JSONFormatter isn't handling functions as Field values

[xandrewrampulla]

When using the JSONFormatter, if I accidentally pass a function as a Field value, the entire log message is lost. It would be better if only that one field was lost (even better would be to log that the field couldn't be translated into JSON properly).

Simple example code

package main

import (
	log "github.com/sirupsen/logrus"
)

func myfun() string {
	return ""
}

func main() {

	log.SetFormatter(&log.JSONFormatter{})

	log.WithFields(log.Fields{
		"animal": "walrus",
		"myfunc": myfun,
	}).Info("A walrus appears")
}

Current output
Failed to obtain reader, Failed to marshal fields to JSON, json: unsupported type: func() string

[dgsb]

Indeed this is annoying

[smacker]

I got the same error but with a pointer to function:

package main

import (
	log "github.com/sirupsen/logrus"
)

func main() {
	myfun := func() {}
	log.SetFormatter(&log.JSONFormatter{})
	log.WithFields(log.Fields{
		"animal": "walrus",
		"myfunc": &myfun,
	}).Info("A walrus appears")
}

results in Failed to obtain reader, Failed to marshal fields to JSON, json: unsupported type: func()

Because logrus loses all context it's very hard to find in the code base where the error has happened.
I propose the same fix: #870

[dimatkach]

I am still seeing this issue.

      import (
         log "github.com/sirupsen/logrus"
      )
      type Foo struct {
         foo func() string
      }


     func main() {
        foo :=  Foo {
          func () string { return "foo" }
         }
   
        log.SetFormatter(&log.JSONFormatter{})
        log.WithField("foo", foo).Info("Foo!")
      }

It looks like the PR referenced above only fixes the case where field itself is a func, but if it is a struct that has a func field somewhere inside of it, there is still a problem. The solution either needs to be more involved, and go recursively inside each of the struct.

[linnaname]

I am still seeing this issue in v1.7.0

Test Code:
log.SetFormatter(&log.JSONFormatter{})
req,_ := http.NewRequest("POST", "127.0.0.1",nil)
log.WithFields(log.Fields{ "req": req, }).Error("new request failed")

Output:Failed to obtain reader, failed to marshal fields to JSON, json: unsupported type: func() (io.ReadCloser, error)

[oxzi]

Today I came across the same error for a struct which has a function as a field type. As a workaround, a tag can be added to the field, so that this is not taken into account for the JSON, json:"-".

[vishalkanaujia]

If you are logging HTTP request/response, use httputil.DumpRequest/ httputil.DumpResponse instead of zap.Any