libnetwork/pasta: add new Setup2 to return result

Currently both callers in podman and buildah join and inspect the netns
to get the local ip configured by pasta in order to add it to
/etc/hosts. So instead of doing this in two places let's just do it here
once and return the result to the caller.

In order to not cause vendoring issues I decided against breaking the
API and added a new Setup2 function instead. I will then update
podman and buildah to make use of it.

Also I plan on adding more fields in the result, i.e. dns address.

Because this now depends on linux only functionality make sure to only
build it on linux, pasta only works on linux anyway so this is not a
problem.

Signed-off-by: Paul Holzinger <pholzing@redhat.com>

common/libnetwork/pasta/pasta_linux.go

@@ -13,18 +13,16 @@ package pasta
 import (
 	"errors"
 	"fmt"
+	"net"
 	"os/exec"
 	"strings"
 
+	"github.com/containernetworking/plugins/pkg/ns"
 	"github.com/containers/common/libnetwork/types"
 	"github.com/containers/common/pkg/config"
 	"github.com/sirupsen/logrus"
 )
 
-const (
-	BinaryName = "pasta"
-)
-
 type SetupOptions struct {
 	// Config used to get pasta options and binary path via HelperBinariesDir
 	Config *config.Config
@@ -37,11 +35,16 @@ type SetupOptions struct {
 	ExtraOptions []string
 }
 
-// Setup start the pasta process for the given netns.
-// The pasta binary is looked up in the HelperBinariesDir and $PATH.
-// Note that there is no need any special cleanup logic, the pasta process will
-// automatically exit when the netns path is deleted.
 func Setup(opts *SetupOptions) error {
+	_, err := Setup2(opts)
+	return err
+}
+
+// Setup2 start the pasta process for the given netns.
+// The pasta binary is looked up in the HelperBinariesDir and $PATH.
+// Note that there is no need for any special cleanup logic, the pasta
+// process will automatically exit when the netns path is deleted.
+func Setup2(opts *SetupOptions) (*SetupResult, error) {
 	NoTCPInitPorts := true
 	NoUDPInitPorts := true
 	NoTCPNamespacePorts := true
@@ -51,7 +54,7 @@ func Setup(opts *SetupOptions) error {
 
 	path, err := opts.Config.FindHelperBinary(BinaryName, true)
 	if err != nil {
-		return fmt.Errorf("could not find pasta, the network namespace can't be configured: %w", err)
+		return nil, fmt.Errorf("could not find pasta, the network namespace can't be configured: %w", err)
 	}
 
 	cmdArgs := []string{}
@@ -72,7 +75,7 @@ func Setup(opts *SetupOptions) error {
 			case "udp":
 				cmdArgs = append(cmdArgs, "-u")
 			default:
-				return fmt.Errorf("can't forward protocol: %s", protocol)
+				return nil, fmt.Errorf("can't forward protocol: %s", protocol)
 			}
 
 			arg := fmt.Sprintf("%s%d-%d:%d-%d", addr,
@@ -140,10 +143,10 @@ func Setup(opts *SetupOptions) error {
 	if err != nil {
 		exitErr := &exec.ExitError{}
 		if errors.As(err, &exitErr) {
-			return fmt.Errorf("pasta failed with exit code %d:\n%s",
+			return nil, fmt.Errorf("pasta failed with exit code %d:\n%s",
 				exitErr.ExitCode(), string(out))
 		}
-		return fmt.Errorf("failed to start pasta: %w", err)
+		return nil, fmt.Errorf("failed to start pasta: %w", err)
 	}
 
 	if len(out) > 0 {
@@ -154,5 +157,22 @@ func Setup(opts *SetupOptions) error {
 		logrus.Infof("pasta logged warnings: %q", string(out))
 	}
 
-	return nil
+	result := &SetupResult{}
+	err = ns.WithNetNSPath(opts.Netns, func(_ ns.NetNS) error {
+		addrs, err := net.InterfaceAddrs()
+		if err != nil {
+			return err
+		}
+		for _, addr := range addrs {
+			// make sure to skip localhost and other special addresses
+			if ipnet, ok := addr.(*net.IPNet); ok && ipnet.IP.IsGlobalUnicast() {
+				result.IPAddresses = append(result.IPAddresses, ipnet.IP)
+			}
+		}
+		return nil
+	})
+	if err != nil {
+		return nil, err
+	}
+	return result, nil
 }

common/libnetwork/pasta/types.go

@@ -0,0 +1,10 @@
+package pasta
+
+import "net"
+
+const BinaryName = "pasta"
+
+type SetupResult struct {
+	// IpAddresses configured by pasta
+	IPAddresses []net.IP
+}