I am having a question about how to implement interfaces correctly in Go
when it comes to third-party packages that use chained methods. I have
compiled an example project below for you so that you can understand the
problem.
package main
import (
myAPI "github.com/hashicorp/vault/api"
)
var myClient *myAPI.Client
type MyProvider interface {
GetClient() MyAPIClient
}
type MyAPIClient interface {
// I want to do this but it does not work
Logical() MyAPILogical
// This works though
// Logical() *myAPI.Logical
}
type MyAPILogical interface {
Write(path string, data map[string]interface{}) (*myAPI.Secret, error)
}
type Provider struct {}
func PublicFunctionIWantToTest(provider MyProvider) {
client := provider.GetClient()
// We normally do something here with the 'client' variable, but important
// is that we forward it later on
privateFunctionThatIsUsedInTheTest(client)
}
func privateFunctionThatIsUsedInTheTest(client MyAPIClient) (*myAPI.Secret,
error) {
return client.Logical().Write(
"/here/goes/some/path",
map[string]interface{}{
"key": "value",
},
)
}
func NewProvider() MyProvider {
return Provider{}
}
func (p Provider) GetClient() MyAPIClient {
return myClient
}
// Empty function just so that this example can be built
func main() {}
As you can see, the package has a chained method Logical().Write() . Since
I want to create tests for PublicFunctionIWantToTest, I want to pass down
all the functionality as interface so that I can use
https://vektra.github.io/mockery/ to create mocks for it.
Unfortunately, I am hitting an issue with my MyAPIClient and the
MyAPILogical interface. Since I can see in the package's documentation
(https://pkg.go.dev/github.com/hashicorp/vault/api@v1.8.1#Logical.Write)
that the Logical() method returns a Logical instance, I want to make it so
that interface method returns the other interface MyAPILogical (line 15).
This does not work though, there is an error on line 47 in the GetClient()
method saying that I would not implement the interface correctly. How could
I do that?
cannot use myClient (variable of type *api.Client) as MyAPIClient value in
return statement: *api.Client does not implement MyAPIClient (wrong type
for method Logical)
have Logical() *api.Logical
want Logical() MyAPILogicalcompilerInvalidIfaceAssign
Thank you kindly
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