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//! ctx.wasm.run (javascript/src/plugin-context wasmAccess + wasm-worker.js) on wasmtime: the
//! same limits and WASM_* error codes, a fresh instance per call, the sha256 checked, compiled
//! modules cached by digest, and a wall-clock limit per call through epoch interruption.
use std::collections::HashMap;
use std::sync::{Arc, Mutex};
use std::time::Duration;
use serde_json::Value;
use sha2::{Digest, Sha256};
use wasmtime::{
Config, Engine, ExternType, Instance, Module, Store, StoreLimits, StoreLimitsBuilder, Trap,
};
pub const MODULE_BYTES: usize = 4 << 20;
/// The default input and output cap per call; a host raises it per run (budget ioBytes) up to IO_BYTES_MAX.
pub const IO_BYTES: usize = 1 << 20;
pub const IO_BYTES_MAX: usize = 16 << 20;
pub const MEMORY_PAGES: usize = 1024;
pub const WALL_TIME_MS: u64 = 5000;
const TICK_MS: u64 = 5;
pub fn sha256_hex(bytes: &[u8]) -> String {
Sha256::digest(bytes)
.iter()
.map(|b| format!("{b:02x}"))
.collect()
}
pub fn entry_ok(entry: &str) -> bool {
let mut chars = entry.chars();
matches!(chars.next(), Some(c) if c.is_ascii_alphabetic() || c == '_')
&& entry.len() <= 256
&& chars.all(|c| c.is_ascii_alphanumeric() || c == '_')
}
/// ATLIBS_WASM_CONCURRENCY: how many runs execute at once in a process (default: its cores). Hosts
/// check it at startup (atlibs: before any command), so a bad value is an error there, not mid-run.
pub fn concurrency() -> Result<usize, String> {
parse_concurrency(std::env::var("ATLIBS_WASM_CONCURRENCY").ok())
}
fn parse_concurrency(value: Option<String>) -> Result<usize, String> {
match value.filter(|v| !v.trim().is_empty()) {
None => Ok(std::thread::available_parallelism().map_or(1, |n| n.get())),
Some(v) => v.trim().parse().ok().filter(|n| *n > 0).ok_or_else(|| {
format!("ATLIBS_WASM_CONCURRENCY must be a positive integer, not {v:?}")
}),
}
}
/// One per process (atlibs's run::Host, the agents service, a bridge run): its semaphore bounds the
/// runs executing at once, so overlapping requests cannot multiply per-instance memory without limit.
pub struct Wasm {
engine: Engine,
cache: Mutex<HashMap<String, Module>>,
timeout_ms: u64,
slots: Arc<tokio::sync::Semaphore>,
}
impl Wasm {
/// Panics on a bad ATLIBS_WASM_CONCURRENCY: check `concurrency()` first to report it.
pub fn new(timeout_ms: u64) -> Arc<Self> {
Self::with_concurrency(timeout_ms, concurrency().unwrap_or_else(|e| panic!("{e}")))
}
pub fn with_concurrency(timeout_ms: u64, slots: usize) -> Arc<Self> {
let mut config = Config::new();
config.epoch_interruption(true);
// The memory cap (StoreLimits.memory_size) is per memory: one 32-bit memory per module, as
// the JS host's capMemory refuses a second memory or memory64.
config.wasm_multi_memory(false);
config.wasm_memory64(false);
// Compiled code cached on disk (wasmtime's default cache dir), so a CLI run skips Cranelift.
config.cache(wasmtime::Cache::from_file(None).ok());
let engine = Engine::new(&config).expect("wasmtime engine");
let ticker = engine.weak();
std::thread::spawn(move || {
while let Some(engine) = ticker.upgrade() {
engine.increment_epoch();
drop(engine);
std::thread::sleep(Duration::from_millis(TICK_MS));
}
});
Arc::new(Self {
engine,
cache: Mutex::default(),
timeout_ms,
slots: Arc::new(tokio::sync::Semaphore::new(
slots.clamp(1, tokio::sync::Semaphore::MAX_PERMITS),
)),
})
}
/// Run `entry` with `input` as JSON; errors are "WASM_<CODE>: message", as the JS host throws.
