apply client/cli polish (#15)

Continuation of #11. Refines the client structure and implements GET.

`clap` is decoupled from the lib code. This is done to avoid any CLI
parsing concerns to leak into the lib. The main motivation for this is
to allow the reader to focus on Tokio concerns and not CLI parsing
concerns.

src/cmd/set.rs

@@ -1,26 +1,19 @@
-use crate::cmd::{
-    utils::{bytes_from_str, duration_from_ms_str},
-    Parse, ParseError,
-};
 use crate::{Connection, Db, Frame};
-use clap::Clap;
+use crate::cmd::{Parse, ParseError};
 
 use bytes::Bytes;
-use std::io;
 use std::time::Duration;
 use tracing::{debug, instrument};
 
-#[derive(Clap, Debug)]
+#[derive(Debug)]
 pub struct Set {
     /// the lookup key
     pub(crate) key: String,
 
     /// the value to be stored
-    #[clap(parse(from_str = bytes_from_str))]
     pub(crate) value: Bytes,
 
-    /// duration in milliseconds
-    #[clap(parse(try_from_str = duration_from_ms_str))]
+    /// When to expire the key
     pub(crate) expire: Option<Duration>,
 }
 
@@ -52,14 +45,15 @@ impl Set {
         Ok(Set { key, value, expire })
     }
 
-    #[instrument]
-    pub(crate) async fn apply(self, db: &Db, dst: &mut Connection) -> io::Result<()> {
+    #[instrument(skip(db))]
+    pub(crate) async fn apply(self, db: &Db, dst: &mut Connection) -> crate::Result<()> {
         // Set the value
         db.set(self.key, self.value, self.expire);
 
         let response = Frame::Simple("OK".to_string());
         debug!(?response);
-        dst.write_frame(&response).await
+        dst.write_frame(&response).await?;
+        Ok(())
     }
 
     pub(crate) fn into_frame(self) -> Frame {