Implement slasher (#1567)

This is an implementation of a slasher that lives inside the BN and can be enabled via `lighthouse bn --slasher`.

Features included in this PR:

- [x] Detection of attester slashing conditions (double votes, surrounds existing, surrounded by existing)
- [x] Integration into Lighthouse's attestation verification flow
- [x] Detection of proposer slashing conditions
- [x] Extraction of attestations from blocks as they are verified
- [x] Compression of chunks
- [x] Configurable history length
- [x] Pruning of old attestations and blocks
- [x] More tests

Future work:

* Focus on a slice of history separate from the most recent N epochs (e.g. epochs `current - K` to `current - M`)
* Run out-of-process
* Ingest attestations from the chain without a resync

Design notes are here https://hackmd.io/@sproul/HJSEklmPL

beacon_node/src/cli.rs

@@ -359,6 +359,80 @@ pub fn cli_app<'a, 'b>() -> App<'a, 'b> {
                 .value_name("NUM_SLOTS")
                 .takes_value(true)
         )
+        /*
+         * Slasher.
+         */
+        .arg(
+            Arg::with_name("slasher")
+                .long("slasher")
+                .help(
+                    "Run a slasher alongside the beacon node. It is currently only recommended for \
+                     expert users because of the immaturity of the slasher UX and the extra \
+                     resources required."
+                )
+                .takes_value(false)
+        )
+        .arg(
+            Arg::with_name("slasher-dir")
+                .long("slasher-dir")
+                .help(
+                    "Set the slasher's database directory."
+                )
+                .value_name("PATH")
+                .takes_value(true)
+                .requires("slasher")
+        )
+        .arg(
+            Arg::with_name("slasher-update-period")
+                .long("slasher-update-period")
+                .help(
+                    "Configure how often the slasher runs batch processing."
+                )
+                .value_name("SECONDS")
+                .requires("slasher")
+                .takes_value(true)
+        )
+        .arg(
+            Arg::with_name("slasher-history-length")
+                .long("slasher-history-length")
+                .help(
+                    "Configure how many epochs of history the slasher keeps. Immutable after \
+                     initialization."
+                )
+                .value_name("EPOCHS")
+                .requires("slasher")
+                .takes_value(true)
+        )
+        .arg(
+            Arg::with_name("slasher-max-db-size")
+                .long("slasher-max-db-size")
+                .help(
+                    "Maximum size of the LMDB database used by the slasher."
+                )
+                .value_name("GIGABYTES")
+                .requires("slasher")
+                .takes_value(true)
+        )
+        .arg(
+            Arg::with_name("slasher-chunk-size")
+                .long("slasher-chunk-size")
+                .help(
+                    "Number of epochs per validator per chunk stored on disk."
+                )
+                .value_name("EPOCHS")
+                .requires("slasher")
+                .takes_value(true)
+        )
+        .arg(
+            Arg::with_name("slasher-validator-chunk-size")
+                .long("slasher-validator-chunk-size")
+                .help(
+                    "Number of validators per chunk stored on disk."
+                )
+                .value_name("NUM_VALIDATORS")
+                .requires("slasher")
+                .takes_value(true)
+        )
         .arg(
             Arg::with_name("wss-checkpoint")
                 .long("wss-checkpoint")

beacon_node/src/config.rs

@@ -351,6 +351,43 @@ pub fn get_config<E: EthSpec>(
         };
     }
 
+    if cli_args.is_present("slasher") {
+        let slasher_dir = if let Some(slasher_dir) = cli_args.value_of("slasher-dir") {
+            PathBuf::from(slasher_dir)
+        } else {
+            client_config.data_dir.join("slasher_db")
+        };
+
+        let mut slasher_config = slasher::Config::new(slasher_dir);
+
+        if let Some(update_period) = clap_utils::parse_optional(cli_args, "slasher-update-period")?
+        {
+            slasher_config.update_period = update_period;
+        }
+
+        if let Some(history_length) =
+            clap_utils::parse_optional(cli_args, "slasher-history-length")?
+        {
+            slasher_config.history_length = history_length;
+        }
+
+        if let Some(max_db_size) = clap_utils::parse_optional(cli_args, "slasher-max-db-size")? {
+            slasher_config.max_db_size_gbs = max_db_size;
+        }
+
+        if let Some(chunk_size) = clap_utils::parse_optional(cli_args, "slasher-chunk-size")? {
+            slasher_config.chunk_size = chunk_size;
+        }
+
+        if let Some(validator_chunk_size) =
+            clap_utils::parse_optional(cli_args, "slasher-validator-chunk-size")?
+        {
+            slasher_config.validator_chunk_size = validator_chunk_size;
+        }
+
+        client_config.slasher = Some(slasher_config);
+    }
+
     Ok(client_config)
 }
 

beacon_node/src/lib.rs

@@ -17,8 +17,10 @@ use beacon_chain::{
 };
 use clap::ArgMatches;
 use environment::RuntimeContext;
+use slasher::Slasher;
 use slog::{info, warn};
 use std::ops::{Deref, DerefMut};
+use std::sync::Arc;
 use types::EthSpec;
 
 /// A type-alias to the tighten the definition of a production-intended `Client`.
@@ -82,6 +84,16 @@ impl<E: EthSpec> ProductionBeaconNode<E> {
             .http_api_config(client_config.http_api.clone())
             .disk_store(&db_path, &freezer_db_path_res?, store_config)?;
 
+        let builder = if let Some(slasher_config) = client_config.slasher.clone() {
+            let slasher = Arc::new(
+                Slasher::open(slasher_config, log.new(slog::o!("service" => "slasher")))
+                    .map_err(|e| format!("Slasher open error: {:?}", e))?,
+            );
+            builder.slasher(slasher)
+        } else {
+            builder
+        };
+
         let builder = builder
             .beacon_chain_builder(client_genesis, client_config_1)
             .await?;