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xsnap.js
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xsnap.js
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/* global process */
/* eslint no-await-in-loop: ["off"] */
/**
* @typedef {typeof import('child_process').spawn} Spawn
* @typedef {import('stream').Writable} Writable
*/
/**
* @template T
* @typedef {import('./defer').Deferred<T>} Deferred
*/
import { finished } from 'stream/promises';
import { PassThrough, Readable } from 'stream';
import { promisify } from 'util';
import { makeNetstringReader, makeNetstringWriter } from '@endo/netstring';
import { makeNodeReader, makeNodeWriter } from '@endo/stream-node';
import { makePromiseKit, racePromises } from '@endo/promise-kit';
import { forever } from '@agoric/internal';
import { ErrorCode, ErrorSignal, ErrorMessage, METER_TYPE } from '../api.js';
import { defer } from './defer.js';
const { Fail, quote: q } = assert;
// This will need adjustment, but seems to be fine for a start.
export const DEFAULT_CRANK_METERING_LIMIT = 1e8;
const encoder = new TextEncoder();
const decoder = new TextDecoder();
const COMMAND_BUF = encoder.encode('?');
const QUERY = '?'.charCodeAt(0);
const QUERY_RESPONSE_BUF = encoder.encode('/');
const OK = '.'.charCodeAt(0);
const ERROR = '!'.charCodeAt(0);
const OK_SEPARATOR = 1;
const SNAPSHOT_SAVE_FD = 7;
const SNAPSHOT_LOAD_FD = 8;
const { freeze } = Object;
const noop = freeze(() => {});
/**
* @param {Uint8Array} arg
* @returns {Uint8Array}
*/
function echoCommand(arg) {
return arg;
}
const safeHintFromDescription = description =>
description.replaceAll(/[^a-zA-Z0-9_.-]/g, '-');
/**
* @param {XSnapOptions} options
*
* @typedef {object} XSnapOptions
* @property {string} os
* @property {Spawn} spawn
* @property {Pick<typeof import('fs/promises'), 'open' | 'stat' | 'unlink'> & Pick<typeof import('fs'), 'createReadStream'> & Pick<typeof import('tmp'), 'tmpName'>} fs
* @property {(request:Uint8Array) => Promise<Uint8Array>} [handleCommand]
* @property {string} [name]
* @property {boolean} [debug]
* @property {number} [netstringMaxChunkSize] in bytes (must be an integer)
* @property {number} [parserBufferSize] in kB (must be an integer)
* @property {AsyncIterable<Uint8Array>} [snapshotStream]
* @property {string} [snapshotDescription]
* @property {boolean} [snapshotUseFs]
* @property {'ignore' | 'inherit'} [stdout]
* @property {'ignore' | 'inherit'} [stderr]
* @property {number} [meteringLimit]
* @property {Record<string, string>} [env]
*/
export async function xsnap(options) {
const {
os,
spawn,
fs,
name = '<unnamed xsnap worker>',
handleCommand = echoCommand,
debug = false,
netstringMaxChunkSize = undefined,
parserBufferSize = undefined,
snapshotStream,
snapshotDescription = snapshotStream && 'unknown',
snapshotUseFs = false,
stdout = 'ignore',
stderr = 'ignore',
meteringLimit = DEFAULT_CRANK_METERING_LIMIT,
env = process.env,
} = options;
const platform = {
Linux: 'lin',
Darwin: 'mac',
Windows_NT: 'win',
}[os];
if (platform === undefined) {
throw Error(`xsnap does not support platform ${os}`);
}
/** @type {(opts: import('tmp').TmpNameOptions) => Promise<string>} */
const ptmpName = fs.tmpName && promisify(fs.tmpName);
const makeLoadSnapshotHandlerWithFS = async () => {
assert(snapshotStream);
const snapPath = await ptmpName({
template: `load-snapshot-${safeHintFromDescription(
snapshotDescription,
)}-XXXXXX.xss`,
});
const afterSpawn = async () => {};
const cleanup = async () => fs.unlink(snapPath);
try {
const tmpSnap = await fs.open(snapPath, 'w');
await tmpSnap.writeFile(
// @ts-expect-error incorrect typings, does support AsyncIterable
snapshotStream,
);
await tmpSnap.close();
} catch (e) {
await cleanup();
throw e;
}
return harden({
snapPath,
afterSpawn,
cleanup,
});
};
