feat(log): add slog-backed Logger type (#22347)

log/CHANGELOG.md

@@ -25,6 +25,7 @@ Each entry must include the Github issue reference in the following format:
 ### Improvements
 
 * [#22233](https://github.com/cosmos/cosmos-sdk/pull/22233) Use sonic json library for faster json handling
+* [#22347](https://github.com/cosmos/cosmos-sdk/pull/22347) Add cosmossdk.io/log/slog to allow using a standard library log/slog-backed logger.
 
 ## [v1.4.1](https://github.com/cosmos/cosmos-sdk/releases/tag/log/v1.4.1) - 2024-08-16
 

log/README.md

@@ -1,3 +1,5 @@
 # Log
 
 The `cosmossdk.io/log` provides a zerolog logging implementation for the Cosmos SDK and Cosmos SDK modules.
+
+To use a logger wrapping an instance of the standard library's `log/slog` package, use `cosmossdk.io/log/slog`.

log/slog/logger.go

@@ -0,0 +1,50 @@
+// Package slog contains a Logger type that satisfies [cosmossdk.io/log.Logger],
+// backed by a standard library [*log/slog.Logger].
+package slog
+
+import (
+	"log/slog"
+
+	"cosmossdk.io/log"
+)
+
+var _ log.Logger = Logger{}
+
+// Logger satisfies [log.Logger] with logging backed by
+// an instance of [*slog.Logger].
+type Logger struct {
+	log *slog.Logger
+}
+
+// NewCustomLogger returns a Logger backed by an existing slog.Logger instance.
+// All logging methods are called directly on the *slog.Logger;
+// therefore it is the caller's responsibility to configure message filtering,
+// level filtering, output format, and so on.
+func NewCustomLogger(log *slog.Logger) Logger {
+	return Logger{log: log}
+}
+
+func (l Logger) Info(msg string, keyVals ...any) {
+	l.log.Info(msg, keyVals...)
+}
+
+func (l Logger) Warn(msg string, keyVals ...any) {
+	l.log.Warn(msg, keyVals...)
+}
+
+func (l Logger) Error(msg string, keyVals ...any) {
+	l.log.Error(msg, keyVals...)
+}
+
+func (l Logger) Debug(msg string, keyVals ...any) {
+	l.log.Debug(msg, keyVals...)
+}
+
+func (l Logger) With(keyVals ...any) log.Logger {
+	return Logger{log: l.log.With(keyVals...)}
+}
+
+// Impl returns l's underlying [*slog.Logger].
+func (l Logger) Impl() any {
+	return l.log
+}

log/slog/logger_test.go

@@ -0,0 +1,92 @@
+package slog_test
+
+import (
+	"bytes"
+	"encoding/json"
+	stdslog "log/slog"
+	"testing"
+
+	"cosmossdk.io/log/slog"
+)
+
+func TestSlog(t *testing.T) {
+	var buf bytes.Buffer
+	h := stdslog.NewJSONHandler(&buf, &stdslog.HandlerOptions{
+		Level: stdslog.LevelDebug,
+	})
+	logger := slog.NewCustomLogger(stdslog.New(h))
+
+	type logLine struct {
+		Level string `json:"level"`
+		Msg   string `json:"msg"`
+		Num   int    `json:"num"`
+	}
+
+	var line logLine
+
+	logger.Debug("Message one", "num", 1)
+	if err := json.Unmarshal(buf.Bytes(), &line); err != nil {
+		t.Fatal(err)
+	}
+	if want := (logLine{
+		Level: stdslog.LevelDebug.String(),
+		Msg:   "Message one",
+		Num:   1,
+	}); want != line {
+		t.Fatalf("unexpected log record: want %v, got %v", want, line)
+	}
+
+	buf.Reset()
+	logger.Info("Message two", "num", 2)
+	if err := json.Unmarshal(buf.Bytes(), &line); err != nil {
+		t.Fatal(err)
+	}
+	if want := (logLine{
+		Level: stdslog.LevelInfo.String(),
+		Msg:   "Message two",
+		Num:   2,
+	}); want != line {
+		t.Fatalf("unexpected log record: want %v, got %v", want, line)
+	}
+
+	buf.Reset()
+	logger.Warn("Message three", "num", 3)
+	if err := json.Unmarshal(buf.Bytes(), &line); err != nil {
+		t.Fatal(err)
+	}
+	if want := (logLine{
+		Level: stdslog.LevelWarn.String(),
+		Msg:   "Message three",
+		Num:   3,
+	}); want != line {
+		t.Fatalf("unexpected log record: want %v, got %v", want, line)
+	}
+
+	buf.Reset()
+	logger.Error("Message four", "num", 4)
+	if err := json.Unmarshal(buf.Bytes(), &line); err != nil {
+		t.Fatal(err)
+	}
+	if want := (logLine{
+		Level: stdslog.LevelError.String(),
+		Msg:   "Message four",
+		Num:   4,
+	}); want != line {
+		t.Fatalf("unexpected log record: want %v, got %v", want, line)
+	}
+
+	wLogger := logger.With("num", 5)
+	buf.Reset()
+	wLogger.Info("Using .With")
+
+	if err := json.Unmarshal(buf.Bytes(), &line); err != nil {
+		t.Fatal(err)
+	}
+	if want := (logLine{
+		Level: stdslog.LevelInfo.String(),
+		Msg:   "Using .With",
+		Num:   5,
+	}); want != line {
+		t.Fatalf("unexpected log record: want %v, got %v", want, line)
+	}
+}