[Bug] - Nil pointer exception

[sujit-baniya]

panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x8 pc=0x48721c3]

goroutine 187 [running]:
github.com/goccy/go-json/internal/encoder/vm.Run(0xc002f276c0, {0xc001d27c00, 0xc001070180, 0x0}, 0x0)
        /Users/sujit/go/pkg/mod/github.com/goccy/go-json@v0.7.8/internal/encoder/vm/vm.go:197 +0x2f5a3
github.com/goccy/go-json.encodeRunCode(0x4de31c0, {0xc001d27c00, 0x6806d90, 0xc0009bf580}, 0xc00106e000)
        /Users/sujit/go/pkg/mod/github.com/goccy/go-json@v0.7.8/encode.go:307 +0x68
github.com/goccy/go-json.encode(0xc002f276c0, {0x4de31c0, 0xc0011cb7d0})
        /Users/sujit/go/pkg/mod/github.com/goccy/go-json@v0.7.8/encode.go:232 +0x21c
github.com/goccy/go-json.marshal({0x4de31c0, 0xc0011cb7d0}, {0x0, 0x0, 0x40169aa})
        /Users/sujit/go/pkg/mod/github.com/goccy/go-json@v0.7.8/encode.go:147 +0xba
github.com/goccy/go-json.MarshalWithOption(...)
        /Users/sujit/go/pkg/mod/github.com/goccy/go-json@v0.7.8/json.go:186
github.com/goccy/go-json.Marshal({0x4de31c0, 0xc0011cb7d0})
        /Users/sujit/go/pkg/mod/github.com/goccy/go-json@v0.7.8/json.go:171 +0x2a

[goccy]

I cannot investigate from this information. Could you share me the reproducible code ?

[sujit-baniya]

The error started to occur after latest upgrade of this library.
The application is huge... don't know where the error is coming from. Thus I can't create reproducible code. Replacing with standard json package, it worked

[zJeremiah]

Here is an example of the nil pointer error.

package main

import (
	"fmt"
	"net/http"
	"time"

	"github.com/goccy/go-json"
)

func main() {
	c := http.DefaultClient
	req, _ := http.NewRequest("GET", "http://localhost:9999/bad/request", nil)
	_, err := c.Do(req)

	s, err := json.Marshal(struct {
		Time string      `json:"time"`
		Data interface{} `json:"data"`
	}{
		Time: time.Now().Format(time.RFC3339),
		Data: err,
	})
	if err != nil {
		fmt.Println(err)
	}

	fmt.Println(s)
}

[signal SIGSEGV: segmentation violation code=0x1 addr=0x8 pc=0x1261783]

goroutine 1 [running]:
github.com/goccy/go-json/internal/encoder/vm.Run(0xc000244000, {0xc000242000, 0x0, 0x0}, 0x0)
	/Users/jeremiah.zink/go/pkg/mod/github.com/goccy/go-json@v0.7.8/internal/encoder/vm/vm.go:197 +0x2f5a3
github.com/goccy/go-json.encodeRunCode(0x12b4a60, {0xc000242000, 0x15660e8, 0xc000228040}, 0xc000242400)
	/Users/jeremiah.zink/go/pkg/mod/github.com/goccy/go-json@v0.7.8/encode.go:307 +0x68
github.com/goccy/go-json.encode(0xc000244000, {0x12b4a60, 0xc000220040})
	/Users/jeremiah.zink/go/pkg/mod/github.com/goccy/go-json@v0.7.8/encode.go:232 +0x21c
github.com/goccy/go-json.marshal({0x12b4a60, 0xc000220040}, {0x0, 0x0, 0xc00021ff50})
	/Users/jeremiah.zink/go/pkg/mod/github.com/goccy/go-json@v0.7.8/encode.go:147 +0xba
github.com/goccy/go-json.MarshalWithOption(...)
	/Users/jeremiah.zink/go/pkg/mod/github.com/goccy/go-json@v0.7.8/json.go:186
github.com/goccy/go-json.Marshal({0x12b4a60, 0xc000220040})
	/Users/jeremiah.zink/go/pkg/mod/github.com/goccy/go-json@v0.7.8/json.go:171 +0x2a
main.main()

[orisano]

This is the reproducible test code.

func TestIssue290(t *testing.T) {
	type Issue290 interface {
		A()
	}
	var a struct {
		A Issue290
	}
	if b, err := stdjson.Marshal(a); err == nil {
		t.Log(string(b))
                 // {"A":null}
	}
	if b, err := json.Marshal(a); err == nil { // panicked
		t.Log(string(b))
	}
}

Maybe, the cause is untyped nil.

[sujit-baniya]

Any expected update @goccy

[zimmski]

We just ran into this. Here is my reproducer which looks similar to what @orisano reported. What i find interesting is that an empty interface declaration does not trigger the problem: You need an interface with a method.

package main

import (
	"encoding/json"
	"fmt"

	goccy "github.com/goccy/go-json"
)

func main() {
	type Empty interface{}
	type NonEmpty interface {
		A()
	}

	type SomeStruct struct {
		Empty    Empty
		NonEmpty NonEmpty // Comment this line and you will receive no panic.
	}

	originalEncoded, originalError := json.Marshal(SomeStruct{}) // Works
	fmt.Printf("Original: %s\n-> %s\n", originalEncoded, originalError)

	goccyEncoded, goccyError := goccy.Marshal(SomeStruct{}) // Panics
	fmt.Printf("Original: %s\n-> %s\n", goccyEncoded, goccyError)
}

Original: {"Empty":null,"NonEmpty":null}
-> %!s(<nil>)
panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x8 pc=0x5104e3]

goroutine 1 [running]:
github.com/goccy/go-json/internal/encoder/vm.Run(0xc000102dd0, {0xc000028400, 0x0, 0x400}, 0xc0000320c0)
        src/github.com/goccy/go-json/internal/encoder/vm/vm.go:197 +0x2f5a3
github.com/goccy/go-json.encodeRunCode(0x524c20, {0xc000028400, 0x65fda8, 0xc000032080}, 0xc000028800)
        src/github.com/goccy/go-json/encode.go:307 +0x68
github.com/goccy/go-json.encode(0xc000102dd0, {0x524c20, 0xc00006a060})
        src/github.com/goccy/go-json/encode.go:232 +0x21c
github.com/goccy/go-json.marshal({0x524c20, 0xc00006a060}, {0x0, 0x0, 0xc00005df50})
        src/github.com/goccy/go-json/encode.go:147 +0xba
github.com/goccy/go-json.MarshalWithOption(...)
        src/github.com/goccy/go-json/json.go:186
github.com/goccy/go-json.Marshal({0x524c20, 0xc00006a060})
        src/github.com/goccy/go-json/json.go:171 +0x2a
main.main()
        tt.go:24 +0x10a
exit status 2

@goccy hope that helps!