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Rethinking Errors in Go
Marcel van Lohuizen
Go core team
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r, err := os.Open(“foo.txt”)
if err != nil {
return fmt.Errorf(“oops: %v”, err)
}
defer r.Close()
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Semantics first!
Why?
error handling can be tricky
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func writeToGS(c net.Context, bkt, dst string, r io.Reader) (err error) {
w := client.Bucket(bkt).Object(dst).NewWriter(c)
defer w.CloseWithError(err)
if _, err = io.Copy(w, r); err != nil {
return fmt.Errorf(“oops: %v”, err)
}
return nil
}
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func writeToGS(c net.Context, bkt, dst string, r io.Reader) (err error) {
err = errPanicking
w := client.Bucket(bkt).Object(dst).NewWriter(c)
defer w.CloseWithError(err)
if _, err = io.Copy(w, r); err != nil {
return fmt.Errorf(“oops: %v”, err)
}
return err
}
var errPanicking = errors.New(“panicking”)
handle panic FAIL
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func writeToGS(c net.Context, bkt, dst string, r io.Reader) (err error) {
w := client.Bucket(bkt).Object(dst).NewWriter(c)
err = errPanicking
defer func() {
if err != nil {
_ = w.CloseWithError(err)
} else if err = w.Close(); err != nil {
err = fmt.Errorf(“oh noes: %v”, err)
}
}
if _, err = io.Copy(w, r); err != nil {
return fmt.Errorf(“oops: %v”, err)
}
return err
}
return error from Close FAIL
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func writeToGS(c net.Context, bkt, dst string, r io.Reader) (err error) {
w := client.Bucket(bkt).Object(dst).NewWriter(c)
err = errPanicking
defer func() {
if err != nil {
_ = w.CloseWithError(err)
} else if err = w.Close(); err != nil {
err = fmt.Errorf(“oh noes: %v”, err)
}
}()
if _, err = io.Copy(w, r); err != nil {
return fmt.Errorf(“oops: %v”, err)
}
return nil
}
var errPanicking = errors.New(“panicking”)
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how to approach simplifying this?
semantics first!
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Close
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error
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panic
error
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an error is recoverable
panic is not
(sort of)
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there is overlap
not recognized in Go
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Burner package
(github.com/mpvl/errc)
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funnel all errors,
including panics,
to a single error variable
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func writeToGS(c net.Context, bkt, dst string, r io.Reader) (err error) {
e := errc.Catch(&err)
defer e.Handle()
w := client.Bucket(bkt).Object(dst).NewWriter(c)
e.Defer(w.CloseWithError, msg(“oh noes”))
_, err = io.Copy(w, r)
e.Must(err, msg(“oh no”))
return nil
}
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semantics first pays off!
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Try it out!
Feedback Welcome!
Marcel van Lohuizen, Go core Team
github.com/mpvl/errc
github.com/mpvl/errd
@mpvl_