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Module

std/http/etag.ts

The Deno Standard Library
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// Copyright 2018-2024 the Deno authors. All rights reserved. MIT license.// This module is browser compatible.
/** * Provides functions for dealing with and matching ETags, including * {@linkcode calculate} to calculate an etag for a given entity, * {@linkcode ifMatch} for validating if an ETag matches against a `If-Match` * header and {@linkcode ifNoneMatch} for validating an Etag against an * `If-None-Match` header. * * See further information on the `ETag` header on * {@link https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/ETag | MDN}. * * @module */
import { encodeBase64 as base64Encode } from "../encoding/base64.ts";
/** * Just the part of {@linkcode Deno.FileInfo} that is required to calculate an `ETag`, * so partial or user generated file information can be passed. */export interface FileInfo { /** The last modification time of the file. This corresponds to the `mtime` * field from `stat` on Linux/Mac OS and `ftLastWriteTime` on Windows. This * may not be available on all platforms. */ mtime: Date | null; /** The size of the file, in bytes. */ size: number;}
/** Represents an entity that can be used for generating an ETag. */export type Entity = string | Uint8Array | FileInfo;
const encoder = new TextEncoder();
const DEFAULT_ALGORITHM: AlgorithmIdentifier = "SHA-256";
/** Options for {@linkcode calculate}. */export interface ETagOptions { /** * A digest algorithm to use to calculate the etag. * * @default {"SHA-256"} */ algorithm?: AlgorithmIdentifier;
/** Override the default behavior of calculating the `ETag`, either forcing * a tag to be labelled weak or not. */ weak?: boolean;}
function isFileInfo(value: unknown): value is FileInfo { return Boolean( value && typeof value === "object" && "mtime" in value && "size" in value, );}
async function calcEntity( entity: string | Uint8Array, { algorithm = DEFAULT_ALGORITHM }: ETagOptions,) { // a short circuit for zero length entities if (entity.length === 0) { return `0-47DEQpj8HBSa+/TImW+5JCeuQeR`; }
if (typeof entity === "string") { entity = encoder.encode(entity); }
const hash = base64Encode(await crypto.subtle.digest(algorithm, entity)) .substring(0, 27);
return `${entity.length.toString(16)}-${hash}`;}
async function calcFileInfo( fileInfo: FileInfo, { algorithm = DEFAULT_ALGORITHM }: ETagOptions,) { if (fileInfo.mtime) { const hash = base64Encode( await crypto.subtle.digest( algorithm, encoder.encode(fileInfo.mtime.toJSON()), ), ).substring(0, 27); return `${fileInfo.size.toString(16)}-${hash}`; }}
/** * Calculate an ETag for an entity. When the entity is a specific set of data * it will be fingerprinted as a "strong" tag, otherwise if it is just file * information, it will be calculated as a weak tag. * * ```ts * import { calculate } from "https://deno.land/std@$STD_VERSION/http/etag.ts"; * import { assert } from "https://deno.land/std@$STD_VERSION/assert/assert.ts" * * const body = "hello deno!"; * * const etag = await calculate(body); * assert(etag); * * const res = new Response(body, { headers: { etag } }); * ``` */export async function calculate( entity: Entity, options: ETagOptions = {},): Promise<string | undefined> { const weak = options.weak ?? isFileInfo(entity); const tag = await (isFileInfo(entity) ? calcFileInfo(entity, options) : calcEntity(entity, options));
return tag ? weak ? `W/"${tag}"` : `"${tag}"` : undefined;}
/** A helper function that takes the value from the `If-Match` header and a * calculated etag for the target. By using strong comparison, return `true` if * the values match, otherwise `false`. * * See MDN's [`If-Match`](https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/If-Match) * article for more information on how to use this function. * * ```ts * import { * calculate, * ifMatch, * } from "https://deno.land/std@$STD_VERSION/http/etag.ts"; * import { assert } from "https://deno.land/std@$STD_VERSION/assert/assert.ts" * * const body = "hello deno!"; * * Deno.serve(async (req) => { * const ifMatchValue = req.headers.get("if-match"); * const etag = await calculate(body); * assert(etag); * if (!ifMatchValue || ifMatch(ifMatchValue, etag)) { * return new Response(body, { status: 200, headers: { etag } }); * } else { * return new Response(null, { status: 412, statusText: "Precondition Failed"}); * } * }); * ``` */export function ifMatch( value: string | null, etag: string | undefined,): boolean { // Weak tags cannot be matched and return false. if (!value || !etag || etag.startsWith("W/")) { return false; } if (value.trim() === "*") { return true; } const tags = value.split(/\s*,\s*/); return tags.includes(etag);}
/** A helper function that takes the value from the `If-None-Match` header and * a calculated etag for the target entity and returns `false` if the etag for * the entity matches the supplied value, otherwise `true`. * * See MDN's [`If-None-Match`](https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/If-None-Match) * article for more information on how to use this function. * * ```ts * import { * calculate, * ifNoneMatch, * } from "https://deno.land/std@$STD_VERSION/http/etag.ts"; * import { assert } from "https://deno.land/std@$STD_VERSION/assert/assert.ts" * * const body = "hello deno!"; * * Deno.serve(async (req) => { * const ifNoneMatchValue = req.headers.get("if-none-match"); * const etag = await calculate(body); * assert(etag); * if (!ifNoneMatch(ifNoneMatchValue, etag)) { * return new Response(null, { status: 304, headers: { etag } }); * } else { * return new Response(body, { status: 200, headers: { etag } }); * } * }); * ``` */export function ifNoneMatch( value: string | null, etag: string | undefined,): boolean { if (!value || !etag) { return true; } if (value.trim() === "*") { return false; } etag = etag.startsWith("W/") ? etag.slice(2) : etag; const tags = value.split(/\s*,\s*/).map((tag) => tag.startsWith("W/") ? tag.slice(2) : tag ); return !tags.includes(etag);}