Decentralized Twitter: A microblogging service running on the Ethereum blockchain
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README.md

Decentralized Twitter

This repository contains the code of a decentralized microblogging service running on the Ethereum blockchain.

The service provides basic Twitter-like functionality to tweet messages of up to 160 characters.

Here, decentralization means there is no company or central authority in control of what is being published.

The system is censorship resistant in the sense that once a message is published, it can only be removed by the publisher.

All accounts can receive donations in Ethereum's Ether crypto currency. Being able to receive donations can be an incentive to run a decentralized microblogging feed.

To not expose the user's social graph to the world, following other accounts is not supported on purpose.

If you want to edit the source files, you can use Ethereum's Mix IDE which can be found here. In the repository, there is a Mix IDE project file called .mix, it also contains some test cases used during development. Mix can simulate a local blockchain for testing.

Contents

Install

Install geth and start it by entering

geth --rpc --rpccorsdomain="http://ethertweet.net"

Read Tweets in the Web Browser

With geth running, open http://ethertweet.net/ui in your web browser.

You should see a menu of existing accounts and the corresponding tweets, as shown in this picture:

EtherTweetScreenshot

Using the Geth Command Line

Posting tweets is not yet supported using the web browser. Instead, you have to use the geth command line.

After starting geth as shown above, open a second shell and start the interactive geth interface by running

geth attach

Your prompt should change to >

As a test, get the status by entering:

> eth

You should see various ethereum statistics like the current block number.

All commands below assume you are in the interactive geth interface.

Read Tweets on the Command Line

An example how to read tweets of an existing account.

See section Browse Accounts below, to learn how to explore all existing accounts.

Create a local variable TweetAccount to point to the existing account. Here, the address of the test account 0x9e82d1745c6c9c04a6cfcde102837cf0f25efc56 is used. Change this address in the code block below to read tweets of other accounts.

Copy the following code block and paste it into the interactive geth interface:

var TweetAccount = web3.eth.contract([{"constant":true,"inputs":[],"name":"getOwnerAddress","outputs":[{"name":"adminAddress","type":"address"}],"type":"function"},{"constant":false,"inputs":[],"name":"adminDeleteAccount","outputs":[],"type":"function"},{"constant":false,"inputs":[{"name":"receiver","type":"address"}],"name":"adminRetrieveDonations","outputs":[],"type":"function"},{"constant":true,"inputs":[],"name":"getLatestTweet","outputs":[{"name":"tweetString","type":"string"},{"name":"timestamp","type":"uint256"},{"name":"numberOfTweets","type":"uint256"}],"type":"function"},{"constant":true,"inputs":[],"name":"isAdmin","outputs":[{"name":"isAdmin","type":"bool"}],"type":"function"},{"constant":true,"inputs":[{"name":"tweetId","type":"uint256"}],"name":"getTweet","outputs":[{"name":"tweetString","type":"string"},{"name":"timestamp","type":"uint256"}],"type":"function"},{"constant":true,"inputs":[],"name":"getNumberOfTweets","outputs":[{"name":"numberOfTweets","type":"uint256"}],"type":"function"},{"constant":true,"inputs":[{"name":"tweetString","type":"string"}],"name":"tweet","outputs":[{"name":"result","type":"int256"}],"type":"function"},{"inputs":[],"type":"constructor"}]).at("0x9e82d1745c6c9c04a6cfcde102837cf0f25efc56"); TweetAccount

Get latest tweet of the account with:

TweetAccount.getLatestTweet()

Expected result is:

["hello world", 1446832323, 1]

The resulting JSON array contains: [tweet string, timestamp of tweet, total number of tweets].

Use a tool like unixtimestamp.com to convert timestamps.

Get total number of tweets:

TweetAccount.getNumberOfTweets()

Get a specific tweet. For example, get the first tweet, tweet number 0:

TweetAccount.getTweet(0)

Ether

For account creation, registration and tweeting, you have to get Ethereum's crypto currency Ether. You can either buy Ether for Dollar/Euro or trade Ether for Bitcoin. Instructions can be found here: ethereum.org/ether. For example, you can use the kraken.com crypto currency exchange.

Pricing is as following:

Date Account Creation Price per Tweet
2015 December 0.02384905 ether or 0.00420185 ether or
$0.020/€0,018 or $0.003/€0.003
roughly 2 cents roughly one third of a cent
2016 March 0.00772476 ether or 0.00182126 ether or
$0.10/€0.09 or $0.02/€0.02 or
roughly 10 cents roughly two cents

For current rates see the currency pairs eth/usd or eth/eur on kraken.com/charts.

