Handle clap errors manually and don't reset SIGPIPE (#6012)

Instead of resetting `SIGPIPE` to the system default handler, we now
handle a clap error manually and ignore any error when writing to
`stdout`/`stderr`. In this way, the node does not silently stops when it
encounters a `SIGPIPE` in normal mode and we still support piping of the
cli output.

substrate/bin/node/cli/src/command.rs

@@ -63,8 +63,6 @@ impl SubstrateCli for Cli {
 
 /// Parse command line arguments into service configuration.
 pub fn run() -> Result<()> {
-	sc_cli::reset_signal_pipe_handler()?;
-
 	let cli = Cli::from_args();
 
 	match &cli.subcommand {

substrate/client/cli/src/lib.rs

@@ -129,7 +129,27 @@ pub trait SubstrateCli: Sized {
 				AppSettings::SubcommandsNegateReqs,
 			]);
 
-		<Self as StructOpt>::from_clap(&app.get_matches_from(iter))
+		let matches = match app.get_matches_from_safe(iter) {
+			Ok(matches) => matches,
+			Err(mut e) => {
+				// To support pipes, we can not use `writeln!` as any error
+				// results in a "broken pipe" error.
+				//
+				// Instead we write directly to `stdout` and ignore any error
+				// as we exit afterwards anyway.
+				e.message.extend("\n".chars());
+
+				if e.use_stderr() {
+					let _ = std::io::stderr().write_all(e.message.as_bytes());
+					std::process::exit(1);
+				} else {
+					let _ = std::io::stdout().write_all(e.message.as_bytes());
+					std::process::exit(0);
+				}
+			},
+		};
+
+		<Self as StructOpt>::from_clap(&matches)
 	}
 
 	/// Helper function used to parse the command line arguments. This is the equivalent of
@@ -264,21 +284,3 @@ fn kill_color(s: &str) -> String {
 	}
 	RE.replace_all(s, "").to_string()
 }
-
-/// Reset the signal pipe (`SIGPIPE`) handler to the default one provided by the system.
-/// This will end the program on `SIGPIPE` instead of panicking.
-///
-/// This should be called before calling any cli method or printing any output.
-pub fn reset_signal_pipe_handler() -> Result<()> {
-	#[cfg(target_family = "unix")]
-	{
-		use nix::sys::signal;
-
-		unsafe {
-			signal::signal(signal::Signal::SIGPIPE, signal::SigHandler::SigDfl)
-				.map_err(|e| Error::Other(e.to_string()))?;
-		}
-	}
-
-	Ok(())
-}