serde_json::json;
use std::collections::HashMap;

#[tokio::main]
async fn main() -> anyhow::Result<()> {
    let service = InMemorySessionService::new();
    
    // Create session with initial state
    let mut initial_state = HashMap::new();
    initial_state.insert(format!("{}name", KEY_PREFIX_USER), json!("Alice"));
    initial_state.insert("topic".to_string(), json!("Getting started"));
    
    let session = service.create(CreateRequest {
        app_name: "demo".to_string(),
        user_id: "alice".to_string(),
        session_id: None,
        state: initial_state,
    }).await?;
    
    println!("Created session: {}", session.id());
    
    // Check state
    let state = session.state();
    println!("User name: {:?}", state.get("user:name"));
    println!("Topic: {:?}", state.get("topic"));
    
    // Append an event
    let event = Event::new("inv_001");
    service.append_event(session.id(), event).await?;
    
    // Retrieve session with events
    let session = service.get(GetRequest {
        app_name: "demo".to_string(),
        user_id: "alice".to_string(),
        session_id: session.id().to_string(),
        num_recent_events: None,
        after: None,
    }).await?;
    
    println!("Events: {}", session.events().len());
    
    // List all sessions
    let sessions = service.list(ListRequest {
        app_name: "demo".to_string(),
        user_id: "alice".to_string(),
    }).await?;
    
    println!("Total sessions: {}", sessions.len());
    
    // Delete session
    service.delete(DeleteRequest {
        app_name: "demo".to_string(),
        user_id: "alice".to_string(),
        session_id: session.id().to_string(),
    }).await?;
    
    println!("Session deleted");
    
    Ok(())
}

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