Add nerdctl build --add-host option support

This change refactors the parse extra hosts logic from container run
command and adds support for image build add-host flag.

Signed-off-by: Austin Vazquez <macedonv@amazon.com>

cmd/nerdctl/builder/builder_build.go

@@ -45,6 +45,7 @@ If Dockerfile is not present and -f is not specified, it will look for Container
 		SilenceErrors: true,
 	}
 	helpers.AddStringFlag(buildCommand, "buildkit-host", nil, "", "BUILDKIT_HOST", "BuildKit address")
+	buildCommand.Flags().StringArray("add-host", nil, "Add a custom host-to-IP mapping (format: \"host:ip\")")
 	buildCommand.Flags().StringArrayP("tag", "t", nil, "Name and optionally a tag in the 'name:tag' format")
 	buildCommand.Flags().StringP("file", "f", "", "Name of the Dockerfile")
 	buildCommand.Flags().String("target", "", "Set the target build stage to build")
@@ -92,6 +93,10 @@ func processBuildCommandFlag(cmd *cobra.Command, args []string) (types.BuilderBu
 	if err != nil {
 		return types.BuilderBuildOptions{}, err
 	}
+	extraHosts, err := cmd.Flags().GetStringArray("add-host")
+	if err != nil {
+		return types.BuilderBuildOptions{}, err
+	}
 	platform, err := cmd.Flags().GetStringSlice("platform")
 	if err != nil {
 		return types.BuilderBuildOptions{}, err
@@ -232,6 +237,7 @@ func processBuildCommandFlag(cmd *cobra.Command, args []string) (types.BuilderBu
 		Stdin:                cmd.InOrStdin(),
 		NetworkMode:          network,
 		ExtendedBuildContext: extendedBuildCtx,
+		ExtraHosts:           extraHosts,
 	}, nil
 }
 

cmd/nerdctl/builder/builder_build_test.go

@@ -957,3 +957,32 @@ func TestBuildAttestation(t *testing.T) {
 
 	testCase.Run(t)
 }
+
+func TestBuildAddHost(t *testing.T) {
+	nerdtest.Setup()
+
+	testCase := &test.Case{
+		Require: test.Require(
+			nerdtest.Build,
+		),
+		Cleanup: func(data test.Data, helpers test.Helpers) {
+			helpers.Anyhow("rmi", "-f", data.Identifier())
+		},
+		Setup: func(data test.Data, helpers test.Helpers) {
+			dockerfile := fmt.Sprintf(`FROM %s
+RUN ping -c 5 alpha
+RUN ping -c 5 beta
+`, testutil.CommonImage)
+			buildCtx := data.TempDir()
+			err := os.WriteFile(filepath.Join(buildCtx, "Dockerfile"), []byte(dockerfile), 0o600)
+			assert.NilError(helpers.T(), err)
+			data.Set("buildCtx", buildCtx)
+		},
+		Command: func(data test.Data, helpers test.Helpers) test.TestableCommand {
+			return helpers.Command("build", data.Get("buildCtx"), "-t", data.Identifier(), "--add-host", "alpha:127.0.0.1", "--add-host", "beta:127.0.0.1")
+		},
+		Expected: test.Expects(0, nil, nil),
+	}
+
+	testCase.Run(t)
+}

docs/command-reference.md

@@ -714,8 +714,9 @@ Flags:
 - :whale: `--label`: Set metadata for an image
 - :whale: `--network=(default|host|none)`: Set the networking mode for the RUN instructions during build.(compatible with `buildctl build`)
 - :whale: `--build-context`: Set additional contexts for build (e.g. dir2=/path/to/dir2, myorg/myapp=docker-image://path/to/myorg/myapp)
+- :whale: `--add-host`: Add a custom host-to-IP mapping (format: `host:ip`)
 
-Unimplemented `docker build` flags: `--add-host`, `--squash`
+Unimplemented `docker build` flags: `--squash`
 
 ### :whale: nerdctl commit
 

pkg/api/types/builder_types.go

@@ -71,6 +71,8 @@ type BuilderBuildOptions struct {
 	NetworkMode string
 	// Pull determines if we should try to pull latest image from remote. Default is buildkit's default.
 	Pull *bool
+	// ExtraHosts is a set of custom host-to-IP mappings.
+	ExtraHosts []string
 }
 
