From: Daniel Swarbrick <dswarbrick@debian.org>
Date: Wed, 12 Feb 2025 16:11:36 +0100
Subject: Reinstate promlog package

Forwarded: not-needed
Last-Update: 2025-02-12

Some exporters have not yet migrated to the promslog package and still
depend on the older promlog wrapper. This patch can be dropped once all
downstream dependencies have migrated to promslog.
---
 promlog/flag/flag.go |  53 ++++++++++++++
 promlog/log.go       | 196 +++++++++++++++++++++++++++++++++++++++++++++++++++
 promlog/log_test.go  | 113 +++++++++++++++++++++++++++++
 3 files changed, 362 insertions(+)
 create mode 100644 promlog/flag/flag.go
 create mode 100644 promlog/log.go
 create mode 100644 promlog/log_test.go

diff --git a/promlog/flag/flag.go b/promlog/flag/flag.go
new file mode 100644
index 0000000..7c3f1d6
--- /dev/null
+++ b/promlog/flag/flag.go
@@ -0,0 +1,53 @@
+// Copyright 2017 The Prometheus Authors
+// 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.
+
+// Deprecated: This package has been deprecated in favor of migrating to
+// `github.com/prometheus/common/promslog` which uses the Go standard library
+// `log/slog` package.
+package flag
+
+import (
+	"strings"
+
+	kingpin "gopkg.in/alecthomas/kingpin.v2"
+
+	"github.com/prometheus/common/promlog" //nolint:staticcheck
+)
+
+// LevelFlagName is the canonical flag name to configure the allowed log level
+// within Prometheus projects.
+const LevelFlagName = "log.level"
+
+// LevelFlagHelp is the help description for the log.level flag.
+var LevelFlagHelp = "Only log messages with the given severity or above. One of: [" + strings.Join(promlog.LevelFlagOptions, ", ") + "]"
+
+// FormatFlagName is the canonical flag name to configure the log format
+// within Prometheus projects.
+const FormatFlagName = "log.format"
+
+// FormatFlagHelp is the help description for the log.format flag.
+var FormatFlagHelp = "Output format of log messages. One of: [" + strings.Join(promlog.FormatFlagOptions, ", ") + "]"
+
+// AddFlags adds the flags used by this package to the Kingpin application.
+// To use the default Kingpin application, call AddFlags(kingpin.CommandLine)
+func AddFlags(a *kingpin.Application, config *promlog.Config) {
+	config.Level = &promlog.AllowedLevel{}
+	a.Flag(LevelFlagName, LevelFlagHelp).
+		Default("info").HintOptions(promlog.LevelFlagOptions...).
+		SetValue(config.Level)
+
+	config.Format = &promlog.AllowedFormat{}
+	a.Flag(FormatFlagName, FormatFlagHelp).
+		Default("logfmt").HintOptions(promlog.FormatFlagOptions...).
+		SetValue(config.Format)
+}
diff --git a/promlog/log.go b/promlog/log.go
new file mode 100644
index 0000000..24a1162
--- /dev/null
+++ b/promlog/log.go
@@ -0,0 +1,196 @@
+// Copyright 2017 The Prometheus Authors
+// 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 promlog defines standardised ways to initialize Go kit loggers
+// across Prometheus components.
+// It should typically only ever be imported by main packages.
+//
+// Deprecated: This package has been deprecated in favor of migrating to
+// `github.com/prometheus/common/promslog` which uses the Go standard library
+// `log/slog` package.
+package promlog
+
+import (
+	"fmt"
+	"os"
+	"sync"
+	"time"
+
+	"github.com/go-kit/log"
+	"github.com/go-kit/log/level"
+)
+
+var (
+	// This timestamp format differs from RFC3339Nano by using .000 instead
+	// of .999999999 which changes the timestamp from 9 variable to 3 fixed
+	// decimals (.130 instead of .130987456).
+	timestampFormat = log.TimestampFormat(
+		func() time.Time { return time.Now().UTC() },
+		"2006-01-02T15:04:05.000Z07:00",
+	)
+
+	LevelFlagOptions  = []string{"debug", "info", "warn", "error"}
+	FormatFlagOptions = []string{"logfmt", "json"}
+)
+
+// AllowedLevel is a settable identifier for the minimum level a log entry
+// must be have.
