Set Graffiti via CLI (#1320)

## Issue Addressed

Closes #1319 

## Proposed Changes

This issue:
1. Allows users to edit their Graffiti via the cli option `--graffiti`. If the graffiti is too long, lighthouse will not start and throw an error message. Otherwise, it will set the Graffiti to be the one provided by the user, right-padded with 0s.
2. Create a new `Graffiti` type and unify the code around it. With this type, everything is enforced at compile-time, and the code can be (I think...) panic-free! :)

## Additional info

Currently, only `&str` are supported, as this is the returned type by `.arg("graffiti")`.
Since this is user-input, I tried being as careful as I could. This is also why I created the `Graffiti` type, to make sure I could check as much as possible at compile time.

beacon_node/beacon_chain/src/beacon_chain.rs

@@ -49,12 +49,6 @@ use types::*;
 
 pub type ForkChoiceError = fork_choice::Error<crate::ForkChoiceStoreError>;
 
-// Text included in blocks.
-// Must be 32-bytes or panic.
-//
-//                          |-------must be this long------|
-pub const GRAFFITI: &str = "sigp/lighthouse-0.1.2-prerelease";
-
 /// The time-out before failure during an operation to take a read/write RwLock on the canonical
 /// head.
 pub const HEAD_LOCK_TIMEOUT: Duration = Duration::from_secs(1);
@@ -224,6 +218,8 @@ pub struct BeaconChain<T: BeaconChainTypes> {
     pub disabled_forks: Vec<String>,
     /// Logging to CLI, etc.
     pub(crate) log: Logger,
+    /// Arbitrary bytes included in the blocks.
+    pub(crate) graffiti: Graffiti,
 }
 
 type BeaconBlockAndState<T> = (BeaconBlock<T>, BeaconState<T>);
@@ -1615,9 +1611,6 @@ impl<T: BeaconChainTypes> BeaconChain<T> {
             state.latest_block_header.canonical_root()
         };
 
-        let mut graffiti: [u8; 32] = [0; 32];
-        graffiti.copy_from_slice(GRAFFITI.as_bytes());
-
         let (proposer_slashings, attester_slashings) = self.op_pool.get_slashings(&state);
 
         let eth1_data = eth1_chain.eth1_data_for_block_production(&state, &self.spec)?;
@@ -1649,7 +1642,7 @@ impl<T: BeaconChainTypes> BeaconChain<T> {
                 body: BeaconBlockBody {
                     randao_reveal,
                     eth1_data,
-                    graffiti,
+                    graffiti: self.graffiti.clone(),
                     proposer_slashings: proposer_slashings.into(),
                     attester_slashings: attester_slashings.into(),
                     attestations: self

beacon_node/beacon_chain/src/builder.rs

@@ -27,7 +27,8 @@ use std::sync::Arc;
 use std::time::Duration;
 use store::{HotColdDB, ItemStore};
 use types::{
-    BeaconBlock, BeaconState, ChainSpec, EthSpec, Hash256, Signature, SignedBeaconBlock, Slot,
+    BeaconBlock, BeaconState, ChainSpec, EthSpec, Graffiti, Hash256, Signature, SignedBeaconBlock,
+    Slot,
 };
 
 pub const PUBKEY_CACHE_FILENAME: &str = "pubkey_cache.ssz";
@@ -110,6 +111,7 @@ pub struct BeaconChainBuilder<T: BeaconChainTypes> {
     spec: ChainSpec,
     disabled_forks: Vec<String>,
     log: Option<Logger>,
+    graffiti: Graffiti,
 }
 
 impl<TStoreMigrator, TSlotClock, TEth1Backend, TEthSpec, TEventHandler, THotStore, TColdStore>
@@ -155,6 +157,7 @@ where
             validator_pubkey_cache: None,
             spec: TEthSpec::default_spec(),
             log: None,
+            graffiti: Graffiti::default(),
         }
     }
 
@@ -396,6 +399,12 @@ where
         self
     }
 
+    /// Sets the `graffiti` field.
+    pub fn graffiti(mut self, graffiti: Graffiti) -> Self {
+        self.graffiti = graffiti;
+        self
+    }
+
     /// Consumes `self`, returning a `BeaconChain` if all required parameters have been supplied.
     ///
     /// An error will be returned at runtime if all required parameters have not been configured.
@@ -523,6 +532,7 @@ where
             validator_pubkey_cache: TimeoutRwLock::new(validator_pubkey_cache),
             disabled_forks: self.disabled_forks,
             log: log.clone(),
+            graffiti: self.graffiti,
         };
 
         let head = beacon_chain

beacon_node/client/src/builder.rs

@@ -134,6 +134,7 @@ where
         let eth_spec_instance = self.eth_spec_instance.clone();
         let data_dir = config.data_dir.clone();
         let disabled_forks = config.disabled_forks.clone();
+        let graffiti = config.graffiti.clone();
 
         let store =
             store.ok_or_else(|| "beacon_chain_start_method requires a store".to_string())?;
@@ -151,7 +152,8 @@ where
             .store_migrator(store_migrator)
             .data_dir(data_dir)
             .custom_spec(spec.clone())
-            .disabled_forks(disabled_forks);
+            .disabled_forks(disabled_forks)
+            .graffiti(graffiti);
 
         let chain_exists = builder
             .store_contains_beacon_chain()

beacon_node/client/src/config.rs

@@ -2,6 +2,7 @@ use network::NetworkConfig;
 use serde_derive::{Deserialize, Serialize};
 use std::fs;
 use std::path::PathBuf;
+use types::Graffiti;
 
 pub const DEFAULT_DATADIR: &str = ".lighthouse";
 
@@ -55,6 +56,8 @@ pub struct Config {
     pub sync_eth1_chain: bool,
     /// A list of hard-coded forks that will be disabled.
     pub disabled_forks: Vec<String>,
+    /// Graffiti to be inserted everytime we create a block.
+    pub graffiti: Graffiti,
     #[serde(skip)]
     /// The `genesis` field is not serialized or deserialized by `serde` to ensure it is defined
     /// via the CLI at runtime, instead of from a configuration file saved to disk.
@@ -84,6 +87,7 @@ impl Default for Config {
             sync_eth1_chain: false,
             eth1: <_>::default(),
             disabled_forks: Vec::new(),
+            graffiti: Graffiti::default(),
         }
     }
 }

beacon_node/src/cli.rs

@@ -1,5 +1,11 @@
 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"])
@@ -227,4 +233,16 @@ pub fn cli_app<'a, 'b>() -> App<'a, 'b> {
                 .long("purge-db")
                 .help("If present, the chain database will be deleted. Use with caution.")
         )
+
+        /*
+         * Misc.
+         */
+        .arg(
+            Arg::with_name("graffiti")
+                .long("graffiti")
+                .help("Specify your custom graffiti to be included in blocks.")
+                .value_name("GRAFFITI")
+                .default_value(DEFAULT_GRAFFITI)
+                .takes_value(true)
+        )
 }

beacon_node/src/config.rs

@@ -10,7 +10,7 @@ use std::fs;
 use std::net::{IpAddr, Ipv4Addr, ToSocketAddrs};
 use std::net::{TcpListener, UdpSocket};
 use std::path::PathBuf;
-use types::{ChainSpec, EthSpec};
+use types::{ChainSpec, EthSpec, GRAFFITI_BYTES_LEN};
 
 pub const BEACON_NODE_DIR: &str = "beacon";
 pub const NETWORK_DIR: &str = "network";
@@ -343,6 +343,22 @@ 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 {
+            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);
+        }
+    }
+
     Ok(client_config)
 }