use fs2 advisory file lock on startup (#2600)

Cargo.lock

@@ -669,6 +669,15 @@ name = "foreign-types-shared"
 version = "0.1.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 
+[[package]]
+name = "fs2"
+version = "0.4.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+dependencies = [
+ "libc 0.2.48 (registry+https://github.com/rust-lang/crates.io-index)",
+ "winapi 0.3.6 (registry+https://github.com/rust-lang/crates.io-index)",
+]
+
 [[package]]
 name = "fuchsia-cprng"
 version = "0.1.1"
@@ -947,6 +956,7 @@ dependencies = [
  "blake2-rfc 0.2.18 (registry+https://github.com/rust-lang/crates.io-index)",
  "bufstream 0.1.4 (registry+https://github.com/rust-lang/crates.io-index)",
  "chrono 0.4.6 (registry+https://github.com/rust-lang/crates.io-index)",
+ "fs2 0.4.3 (registry+https://github.com/rust-lang/crates.io-index)",
  "futures 0.1.25 (registry+https://github.com/rust-lang/crates.io-index)",
  "grin_api 1.0.1",
  "grin_chain 1.0.1",
@@ -3215,6 +3225,7 @@ dependencies = [
 "checksum fnv 1.0.6 (registry+https://github.com/rust-lang/crates.io-index)" = "2fad85553e09a6f881f739c29f0b00b0f01357c743266d478b68951ce23285f3"
 "checksum foreign-types 0.3.2 (registry+https://github.com/rust-lang/crates.io-index)" = "f6f339eb8adc052cd2ca78910fda869aefa38d22d5cb648e6485e4d3fc06f3b1"
 "checksum foreign-types-shared 0.1.1 (registry+https://github.com/rust-lang/crates.io-index)" = "00b0228411908ca8685dba7fc2cdd70ec9990a6e753e89b6ac91a84c40fbaf4b"
+"checksum fs2 0.4.3 (registry+https://github.com/rust-lang/crates.io-index)" = "9564fc758e15025b46aa6643b1b77d047d1a56a1aea6e01002ac0c7026876213"
 "checksum fuchsia-cprng 0.1.1 (registry+https://github.com/rust-lang/crates.io-index)" = "a06f77d526c1a601b7c4cdd98f54b5eaabffc14d5f2f0296febdc7f357c6d3ba"
 "checksum fuchsia-zircon 0.3.3 (registry+https://github.com/rust-lang/crates.io-index)" = "2e9763c69ebaae630ba35f74888db465e49e259ba1bc0eda7d06f4a067615d82"
 "checksum fuchsia-zircon-sys 0.3.3 (registry+https://github.com/rust-lang/crates.io-index)" = "3dcaa9ae7725d12cdb85b3ad99a434db70b468c09ded17e012d86b5c1010f7a7"

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.