handler.go•4.43 kB
// Copyright 2024 Google LLC
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package log
import (
"context"
"fmt"
"io"
"log/slog"
"sync"
"time"
"go.opentelemetry.io/otel/trace"
)
// ValueTextHandler is a [Handler] that writes Records to an [io.Writer] with values separated by spaces.
type ValueTextHandler struct {
h slog.Handler
mu *sync.Mutex
out io.Writer
}
// NewValueTextHandler creates a [ValueTextHandler] that writes to out, using the given options.
func NewValueTextHandler(out io.Writer, opts *slog.HandlerOptions) *ValueTextHandler {
if opts == nil {
opts = &slog.HandlerOptions{}
}
return &ValueTextHandler{
out: out,
h: slog.NewTextHandler(out, &slog.HandlerOptions{
Level: opts.Level,
AddSource: opts.AddSource,
ReplaceAttr: nil,
}),
mu: &sync.Mutex{},
}
}
func (h *ValueTextHandler) Enabled(ctx context.Context, level slog.Level) bool {
return h.h.Enabled(ctx, level)
}
func (h *ValueTextHandler) WithAttrs(attrs []slog.Attr) slog.Handler {
return &ValueTextHandler{h: h.h.WithAttrs(attrs), out: h.out, mu: h.mu}
}
func (h *ValueTextHandler) WithGroup(name string) slog.Handler {
return &ValueTextHandler{h: h.h.WithGroup(name), out: h.out, mu: h.mu}
}
// Handle formats its argument [Record] as a single line of space-separated values.
// Example output format: 2024-11-12T15:08:11.451377-08:00 INFO "Initialized 0 sources.\n"
func (h *ValueTextHandler) Handle(ctx context.Context, r slog.Record) error {
buf := make([]byte, 0, 1024)
// time
if !r.Time.IsZero() {
buf = h.appendAttr(buf, slog.Time(slog.TimeKey, r.Time))
}
// level
buf = h.appendAttr(buf, slog.Any(slog.LevelKey, r.Level))
// message
buf = h.appendAttr(buf, slog.String(slog.MessageKey, r.Message))
r.Attrs(func(a slog.Attr) bool {
buf = h.appendAttr(buf, a)
return true
})
buf = append(buf, "\n"...)
h.mu.Lock()
defer h.mu.Unlock()
_, err := h.out.Write(buf)
return err
}
// appendAttr is responsible for formatting a single attribute
func (h *ValueTextHandler) appendAttr(buf []byte, a slog.Attr) []byte {
// Resolve the Attr's value before doing anything else.
a.Value = a.Value.Resolve()
// Ignore empty Attrs.
if a.Equal(slog.Attr{}) {
return buf
}
switch a.Value.Kind() {
case slog.KindString:
// Quote string values, to make them easy to parse.
buf = fmt.Appendf(buf, "%q ", a.Value.String())
case slog.KindTime:
// Write times in a standard way, without the monotonic time.
buf = fmt.Appendf(buf, "%s ", a.Value.Time().Format(time.RFC3339Nano))
case slog.KindGroup:
attrs := a.Value.Group()
// Ignore empty groups.
if len(attrs) == 0 {
return buf
}
for _, ga := range attrs {
buf = h.appendAttr(buf, ga)
}
default:
buf = fmt.Appendf(buf, "%s ", a.Value)
}
return buf
}
// spanContextLogHandler is an slog.Handler which adds attributes from the span
// context.
type spanContextLogHandler struct {
slog.Handler
}
// handlerWithSpanContext adds attributes from the span context.
func handlerWithSpanContext(handler slog.Handler) *spanContextLogHandler {
return &spanContextLogHandler{Handler: handler}
}
// Handle overrides slog.Handler's Handle method. This adds attributes from the
// span context to the slog.Record.
func (t *spanContextLogHandler) Handle(ctx context.Context, record slog.Record) error {
// Get the SpanContext from the golang Context.
if s := trace.SpanContextFromContext(ctx); s.IsValid() {
// Add trace context attributes following Cloud Logging structured log format described
// in https://cloud.google.com/logging/docs/structured-logging#special-payload-fields
record.AddAttrs(
slog.Any("logging.googleapis.com/trace", s.TraceID()),
)
record.AddAttrs(
slog.Any("logging.googleapis.com/spanId", s.SpanID()),
)
record.AddAttrs(
slog.Bool("logging.googleapis.com/trace_sampled", s.TraceFlags().IsSampled()),
)
}
return t.Handler.Handle(ctx, record)
}