58 lines
2.2 KiB
TypeScript
58 lines
2.2 KiB
TypeScript
|
/**
|
||
|
|
* Per-file memo for the journal and page listings.
|
||
|
|
*
|
||
|
|
* `listJournalEntries()` and `listPages()` run on every public page render —
|
||
|
|
* the header nav asks whether a journal exists and which pages to link — and
|
||
|
|
* used to read and parse every markdown file each time. The parse is the
|
||
|
|
* expensive part and depends only on the file's bytes, so it is kept here,
|
||
|
|
* keyed on the file's identity and stamp: inode, size and mtime in
|
||
|
|
* nanoseconds.
|
||
|
|
*
|
||
|
|
* An admin save goes through atomicWrite (temp file + rename), which always
|
||
|
|
* produces a new inode, so a save is seen by the very next listing, in this
|
||
|
|
* module instance or any other. An edit in place changes mtime. The stat is
|
||
|
|
* taken before the read, so a write landing between the two at worst stores
|
||
|
|
* the new bytes under the old stamp — which the next stat no longer matches,
|
||
|
|
* so the file is simply read again. Stale bytes under a current stamp cannot
|
||
|
|
* happen.
|
||
|
|
*
|
||
|
|
* Values are handed out as copies: a caller that mutates an entry must not
|
||
|
|
* change what the next request sees.
|
||
|
|
*/
|
||
|
|
|
||
|
|
import fs from 'fs/promises';
|
||
|
|
|
||
|
|
interface Cached<T> {
|
||
|
|
stamp: string;
|
||
|
|
value: T;
|
||
|
|
}
|
||
|
|
|
||
|
|
export class ParsedFileCache<T> {
|
||
|
|
private readonly entries = new Map<string, Cached<T>>();
|
||
|
|
|
||
|
|
constructor(private readonly parse: (raw: string) => T) {}
|
||
|
|
|
||
|
|
/**
|
||
|
|
* Parsed contents of `filePath`, from the memo when the file is unchanged.
|
||
|
|
* Throws like `fs.readFile` for a missing or unreadable file, and like
|
||
|
|
* `parse` for one that does not parse — neither outcome is cached.
|
||
|
|
*/
|
||
|
|
async read(filePath: string): Promise<T> {
|
||
|
|
const st = await fs.stat(filePath, { bigint: true });
|
||
|
|
const stamp = `${st.ino}:${st.size}:${st.mtimeNs}`;
|
||
|
|
const hit = this.entries.get(filePath);
|
||
|
|
if (hit && hit.stamp === stamp) return structuredClone(hit.value);
|
||
|
|
|
||
|
|
const value = this.parse(await fs.readFile(filePath, 'utf8'));
|
||
|
|
this.entries.set(filePath, { stamp, value });
|
||
|
|
return structuredClone(value);
|
||
|
|
}
|
||
|
|
|
||
|
|
/** Drop entries for files a listing no longer found, so deletes do not pile up. */
|
||
|
|
retain(filePaths: Set<string>): void {
|
||
|
|
for (const key of this.entries.keys()) {
|
||
|
|
if (!filePaths.has(key)) this.entries.delete(key);
|
||
|
|
}
|
||
|
|
}
|
||
|
|
}
|