+type AllowedLevel struct {
+	s string
+	o level.Option
+}
+
+func (l *AllowedLevel) UnmarshalYAML(unmarshal func(interface{}) error) error {
+	var s string
+	type plain string
+	if err := unmarshal((*plain)(&s)); err != nil {
+		return err
+	}
+	if s == "" {
+		return nil
+	}
+	lo := &AllowedLevel{}
+	if err := lo.Set(s); err != nil {
+		return err
+	}
+	*l = *lo
+	return nil
+}
+
+func (l *AllowedLevel) String() string {
+	return l.s
+}
+
+// Set updates the value of the allowed level.
+func (l *AllowedLevel) Set(s string) error {
+	switch s {
+	case "debug":
+		l.o = level.AllowDebug()
+	case "info":
+		l.o = level.AllowInfo()
+	case "warn":
+		l.o = level.AllowWarn()
+	case "error":
+		l.o = level.AllowError()
+	default:
+		return fmt.Errorf("unrecognized log level %q", s)
+	}
+	l.s = s
+	return nil
+}
+
+// AllowedFormat is a settable identifier for the output format that the logger can have.
+type AllowedFormat struct {
+	s string
+}
+
+func (f *AllowedFormat) String() string {
+	return f.s
+}
+
+// Set updates the value of the allowed format.
+func (f *AllowedFormat) Set(s string) error {
+	switch s {
+	case "logfmt", "json":
+		f.s = s
+	default:
+		return fmt.Errorf("unrecognized log format %q", s)
+	}
+	return nil
+}
+
+// Config is a struct containing configurable settings for the logger
+type Config struct {
+	Level  *AllowedLevel
+	Format *AllowedFormat
+}
+
+// New returns a new leveled oklog logger. Each logged line will be annotated
+// with a timestamp. The output always goes to stderr.
+func New(config *Config) log.Logger {
+	if config.Format != nil && config.Format.s == "json" {
+		return NewWithLogger(log.NewJSONLogger(log.NewSyncWriter(os.Stderr)), config)
+	}
+
+	return NewWithLogger(log.NewLogfmtLogger(log.NewSyncWriter(os.Stderr)), config)
+}
+
+// NewWithLogger returns a new leveled oklog logger with a custom log.Logger.
+// Each logged line will be annotated with a timestamp.
+func NewWithLogger(l log.Logger, config *Config) log.Logger {
+	if config.Level != nil {
+		l = log.With(l, "ts", timestampFormat, "caller", log.Caller(5))
+		l = level.NewFilter(l, config.Level.o)
+	} else {
+		l = log.With(l, "ts", timestampFormat, "caller", log.DefaultCaller)
+	}
+	return l
+}
+
+// NewDynamic returns a new leveled logger. Each logged line will be annotated
+// with a timestamp. The output always goes to stderr. Some properties can be
+// changed, like the level.
+func NewDynamic(config *Config) *logger {
+	if config.Format != nil && config.Format.s == "json" {
+		return NewDynamicWithLogger(log.NewJSONLogger(log.NewSyncWriter(os.Stderr)), config)
+	}
+
+	return NewDynamicWithLogger(log.NewLogfmtLogger(log.NewSyncWriter(os.Stderr)), config)
+}
+
+// NewDynamicWithLogger returns a new leveled logger with a custom io.Writer.
+// Each logged line will be annotated with a timestamp.
+// Some properties can be changed, like the level.
+func NewDynamicWithLogger(l log.Logger, config *Config) *logger {
+	lo := &logger{
+		base:    l,
+		leveled: l,
+	}
+
+	if config.Level != nil {
+		lo.SetLevel(config.Level)
+	}
+
+	return lo
+}
+
+type logger struct {
+	base         log.Logger
+	leveled      log.Logger
+	currentLevel *AllowedLevel
+	mtx          sync.Mutex
+}
+
+// Log implements logger.Log.
+func (l *logger) Log(keyvals ...interface{}) error {
+	l.mtx.Lock()
+	defer l.mtx.Unlock()
+	return l.leveled.Log(keyvals...)
+}
+
+// SetLevel changes the log level.
