v0 Impl

1 files changed, 132 insertions, 0 deletions

diff --git a/src/lib.go b/src/lib.go
new file mode 100644
index 0000000..04ac41e
--- /dev/null
+++ b/src/lib.go
@@ -0,0 +1,132 @@
+package binder
+
+import (
+	"fmt"
+	"io"
+	"net"
+	"os"
+	"os/user"
+	"strconv"
+	"syscall"
+
+	g "euandre.org/gobang/src"
+)
+
+
+
+type CLIArgs struct {
+	FromAddr string
+	ToAddr   string
+}
+
+
+
+const USER = "nobody"
+
+
+
+var EmitActiveConnection = g.MakeGauge("active-connections")
+
+
+
+func dropPrivileges(username string) {
+	g.Info("Dropping privileges", "drop-root-init")
+
+	user, err := user.Lookup(username)
+	g.FatalIf(err)
+
+	gid, err := strconv.Atoi(user.Gid)
+	g.FatalIf(err)
+
+	uid, err := strconv.Atoi(user.Uid)
+	g.FatalIf(err)
+
+	err = syscall.Setgid(gid)
+	g.FatalIf(err)
+
+	err = syscall.Setgroups([]int{})
+	g.FatalIf(err)
+
+	err = syscall.Setuid(uid)
+	g.FatalIf(err)
+
+	g.Info("Privileges dropped", "drop-root-end")
+}
+
+func isRunningAsRoot() bool {
+	return os.Geteuid() == 0
+}
+
+func copyData(closer chan struct{}, from io.Reader, to io.Writer) {
+	io.Copy(to, from)
+	closer <- struct{}{}
+}
+
+func ParseArgs(args []string) CLIArgs {
+	if len(args) != 3 {
+		fmt.Fprintf(
+			os.Stderr,
+			"Usage: %s FROM-ADDRESS TO-ADDRESS\n",
+			args[0],
+		)
+		os.Exit(2)
+	}
+	return CLIArgs {
+		FromAddr: args[1],
+		ToAddr:   args[2],
+	}
+}
+
+func DropRoot() {
+	if isRunningAsRoot() {
+		dropPrivileges(USER)
+		if isRunningAsRoot() {
+			panic("Failed to drop privileges")
+		}
+	}
+}
+
+func Start(toAddr string, listener net.Listener) {
+	for {
+		connFrom, err := listener.Accept()
+		if err != nil {
+			g.Warning(
+				"Error accepting connection",
+				"accept-connection",
+				"err", err,
+			)
+			continue
+		}
+		defer connFrom.Close()
+		EmitActiveConnection.Inc()
+
+		connTo, err := net.Dial("unix", toAddr)
+		if err != nil {
+			g.Error(
+				"Error dialing connection",
+				"dial-connection",
+				"err", err,
+			)
+			return
+		}
+		defer connTo.Close()
+
+		closer := make(chan struct{}, 2)
+		go copyData(closer, connFrom, connTo)
+		go copyData(closer, connTo, connFrom)
+		go func() {
+			<-closer
+			EmitActiveConnection.Dec()
+		}()
+	}
+}
+
+
+func Main() {
+	args := ParseArgs(os.Args)
+	listener, err := net.Listen("tcp", args.FromAddr)
+	g.FatalIf(err)
+
+	DropRoot()
+	Start(args.ToAddr, listener)
+}