 // BuilderPruneOptions specifies options for `nerdctl builder prune`.

pkg/cmd/builder/build.go

@@ -40,6 +40,7 @@ import (
 	"github.com/containerd/nerdctl/v2/pkg/api/types"
 	"github.com/containerd/nerdctl/v2/pkg/buildkitutil"
 	"github.com/containerd/nerdctl/v2/pkg/clientutil"
+	"github.com/containerd/nerdctl/v2/pkg/containerutil"
 	"github.com/containerd/nerdctl/v2/pkg/platformutil"
 	"github.com/containerd/nerdctl/v2/pkg/referenceutil"
 	"github.com/containerd/nerdctl/v2/pkg/strutil"
@@ -453,6 +454,14 @@ func generateBuildctlArgs(ctx context.Context, client *containerd.Client, option
 		}
 	}
 
+	if len(options.ExtraHosts) > 0 {
+		extraHosts, err := containerutil.ParseExtraHosts(options.ExtraHosts, options.GOptions.HostGatewayIP, "=")
+		if err != nil {
+			return "", nil, false, "", nil, nil, err
+		}
+		buildctlArgs = append(buildctlArgs, "--opt=add-hosts="+strings.Join(extraHosts, ","))
+	}
+
 	return buildctlBinary, buildctlArgs, needsLoading, metaFile, tags, cleanup, nil
 }
 

pkg/cmd/container/create.go

@@ -30,7 +30,6 @@ import (
 	"strings"
 
 	dockercliopts "github.com/docker/cli/opts"
-	dockeropts "github.com/docker/docker/opts"
 	"github.com/opencontainers/runtime-spec/specs-go"
 
 	containerd "github.com/containerd/containerd/v2/client"
@@ -323,22 +322,12 @@ func Create(ctx context.Context, client *containerd.Client, args []string, netMa
 	}
 	internalLabels.name = options.Name
 	internalLabels.pidFile = options.PidFile
-	internalLabels.extraHosts = strutil.DedupeStrSlice(netManager.NetworkOptions().AddHost)
-	for i, host := range internalLabels.extraHosts {
-		if _, err := dockercliopts.ValidateExtraHost(host); err != nil {
-			return nil, generateRemoveOrphanedDirsFunc(ctx, id, dataStore, internalLabels), err
-		}
-		parts := strings.SplitN(host, ":", 2)
-		// If the IP Address is a string called "host-gateway", replace this value with the IP address stored
-		// in the daemon level HostGateway IP config variable.
-		if len(parts) == 2 && parts[1] == dockeropts.HostGatewayName {
-			if options.GOptions.HostGatewayIP == "" {
-				return nil, generateRemoveOrphanedDirsFunc(ctx, id, dataStore, internalLabels), fmt.Errorf("unable to derive the IP value for host-gateway")
-			}
-			parts[1] = options.GOptions.HostGatewayIP
-			internalLabels.extraHosts[i] = fmt.Sprintf(`%s:%s`, parts[0], parts[1])
-		}
+
+	extraHosts, err := containerutil.ParseExtraHosts(netManager.NetworkOptions().AddHost, options.GOptions.HostGatewayIP, ":")
+	if err != nil {
+		return nil, generateRemoveOrphanedDirsFunc(ctx, id, dataStore, internalLabels), err
 	}
+	internalLabels.extraHosts = extraHosts
 
 	internalLabels.rm = containerutil.EncodeContainerRmOptLabel(options.Rm)
 

pkg/containerutil/containerutil.go

@@ -28,6 +28,8 @@ import (
 	"strings"
 	"time"
 
+	dockercliopts "github.com/docker/cli/opts"
+	dockeropts "github.com/docker/docker/opts"
 	"github.com/moby/sys/signal"
 	"github.com/opencontainers/runtime-spec/specs-go"
 
@@ -49,6 +51,7 @@ import (
 	"github.com/containerd/nerdctl/v2/pkg/portutil"
 	"github.com/containerd/nerdctl/v2/pkg/rootlessutil"
 	"github.com/containerd/nerdctl/v2/pkg/signalutil"
+	"github.com/containerd/nerdctl/v2/pkg/strutil"
 	"github.com/containerd/nerdctl/v2/pkg/taskutil"
 )
 
