http-etag

HTTP ETag middleware for standard Request and Response.

What

Middleware for ETag header field.

Calculate the hash value from the response body and fill in the ETag header field.

Middleware

For a definition of Universal HTTP middleware, see the http-middleware project.

Usage

Middleware factory is exported by default.

By default, the SHA-1 algorithm of the Web Crypto API is used. This is because it requires no additional code and is faster.

import etag from "https://deno.land/x/http_etag@$VERSION/mod.ts";
import { assertEquals } from "https://deno.land/std/testing/asserts.ts";

const middleware = etag();
const response = await middleware(
  new Request("http://localhost"),
  (request) => new Response("ok"),
);

assertEquals(response.headers.get("etag"), `"<body:SHA-1>"`);

Customize hash algorithm

You can change the hash algorithm from the digest filed.

import etag from "https://deno.land/x/http_etag@$VERSION/mod.ts";
import { assertEquals } from "https://deno.land/std/testing/asserts.ts";

const middleware = etag({
  digest: (data) => crypto.subtle.digest("sha-256", data),
});
const response = await middleware(
  new Request("http://localhost"),
  (request) => new Response("ok"),
);

assertEquals(response.headers.get("etag"), `"<body:SHA-256>"`);

The digest function must satisfy the following interfaces:

interface Digest {
  (data: ArrayBuffer): ArrayBuffer | Promise<ArrayBuffer>;
}

Effects

Middleware will effect following:

HTTP Headers
- ETag

Conditions

For safety, middleware is executed only if the following conditions are met:

The body exists
The body is readable
The ETag header does not exist

License

Released under the MIT license