feat: validation for registry/namespace to not contain image name (#601)

* initial validation for registry/namespace to not contain image name

* Update function.go

* supporting nested namespace

client.go

@@ -588,7 +588,7 @@ func (c *Client) Build(ctx context.Context, path string) (err error) {
 		return
 	}
 
-	// TODO: create a statu structure and return it here for optional
+	// TODO: create a status structure and return it here for optional
 	// use by the cli for user echo (rather than rely on verbose mode here)
 	message := fmt.Sprintf("🙌 Function image built: %v", f.Image)
 	if runtime.GOOS == "windows" {

cmd/build.go

@@ -1,6 +1,7 @@
 package cmd
 
 import (
+	"errors"
 	"fmt"
 
 	"github.com/AlecAivazis/survey/v2"
@@ -83,6 +84,23 @@ kn func build --builder cnbs/sample-builder:bionic
 	return cmd
 }
 
+func ValidNamespaceAndRegistry() survey.Validator {
+	return func(val interface{}) error {
+
+		// if the value passed in is the zero value of the appropriate type
+		if len(val.(string)) == 0 {
+			return errors.New("Value is required")
+		}
+
+		_, err := fn.DerivedImage("", val.(string)) //image can be derived without any error
+
+		if err != nil {
+			return errors.New(val.(string) + " Registry and Namespace are required (ie. docker.io/tigerteam). The image name will be derived from the function name.")
+		}
+		return nil
+	}
+}
+
 func runBuild(cmd *cobra.Command, _ []string, clientFn buildClientFn) (err error) {
 	config, err := newBuildConfig().Prompt()
 	if err != nil {
@@ -111,7 +129,7 @@ func runBuild(cmd *cobra.Command, _ []string, clientFn buildClientFn) (err error
 
 			err = survey.AskOne(
 				&survey.Input{Message: "Registry for Function images:"},
-				&config.Registry, survey.WithValidator(survey.Required))
+				&config.Registry, survey.WithValidator(ValidNamespaceAndRegistry()))
 			if err != nil {
 				if err == terminal.InterruptErr {
 					return nil

function.go

@@ -156,7 +156,7 @@ func (f Function) ImageWithDigest() string {
 // DerivedImage returns the derived image name (OCI container tag) of the
 // Function whose source is at root, with the default registry for when
 // the image has to be calculated (derived).
-// The following are eqivalent due to the use of DefaultRegistry:
+// The following are equivalent due to the use of DefaultRegistry:
 // registry:  docker.io/myname
 //            myname
 // A full image name consists of registry, image name and tag.
@@ -194,14 +194,20 @@ func DerivedImage(root, registry string) (image string, err error) {
 	// therefore derive the image tag from the defined registry and name.
 	// form:    [registry]/[user]/[function]:latest
 	// example: quay.io/alice/my.function.name:latest
+	// Also nested namespaces should be supported:
+	// form:    [registry]/[parent]/[user]/[function]:latest
+	// example: quay.io/project/alice/my.function.name:latest
 	registry = strings.Trim(registry, "/") // too defensive?
 	registryTokens := strings.Split(registry, "/")
 	if len(registryTokens) == 1 {
+		//namespace provided only 'alice'
 		image = DefaultRegistry + "/" + registry + "/" + f.Name
-	} else if len(registryTokens) == 2 {
+	} else if len(registryTokens) == 2 || len(registryTokens) == 3 {
+		// registry/namespace provided `quay.io/alice` or registry/parent-namespace/namespace provided `quay.io/project/alice`
 		image = registry + "/" + f.Name
-	} else {
+	} else if len(registryTokens) > 3 { // the name of the image is also provided `quay.io/alice/my.function.name`
-		err = fmt.Errorf("registry should be either 'namespace' or 'registry/namespace'")
+		err = fmt.Errorf("registry should be either 'namespace', 'registry/namespace' or 'registry/parent/namespace', the name of the image will be derived from the function name.")
+		return
 	}
 
 	// Explicitly append :latest.  We currently expect source control to drive