imccyu
1529be6fd4
Atomic whole-file replacement (same-dir temp + fsync + rename + parent fsync); the in-memory unit state is authoritative and the file is always the current net state, pretty-printed. Missing files open as empty units and materialize on first write; foreign or unparsable files reject with malformed-medium, stored-version drift with version-mismatch.
54 lines
1.8 KiB
TypeScript
54 lines
1.8 KiB
TypeScript
/**
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* Atomic whole-file replacement for the JSON backend.
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*
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* Publish protocol: write a same-directory temp file, fsync it, then
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* `rename()` over the target. Rename is an atomic replace on POSIX and on
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* Windows (libuv maps it to `MoveFileExW(..., MOVEFILE_REPLACE_EXISTING)`),
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* and replacement is the intended semantic here — unlike the session-log
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* backend's link()+unlink() no-clobber protocol, a unit file has exactly one
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* writer per process and last-write-wins is correct. After the rename the
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* parent directory is fsynced on POSIX so the new entry is crash-durable.
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* @module @deepseek-ai/dsh-storage-json/src/atomic
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*/
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import { open, rename, rm } from 'node:fs/promises'
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import { dirname, join } from 'node:path'
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import { randomUUID } from 'node:crypto'
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/**
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* Durably replace `path` with `data`.
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* @param path - Absolute target file path.
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* @param data - Full new file content.
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* @returns resolution after the replacement is crash-durable.
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*/
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export async function writeAtomic(path: string, data: string): Promise<void> {
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const tmp = join(dirname(path), `.${randomUUID()}.tmp`)
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try {
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const handle = await open(tmp, 'wx', 0o600)
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try {
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await handle.writeFile(data, 'utf8')
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await handle.sync()
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} finally {
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await handle.close()
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}
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await rename(tmp, path)
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await fsyncDirectory(dirname(path))
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} catch (error) {
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await rm(tmp, { force: true })
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throw error
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}
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}
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/** fsync a POSIX directory so a just-renamed entry is crash-durable. */
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/* v8 ignore start -- Windows rejects O_RDONLY directory opens; POSIX coverage exercises this. */
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async function fsyncDirectory(path: string): Promise<void> {
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if (process.platform === 'win32') return
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const handle = await open(path, 'r')
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try {
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await handle.sync()
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} finally {
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await handle.close()
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}
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}
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/* v8 ignore stop */
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