InstancePrototype oneOf Constraint Validation Failure #133
Description
When creating VPC instances using InstancePrototypeInstanceByImageInstanceByImageInstanceByNetworkAttachment in vpc-go-sdk v0.74.0 and v0.74.1, the VPC API returns the error:
Expected only one oneOf fields to be set: got 0
This error occurs even when all required fields are properly set in the Go struct. The issue appears to be related to JSON marshaling of interface-typed fields.
Environment
- SDK Version: github.com/IBM/vpc-go-sdk v0.74.1 (also occurs in v0.74.0)
- Go Version: 1.24.6
- API Version: 2025-09-30
- Region: eu-de
Expected Behavior
Creating a VPC instance with the following code should succeed:
imageID := "r010-17a6c2b3-c93b-4018-87ca-f078ef21e02b"
zoneName := "eu-de-2"
profileName := "bx2-2x8"
vpcID := "r010-vpc-id"
subnetID := "subnet-id"
primaryNetworkAttachment := &vpcv1.InstanceNetworkAttachmentPrototype{
VirtualNetworkInterface: &vpcv1.InstanceNetworkAttachmentPrototypeVirtualNetworkInterfaceVirtualNetworkInterfacePrototypeInstanceNetworkAttachmentContext{
Subnet: &vpcv1.SubnetIdentityByID{ID: &subnetID},
},
}
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,
}
result, response, err := vpcService.CreateInstance(&vpcv1.CreateInstanceOptions{
InstancePrototype: instancePrototype,
})Actual Behavior
The VPC API returns an error:
Expected only one oneOf fields to be set: got 0
Analysis
The issue appears to be in how the SDK marshals interface-typed fields to JSON. When examining the struct before the API call, all fields are non-nil. However, when the struct is marshaled to JSON (which the HTTP client does before sending the request), interface fields are not being properly serialized.
Evidence
I created a unit test that demonstrates the marshaling issue:
// Create instance prototype with all fields set
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
fmt.Println(instancePrototype.Image != nil) // true
fmt.Println(instancePrototype.Zone != nil) // true
fmt.Println(instancePrototype.VPC != nil) // true
// Marshal to JSON (like the HTTP client does)
jsonBytes, _ := json.Marshal(instancePrototype)
jsonString := string(jsonBytes)
// Check if fields are in JSON
fmt.Println(strings.Contains(jsonString, "image")) // false (UNEXPECTED)
fmt.Println(strings.Contains(jsonString, "zone")) // false (UNEXPECTED)
fmt.Println(strings.Contains(jsonString, "vpc")) // false (UNEXPECTED)The unit test shows that even though the interface fields are non-nil in Go, they are omitted from the JSON output. This causes the VPC API to receive an incomplete payload that fails oneOf validation.