Clean up code

nats-client/src/chat_message.rs

@@ -0,0 +1,49 @@
+use core::fmt;
+use std::{error::Error, fmt::Display};
+
+use serde::{Deserialize, Serialize};
+
+#[derive(Serialize, Deserialize)]
+pub struct ChatMessage {
+    pub author: String,
+    pub message: String,
+}
+
+impl Display for ChatMessage {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        write!(f, "Message from {}: {}", self.author, self.message)
+    }
+}
+
+impl TryFrom<Vec<u8>> for ChatMessage {
+    type Error = NatsParsingError;
+
+    fn try_from(value: Vec<u8>) -> Result<Self, Self::Error> {
+        let as_string = &String::from_utf8(value).map_err(|_| NatsParsingError::NoValidUtf8)?;
+        let to_return =
+            serde_json::from_str(as_string).map_err(|_| NatsParsingError::CannotDeserializeJson)?;
+        Ok(to_return)
+    }
+}
+
+#[derive(Debug)]
+pub enum NatsParsingError {
+    // Message was no string at all
+    NoValidUtf8,
+    // Message could be invalid json or json not matching the struct you want to deserialize
+    CannotDeserializeJson,
+}
+
+impl Error for NatsParsingError {}
+
+impl Display for NatsParsingError {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        let message = match self {
+            NatsParsingError::NoValidUtf8 => "NATS message was no valid UTF-8 string.",
+            NatsParsingError::CannotDeserializeJson => {
+                "NATS message is not a valid / expected json."
+            }
+        };
+        writeln!(f, "{}", message)
+    }
+}

nats-client/src/main.rs

@@ -1,73 +1,40 @@
+use nats::Connection;
 use std::{
-    fmt::{self, Display},
     io::{self, BufRead},
+    process::exit,
 };
 
-use nats::Connection;
-use serde::{Deserialize, Serialize};
+use crate::chat_message::ChatMessage;
 
-#[derive(Serialize, Deserialize)]
-struct Message {
-    author: String,
-    message: String,
-}
+mod chat_message;
+mod nats_cli;
 
-impl Display for Message {
-    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
-        write!(f, "Message from {}: {}", self.author, self.message)
+fn main() {
+    let result = run_chat_program();
+    if let Err(e) = result {
+        match e.kind() {
+            io::ErrorKind::ConnectionRefused => {
+                eprintln!("Connection to server is refused. Please check if it is really running.");
+                exit(1);
+            }
+            _ => panic!("{}", e),
+        }
     }
 }
 
-const SUBJECT_MESSAGES: &str = "here.happens.messaging";
-
-fn main() -> io::Result<()> {
-    let nc = nats::connect("127.0.0.1")?;
-
+fn run_chat_program() -> io::Result<()> {
+    let nc = nats_cli::connect_to_nats()?;
     let username = ask_user_name();
     println!(
         "Hello {}, please write your message. Use q to quit:",
         username
     );
 
-    let my_username = username.clone();
-    let sub = nc.subscribe(SUBJECT_MESSAGES)?.with_handler(move |msg| {
-        // This runs in a separate Thread
-        let message: Message = serde_json::from_str(&String::from_utf8(msg.data).unwrap()).unwrap();
+    let subscription = nats_cli::subscribe_to_chat_messages(username.clone(), &nc)?;
 
-        // Do not show messages from me
-        if message.author != my_username {
-            println!("Received {}", message);
-        }
-        Ok(())
-    });
+    user_message_writing_loop(&username, &nc)?;
 
-    let stdin = io::stdin();
-    for line in stdin.lock().lines() {
-        let line = line.unwrap();
-        let line = line.trim();
-        if line.is_empty() {
-            continue;
-        }
-
-        if line == "q" || line == "Q" {
-            break;
-        }
-
-        publish_message(
-            &Message {
-                author: username.clone(),
-                message: line.to_string(),
-            },
-            &nc,
-        )?;
-    }
-    sub.unsubscribe()?;
-    Ok(())
-}
-
-fn publish_message(message: &Message, nc: &Connection) -> io::Result<()> {
-    let json_string_utf8 = serde_json::to_string(message).expect("Cannot serialize message");
-    nc.publish(SUBJECT_MESSAGES, json_string_utf8)?;
+    subscription.unsubscribe()?;
     Ok(())
 }
 
@@ -84,3 +51,27 @@ fn ask_user_name() -> String {
     }
     input_text
 }
+
+fn user_message_writing_loop(username: &str, nc: &Connection) -> io::Result<()> {
+    let stdin = io::stdin();
+    for line in stdin.lock().lines() {
+        let line = line.unwrap();
+        let line = line.trim();
+        if line.is_empty() {
+            continue;
+        }
+
+        if line == "q" || line == "Q" {
+            break;
+        }
+
+        nats_cli::publish_message(
+            &ChatMessage {
+                author: username.to_string(),
+                message: line.to_string(),
+            },
+            &nc,
+        )?;
+    }
+    Ok(())
+}

nats-client/src/nats_cli.rs

@@ -0,0 +1,38 @@
+use std::io;
+
+use nats::{Connection, Handler};
+
+use crate::chat_message::ChatMessage;
+
+const SERVER: &str = "127.0.0.1";
+const SUBJECT_MESSAGES: &str = "here.happens.messaging";
+
+pub fn connect_to_nats() -> io::Result<Connection> {
+    nats::connect(SERVER)
+}
+
+pub fn subscribe_to_chat_messages(username: String, nc: &Connection) -> io::Result<Handler> {
+    // This runs the closure in a separate Thread
+    let subscription =
+        nc.subscribe(SUBJECT_MESSAGES)?
+            .with_handler(move |msg| -> Result<(), io::Error> {
+                match ChatMessage::try_from(msg.data) {
+                    Ok(message) => {
+                        // Do not show messages from me
+                        if message.author != username {
+                            println!("Received {}", message);
+                        }
+                    }
+                    Err(e) => eprintln!("{}", e),
+                };
+                Ok(())
+            });
+    Ok(subscription)
+}
+
+pub fn publish_message(message: &ChatMessage, nc: &Connection) -> io::Result<()> {
+    let json_string_utf8 = serde_json::to_string(message).expect("Cannot serialize message");
+    // TODO: there is no error if server is offline
+    nc.publish(SUBJECT_MESSAGES, json_string_utf8)?;
+    Ok(())
+}