More comments and tweak details (#33)

Co-authored-by: Alice Ryhl <alice@ryhl.io>

Author: carllerche

README.md

@@ -10,6 +10,20 @@ application.
 **Disclaimer** Don't even think about trying to use this in production... just
 don't.
 
+## Why Redis
+
+The primary goal of this project is teaching Tokio. Doing this requires a
+project with a wide range of features with a focus on implementation simplicity.
+Redis, an in-memory database, provides a wide range of features and uses a
+simple wire protocol. The wide range of features allows demonstrating many Tokio
+patterns in a "real world" context.
+
+The Redis wire protocol documentation can be found [here](https://redis.io/topics/protocol).
+
+The set of commands Redis provides can be found
+[here](https://redis.io/commands).
+
+
 ## Running
 
 The repository provides a server, client library, and some client executables
@@ -117,6 +131,12 @@ the server to update the active subscriptions.
 The server uses a `std::sync::Mutex` and **not** a Tokio mutex to synchronize
 access to shared state. See [`db.rs`](src/db.rs) for more details.
 
+### Testing asynchronous code that relies on time
+
+In [`tests/server.rs`](tests/server.rs), there are tests for key expiration.
+These tests depend on time passing. In order to make the tests deterministic,
+time is mocked out using Tokio's testing utilities.
+
 ## Contributing
 
 Contributions to `mini-redis` are welcome. Keep in mind, the goal of the project
@@ -128,6 +148,9 @@ demonstrate a new pattern.
 
 Contributions should come with extensive comments targetted to new Tokio users.
 
+Contributions that only focus on clarifying and improving comments are very
+welcome.
+
 ## FAQ
 
 #### Should I use this in production?

examples/sub.rs

@@ -29,9 +29,9 @@ pub async fn main() -> Result<()> {
     let mut subscriber = client.subscribe(vec!["foo".into()]).await?;
 
     // await messages on channel foo
-    let msg = subscriber.next_message().await? ;
-    println!("got message from the channel: {}; message = {:?}", msg.channel, msg.content);
-
+    if let Some(msg) = subscriber.next_message().await? {
+        println!("got message from the channel: {}; message = {:?}", msg.channel, msg.content);
+    }
 
     Ok(())
 }

src/bin/cli.rs

@@ -63,6 +63,7 @@ async fn main() -> mini_redis::Result<()> {
     // Establish a connection
     let mut client = client::connect(&addr).await?;
 
+    // Process the requested command
     match cli.command {
         Command::Get { key } => {
             if let Some(value) = client.get(&key).await? {

src/bin/server.rs

@@ -1,3 +1,11 @@
+//! mini-redis server.
+//!
+//! This file is the entry point for the server implemented in the library. It
+//! performs command line parsing and passes the arguments on to
+//! `mini_redis::server`.
+//!
+//! The `clap` crate is used for parsing arguments.
+
 use mini_redis::{server, DEFAULT_PORT};
 
 use clap::Clap;