nel-middleware

HTTP network error logging(NEL) middleware.

Compliant with W3C, Network Error Logging.

Middleware

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

Usage

Middleware adds the NEL header to the response.

import {
  type Handler,
  nel,
} from "https://deno.land/x/nel_middleware@$VERSION/mod.ts";
import { assert } from "https://deno.land/std/testing/asserts.ts";

declare const request: Request;
declare const handler: Handler;

const middleware = nel({ report_to: "default", max_age: 86400 });
const response = await middleware(request, handler);

assert(response.headers.has("nel"));

yield:

NEL: {"report_to":"default","max_age":86400}

Policy

Specifying NEL policy is mandatory.

| Name | Type | Required | Description | | ------------------ | ---------- | :------: | --------------------------------------------------- | | max_age | number | ✅ | NEL policy lifetime. | | report_to | string | - | Endpoint group to which the report will be sent. | | include_subdomains | boolean | - | Whether to enable origin subdomains. | | success_fraction | number | - | Sampling rate for successful network requests. | | failure_fraction | number | - | Sampling rate for failed network requests. | | request_headers | string[] | - | Request header field to be included in the report. | | response_headers | string[] | - | Response header field to be included in the report. |

Serialization error

If serialization fails, an error may be thrown.

Cases that throw an error are as follows:

• max_age is not non-negative integer
• success_fraction and failure_fraction is not unit interval

import { nel } from "https://deno.land/x/nel_middleware@$VERSION/middleware.ts";
import { assertThrows } from "https://deno.land/std/testing/asserts.ts";

assertThrows(() => nel({ max_age: NaN }));
assertThrows(() => nel({ max_age: 0, success_fraction: 1.1 }));
assertThrows(() => nel({ max_age: 0, failure_fraction: -1 }));

Conditions

Middleware will execute if all of the following conditions are met:

• NEL header does not exist in response

Effects

Middleware may make changes to the following elements of the HTTP message.

• HTTP Headers
  • NEL

API

All APIs can be found in the deno doc.

License

Copyright © 2023-present httpland.

Released under the MIT license