fix(app): report a crash instead of vanishing, and cap the log

app/Uplink/log.tsadded+92-0

Changes to app/Uplink/log.ts

		@@ -0,0 +1,92 @@
	1	+import { appendFileSync, mkdirSync, renameSync, statSync } from 'node:fs'
	2	+import { dirname } from 'node:path'
	3	+import process from 'node:process'
	4	+import { LOG_MAX_BYTES, LOG_PATH } from './settings'
	5	+
	6	+/**
	7	+ * ~/Library/Logs/Uplink.log, which is the whole support story for a
	8	+ * downloadable app: no crash reporting, no diagnostics bundle, and stdout that
	9	+ * nobody is attached to.
	10	+ *
	11	+ * So this file has two jobs the previous inline version did not do. It stays
	12	+ * within a size, because a watcher polling every two seconds appends forever.
	13	+ * And it survives a crash, because the failure most worth explaining was the
	14	+ * one the file could not describe: an uncaught throw went to a stderr the
	15	+ * LaunchAgent does not capture, and the process vanished with the log's last
	16	+ * line being whatever succeeded before it.
	17	+ */
	18	+
	19	+// Checked on a counter rather than on every append: the watcher writes on a
	20	+// two second poll, and a stat per line would be most of the work.
	21	+const ROTATE_EVERY = 200
	22	+let writes = 0
	23	+
	24	+/**
	25	+ * One timestamped line. Never throws: `~/Library/Logs` can be missing or
	26	+ * unwritable, and a crash reporter that crashes is worse than none.
	27	+ */
	28	+export function writeLog(line: string, path: string = LOG_PATH, maxBytes: number = LOG_MAX_BYTES): void {
	29	+ try {
	30	+ // Every write, not only on the rotation check: a directory that goes away
	31	+ // mid-run should not cost 200 lines before anyone notices.
	32	+ mkdirSync(dirname(path), { recursive: true })
	33	+ if (writes++ % ROTATE_EVERY === 0)
	34	+ rotate(path, maxBytes)
	35	+ appendFileSync(path, `${new Date().toISOString()} ${line}\n`)
	36	+ }
	37	+ catch {
	38	+ // Nothing useful left to do: the place errors are reported is the thing
	39	+ // that failed.
	40	+ }
	41	+}
	42	+
	43	+/**
	44	+ * One rotation, keeping `Uplink.log.1`. Kept rather than deleted because the
	45	+ * lines leading up to a crash are the ones worth reading, and a rotation
	46	+ * triggered by that crash's own output would otherwise throw them away.
	47	+ */
	48	+export function rotate(path: string = LOG_PATH, maxBytes: number = LOG_MAX_BYTES): void {
	49	+ if ((statSync(path, { throwIfNoEntry: false })?.size ?? 0) > maxBytes)
	50	+ renameSync(path, `${path}.1`)
	51	+}
	52	+
	53	+/**
	54	+ * Name, message and stack, and nothing else. A stack can carry a frame
	55	+ * argument in some runtimes, and a text somebody sent is not ours to write to
	56	+ * a file that outlives the run.
	57	+ */
	58	+export function describeFatal(error: unknown): string {
	59	+ return error instanceof Error
	60	+ ? `${error.name}: ${error.message}\n${error.stack ?? '(no stack)'}`
	61	+ : String(error)
	62	+}
	63	+
	64	+/**
	65	+ * Report an uncaught throw or a rejected promise, then stop.
	66	+ *
	67	+ * Stopping is the point. A handler that swallows the error leaves the agent
	68	+ * half alive: the watcher is gone and the loopback server is not, so the
	69	+ * menubar reports a healthy app that answers nothing.
	70	+ */
	71	+export function installCrashHandlers(options: { path?: string, shutdown?: (code: number) => void } = {}): void {
	72	+ const shutdown = options.shutdown ?? ((code: number) => process.exit(code))
	73	+ let fatal = false
	74	+
	75	+ const report = (kind: string, error: unknown): void => {
	76	+ // Running twice turns one crash into two, and the second is never the
	77	+ // interesting one.
	78	+ if (fatal)
	79	+ return
	80	+ fatal = true
	81	+ const described = `[uplink] ${kind}: ${describeFatal(error)}`
	82	+ // Whatever the TTY says. From a terminal the developer also gets it on
	83	+ // stderr; the file gets the same entry either way.
	84	+ writeLog(described, options.path)
	85	+ if (process.stdout.isTTY)
	86	+ console.error(described)
	87	+ shutdown(1)
	88	+ }
	89	+
	90	+ process.on('uncaughtException', error => report('uncaught exception', error))
	91	+ process.on('unhandledRejection', reason => report('unhandled rejection', reason))
	92	+}