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(not so) Simple storage

A bare-bones example on how to use IPFS and Ethereum from the same application. Check this wiki for the original, Ethereum-only idea.

Description

This application deploys a contract to an Ethereum blockchain (the public Ethereum testnet or a local Ethereum testnet) and uses it to keep track of an image stored in an IPFS blockchain (the public IPFS "testnet" or a local IPFS testnet). The image itself is stored in the IPFS file system - the only data stored in the Ethereum contract is the IPFS hash that corresponds to the image. [Images are used in the examples below, but any other file types could be used as well]

Requirements

1. An Ethereum node with one or more accounts unlocked (e.g, --unlock 0), RPC enabled (--rpc) and the proper RPC CORS set up (e.g, --rpccorsdomain = "*")
2. An IPFS node that doesn't block API calls from external origins (more on this below)
3. A modern web browser (preferably Opera) //! opinion detected :)

Local Ethereum node

Check out this guide if you want to run a local Ethereum node.

Local IPFS node

First, install IPFS on your machine.

I suggest you don't override the IPFS directory associated to your localhost's user (normally at ~/.ipfs), so the first thing you want to do is set up an IPFS directory specific for development. You can define one under the current project's root, after you check out this repo:

$ export IPFS_PATH=.ipfs
$ ipfs init

After that, you need to loosen your IPFS node's CORS restrictions:

$ ipfs config --json API.HTTPHeaders.Access-Control-Allow-Origin '["*"]'
$ ipfs config --json Gateway.HTTPHeaders.Access-Control-Allow-Origin '["*"]'

You can now start the IPFS daemon:

$ ipfs daemon

Project structure

• ipfs.js The IPFS interface in JavaScript (repository here). You can find the source (broweserified) code here

• web3.min.js The Ethereum interface in JavaScript (repository here)

• NotSoSimpleStorage.sol Ethereum contract written in Solidity

• NotSoSimpleStorage.html The web application itself. It contains the core logic behind the interactions to IPFS and Ethereum

Usage

Open NotSoSimpleStorage.html in a text editor and replace the values under the config section according to your setup:

// Config
var ipfsHost    = 'localhost',
    ipfsAPIPort = '5001',
    ipfsWebPort = '8080',
    web3Host    = 'localhost',
    web3Port    = '8545';

Now open NotSoSimpleStorage.html from your web browser (no web server needed). You'll need a JavaScript console to use the application - most web browsers come with one installed out of the box. From there, just follow the instructions on the web page.