agentsight_ext_runtime/
lib.rs

1// SPDX-License-Identifier: MIT
2// Copyright (c) 2026 eunomia-bpf org.
3
4use wasmtime::component::{Component, Linker, ResourceTable};
5use wasmtime::{Config, Engine, Store, StoreLimits, StoreLimitsBuilder};
6use wasmtime_wasi::{WasiCtx, WasiCtxView, WasiView};
7
8const DEFAULT_MEMORY_BYTES: usize = 64 * 1024 * 1024;
9const DEFAULT_FUEL: u64 = 10_000_000;
10const MAX_CORE_INSTANCES: usize = 16;
11const MAX_MEMORIES: usize = 4;
12const MAX_TABLES: usize = 8;
13const MAX_COMPONENT_BYTES: usize = 16 * 1024 * 1024;
14const MAX_CONTENT_BYTES: usize = 16 * 1024 * 1024;
15const MAX_METADATA_BYTES: usize = 64 * 1024;
16
17struct ExtStore {
18    limits: StoreLimits,
19    table: ResourceTable,
20    wasi: WasiCtx,
21}
22
23impl WasiView for ExtStore {
24    fn ctx(&mut self) -> WasiCtxView<'_> {
25        WasiCtxView {
26            ctx: &mut self.wasi,
27            table: &mut self.table,
28        }
29    }
30}
31
32/// Bounded in-process host for WebAssembly Components.
33///
34/// WASI P2 is linked for ABI compatibility, but the default context inherits
35/// no arguments, environment, stdio, directories, or network access. TCP/UDP
36/// are disabled outright. AgentSight-specific authority must be linked by an
37/// explicit capability-bearing host interface.
38///
39/// Component compilation is only exposed for trusted components shipped with
40/// AgentSight. This type is not an upload boundary for arbitrary user-supplied
41/// Wasm. Execution and input sizes are bounded independently.
42pub struct ExtRuntime {
43    engine: Engine,
44}
45
46impl ExtRuntime {
47    pub fn new() -> Result<Self, wasmtime::Error> {
48        let mut config = Config::new();
49        config.consume_fuel(true);
50        Ok(Self {
51            engine: Engine::new(&config)?,
52        })
53    }
54
55    fn store(&self) -> Result<Store<ExtStore>, wasmtime::Error> {
56        let mut wasi = WasiCtx::builder();
57        wasi.allow_tcp(false).allow_udp(false);
58        let mut store = Store::new(
59            &self.engine,
60            ExtStore {
61                limits: StoreLimitsBuilder::new()
62                    .memory_size(DEFAULT_MEMORY_BYTES)
63                    .instances(MAX_CORE_INSTANCES)
64                    .memories(MAX_MEMORIES)
65                    .tables(MAX_TABLES)
66                    .build(),
67                table: ResourceTable::new(),
68                wasi: wasi.build(),
69            },
70        );
71        store.limiter(|state| &mut state.limits);
72        store.set_fuel(DEFAULT_FUEL)?;
73        Ok(store)
74    }
75
76    pub fn session_parse(
77        &self,
78        component_bytes: &[u8],
79        agent: &str,
80        path: &str,
81        updated_ms: u64,
82        content: &str,
83    ) -> Result<Option<String>, wasmtime::Error> {
84        validate_session_input(component_bytes, agent, path, content)?;
85        let component = Component::from_binary(&self.engine, component_bytes)?;
86        let mut linker = Linker::<ExtStore>::new(&self.engine);
87        wasmtime_wasi::p2::add_to_linker_sync(&mut linker)?;
88        let mut store = self.store()?;
89        let instance = linker.instantiate(&mut store, &component)?;
90        let parse = instance.get_typed_func::<(String, String, u64, String), (Option<String>,)>(
91            &mut store, "parse",
92        )?;
93        Ok(parse
94            .call(
95                &mut store,
96                (
97                    agent.to_owned(),
98                    path.to_owned(),
99                    updated_ms,
100                    content.to_owned(),
101                ),
102            )?
103            .0)
104    }
105}
106
107fn validate_session_input(
108    component_bytes: &[u8],
109    agent: &str,
110    path: &str,
111    content: &str,
112) -> Result<(), wasmtime::Error> {
113    if component_bytes.len() > MAX_COMPONENT_BYTES {
114        return Err(wasmtime::Error::msg("extension component exceeds 16 MiB"));
115    }
116    if content.len() > MAX_CONTENT_BYTES {
117        return Err(wasmtime::Error::msg("session content exceeds 16 MiB"));
118    }
119    if agent.len().saturating_add(path.len()) > MAX_METADATA_BYTES {
120        return Err(wasmtime::Error::msg("session metadata exceeds 64 KiB"));
121    }
122    Ok(())
123}
124
125#[cfg(test)]
126mod tests {
127    use super::*;
128
129    #[test]
130    fn rejects_oversized_component_content_and_metadata() {
131        assert!(
132            validate_session_input(&vec![0; MAX_COMPONENT_BYTES + 1], "codex", "x", "x").is_err()
133        );
134        assert!(
135            validate_session_input(&[], "codex", "x", &"x".repeat(MAX_CONTENT_BYTES + 1)).is_err()
136        );
137        assert!(validate_session_input(&[], &"a".repeat(MAX_METADATA_BYTES), "x", "x").is_err());
138    }
139}
agentsight_ext_runtime/lib.rs

agentsight_ext_runtime/
lib.rs
