[BUG] - devslog try to read unexported field which may cause panic.

[violin0622]

Describe the bug
when formatting struct attributes, devslog try to read the unexported fields using reflect,
this behaviour cause panic.

To Reproduce
Given the codes below:

// play/ref/main.go
package main

import (
    "fmt"
    "reflect"

    "play/ref/subpack"
)

func main() {
    var s subpack.S

    fmt.Println(`hello world`)
    fmt.Println(reflect.ValueOf(s).Field(0).Interface())
}

// play/ref/subpack/subpack.go
package subpack

type S struct {
    unexported string
}

build and run it, program will panic with:

$ go run .
hello world
panic: reflect.Value.Interface: cannot return value obtained from unexported field or method

goroutine 1 [running]:
reflect.valueInterface({0x100d175c0?, 0x100dd26a0?, 0x1400009cf18?}, 0x1?)
        /opt/homebrew/Cellar/go/1.21.6/libexec/src/reflect/value.go:1501 +0xc8
reflect.Value.Interface(...)
        /opt/homebrew/Cellar/go/1.21.6/libexec/src/reflect/value.go:1490
main.main()
        /Users/violin/Workspace/golang/play/ref/main.go:14 +0xc4
exit status 2

As for devlog, given the codes below:

package main

import (
	"context"
	"log/slog"
	"net"
	"os"

	"github.com/golang-cz/devslog"
	grpclog "github.com/grpc-ecosystem/go-grpc-middleware/v2/interceptors/logging"
	"google.golang.org/grpc"
	"google.golang.org/grpc/reflection"
)

func main() {
	slog.SetDefault(slog.New(devslog.NewHandler(os.Stderr, nil)))

	logger, opts := grpclog.LoggerFunc(func(
		ctx context.Context,
		lvl grpclog.Level,
		msg string, fields ...any,
	) {
		slog.Default().Log(ctx, slog.Level(lvl), msg, fields...)
	}), []grpclog.Option{grpclog.WithLogOnEvents(grpclog.PayloadReceived, grpclog.PayloadSent)}

	svr := grpc.NewServer(
		grpc.ChainUnaryInterceptor(
			grpclog.UnaryServerInterceptor(logger, opts...)),
		grpc.ChainStreamInterceptor(
			grpclog.StreamServerInterceptor(logger, opts...)))
	reflection.Register(svr)
	l, _ := net.Listen(`tcp`, `:8000`)
	svr.Serve(l)
}

when calling grpc, server will panic in devslog:

$ grpcurl -plaintext localhost:8000 list
panic: reflect.Value.Interface: cannot return value obtained from unexported field or method

