157 lines
5.4 KiB
JavaScript
157 lines
5.4 KiB
JavaScript
/**
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* 主机身份的租约式判定。
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*
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* 动手之前要先知道「我要改的这份宿主到底是不是我现在跑着的这一份」。
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* 老版本只比路径字符串，有三种情况会被骗：
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*
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* 1. 目标被换成了符号链接 / 目录联接（junction）→ 看到的是另一份文件；
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* 2. 同一路径下文件被替换（重装、换版本、另一个进程写入）→ 路径对、内容不对；
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* 3. 路径大小写在 Windows 上不敏感 → `C:\App` 与 `c:\app` 被当成两份；
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* 反过来，含 `..` 的相对路径会被当成另一处。
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*
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* 这里给出一份可比较的 **identity**（身份）：真实路径 + 大小 + mtime + 前若干字节的
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* 摘要。写入前后各取一次，不一致就拒绝，而不是写完再发现问题。
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* 参考 IG5 `source/attachment_lease.js` 的 owner/nonce 思路，但只保留与改文件相关的部分。
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*/
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import fs from "node:fs";
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import path from "node:path";
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import { createHash } from "node:crypto";
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const HEAD_BYTES = 64 * 1024;
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/** Windows 上大小写不敏感；统一归一化后再比较，避免同一份被当成两份。 */
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export function normalizeKey(p) {
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const resolved = path.resolve(String(p || ""));
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const lowered = process.platform === "win32" ? resolved.toLowerCase() : resolved;
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return lowered.replace(/\\/g, "/");
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}
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export function samePath(a, b) {
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if (!a || !b) return false;
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return normalizeKey(a) === normalizeKey(b);
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}
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/** 真实路径（解析链接与联接）；不存在或无权读取时退回归一化的绝对路径。 */
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export function realPathOf(p) {
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try {
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return fs.realpathSync.native(p);
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} catch {
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return path.resolve(String(p || ""));
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}
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}
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function headDigest(fp, size) {
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const length = Math.min(HEAD_BYTES, Math.max(0, size));
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if (length === 0) return "";
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const fd = fs.openSync(fp, "r");
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try {
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const buffer = Buffer.alloc(length);
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const read = fs.readSync(fd, buffer, 0, length, 0);
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return createHash("sha256").update(buffer.subarray(0, read)).digest("hex");
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} finally {
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fs.closeSync(fd);
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}
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}
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/**
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* 取一份文件的身份。文件不存在时返回 `{ exists: false, path, key }`，
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* 这是正常结果而不是错误——「目标还没建」和「我读不到」必须分开。
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*/
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export function fileIdentity(fp) {
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const key = normalizeKey(fp);
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const real = realPathOf(fp);
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let stat;
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try {
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stat = fs.statSync(fp);
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} catch (error) {
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const missing = error && error.code === "ENOENT";
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return { exists: false, path: String(fp || ""), real, key, missing, error: missing ? "" : String(error && error.message ? error.message : error) };
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}
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if (!stat.isFile()) {
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return { exists: false, path: String(fp || ""), real, key, missing: false, error: "not a regular file" };
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}
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return {
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exists: true,
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path: String(fp || ""),
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real,
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realKey: normalizeKey(real),
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key,
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size: stat.size,
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mtimeMs: stat.mtimeMs,
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mode: stat.mode,
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head: headDigest(fp, stat.size),
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};
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}
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/** 同一份文件的两次观测是否可视为「没动过」。 */
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export function sameIdentity(a, b) {
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if (!a || !b) return false;
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if (a.exists !== b.exists) return false;
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if (!a.exists) return true;
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return a.realKey === b.realKey && a.size === b.size && a.mtimeMs === b.mtimeMs && a.head === b.head;
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}
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/**
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* 写入前后的守卫。用法：
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*
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* const lease = await acquireLease(fp);
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* ...写...
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* const verdict = lease.verify(true); // mustExist=true 表示写完必须存在
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* if (!verdict.ok) → 回滚并报错
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*
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* `stale` 表示「拿租约之后别人动过」；`changed` 表示「我写完之后内容没落地」。
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*/
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export function acquireLease(fp) {
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const before = fileIdentity(fp);
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let released = false;
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return {
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path: String(fp || ""),
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before,
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/** 目标是否本来就不存在（新建文件的合法场景）。 */
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created: !before.exists,
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verify(mustExist = false) {
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const after = fileIdentity(fp);
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if (released && !mustExist) return { ok: true, after };
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if (mustExist && !after.exists) {
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return { ok: false, reason: "missing-after-write", before, after };
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}
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if (!mustExist && !before.exists) {
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return after.exists ? { ok: true, after, appeared: true } : { ok: true, after };
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}
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if (!sameIdentity(before, after) && !after.exists) {
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return { ok: false, reason: "vanished", before, after };
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}
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return { ok: true, after, changed: !sameIdentity(before, after) };
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},
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release() {
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released = true;
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},
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};
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}
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/**
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* 原子写：先写同目录临时文件再 rename，避免半写坏文件。
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* 已存在文件保留其 mode（Windows 上 best-effort）。
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*/
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export function writeFileAtomic(fp, data, opts = {}) {
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const target = path.resolve(String(fp || ""));
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const dir = path.dirname(target);
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fs.mkdirSync(dir, { recursive: true });
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const temp = path.join(dir, `.${path.basename(target)}.${process.pid}.${Date.now().toString(36)}.tmp`);
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const buffer = Buffer.isBuffer(data) ? data : Buffer.from(String(data ?? ""), opts.encoding || "utf8");
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let mode;
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try {
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mode = fs.statSync(target).mode;
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} catch {
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mode = undefined;
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}
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fs.writeFileSync(temp, buffer, { mode: mode ?? 0o644, flag: "wx" });
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try {
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fs.renameSync(temp, target);
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} catch (error) {
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try { fs.unlinkSync(temp); } catch { /* 清不掉也不掩盖原错误 */ }
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throw error;
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}
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return { path: target, bytes: buffer.length };
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}
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