pub async fn run(
self: &Arc<Self>,
module: Arc<Vec<u8>>,
sha256: Option<String>,
entry: String,
input: &Value,
io_bytes: usize,
) -> Result<Value, String> {
let io = if io_bytes == 0 { IO_BYTES } else { io_bytes.min(IO_BYTES_MAX) };
if module.len() > MODULE_BYTES {
return Err(format!(
"WASM_TOO_LARGE: module exceeds {MODULE_BYTES} bytes"
));
}
if !entry_ok(&entry) {
return Err("WASM_ABI_INVALID: entry must be an export name".into());
}
let input = serde_json::to_vec(input).map_err(|e| format!("WASM_ABI_INVALID: {e}"))?;
if input.len() > io {
return Err(format!("WASM_TOO_LARGE: input exceeds {io} bytes"));
}
// Queued here (FIFO) rather than on the blocking pool; the wall-time limit starts in call(),
// so time spent waiting for a slot is not counted against it.
let permit = self.slots.clone().acquire_owned().await.map_err(|e| format!("WASM_UNAVAILABLE: {e}"))?;
let this = self.clone();
tokio::task::spawn_blocking(move || {
// held until the blocking task ends, even when the caller stops waiting (its memory is live till then)
let _permit = permit;
let digest = sha256_hex(&module);
if sha256.is_some_and(|s| s.to_lowercase() != digest) {
return Err("WASM_DIGEST_MISMATCH: module digest does not match sha256".into());
}
let compiled = this.compile(&digest, &module)?;
this.call(&compiled, &entry, &input, io)
})
.await
.map_err(|e| format!("WASM_UNAVAILABLE: {e}"))?
}
/// The entries `module` exports (its functions but alloc), so a host can answer "no entry X (a, b)"
/// before a run. Compiles it (cached, as run does).
pub fn entries(&self, module: &[u8]) -> Result<Vec<String>, String> {
let compiled = self.compile(&sha256_hex(module), module)?;
Ok(compiled.exports().filter(|e| matches!(e.ty(), ExternType::Func(_)) && e.name() != "alloc").map(|e| e.name().to_string()).collect())
}
fn compile(&self, digest: &str, bytes: &[u8]) -> Result<Module, String> {
let cached = self.cache.lock().unwrap().get(digest).cloned();
let module = match cached {
Some(module) => module,
None => {
let module = Module::new(&self.engine, bytes)
.map_err(|e| format!("WASM_ABI_INVALID: {e}"))?;
self.cache
.lock()
.unwrap()
.insert(digest.into(), module.clone());
module
}
};
if module.imports().len() > 0 {
return Err("WASM_IMPORTS_NOT_ALLOWED: modules must not declare imports".into());
}
// A minimum over the cap is refused here, as the JS host's capMemory does.
if module.exports().any(
|e| matches!(e.ty(), ExternType::Memory(m) if m.minimum() > MEMORY_PAGES as u64),
) {
return Err(format!(
"WASM_TOO_LARGE: memory exceeds {MEMORY_PAGES} pages"
));
}
Ok(module)
}
fn call(&self, module: &Module, entry: &str, input: &[u8], io: usize) -> Result<Value, String> {
// The memory cap holds inside the call: memory.grow past it returns -1 (the JS host caps
// the module's declared maximum, capMemory, to the same effect).