const makeLoadSnapshotHandlerWithPipe = async () => {
let done = Promise.resolve();
const cleanup = async () => done;
/** @param {Writable} loadSnapshotsStream */
const afterSpawn = async loadSnapshotsStream => {
assert(snapshotStream);
const destStream = loadSnapshotsStream;
const sourceStream = Readable.from(snapshotStream);
sourceStream.pipe(destStream, { end: false });
done = finished(sourceStream);
done.catch(noop).then(() => sourceStream.unpipe(destStream));
};
return harden({
snapPath: `@${SNAPSHOT_LOAD_FD}:${safeHintFromDescription(
snapshotDescription,
)}`,
afterSpawn,
cleanup,
});
};
let bin = new URL(
`../xsnap-native/xsnap/build/bin/${platform}/${
debug ? 'debug' : 'release'
}/xsnap-worker`,
import.meta.url,
).pathname;
/** @type {Deferred<void>} */
const vatExit = defer();
assert(!/^-/.test(name), `name '${name}' cannot start with hyphen`);
let loadSnapshotHandler = await (snapshotStream &&
(snapshotUseFs
? makeLoadSnapshotHandlerWithFS
: makeLoadSnapshotHandlerWithPipe)());
let args = [name];
if (loadSnapshotHandler) {
args.push('-r', loadSnapshotHandler.snapPath);
}
if (meteringLimit) {
args.push('-l', `${meteringLimit}`);
}
if (parserBufferSize) {
args.push('-s', `${parserBufferSize}`);
}
if (env.XSNAP_DEBUG_RR) {
args = [bin, ...args];
bin = 'rr';
console.log('XSNAP_DEBUG_RR', { bin, args });
}
const xsnapProcess = spawn(bin, args, {
stdio: [
'ignore', // 0: stdin
stdout, // 1: stdout
stderr, // 2: stderr
'pipe', // 3: messagesToXsnap
'pipe', // 4: messagesFromXsnap
'ignore', // 5: XSBug
'ignore', // 6: XSProfiler
snapshotUseFs ? 'ignore' : 'pipe', // 7: snapshotSaveStream
snapshotUseFs || !snapshotStream ? 'ignore' : 'pipe', // 8: snapshotLoadStream
],
});
xsnapProcess.once('exit', (code, signal) => {
if (code === 0) {
vatExit.resolve();
} else if (signal !== null) {
const reason = new ErrorSignal(
signal,
`${name} exited due to signal ${signal}`,
);
vatExit.reject(reason);
} else if (code === null) {
throw TypeError('null code???');
} else {
const reason = new ErrorCode(
code,
`${name} exited: ${ErrorMessage[code] || 'unknown error'}`,
);
vatExit.reject(reason);
}
});
const vatCancelled = vatExit.promise.then(() => {
throw Error(`${name} exited`);
});
const xsnapProcessStdio =
/** @type {[undefined, Readable, Readable, Writable, Readable, undefined, undefined, Readable, Writable]} */ (
/** @type {(Readable | Writable | undefined | null)[]} */ (
xsnapProcess.stdio
)
);
const messagesToXsnap = makeNetstringWriter(
makeNodeWriter(xsnapProcessStdio[3]),
);
const messagesFromXsnap = makeNetstringReader(
makeNodeReader(xsnapProcessStdio[4]),
{ maxMessageLength: netstringMaxChunkSize },
);
const snapshotSaveStream = xsnapProcessStdio[SNAPSHOT_SAVE_FD];
const snapshotLoadStream = xsnapProcessStdio[SNAPSHOT_LOAD_FD];
await loadSnapshotHandler?.afterSpawn(snapshotLoadStream);
if (loadSnapshotHandler) {
vatExit.promise.catch(noop).then(() => {
if (loadSnapshotHandler) {
const { cleanup } = loadSnapshotHandler;
loadSnapshotHandler = undefined;
return cleanup();
}
});
}
/** @type {Promise<void>} */
let baton = Promise.resolve();
/**
* @template T
* @typedef {object} RunResult
* @property {T} reply
* @property {{ meterType: string, allocate: number|null, compute: number|null, timestamps: number[]|null }} meterUsage
*/
/**
* @returns {Promise<RunResult<Uint8Array>>}
*/
async function runToIdle() {
for await (const _ of forever) {
const iteration = await messagesFromXsnap.next(undefined);
if (loadSnapshotHandler) {
const { cleanup } = loadSnapshotHandler;
loadSnapshotHandler = undefined;
await cleanup();
}
if (iteration.done) {
xsnapProcess.kill();
return vatCancelled;
}
const { value: message } = iteration;
if (message.byteLength === 0) {
// A protocol error kills the xsnap child process and breaks the baton
// chain with a terminal error.
