migrate: move flock and hash utilities to shared package (#22640)

2 files changed, 361 insertions, 0 deletions

diff --git a/packages/shared/src/util/flock.ts b/packages/shared/src/util/flock.ts
new file mode 100644
index 000000000..4a1df1dee
--- /dev/null
+++ b/packages/shared/src/util/flock.ts
@@ -0,0 +1,354 @@
+import path from "path"
+import os from "os"
+import { randomBytes, randomUUID } from "crypto"
+import { mkdir, readFile, rm, stat, utimes, writeFile } from "fs/promises"
+import { Hash } from "./hash"
+import { Effect } from "effect"
+
+export type FlockGlobal = {
+  state: string
+}
+
+export namespace Flock {
+  let global: FlockGlobal | undefined
+
+  export function setGlobal(g: FlockGlobal) {
+    global = g
+  }
+
+  const root = () => {
+    if (!global) throw new Error("Flock global not set")
+    return path.join(global.state, "locks")
+  }
+
+  // Defaults for callers that do not provide timing options.
+  const defaultOpts = {
+    staleMs: 60_000,
+    timeoutMs: 5 * 60_000,
+    baseDelayMs: 100,
+    maxDelayMs: 2_000,
+  }
+
+  export interface WaitEvent {
+    key: string
+    attempt: number
+    delay: number
+    waited: number
+  }
+
+  export type Wait = (input: WaitEvent) => void | Promise<void>
+
+  export interface Options {
+    dir?: string
+    signal?: AbortSignal
+    staleMs?: number
+    timeoutMs?: number
+    baseDelayMs?: number
+    maxDelayMs?: number
+    onWait?: Wait
+  }
+
+  type Opts = {
+    staleMs: number
+    timeoutMs: number
+    baseDelayMs: number
+    maxDelayMs: number
+  }
+
+  type Owned = {
+    acquired: true
+    startHeartbeat: (intervalMs?: number) => void
+    release: () => Promise<void>
+  }
+
+  export interface Lease {
+    release: () => Promise<void>
+    [Symbol.asyncDispose]: () => Promise<void>
+  }
+
+  function code(err: unknown) {
+    if (typeof err !== "object" || err === null || !("code" in err)) return
+    const value = err.code
+    if (typeof value !== "string") return
+    return value
+  }
+
+  function sleep(ms: number, signal?: AbortSignal) {
+    return new Promise<void>((resolve, reject) => {
+      if (signal?.aborted) {
+        reject(signal.reason ?? new Error("Aborted"))
+        return
+      }
+
+      let timer: NodeJS.Timeout | undefined
+
+      const done = () => {
+        signal?.removeEventListener("abort", abort)
+        resolve()
+      }
+
+      const abort = () => {
+        if (timer) {
+          clearTimeout(timer)
+        }
+        signal?.removeEventListener("abort", abort)
+        reject(signal?.reason ?? new Error("Aborted"))
+      }
+
+      signal?.addEventListener("abort", abort, { once: true })
+      timer = setTimeout(done, ms)
+    })
+  }
+
+  function jitter(ms: number) {
+    const j = Math.floor(ms * 0.3)
+    const d = Math.floor(Math.random() * (2 * j + 1)) - j
+    return Math.max(0, ms + d)
+  }
+
+  function mono() {
+    return performance.now()
+  }
+
+  function wall() {
+    return performance.timeOrigin + mono()
+  }
+
+  async function stats(file: string) {
+    try {
+      return await stat(file)
+    } catch (err) {
+      const errCode = code(err)
+      if (errCode === "ENOENT" || errCode === "ENOTDIR") return
+      throw err
+    }
+  }
+
+  async function stale(lockDir: string, heartbeatPath: string, metaPath: string, staleMs: number) {
+    // Stale detection allows automatic recovery after crashed owners.
