refactor: migrate net operation to KCP

kcp/src/error.rs

@@ -0,0 +1,56 @@
+use std::{
+    error::Error as StdError,
+    io::{self, ErrorKind},
+};
+
+/// KCP protocol errors
+#[derive(Debug, thiserror::Error)]
+pub enum Error {
+    #[error("conv inconsistent, expected {0}, found {1}")]
+    ConvInconsistent(u32, u32),
+    #[error("invalid mtu {0}")]
+    InvalidMtu(usize),
+    #[error("invalid segment size {0}")]
+    InvalidSegmentSize(usize),
+    #[error("invalid segment data size, expected {0}, found {1}")]
+    InvalidSegmentDataSize(usize, usize),
+    #[error("{0}")]
+    IoError(
+        #[from]
+        #[source]
+        io::Error,
+    ),
+    #[error("need to call update() once")]
+    NeedUpdate,
+    #[error("recv queue is empty")]
+    RecvQueueEmpty,
+    #[error("expecting fragment")]
+    ExpectingFragment,
+    #[error("command {0} is not supported")]
+    UnsupportedCmd(u8),
+    #[error("user's send buffer is too big")]
+    UserBufTooBig,
+    #[error("user's recv buffer is too small")]
+    UserBufTooSmall,
+    #[error("token mismatch, expected {0}, found {1}")]
+    TokenMismatch(u32, u32),
+}
+
+fn make_io_error<T>(kind: ErrorKind, msg: T) -> io::Error
+where
+    T: Into<Box<dyn StdError + Send + Sync>>,
+{
+    io::Error::new(kind, msg)
+}
+
+impl From<Error> for io::Error {
+    fn from(err: Error) -> Self {
+        let kind = match err {
+            Error::IoError(err) => return err,
+            Error::RecvQueueEmpty | Error::ExpectingFragment => ErrorKind::WouldBlock,
+            _ => ErrorKind::Other,
+        };
+
+        make_io_error(kind, err)
+    }
+}