How to add a custom JSON-RPC endpoint to geth?

Question

I'm building an Ethereum private network and I want to make a custom JSON-RPC endpoint.

I've been customizing and adding some things in the go-ethereum source code but I don't know yet where to look to make this and which files would be involved...

Answer 1

Trying different things I found that the answer is very simple:

Just by adding a method in go-ethereum/internal/ethapi/api.go let's say "MyMethod", it will map to the JSON-RPC method "eth_myMethod" like so:

// go-ethereum/internal/ethapi/api.go
func (s *PublicTransactionPoolAPI) MyMethod(ctx context.Context, text string) error {
    log.Info(text)
    return nil
}

RPC call:

{
    "jsonrpc": "2.0",
    "method": "eth_myMethod",
    "params": [
        "Hello, World!"
    ],
    "id": 1
}

That will return:

{
    "jsonrpc": "2.0",
    "id": 1,
    "result": null
}

And will print Hello, World! in the console.