+    const now = wall()
+    const heartbeat = await stats(heartbeatPath)
+    if (heartbeat) {
+      return now - heartbeat.mtimeMs > staleMs
+    }
+
+    const meta = await stats(metaPath)
+    if (meta) {
+      return now - meta.mtimeMs > staleMs
+    }
+
+    const dir = await stats(lockDir)
+    if (!dir) {
+      return false
+    }
+
+    return now - dir.mtimeMs > staleMs
+  }
+
+  async function tryAcquireLockDir(lockDir: string, opts: Opts): Promise<Owned | { acquired: false }> {
+    const token = randomUUID?.() ?? randomBytes(16).toString("hex")
+    const metaPath = path.join(lockDir, "meta.json")
+    const heartbeatPath = path.join(lockDir, "heartbeat")
+
+    try {
+      await mkdir(lockDir, { mode: 0o700 })
+    } catch (err) {
+      if (code(err) !== "EEXIST") {
+        throw err
+      }
+
+      if (!(await stale(lockDir, heartbeatPath, metaPath, opts.staleMs))) {
+        return { acquired: false }
+      }
+
+      const breakerPath = lockDir + ".breaker"
+      try {
+        await mkdir(breakerPath, { mode: 0o700 })
+      } catch (claimErr) {
+        const errCode = code(claimErr)
+        if (errCode === "EEXIST") {
+          const breaker = await stats(breakerPath)
+          if (breaker && wall() - breaker.mtimeMs > opts.staleMs) {
+            await rm(breakerPath, { recursive: true, force: true }).catch(() => undefined)
+          }
+          return { acquired: false }
+        }
+
+        if (errCode === "ENOENT" || errCode === "ENOTDIR") {
+          return { acquired: false }
+        }
+
+        throw claimErr
+      }
+
+      try {
+        // Breaker ownership ensures only one contender performs stale cleanup.
+        if (!(await stale(lockDir, heartbeatPath, metaPath, opts.staleMs))) {
+          return { acquired: false }
+        }
+
+        await rm(lockDir, { recursive: true, force: true })
+
+        try {
+          await mkdir(lockDir, { mode: 0o700 })
+        } catch (retryErr) {
+          const errCode = code(retryErr)
+          if (errCode === "EEXIST" || errCode === "ENOTEMPTY") {
+            return { acquired: false }
+          }
+          throw retryErr
+        }
+      } finally {
+        await rm(breakerPath, { recursive: true, force: true }).catch(() => undefined)
+      }
+    }
+
+    const meta = {
+      token,
+      pid: process.pid,
+      hostname: os.hostname(),
+      createdAt: new Date().toISOString(),
+    }
+
+    await writeFile(heartbeatPath, "", { flag: "wx" }).catch(async () => {
+      await rm(lockDir, { recursive: true, force: true })
+      throw new Error("Lock acquired but heartbeat already existed (possible compromise).")
+    })
+
+    await writeFile(metaPath, JSON.stringify(meta, null, 2), { flag: "wx" }).catch(async () => {
+      await rm(lockDir, { recursive: true, force: true })
+      throw new Error("Lock acquired but meta.json already existed (possible compromise).")
+    })
+
+    let timer: NodeJS.Timeout | undefined
+
+    const startHeartbeat = (intervalMs = Math.max(100, Math.floor(opts.staleMs / 3))) => {
+      if (timer) return
+      // Heartbeat prevents long critical sections from being evicted as stale.
+      timer = setInterval(() => {
+        const t = new Date()
+        void utimes(heartbeatPath, t, t).catch(() => undefined)
+      }, intervalMs)
+      timer.unref?.()
+    }
+
+    const release = async () => {
+      if (timer) {
+        clearInterval(timer)
+        timer = undefined
+      }
+
+      const current = await readFile(metaPath, "utf8")
+        .then((raw) => {
+          const parsed = JSON.parse(raw)
+          if (!parsed || typeof parsed !== "object") return {}
+          return {
+            token: "token" in parsed && typeof parsed.token === "string" ? parsed.token : undefined,
+          }
+        })
+        .catch((err) => {
+          const errCode = code(err)
+          if (errCode === "ENOENT" || errCode === "ENOTDIR") {
+            throw new Error("Refusing to release: lock is compromised (metadata missing).")
