express-sharp-server

express-sharp-server is a middleware that offers a restful image server based on node-sharp.

npm install express-sharp-server

express-sharp-server is an evolving express middleware to implement an easy-to-use image server, with a focus on extraction of image parts. The goal is to provide all prominent functions of the node-sharp library in a express middleware.

Server

const express = require('express');
const image = require('express-sharp-server');
 
const server = express();
 
// express-sharp-server expects at least a data folder 
// where the image data can be stored.
 
server.use(image({
    data_dir: '/data/'
}));
 
server.listen(8080);

express-sharp-server supports running in a node cluster enviroment, which improves the performance considerably. See cluster.

Options

The following options can be set:

Parameter	Description
base_route	The base_route is used to configure the endpoint, where the middleware listen. Defaults to '/'.
base_url	The base_url is a prefix for the image urls generated in the json responce _links.self.href useful if the server is behind a proxy. Defaults to '/'.
data_dir	The data_dir is used to save the upload and cache files. If upload_dir is not set, data_dir + '/upload/' is created for uploads, If cache_dir is not set, data_dir + '/cache/' is used. Mandatory, if upload_dir or cache_dir is not set.
upload_dir	The directory where the image uploads to be saved. Optional.
cache_dir	The directory where the image cache to be saved. Optional.
logger	optional, a instance to winston logger. Optional.

Basic Usage

First of all, images can be uploaded.

curl -F "Document=@elefants.jpg" http://localhost:8080

In addition, it is possible to reference an image from another server by sending a image url:

{
    "_links": {
        "origin": {
            "href": "https://upload.wikimedia.org/wikipedia/commons/d/d7/Elefantes_Gustavo_Gerdel.jpg"
        }
    }
}

curl --header "Content-Type: application/json" \
  --request POST \
  --data '{ "_links": { "origin": { "href": "https://upload.wikimedia.org/wikipedia/commons/d/d7/Elefantes_Gustavo_Gerdel.jpg" } } }' \
  http://localhost:8080/

In any case, the server responds with the following payload in json.

{
    "metadata": {
        "width": 1200,
        "height": 800,
        "channels": 3,
        "density": 300,
        "mimetype": "image/jpeg",
        "format": "jpeg"
    },
    "created": {
        "datetime": "2019-01-04T23:45:30.873Z"
    },
    "_links": {
        "self": {
            "href": "/0c97f820639ecbbbba0255ceb7a5f962"
        }
    }
}

The image is now stored on the server and can now be retrieved via the url specified as _links.self.href

curl http://localhost:8080/0c97f820639ecbbbba0255ceb7a5f962

The underlying information on the server can be queried if in addition an "Accept: application/json" header is sent.

curl --header "Accept: application/json" \
    http://localhost:8080/0c97f820639ecbbbba0255ceb7a5f962

It is possible to store userdata to an image resource, see userdata.

Features

The following parameter can be mixed.

Parameter	Comment
width	The width of the image, The aspect ratio is retained if no height parameter is present.
height	The height of the image, The aspect ratio is retained if no width parameter is present.
polygon	Can be used to extract a partion of the image. If the Polygon is not recangular, the oferlapping parts of the source image are masked with a uniform color.
rotation	Rotation of the extracted image.
grayscale	Remove color from the image.

See examples for more information.

Todos

The node-sharp library has far more features, this middleware currently offers. In the future, more of its functionality will be implemented in express-sharp-server.

The Caching functionality, even if it supports worker, ist very simple and need to be improved in future.

Finally, there is no method to remove a image resource, or list all available resources. This is the next functionality to implement.

Tests

To run the test suite, first install the dependencies, then run npm test:

$ npm install
$ npm test

Licensing

Copyright 2019 Marcel Bretschneider.

Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at https://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.