vinodworks / imagehoster

Image uploader and proxy

imagehoster

Steem-powered image hosting and proxying service.

Developing

With node.js installed, run:

make devserver

This will pull in all dependencies and spin up a hot-reloading development server.

Run make lint to run the autolinter, make test to run the unit tests.

Configuration

Defaults are in <./config/default.toml> and can be overridden by env vars as defined in <./config/custom-environment-variables.toml>

Load order is: env vars > config/$NODE_ENV.toml > config/default.toml

See the config module docs for more details.

API

Responses should be determined by the Content-Type header, errors will have a status of >=400 and a Content-Type of application/json with the body in the format:

{
    "error": {
        "name": "error_name",
        "info": {"optional": "metadata"}
    }
}

POST /<username>/<signature> - upload an image.

Multipart image upload, will only consider first file if there are multiple.

Returns a JSON object containing the url to the uploaded image, example:

{
    "url": "https://images.example.com/DQmZi174Xz96UrRVBMNRHb6A2FfU3z1HRPwPPQCgSMgdiUT/test.jpg"
}

Requires a signature from a Steem account in good standing, see the "Signing uploads" section below for more information.

GET /<image_hash>/[<filename>] - fetch an uploaded image.

Download a previously uploaded image.

filename is optional but can be provided to help users and applications understand the content type (Content-Type header will still always reflect actual image type).

GET /p/<b58_image_url>[?options] - proxy and resize an image.

Downloads and serves the provided image, note that a copy will be taken of the image and that will be served on subsequent requests so even if the upstream is removed or changes you will still get the original from the proxy endpoint.

Params

• b58_image_url - Base58 encoded utf8 string containing the url to the image you wish to proxy.

Options

The options are set as query-strings and control how the image is transformed before being proxied.

• width - Desired image width.
• height - Desired image height.
• mode - Resizing mode.
  • cover default - When set the image will be center cropped if the original aspect ratio does not match the aspect ratio of the upstream image.
  • fit - Does not crop the image, it will always keep the upstream aspect ratio and resized to fit within the width and height given.
• format - Output image encoding.
  • match default - Matches the encoding of the upstream image.
  • jpeg - Use JPEG encoding.
  • png - Use PNG encoding.
  • webp - Use WebP encoding.

If only width or height are given their counterpart will be calculated based on the upstream image aspect ratio.

Examples

Upstream image: https://ipfs.io/ipfs/QmXa4dAFEhGEuZaX7uUSEvBjbEY5mPxkaS2zHZSnHvocpn (Base58 encoded 46aP2QbqUqBqwzwxM6L1P6uLNceBDDCM9ZJdv282fpHyc9Wgcz1FduB11aVXtczv9TiCSHF1eEmnRSSdQWQEXA5krJNq)

Proxy the image as-is:

https://steemitimages.com/p/46aP2QbqUqBqwzwxM6L1P6uLNceBDDCM9ZJdv282fpHyc9Wgcz1FduB11aVXtczv9TiCSHF1eEmnRSSdQWQEXA5krJNq

Center cropped 512x512px avatar image in WebP format:

https://steemitimages.com/p/46aP2QbqUqBqwzwxM6L1P6uLNceBDDCM9ZJdv282fpHyc9Wgcz1FduB11aVXtczv9TiCSHF1eEmnRSSdQWQEXA5krJNq?width=512&height=512&format=webp

Aspect resized image fitting inside a 200x500px container:

https://steemitimages.com/p/46aP2QbqUqBqwzwxM6L1P6uLNceBDDCM9ZJdv282fpHyc9Wgcz1FduB11aVXtczv9TiCSHF1eEmnRSSdQWQEXA5krJNq?width=200&height=500&mode=fit

Aspect resized image with variable width and a height of max 100px:

https://steemitimages.com/p/46aP2QbqUqBqwzwxM6L1P6uLNceBDDCM9ZJdv282fpHyc9Wgcz1FduB11aVXtczv9TiCSHF1eEmnRSSdQWQEXA5krJNq?&height=100

GET /<width>x<height>/<image_url> - proxy and resize an image.

DEPRECATED

Downloads and serves the provided image_url, note that a copy will be taken of the image and that will be served on subsequent requests so even if the upstream is removed or changes you will still get the original from the proxy endpoint.

width and height can be set to 0 to preserve the image dimensions, if they are >0 the image will be aspect resized (down-sample only) to fit inside the rectangle.

GET /u/<username>/avatar/[<size>] - get user avatar image.

Serves the avatar for username, if no avatar is set a default image will be served (set in service config).

Sizes are:

• small - 64x64
• medium - 128x128
• large - 512x512

Note that the avatars follow the same sizing rules as proxied images, so you are not guaranteed to get a square image, just an image fitting inside of the size square.

Signing uploads

Uploads require a signature made with by a Steem account's posting authority, further that account has to be above a (service configurable) reputation threshold.

Creating a signature (psuedocode):

signature = secp256k1_sign(sha256('ImageSigningChallenge'+image_data), account_private_posting_key)

Creating a signature (node.js & dsteem)

#!/usr/bin/env node

const dsteem = require('dsteem')
const crypto = require('crypto')
const fs = require('fs')

const [wif, file] = process.argv.slice(2)

if (!wif || !file) {
    process.stderr.write(`Usage: ./sign.js <posting_wif> <file>\n`)
    process.exit(1)
}

const data = fs.readFileSync(file)
const key = dsteem.PrivateKey.fromString(wif)
const imageHash = crypto.createHash('sha256')
    .update('ImageSigningChallenge')
    .update(data)
    .digest()

process.stdout.write(key.sign(imageHash).toString() + '\n')

$ ./sign.js 5J9jN691Gf3MKdwvqWVx54drx9qub6koyA3mjhenyN12CURua8W test.jpg
1f78d007a0b12cd17f2d349446c3f9b7cfa096ae53903a11608d6232781fb994a2086263f21e4da831d2a2b0b372f701b83042a629ba3d87791d05f393d5504db2