If you like this project, please consider sending donations in Ether to 0x93a4a6c05c5cfb945f6ccaea223723561670c204 or donations in Bitcoin to 3PyW7MNRJzpw13JFVendeTFt7dcXmFq4pd.

Create an Account

Create a new account and make it known to the world by registering an account name in the registry.

To be able to create an account, you have to own some Ether in the local account created by geth. Check local account balance:

web3.fromWei(eth.getBalance(eth.coinbase), "ether")

Copy and paste the following block into the geth interface to deploy your account code to the ethereum blockchain:

var MyTweetAccount = web3.eth.contract([{"constant":true,"inputs":[],"name":"getOwnerAddress","outputs":[{"name":"adminAddress","type":"address"}],"type":"function"},{"constant":false,"inputs":[],"name":"adminDeleteAccount","outputs":[],"type":"function"},{"constant":false,"inputs":[{"name":"receiver","type":"address"}],"name":"adminRetrieveDonations","outputs":[],"type":"function"},{"constant":true,"inputs":[],"name":"getLatestTweet","outputs":[{"name":"tweetString","type":"string"},{"name":"timestamp","type":"uint256"},{"name":"numberOfTweets","type":"uint256"}],"type":"function"},{"constant":true,"inputs":[],"name":"isAdmin","outputs":[{"name":"isAdmin","type":"bool"}],"type":"function"},{"constant":true,"inputs":[{"name":"tweetId","type":"uint256"}],"name":"getTweet","outputs":[{"name":"tweetString","type":"string"},{"name":"timestamp","type":"uint256"}],"type":"function"},{"constant":true,"inputs":[],"name":"getNumberOfTweets","outputs":[{"name":"numberOfTweets","type":"uint256"}],"type":"function"},{"constant":true,"inputs":[{"name":"tweetString","type":"string"}],"name":"tweet","outputs":[{"name":"result","type":"int256"}],"type":"function"},{"inputs":[],"type":"constructor"}]).new( { from: web3.eth.accounts[0], data: '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', gas: 3000000 }, function(e, contract){ if (typeof contract.address != 'undefined') { console.log(e, contract); console.log('Contract mined! address: ' + contract.address + ' transactionHash: ' + contract.transactionHash); } })

If you are curious how this ethereum byte code was created, have a look at the deploy directory in this repository. Also, have a look at the TweetAccount.sol source file, it contains a lot of comments to explain what the code does.

After some time, you should see a message like:

Contract mined! address: 0x9e82d1745c6c9c04a6cfcde102837cf0f25efc56 transactionHash: 0xd458166ead4d6d398fd0c76616d57093798e86716dd4169d2846295223768f1f

Congratulations! You just wrote your first code to the blockchain and successfully created your account!

You can use the adminRetrieveDonations() function to withdraw donations your account received, see Solidity API section below.

Section Register Account Name explains how you can assign a name to this account address so others can find your account by name.

Post a new Tweet

This example tweets hello world with the MyTweetAccount created above:

MyTweetAccount.tweet.sendTransaction("hello world", {from: eth.coinbase, gas: 200000})

Note that you have to own Ether to be able to tweet. See previous example how to check your account balance.

You should see a message like I1210 13:33:35.411646 58618 xeth.go:1028] Tx(0x8b253799a87efd08133e4f2b7dcece785a05d6de075c92435da48cb61009ac7e) to: 0x9e82d1745c6c9c04a6cfcde102837cf0f25efc56 in the geth logs.

Check:

MyTweetAccount.getLatestTweet()

Should display ["hello world", 1449750863, 1]. That means latest tweet is hello world, tweetet at unix timestamp 1449750863 with a total of 1 tweets for this account. Use a tool like unixtimestamp.com to convert timestamps.

More checks:

MyTweetAccount.getNumberOfTweets()

Should return 1

MyTweetAccount.getTweet(0)

Should return ["hello world", 1449750863, 1]

If you want to post another tweet at a later time, do the following:

  • Define a variable for your tweet account as described in section Reading Tweets on the Command Line.
  • Post a new tweet by creating a transaction with tweet.sendTransaction as descibed in this section.

Register Account Name

To make your account known to the world, give it a name and register it in the account registry.

Then, others only have to remember your account name and do not need to write down the long and complicated account address.

