Add IPC support (#6348)

This is useful for both security and performance reasons. IPC is faster
than TCP, and it is subject to OS access controls.

substrate/client/cli/src/commands/mod.rs

@@ -285,6 +285,12 @@ macro_rules! substrate_cli_subcommands {
 				}
 			}
 
+			fn rpc_ipc(&self) -> $crate::Result<::std::option::Option<::std::string::String>> {
+				match self {
+					$($enum::$variant(cmd) => cmd.rpc_ipc()),*
+				}
+			}
+
 			fn rpc_http(&self) -> $crate::Result<::std::option::Option<::std::net::SocketAddr>> {
 				match self {
 					$($enum::$variant(cmd) => cmd.rpc_http()),*

substrate/client/cli/src/commands/run_cmd.rs

@@ -122,6 +122,10 @@ pub struct RunCmd {
 	#[structopt(long = "prometheus-external")]
 	pub prometheus_external: bool,
 
+	/// Specify IPC RPC server path
+	#[structopt(long = "ipc-path", value_name = "PATH")]
+	pub ipc_path: Option<String>,
+
 	/// Specify HTTP RPC server TCP port.
 	#[structopt(long = "rpc-port", value_name = "PORT")]
 	pub rpc_port: Option<u16>,
@@ -434,6 +438,10 @@ impl CliConfiguration for RunCmd {
 		Ok(Some(SocketAddr::new(interface, self.rpc_port.unwrap_or(9933))))
 	}
 
+	fn rpc_ipc(&self) -> Result<Option<String>> {
+		Ok(self.ipc_path.clone())
+	}
+
 	fn rpc_ws(&self) -> Result<Option<SocketAddr>> {
 		let interface = rpc_interface(
 			self.ws_external,