fix(api): Add custom JSON marshaling for InstancePrototype interface fields

Instance provisioning fails with "Expected only one oneOf fields to be set: got 0" errors when using InstancePrototype types with interface-typed fields.

Go's default JSON marshaling omits interface-typed fields in certain contexts. oneOf discriminator fields (image, zone, vpc, primary_network_attachment) are missing from the JSON payload, causing VPC API validation to fail.

This commit add custom MarshalJSON methods to 8 InstancePrototype variant types that explicitly serialize all fields including interface types.

Fixes: #133
Signed-off-by: Josephine Pfeiffer <[email protected]>

Author: pfeifferj

vpcv1/instance_prototype_marshal_test.go

@@ -0,0 +1,91 @@
+package vpcv1_test
+
+import (
+	"encoding/json"
+	"strings"
+	"testing"
+
+	"github.com/IBM/vpc-go-sdk/vpcv1"
+)
+
+func TestInstancePrototypeMarshalBug(t *testing.T) {
+	// Create the prototype exactly like Karpenter does
+	imageID := "r010-test-image-id"
+	zoneName := "eu-de-2"
+	profileName := "bx2-2x8"
+	vpcID := "r010-test-vpc-id"
+	instanceName := "test-instance"
+	subnetID := "test-subnet-id"
+
+	// Create VNI prototype
+	vniPrototype := &vpcv1.InstanceNetworkAttachmentPrototypeVirtualNetworkInterfaceVirtualNetworkInterfacePrototypeInstanceNetworkAttachmentContext{
+		Subnet: &vpcv1.SubnetIdentityByID{
+			ID: &subnetID,
+		},
+	}
+
+	primaryNetworkAttachment := &vpcv1.InstanceNetworkAttachmentPrototype{
+		VirtualNetworkInterface: vniPrototype,
+	}
+
+	// Create instance prototype
+	instancePrototype := &vpcv1.InstancePrototypeInstanceByImageInstanceByImageInstanceByNetworkAttachment{
+		Image:                    &vpcv1.ImageIdentityByID{ID: &imageID},
+		Zone:                     &vpcv1.ZoneIdentityByName{Name: &zoneName},
+		Profile:                  &vpcv1.InstanceProfileIdentityByName{Name: &profileName},
+		VPC:                      &vpcv1.VPCIdentityByID{ID: &vpcID},
+		Name:                     &instanceName,
+		PrimaryNetworkAttachment: primaryNetworkAttachment,
+	}
+
+	// Verify fields are set
+	if instancePrototype.Image == nil {
+		t.Fatal("Image field should not be nil")
+	}
+	if instancePrototype.Zone == nil {
+		t.Fatal("Zone field should not be nil")
+	}
+	if instancePrototype.VPC == nil {
+		t.Fatal("VPC field should not be nil")
+	}
+	if instancePrototype.Profile == nil {
+		t.Fatal("Profile field should not be nil")
+	}
+
+	// Marshal to JSON
+	jsonBytes, err := json.MarshalIndent(instancePrototype, "", "  ")
+	if err != nil {
+		t.Fatalf("JSON marshaling failed: %v", err)
+	}
+
+	jsonString := string(jsonBytes)
+	t.Logf("Marshaled JSON:\n%s\n", jsonString)
+
+	// These assertions will FAIL if the bug exists
+	if !strings.Contains(jsonString, `"image"`) {
+		t.Error("JSON should contain image field - BUG CONFIRMED")
+	}
+	if !strings.Contains(jsonString, `"zone"`) {
+		t.Error("JSON should contain zone field - BUG CONFIRMED")
+	}
+	if !strings.Contains(jsonString, `"vpc"`) {
+		t.Error("JSON should contain vpc field - BUG CONFIRMED")
+	}
+	if !strings.Contains(jsonString, `"profile"`) {
+		t.Error("JSON should contain profile field - BUG CONFIRMED")
+	}
+
+	// Verify actual values
+	if !strings.Contains(jsonString, imageID) {
+		t.Error("JSON should contain image ID value")
+	}
+	if !strings.Contains(jsonString, zoneName) {
+		t.Error("JSON should contain zone name value")
+	}
+	if !strings.Contains(jsonString, vpcID) {
+		t.Error("JSON should contain VPC ID value")
+	}
+	if !strings.Contains(jsonString, profileName) {
+		t.Error("JSON should contain profile name value")
+	}
+}