let limits: StoreLimits = StoreLimitsBuilder::new()
.memory_size(MEMORY_PAGES * 65536)
.memories(1)
.instances(1)
.build();
let mut store = Store::new(&self.engine, limits);
store.limiter(|limits| limits);
store.set_epoch_deadline(self.timeout_ms.div_ceil(TICK_MS).max(1));
store.epoch_deadline_trap();
let timeout = |e: wasmtime::Error| -> String {
match e.downcast_ref::<Trap>() {
Some(Trap::Interrupt) => format!(
"WASM_TIMEOUT: {entry} ran longer than {} ms",
self.timeout_ms
),
Some(trap) => format!("WASM_TRAP: {}", v8_message(*trap)),
None => format!("WASM_TRAP: {e}"),
}
};
let instance = Instance::new(&mut store, module, &[]).map_err(timeout)?;
let (Some(memory), Some(alloc), Some(func)) = (
instance.get_memory(&mut store, "memory"),
instance.get_func(&mut store, "alloc"),
instance.get_func(&mut store, entry),
) else {
return Err(format!(
"WASM_ABI_INVALID: module must export memory, alloc and {entry}"
));
};
let alloc = alloc
.typed::<i32, i32>(&store)
.map_err(|e| format!("WASM_TRAP: {e}"))?;
let func = func
.typed::<(i32, i32), i64>(&store)
.map_err(|_| format!("WASM_ABI_INVALID: {entry} must return i64"))?;
let pointer = alloc
.call(&mut store, input.len() as i32)
.map_err(timeout)? as u32 as usize;
memory
.write(&mut store, pointer, input)
.map_err(|e| format!("WASM_TRAP: {e}"))?;
let packed = func
.call(&mut store, (pointer as i32, input.len() as i32))
.map_err(timeout)? as u64;
let size = memory.data_size(&store);
if size > MEMORY_PAGES * 65536 {
return Err(format!(
"WASM_TOO_LARGE: memory exceeds {MEMORY_PAGES} pages"
));
}
let (out_ptr, out_len) = ((packed >> 32) as usize, (packed & 0xffff_ffff) as usize);
if out_len > io {
return Err(format!("WASM_OUTPUT_INVALID: output exceeds {io} bytes"));
}
if out_ptr + out_len > size {
return Err("WASM_OUTPUT_INVALID: output points outside memory".into());
}
let bytes = &memory.data(&store)[out_ptr..out_ptr + out_len];
std::str::from_utf8(bytes)
.ok()
.and_then(|text| serde_json::from_str(text).ok())
.ok_or_else(|| "WASM_OUTPUT_INVALID: output is not JSON".into())
}
}
/// ctx.wasm.run bound to one module's bytes and expected sha256.
pub struct Bound {
pub wasm: Arc<Wasm>,
pub bytes: Arc<Vec<u8>>,
pub sha256: Option<String>,
}
impl crate::run::Runner for Bound {
fn run(&self, entry: String, input: Value, io_bytes: usize) -> crate::BoxFut<'_, Result<Value, String>> {
Box::pin(async move {
self.wasm
.run(self.bytes.clone(), self.sha256.clone(), entry, &input, io_bytes)
.await
})
}
}
/// V8's wording for wasm traps, so WASM_TRAP messages match the JS host.
fn v8_message(trap: Trap) -> String {
match trap {
Trap::UnreachableCodeReached => "unreachable",
Trap::MemoryOutOfBounds | Trap::HeapMisaligned => "memory access out of bounds",
Trap::IntegerDivisionByZero => "divide by zero",
Trap::IntegerOverflow => "divide result unrepresentable",
Trap::BadConversionToInteger => "float unrepresentable in integer range",
Trap::TableOutOfBounds => "table index is out of bounds",
Trap::IndirectCallToNull | Trap::BadSignature => {
"null function or function signature mismatch"
}
Trap::StackOverflow => "Maximum call stack size exceeded",
other => return other.to_string(),
}
.into()
}
#[cfg(test)]
mod tests {
use super::*;
// (module (memory (export "memory") 1) (func (export "alloc") (param i32) (result i32) i32.const 16)
// (func (export "spin") (param i32 i32) (result i64) (loop br 0) i64.const 0)
// (func (export "boom") (param i32 i32) (result i64) unreachable)
// (func (export "echo") (param i32 i32) (result i64) i64.const 16 i64.const 32 i64.shl local.get 1 i64.extend_i32_u i64.or))
// Hand-assembled binary of the module above (no wat dependency).
fn toy() -> Vec<u8> {
let mut m = vec![0, 0x61, 0x73, 0x6d, 1, 0, 0, 0];
let section = |m: &mut Vec<u8>, id: u8, body: Vec<u8>| {
m.push(id);
m.push(body.len() as u8);
m.extend(body);
};
section(
&mut m,
1,
vec![2, 0x60, 1, 0x7f, 1, 0x7f, 0x60, 2, 0x7f, 0x7f, 1, 0x7e],
);
section(&mut m, 3, vec![4, 0, 1, 1, 1]);
section(&mut m, 5, vec![1, 0, 1]);
let mut exports = vec![5];
for (name, kind, index) in [
("memory", 2u8, 0u8),
("alloc", 0, 0),
("spin", 0, 1),
("boom", 0, 2),
("echo", 0, 3),
] {
exports.push(name.len() as u8);
exports.extend(name.as_bytes());
exports.extend([kind, index]);
}
section(&mut m, 7, exports);
let bodies: [Vec<u8>; 4] = [
vec![0, 0x41, 16, 0x0b],
vec![0, 0x03, 0x40, 0x0c, 0, 0x0b, 0x42, 0, 0x0b],
vec![0, 0x00, 0x0b],
vec![0, 0x42, 16, 0x42, 32, 0x86, 0x20, 1, 0xad, 0x84, 0x0b],
];
let mut code = vec![4];
for body in bodies {
code.push(body.len() as u8);
code.extend(body);
}
section(&mut m, 10, code);
m
}
// exports memory (min pages, no maximum, as rustc emits), alloc, and grow: memory.grow(2000),
// then {"grew":false} when that returned -1, else {"grew":true}. The same bytes are in
// javascript/src/plugin-context/wasm.test.mjs.
