# README
👞 clog
Context-aware slog
slog was added in Go 1.21, so using this requires Go 1.21 or later.
Usage
Context Logger
The context Logger can be used to use Loggers from the context. This is sometimes preferred over the Context Handler, since this can make it easier to use different loggers in different contexts (e.g. testing).
This approach is heavily inspired by
knative.dev/pkg/logging, but with zero dependencies outside the standard library (compare with pkg/logging's deps).
package main
import (
"context"
"log/slog"
"github.com/chainguard-dev/clog"
)
func main() {
// One-time setup
log := clog.New(slog.Default().Handler()).With("a", "b")
ctx := clog.WithLogger(context.Background(), log)
f(ctx)
}
func f(ctx context.Context) {
// Grab logger from context and use.
log := clog.FromContext(ctx)
log.Info("in f")
// Add logging context and pass on.
ctx = clog.WithLogger(ctx, log.With("f", "hello"))
g(ctx)
}
func g(ctx context.Context) {
// Grab logger from context and use.
log := clog.FromContext(ctx)
log.Info("in g")
// Package level context loggers are also aware
clog.ErrorContext(ctx, "asdf")
}
$ go run .
2009/11/10 23:00:00 INFO in f a=b
2009/11/10 23:00:00 INFO in g a=b f=hello
2009/11/10 23:00:00 ERROR asdf a=b f=hello
Testing
The slogtest package provides utilities to make it easy to create loggers that
will use the native testing logging.
func TestFoo(t *testing.T) {
ctx := slogtest.TestContextWithLogger(t)
for _, tc := range []string{"a", "b"} {
t.Run(tc, func(t *testing.T) {
clog.FromContext(ctx).Infof("hello world")
})
}
}
$ go test -v ./examples/logger
=== RUN TestLog
=== RUN TestLog/a
=== NAME TestLog
slogtest.go:20: time=2023-12-12T18:42:53.020-05:00 level=INFO msg="hello world"
=== RUN TestLog/b
=== NAME TestLog
slogtest.go:20: time=2023-12-12T18:42:53.020-05:00 level=INFO msg="hello world"
--- PASS: TestLog (0.00s)
--- PASS: TestLog/a (0.00s)
--- PASS: TestLog/b (0.00s)
PASS
ok github.com/chainguard-dev/clog/examples/logger
Context Handler
The context Handler can be used to insert values from the context.
func init() {
slog.SetDefault(slog.New(clog.NewHandler(slog.NewTextHandler(os.Stdout, nil))))
}
func main() {
ctx := context.Background()
ctx = clog.WithValues(ctx, "foo", "bar")
// Use slog package directly
slog.InfoContext(ctx, "hello world", slog.Bool("baz", true))
// glog / zap style (note: can't pass additional attributes)
clog.ErrorContextf(ctx, "hello %s", "world")
}
$ go run .
time=2009-11-10T23:00:00.000Z level=INFO msg="hello world" baz=true foo=bar
time=2009-11-10T23:00:00.000Z level=ERROR msg="hello world" foo=bar
Google Cloud Platform support
This package also provides a GCP-optimized JSON handler for structured logging and trace attribution.
See ./gcp/README.md for details.
# Functions
Debug calls Debug on the default logger.
DebugContext calls DebugContext on the context logger.
DebugContextf calls DebugContextf on the context logger.
Debugf calls Debugf on the default logger.
DefaultLogger returns a new logger that uses the default [slog.Logger].
Error calls Error on the default logger.
ErrorContext calls ErrorContext on the context logger.
ErrorContextf calls ErrorContextf on the context logger.
Errorf calls Errorf on the default logger.
Fatal calls Error on the default logger, then exits.
FatalContext calls ErrorContext on the context logger, then exits.
FatalContextf calls ErrorContextf on the context logger, then exits.
Fatalf calls Errorf on the default logger, then exits.
No description provided by the author
Info calls Info on the default logger.
InfoContext calls InfoContext on the context logger.
InfoContextf calls InfoContextf on the context logger.
Infof calls Infof on the default logger.
New returns a new logger that wraps the given [slog.Handler].
NewHandler configures a new context aware slog handler.
NewLogger returns a new logger that wraps the given [slog.Logger] with the default context.
NewLoggerWithContext returns a new logger that wraps the given [slog.Logger].
New returns a new logger that wraps the given [slog.Handler].
Warn calls Warn on the default logger.
WarnContext calls WarnContext on the context logger.
WarnContextf calls WarnContextf on the context logger.
Warnf calls Warnf on the default logger.
With calls [Logger.With] on the default logger.
No description provided by the author
With returns a new context with the given values.