How can I connect to public chain using web3?

Question

I have used web3 to interact with my private chain by using :

web3.setProvider(new web3.providers.HttpProvider("http://localhost:8012"));

But How can I connect to Public Network using web3?

I am trying to make a web interface for interaction with my contract( which deployes, where you can use all the functions provided by my contract using my web interface. I have done this on private network and everything worked seamlessly.
But now I have doubt that whether I can replicate same on public network.
For example let my contract address be x and contract ABI be y and I have a function named transfer to transfer coins. I have done this on private network:

web3.setProvider(new web3.providers.HttpProvider("http://localhost:8012"));
var contract1=web3.eth.contract(y).at(x);
contract1.transfer(to, amount, {from: frm});

Also can I unlock my account using RPC ? I mean if my users want to create an address, If I can ask for password from them and use web3.personal.newAccount(password);.

To summarise:

1. Can I access my contract on Public network using web3? If yes, How?
2. Is personal exposed over RPC? I mean if I have to generate addresses or unlock account using web3, how can I do that?
3. There are api that provide Ethereum addresses, how do they work?

Answer 1

This is how you access ehtereum public network

new Web3.providers.HttpProvider('https://api.myetherapi.com/eth')

Answer 2

1. Yes, you can access to your contract on the Ethereum mainnet or testnet (public chains) after publishing a contract, exactly like you do for the private chain. You have to connect your client code (Web3 JS) to a running Ethereum node through RPC. This running node can be:

   • A node running locally on the client machine (http://localhost:8545)
   • A remote node (provided by your organisation)
   • A 3rd party node

2. Personal is not exposed. The accounts and transactions are handled most of the time by an Ethereum browser such as Mist or Google Chome (+plugin Metamask). The Ethereum browser allows to:

   • Connect to a node
   • Create an account
   • Fund an account
   • Send transaction

For example, every time your client will try to execute a sendTransaction or a contract written functions like you wrote

var contract1=web3.eth.contract(y).at(x);
contract1.transfer(to, amount, {from: frm});

it will open a popup asking the user to approve the transaction.

Examples of Metamask

3. If you want to manage yourself all this part, I haven't tried but I guess you can use a library like eth-lightwallet

Hope this helps you.