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//! Host built-ins callable from `run_code` (ADR 0005): MCP resources and
//! watches. They are catalog entries whose routing name starts with
//! [`PREFIX`], so they never collide with an MCP tool.
use std::future::Future;
use std::pin::Pin;
use std::sync::Arc;
use serde_json::{json, Value};
use super::watch::WatchManager;
use crate::resources::ResourceSource;
use crate::tools::{ToolCallOutput, ToolDefinition, ToolError};
/// Routing prefix for built-ins; not a valid MCP tool name prefix in practice.
pub const PREFIX: &str = "asyncai::";
#[derive(Default)]
pub struct Builtins {
pub resources: Option<Arc<dyn ResourceSource>>,
pub watches: Option<Arc<WatchManager>>,
}
fn string() -> Value {
json!({"type": "string"})
}
fn object(properties: Value, required: &[&str]) -> Value {
json!({"type": "object", "properties": properties, "required": required})
}
impl Builtins {
/// Python-facing definitions; names are Python identifiers.
pub fn definitions(&self) -> Vec<ToolDefinition> {
let mut definitions = Vec::new();
if self.resources.is_none() {
return definitions;
}
let mut list = ToolDefinition::new(
"list_resources",
Some("List MCP resources and resource templates. `uri` is the URI, or an RFC 6570 template when `template` is true (fill in the {placeholders}); `example` is ready-to-adapt code; `subscribable` ones can be watched.\nExample: [(r[\"uri\"], r.get(\"example\")) for r in await list_resources() if r[\"subscribable\"]]"),
object(json!({}), &[]),
);
list.output_schema = Some(json!({"type": "array", "items": {
"type": "object",
"properties": {
"uri": string(), "template": {"type": "boolean"}, "name": string(),
"description": string(), "example": string(), "mime_type": string(),
"server": string(), "subscribable": {"type": "boolean"},
},
"required": ["uri", "template", "name", "server", "subscribable"],
"additionalProperties": false,
}}));
list.read_only = Some(true);
definitions.push(list);
let mut read = ToolDefinition::new(
"read_resource",
Some("Read one MCP resource; JSON arrives parsed.\nExample: await read_resource(uri=\"memo://notes\")"),
object(json!({"uri": string()}), &["uri"]),
);
read.read_only = Some(true);
definitions.push(read);
if self.watches.is_none() {
return definitions;
}
let mut start = ToolDefinition::new(
"watch_start",
Some("Watch an MCP resource for changes (pushed, no polling). Asked to monitor or watch something: call this first, then refine. Changes arrive later as <watch-event> messages; bursts are merged and a line repeated for the same object is dropped. Without on_event each event becomes a line like `MODIFIED ns/name (status.phase: Pending→Running)`. `on_event` is optional Python run per event with `event` defined: {type: ADDED|MODIFIED|DELETED, object, old (previous object or None), changed (dotted paths, MODIFIED only)}; its last expression is the line, None drops the event. on_event may only call read-only tools; helpers like dig() work there.\nExample: await watch_start(name=\"vms\", uri=\"kcp-events://watch/root/computevms\", on_event=\"f\\\"{event['type']} {dig(event, 'object.metadata.name')} {dig(event, 'old.status.phase')}->{dig(event, 'object.status.phase')}\\\" if event['type'] != 'MODIFIED' or 'status.phase' in event.get('changed', []) else None\")"),
object(
json!({"name": string(), "uri": string(), "on_event": string()}),
&["name", "uri"],
),
);
start.output_schema = Some(object(
json!({"name": string(), "uri": string(), "shape": {"enum": ["state", "event-log"]}}),
&[],
));
definitions.push(start);
let mut stop = ToolDefinition::new(
"watch_stop",
Some(
"Stop a watch. Returns whether it existed.\nExample: await watch_stop(name=\"cm\")",
),
object(json!({"name": string()}), &["name"]),
);
stop.output_schema = Some(json!({"type": "boolean"}));
definitions.push(stop);
let mut list_watches = ToolDefinition::new(
"watch_list",
Some("Active watches.\nExample: [w[\"name\"] for w in await watch_list()]"),
object(json!({}), &[]),
);
list_watches.output_schema = Some(json!({"type": "array", "items": object(
json!({"name": string(), "uri": string(), "shape": string(), "events": {"type": "integer"}, "notices": {"type": "integer"}}),
&[],
)}));
list_watches.read_only = Some(true);
definitions.push(list_watches);
definitions
}
/// Boxed so the watch task → filter → built-in → `watch_start` →
/// spawn(watch task) cycle has a nameable `Send` future.
pub fn call<'a>(
&'a self,
name: &'a str,
arguments: Value,
) -> Pin<Box<dyn Future<Output = Result<ToolCallOutput, ToolError>> + Send + 'a>> {
Box::pin(self.call_inner(name, arguments))
}
async fn call_inner(&self, name: &str, arguments: Value) -> Result<ToolCallOutput, ToolError> {
let text = |key: &str| {
arguments
.get(key)
.and_then(Value::as_str)
.map(str::to_string)
.ok_or_else(|| ToolError::new(format!("{name}() requires {key}")))
};
let resources = self
.resources
.as_ref()
.ok_or_else(|| ToolError::new("no MCP resources available"))?;
let watches = || {
self.watches
.as_ref()
.ok_or_else(|| ToolError::new(format!("{name}() is not available here")))
};
let json_output = |value: Value| Ok(ToolCallOutput::text(value.to_string()));
match name {
"list_resources" => json_output(json!(resources.list_resources().await?)),
"read_resource" => Ok(ToolCallOutput::text(
resources.read_resource(&text("uri")?).await?.text,
)),
"watch_start" => {
let on_event = match arguments.get("on_event") {
None | Some(Value::Null) => None,
Some(Value::String(code)) if !looks_like_object_repr(code) => {
Some(code.clone())
}
Some(other) => {
return Ok(ToolCallOutput::error(format!(
"on_event must be Python source text (a str), not a function or object (got {}). \
Functions do not cross into the watch scope; pass the body as a string, e.g. \
on_event=\"f\\\"{{event['type']}} {{dig(event, 'object.metadata.name')}}\\\"\"",
crate::resources::truncate(&other.to_string(), 80)
)))
}
};
match watches()?
.start(&text("name")?, &text("uri")?, on_event)
.await
{
Ok(value) => json_output(value),
Err(message) => Ok(ToolCallOutput::error(message)),
}
}
"watch_stop" => json_output(json!(watches()?.stop(&text("name")?))),
"watch_list" => json_output(watches()?.list()),
other => Err(ToolError::new(format!("unknown built-in {other}"))),
}
}
}
/// A Python object that crossed the sandbox boundary as its `repr()`:
/// `Repr("<function 'fmt' at 0xec>")`, `<function f at ...>`, `<lambda>`.
fn looks_like_object_repr(code: &str) -> bool {
let code = code.trim();
let inner = code
.strip_prefix("Repr(")
.map(|rest| rest.trim_start_matches(['"', '\'']))
.unwrap_or(code);
[
"<function",
"<lambda",
"<bound method",
"<built-in",
"<coroutine",
]
.iter()
.any(|prefix| inner.starts_with(prefix))
}
