add pub sub client implementation with examples (#22)

* add pub sub client implementation with examples

* replace subscribed_channels list Vec with HashSet to avoid duplicates

* update Subscriber to use async-stream instead of manual Stream impl

* revert update to error handling server.rs, as #21 handles it

* remove uneeded recursion limit extension

src/cmd/publish.rs

@@ -4,8 +4,8 @@ use bytes::Bytes;
 
 #[derive(Debug)]
 pub struct Publish {
-    channel: String,
-    message: Bytes,
+    pub(crate) channel: String,
+    pub(crate) message: Bytes,
 }
 
 impl Publish {
@@ -24,4 +24,13 @@ impl Publish {
         dst.write_frame(&response).await?;
         Ok(())
     }
+
+    pub(crate) fn into_frame(self) -> Frame {
+        let mut frame = Frame::array();
+        frame.push_bulk(Bytes::from("publish".as_bytes()));
+        frame.push_bulk(Bytes::from(self.channel.into_bytes()));
+        frame.push_bulk(self.message);
+
+        frame
+    }
 }

src/cmd/subscribe.rs

@@ -1,5 +1,5 @@
-use crate::{Command, Connection, Db, Frame, Shutdown};
 use crate::cmd::{Parse, ParseError};
+use crate::{Command, Connection, Db, Frame, Shutdown};
 
 use bytes::Bytes;
 use tokio::select;
@@ -7,12 +7,12 @@ use tokio::stream::{StreamExt, StreamMap};
 
 #[derive(Debug)]
 pub struct Subscribe {
-    channels: Vec<String>,
+    pub(crate) channels: Vec<String>,
 }
 
-#[derive(Debug)]
+#[derive(Clone, Debug)]
 pub struct Unsubscribe {
-    channels: Vec<String>,
+    pub(crate) channels: Vec<String>,
 }
 
 impl Subscribe {
@@ -98,8 +98,8 @@ impl Subscribe {
                 res = dst.read_frame() => {
                     let frame = match res? {
                         Some(frame) => frame,
-                        // How to handle remote client closing write half
-                        None => unimplemented!(),
+                        // How to handle remote client closing write half?
+                        None => return Ok(())
                     };
 
                     // A command has been received from the client.
@@ -147,6 +147,15 @@ impl Subscribe {
             };
         }
     }
+
+    pub(crate) fn into_frame(self) -> Frame {
+        let mut frame = Frame::array();
+        frame.push_bulk(Bytes::from("subscribe".as_bytes()));
+        for channel in self.channels {
+            frame.push_bulk(Bytes::from(channel.into_bytes()));
+        }
+        frame
+    }
 }
 
 impl Unsubscribe {
@@ -166,4 +175,13 @@ impl Unsubscribe {
 
         Ok(Unsubscribe { channels })
     }
+
+    pub(crate) fn into_frame(self) -> Frame {
+        let mut frame = Frame::array();
+        frame.push_bulk(Bytes::from("unsubscribe".as_bytes()));
+        for channel in self.channels {
+            frame.push_bulk(Bytes::from(channel.into_bytes()));
+        }
+        frame
+    }
 }