xsnapProcess.kill();
throw Error('xsnap protocol error: received empty message');
} else if (message[0] === OK) {
let meterInfo = { compute: null, allocate: null, timestamps: [] };
const meterSeparator = message.indexOf(OK_SEPARATOR, 1);
if (meterSeparator >= 0) {
// The message is `.meterdata\1reply`.
const meterData = message.subarray(1, meterSeparator);
// We parse the meter data as JSON
meterInfo = JSON.parse(decoder.decode(meterData));
// assert(typeof meterInfo === 'object');
}
const meterUsage = {
meterType: METER_TYPE,
...meterInfo,
};
// console.log('have meterUsage', meterUsage);
return {
reply: message.subarray(meterSeparator < 0 ? 1 : meterSeparator + 1),
meterUsage,
};
} else if (message[0] === ERROR) {
throw Error(
`Uncaught exception in ${name}: ${decoder.decode(
message.subarray(1),
)}`,
);
} else if (message[0] === QUERY) {
const commandResult = await handleCommand(message.subarray(1));
await messagesToXsnap.next([QUERY_RESPONSE_BUF, commandResult]);
} else {
// unrecognized responses also kill the process
xsnapProcess.kill();
const m = decoder.decode(message);
throw Error(`xsnap protocol error: received unknown message <<${m}>>`);
}
}
throw Error(`unreachable, but tools don't know that`);
}
/**
* @param {string} code
* @returns {Promise<RunResult<Uint8Array>>}
*/
async function evaluate(code) {
const result = baton.then(async () => {
await messagesToXsnap.next(encoder.encode(`e${code}`));
return runToIdle();
});
baton = result.then(noop, noop);
return racePromises([vatCancelled, result]);
}
/**
* @param {string} fileName
* @returns {Promise<void>}
*/
async function execute(fileName) {
const result = baton.then(async () => {
await messagesToXsnap.next(encoder.encode(`s${fileName}`));
await runToIdle();
});
baton = result.then(noop, noop);
return racePromises([vatCancelled, result]);
}
/**
* @param {string} fileName
* @returns {Promise<void>}
*/
async function importModule(fileName) {
const result = baton.then(async () => {
await messagesToXsnap.next(encoder.encode(`m${fileName}`));
await runToIdle();
});
baton = result.then(noop, noop);
return racePromises([vatCancelled, result]);
}
/**
* @returns {Promise<void>}
*/
async function isReady() {
const result = baton.then(async () => {
await messagesToXsnap.next(encoder.encode(`R`));
await runToIdle();
});
baton = result.then(noop, noop);
return racePromises([vatCancelled, result]);
}
/**
* @param {Uint8Array} message
* @returns {Promise<RunResult<Uint8Array>>}
*/
async function issueCommand(message) {
const result = baton.then(async () => {
await messagesToXsnap.next([COMMAND_BUF, message]);
return runToIdle();
});
baton = result.then(noop, noop);
return racePromises([vatCancelled, result]);
}
/**
* @param {string} message
* @returns {Promise<RunResult<string>>}
*/
async function issueStringCommand(message) {
const result = await issueCommand(encoder.encode(message));
return { ...result, reply: decoder.decode(result.reply) };
}
/**
* @param {string} description
* @param {import('@endo/promise-kit').PromiseKit<void>} batonKit
* @returns {AsyncGenerator<Uint8Array, void, undefined>}
*/
async function* makeSnapshotInternal(description, batonKit) {
const output = new PassThrough({ highWaterMark: 1024 * 1024 });
let piped = false;
let cleaned = false;
let done = Promise.resolve();
let snapshotReadSize = 0;
/** @type {number | undefined} */
let snapshotSize;
await null;
try {
/** @type {string} */
let snapPath;
/** @type {Readable} */
let sourceStream;
const maybePipe = () => {
if (!piped && !cleaned) {
sourceStream.pipe(output);
piped = true;
}
};
if (snapshotUseFs) {
// TODO: Refactor to use tmpFile rather than tmpName.
