Middlewares

A middleware is a mechanism you can add to the server, doing some work on each request.

This can be inside a plugin, but also directly written into Admin > Options > Server code.

Language is JavaScript, executed by Node.js. More details in the plugins documentation.

A middleware has the form of a function that receives a Context object as a parameter. The context object contains all information about the http request and the http response.

Basic examples

Setting http header

exports.middleware = ctx => ctx.set('x-my-header', 'some value')

Custom reply to some address

exports.middleware = ctx => {
  if (ctx.path === '/some/address')
    ctx.body = 'my content'
}

Allow only Chrome as browser

exports.middleware = ctx => ctx.get('user-agent').includes('Chrome') || ctx.socket.destroy()

Calculate MD5 on uploads

(from version 0.53.0)

Sending back MD5 with a header, by processing incoming stream.

While technically this is not a middleware, it still acts similarly to one.

exports.init = api => {
    const { createHash } = api.require('crypto')
    const { Transform } = api.require('stream')
    return { // at exit time, "unload" will ensure the event "uploadStart" is unsubscribed
        unload: api.events.on('uploadStart', obj => {
            const hasher = createHash('md5')
            const original = obj.writeStream
            obj.writeStream = new Transform({
                transform(chunk, encoding, cb) {
                    hasher.update(chunk)
                    original.write(chunk, encoding, cb)
                },
                flush(cb) {
                    obj.ctx.set({ 'X-MD5': hasher.digest('hex') })
                    cb()
                },
            })            
        })
    }
}