fn grow(min: u16) -> Vec<u8> {
let memory: &[u8] = if min == 1 {
&[0x05, 0x03, 0x01, 0x00, 0x01]
} else {
&[0x05, 0x04, 0x01, 0x00, 0xd0, 0x0f]
};
[
&[
0x00, 0x61, 0x73, 0x6d, 0x01, 0x00, 0x00, 0x00, 0x01, 0x0c, 0x02, 0x60, 0x01, 0x7f,
0x01, 0x7f, 0x60, 0x02, 0x7f, 0x7f, 0x01, 0x7e, 0x03, 0x03, 0x02, 0x00, 0x01,
][..],
memory,
&[
0x07, 0x19, 0x03, 0x06, 0x6d, 0x65, 0x6d, 0x6f, 0x72, 0x79, 0x02, 0x00, 0x05, 0x61,
0x6c, 0x6c, 0x6f, 0x63, 0x00, 0x00, 0x04, 0x67, 0x72, 0x6f, 0x77, 0x00, 0x01, 0x0a,
0x1f, 0x02, 0x05, 0x00, 0x41, 0xc0, 0x00, 0x0b, 0x17, 0x00, 0x41, 0xd0, 0x0f, 0x40,
0x00, 0x41, 0x7f, 0x46, 0x04, 0x7e, 0x42, 0x0e, 0x05, 0x42, 0x8d, 0x80, 0x80, 0x80,
0x80, 0x02, 0x0b, 0x0b, 0x0b, 0x23, 0x01, 0x00, 0x41, 0x00, 0x0b, 0x1d,
],
br#"{"grew":false}"#,
&[0, 0],
br#"{"grew":true}"#,
]
.concat()
}
#[tokio::test]
async fn memory_cap_holds_inside_the_call() {
let wasm = Wasm::new(1000);
let input = serde_json::json!({});
assert_eq!(
wasm.run(Arc::new(grow(1)), None, "grow".into(), &input, 0)
.await
.unwrap(),
serde_json::json!({ "grew": false })
);
assert_eq!(
wasm.run(Arc::new(grow(2000)), None, "grow".into(), &input, 0)
.await
.unwrap_err(),
"WASM_TOO_LARGE: memory exceeds 1024 pages"
);
// A second memory (or memory64) would escape the per-memory cap: refused at compile.
let one = grow(1);
let two = [&one[..27], &[0x05, 0x05, 0x02, 0x00, 0x01, 0x00, 0x01], &one[32..]].concat();
let mut wide = one.clone();
wide[30] = 0x04;
for module in [two, wide] {
let e = wasm.run(Arc::new(module), None, "grow".into(), &input, 0).await.unwrap_err();
assert!(e.starts_with("WASM_ABI_INVALID: "), "{e}");
}
}
// Each spin executes for its full wall time T, so with 2 slots the (2k+1)th and (2k+2)th runs end
// no earlier than (k+1)·T (never more than 2 at once), and the first two end together (2 at once).
// The echo queued behind them waits ~3T, longer than T, and still succeeds.
