Methods of attaching data to an ethereum address?

Question

I'm trying to setup a system where you can attach a name and website url to an ethereum address. Then have it get called back in an ethereum block explorer I'm building. What are some ways where a user can attach this data to their own account? And how would one call it back? I know you can attach data when you send out via the HEX values, but how would one do it in this scenario?

Answer 1

Here's a simple example with the users maintaining their own information.

For simplicity, I've got the users first registering with a function made for that purpose, and then updating (if needed) with functions made for that purpose.

pragma solidity ^0.4.6;

contract UserRegistry {

    struct UserStruct {
        string name;
        string url;
        uint userListPointer;
    }

    address[] public userList;
    mapping(address => UserStruct) public userStructs;

    function isUser(address user)
        public 
        constant
        returns(bool isIndeed)
    {
        if(userList.length==0) return false;
        return userList[userStructs[user].userListPointer]==user;
    }

    // Assuming user is trusted to maintain information about themselves ... 

    function registerAsUser(string name, string url)
        public
        returns(bool success)
    {
        if(isUser(msg.sender)) throw; // duplicate prohibited
        userStructs[msg.sender].name = name;
        userStructs[msg.sender].url = url;
        userStructs[msg.sender].userListPointer = userList.push(msg.sender) - 1;
        return true;
    }

    function updateUserName(string name)
        public
        returns(bool success)
    {
        if(!isUser(msg.sender)) throw;
        userStructs[msg.sender].name = name;
        return true;
    }

    function updateUserUrl(string url)
        public
        returns(bool success)
    {
        if(!isUser(msg.sender)) throw;
        userStructs[msg.sender].url = url;
        return true;
    }

}

Client side depends on the language. Assuming Web3 JavaScript and Truffle framework, client would do something like this (not tested):

var address = "0x123";
var userRegistry;
UserRegistry.deployed().then(function(instance) { userRegistry = instance; });

// is this address registered?
userRegistry.isUser(address).then(function(isIndeed) { console.log("Is registered", isIndeed); });

// what information do we have about this user?
userRegistry.userStructs(address).then(function(userInfo) { console.log("User Info:", userInfo); });

Also possible to iterate over the list of registered addresses:

// get address from row 0 on the list
userRegistry.userList(0).then(function(addr) { console.log("address:", addr); });

Can add a simple a simple contract function to get a count to help with iteration over the keys

function getUserCount() public constant returns(uint userCount) {
  return userList.length;
}

Function results in Remix to show it working:

Possible to extend this with delete function; omitted for brevity.

Hope it helps.