Let server banner be configurable

This lets the operator set a custom server banner using the
configuration flag --server-banner. In addition it adds the daemon
version to the banner.

src/app.rs

 use bitcoin::util::hash::Sha256dHash;
 use std::sync::{Arc, Mutex};
 
-use crate::{daemon, errors::*, index, signal::Waiter, store};
+use crate::{config::Config, daemon, errors::*, index, signal::Waiter, store};
 
 pub struct App {
     store: store::DBStore,
     index: index::Index,
     daemon: daemon::Daemon,
+    banner: String,
     tip: Mutex<Sha256dHash>,
 }
 
@@ -15,11 +16,13 @@ impl App {
         store: store::DBStore,
         index: index::Index,
         daemon: daemon::Daemon,
+        config: &Config,
     ) -> Result<Arc<App>> {
         Ok(Arc::new(App {
             store,
             index,
             daemon: daemon.reconnect()?,
+            banner: config.server_banner.clone(),
             tip: Mutex::new(Sha256dHash::default()),
         }))
     }
@@ -46,4 +49,12 @@ impl App {
         }
         Ok(new_block)
     }
+
+    pub fn get_banner(&self) -> Result<String> {
+        Ok(format!(
+            "{}\n{}",
+            self.banner,
+            self.daemon.get_subversion()?
+        ))
+    }
 }

src/bin/electrs.rs

@@ -54,7 +54,7 @@ fn run_server(config: &Config) -> Result<()> {
     }
     .enable_compaction(); // enable auto compactions before starting incremental index updates.
 
-    let app = App::new(store, index, daemon)?;
+    let app = App::new(store, index, daemon, &config)?;
     let tx_cache = TransactionCache::new(config.tx_cache_size);
     let query = Query::new(app.clone(), &metrics, tx_cache);
 

src/config.rs

@@ -26,6 +26,7 @@ pub struct Config {
     pub index_batch_size: usize,
     pub bulk_index_threads: usize,
     pub tx_cache_size: usize,
+    pub server_banner: String,
 }
 
 impl Config {
@@ -108,6 +109,12 @@ impl Config {
                     .help("Number of transactions to keep in for query LRU cache")
                     .default_value("10000")  // should be enough for a small wallet.
             )
+            .arg(
+                Arg::with_name("server_banner")
+                    .long("server-banner")
+                    .help("The banner to be shown in the Electrum console")
+                    .default_value("Welcome to electrs (Electrum Rust Server)!")
+            )
             .get_matches();
 
         let network_name = m.value_of("network").unwrap_or("mainnet");
@@ -192,6 +199,7 @@ impl Config {
             index_batch_size: value_t_or_exit!(m, "index_batch_size", usize),
             bulk_index_threads,
             tx_cache_size: value_t_or_exit!(m, "tx_cache_size", usize),
+            server_banner: value_t_or_exit!(m, "server_banner", String),
         };
         eprintln!("{:?}", config);
         config

src/daemon.rs

@@ -441,6 +441,10 @@ impl Daemon {
         Ok(from_value(info).chain_err(|| "invalid network info")?)
     }
 
+    pub fn get_subversion(&self) -> Result<String> {
+        Ok(self.getnetworkinfo()?.subversion)
+    }
+
     pub fn getbestblockhash(&self) -> Result<Sha256dHash> {
         parse_hash(&self.request("getbestblockhash", json!([]))?).chain_err(|| "invalid blockhash")
     }

src/query.rs

@@ -486,4 +486,8 @@ impl Query {
         }
         last_fee_rate * 1e-5 // [BTC/kB] = 10^5 [sat/B]
     }
+
+    pub fn get_banner(&self) -> Result<String> {
+        self.app.get_banner()
+    }
 }

src/rpc.rs

@@ -106,7 +106,7 @@ impl Connection {
     }
 
     fn server_banner(&self) -> Result<Value> {
-        Ok(json!("Welcome to RustElectrum Server!\n"))
+        Ok(json!(self.query.get_banner()?))
     }
 
     fn server_donation_address(&self) -> Result<Value> {