From 1ac108a7c52664d8ddd893685dd87d90b9cc5a2e Mon Sep 17 00:00:00 2001
From: Juyeong Maing <mjy9088@naver.com>
Date: Fri, 13 Jun 2025 16:34:30 +0900
Subject: [PATCH] Add test for parsing concatenated messages

---
 client/src/main.rs               | 27 ++++++++++++++++--
 messages/Cargo.toml              |  3 ++
 messages/tests/partial_stream.rs | 47 ++++++++++++++++++++++++++++++++
 3 files changed, 74 insertions(+), 3 deletions(-)
 create mode 100644 messages/tests/partial_stream.rs

diff --git a/client/src/main.rs b/client/src/main.rs
index 35b35e5..77c0846 100644
--- a/client/src/main.rs
+++ b/client/src/main.rs
@@ -42,15 +42,21 @@ impl EventLoopWrapper {
 /// 서버 메시지 수신 태스크 (읽기 전용)
 async fn network_listener(mut read_half: OwnedReadHalf, tx: mpsc::Sender<ServerMessage>) {
     use tokio::io::AsyncReadExt;
-    let mut buffer = vec![0u8; 1024];
+
+    let mut read_buf = vec![0u8; 1024];
+    let mut buf = Vec::<u8>::new();
+
     loop {
-        match read_half.read(&mut buffer).await {
+        match read_half.read(&mut read_buf).await {
             Ok(0) => {
                 println!("Server disconnected.");
                 break;
             }
             Ok(n) => {
-                if let Ok(msg) = bincode::deserialize::<ServerMessage>(&buffer[..n]) {
+                buf.extend_from_slice(&read_buf[..n]);
+
+                while let Ok((msg, consumed)) = try_deser::<ServerMessage>(&buf) {
+                    buf.drain(..consumed);
                     if tx.send(msg).await.is_err() {
                         eprintln!("Failed to send server message to channel");
                     }
@@ -65,6 +71,21 @@ async fn network_listener(mut read_half: OwnedReadHalf, tx: mpsc::Sender<ServerM
     println!("network_listener finished.");
 }
 
+fn try_deser<T: serde::de::DeserializeOwned>(buf: &[u8]) -> Result<(T, usize), bincode::Error> {
+    let mut cur = std::io::Cursor::new(buf);
+
+    match bincode::deserialize_from(&mut cur) {
+        Ok(m) => Ok((m, cur.position() as usize)),
+
+        Err(e) => match *e {
+            bincode::ErrorKind::Io(ref io_err) if io_err.kind() == std::io::ErrorKind::UnexpectedEof => {
+                Err(e)
+            }
+            _ => panic!("Invalid data during deserialization: {:?}", e),
+        },
+    }
+}
+
 #[tokio::main]
 async fn main() {
     let server_addr = env::args().nth(1).unwrap_or_else(|| {
diff --git a/messages/Cargo.toml b/messages/Cargo.toml
index 22dbd57..96c1d86 100644
--- a/messages/Cargo.toml
+++ b/messages/Cargo.toml
@@ -6,3 +6,6 @@ edition = "2021"
 [dependencies]
 serde = { version = "1.0.217", features = ["derive"] }
 map-types = { version = "0.1.0", path = "../map_types" }
+
+[dev-dependencies]
+bincode = "1.3"
diff --git a/messages/tests/partial_stream.rs b/messages/tests/partial_stream.rs
new file mode 100644
index 0000000..79ee3e8
--- /dev/null
+++ b/messages/tests/partial_stream.rs
@@ -0,0 +1,47 @@
+use messages::{ServerMessage, PlayerAction, PlayerPosition};
+use bincode;
+
+fn try_deser<T: serde::de::DeserializeOwned>(buf: &[u8]) -> Result<(T, usize), bincode::Error> {
+    let mut cur = std::io::Cursor::new(buf);
+    match bincode::deserialize_from(&mut cur) {
+        Ok(m) => Ok((m, cur.position() as usize)),
+        Err(e) => match *e {
+            bincode::ErrorKind::Io(ref io_err) if io_err.kind() == std::io::ErrorKind::UnexpectedEof => Err(e),
+            _ => panic!("Invalid data during deserialization: {:?}", e),
+        },
+    }
+}
+
+#[test]
+fn parse_two_messages_from_partial_third() {
+    // prepare three messages
+    let msg1 = ServerMessage::Init { your_player_id: 1, your_position: PlayerPosition::NotInWorld };
+    let msg2 = ServerMessage::PlayerAction { action: PlayerAction::DestroyBlock };
+    let msg3 = ServerMessage::Init { your_player_id: 2, your_position: PlayerPosition::NotInWorld };
+
+    let mut buf = Vec::new();
+    bincode::serialize_into(&mut buf, &msg1).unwrap();
+    bincode::serialize_into(&mut buf, &msg2).unwrap();
+    let partial = bincode::serialize(&msg3).unwrap();
+    let cut = partial.len() / 2;
+    buf.extend_from_slice(&partial[..cut]);
+
+    // first message
+    let (parsed1, consumed1) = try_deser::<ServerMessage>(&buf).unwrap();
+    match parsed1 {
+        ServerMessage::Init { your_player_id, .. } => assert_eq!(your_player_id, 1),
+        _ => panic!("Unexpected variant for first message"),
+    }
+    buf.drain(..consumed1);
+
+    // second message
+    let (parsed2, consumed2) = try_deser::<ServerMessage>(&buf).unwrap();
+    match parsed2 {
+        ServerMessage::PlayerAction { action: PlayerAction::DestroyBlock } => {},
+        _ => panic!("Unexpected variant for second message"),
+    }
+    buf.drain(..consumed2);
+
+    // third message should be incomplete
+    assert!(try_deser::<ServerMessage>(&buf).is_err());
+}