snapPath = await ptmpName({
template: `make-snapshot-${safeHintFromDescription(
description,
)}-XXXXXX.xss`,
});
// For similarity with the pipe mode, we want to have a `sourceStream`
// available right away. However in FS mode, the temporary file will
// only be populated and ready to read after the command to xsnap
// returns.
// To work around this we create a file in `w+` mode first, create a
// readable stream immediately, then instruct xsnap to write into the
// same file (which it does with wb mode, re-truncating the file), and
// then wait for the command response to pipe the file stream into the
// output, causing the file read to begin.
const handle = await fs.open(snapPath, 'w+');
// @ts-expect-error 'close' event added in Node 15.4
handle.on('close', () => {
fs.unlink(snapPath);
});
sourceStream = handle.createReadStream();
finished(output).finally(() => sourceStream.destroy());
} else {
sourceStream = snapshotSaveStream;
snapPath = `@${SNAPSHOT_SAVE_FD}`;
// It's only safe to hook the shared save stream once we get the baton,
// ensuring that any previous save stream usage has ended. However we
// must start the flow before receiving the command's response or the
// xsnap process would block on a full pipe, causing an IPC deadlock.
batonKit.promise.then(maybePipe);
}
const cleanup = () => {
if (cleaned) return;
cleaned = true;
sourceStream.unpipe(output);
// eslint-disable-next-line no-use-before-define
output.off('data', onData);
output.end();
};
const checkDone = () => {
if (snapshotSize !== undefined && snapshotReadSize >= snapshotSize) {
cleanup();
}
};
const onData = chunk => {
snapshotReadSize += chunk.length;
checkDone();
};
output.on('data', onData);
const result = batonKit.promise.then(async () => {
// Tell xsnap to write the snapshot to the FS or the pipe
await messagesToXsnap.next(encoder.encode(`w${snapPath}`));
const { reply } = await runToIdle();
const lengthStr = decoder.decode(reply);
if (lengthStr.length) {
snapshotSize = Number(lengthStr);
// The snapshot was written successfully, start piping to the
// output in FS mode
maybePipe();
} else {
// This will cause the `finally` clause to throw, and inform any
// stream consumer any data seen so far is invalid
snapshotSize = -1;
}
checkDone();
});
batonKit.resolve(result);
done = racePromises([vatCancelled, result]);
done.catch(() => cleanup());
yield* output;
} finally {
await done;
(piped && snapshotReadSize === snapshotSize) ||
Fail`Snapshot size does not match. saved=${q(snapshotSize)}, read=${q(
snapshotReadSize,
)}`;
}
}
/**
* @param {string} [description]
* @returns {AsyncGenerator<Uint8Array, void, undefined>}
*/
function makeSnapshotStream(description = 'unknown') {
const { promise: internalResult, ...batonKitResolvers } = makePromiseKit();
const batonKit = { promise: baton, ...batonKitResolvers };
baton = internalResult.then(noop, noop);
return makeSnapshotInternal(description, batonKit);
}
/**
* @returns {Promise<void>}
*/
async function close() {
baton = baton.then(async () => {
const running = await racePromises([
vatExit.promise.then(() => false),
Promise.resolve(true),
]);
await (running && messagesToXsnap.next(encoder.encode(`q`)));
await messagesToXsnap.return(undefined);
throw Error(`${name} closed`);
});
baton.catch(noop); // Suppress Node.js unhandled exception warning.
return vatExit.promise;
}
/**
* @returns {Promise<void>}
*/
async function terminate() {
xsnapProcess.kill();
baton = Promise.reject(Error(`${name} terminated`));
baton.catch(noop); // Suppress Node.js unhandled exception warning.
// Mute the vatExit exception: it is expected.
return vatExit.promise.catch(noop);
}
return freeze({
name,
issueCommand,
issueStringCommand,
isReady,
close,
terminate,
evaluate,
execute,
import: importModule,
makeSnapshotStream,
});
}