feat: Add getters to server response

Allow different steps inside a server function to get the current state
of the response objects.

Signed-off-by: Maximilian Blatt <mbxd12@web.de>

error.go

@@ -0,0 +1,14 @@
+package server
+
+import "fmt"
+
+type errNotFound string
+
+func (e errNotFound) Error() string {
+	return fmt.Sprintf("not found: %s", string(e))
+}
+
+func IsNotFoundError(err error) bool {
+	_, ok := err.(*errNotFound)
+	return ok
+}

server.go

@@ -114,6 +114,13 @@ func (r *RunServerFunctionResponse) SetComposite(o runtime.Object, mods ...Resou
 	return nil
 }
 
+func (r *RunServerFunctionResponse) GetComposite(target runtime.Object) error {
+	if r.DesiredComposite == nil || r.DesiredComposite.Resource == nil {
+		return nil // Return an error here?
+	}
+	return resource.AsObject(r.DesiredComposite.Resource, target)
+}
+
 func (r *RunServerFunctionResponse) SetComposedRaw(name string, res *fnapi.Resource) {
 	if r.DesiredComposed == nil {
 		r.DesiredComposed = map[string]*fnapi.Resource{}
@@ -136,6 +143,14 @@ func (r *RunServerFunctionResponse) SetComposed(name string, o runtime.Object, m
 	return nil
 }
 
+func (r *RunServerFunctionResponse) GetComposed(name string, target runtime.Object) error {
+	state, exists := r.DesiredComposed[name]
+	if !exists {
+		return errNotFound(name)
+	}
+	return resource.AsObject(state.Resource, target)
+}
+
 func (r *RunServerFunctionResponse) SetContextField(key string, value any) error {
 	if r.DesiredContext == nil {
 		r.DesiredContext = &structpb.Struct{

server_function.go

@@ -45,6 +45,10 @@ type ServerFunctionResponse interface {
 	// resource for the given name.
 	SetComposite(o runtime.Object, mods ...ResourceModifier) error
 
+	// GetComposite gets the current state of the composite resource of this
+	// response and writes its contents into the given target object.
+	GetComposite(target runtime.Object) error
+
 	// SetCompositeRaw sets the desired response state directly using the
 	// native SDK types.
 	//
@@ -56,6 +60,10 @@ type ServerFunctionResponse interface {
 	// identified by the given name for this function's response.
 	SetComposed(name string, o runtime.Object, mods ...ResourceModifier) error
 
+	// GetComposed looks up the composed resource in the current response object
+	// and writes its contents into the given target object.
+	GetComposed(name string, target runtime.Object) error
+
 	// SetComposedRaw sets the desired composed resource state directly using
 	// the native SDK types.
 	//