Add concept of beacon node configuration TOML

beacon_node/Cargo.toml

@@ -5,7 +5,9 @@ authors = ["Paul Hauner <paul@paulhauner.com>", "Age Manning <Age@AgeManning.com
 edition = "2018"
 
 [dependencies]
+dirs = "1.0.3"
 types = { path = "../eth2/types" }
+toml = "^0.5"
 store = { path = "./store" }
 client = { path = "client" }
 fork_choice = { path = "../eth2/fork_choice" }

beacon_node/client/src/client_config.rs

@@ -8,7 +8,7 @@ use std::path::PathBuf;
 /// The core configuration of a Lighthouse beacon node.
 #[derive(Debug, Clone, Serialize, Deserialize)]
 pub struct ClientConfig {
-    data_dir: String,
+    pub data_dir: String,
     pub spec: String,
     pub db_type: String,
     db_name: String,

beacon_node/src/main.rs

@@ -5,6 +5,13 @@ mod run;
 use clap::{App, Arg};
 use client::ClientConfig;
 use slog::{crit, o, Drain};
+use std::fs;
+use std::fs::File;
+use std::io::prelude::*;
+
+pub const SAMPLE_CONFIG_FILENAME: &str = "beacon_node_config.sample.toml";
+pub const CONFIG_FILENAME: &str = "beacon_node_config.toml";
+pub const DEFAULT_DATA_DIR: &str = ".lighthouse";
 
 fn main() {
     let decorator = slog_term::TermDecorator::new().build();
@@ -22,7 +29,8 @@ fn main() {
                 .long("datadir")
                 .value_name("DIR")
                 .help("Data directory for keys and databases.")
-                .takes_value(true),
+                .takes_value(true)
+                .default_value(DEFAULT_DATA_DIR),
         )
         // network related arguments
         .arg(
@@ -94,7 +102,13 @@ fn main() {
         )
         .get_matches();
 
-    let mut config = ClientConfig::default();
+    let mut config = match load_config(matches.value_of("data_dir")) {
+        Ok(c) => c,
+        Err(e) => {
+            crit!(logger, "Failed to load/generate a ChainConfig"; "error" => format!("{:?}", e));
+            return;
+        }
+    };
 
     match config.apply_cli_args(&matches) {
         Ok(()) => (),
@@ -109,3 +123,42 @@ fn main() {
         Err(e) => crit!(logger, "Beacon node failed to start"; "reason" => format!("{:}", e)),
     }
 }
+
+/// Loads a `ClientConfig` from file. If unable to load from file, generates a default
+/// configuration and saves that as a sample file.
+fn load_config(data_dir: Option<&str>) -> Result<ClientConfig, String> {
+    let data_dir = data_dir.unwrap_or_else(|| DEFAULT_DATA_DIR);
+
+    let path = dirs::home_dir()
+        .ok_or_else(|| "Unable to locate home directory")?
+        .join(&data_dir);
+    fs::create_dir_all(&path).map_err(|_| "Unable to open data_dir")?;
+
+    if let Ok(mut file) = File::open(path.join(CONFIG_FILENAME)) {
+        let mut contents = String::new();
+        file.read_to_string(&mut contents).map_err(|e| {
+            format!(
+                "Unable to read existing {}. Error: {:?}",
+                CONFIG_FILENAME, e
+            )
+        })?;
+
+        toml::from_str(&contents).map_err(|_| format!("Unable to parse {}", CONFIG_FILENAME))
+    } else {
+        let mut config = ClientConfig::default();
+        config.data_dir = data_dir.to_string();
+
+        if let Ok(mut file) = File::create(path.join(SAMPLE_CONFIG_FILENAME)) {
+            let toml_encoded = toml::to_string(&config).map_err(|e| {
+                format!(
+                    "Failed to write configuration to {}. Error: {:?}",
+                    SAMPLE_CONFIG_FILENAME, e
+                )
+            })?;
+            file.write_all(toml_encoded.as_bytes())
+                .expect(&format!("Unable to write to {}", SAMPLE_CONFIG_FILENAME));
+        }
+
+        Ok(config)
+    }
+}