- JSON Structured logging
- Logger with format method(printf-style)
- Development mode with human-friendly output
- WithCallerSkip to skip caller
- Context extractor for Record context
- Custom time formatter for buildin attribute time value
More examples can be found in examples.
Because zlog implements the slog.Handler interface, you can create a zlog.JSONHander and use slog.Logger.
import (
"context"
"log/slog"
"github.com/icefed/zlog"
)
func main() {
h := zlog.NewJSONHandler(&zlog.Config{
HandlerOptions: slog.HandlerOptions{
Level: slog.LevelDebug,
},
})
log := slog.New(h)
log.Info("hello world")
// ...
log.With(slog.String("app", "test")).
Error("db execution failed", "error", err)
log.LogAttrs(context.Background(), slog.LevelInfo, "this is a info message", slog.String("app", "test"))
}Or you can use zlog.Logger, which implements all slog.Logger methods and is compatible. Then you can use Infof and other methods that support format format.
import (
"context"
"log/slog"
"github.com/icefed/zlog"
)
func main() {
h := zlog.NewJSONHandler(&zlog.Config{
HandlerOptions: slog.HandlerOptions{
Level: slog.LevelDebug,
},
})
log := zlog.New(h)
log.Info("hello world")
log.Log(context.Background(), slog.LevelInfo, "this is a info message")
// ...
log.Debugf("get value %s from map by key %s", v, k)
}Development mode, like zap development, outputs buildin attributes in Text format for better readability. If development mode is enabled and writer is a terminal, the level field will be printed in color.
package main
import (
"log/slog"
"github.com/icefed/zlog"
)
func main() {
// start development mode with Config
h := zlog.NewJSONHandler(&zlog.Config{
HandlerOptions: slog.HandlerOptions{
Level: slog.LevelDebug,
},
Development: true,
})
// turn on development mode with WithOptions
h = h.WithOptions(zlog.WithDevelopment(true))
log := zlog.New(h)
log.Debug("Processing data file", "file", "data.json")
log.Info("Application started successfully",
slog.String("version", "1.0.0"),
slog.String("environment", "dev"))
log.Warn("Deprecated method 'foo()' is being used", slog.Int("warning_code", 123))
log.Error("Failed to connect to the database", "error_code", 500, "component", "DatabaseConnection")
}Outputs:
Set StacktraceEnabled to true to enable printing log stack trace, the default print slog.LevelError above the level,
h := zlog.NewJSONHandler(&zlog.Config{
HandlerOptions: slog.HandlerOptions{
Level: slog.LevelDebug,
},
StacktraceEnabled: true,
})
// set custom stacktrace key
h = h.WithOptions(zlog.WithStacktraceKey("stack"))By default, when printing logs, the time field is formatted with RFC3339Milli(2006-01-02T15:04:05.999Z07:00). If you want to modify the format, you can configure TimeFormatter in Config.
h := zlog.NewJSONHandler(&zlog.Config{
HandlerOptions: slog.HandlerOptions{
Level: slog.LevelDebug,
},
TimeFormatter: func(buf []byte,t time.Time) []byte {
return t.AppendFormat(buf, time.RFC3339Nano)
},
})
log := zlog.New(h)
log.Info("this is a log message with RFC3339Nano format")
// use int timestamp format with microsecond precision
log = log.WithOptions(zlog.WithTimeFormatter(func(buf []byte, t time.Time) []byte {
return strconv.AppendInt(buf, t.UnixMicro(), 10)
}))
log.Info("this is a log message in int timestamp format")Outputs:
{"time":"2023-09-09T19:02:28.704746+08:00","level":"INFO","msg":"this is a log message with RFC3339Nano format"}
{"time":"1694257348705059","level":"INFO","msg":"this is a log message with int timestamp format"}
We often need to extract the value from the context and print it to the log, for example, an apiserver receives a user request and prints trace and user information to the log.
This example shows how to use the context, and print OpenTelemetry trace in log. If you have an api server that supports OpenTelemetry, you can use this example in your handler middleware and print trace in each log.
package main
import (
"context"
"log/slog"
"go.opentelemetry.io/otel"
sdktrace "go.opentelemetry.io/otel/sdk/trace"
"go.opentelemetry.io/otel/sdk/trace/tracetest"
"go.opentelemetry.io/otel/trace"
"github.com/icefed/zlog"
)
// traceContextExtractor implement the ContextExtractor, extracts trace context from context
func traceContextExtractor(ctx context.Context) []slog.Attr {
spanContext := trace.SpanContextFromContext(ctx)
if spanContext.IsValid() {
return []slog.Attr{
slog.Group("trace",
slog.String("traceID", spanContext.TraceID().String()),
slog.String("spanID", spanContext.SpanID().String()),
),
}
}
return nil
}
func parentFun(ctx context.Context, tracer trace.Tracer) {
ctx, parentSpan := tracer.Start(ctx, "caller1")
defer parentSpan.End()
// print log
slog.InfoContext(ctx, "call parentFun")
childFun(ctx, tracer)
}
func childFun(ctx context.Context, tracer trace.Tracer) {
ctx, childSpan := tracer.Start(ctx, "caller2")
defer childSpan.End()
// print log
slog.InfoContext(ctx, "call childFun")
}
func main() {
// create a logger with traceContextExtractor
h := zlog.NewJSONHandler(nil)
h = h.WithOptions(zlog.WithContextExtractor(traceContextExtractor))
log := slog.New(h)
slog.SetDefault(log)
// prepare a call with trace context
exporter := tracetest.NewInMemoryExporter()
tracerProvider := sdktrace.NewTracerProvider(
sdktrace.WithBatcher(exporter),
)
otel.SetTracerProvider(tracerProvider)
tracer := otel.Tracer("api")
ctx := context.Background()
parentFun(ctx, tracer)
}Outputs:
{"time":"2023-09-08T20:12:14.733","level":"INFO","msg":"call parentFun","trace":{"traceID":"95f0717d9da16177176efdbc7c06bfbd","spanID":"7718edf7b2a8388d"}}
{"time":"2023-09-08T20:12:14.733","level":"INFO","msg":"call childFun","trace":{"traceID":"95f0717d9da16177176efdbc7c06bfbd","spanID":"ef83f673951742b0"}}
Test modified from zap benchmarking suite.
