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✨ Allow sorting middleware #696

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✨ Allow sorting middleware #696

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9 changes: 9 additions & 0 deletions docs/api/backend.md
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Original file line number Diff line number Diff line change
Expand Up @@ -251,6 +251,15 @@ backend.use(action, middleware)

> A [middleware]({{ site.baseurl }}{% link middleware/index.md %}) function

`order` -- number

Optional
{: .label .label-grey }

> Default: `0`

> The order to run this middleware relative to other middlewares. Middleware with higher `order` will run later. Ties are broken on registration order.

### addProjection()

Defines a [projection]({{ site.baseurl }}{% link projections.md %}).
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8 changes: 6 additions & 2 deletions lib/backend.js
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Expand Up @@ -183,15 +183,19 @@ Backend.prototype.addProjection = function(name, collection, fields) {
/**
* Add middleware to an action or array of actions
*/
Backend.prototype.use = function(action, fn) {
Backend.prototype.use = function(action, fn, order) {
if (Array.isArray(action)) {
for (var i = 0; i < action.length; i++) {
this.use(action[i], fn);
this.use(action[i], fn, order);
}
return this;
}
fn.__order = order || 0;
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@alecgibson alecgibson Jul 24, 2025 •
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I don't know how hacky/icky it is to define a property on the middleware function itself.

Ideally I would have wrapped this into an object or something:

{fn, order}

...but this.middleware isn't prefixed, so consumers may technically assume it as part of the public API.

If I had access to modern ES features, I'd maybe use a WeakMap to avoid mutating the function, but we still technically target ES3.

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There's also a bug here where if someone registers the same middleware on 2 different servers (in the same thread) with different orders, it'll overwrite the first order with the second order

var fns = this.middleware[action] || (this.middleware[action] = []);
fns.push(fn);
fns.sort(function(a, b) {
return a.__order - b.__order;
});
return this;
};

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119 changes: 119 additions & 0 deletions test/middleware.js
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Expand Up @@ -6,6 +6,7 @@ var errorHandler = util.errorHandler;
var ShareDBError = require('../lib/error');
var sinon = require('sinon');
var ACTIONS = require('../lib/message-actions').ACTIONS;
var async = require('async');

var ERROR_CODE = ShareDBError.CODES;

Expand Down Expand Up @@ -35,6 +36,124 @@ describe('middleware', function() {
var response = this.backend.use(['submit', 'connect'], function() {});
expect(response).equal(this.backend);
});

describe('sorting', function() {
var calls;

beforeEach(function() {
calls = [];
});

it('defaults to insertion order', function(done) {
var a = makeMiddleware();
var b = makeMiddleware();
var c = makeMiddleware();

this.backend.use('readSnapshots', a);
this.backend.use('readSnapshots', b);
this.backend.use('readSnapshots', c);

var connection = this.backend.connect();
var doc = connection.get('dogs', 'fido');

async.series([
doc.fetch.bind(doc),
function(next) {
expect(calls).to.eql([a, b, c]);
next();
}
], done);
});

it('sorts middleware by order', function(done) {
var a = makeMiddleware();
var b = makeMiddleware();
var c = makeMiddleware();

this.backend.use('readSnapshots', a, 2);
this.backend.use('readSnapshots', b, 1);
this.backend.use('readSnapshots', c, 3);

var connection = this.backend.connect();
var doc = connection.get('dogs', 'fido');

async.series([
doc.fetch.bind(doc),
function(next) {
expect(calls).to.eql([b, a, c]);
next();
}
], done);
});

it('defaults order to 0', function(done) {
var a = makeMiddleware();
var b = makeMiddleware();
var c = makeMiddleware();

this.backend.use('readSnapshots', a);
this.backend.use('readSnapshots', b, 1);
this.backend.use('readSnapshots', c, -1);

var connection = this.backend.connect();
var doc = connection.get('dogs', 'fido');

async.series([
doc.fetch.bind(doc),
function(next) {
expect(calls).to.eql([c, a, b]);
next();
}
], done);
});

it('can sort using MAX_SAFE_INTEGER and MIN_SAFE_INTEGER', function(done) {
var a = makeMiddleware();
var b = makeMiddleware();

this.backend.use('readSnapshots', a, Number.MAX_SAFE_INTEGER);
this.backend.use('readSnapshots', b, Number.MIN_SAFE_INTEGER);

var connection = this.backend.connect();
var doc = connection.get('dogs', 'fido');

async.series([
doc.fetch.bind(doc),
function(next) {
expect(calls).to.eql([b, a]);
next();
}
], done);
});


it('can sort using MAX_VALUE', function(done) {
var a = makeMiddleware();
var b = makeMiddleware();

this.backend.use('readSnapshots', a, Number.MAX_VALUE);
this.backend.use('readSnapshots', b, -Number.MAX_VALUE);

var connection = this.backend.connect();
var doc = connection.get('dogs', 'fido');

async.series([
doc.fetch.bind(doc),
function(next) {
expect(calls).to.eql([b, a]);
next();
}
], done);
});

function makeMiddleware() {
var fn = function(context, next) {
calls.push(fn);
next();
};
return fn;
}
});
});

describe('connect', function() {
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