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/** * These functions are copied over from the Deno standard library, with possible * minor/negligible adaptations. The license for the standard library is as * follows: * * MIT License Copyright 2018-2022 the Deno authors. * * Permission is hereby granted, free of charge, to any person obtaining a copy * of this software and associated documentation files (the "Software"), to deal * in the Software without restriction, including without limitation the rights * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell * copies of the Software, and to permit persons to whom the Software is * furnished to do so, subject to the following conditions: * * The above copyright notice and this permission notice shall be included in * all copies or substantial portions of the Software. * * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE * SOFTWARE. */
import { hex } from "./deps.ts";
const encoder = new TextEncoder();const decoder = new TextDecoder();
// These next three definitions come from// https://deno.land/std@0.145.0/http/file_server.ts
/** Algorithm used to determine etag */export type EtagAlgorithm =  | "fnv1a"  | "sha-1"  | "sha-256"  | "sha-384"  | "sha-512";
// The fnv-1a hash function.function fnv1a(buf: string): string {  let hash = 2166136261; // 32-bit FNV offset basis  for (let i = 0; i < buf.length; i++) {    hash ^= buf.charCodeAt(i);    // Equivalent to `hash *= 16777619` without using BigInt    // 32-bit FNV prime    hash += (hash << 1) + (hash << 4) + (hash << 7) + (hash << 8) +      (hash << 24);  }  // 32-bit hex string  return (hash >>> 0).toString(16);}
// Generates a hash for the provided stringexport async function createEtagHash(  message: string,  algorithm: EtagAlgorithm = "fnv1a",): Promise<string> {  if (algorithm === "fnv1a") {    return fnv1a(message);  }  const msgUint8 = encoder.encode(message);  const hashBuffer = await crypto.subtle.digest(algorithm, msgUint8);  return decoder.decode(hex.encode(new Uint8Array(hashBuffer)));}
// This next function comes from https://deno.land/std@0.145.0/http/util.ts
/** Returns true if the etags match. Weak etag comparisons are handled. */export function compareEtag(a: string, b: string): boolean {  if (a === b) {    return true;  }  if (a.startsWith("W/") && !b.startsWith("W/")) {    return a.slice(2) === b;  }  if (!a.startsWith("W/") && b.startsWith("W/")) {    return a === b.slice(2);  }  return false;}
// This function is adapted from// https://deno.land/std@0.145.0/http/file_server.ts
/** Checks if a response to a request should 304 based on etag headers. */export function should304({ req, etag, modified }: {  req: Request,  etag: string,  modified: Date,}): boolean {  const noneMatch = req.headers.get("if-none-match");  const modifiedSince = req.headers.get("if-modified-since");  if (    (noneMatch && compareEtag(noneMatch, etag)) ||    (noneMatch === null && modifiedSince && (      modified.getTime() < new Date(modifiedSince).getTime() + 1000    ))  ) {    return true;  }  return false;}