etag.ts — astro Source File

Source Code

/**
 * FNV-1a Hash implementation
 * @author Travis Webb (tjwebb) <me@traviswebb.com>
 *
 * Ported from https://github.com/tjwebb/fnv-plus/blob/master/index.js
 * License https://github.com/tjwebb/fnv-plus#license
 *
 * Simplified, optimized and add modified for 52 bit, which provides a larger hash space
 * and still making use of Javascript's 53-bit integer space.
 */
const fnv1a52 = (str: string) => {
	const len = str.length;
	let i = 0,
		t0 = 0,
		v0 = 0x2325,
		t1 = 0,
		v1 = 0x8422,
		t2 = 0,
		v2 = 0x9ce4,
		t3 = 0,
		v3 = 0xcbf2;

	while (i < len) {
		v0 ^= str.charCodeAt(i++);
		t0 = v0 * 435;
		t1 = v1 * 435;
		t2 = v2 * 435;
		t3 = v3 * 435;
		t2 += v0 << 8;
		t3 += v1 << 8;
		t1 += t0 >>> 16;
		v0 = t0 & 65535;
		t2 += t1 >>> 16;
		v1 = t1 & 65535;
		v3 = (t3 + (t2 >>> 16)) & 65535;
		v2 = t2 & 65535;
	}

	return (v3 & 15) * 281474976710656 + v2 * 4294967296 + v1 * 65536 + (v0 ^ (v3 >> 4));
};

export const etag = (payload: string, weak = false) => {
	const prefix = weak ? 'W/"' : '"';
	return prefix + fnv1a52(payload).toString(36) + payload.length.toString(36) + '"';
};