Panic when getting a guild member's permissions.

[holedaemon]

Description
When attempting to get a guild member's permissions a panic occurs. From my testing, it only occurs when using the instance of GuildMember passed with a new message. If you manually call a member with Guild(...).Member(...) and use that, the panic does not occur.

What did you do?
Within my message handler function, I call the Guild and Channel with the appropriate client methods. Then, I call *message.Member.PermissionsIn(...) and the panic occurs.

What did you expect to see?
A guild member's permissions in a channel printed to stdout.

What did you see instead?
A panic resulting from the call to PermissionsIn().

What version of the module are you using ?
v0.15.0

Below is the code I used to test:

package main

import (
	"context"
	"fmt"
	"os"
	"os/signal"

	"github.com/skwair/harmony"
)

type bot struct {
	client *harmony.Client
}

func main() {
	b := &bot{}
	token := os.Getenv("HARMONY_TEST_TOKEN")
	client, err := harmony.NewClient(token)

	if err != nil {
		fmt.Println(err)
		return
	}

	b.client = client
	b.client.OnMessageCreate(b.message)

	if err := b.client.Connect(context.Background()); err != nil {
		fmt.Println(err)
		return
	}
	defer b.client.Disconnect()

	close := make(chan os.Signal, 1)
	signal.Notify(close, os.Interrupt)
	<-close
}

func (b *bot) message(m *harmony.Message) {
	if m.Content == "!perms" {
		guild, err := b.client.Guild(m.GuildID).Get(context.Background())

		if err != nil {
			fmt.Println(err)
			return
		}

		channel, err := b.client.Channel(m.ChannelID).Get(context.Background())

		if err != nil {
			fmt.Println(err)
			return
		}

		var permissions int

		// With GuildMember from API
		member, err := b.client.Guild(m.GuildID).Member(context.Background(), m.Author.ID)

		if err != nil {
			fmt.Println(err)
			return
		}

		permissions = member.PermissionsIn(guild, channel)
		fmt.Println("API:", permissions)

		// With GuildMember from Message
		permissions = m.Member.PermissionsIn(guild, channel)
		fmt.Println("Message:", permissions)

	}
}

And the output from that:

λ go run .
API:  2146958591
panic: runtime error: invalid memory address or nil pointer dereference
[signal 0xc0000005 code=0x0 addr=0x0 pc=0x66f60d]

goroutine 39 [running]:
github.com/skwair/harmony.computeBasePermissions(0xc000214680, 0xc000107f40, 0xc000167930)
        C:/Users/Eli/go/pkg/mod/github.com/skwair/harmony@v0.15.0/guild_permission.go:7 +0x3d
github.com/skwair/harmony.(*GuildMember).PermissionsIn(0xc000107f40, 0xc000214680, 0xc0001dab40, 0x2)
        C:/Users/Eli/go/pkg/mod/github.com/skwair/harmony@v0.15.0/guild_member.go:27 +0x3c
main.(*bot).message(0xc00009c018, 0xc000108a80)
        C:/Users/Eli/projects/go/harmony-test/main.go:71 +0x419
github.com/skwair/harmony.messageCreateHandler.handle(0xc00005abf0, 0x69dae0, 0xc000108a80)
        C:/Users/Eli/go/pkg/mod/github.com/skwair/harmony@v0.15.0/events.go:329 +0x48
created by github.com/skwair/harmony.(*Client).handle
        C:/Users/Eli/go/pkg/mod/github.com/skwair/harmony@v0.15.0/dispatch.go:351 +0xe0
exit status 2

[skwair]

Hey, thanks for the report! I'll try to reproduce later today and I'll release a new version with a fix, this definitely looks like a bug.

[skwair]

Okay so I can definitely reproduce with your example but it turns out discord only sends a partial GuildMember object on Message objects.

I'll probably create a dedicated PartialGuildMember object which only has the fields set in those events to avoid having future panics like this one.

A solution to avoid the API call could be to use the client state (if enabled - which is the default behavior):

member := findMember(m.Author.ID, b.client.State.Guild(m.GuildID).Members)
if member != nil {
	permissions = member.PermissionsIn(guild, channel)
	fmt.Println("State:", permissions)
}

findMember would be a quick helper function:

// findMember looks for the guild member having the given id in the given list of member.
// It returns nil if the member could not be found.
func findMember(id string, members []harmony.GuildMember) *harmony.GuildMember {
	for _, m := range members {
		if m.User.ID == id {
			return &m
		}
	}

	return nil
}

Else, if you can't use the state (because your bot requires to be stateless) depending on what you want to do with the permissions, you should have access to the role ids of the message author (m.Member.Roles).

[holedaemon]

Awesome. I implemented your solution, works perfectly, thanks! :)

[skwair]

Great! Thanks again for the report I'll still make the change to avoid the potential panic 🙂