Custom Header

Abstract
This is perhaps the simplest possible plugin that actually does something useful. A custom header and value are added to every outgoing response that matches a given path-pattern.

Motivation

Outgoing headers are an integral part of the request/response cycle serving to provide additional information to the requestor beyond what's available through standard HTTP headers or the response body. Extra headers are especially important when establishing your own protocol for database requests using the PUT, PATCH, POST, and DELETE methods.

Error messages are perhaps the most common use for custom headers, but other uses related the server's state; resource metadata; alternative content; and so forth, are possible.

Customization

This plugin is open source and can be used as is, or repurposed into something less whimsical than just "Hello World!", such as:

• Adding custom headers during development for debugging, version control, etc.
• Conditionally adding custom headers that are intended for consumption by log monitoring utilities.
• Providing custom headers in alternative languages to advertise non-obvious features of your website.

Download

The plugin module is available from NPM. Before proceeding, you should already have Node.js and RWSERVE configured and tested.

This module should be installed on your web server in a well-defined place, so that it can be discovered by RWSERVE. The standard place for public domain plugins is /srv/rwserve-plugins.

cd /srv/rwserve-plugins
npm install rwserve-custom-header
						

Configuration is Everything

Make the software available by declaring it in the plugins section of your configuration file. For detailed instructions on how to do this, refer to the plugins documentation on the Read Write Tools HTTP/2 Server website.

TL;DR

plugins {
    rwserve-custom-header {
        location `/srv/rwserve-plugins/node_modules/rwserve-custom-header/dist/index.js`
        config {
            header-name   clacks-overhead
            header-value  GNU Terry Pratchett
        }
    }
    router {
        `*`  *methods=GET,HEAD,PUT,PATCH,POST,DELETE,OPTIONS,TRACE  *plugin=rwserve-custom-header
    }    
}
						

The config settings are straightforward:

header-name is the name of the response header you wish to add. The HTTP/2 protocol requires this name to comprise only lowercase letters, digits, and HYPHENs.

header-value is the string value you wish to associate with the header. This value should consist of ISO-8859-1 characters only. UTF-8 characters can be used, but only when encoded according to the specification in IETF RFC 5987 "Character Set and Language Encoding for Hypertext Transfer Protocol (HTTP) Header Field Parameters"

The sample router shown above will route all messages (`*`) for any HTTP method, to the plugin.

Cookbook

A full configuration file with typical settings for a server running on localhost port 7443, is included in this NPM module at etc/custom-header-config. To use this configuration file, adjust these variables if they don't match your server setup:

$PLUGIN-PATH='/srv/rwserve-plugins/node_modules/rwserve-custom-header/dist/index.js'
$PRIVATE-KEY='/etc/pki/tls/private/localhost.key'
$CERTIFICATE='/etc/pki/tls/certs/localhost.crt'
$DOCUMENTS-PATH='/srv/rwserve/configuration-docs'
						

Deployment

Once you've tested the plugin and are ready to go live, adjust your production web server's configuration in /etc/rwserve/rwserve.conf and restart it using systemd. . .

[user@host ~]# systemctl restart rwserve
						

. . . then monitor its request/response activity with journald.

[user@host ~]# journalctl -u rwserve -ef
						

Prerequisites

This is a plugin for the Read Write Tools HTTP/2 Server, which works on Linux platforms.

Software	Minimum Version	Most Recent Version
Ubuntu	16 Xenial Xerus	16 Xenial Xerus
Debian	9 Stretch	10 Buster
openSUSE	openSUSE 15.1	openSUSE 15.1
Fedora	Fedora 27	Fedora 32
CentOS	CentOS 7.4	CentOS 8.1
RHEL	RHEL 7.8	RHEL 8.2
RWSERVE	RWSERVE 1.0.1	RWSERVE 1.0.47
Node.js	Node.js 10.3	Node.js 12.17

Review

Lessons
This plugin demonstrates a basic pattern that many plugins follow: Accessing configuration variables from the plugin. Omitting any calls to setStatusCode(), thus allowing the full request/response processing sequence to continue unimpeded. Find other plugins for the Read Write Tools HTTP/2 Server using npm with these keywords: rwserve, http2, plugins.

License

The rwserve-custom-header plugin is licensed under the MIT License.

MIT License

Copyright © 2023 Read Write Tools.

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.

Availability

Source code	github
Package installation	NPM
Documentation	Read Write Hub