Create a variable for the account registry. Copy and paste the following block into the geth interface:

var TweetRegistry = eth.contract([{"constant":false,"inputs":[{"name":"name","type":"string"}],"name":"adminUnregister","outputs":[],"type":"function"},{"constant":false,"inputs":[{"name":"name","type":"string"},{"name":"accountAddress","type":"address"}],"name":"register","outputs":[{"name":"result","type":"int256"}],"type":"function"},{"constant":true,"inputs":[],"name":"getNumberOfAccounts","outputs":[{"name":"numberOfAccounts","type":"uint256"}],"type":"function"},{"constant":false,"inputs":[],"name":"adminRetrieveDonations","outputs":[],"type":"function"},{"constant":true,"inputs":[{"name":"name","type":"string"}],"name":"getAddressOfName","outputs":[{"name":"addr","type":"address"}],"type":"function"},{"constant":false,"inputs":[],"name":"adminDeleteRegistry","outputs":[],"type":"function"},{"constant":false,"inputs":[{"name":"accountAdmin","type":"address"}],"name":"adminSetAccountAdministrator","outputs":[],"type":"function"},{"constant":false,"inputs":[{"name":"registrationDisabled","type":"bool"}],"name":"adminSetRegistrationDisabled","outputs":[],"type":"function"},{"constant":true,"inputs":[{"name":"addr","type":"address"}],"name":"getNameOfAddress","outputs":[{"name":"name","type":"string"}],"type":"function"},{"constant":false,"inputs":[],"name":"unregister","outputs":[{"name":"unregisteredAccountName","type":"string"}],"type":"function"},{"constant":true,"inputs":[{"name":"id","type":"uint256"}],"name":"getAddressOfId","outputs":[{"name":"addr","type":"address"}],"type":"function"},{"inputs":[],"type":"constructor"}]).at("0xe0f278b72097e563b09d7dc94c6f75aff5e83298"); TweetRegistry

Register account name test for the account MyTweetAccount (from the previous example) into the TweetRegistry. Please note you have to use a different account name than "test" since it is already taken.

TweetRegistry.register.sendTransaction("test", MyTweetAccount.address, {from: eth.coinbase, gas: 200000})

Browse Accounts

Access accounts by name without having to use the account address directly. You can also look up all existing accounts.

Use the TweetRegistry variable created in the previous section to look up accounts. Once you know the address of the account you want to read, use instructions in section Read Tweets to continue.

Get address of account called test: TweetRegistry.getAddressOfName("test")

Get total amount of accounts registered: TweetRegistry.getNumberOfAccounts()

Get address of the first account registered ever: TweetRegistry.getAddressOfId(0). Change ID to iterate over all accounts.

Get name of account address: TweetRegistry.getNameOfAddress("0x36b47d7c8fef8daf5d0b4477dcc8def158d4255f")

Solidity API

This decentralized app is written in the Solidity programming language. Documentation is available at solidity.readthedocs.org.

Have a look at the README.md in the deploy directory of this repository. It explains how compilation from Solidity source code to the Ethereum byte code was done.

The TweetAccount.sol source file contains a lot of comments to explain what the code does.

contract TweetAccount{
 function TweetAccount()
 function getOwnerAddress()constant returns(address adminAddress)
 function adminDeleteAccount()
 function adminRetrieveDonations(address receiver)
 function getLatestTweet()constant returns(string tweetString,uint256 timestamp,uint256 numberOfTweets)
 function isAdmin()constant returns(bool isAdmin)
 function getTweet(uint256 tweetId)constant returns(string tweetString,uint256 timestamp)
 function getNumberOfTweets()constant returns(uint256 numberOfTweets)
 function tweet(string tweetString)constant returns(int256 result)
}

contract TweetRegistry{
 function TweetRegistry()
 function adminUnregister(string name)
 function register(string name,address accountAddress)returns(int256 result)
 function getNumberOfAccounts()constant returns(uint256 numberOfAccounts)
 function adminRetrieveDonations()
 function getAddressOfName(string name)constant returns(address addr)
 function adminDeleteRegistry()
 function adminSetAccountAdministrator(address accountAdmin)
 function adminSetRegistrationDisabled(bool registrationDisabled)
 function getNameOfAddress(address addr)constant returns(string name)
 function unregister()returns(string unregisteredAccountName)
 function getAddressOfId(uint256 id)constant returns(address addr)
}

Web3 Javascript API

Geth uses javascript in its interactive interface. Documentation is available here.

The javascript code used in the examples above was created automatically on deploy. See the README.md in the deploy directory for more information

The files deploy/tweet-account.deploy/interface.txt and deploy/tweet-registry.deploy/interface.txt contain the actual javascript interface.

More Geth Commands

Get your account address (called coinbase):

eth.coinbase

You should see an ethereum account address starting with 0x.

Get number of pending transactions:

eth.getBlockTransactionCount("pending")

Contributors

Links

License

GPL v3

Copyright (C) 2015-2016 Jahn Bertsch

This program is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation in version 3.

This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with this program.  If not, see <http://www.gnu.org/licenses/>.