move implementation to internal/ directory (#828)

internal/util/tcpsock/tcpsock.go

@@ -0,0 +1,27 @@
+package tcpsock
+
+import (
+	"context"
+	"net"
+	"syscall"
+)
+
+func Listen(address string, tryFreeBind bool) (*net.TCPListener, error) {
+	control := func(network, address string, c syscall.RawConn) error {
+		if tryFreeBind {
+			if err := freeBind(network, address, c); err != nil {
+				return err
+			}
+		}
+		return nil
+	}
+	var listenConfig = net.ListenConfig{
+		Control: control,
+	}
+
+	l, err := listenConfig.Listen(context.Background(), "tcp", address)
+	if err != nil {
+		return nil, err
+	}
+	return l.(*net.TCPListener), nil
+}

internal/util/tcpsock/tcpsock_freebind_freebsd.go

@@ -0,0 +1,26 @@
+//go:build freebsd
+// +build freebsd
+
+package tcpsock
+
+import (
+	"fmt"
+	"syscall"
+)
+
+func freeBind(network, address string, c syscall.RawConn) error {
+	var err, sockerr error
+	err = c.Control(func(fd uintptr) {
+		if network == "tcp6" {
+			sockerr = syscall.SetsockoptInt(int(fd), syscall.IPPROTO_IPV6, syscall.IPV6_BINDANY, 1)
+		} else if network == "tcp4" {
+			sockerr = syscall.SetsockoptInt(int(fd), syscall.IPPROTO_IP, syscall.IP_BINDANY, 1)
+		} else {
+			sockerr = fmt.Errorf("expecting 'tcp6' or 'tcp4', got %q", network)
+		}
+	})
+	if err != nil {
+		return err
+	}
+	return sockerr
+}

internal/util/tcpsock/tcpsock_freebind_linux.go

@@ -0,0 +1,20 @@
+//go:build linux
+// +build linux
+
+package tcpsock
+
+import (
+	"syscall"
+)
+
+func freeBind(network, address string, c syscall.RawConn) error {
+	var err, sockerr error
+	err = c.Control(func(fd uintptr) {
+		// apparently, this works for both IPv4 and IPv6
+		sockerr = syscall.SetsockoptInt(int(fd), syscall.SOL_IP, syscall.IP_FREEBIND, 1)
+	})
+	if err != nil {
+		return err
+	}
+	return sockerr
+}

internal/util/tcpsock/tcpsock_freebind_unsupported.go

@@ -0,0 +1,13 @@
+//go:build !linux && !freebsd
+// +build !linux,!freebsd
+
+package tcpsock
+
+import (
+	"fmt"
+	"syscall"
+)
+
+func freeBind(network, address string, c syscall.RawConn) error {
+	return fmt.Errorf("IP_FREEBIND equivalent functionality not supported  on this platform")
+}