Defining “listen,” “listenaddr” and “discovery” ports from admin.nodeinfo?

Question

f you type "admin.nodeInfo" at the javascript console, you will see:

 listenAddr: "[::]:<value>",
  name: "Geth/v1.6.1-stable-021c3c28/linux-amd64/go1.8.1",
  ports: {
    discovery: <value>,
    listener: <value>
  },

(along with a bunch of other stuff, of course.)

So we have these three ports: listenAddr, listener, discovery. What does each one of them mean in this context.

I am not asking about the RPC port or the websockets port. I am specifically asking about the thing that I just mentioned.

Answer 1

There are basically three important ports. The first is discovery port, and other two are listener ports:

1. Discovery port: (default is 30303). This port is used for connecting to other geth nodes.
2. RPC port: (default is 8545). This port is used to send JSON-rpc requests to the geth client.
3. Websocket port: (default is 8546) You can connect to geth client using websockets.

All of them are independent process and hence cannot be run on same ports.

Answer 2

listenAddr is an address , i.e. contains IP+port number

listener is only a port number

discovery is also port number for finding new peers

---

The word listener has a meaning of a connecting gate, for example,this is another piece of ethereum's source ('node/node.go'):

    ipcListener net.Listener // IPC RPC listener socket to serve API requests
    httpListener  net.Listener // HTTP RPC listener socket to server API requests
    wsListener net.Listener // Websocket RPC listener socket to server API requests

In Go Listener is a standard type:

A Listener is a generic network listener for stream-oriented protocols.

Multiple goroutines may invoke methods on a Listener simultaneously.

    type Listener interface {
            // Accept waits for and returns the next connection to the listener.
            Accept() (Conn, error)

            // Close closes the listener.
            // Any blocked Accept operations will be unblocked and return errors.
            Close() error

            // Addr returns the listener's network address.
            Addr() Addr
    }

This is the meaning of the word listener , but ListenAddr is the full address of the socket. it is defined in Linux kernel as this struct:

#include <netinet/in.h>

struct sockaddr_in {
    short            sin_family;   // e.g. AF_INET
    unsigned short   sin_port;     // e.g. htons(3490)
    struct in_addr   sin_addr;     // see struct in_addr, below
    char             sin_zero[8];  // zero this if you want to
};

The fields sin_addr and sin_port together is the variable listenAddr, in fact, this is what the method Addr() should return.

But in Ethereum code, by saying listener they don't refer to the Interface listener nor the object that implements listener interface, they refer to the port number.