Go-Ethereum – How to Generate a New Address Using Json-RPC

RPC over HTTP is inherently unsafe, as any browser tab may access your server. Because of this, any functionality that was deemed unsafe for public consumption is not available by default on the HTTP interface.

You have two options: you can either force enable the things you're missing via --rpcapi, just make sure you're clear with the security consequences. The other and better solution is to do API requests via the IPC channel, which has all methods enabled by default.

For a full list of Geth 1.3.x management methods see https://github.com/ethereum/go-ethereum/wiki/Go-ethereum-management-API's . This list will be significantly expanded with the 1.4 release.

Filters work a little bit different. Filters require LOGs to be emitted from an EVM execution (i.e. a contract). Solidity makes this easy for you by allowing you to fire events (compiled events generate LOGs).

Let's take the following contract:

contract T {
    event res(uint indexed out)
    function echo(uint in) {
         res(i);
    }
}

When the method echo is invoked on the contract it fires the solidity event res. These events can be caught using the eth_newFilter and queried using eth_getFilterChanges.

When creating a filter for a specific event (e.g. res) we need to derive the event signature first. Signatures are generated using the first 4 bytes of the keccak hash of the event's definition (i.e. res(uint)): keccak("res(uint)"). This then becomes the first argument for the eth_newFilter's topics.

Any of the arguments in the definition of the event that have the indexed keyword (as in the example contract listed above) can also be used to filter on. Let's say we only want to catch events for the number 6, we would then construct the following JSON-RPC:

curl -X POST --data '{"jsonrpc":"2.0","method":"eth_newFilter","params":[{"address": "0xaddress", topics:["KECCAK_HASH", "0x6"], "fromBlock":"latest","toBlock":"latest"}],"id":2}' localhost:8545 {"id":2,"jsonrpc":"2.0","result":"0x0"}

Now whenever the method echo(6) is invoked on the contract you'll be able to query the result using the eth_getFilterChanges.

Please see the solidity docs on events for more information.