Node + Express + Sharp

Install and start the application

Get the code from this github repository :

# download an image hosted in a github repository
$ git clone \
    --depth 1 \
    https://github.com/jeromedecoster/black-white-node-express-sharp.git \
    /tmp/bw

# cd + install
$ cd /tmp/bw && npm install

If you look at index.js, the code is really simple :

• We use multer with the MemoryStorage.
• We use greyscale and toBuffer.

const app = express()
app.use(express.static('public'))

// memory storage
var upload = multer({ storage: multer.memoryStorage() })

app.post('/upload', upload.single('file'), (req, res) => {

    // convert
    sharp(req.file.buffer)
        .greyscale()
        .toBuffer(function (err, buffer) {
            // add a header to display the image rather than download it
            res.header('Content-Type', 'image/jpeg')
            res.send(buffer)
        })
})

Let’s start the server :

# start the server
$ node .

Convert an image using a HTML form

If you open localhost:3000 you should see :

This is a multipart/form-data form grabbed from tympanus.

Select the file /tmp/bw/bird.jpg and upload it :

Now you should be redirected to /upload and see :

Convert an image using curl

We can use curl to upload then save the gray version :

• We use the -X, –request option send a POST request.
• We use the -F, –form <name=content> option to select the file.
• We use the -s, –silent option.
• We use the -o, –output option to save the file.

# upload `bird.jpg` and save the result as `bird-gray.jpg`
$  curl --request POST \
    --form "file=@bird.jpg" \
    --silent \
    http://localhost:3000/upload \
    --output bird-gray.jpg