invalid memory address or nil pointer dereference

[sedgwickz]

In the main function, defer xxx().Close() reported panic error, that xxx was a function which returns the *mgo.Session pointer. I was not sure what happened.

The directory structure as below:

├── db
│   ├── db.go  (return the *mgo.Seesion by xxx public function)
│   └── import.go
└── main.go (use defer xxx.Close())

panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x0 pc=0x11db3f6]

goroutine 1 [running]:
github.com/globalsign/mgo.(*Session).Close(0x0)
        /Users/sedgwickz/Documents/golang/src/github.com/globalsign/mgo/session.go:2059 +0x26
main.main()
        /Users/sedgwickz/Documents/golang/src/github.com/grewords/main.go:17 +0x94
exit status 2

[maitesin]

Hi @sedgwickz,

Thanks for reporting this issue. We might need some more information about the problem in order to help you. Can you provide a snippet of code that can reproduce this issue? Moreover, what is the version of Go, mgo you are using? And in which operating system are you having this issue.

Oscar

[sedgwickz]

Hi @maitesin

Thank you for your reply. I have made a demo program to indicate my problem, but not sure if there is something wrong with mgo or by my own ill used. I think you can check and review my code to find some clues. And related information is as below, but I am sure how to find the mgo version.

go1.10.2 darwin/amd64

testMGO.zip

[Sayan-]

Hi @sedgwickz

There is a scope issue in db/db.go:

func init() {
    log.Println("db initial...")
    session, err := mgo.Dial("mongodb://127.0.0.1:27017")
    if err != nil {
        panic(err)
    }
    database = session.DB("testdb")
}

session is being shadowed in init. You can rewrite init as:

func init() {
    var err error
    log.Println("db initial...")
    session, err = mgo.Dial("mongodb://127.0.0.1:27017")
    if err != nil {
        panic(err)
    }
    database = session.DB("testdb")
}

to get your expected behavior

[domodwyer]

Hi @sedgwickz

@Sayan- nailed it (nice!) so I'm going to close this.

Dom