feat: allow to bind to multiple host IP addresses specified as CIDR prefix in x-ports (#358)

Signed-off-by: Miek Gieben <miek@miek.nl>
Co-authored-by: Pasha Sviderski <me@psviderski.name>

internal/machine/docker/interface.go

@@ -0,0 +1,34 @@
+package docker
+
+import (
+	"fmt"
+	"net"
+	"net/netip"
+)
+
+// addrOfPrefix checks the interfaces and returns the address of each interface that was contained in the prefix.
+func addrOfPrefix(prefix netip.Prefix) ([]string, error) {
+	ifis, err := net.Interfaces()
+	if err != nil {
+		return nil, err
+	}
+	var addrs []string
+	for _, ifi := range ifis {
+		ifaddrs, _ := ifi.Addrs()
+		for _, addr := range ifaddrs {
+			ipnet, ok := addr.(*net.IPNet)
+			if !ok {
+				continue
+			}
+			nip, _ := netip.ParseAddr(ipnet.IP.String()) // round about way is needed to get ipv6 addrs, not mapped v4 in v6.
+			if prefix.Contains(nip) {
+				addrs = append(addrs, nip.String())
+			}
+		}
+	}
+	if len(addrs) == 0 {
+		return nil, fmt.Errorf("no host addresses are contained in prefix '%s'", prefix)
+	}
+
+	return addrs, nil
+}

internal/machine/docker/server.go

@@ -620,7 +620,24 @@ func (s *Server) CreateServiceContainer(
 		if p.HostIP.IsValid() {
 			portBindings[port][0].HostIP = p.HostIP.String()
 		}
+
+		if p.HostPrefix.IsValid() {
+			addrs, err := addrOfPrefix(p.HostPrefix)
+			if err != nil {
+				return nil, err
+			}
+			// p.HostIP was not valid, so the first IP can be set in the above added PortBindings, the rest is
+			// just appended.
+			portBindings[port][0].HostIP = addrs[0]
+			for _, addr := range addrs[1:] {
+				portBindings[port] = append(portBindings[port], nat.PortBinding{
+					HostPort: strconv.Itoa(int(p.PublishedPort)),
+					HostIP:   addr,
+				})
+			}
+		}
 	}
+
 	hostConfig := &container.HostConfig{
 		CapAdd:       spec.Container.CapAdd,
 		CapDrop:      spec.Container.CapDrop,