Feature/kcp transport#126
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- Add Transport::Kcp variant to the Transport enum
- Add KcpSettings config struct (mode, send_window, recv_window, mtu)
- Add KcpMode enum (normal, fast, turbo, gaming, file_transfer)
- Add kcp_settings field to ServerConfig and ClientConfig
- Implement kcp_server.rs: KcpStreamWrapper + start_kcp_servers()
- Implement kcp_stream.rs: AsyncStream wrapper for kcp_tokio::KcpStream
- Update tcp_server.rs: dispatch Transport::Kcp to start_kcp_servers
- Update socket_connector_impl.rs: KCP client connection support
- Add validation in validate.rs for kcp_settings/transport consistency
Example YAML configuration:
- address: 0.0.0.0:12345
transport: kcp
kcp_settings:
mode: fast
protocol:
type: socks
Add KCP (KCP reliable UDP protocol) as a new transport layer, enabling
use of KCP-based proxying alongside the existing TCP and QUIC transports.
## Overview
KCP is a reliable ARQ (Automatic Repeat reQuest) protocol that runs over
UDP. It provides lower latency than TCP at the cost of higher bandwidth
usage, making it suitable for latency-sensitive proxy scenarios.
## Implementation
### New files
- src/kcp_server.rs -- KCP listener, per-connection tokio::spawn, maps
KcpSettings/KcpMode config into KcpConfig presets
- src/kcp_stream.rs -- KcpStreamWrapper: wraps kcp_tokio::KcpStream to
implement AsyncStream (AsyncRead + AsyncWrite + AsyncPing)
### KcpStreamWrapper::poll_shutdown behaviour
KCP has no half-close concept. Calling KcpStream::close() sets closed=true
which causes poll_read to immediately return 0 bytes (EOF). This breaks
Vision VLESS where copy_bidirectional calls shutdown on the write side
while the read side is still waiting for the VLESS response.
Fix: poll_shutdown only flushes pending writes. The KCP connection is
fully closed when KcpStreamWrapper is dropped, which happens naturally
once both directions are done. TCP and QUIC transports are unaffected.
### stream_mode
kcp-tokio default (stream_mode=false / message mode) is preserved for
Normal, Fast, Turbo, and Gaming presets. Only FileTransfer explicitly
enables stream_mode=true (already done by KcpConfig::file_transfer()).
Message mode avoids unnecessary window-probe (WASK) packets that appear
as a flood of 24-byte UDP datagrams in tcpdump when stream_mode=true.
### Config extensions
- Transport enum: new Kcp variant
- ServerConfig, ClientConfig: new kcp_settings: Option<KcpSettings> field
- KcpSettings: mode, send_window, recv_window, mtu
- KcpMode: Normal | Fast | Turbo | Gaming | FileTransfer
- All existing test initialisers updated with kcp_settings: None
### main.rs
- tracing_subscriber wired up so kcp-tokio/kcp-core tracing events
are visible via RUST_LOG=kcp_tokio=debug,kcp_core=debug
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This pull request reffers to #125
Code was added with support of copilot vscode feature (Claude Sonnet 4.6).