ociplex: Implement the 'features' subcommand

The `runc features` subcommand returns a JSON formatted string listing the
supported features. It is not documented, but it was implemented here:
opencontainers/runc#3296.

Based on the code, it does not seem to take any option.

Signed-off-by: Christophe de Dinechin <dinechin@redhat.com>

crates/ociplex/src/backend/cli.rs

@@ -343,6 +343,11 @@ impl Backend for CliBackend {
         self.invoke(backargs)
     }
 
+    fn features(&self, _args: liboci_cli::Features) -> Result<()> {
+        let backargs: Vec<OsString> = vec!["features".into()];
+        self.invoke(backargs)
+    }
+
     fn list(&self, args: liboci_cli::List) -> Result<()> {
         let mut backargs = Vec::<OsString>::new();
 
@@ -359,11 +364,13 @@ impl Backend for CliBackend {
 
         self.invoke(backargs)
     }
+
     fn pause(&self, args: liboci_cli::Pause) -> Result<()> {
         let backargs: Vec<OsString> = vec!["pause".into(), args.container_id.into()];
 
         self.invoke(backargs)
     }
+
     fn ps(&self, args: liboci_cli::Ps) -> Result<()> {
         let mut backargs = Vec::<OsString>::new();
 

crates/ociplex/src/backend/mod.rs

@@ -39,6 +39,7 @@ pub trait Backend: Debug {
             CommonCmd::Checkpointt(args) => self.checkpoint(args),
             CommonCmd::Events(args) => self.events(args),
             CommonCmd::Exec(args) => self.exec(args),
+            CommonCmd::Features(args) => self.features(args),
             CommonCmd::List(args) => self.list(args),
             CommonCmd::Pause(args) => self.pause(args),
             CommonCmd::Ps(args) => self.ps(args),
@@ -66,6 +67,9 @@ pub trait Backend: Debug {
     fn exec(&self, args: liboci_cli::Exec) -> Result<()> {
         Err(anyhow!("exec subcommand unimplemented: {:?}", args))
     }
+    fn features(&self, args: liboci_cli::Features) -> Result<()> {
+        Err(anyhow!("features subcommand unimplemented: {:?}", args))
+    }
     fn list(&self, args: liboci_cli::List) -> Result<()> {
         Err(anyhow!("list subcommand unimplemented: {:?}", args))
     }

crates/ociplex/src/backend/trivial.rs

@@ -49,6 +49,9 @@ impl Backend for TrivialBackend {
     fn exec(&self, args: liboci_cli::Exec) -> Result<()> {
         Err(anyhow!("trivial: {:?}", args))
     }
+    fn features(&self, args: liboci_cli::Features) -> Result<()> {
+        Err(anyhow!("trivial: {:?}", args))
+    }
     fn list(&self, args: liboci_cli::List) -> Result<()> {
         Err(anyhow!("trivial: {:?}", args))
     }