+          }
+          if (err instanceof SyntaxError) {
+            throw new Error("Refusing to release: lock is compromised (metadata invalid).")
+          }
+          throw err
+        })
+      // Token check prevents deleting a lock that was re-acquired by another process.
+      if (current.token !== token) {
+        throw new Error("Refusing to release: lock token mismatch (not the owner).")
+      }
+
+      await rm(lockDir, { recursive: true, force: true })
+    }
+
+    return {
+      acquired: true,
+      startHeartbeat,
+      release,
+    }
+  }
+
+  async function acquireLockDir(
+    lockDir: string,
+    input: { key: string; onWait?: Wait; signal?: AbortSignal },
+    opts: Opts,
+  ) {
+    const stop = mono() + opts.timeoutMs
+    let attempt = 0
+    let waited = 0
+    let delay = opts.baseDelayMs
+
+    while (true) {
+      input.signal?.throwIfAborted()
+
+      const res = await tryAcquireLockDir(lockDir, opts)
+      if (res.acquired) {
+        return res
+      }
+
+      if (mono() > stop) {
+        throw new Error(`Timed out waiting for lock: ${input.key}`)
+      }
+
+      attempt += 1
+      const ms = jitter(delay)
+      await input.onWait?.({
+        key: input.key,
+        attempt,
+        delay: ms,
+        waited,
+      })
+      await sleep(ms, input.signal)
+      waited += ms
+      delay = Math.min(opts.maxDelayMs, Math.floor(delay * 1.7))
+    }
+  }
+
+  export async function acquire(key: string, input: Options = {}): Promise<Lease> {
+    input.signal?.throwIfAborted()
+    const cfg: Opts = {
+      staleMs: input.staleMs ?? defaultOpts.staleMs,
+      timeoutMs: input.timeoutMs ?? defaultOpts.timeoutMs,
+      baseDelayMs: input.baseDelayMs ?? defaultOpts.baseDelayMs,
+      maxDelayMs: input.maxDelayMs ?? defaultOpts.maxDelayMs,
+    }
+    const dir = input.dir ?? root()
+
+    await mkdir(dir, { recursive: true })
+    const lockfile = path.join(dir, Hash.fast(key) + ".lock")
+    const lock = await acquireLockDir(
+      lockfile,
+      {
+        key,
+        onWait: input.onWait,
+        signal: input.signal,
+      },
+      cfg,
+    )
+    lock.startHeartbeat()
+
+    const release = () => lock.release()
+    return {
+      release,
+      [Symbol.asyncDispose]() {
+        return release()
+      },
+    }
+  }
+
+  export async function withLock<T>(key: string, fn: () => Promise<T>, input: Options = {}) {
+    await using _ = await acquire(key, input)
+    input.signal?.throwIfAborted()
+    return await fn()
+  }
+
+  export const effect = Effect.fn("Flock.effect")(function* (key: string) {
+    return yield* Effect.acquireRelease(
+      Effect.promise((signal) => Flock.acquire(key, { signal })),
+      (foo) => Effect.promise(() => foo.release()),
+    ).pipe(Effect.asVoid)
+  })
+}
diff --git a/packages/shared/src/util/hash.ts b/packages/shared/src/util/hash.ts
new file mode 100644
index 000000000..680e0f40b
--- /dev/null
+++ b/packages/shared/src/util/hash.ts
@@ -0,0 +1,7 @@
+import { createHash } from "crypto"
+
+export namespace Hash {
+  export function fast(input: string | Buffer): string {
+    return createHash("sha1").update(input).digest("hex")
+  }
+}