Add strict fields into log

[kotyara85]

Hey there,
Let's say if I have a struct

type logFormat struct {
	Level        string    `json:"level,omitempty"`
	ClientIP     string    `json:"client_ip,omitempty"`
	Method       string    `json:"method,omitempty"`
	Path         string    `json:"path,omitempty"`
}

if there a way add it to zap logger in flat without sub field?

I was able easy to do this:

{"level":"info","ts":1605346064.461162,"caller":"logger/logger.go:109","msg":"","log":{"level":"WARNING","client_ip":"::1","method":"GET","path":"/api"}}

with sugar.Infow("", zap.Reflect("log", log))

but would be nice to construct something like this instead without using individual zap fields

{"level":"info","ts":1605346064.461162,"caller":"logger/logger.go:109","msg:"","client_ip":"::1","method":"GET","path":"/api"}

Thanks

[prashantv]

This isn't possible for reflected objects (as the encoder interface takes the object to reflect and decides how to encode it, not zap, and the encoder wraps the fields in an object), but it is possible if:

• We add a new InlineObject feature in zap, which I have a simple PoC for.
• The struct implements zap.ObjectMarshaler.

Here's a small example showing it in action:

type request struct {
	URL string
	IP  string
}

func (r request) MarshalLogObject(enc zapcore.ObjectEncoder) error {
	enc.AddString("url", r.URL)
	enc.AddString("ip", r.IP)
	return nil
}

func ExampleObject() {
	logger := zap.NewExample()
	defer logger.Sync()

	req := &request{"/test", "127.0.0.1"}
	logger.Info("new request, in nested object", zap.Object("req", req))
	logger.Info("new request, inline", zap.InlineObject(req))
	// Output:
	// {"level":"info","msg":"new request, in nested object","req":{"url":"/test","ip":"127.0.0.1"}}
	// {"level":"info","msg":"new request, inline","url":"/test","ip":"127.0.0.1"}
}

If this seems useful, I can add tests and make a PR out of it.

cc @abhinav Does this seem generally useful?

[dharmjit]

This can be useful if applications need to have strict custom logging schema.

[prashantv]

This is now possible using zap.Inline, please see #912 for the implementation along with examples + tests.