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package main
import (
"bytes"
"context"
"encoding/base64"
"encoding/binary"
"errors"
"fmt"
"io"
"log/slog"
"math/rand"
"net"
"os"
"os/signal"
"path"
"sync"
"time"
)
const defaultReadTimeout = 2 * time.Second
type BridgeInfo struct {
ID uint
OriginSocketPath string
DestinationAddress string
}
func main() {
slog.Info("starting cthcous...")
ports := []uint{1234, 4321}
socketDir := "./"
bridgeInfos := make([]BridgeInfo, len(ports))
for i, port := range ports {
socketPath := fmt.Sprintf("%s/%d.socket", socketDir, port)
socketPath = path.Clean(socketPath)
bridgeInfos[i] = BridgeInfo{
ID: uint(i),
OriginSocketPath: socketPath,
DestinationAddress: fmt.Sprintf(":%d", port),
}
}
wg := &sync.WaitGroup{}
ctx, _ := signal.NotifyContext(context.Background(), os.Interrupt, os.Kill)
slog.Info("will open socket bridges.", slog.Any("bridges", bridgeInfos))
for _, bridgeInfo := range bridgeInfos {
bridgeLogger := slog.Default().With(slog.Group(
"bridge",
slog.Any("id", bridgeInfo.ID),
slog.String("origin", bridgeInfo.OriginSocketPath),
slog.String("destination", bridgeInfo.DestinationAddress),
))
bridgeLogger.Info("opening bridge socket...")
wg.Add(1)
go openBridgeSocket(ctx, wg, bridgeLogger, bridgeInfo)
}
wg.Wait()
}
func openBridgeSocket(ctx context.Context, wg *sync.WaitGroup, logger *slog.Logger, info BridgeInfo) {
defer wg.Done()
source, err := net.Listen("unix", info.OriginSocketPath)
if err != nil {
logger.Error("could not listen on socket.", slog.Any("error", err))
return
}
source.(*net.UnixListener).SetUnlinkOnClose(true)
closeOnCtx(ctx, logger, source)
logger.Info("bridge socket opened. listening...")
for {
conn, err := source.Accept()
if err != nil {
if errors.Is(err, net.ErrClosed) {
logger.Info("bridge socket closed.")
break
}
logger.Error("could not accept connection.", slog.Any("error", err))
continue
}
conn.SetReadDeadline(time.Now().Add(defaultReadTimeout))
closeOnCtx(ctx, logger, conn)
// Connections to UNIX sockets don't have remote addresses.
// To make it easier to identify connections, we generate a random ID.
connID := makeID()
connLogger := logger.With(slog.Group("connection", slog.String("id", connID)))
connLogger.Info("accepted connection. beginning bridge.")
go bridgeDataFromOriginToDestination(ctx, logger, conn, info)
}
}
func bridgeDataFromOriginToDestination(ctx context.Context, logger *slog.Logger, source net.Conn, info BridgeInfo) {
data := bytes.NewBuffer([]byte{})
for {
buffer := make([]byte, 1024)
n, err := source.Read(buffer)
if err != nil {
if errors.Is(err, io.EOF) {
logger.Info("received EOF. closing connection...")
break
}
if errors.Is(err, os.ErrDeadlineExceeded) {
logger.Warn("read deadline exceeded. closing origin connection...")
break
}
logger.Error("could not read from connection due to unknown error. closing origin connection...", slog.Any("error", err))
break
}
_, err = data.Write(buffer[:n])
if err != nil {
logger.Error("could not write to buffer due to unknown error. closing origin connection...", slog.Any("error", err))
break
}
}
source.Close()
logger.Info("origin connection completed. attempting write to destination...")
destination, err := net.Dial("tcp", info.DestinationAddress)
if err != nil {
logger.Error("could not connect to destination socket. bridge aborted.", slog.Any("error", err))
return
}
defer destination.Close()
_, err = destination.Write(data.Bytes())
if err != nil {
logger.Error("could not write to destination socket. bridge aborted.", slog.Any("error", err))
return
}
logger.Info("write to destination socket successful.")
logger.Info("bridge completed.")
}
func closeOnCtx(ctx context.Context, logger *slog.Logger, closer io.Closer) {
go func() {
<-ctx.Done()
if err := closer.Close(); err != nil {
if errors.Is(err, net.ErrClosed) {
logger.Warn("socket or connection already closed. harmless race condition.")
return
}
logger.Error("could not close socket or connection after finished context.", slog.Any("error", err))
}
}()
}
func makeID() string {
r := rand.Uint64()
b := [8]byte{}
binary.LittleEndian.PutUint64(b[:], r)
return base64.StdEncoding.EncodeToString(b[:])
}
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