Don't defer Close() on writable files (2017) 2 years ago
This is a contrived example, but imagine a situation where I have a file I want to write on disk and then have a reference to it in a database. If I have a flow like:
func UpdateUser(user *User) (err error) {
f, err := os.Create("/some/file.txt")
if err != nil {
return err
}
defer CheckClose(f, &err)
if _, err := f.Write(somedata); err != nil {
return err
}
if err := db.UpdateUser(user, "/some/file.txt"); err != nil {
return err
}
return
}
The core problem is that the error checking is not done soon enough, either because Go programmers are conditioned to `defer f.Close()` from nearly all example code -- most of it demonstrating reads, not writes -- or because they are handling the error, but only in a deferred function, not earlier.
A more correct way to do this would be:
func UpdateUser(user *User) error {
f, err := os.Create("/some/file.txt")
if err != nil {
return err
}
defer f.Close()
if _, err := f.Write(somedata); err != nil {
return err
}
if err := f.Sync(); err != nil {
return err
}
if err := f.Close(); err != nil {
return err
}
if err := db.UpdateUser(user, "/some/file.txt"); err != nil {
return err
}
}