use fs2 advisory file lock on startup (#2600)

servers/Cargo.toml

@@ -11,6 +11,7 @@ edition = "2018"
 
 [dependencies]
 hyper = "0.12"
+fs2 = "0.4"
 futures = "0.1"
 http = "0.1"
 hyper-staticfile = "0.3"

servers/src/common/types.rs

@@ -48,6 +48,8 @@ pub enum Error {
 	Pool(pool::PoolError),
 	/// Invalid Arguments.
 	ArgumentError(String),
+	/// Error originating from some I/O operation (likely a file on disk).
+	IOError(std::io::Error),
 }
 
 impl From<core::block::Error> for Error {
@@ -60,7 +62,11 @@ impl From<chain::Error> for Error {
 		Error::Chain(e)
 	}
 }
-
+impl From<std::io::Error> for Error {
+	fn from(e: std::io::Error) -> Error {
+		Error::IOError(e)
+	}
+}
 impl From<p2p::Error> for Error {
 	fn from(e: p2p::Error) -> Error {
 		Error::P2P(e)

servers/src/grin/server.rs

@@ -16,9 +16,15 @@
 //! the peer-to-peer server, the blockchain and the transaction pool) and acts
 //! as a facade.
 
+use std::fs;
+use std::fs::File;
+use std::io::prelude::*;
+use std::path::Path;
 use std::sync::Arc;
 use std::{thread, time};
 
+use fs2::FileExt;
+
 use crate::api;
 use crate::api::TLSConfig;
 use crate::chain;
@@ -59,6 +65,8 @@ pub struct Server {
 	state_info: ServerStateInfo,
 	/// Stop flag
 	pub stop_state: Arc<Mutex<StopState>>,
+	/// Maintain a lock_file so we do not run multiple Grin nodes from same dir.
+	lock_file: Arc<File>,
 }
 
 impl Server {
@@ -102,8 +110,36 @@ impl Server {
 		}
 	}
 
+	// Exclusive (advisory) lock_file to ensure we do not run multiple
+	// instance of grin server from the same dir.
+	// This uses fs2 and should be safe cross-platform unless somebody abuses the file itself.
+	fn one_grin_at_a_time(config: &ServerConfig) -> Result<Arc<File>, Error> {
+		let path = Path::new(&config.db_root);
+		fs::create_dir_all(path.clone())?;
+		let path = path.join("grin.lock");
+		let lock_file = fs::OpenOptions::new()
+			.read(true)
+			.write(true)
+			.create(true)
+			.open(&path)?;
+		lock_file.try_lock_exclusive().map_err(|e| {
+			let mut stderr = std::io::stderr();
+			writeln!(
+				&mut stderr,
+				"Failed to lock {:?} (grin server already running?)",
+				path
+			)
+			.expect("Could not write to stderr");
+			e
+		})?;
+		Ok(Arc::new(lock_file))
+	}
+
 	/// Instantiates a new server associated with the provided future reactor.
 	pub fn new(config: ServerConfig) -> Result<Server, Error> {
+		// Obtain our lock_file or fail immediately with an error.
+		let lock_file = Server::one_grin_at_a_time(&config)?;
+
 		// Defaults to None (optional) in config file.
 		// This translates to false here.
 		let archive_mode = match config.archive_mode {
@@ -264,6 +300,7 @@ impl Server {
 				..Default::default()
 			},
 			stop_state,
+			lock_file,
 		})
 	}
 
@@ -451,6 +488,7 @@ impl Server {
 	pub fn stop(&self) {
 		self.p2p.stop();
 		self.stop_state.lock().stop();
+		let _ = self.lock_file.unlock();
 	}
 
 	/// Pause the p2p server.