Add nerdctl build --add-host option support

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

@@ -453,6 +453,14 @@ func generateBuildctlArgs(ctx context.Context, client *containerd.Client, option
 		}
 	}
 
+	if len(options.ExtraHosts) > 0 {
+		hosts, err := parseExtraHosts(options.ExtraHosts)
+		if err != nil {
+			return "", nil, false, "", nil, nil, err
+		}
+		buildctlArgs = append(buildctlArgs, "--opt=add-hosts="+strings.Join(hosts, ","))
+	}
+
 	return buildctlBinary, buildctlArgs, needsLoading, metaFile, tags, cleanup, nil
 }
 
@@ -605,3 +613,18 @@ func readOCIIndexFromPath(path string) (*ocispec.Index, error) {
 	}
 	return ociIndex, nil
 }
+
+func parseExtraHosts(extraHosts []string) ([]string, error) {
+	hosts := make([]string, 0, len(extraHosts))
+	for _, hostIPMapping := range extraHosts {
+		host, ip, ok := strings.Cut(hostIPMapping, ":")
+		if !ok {
+			host, ip, ok = strings.Cut(hostIPMapping, "=")
+		}
+		if !ok || host == "" || ip == "" {
+			return nil, fmt.Errorf("invalid host %s", hostIPMapping)
+		}
+		hosts = append(hosts, host+"="+ip)
+	}
+	return hosts, nil
+}