Unable to use `go-jose/go-jose`

[Cyb3r-Jak3]

The following program sample.go triggers an unexpected result

package main

import (
	"fmt"

	"github.com/go-jose/go-jose/v3"
)

func main() {
	fmt.Println(jose.A128GCM)
}

Expected result

go run main.go
A128GCM

Got

yaegi ./main.go
go-jose/go-jose/v3/json/encode.go:650:48: cannot use type *json.encodeState as type io.Writer

Yaegi Version

v0.14.3

Additional Notes

No response

[jmanero]

It looks like the interpreter may not be handling embedding in an unexported type. This it the json.encodeState type from go-jose:

// An encodeState encodes JSON into a bytes.Buffer.
type encodeState struct {
	bytes.Buffer // accumulated output
	scratch      [64]byte
}

bytes.Buffer should implement io.Writer

[ssbeatty]

Struct embedding doesn't seem to work very well at the moment
In this code

package main

import (
	"bytes"
	"reflect"
)

func main() {
	tt := reflect.StructOf([]reflect.StructField{
		{Name: "Buffer", Type: reflect.TypeOf(bytes.Buffer{}), Anonymous: true},
	})

	if _, present := tt.MethodByName("Write"); present {
		println("tt has Write func")
	} else {
		println("tt has not Write func")
	}

	bt := reflect.StructOf([]reflect.StructField{
		{Name: "Buffer", Type: reflect.TypeOf(&bytes.Buffer{}), Anonymous: true},
	})

	if _, present := bt.MethodByName("Write"); present {
		println("bt has Write func")
	} else {
		println("bt has not Write func")
	}
}


// ouput
// tt has not Write func
// bt has Write func

When the field type passed into reflect.StructOf is pointer/non-pointer, the number of methods that reflect.Type can obtain is different

So in

yaegi/interp/run.go

Line 542 in 9d65860

if dest.Kind() == reflect.Interface && src.Implements(dest) {

Is it more reasonable to change to the following code

	if dest.Kind() == reflect.Interface {
		if src.Kind() == reflect.Pointer {
			return src.Elem().Implements(dest)
		} else {
			return src.Implements(dest)
		}
	}

With this modification, the following code will work fine

// An encodeState encodes JSON into a bytes.Buffer.
type encodeState struct {
	*bytes.Buffer // accumulated output
	scratch      [64]byte
}

But if a structure is directly embedded, and the methods of this structure all contain pointers, there is nothing can do

Maybe reflect.PtrTo(rtype).Implements(typ) can implement

[taliesins]

@Cyb3r-Jak3 you may be interested in looking at: https://github.com/taliesins/traefik-plugin-oidc/tree/main/jwt

We hacked it to work with yaegi

[Cyb3r-Jak3]

@taliesins Thanks! I will take a look