chore(restrictednet): internal/restrictednet package (#3361)

internal/restrictednet/https.go

@@ -0,0 +1,202 @@
+package restrictednet
+
+import (
+	"context"
+	"crypto/tls"
+	"errors"
+	"fmt"
+	"net"
+	"net/http"
+	"net/netip"
+	"os"
+	"time"
+
+	"github.com/jsimonetti/rtnetlink"
+	"github.com/qdm12/gluetun/internal/pmtud/constants"
+)
+
+// OpenHTTPS opens temporary restrictive firewall output for one HTTPS destination.
+// The returned [*http.Client] must be used sequentially only, and each request must
+// have its response body fully read/discarded and then closed.
+// The returned cleanup function must be called to remove the temporary firewall rule and close connections.
+func (c *Client) OpenHTTPS(ctx context.Context, destinationTLSName string, destinationAddrPort netip.AddrPort,
+) (httpClient *http.Client, cleanup func() error, err error) {
+	fd, sourceAddrPort, err := bindSourceConnection(destinationAddrPort.Addr())
+	if err != nil {
+		return nil, nil, fmt.Errorf("binding source port: %w", err)
+	}
+
+	const remove = false
+	err = c.firewall.AcceptOutputFromIPPortToIPPort(ctx, "tcp", c.outboundInterface,
+		sourceAddrPort, destinationAddrPort, remove)
+	if err != nil {
+		closeFD(fd)
+		return nil, nil, fmt.Errorf("allowing output traffic through firewall: %w", err)
+	}
+
+	connection, err := connectSourceConnection(ctx, fd, destinationAddrPort)
+	if err != nil {
+		const remove = true
+		_ = c.firewall.AcceptOutputFromIPPortToIPPort(context.Background(), "tcp", c.outboundInterface,
+			sourceAddrPort, destinationAddrPort, remove)
+		return nil, nil, fmt.Errorf("connecting source socket: %w", err)
+	}
+
+	dial := makeDial(connection, destinationTLSName)
+	httpClient = newHTTPSClient(destinationTLSName, dial)
+	cleanup = func() error {
+		var errs []error
+		httpClient.CloseIdleConnections()
+		err := connection.Close()
+		if err != nil && !errors.Is(err, net.ErrClosed) {
+			errs = append(errs, fmt.Errorf("closing connection: %w", err))
+		}
+		const remove = true
+		err = c.firewall.AcceptOutputFromIPPortToIPPort(context.Background(), "tcp", c.outboundInterface,
+			sourceAddrPort, destinationAddrPort, remove)
+		if err != nil {
+			errs = append(errs, fmt.Errorf("removing output traffic rule: %w", err))
+		}
+		if len(errs) > 0 {
+			return errors.Join(errs...)
+		}
+		return nil
+	}
+	return httpClient, cleanup, nil
+}
+
+type dialFunc func(ctx context.Context, network, address string) (net.Conn, error)
+
+func newHTTPSClient(destinationTLSName string, dial dialFunc) *http.Client {
+	const timeout = 5 * time.Second
+	transport := &http.Transport{
+		MaxIdleConns:        1,
+		MaxIdleConnsPerHost: 1,
+		MaxConnsPerHost:     1,
+		TLSClientConfig: &tls.Config{
+			MinVersion: tls.VersionTLS12,
+			ServerName: destinationTLSName,
+		},
+		DialContext: dial,
+	}
+	return &http.Client{
+		Timeout:   timeout,
+		Transport: transport,
+	}
+}
+
+func makeDial(connection net.Conn, tlsName string) dialFunc {
+	_, destinationPort, err := net.SplitHostPort(connection.RemoteAddr().String())
+	if err != nil {
+		panic(err) // connection remote address should always be in the form "host:port"
+	}
+	expectedAddress := net.JoinHostPort(tlsName, destinationPort)
+	used := false
+	return func(_ context.Context, network, address string) (net.Conn, error) {
+		if used {
+			return nil, errors.New("dial function called more than once")
+		}
+		used = true
+		switch network {
+		case "tcp", "tcp4", "tcp6":
+		default:
+			return nil, fmt.Errorf("unexpected dial network %q", network)
+		}
+		if address != expectedAddress {
+			return nil, fmt.Errorf("unexpected dial address %q (expected %q)", address, expectedAddress)
+		}
+		return connection, nil
+	}
+}
+
+func bindSourceConnection(destinationIP netip.Addr) (fd int, sourceAddr netip.AddrPort, err error) {
+	sourceIP, err := sourceIPForDestination(destinationIP)
+	if err != nil {
+		return 0, netip.AddrPort{}, fmt.Errorf("finding source IP: %w", err)
+	}
+
+	family := constants.AF_INET
+	if sourceIP.Is6() {
+		family = constants.AF_INET6
+	}
+
+	fd, err = newTCPSockStream(family)
+	if err != nil {
+		return 0, netip.AddrPort{}, fmt.Errorf("creating socket: %w", err)
+	}
+
+	bindAddrPort := netip.AddrPortFrom(sourceIP, 0)
+	err = bindFD(fd, bindAddrPort)
+	if err != nil {
+		closeFD(fd)
+		return 0, netip.AddrPort{}, fmt.Errorf("binding socket: %w", err)
+	}
+
+	sourceAddr, err = fdToSourceAddr(fd)
+	if err != nil {
+		closeFD(fd)
+		return 0, netip.AddrPort{}, fmt.Errorf("getting source address: %w", err)
+	}
+
+	return fd, sourceAddr, nil
+}
+
+func connectSourceConnection(ctx context.Context, fd int, destinationAddrPort netip.AddrPort) (
+	connection net.Conn, err error,
+) {
+	err = connectFD(ctx, fd, destinationAddrPort)
+	if err != nil {
+		closeFD(fd)
+		return nil, fmt.Errorf("connecting socket: %w", err)
+	}
+
+	file := os.NewFile(uintptr(fd), "")
+	if file == nil {
+		closeFD(fd)
+		return nil, fmt.Errorf("creating socket file for destination %s", destinationAddrPort)
+	}
+	defer file.Close()
+
+	connection, err = net.FileConn(file)
+	if err != nil {
+		return nil, fmt.Errorf("wrapping socket connection: %w", err)
+	}
+
+	return connection, nil
+}
+
+func sourceIPForDestination(destinationIP netip.Addr) (srcIP netip.Addr, err error) {
+	conn, err := rtnetlink.Dial(nil)
+	if err != nil {
+		return netip.Addr{}, err
+	}
+	defer conn.Close()
+
+	family := uint8(constants.AF_INET)
+	if destinationIP.Is6() {
+		family = constants.AF_INET6
+	}
+
+	requestMessage := &rtnetlink.RouteMessage{
+		Family: family,
+		Attributes: rtnetlink.RouteAttributes{
+			Dst: destinationIP.AsSlice(),
+		},
+	}
+	messages, err := conn.Route.Get(requestMessage)
+	if err != nil {
+		return netip.Addr{}, fmt.Errorf("getting routes to %s: %w", destinationIP, err)
+	}
+
+	for _, message := range messages {
+		if message.Attributes.Src == nil {
+			continue
+		}
+		if message.Attributes.Src.To4() == nil {
+			return netip.AddrFrom16([16]byte(message.Attributes.Src)), nil
+		}
+		return netip.AddrFrom4([4]byte(message.Attributes.Src)), nil
+	}
+
+	return netip.Addr{}, fmt.Errorf("no route to %s", destinationIP)
+}