goroutine 10 [running]:
reflect.valueInterface({0x104ef3ca0?, 0x14000030a50?, 0x19?}, 0x99?)
        /opt/homebrew/Cellar/go/1.21.6/libexec/src/reflect/value.go:1501 +0xc8
reflect.Value.Interface(...)
        /opt/homebrew/Cellar/go/1.21.6/libexec/src/reflect/value.go:1490
github.com/golang-cz/devslog.(*developHandler).formatStruct(0x104ef3ca0?, {0x104f3c148, 0x104ef3ca0}, {0x104ef3ca0?, 0x14000030a50?, 0x104a35e14?}, 0x1)
        /Users/violin/Workspace/golang/play/ref/devslog/devslog.go:503 +0x80
github.com/golang-cz/devslog.(*developHandler).elementType(0x140001ad4d0, {0x104f3c148, 0x104ef3ca0}, {0x104ef3ca0, 0x14000030a50, 0x1b9}, 0x0, 0x10)
        /Users/violin/Workspace/golang/play/ref/devslog/devslog.go:541 +0xff0
github.com/golang-cz/devslog.(*developHandler).formatStruct(0x1051f491c?, {0x104f3c148, 0x104f07fc0}, {0x104f07fc0?, 0x14000030a50?, 0x0?}, 0x0)
        /Users/violin/Workspace/golang/play/ref/devslog/devslog.go:520 +0x714
github.com/golang-cz/devslog.(*developHandler).colorize(0x140001ad4d0, {0x1400011a800, 0x47, 0x400}, {0x14000294000, 0x9, 0x104d84be5?}, 0x0, {0x10527cea0, 0x0, ...})
        /Users/violin/Workspace/golang/play/ref/devslog/devslog.go:336 +0x2174
github.com/golang-cz/devslog.(*developHandler).processAttributes(0x140001ad4d0, {0x1400011a800, 0x47, 0x400}, 0x140001c3048)
        /Users/violin/Workspace/golang/play/ref/devslog/devslog.go:241 +0x290
github.com/golang-cz/devslog.(*developHandler).Handle(_, {_, _}, {{0xc1669326378f4058, 0x373936, 0x105247ec0}, {0x104d8d46a, 0x10}, 0x0, 0x104d84be5, ...})
        /Users/violin/Workspace/golang/play/ref/devslog/devslog.go:157 +0x2b0
log/slog.(*Logger).log(0x140000214a0, {0x104f35138, 0x140002881b0}, 0x0, {0x104d8d46a, 0x10}, {0x1400014b340, 0x12, 0x1c})
        /opt/homebrew/Cellar/go/1.21.6/libexec/src/log/slog/logger.go:225 +0x15c
log/slog.(*Logger).Log(...)
        /opt/homebrew/Cellar/go/1.21.6/libexec/src/log/slog/logger.go:158
main.main.func1({0x104f35138?, 0x140002881b0?}, 0x1c?, {0x104d8d46a?, 0x140001c3578?}, {0x1400014b340?, 0x4?, 0x4?})
        /Users/violin/Workspace/golang/play/ref/main.go:23 +0xb0
github.com/grpc-ecosystem/go-grpc-middleware/v2/interceptors/logging.LoggerFunc.Log(0x140001fa1c0?, {0x104f35138?, 0x140002881b0?}, 0x140001c3578?, {0x104d8d46a?, 0x104a27c0c?}, {0x1400014b340?, 0x104a274e4?, 0x104a3be90?})
        /Users/violin/.go/pkg/mod/github.com/grpc-ecosystem/go-grpc-middleware/v2@v2.0.1/interceptors/logging/logging.go:202 +0x54
github.com/grpc-ecosystem/go-grpc-middleware/v2/interceptors/logging.(*reporter).PostMsgReceive(0x14000119d60, {0x104f07fc0?, 0x14000030a50}, {0x0, 0x0}, 0x0?)
        /Users/violin/.go/pkg/mod/github.com/grpc-ecosystem/go-grpc-middleware/v2@v2.0.1/interceptors/logging/interceptors.go:119 +0x550
github.com/grpc-ecosystem/go-grpc-middleware/v2/interceptors.(*monitoredServerStream).RecvMsg(0x14000288210, {0x104f07fc0, 0x14000030a50})
        /Users/violin/.go/pkg/mod/github.com/grpc-ecosystem/go-grpc-middleware/v2@v2.0.1/interceptors/server.go:63 +0x9c
google.golang.org/grpc/reflection/grpc_reflection_v1.(*serverReflectionServerReflectionInfoServer).Recv(0x140000219f0)
        /Users/violin/.go/pkg/mod/google.golang.org/grpc@v1.60.1/reflection/grpc_reflection_v1/reflection_grpc.pb.go:142 +0x58
google.golang.org/grpc/reflection.(*serverReflectionServer).ServerReflectionInfo(0x140001af980, {0x104f38288, 0x140000219f0})
        /Users/violin/.go/pkg/mod/google.golang.org/grpc@v1.60.1/reflection/serverreflection.go:259 +0x74
google.golang.org/grpc/reflection/grpc_reflection_v1._ServerReflection_ServerReflectionInfo_Handler({0x104ed71e0?, 0x140001af980}, {0x104f35f28?, 0x14000288210})
        /Users/violin/.go/pkg/mod/google.golang.org/grpc@v1.60.1/reflection/grpc_reflection_v1/reflection_grpc.pb.go:123 +0x98
github.com/grpc-ecosystem/go-grpc-middleware/v2/interceptors/logging.StreamServerInterceptor.StreamServerInterceptor.func2({0x104ed71e0, 0x140001af980}, {0x104f36000, 0x1400028a000}, 0x104e67c80?, 0x104f2e6e8)
        /Users/violin/.go/pkg/mod/github.com/grpc-ecosystem/go-grpc-middleware/v2@v2.0.1/interceptors/server.go:35 +0x250
google.golang.org/grpc.(*Server).processStreamingRPC(0x14000181000, {0x104f35138, 0x140002880c0}, {0x104f38510, 0x140001b29c0}, 0x14000001680, 0x140001afaa0, 0x105235cc0, 0x0)
        /Users/violin/.go/pkg/mod/google.golang.org/grpc@v1.60.1/server.go:1673 +0xec8
google.golang.org/grpc.(*Server).handleStream(0x14000181000, {0x104f38510, 0x140001b29c0}, 0x14000001680)
        /Users/violin/.go/pkg/mod/google.golang.org/grpc@v1.60.1/server.go:1787 +0xc18
google.golang.org/grpc.(*Server).serveStreams.func2.1()
        /Users/violin/.go/pkg/mod/google.golang.org/grpc@v1.60.1/server.go:1016 +0x5c
created by google.golang.org/grpc.(*Server).serveStreams.func2 in goroutine 9
        /Users/violin/.go/pkg/mod/google.golang.org/grpc@v1.60.1/server.go:1027 +0x138

This is because devlog is trying to read XXXRequest.state.atomicMessageInfo.GoReflectType.t, which is type of reflect.Type

Expected behavior
formatStruct() method should ignore and skip the unexported fields in struct, for reading an unexported field of other package is dangerous and useless.

[david-littlefarmer]

Resolved with #31