feat(proto): add backend message reader

proto/src/reader/backend.rs

@@ -0,0 +1,58 @@
+use crate::message::backend::BackendMessage;
+use crate::reader::oneway::OneWayProtoReader;
+use async_trait::async_trait;
+
+#[async_trait]
+pub trait BackendProtoReader: OneWayProtoReader<BackendMessage> {}
+
+#[async_trait]
+impl<R> BackendProtoReader for R where R: OneWayProtoReader<BackendMessage> {}
+
+#[cfg(test)]
+mod tests {
+    use crate::message::backend::{
+        AuthenticationOkData, BackendKeyDataData, BackendMessage, CommandCompleteData,
+    };
+    use crate::reader::oneway::OneWayProtoReader;
+    use crate::reader::protoreader::ProtoReader;
+    use std::io::Cursor;
+    use tokio::io::{AsyncBufReadExt, BufReader};
+
+    #[tokio::test]
+    async fn test_message_sequence() {
+        let data = [
+            b'R', 0, 0, 0, 8, 0, 0, 0, 123, b'K', 0, 0, 0, 12, 0, 0, 0, 111, 0, 0, 0, 222, b'C', 0,
+            0, 0, 8, b'A', b'B', b'C', 0,
+        ];
+
+        let reader = BufReader::new(Cursor::new(&data));
+        let mut reader = ProtoReader::new(reader, 1024);
+
+        let msg = reader.read_proto().await;
+        assert!(matches!(
+            msg,
+            Ok(BackendMessage::AuthenticationOk(AuthenticationOkData {
+                status: 123
+            }))
+        ));
+
+        let msg = reader.read_proto().await;
+        assert!(matches!(
+            msg,
+            Ok(BackendMessage::BackendKeyData(BackendKeyDataData {
+                process: 111,
+                secret: 222
+            }))
+        ));
+
+        let msg = reader.read_proto().await;
+        assert!(match msg {
+            Ok(BackendMessage::CommandComplete(CommandCompleteData { tag })) =>
+                tag.as_str() == "ABC",
+            _ => false,
+        });
+
+        let rest = reader.inner.fill_buf().await.unwrap();
+        assert!(rest.is_empty());
+    }
+}

proto/src/reader/mod.rs

@@ -1,3 +1,4 @@
+pub mod backend;
 pub mod frontend;
 pub mod oneway;
 pub mod protoreader;