Express/connect middleware that does HTTP content negotiation for static files

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1.0.06 years ago11 years agoMinified + gzip package size for express-negotiator in KB


Express/connect middleware for doing content negotiation with static files on disc. Heavily inspired by Apache's modnegotiation.
Negotiator rewrites req.url to the negotiated file name based on these factors (in descending order of importance):
  • Whether req.url matches a file name on disc exactly
  • The locale GET parameter
  • The value of a locale cookie (optional, specified by options.cookieName)
  • The Accept-Language and Accept headers

... and of course the availability of suitable files on disc. If no acceptable match is found, req.url is left untouched.
Like mod_negotiation, express-negotiator interprets the extensions of the files on disc as an unordered set. A file called would be treated the same as one called except when the request url specifies an exact match.
The negotiator middleware is intended to run right before static pointed at the same directory as options.root.
If options.cookieName is specified, the cookieParser middleware must also be in the middleware chain.
Conditional requests
When the url is rewritten, negotiator sets the ETag header to the same value as the static middleware would ("<size>-<modificationTime>"), but with the negotiated Content-Type and locale id bits suffixed. This prevents false positive 304 responses with If-None-Match when the same client (or reverse proxy) requests the same url later with different headers (eg. after a locale cookie change). That would happen if the files happened to have the same size and modification times.
Also, the If-Modified-Since header is removed since that would cause the static middleware to reply 304 Not Modified in similar situations. ETags are a superior concept anyway.
Make sure you have node.js and npm installed, then run:
$ npm install express-negotiator
Example usage
var express = require('express'),
    negotiator = require('express-negotiator'),
    root = '/path/to/static/files',
    app = express.createServer();

    .use(negotiator({root: root, cookieName: 'mycookie'}))

If the root dir contains the files index.en.html, index.da.html, and foo.png these example requests would be rewritten as follows:
GET / HTTP/1.1
Accept: text/html
Accept-Language: en

=> /index.en.html
Response ETag: "<size>-<modificationTime>-text/html-en"

GET /?locale=da HTTP/1.1
Accept: text/html
Accept-Language: en

=> /index.da.html
Response ETag: "<size>-<modificationTime>-text/html-da"

GET /index HTTP/1.1
Cookie: mycookie=da
Accept: text/html
Accept-Language: en

=> /index.da.html
Response ETag: "<size>-<modificationTime>-text/html-da"

GET /foo HTTP/1.1
Accept: image/*

=> /foo.png
Response ETag: "<size>-<modificationTime>-image/png"

See the test suite for more examples.
express-negotiator is licensed under a standard 3-clause BSD license -- see the LICENSE file for details.