goos: darwin
goarch: arm64
pkg: github.com/icefed/zlog/benchmarks
BenchmarkDisabledWithoutFields/slog-10 1000000000 0.6019 ns/op 0 B/op 0 allocs/op
BenchmarkDisabledWithoutFields/slog_with_zlog-10 1000000000 0.5913 ns/op 0 B/op 0 allocs/op
BenchmarkDisabledWithoutFields/zlog-10 1000000000 0.5496 ns/op 0 B/op 0 allocs/op
BenchmarkDisabledWithoutFields/slog_with_zap-10 1000000000 0.8184 ns/op 0 B/op 0 allocs/op
BenchmarkDisabledWithoutFields/zap-10 1000000000 0.6048 ns/op 0 B/op 0 allocs/op
BenchmarkDisabledWithoutFields/zerolog-10 1000000000 0.3016 ns/op 0 B/op 0 allocs/op
BenchmarkDisabledAddingFields/slog-10 57371786 208.7 ns/op 576 B/op 6 allocs/op
BenchmarkDisabledAddingFields/slog_with_zlog-10 56256844 208.3 ns/op 576 B/op 6 allocs/op
BenchmarkDisabledAddingFields/zlog-10 58574133 205.8 ns/op 576 B/op 6 allocs/op
BenchmarkDisabledAddingFields/slog_with_zap-10 58468917 206.9 ns/op 576 B/op 6 allocs/op
BenchmarkDisabledAddingFields/zap-10 41587197 295.7 ns/op 864 B/op 6 allocs/op
BenchmarkDisabledAddingFields/zerolog-10 303398799 39.08 ns/op 88 B/op 2 allocs/op
BenchmarkWithoutFields/slog-10 47158194 231.9 ns/op 0 B/op 0 allocs/op
BenchmarkWithoutFields/slog_with_zlog-10 143867673 81.77 ns/op 0 B/op 0 allocs/op
BenchmarkWithoutFields/zlog-10 182174908 64.98 ns/op 0 B/op 0 allocs/op
BenchmarkWithoutFields/slog_with_zap-10 125818678 95.04 ns/op 0 B/op 0 allocs/op
BenchmarkWithoutFields/zap-10 169056685 72.34 ns/op 0 B/op 0 allocs/op
BenchmarkWithoutFields/zerolog-10 348895234 35.03 ns/op 0 B/op 0 allocs/op
BenchmarkAccumulatedContext/slog-10 51551946 241.8 ns/op 0 B/op 0 allocs/op
BenchmarkAccumulatedContext/slog_with_zlog-10 138282912 90.81 ns/op 0 B/op 0 allocs/op
BenchmarkAccumulatedContext/zlog-10 184607311 66.28 ns/op 0 B/op 0 allocs/op
BenchmarkAccumulatedContext/slog_with_zap-10 132471319 89.32 ns/op 0 B/op 0 allocs/op
BenchmarkAccumulatedContext/zap-10 167639162 76.73 ns/op 0 B/op 0 allocs/op
BenchmarkAccumulatedContext/zerolog-10 314418170 36.53 ns/op 0 B/op 0 allocs/op
BenchmarkAddingFields/slog-10 4498432 2639 ns/op 3951 B/op 38 allocs/op
BenchmarkAddingFields/slog_with_zlog-10 9287110 1300 ns/op 1344 B/op 20 allocs/op
BenchmarkAddingFields/zlog-10 9383146 1290 ns/op 1344 B/op 20 allocs/op
BenchmarkAddingFields/slog_with_zap-10 6758552 1776 ns/op 2218 B/op 23 allocs/op
BenchmarkAddingFields/zap-10 8615821 1389 ns/op 1508 B/op 18 allocs/op
BenchmarkAddingFields/zerolog-10 9067814 1309 ns/op 2031 B/op 15 allocs/op
BenchmarkKVArgs/slog-10 4663335 2562 ns/op 3586 B/op 40 allocs/op
BenchmarkKVArgs/slog_with_zlog-10 9989289 1186 ns/op 978 B/op 22 allocs/op
BenchmarkKVArgs/zlog-10 10343742 1171 ns/op 978 B/op 22 allocs/op
BenchmarkKVArgs/slog_with_zap-10 7146567 1661 ns/op 1851 B/op 25 allocs/op
BenchmarkKVArgs/zap-10 6913246 1730 ns/op 2352 B/op 24 allocs/op
BenchmarkKVArgs/zerolog-10 4937739 2431 ns/op 3355 B/op 40 allocs/op
PASS
ok github.com/icefed/zlog/benchmarks 471.856s