LogstashFormatter doesn't perform an error type check when setting fields so some errors are not correctly serialised.

[jonoradich]

This is essentially the same issue as #137 but with the LogstashFormatter.

LogstashFormatter:

func (f *LogstashFormatter) Format(entry *logrus.Entry) ([]byte, error) {
    fields := make(logrus.Fields)
    for k, v := range entry.Data {
        fields[k] = v
    }
        ....

JSONFormatter:

func (f *JSONFormatter) Format(entry *Entry) ([]byte, error) {
    data := make(Fields, len(entry.Data)+3)
    for k, v := range entry.Data {
        switch v := v.(type) {
        case error:
            // Otherwise errors are ignored by `encoding/json`
            // https://github.com/Sirupsen/logrus/issues/137
            data[k] = v.Error()
        default:
            data[k] = v
        }
    }
        ...

The resulting error field, using golangs url.Error as an example (https://golang.org/pkg/net/url/#Error), is serialised like so:

"error":{"Op":"Get","URL":"http://example.com","Err":{}}

[aarongreenlee]

Thank you for reporting.

[jonoradich]

Solved by bshuster-repo/logrus-logstash-hook#6.