Error Handling at Spring

nycgolang meetup

Transcript

1. How Spring Handles Errors What we’ve learned; What we’re doing.
5. I need stuff 200 OK
6. I need stuff 400 Bad Request
7. I need stuff 500 Internal Error
8. I need stuff 418 I’m a teapot
9. “Fail Fast”
10. if err != nil { return err }
11. func GetProduct(id int) (Product, error) { product, err := db.Select(...) return product, err }
12. func GetProduct(id int) (Product, error) { product, err := db.Select(...) return product, err } func ContrivedMethod(id int) error { product, err := GetProduct(id) if err != nil { return err } ... }
13. func GetProduct(id int) (Product, error) { product, err := db.Select(...) return product, err } func ContrivedMethod(id int) error { product, err := GetProduct(id) if err != nil { return err } ... } func HandleRequest(id int, w http.ResponseWriter, r *http.Request) { err := ContrivedMethod(id) if err != nil { http.Error(w, err.Error(),...) } ... }
14. strconv.ParseInt: parsing "adsf": invalid syntax
15. strconv.ParseInt: parsing "adsf": invalid syntax pq: duplicate key value violates unique constraint
16. strconv.ParseInt: parsing "adsf": invalid syntax pq: duplicate key value violates unique constraint Product not found
17. Errors Need Context
18. func GetProduct(id int) (Product, error) { product, err := db.Select(...) return product, err } func ContrivedMethod(id int) error { product, err := GetProduct(id) if err != nil { return err } ... } func HandleRequest(id int, w http.ResponseWriter, r *http.Request) { err := ContrivedMethod(id) if err != nil { http.Error(w, err.Error(),...) } ... } Lost Context
19. type SpringError { error stackTrace string }
20. type SpringError { error stackTrace string } Context!
21. func GetProduct(id int) (Product, *SpringError) { product, err := db.Select(...) return product, wrap(err) }
22. No product found main.GetProduct(0x1, 0x1704, 0x2b7a0, ...) /tmp/sandbox244941649/main.go:25 +0xc0 main.ContrivedMethod(0x1, 0x931a0, 0x0, 0x0) /tmp/sandbox244941649/main.go:30 +0x60 main.main() /tmp/sandbox244941649/main.go:34 +0x40
23. strconv.ParseInt: parsing "adf": invalid syntax
24. func GetProduct(id int) (Product, error) { product, err := db.Select(...) return product, err } func ContrivedMethod(id int) error { product, err := GetProduct(id) if err != nil { return err } ... } func HandleRequest(id int, w http.ResponseWriter, r *http.Request) { err := ContrivedMethod(id) if err != nil { http.Error(w, err.Error(),...) } ... } Wrapped? Wrapped?
25. Use Types
26. func GetProduct(id int) (Product, *SpringError) { product, err := db.Select(...) return product, wrap(err) } func ContrivedMethod(id int) *SpringError { product, err := GetProduct(id) if err != nil { return err } ... } func HandleRequest(id int, w http.ResponseWriter, r *http.Request) { err := ContrivedMethod(id) if err != nil { http.Error(w, err.String(),...) } ... } errors get wrapped Already Wrapped!
27. Errors Are Values https://blog.golang.org/errors-are-values
28. func GetProduct(id int) (Product, *SpringError) { product, err := db.Select(...) return product, wrap(err) } func ContrivedMethod(id int) *SpringError { product, err := GetProduct(id) if err != nil { return err } ... } func HandleRequest(id int, w http.ResponseWriter, r *http.Request) { err := ContrivedMethod(id) if err != nil { http.Error(w, err.String(),...) } ... }
29. func GetProduct(id int) (Product, *SpringError) { product, err := db.Select(...) return product, wrap(err) } func ContrivedMethod(id int) *SpringError { product, err := GetProduct(id) if err != nil { return err } ... } func HandleRequest(id int, w http.ResponseWriter, r *http.Request) { err := ContrivedMethod(id) if err != nil { http.Error(w, err.String(),...) } ... }
30. func GetProduct(id int) (Product, *SpringError) { product, err := db.Select(...) return product, wrap(err) } func ContrivedMethod(id int) *SpringError { product, err := GetProduct(id) if err != nil { return err } ... } func HandleRequest(id int, w http.ResponseWriter, r *http.Request) { err := ContrivedMethod(id) if err != nil { http.Error(w, err.String(),...) } ... }
31. func GetProduct(id int) (Product, *SpringError) { product, err := db.Select(...) return product, wrap(err) } func ContrivedMethod(id int) *SpringError { product, err := GetProduct(id) if err != nil { return err } ... } func HandleRequest(id int, w http.ResponseWriter, r *http.Request) { err := ContrivedMethod(id) if err != nil { http.Error(w, err.String(),...) } ... }
32. func GetProduct(id int) (product Product, err *SpringError) { defer annotateError(&err, “fetching product with id %d”, id) product, err := db.Select(...) return product, wrap(err) }
33. func HandleRequest(id int, w http.ResponseWriter, r *http.Request) { err := ContrivedMethod(id) if err != nil { err.Annotate(“request for %s”, request.URL.String()) http.Error(w, err.String(),...) } ... }
34. Product not found in request for /product/1124 fetching product with id 1124 main.GetProduct(0x1, 0x1704, 0x2b7a0, ...) /tmp/sandbox244941649/main.go:25 +0xc0 main.ContrivedMethod(0x1, 0x931a0, 0x0, 0x0) /tmp/sandbox244941649/main.go:30 +0x60 main.main() /tmp/sandbox244941649/main.go:34 +0x40
35. Recap • We used to see hard to understand errors in production. • Now we don’t. • Add context to your errors. • Use the type system to enforce that every error is addressed. • Make it easy to add extra context where it is helpful
36. Questions? @jimtla or jim@shopspring.com