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Support error array in field when using json formatter #1413

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Support error array in field when using json formatter #1413

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10 changes: 10 additions & 0 deletions json_formatter.go
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Original file line number Diff line number Diff line change
Expand Up @@ -59,6 +59,14 @@ type JSONFormatter struct {
PrettyPrint bool
}

func errorsArrayToStrings(errs []error) []string {
strs := make([]string, len(errs))
for i, err := range errs {
strs[i] = err.Error()
}
return strs
}

// Format renders a single log entry
func (f *JSONFormatter) Format(entry *Entry) ([]byte, error) {
data := make(Fields, len(entry.Data)+4)
Expand All @@ -68,6 +76,8 @@ func (f *JSONFormatter) Format(entry *Entry) ([]byte, error) {
// Otherwise errors are ignored by `encoding/json`
// https://github.com/sirupsen/logrus/issues/137
data[k] = v.Error()
case []error:
data[k] = errorsArrayToStrings(v)
Comment on lines +79 to +80

@thaJeztah thaJeztah Feb 27, 2026

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Slightly thinking out loud here; now that go stdlib provides native support for "multi-errors" through errors.Join, I wonder if this is something that would be better fixed in the code using logrus.

i.e.; instead of WithField("errors", []error{...}), to use WithError(errors.Join(errs....)) (or similar)

@thaJeztah thaJeztah Feb 27, 2026

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The tricky bit is that logrus will (probably) never be able to fully cover all scenarios; if such a []error (or a regular error) would be part of a struct that's set as field; it would probably still produce a non-string output for the error(s).

default:
data[k] = v
}
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32 changes: 31 additions & 1 deletion json_formatter_test.go
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Expand Up @@ -24,7 +24,37 @@ func TestErrorNotLost(t *testing.T) {
}

if entry["error"] != "wild walrus" {
t.Fatal("Error field not set")
t.Fatal("Error field not correct: ", entry["error"])
}
}

func TestErrorsNotLost(t *testing.T) {
formatter := &JSONFormatter{}

b, err := formatter.Format(
WithField("errors", []error{
errors.New("wild walrus"),
errors.New("mild wombat"),
}),
)
if err != nil {
t.Fatal("Unable to format entry: ", err)
}

entry := make(map[string]interface{})
err = json.Unmarshal(b, &entry)
if err != nil {
t.Fatal("Unable to unmarshal formatted entry: ", err)
}

fmt.Println(string(b))

errs, ok := entry["errors"].([]interface{})
if !ok {
t.Fatalf("Errors field type not correct: %T", entry["errors"])
}
if errs[0] != "wild walrus" || errs[1] != "mild wombat" {
t.Fatal("Error field not correct: ", entry["errors"])
}
}

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