#!/bin/bash

pwd=`pwd`

cd $pwd/plugin
go build -buildmode=plugin -o plugin.so

cd $pwd/test
go build
./test

module plugin

go 1.16

package main

import (
	typ "plugin/type"
)

var V *typ.T = &typ.T{"hello plugin", "xd"}

package greeting_type

type T struct {
        Msg    string
        Sender string
}

func (t *T) Greeting() string {
        r := t.Msg + " from " + t.Sender
	return r
}

func (t *T) GreetingWithArg(a string) string {
        r := t.Msg + " from " + t.Sender + " with args:" + a
	return r
}

package main

import (
	"fmt"
	"plugin"
	"reflect"
)

func lookup_symbol(p *plugin.Plugin, sn string) plugin.Symbol {
	f, err := p.Lookup(sn)
	if err != nil {
		fmt.Println(err)
		return nil
	}

	// just diagnostic
	switch v := f.(type) {
	default:
		fmt.Printf("Found symbol %s of type %T\n", sn, v)
	}
	return f
}

func call_method(p *plugin.Plugin, sn, fn string, args []reflect.Value) {
	sym := lookup_symbol(p, sn)
	if sym == nil {
		fmt.Printf("No symbol named %s found\n", sn)
		return
	}

	f := reflect.ValueOf(sym).Elem().MethodByName(fn)
	if !f.IsValid() || f.IsZero() || f.IsNil() {	// anything more ??
		fmt.Printf("No valid method %s for receiver %s found\n", fn, sn)
		return
	}

	// to check validity (number, type) of arguments, etc.

	rv := f.Call(args)

	// need an anonymous way to handle results?
	if len(rv) > 0 {
		r := rv[0]
		fmt.Printf("First return value: %#v\n", r)
	}
}

func test_plugin(path, so string) {
	p, err := plugin.Open(path + "/" + so)
	if err != nil {
		fmt.Println(err)
		return
	}

	call_method(p, "V", "Greeting", []reflect.Value{})
	call_method(p, "V", "GreetingWithArg", []reflect.Value{reflect.ValueOf("aa")})

	// illegal
	call_method(p, "V", "GreetingWithArgs", []reflect.Value{reflect.ValueOf("aa"), reflect.ValueOf("bb")})
}

func main() {
	test_plugin("../plugin", "plugin.so")
}

Found symbol V of type **greeting_type.T
unexpected fault address 0xffffffffffffffff
fatal error: fault
[signal SIGSEGV: segmentation violation code=0x1 addr=0xffffffffffffffff pc=0xffffffffffffffff]

goroutine 1 [running]:
runtime.throw(0x546d71, 0x5)
	/home/jixiangdong/util/go.v/src/runtime/panic.go:1112 +0x72 fp=0xc00004fa80 sp=0xc00004fa50 pc=0x4827b2
runtime.sigpanic()
	/home/jixiangdong/util/go.v/src/runtime/signal_unix.go:737 +0x268 fp=0xc00004fab8 sp=0xc00004fa80 pc=0x4975e8
runtime.call32(0xc00007c300, 0xc000011448, 0xc00000e0a8, 0x800000018)
	/home/jixiangdong/util/go.v/src/runtime/asm_amd64.s:547 +0x3e fp=0xc00004fae8 sp=0xc00004fab8 pc=0x4b3efe
reflect.Value.call(0x7f745430c4a0, 0x7f745434e048, 0x293, 0x546b98, 0x4, 0xc00004fe98, 0x0, 0x0, 0x56e5a0, 0xc000066180, ...)
	/home/jixiangdong/util/go.v/src/reflect/value.go:476 +0x8e7 fp=0xc00004fcf0 sp=0xc00004fae8 pc=0x4d6247
reflect.Value.Call(0x7f745430c4a0, 0x7f745434e048, 0x293, 0xc00004fe98, 0x0, 0x0, 0x7f745434e048, 0x293, 0x9)
	/home/jixiangdong/util/go.v/src/reflect/value.go:337 +0xb9 fp=0xc00004fd70 sp=0xc00004fcf0 pc=0x4d5719
main.call_method(0xc00007c1e0, 0x546a12, 0x1, 0x547307, 0x8, 0xc00004fe98, 0x0, 0x0)
	/home/jixiangdong/data/work/example.com/plugin/test/main.go:39 +0x2c5 fp=0xc00004fe50 sp=0xc00004fd70 pc=0x51aba5