# DEP 0001: Version Message Info

```
status: accepted
```

## Motivation

Currently `version` messages are empty, but before releasing in order to anticipate protocol
upgrades, we should include the protocol version. This is for the moment inside `verack`,
but should be moved to `version` since it allows immediately dropping the connection if the
protocol version is incorrect (and indeed is the main purpose of the version message).

Additionally it should include further info which makes debugging connections and negotiation
easier.

## Proposal

| Type                 | Description         | Comment                                                                                                                |
|----------------------|---------------------|------------------------------------------------------------------------------------------------------------------------|
| `u32`                | version             | Identifies protocol version being used by the node                                                                     |
| `u64`                | timestamp           | UNIX timestamp                                                                                                         |
| `u16`                | nonce               | Random nonce, randomly generated everytime a version packet is sent. This nonce is used to detect connections to self. |
| `Url`                | connect_recv_addr   | Network address of the node receiving this message (before resolving)                                                  |
| `Option<Url>`        | resolv_recv_addr    | Network address of the node receiving this message (after resolving)                                                   |
| `Vec<String>`        | ext_send_addr       | (Optional) External address of the node sending this message                                                           |
| `Vec<(String, u32)>` | (services, version) | List of features to be enabled for this connection                                                                     |

`resolv_recv_addr` is optional as inbound connections do not have such an address.

`ext_send_addr` is empty when no external address is set.

The `(services, version)` field can be used to enable certain features in protocols, or even to upgrade protocols to new versions.
When protocols are first attached, they can add their own data to this field which will be communicated in the subsequent version exchange.
Any further negotiation needed can be done using protocol specific messages afterwards.