janisz / zapr

A logr implementation using Zap

Zapr ⚡

A logr implementation using Zap. Can also be used as slog handler.

Usage

Via logr:

package main

import (
    "fmt"

    "go.uber.org/zap"
    "github.com/go-logr/logr"
    "github.com/go-logr/zapr"
)

func main() {
    var log logr.Logger

    zapLog, err := zap.NewDevelopment()
    if err != nil {
        panic(fmt.Sprintf("who watches the watchmen (%v)?", err))
    }
    log = zapr.NewLogger(zapLog)

    log.Info("Logr in action!", "the answer", 42)
}

Via slog:

package main

import (
	"fmt"
	"log/slog"

	"github.com/go-logr/logr/slogr"
	"github.com/go-logr/zapr"
	"go.uber.org/zap"
)

func main() {
	var log *slog.Logger

	zapLog, err := zap.NewDevelopment()
	if err != nil {
		panic(fmt.Sprintf("who watches the watchmen (%v)?", err))
	}
	log = slog.New(slogr.NewSlogHandler(zapr.NewLogger(zapLog)))

	log.Info("Logr in action!", "the answer", 42)
}

Increasing Verbosity

Zap uses semantically named levels for logging (DebugLevel, InfoLevel, WarningLevel, ...). Logr uses arbitrary numeric levels. By default logr's V(0) is zap's InfoLevel and V(1) is zap's DebugLevel (which is numerically -1). Zap does not have named levels that are more verbose than DebugLevel, but it's possible to fake it.

As of zap v1.19.0 you can do something like the following in your setup code:

    zc := zap.NewProductionConfig()
    zc.Level = zap.NewAtomicLevelAt(zapcore.Level(-2))
    z, err := zc.Build()
    if err != nil {
        // ...
    }
    log := zapr.NewLogger(z)

Zap's levels get more verbose as the number gets smaller and more important and the number gets larger (DebugLevel is -1, InfoLevel is 0, WarnLevel is 1, and so on).

The -2 in the above snippet means that log.V(2).Info() calls will be active. -3 would enable log.V(3).Info(), etc. Note that zap's levels are int8 which means the most verbose level you can give it is -128. The zapr implementation will cap V() levels greater than 127 to 127, so setting the zap level to -128 really means "activate all logs".

Implementation Details

For the most part, concepts in Zap correspond directly with those in logr.

Unlike Zap, all fields must be in the form of sugared fields -- it's illegal to pass a strongly-typed Zap field in a key position to any of the logging methods (Log, Error).

The zapr logr.LogSink implementation also implements logr.SlogHandler. That enables slogr.NewSlogHandler to provide a slog.Handler which just passes parameters through to zapr. zapr handles special slog values (Group, LogValuer), regardless of which front-end API is used.