remote: fix implementation of build with --userns=auto for API

`podman-remote` and Libpod API does not supports build with
`--userns=auto` since `IDMappingOptions` were not implemented for API
and bindings, following PR implements passing `IDMappingOptions` via
bindings to API.

Closes: https://github.com/containers/podman/issues/15476

Signed-off-by: Aditya R <arajan@redhat.com>

pkg/api/handlers/compat/images_build.go

@@ -101,6 +101,7 @@ func BuildImage(w http.ResponseWriter, r *http.Request) {
 		ForceRm                 bool     `schema:"forcerm"`
 		From                    string   `schema:"from"`
 		HTTPProxy               bool     `schema:"httpproxy"`
+		IDMappingOptions        string   `schema:"idmappingoptions"`
 		IdentityLabel           bool     `schema:"identitylabel"`
 		Ignore                  bool     `schema:"ignore"`
 		Isolation               string   `schema:"isolation"`
@@ -389,6 +390,14 @@ func BuildImage(w http.ResponseWriter, r *http.Request) {
 		}
 	}
 
+	var idMappingOptions buildahDefine.IDMappingOptions
+	if _, found := r.URL.Query()["idmappingoptions"]; found {
+		if err := json.Unmarshal([]byte(query.IDMappingOptions), &idMappingOptions); err != nil {
+			utils.BadRequest(w, "idmappingoptions", query.IDMappingOptions, err)
+			return
+		}
+	}
+
 	var cacheFrom reference.Named
 	if _, found := r.URL.Query()["cachefrom"]; found {
 		cacheFrom, err = parse.RepoNameToNamedReference(query.CacheFrom)
@@ -644,6 +653,7 @@ func BuildImage(w http.ResponseWriter, r *http.Request) {
 		Excludes:                       excludes,
 		ForceRmIntermediateCtrs:        query.ForceRm,
 		From:                           fromImage,
+		IDMappingOptions:               &idMappingOptions,
 		IgnoreUnrecognizedInstructions: query.Ignore,
 		Isolation:                      isolation,
 		Jobs:                           &jobs,

pkg/bindings/images/build.go

@@ -88,6 +88,13 @@ func Build(ctx context.Context, containerFiles []string, options entities.BuildO
 		}
 		params.Set("additionalbuildcontexts", string(additionalBuildContextMap))
 	}
+	if options.IDMappingOptions != nil {
+		idmappingsOptions, err := jsoniter.Marshal(options.IDMappingOptions)
+		if err != nil {
+			return nil, err
+		}
+		params.Set("idmappingoptions", string(idmappingsOptions))
+	}
 	if buildArgs := options.Args; len(buildArgs) > 0 {
 		bArgs, err := jsoniter.MarshalToString(buildArgs)
 		if err != nil {

test/e2e/build/Containerfile.userns-auto

@@ -0,0 +1,2 @@
+FROM alpine
+RUN cat /proc/self/uid_map

test/e2e/run_userns_test.go

@@ -8,6 +8,7 @@ import (
 	"strings"
 
 	. "github.com/containers/podman/v4/test/utils"
+	"github.com/containers/storage"
 	. "github.com/onsi/ginkgo"
 	. "github.com/onsi/gomega"
 	. "github.com/onsi/gomega/gexec"
@@ -42,6 +43,33 @@ var _ = Describe("Podman UserNS support", func() {
 
 	})
 
+	// Note: Lot of tests for build with --userns=auto are already there in buildah
+	// but they are skipped in podman CI because bud tests are executed in rootfull
+	// environment ( where mappings for the `containers` user is not present in /etc/subuid )
+	// causing them to skip hence this is a redundant test for sanity to make sure
+	// we don't break this feature for podman-remote.
+	It("podman build with --userns=auto", func() {
+		u, err := user.Current()
+		Expect(err).To(BeNil())
+		name := u.Name
+		if name == "root" {
+			name = "containers"
+		}
+		content, err := ioutil.ReadFile("/etc/subuid")
+		if err != nil {
+			Skip("cannot read /etc/subuid")
+		}
+		if !strings.Contains(string(content), name) {
+			Skip("cannot find mappings for the current user")
+		}
+		session := podmanTest.Podman([]string{"build", "-f", "build/Containerfile.userns-auto", "-t", "test", "--userns=auto"})
+		session.WaitWithDefaultTimeout()
+		Expect(session).Should(Exit(0))
+		// `1024` is the default size or length of the range of user IDs
+		// that is mapped between the two user namespaces by --userns=auto.
+		Expect(session.OutputToString()).To(ContainSubstring(fmt.Sprintf("%d", storage.AutoUserNsMinSize)))
+	})
+
 	It("podman uidmapping and gidmapping", func() {
 		session := podmanTest.Podman([]string{"run", "--uidmap=0:100:5000", "--gidmap=0:200:5000", "alpine", "echo", "hello"})
 		session.WaitWithDefaultTimeout()
@@ -157,6 +185,8 @@ var _ = Describe("Podman UserNS support", func() {
 			session.WaitWithDefaultTimeout()
 			Expect(session).Should(Exit(0))
 			l := session.OutputToString()
+			// `1024` is the default size or length of the range of user IDs
+			// that is mapped between the two user namespaces by --userns=auto.
 			Expect(l).To(ContainSubstring("1024"))
 			m[l] = l
 		}