etag-generator

ETag generation and If-None-Match comparison for HTTP caching per RFC 7232.

Quick Start

import { strongETag, decide } from "etag-generator";

const content = "page content";
const etag = strongETag(content);

const result = decide(req.headers, etag);
// → { status: 304, headers: { ETag: "..." } } if cached

API

strongETag(content: string | Buffer): string

Generate strong ETag from content (SHA256, first 27 base64url chars).

weakETag(size: number, mtime: number): string

Generate weak ETag from file size and mtime (for file-based caching).

ifNoneMatch(header: string | undefined, etag: string): boolean

Check If-None-Match header against ETag (handles W/ prefix and * wildcard per RFC 7232).

decide(reqHeaders, etag, lastModified?): { status, headers }

Evaluate conditional request headers; returns 304 if matched, 200 with caching headers otherwise.

fileETag(filePath: string): Promise<string>

Async helper to generate weak ETag from file stats.

Limits

• Strong ETags use SHA256 first 27 base64url chars (not full hash)
• Weak ETags can change despite identical content (mtime-based)
• No Last-Modified evaluation

Part of the ferrow-toolkit collection · Sponsored by Ferrow