Add custom panic hook for RPC port bind

src/rpc.rs

@@ -8,6 +8,7 @@ use service::Service;
 use signature::{Pubkey, Signature};
 use std::mem;
 use std::net::SocketAddr;
+use std::panic;
 use std::sync::atomic::{AtomicBool, Ordering};
 use std::sync::Arc;
 use std::thread::{self, Builder, JoinHandle};
@@ -28,6 +29,10 @@ impl JsonRpcService {
                 let rpc = RpcSolImpl;
                 io.extend_with(rpc.to_delegate());
 
+                panic::set_hook(Box::new(move |_| {
+                    warn!("JSON RPC service unavailable: unable to bind to RPC port {}. \nMake sure this port is not already in use by another application", rpc_addr.port());
+                }));
+
                 let server =
                     ServerBuilder::with_meta_extractor(io, move |_req: &hyper::Request| Meta {
                         request_processor: request_processor.clone(),
@@ -37,6 +42,7 @@ impl JsonRpcService {
                         ]))
                         .start_http(&rpc_addr)
                         .unwrap();
+                let _ = panic::take_hook();
                 loop {
                     if exit.load(Ordering::Relaxed) {
                         server.close();