#[tokio::test]
async fn concurrency_is_bounded_and_queued_time_is_not_wall_time() {
const T: u64 = 300;
let wasm = Wasm::with_concurrency(T, 2);
let module = Arc::new(toy());
let started = std::time::Instant::now();
let run = |entry: &'static str| {
let (wasm, module) = (wasm.clone(), module.clone());
tokio::spawn(async move {
let result = wasm.run(module, None, entry.into(), &serde_json::json!([1]), 0).await;
(result, started.elapsed())
})
};
let spins: Vec<_> = (0..6).map(|_| run("spin")).collect();
let echo = run("echo");
let mut ends = vec![];
for spin in spins {
let (result, end) = spin.await.unwrap();
assert_eq!(result.unwrap_err(), format!("WASM_TIMEOUT: spin ran longer than {T} ms"));
ends.push(end);
}
ends.sort();
for (i, end) in ends.iter().enumerate() {
assert!(*end >= Duration::from_millis((i as u64 / 2 + 1) * (T - 10)), "run {i}: {ends:?}");
}
assert!(ends[1] < Duration::from_millis(2 * T - 50), "two at once: {ends:?}");
let (result, end) = echo.await.unwrap();
assert_eq!(result.unwrap(), serde_json::json!([1]));
assert!(end >= Duration::from_millis(3 * (T - 10)), "queued behind the spins: {end:?}");
}
#[test]
fn concurrency_env_must_be_a_positive_integer() {
let parse = |v: &str| parse_concurrency(Some(v.into()));
assert_eq!((parse("2"), parse(" 3 ")), (Ok(2), Ok(3)));
assert!(parse("").unwrap() >= 1 && parse_concurrency(None).unwrap() >= 1, "unset: the cores");
for bad in ["0", "-1", "two", "1.5"] {
assert_eq!(parse(bad).unwrap_err(), format!("ATLIBS_WASM_CONCURRENCY must be a positive integer, not {bad:?}"));
}
}
#[tokio::test]
async fn limits_and_errors_match_the_js_host() {
let wasm = Wasm::new(200);
let module = Arc::new(toy());
let input = serde_json::json!({ "a": [1, "b"] });
assert_eq!(
wasm.run(module.clone(), None, "echo".into(), &input, 0)
.await
.unwrap(),
input
);
let digest = sha256_hex(&module);
assert!(
wasm.run(
module.clone(),
Some(digest.to_uppercase()),
"echo".into(),
&input, 0
)
.await
.is_ok()
);
// input past 1 MiB: refused by default, let through by a larger io (then it traps: one page of
// memory), and never past IO_BYTES_MAX
let big = serde_json::json!({ "x": "x".repeat(IO_BYTES) });
assert_eq!(wasm.run(module.clone(), None, "echo".into(), &big, 0).await.unwrap_err(), format!("WASM_TOO_LARGE: input exceeds {IO_BYTES} bytes"));
assert!(wasm.run(module.clone(), None, "echo".into(), &big, 2 << 20).await.unwrap_err().starts_with("WASM_TRAP"));
let huge = serde_json::json!({ "x": "x".repeat(IO_BYTES_MAX) });
assert_eq!(wasm.run(module.clone(), None, "echo".into(), &huge, 1 << 30).await.unwrap_err(), format!("WASM_TOO_LARGE: input exceeds {IO_BYTES_MAX} bytes"));
assert_eq!(
wasm.run(module.clone(), Some("00".into()), "echo".into(), &input, 0)
.await
.unwrap_err(),
"WASM_DIGEST_MISMATCH: module digest does not match sha256"
);
assert_eq!(
wasm.run(module.clone(), None, "boom".into(), &input, 0)
.await
.unwrap_err(),
"WASM_TRAP: unreachable"
);
assert_eq!(
wasm.run(module.clone(), None, "nope".into(), &input, 0)
.await
.unwrap_err(),
"WASM_ABI_INVALID: module must export memory, alloc and nope"
);
let entries = wasm.entries(&module).unwrap();
assert!(entries.contains(&"echo".to_string()) && entries.contains(&"boom".to_string()) && !entries.iter().any(|e| e == "alloc" || e == "memory"), "{entries:?}");
assert_eq!(
wasm.run(module.clone(), None, "1x".into(), &input, 0)
.await
.unwrap_err(),
"WASM_ABI_INVALID: entry must be an export name"
);
let started = std::time::Instant::now();
assert_eq!(
wasm.run(module, None, "spin".into(), &input, 0)
.await
.unwrap_err(),
"WASM_TIMEOUT: spin ran longer than 200 ms"
);
assert!(started.elapsed() < Duration::from_secs(2));
}
}
