Lighthouse v0.2.0 (Medalla) (#1452)

## Issue Addressed

NA

## Proposed Changes

- Moves the git-based versioning we were doing into the `lighthouse_version` crate in `common`.
- Removes the `beacon_node/version` crate, replacing it with `lighthouse_version`.
- Bumps the version to `v0.2.0`.

## Additional Info

There are now two types of version string:

1. `const VERSION: &str = Lighthouse/v0.2.0-1419501f2+`
1. `version_with_platform() = Lighthouse/v0.2.0-1419501f2+/x86_64-linux`

(1) is handy cause it's a `const` and shorter. (2) has platform info so it's more useful. Note that the plus-sign (`+`) indicates the the git commit is dirty (it used to be `(modified)` but I had to shorten it to fit into graffiti).

These version strings are now included on:

- `lighthouse --version`
- `lcli --version`
- `curl localhost:5052/node/version`
- p2p messages when we communicate our version

You can update the version by changing this constant (version is not related to a `Cargo.toml`):

b9ad7102d5/common/lighthouse_version/src/lib.rs (L4-L15)

beacon_node/src/cli.rs

@@ -1,11 +1,5 @@
 use clap::{App, Arg};
 
-// Default text included in blocks.
-// Must be 32-bytes or will not build.
-//
-//                              |-------must be this long------|
-const DEFAULT_GRAFFITI: &str = "sigp/lighthouse-0.1.2-prerelease";
-
 pub fn cli_app<'a, 'b>() -> App<'a, 'b> {
     App::new("beacon_node")
         .visible_aliases(&["b", "bn", "beacon"])
@@ -248,9 +242,11 @@ pub fn cli_app<'a, 'b>() -> App<'a, 'b> {
         .arg(
             Arg::with_name("graffiti")
                 .long("graffiti")
-                .help("Specify your custom graffiti to be included in blocks.")
+                .help(
+                    "Specify your custom graffiti to be included in blocks. \
+                    Defaults to the current version and commit, truncated to fit in 32 bytes. "
+                )
                 .value_name("GRAFFITI")
-                .default_value(DEFAULT_GRAFFITI)
                 .takes_value(true)
         )
 }

beacon_node/src/config.rs

@@ -6,6 +6,7 @@ use eth2_libp2p::{Enr, Multiaddr};
 use eth2_testnet_config::Eth2TestnetConfig;
 use slog::{crit, info, Logger};
 use ssz::Encode;
+use std::cmp;
 use std::fs;
 use std::net::{IpAddr, Ipv4Addr, ToSocketAddrs};
 use std::net::{TcpListener, UdpSocket};
@@ -350,21 +351,22 @@ pub fn get_config<E: EthSpec>(
         client_config.genesis = ClientGenesis::DepositContract;
     }
 
-    if let Some(graffiti) = cli_args.value_of("graffiti") {
-        let graffiti_bytes = graffiti.as_bytes();
-        if graffiti_bytes.len() > GRAFFITI_BYTES_LEN {
+    let raw_graffiti = if let Some(graffiti) = cli_args.value_of("graffiti") {
+        if graffiti.len() > GRAFFITI_BYTES_LEN {
             return Err(format!(
                 "Your graffiti is too long! {} bytes maximum!",
                 GRAFFITI_BYTES_LEN
             ));
-        } else {
-            // `client_config.graffiti` is initialized by default to be all 0.
-            // We simply copy the bytes from `graffiti_bytes` in there.
-            //
-            // Panic-free because `graffiti_bytes.len()` <= `GRAFFITI_BYTES_LEN`.
-            client_config.graffiti[..graffiti_bytes.len()].copy_from_slice(graffiti_bytes);
         }
-    }
+
+        graffiti.as_bytes()
+    } else {
+        lighthouse_version::VERSION.as_bytes()
+    };
+
+    let trimmed_graffiti_len = cmp::min(raw_graffiti.len(), GRAFFITI_BYTES_LEN);
+    client_config.graffiti[..trimmed_graffiti_len]
+        .copy_from_slice(&raw_graffiti[..trimmed_graffiti_len]);
 
     Ok(client_config)
 }