PostCSS Url Resolver

PostCSS plugin that resolves urls (CSS imports and images) via http requests.

This plugin is a combination of postcss-import-url, postcss-url-mapper and postcss-base64. It borrows code from all of them and adds some extra features.

Features:

• Recursively resolves @import and url(...) of remote files.
• Optionally inlines images in base64.
• Isomorphic. Works in Node and the browser.
• HTTP client agnostic. It must be provided as a parameter. This also allows providing custom cache or headers.

Requirements:

• Native Promise or a polyfill.

Examples:

/* http://some.remote/file.css */

@import "http://fonts.googleapis.com/css?family=Tangerine";

.bar {
  color: green;
  background-image: url('./img/logo.svg');
}

/* Input example */

.foo {
  color: red;
}

@import url('http://some.remote/file.css');

.baz {
  color: blue;
}

/* Output example */

.foo {
  color: red;
}

@font-face {
  font-family: 'Tangerine';
  font-style: normal;
  font-weight: 400;
  src: local('Tangerine'), url(http://fonts.gstatic.com/s/tangerine/v7/HGfsyCL5WASpHOFnouG-RKCWcynf_cDxXwCLxiixG1c.ttf) format('truetype')
}

.bar {
  color: green;
  background-image: url('http://some.remote/img/logo.svg');
}

.baz {
  color: blue;
}

If options.base64 was specified (true), the background-image would look like:

.bar {
  color: green;
  background-image: url('data:image/svg+xml;base64,PD94bWwgdmVyc2lvbj0iMS4wIiBlbmNvZGluZz0iVVRGLTgiPz4KPHNZz4=');
}

Usage

This plugin is isomorphic (Node + browser environments). For sake of versatility, it does not bundle any http-request package. Therefore, it must be provided as a parameter.

Node

var postcss = require('postcss');
var urlResolver = require('postcss-url-resolver');
var hh = require('http-https');

postcss([urlResolver({
  exclude: /theme.css$/,
  base64: true,

  request: function(opt) {
    return new Promise(function executor(resolve, reject) {
      var req = hh.get(reqOptions, function(res) {
          var body = '';

          res.on('data', function(chunk) {
            body += chunk.toString();
          });

          res.on('end', function() {
            resolve(body);
          });
      });

      req.on('error', reject);
      req.end();
    });
  }
})])

Browser (Webpack)

import postcss from 'postcss';
import urlResolver from 'postcss-url-resolver';
import axios from 'axios';

postcss([ urlResolver({
  exclude: /theme.css$/,
  base64: true,

  request: function(opt) {
    return axios.get(opt.href)
      .then(res => res.data);
  }
})])

Note: axios can also be used in Node environments.

Parameters

• request: Function called to make an HTTP request. It gets a parsed URL object as its only parameter. Must return a promise which resolves to the response body (content). Required.
• recursive: Whether @import should be resolved recursively. Default true.
• base64: Resolves and inlines images in base 64. Default false.
• exclude: A RegExp matching urls that won't be resolved. Default null.

See PostCSS docs for examples for your environment.