🚀 [Feature]: fiberzap accepts custom fields

[mirusky]

Feature Description

I'd like to have a custom field that are user defined zap.Fields.

• For custom structured logging
• To add user defined fields
• Support different entry formats, etc.

Additional Context (optional)

Currently I have an client that want's http headers response into the logging file, that's post processed later. They want all headers, now the fiberzap doesn't have an option for it. Instead of just adding a "respHeaders" field it'll be more extensible to add a custom field that are user definied fields

Code Snippet (optional)

package main

import (
	"log"

	"github.com/gofiber/contrib/fiberzap/v2"
	"github.com/gofiber/fiber/v2"
	"go.uber.org/zap"
)

func main() {
	app := fiber.New()
	logger, _ := zap.NewProduction()

	app.Use(fiberzap.New(fiberzap.Config{
		Logger: logger,
		Fields: []string{"custom"},
		CustomFieldFunc: func(c *fiber.Ctx) []zap.Field {
			var fields []zap.Field

			headers := make(map[string]interface{})

			c.Response().Header.VisitAll(func(k, v []byte) {
				headers[string(k)] = string(v)
			})

			fields = append(fields, zap.Any("headers", headers))

			return fields
		},
	}))

	app.Get("/", func(c *fiber.Ctx) error {
		return c.SendString("Hello, World!")
	})

	log.Fatal(app.Listen(":3000"))
}

Checklist:

• I agree to follow Fiber's Code of Conduct.
• I have checked for existing issues that describe my suggestion prior to opening this one.
• I understand that improperly formatted feature requests may be closed without explanation.

[Jamess-Lucass]

@mirusky Hi, I have literally just ran into a use case for this, have you started working on the feature at all? I don't want to intrude but I have written the code for it before I saw this open issue.

In my implementation I did opt for naming it FieldsFunc instead of CustomFieldsFunc

[Jamess-Lucass]

My use case was using this to inject trace ids into the log, so I can link together APM traces in kibana to specific log records eg.

FieldsFunc: func(c *fiber.Ctx) []zap.Field {
      tr := apm.TransactionFromContext(c.Context())
      traceId := tr.TraceContext().Trace.String()
      
      return []zap.Field{zap.String("trace.id", traceId)}
},

[mirusky]

@Jamess-Lucass I didn't started at all, busy week.

I liked your approach, I was thinking on just add a new case statement for custom and call it when user pass custom on fields values. But the way you did gives more flexibility.