+func (l *logger) SetLevel(lvl *AllowedLevel) {
+	l.mtx.Lock()
+	defer l.mtx.Unlock()
+	if lvl == nil {
+		l.leveled = log.With(l.base, "ts", timestampFormat, "caller", log.DefaultCaller)
+		l.currentLevel = nil
+		return
+	}
+
+	if l.currentLevel != nil && l.currentLevel.s != lvl.s {
+		_ = l.base.Log("msg", "Log level changed", "prev", l.currentLevel, "current", lvl)
+	}
+	l.currentLevel = lvl
+	l.leveled = level.NewFilter(log.With(l.base, "ts", timestampFormat, "caller", log.Caller(5)), lvl.o)
+}
diff --git a/promlog/log_test.go b/promlog/log_test.go
new file mode 100644
index 0000000..395e051
--- /dev/null
+++ b/promlog/log_test.go
@@ -0,0 +1,113 @@
+// Copyright 2020 The Prometheus Authors
+// 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 promlog
+
+import (
+	"fmt"
+	"testing"
+
+	"github.com/go-kit/log/level"
+	"github.com/stretchr/testify/require"
+	"gopkg.in/yaml.v2"
+)
+
+// Make sure creating and using a logger with an empty configuration doesn't
+// result in a panic.
+func TestDefaultConfig(t *testing.T) {
+	logger := New(&Config{})
+
+	err := logger.Log("hello", "world")
+	require.NoError(t, err)
+}
+
+func TestUnmarshallLevel(t *testing.T) {
+	l := &AllowedLevel{}
+	err := yaml.Unmarshal([]byte(`debug`), l)
+	if err != nil {
+		t.Error(err)
+	}
+	if l.s != "debug" {
+		t.Errorf("expected %s, got %s", "debug", l.s)
+	}
+}
+
+func TestUnmarshallEmptyLevel(t *testing.T) {
+	l := &AllowedLevel{}
+	err := yaml.Unmarshal([]byte(``), l)
+	if err != nil {
+		t.Error(err)
+	}
+	if l.s != "" {
+		t.Errorf("expected empty level, got %s", l.s)
+	}
+}
+
+func TestUnmarshallBadLevel(t *testing.T) {
+	l := &AllowedLevel{}
+	err := yaml.Unmarshal([]byte(`debugg`), l)
+	if err == nil {
+		t.Error("expected error")
+	}
+	expErr := `unrecognized log level "debugg"`
+	if err.Error() != expErr {
+		t.Errorf("expected error %s, got %s", expErr, err.Error())
+	}
+	if l.s != "" {
+		t.Errorf("expected empty level, got %s", l.s)
+	}
+}
+
+type recordKeyvalLogger struct {
+	count int
+}
+
+func (r *recordKeyvalLogger) Log(keyvals ...interface{}) error {
+	for _, v := range keyvals {
+		if fmt.Sprintf("%v", v) == "Log level changed" {
+			return nil
+		}
+	}
+	r.count++
+	return nil
+}
+
+func TestDynamic(t *testing.T) {
+	logger := NewDynamic(&Config{})
+
+	debugLevel := &AllowedLevel{}
+	err := debugLevel.Set("debug")
+	require.NoError(t, err)
+	infoLevel := &AllowedLevel{}
+	err = infoLevel.Set("info")
+	require.NoError(t, err)
+
+	recorder := &recordKeyvalLogger{}
+	logger.base = recorder
+	logger.SetLevel(debugLevel)
+	err = level.Debug(logger).Log("hello", "world")
+	require.NoError(t, err)
+	require.Equalf(t, 1, recorder.count, "log not found")
+
+	recorder.count = 0
+	logger.SetLevel(infoLevel)
+	err = level.Debug(logger).Log("hello", "world")
+	require.NoError(t, err)
+	require.Equalf(t, 0, recorder.count, "log found")
+	err = level.Info(logger).Log("hello", "world")
+	require.NoError(t, err)
+	require.Equalf(t, 1, recorder.count, "log not found")
+	err = level.Debug(logger).Log("hello", "world")
+	require.NoError(t, err)
+	require.Equalf(t, 1, recorder.count, "extra log found")
+}