lib/connections: Announce LAN addresses by default (fixes #6928) (#6896)

lib/connections/util.go

@@ -11,6 +11,8 @@ import (
 	"net/url"
 	"strconv"
 	"strings"
+
+	"github.com/syncthing/syncthing/lib/osutil"
 )
 
 func fixupPort(uri *url.URL, defaultPort int) *url.URL {
@@ -32,3 +34,86 @@ func fixupPort(uri *url.URL, defaultPort int) *url.URL {
 
 	return &copyURI
 }
+
+func getURLsForAllAdaptersIfUnspecified(network string, uri *url.URL) []*url.URL {
+	ip, port, err := resolve(network, uri.Host)
+	// Failed to resolve
+	if err != nil || port == 0 {
+		return nil
+	}
+
+	// Not an unspecified address, so no point of substituting with local
+	// interface addresses as it's listening on a specific adapter anyway.
+	if len(ip) != 0 && !ip.IsUnspecified() {
+		return nil
+	}
+
+	hostPorts := getHostPortsForAllAdapters(port)
+	addrs := make([]*url.URL, 0, len(hostPorts))
+	for _, hostPort := range hostPorts {
+		newUri := *uri
+		newUri.Host = hostPort
+		addrs = append(addrs, &newUri)
+	}
+
+	return addrs
+}
+
+func getHostPortsForAllAdapters(port int) []string {
+	nets, err := osutil.GetLans()
+	if err != nil {
+		// Ignore failure.
+		return nil
+	}
+
+	hostPorts := make([]string, 0, len(nets))
+
+	portStr := strconv.Itoa(port)
+
+	for _, network := range nets {
+		// Only IPv4 addresses, as v6 link local require an interface identifiers to work correctly
+		// And non link local in theory are globally routable anyway.
+		if network.IP.To4() == nil {
+			continue
+		}
+		if network.IP.IsLinkLocalUnicast() || (isV4Local(network.IP) && network.IP.IsGlobalUnicast()) {
+			hostPorts = append(hostPorts, net.JoinHostPort(network.IP.String(), portStr))
+		}
+	}
+	return hostPorts
+}
+
+func resolve(network, hostPort string) (net.IP, int, error) {
+	switch network {
+	case "tcp", "tcp4", "tcp6":
+		if addr, err := net.ResolveTCPAddr(network, hostPort); err != nil {
+			return net.IPv4zero, 0, err
+		} else {
+			return addr.IP, addr.Port, nil
+		}
+	case "udp", "udp4", "udp6":
+		if addr, err := net.ResolveUDPAddr(network, hostPort); err != nil {
+			return net.IPv4zero, 0, err
+		} else {
+			return addr.IP, addr.Port, nil
+		}
+	case "ip", "ip4", "ip6":
+		if addr, err := net.ResolveIPAddr(network, hostPort); err != nil {
+			return net.IPv4zero, 0, err
+		} else {
+			return addr.IP, 0, nil
+		}
+	}
+	return net.IPv4zero, 0, net.UnknownNetworkError(network)
+}
+
+func isV4Local(ip net.IP) bool {
+	// See https://go-review.googlesource.com/c/go/+/162998/
+	// We only take the V4 part of that.
+	if ip4 := ip.To4(); ip4 != nil {
+		return ip4[0] == 10 ||
+			(ip4[0] == 172 && ip4[1]&0xf0 == 16) ||
+			(ip4[0] == 192 && ip4[1] == 168)
+	}
+	return false
+}