Custom Error Messages on ENFILE and EMFILE IO Errors (openethereum#8744)

* Custom Error Messages on ENFILE and EMFILE IO Errors

Add custom mapping of ENFILE and EMFILE IO Errors (Failure because of missing system resource) right when chaining ioError into ::util::Network::Error to improve Error Messages given to user

Note: Adds libc as a dependency to util/network

* Use assert-matches for more readable tests

* Fix Wording and consistency

util/network/Cargo.toml

@@ -14,4 +14,9 @@ ethereum-types = "0.3"
 ethkey = { path = "../../ethkey" }
 ipnetwork = "0.12.6"
 rlp = { path = "../rlp" }
+libc = "0.2"
 snappy = { git = "https://github.com/paritytech/rust-snappy" }
+
+
+[dev-dependencies]
+assert_matches = "1.2"

util/network/src/error.rs

@@ -15,6 +15,7 @@
 // along with Parity.  If not, see <http://www.gnu.org/licenses/>.
 
 use std::{io, net, fmt};
+use libc::{ENFILE, EMFILE};
 use io::IoError;
 use {rlp, ethkey, crypto, snappy};
 
@@ -83,7 +84,6 @@ impl fmt::Display for DisconnectReason {
 error_chain! {
 	foreign_links {
 		SocketIo(IoError) #[doc = "Socket IO error."];
-		Io(io::Error) #[doc = "Error concerning the Rust standard library's IO subsystem."];
 		Decompression(snappy::InvalidInput) #[doc = "Decompression error."];
 	}
 
@@ -141,6 +141,34 @@ error_chain! {
 			description("Packet is too large"),
 			display("Packet is too large"),
 		}
+
+		#[doc = "Reached system resource limits for this process"]
+		ProcessTooManyFiles {
+			description("Too many open files in process."),
+			display("Too many open files in this process. Check your resource limits and restart parity"),
+		}
+
+		#[doc = "Reached system wide resource limits"]
+		SystemTooManyFiles {
+			description("Too many open files on system."),
+			display("Too many open files on system. Consider closing some processes/release some file handlers or increas the system-wide resource limits and restart parity."),
+		}
+
+		#[doc = "An unknown IO error occurred."]
+		Io(err: io::Error) {
+			description("IO Error"),
+			display("Unexpected IO error: {}", err),
+		}
+	}
+}
+
+impl From<io::Error> for Error {
+	fn from(err: io::Error) -> Self {
+		match err.raw_os_error() {
+			Some(ENFILE) => ErrorKind::ProcessTooManyFiles.into(),
+			Some(EMFILE) => ErrorKind::SystemTooManyFiles.into(),
+			_ => Error::from_kind(ErrorKind::Io(err))
+		}
 	}
 }
 
@@ -191,3 +219,26 @@ fn test_errors() {
 		_ => panic!("Unexpected error"),
 	}
 }
+
+#[test]
+fn test_io_errors() {
+	use libc::{EMFILE, ENFILE};
+
+	assert_matches!(
+		<Error as From<io::Error>>::from(
+			io::Error::from_raw_os_error(ENFILE)
+			).kind(),
+		ErrorKind::ProcessTooManyFiles);
+
+	assert_matches!(
+		<Error as From<io::Error>>::from(
+			io::Error::from_raw_os_error(EMFILE)
+			).kind(),
+		ErrorKind::SystemTooManyFiles);
+
+	assert_matches!(
+		<Error as From<io::Error>>::from(
+			io::Error::from_raw_os_error(0)
+			).kind(),
+		ErrorKind::Io(_));
+}

util/network/src/lib.rs

@@ -23,6 +23,10 @@ extern crate ethkey;
 extern crate rlp;
 extern crate ipnetwork;
 extern crate snappy;
+extern crate libc;
+
+#[cfg(test)] #[macro_use]
+extern crate assert_matches;
 
 #[macro_use]
 extern crate error_chain;