@@ -606,3 +609,34 @@ func EncodeContainerRmOptLabel(rmOpt bool) string {
 func DecodeContainerRmOptLabel(rmOptLabel string) (bool, error) {
 	return strconv.ParseBool(rmOptLabel)
 }
+
+// ParseExtraHosts takes an array of host-to-IP mapping strings, e.g. "localhost:127.0.0.1",
+// and a hostGatewayIP for resolving mappings to "host-gateway".
+//
+// Returns a map of host-to-IPs or errors if any mapping strings are not correctly formatted.
+func ParseExtraHosts(extraHosts []string, hostGatewayIP, separator string) ([]string, error) {
+	hosts := make([]string, 0, len(extraHosts))
+	for _, hostToIP := range strutil.DedupeStrSlice(extraHosts) {
+		if _, err := dockercliopts.ValidateExtraHost(hostToIP); err != nil {
+			return nil, err
+		}
+
+		parts := strings.SplitN(hostToIP, ":", 2)
+		if len(parts) != 2 {
+			return nil, fmt.Errorf("invalid host-to-IP map %s", hostToIP)
+		}
+
+		host, ip := parts[0], parts[1]
+
+		// If the IP address is a string called "host-gateway", replace this value with the IP address stored
+		// in the daemon level HostGatewayIP config variable.
+		if ip == dockeropts.HostGatewayName && hostGatewayIP == "" {
+			return nil, errors.New("unable to derive the IP value for host-gateway")
+		} else if ip == dockeropts.HostGatewayName {
+			ip = hostGatewayIP
+		}
+
+		hosts = append(hosts, host+separator+ip)
+	}
+	return hosts, nil
+}

pkg/containerutil/containerutil_test.go

@@ -0,0 +1,83 @@
+/*
+   Copyright The containerd Authors.
+
+   Licensed under the Apache License, Version 2.0 (the "License");
+   you may not use this file except in compliance with the License.
+   You may obtain a copy of the License at
+
+       http://www.apache.org/licenses/LICENSE-2.0
+
+   Unless required by applicable law or agreed to in writing, software
+   distributed under the License is distributed on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+   See the License for the specific language governing permissions and
+   limitations under the License.
+*/
+
+package containerutil
+
+import (
+	"reflect"
+	"testing"
+)
+
+func TestParseExtraHosts(t *testing.T) {
+	tests := []struct {
+		name           string
+		extraHosts     []string
+		hostGateway    string
+		separator      string
+		expected       []string
+		expectedErrStr string
+	}{
+		{
+			name:     "NoExtraHosts",
+			expected: []string{},
+		},
+		{
+			name:       "ExtraHosts",
+			extraHosts: []string{"localhost:127.0.0.1", "localhost:[::1]"},
+			separator:  ":",
+			expected:   []string{"localhost:127.0.0.1", "localhost:[::1]"},
+		},
+		{
+			name:       "EqualsSeperator",
+			extraHosts: []string{"localhost:127.0.0.1", "localhost:[::1]"},
+			separator:  "=",
+			expected:   []string{"localhost=127.0.0.1", "localhost=[::1]"},
+		},
+		{
+			name:           "InvalidExtraHostFormat",
+			extraHosts:     []string{"localhost"},
+			expectedErrStr: "bad format for add-host: \"localhost\"",
+		},
+		{
+			name:           "ErrorOnHostGatewayExtraHostWithNoHostGatewayIPSet",
+			extraHosts:     []string{"localhost:host-gateway"},
+			separator:      ":",
+			expectedErrStr: "unable to derive the IP value for host-gateway",
+		},
+		{
+			name:        "HostGatewayIP",
+			extraHosts:  []string{"localhost:host-gateway"},
+			hostGateway: "10.10.0.1",
+			separator:   ":",
+			expected:    []string{"localhost:10.10.0.1"},
+		},
+	}
+
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			extraHosts, err := ParseExtraHosts(test.extraHosts, test.hostGateway, test.separator)
+			if err != nil && err.Error() != test.expectedErrStr {
+				t.Fatalf("expected '%s', actual '%v'", test.expectedErrStr, err)
+			} else if err == nil && test.expectedErrStr != "" {
+				t.Fatalf("expected error '%s' but got none", test.expectedErrStr)
+			}
+
+			if !reflect.DeepEqual(test.expected, extraHosts) {
+				t.Fatalf("expected %v, actual %v", test.expected, extraHosts)
+			}
+		})
+	}
+}