Addressing defer Warnings from Golang errcheck

Overview

When you write code like the following and run errcheck, it flags defer f.Close().

func hoge() error {
    ...
    f, err := os.Open(fpath)
    if err != nil {
        return err
    }

    defer f.Close()
    ...
}

The warning says that f.Close() returns an error, and that error return value is not being checked.

Solution

To work around this, you can fix it as follows.

func hoge() error {
    ...
    f, err := os.Open(fpath)
    if err != nil {
        return err
    }

    defer func() {
        err = f.Close()
        if err != nil {
            log.Fatalln(err)
        }
    }()
    ...
}

However, in the case above, a panic occurs when an error happens.

If you use log.Println instead, the error does get logged, but you cannot handle subsequent processing based on that error.

So I tried fixing it further as shown below.

func hoge() (err error) {
    ...
	f, err := os.Open(filepath.Clean(fpath))
    if err != nil {
        return err
    }

    defer func() {
        if er := f.Close(); er != nil {
            err = er
        }
    }()
    ...
}

With the following steps, you can return the error from f.Close() as the return value of hoge().

• Specify a named return value err error in the return values of the hoge() function
• Store the error returned by f.Close() into err inside the deferred func(){}

Go Playground

References

This topic had already been discussed quite a while ago.

ignore defer calls #55