adk_core/
agent.rs

1use crate::{InvocationContext, Result, event::Event};
2use async_trait::async_trait;
3use futures::stream::Stream;
4use std::pin::Pin;
5use std::sync::Arc;
6
7/// A pinned, boxed stream of [`Event`] results emitted by an agent during execution.
8pub type EventStream = Pin<Box<dyn Stream<Item = Result<Event>> + Send>>;
9
10/// The fundamental trait for all ADK agents.
11///
12/// Every agent — whether a simple LLM wrapper, a multi-step workflow, or a
13/// composite orchestrator — implements this trait. The runtime invokes
14/// [`run`](Self::run) with an [`InvocationContext`] and consumes the returned
15/// [`EventStream`].
16#[async_trait]
17pub trait Agent: Send + Sync {
18    /// Returns the unique name of this agent.
19    fn name(&self) -> &str;
20    /// Returns a human-readable description of this agent's purpose.
21    fn description(&self) -> &str;
22    /// Returns the child agents managed by this agent.
23    fn sub_agents(&self) -> &[Arc<dyn Agent>];
24
25    /// Executes the agent and returns a stream of events.
26    async fn run(&self, ctx: Arc<dyn InvocationContext>) -> Result<EventStream>;
27}
28
29/// A validated context containing engineered instructions and resolved tool instances.
30///
31/// This structure serves as the "Atomic Unit of Capability" for an agent. It guarantees
32/// that the agent's cognitive frame (the instructions telling it what it can do) is
33/// perfectly aligned with its physical capabilities (the binary tool instances bound
34/// to the session).
35///
36/// By using `ResolvedContext`, the framework eliminates "Phantom Tool" hallucinations,
37/// where an agent tries to call a tool that was mentioned in its prompt but never
38/// actually registered in the runtime.
39#[derive(Clone)]
40pub struct ResolvedContext {
41    /// The engineered system instruction.
42    pub system_instruction: String,
43    /// The resolved, executable tools.
44    pub active_tools: Vec<Arc<dyn crate::Tool>>,
45}
46
47impl std::fmt::Debug for ResolvedContext {
48    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
49        f.debug_struct("ResolvedContext")
50            .field("system_instruction_len", &self.system_instruction.len())
51            .field("active_tools_count", &self.active_tools.len())
52            .finish()
53    }
54}
55
56#[cfg(test)]
57mod tests {
58    use super::*;
59    use crate::{Content, ReadonlyContext, RunConfig};
60    use async_stream::stream;
61
62    struct TestAgent {
63        name: String,
64    }
65
66    use crate::{CallbackContext, Session, State};
67    use std::collections::HashMap;
68
69    struct MockState;
70    impl State for MockState {
71        fn get(&self, _key: &str) -> Option<serde_json::Value> {
72            None
73        }
74        fn set(&mut self, _key: String, _value: serde_json::Value) {}
75        fn all(&self) -> HashMap<String, serde_json::Value> {
76            HashMap::new()
77        }
78    }
79
80    struct MockSession;
81    impl Session for MockSession {
82        fn id(&self) -> &str {
83            "session"
84        }
85        fn app_name(&self) -> &str {
86            "app"
87        }
88        fn user_id(&self) -> &str {
89            "user"
90        }
91        fn state(&self) -> &dyn State {
92            &MockState
93        }
94        fn conversation_history(&self) -> Vec<Content> {
95            Vec::new()
96        }
97    }
98
99    #[allow(dead_code)]
100    struct TestContext {
101        content: Content,
102        config: RunConfig,
103        session: MockSession,
104    }
105
106    #[allow(dead_code)]
107    impl TestContext {
108        fn new() -> Self {
109            Self {
110                content: Content::new("user"),
111                config: RunConfig::default(),
112                session: MockSession,
113            }
114        }
115    }
116
117    #[async_trait]
118    impl ReadonlyContext for TestContext {
119        fn invocation_id(&self) -> &str {
120            "test"
121        }
122        fn agent_name(&self) -> &str {
123            "test"
124        }
125        fn user_id(&self) -> &str {
126            "user"
127        }
128        fn app_name(&self) -> &str {
129            "app"
130        }
131        fn session_id(&self) -> &str {
132            "session"
133        }
134        fn branch(&self) -> &str {
135            ""
136        }
137        fn user_content(&self) -> &Content {
138            &self.content
139        }
140    }
141
142    #[async_trait]
143    impl CallbackContext for TestContext {
144        fn artifacts(&self) -> Option<Arc<dyn crate::Artifacts>> {
145            None
146        }
147    }
148
149    #[async_trait]
150    impl InvocationContext for TestContext {
151        fn agent(&self) -> Arc<dyn Agent> {
152            unimplemented!()
153        }
154        fn memory(&self) -> Option<Arc<dyn crate::Memory>> {
155            None
156        }
157        fn session(&self) -> &dyn Session {
158            &self.session
159        }
160        fn run_config(&self) -> &RunConfig {
161            &self.config
162        }
163        fn end_invocation(&self) {}
164        fn ended(&self) -> bool {
165            false
166        }
167    }
168
169    #[async_trait]
170    impl Agent for TestAgent {
171        fn name(&self) -> &str {
172            &self.name
173        }
174
175        fn description(&self) -> &str {
176            "test agent"
177        }
178
179        fn sub_agents(&self) -> &[Arc<dyn Agent>] {
180            &[]
181        }
182
183        async fn run(&self, _ctx: Arc<dyn InvocationContext>) -> Result<EventStream> {
184            let s = stream! {
185                yield Ok(Event::new("test"));
186            };
187            Ok(Box::pin(s))
188        }
189    }
190
191    #[test]
192    fn test_agent_trait() {
193        let agent = TestAgent { name: "test".to_string() };
194        assert_eq!(agent.name(), "test");
195        assert_eq!(agent.description(), "test agent");
196    }
197}
adk_core/agent.rs

adk_core/
agent.rs
