go.uber.org/zap v1.26.0: RedirectStdLog

Clean-room public code sample — generation instructions

Write a brand-new, minimal, self-contained code sample in this clean-room directory.
Do not copy, paraphrase, or reference any existing project source. Work only from this spec.

A csx.json manifest scaffold already exists. Do not recreate it from memory. Preserve its case.goal, packages and symbols; fill its empty case.contract with exact assertions and correct its environment, commands and verifierAdapter for the files you generate.

Goal: verify zap.RedirectStdLog in pkg:golang/go.uber.org/zap@v1.26.0
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:golang/go.uber.org/zap@v1.26.0
Demonstrate these symbols/APIs:
  - zap.RedirectStdLog

Rules:
  - One focused purpose; the smallest project that proves the goal.
  - Include a contract test (test/contract.*) that runs OFFLINE and exits 0 exactly when the goal behavior works.
  - Pin every dependency with a lockfile so resolution is reproducible.
  - No secrets, credentials, or tokens. No real URLs (only example.com or localhost). No absolute paths.
  - No personal names, emails, company names, or project identifiers of any kind.
  - No binaries and no generated output (node_modules, dist, target, venv, .git, .env).
  - Keep it under 200 files and 256KB packed.

{"case":{"caseId":"case:sha256:4aa970a5732730a19335cc9fcb62dbd9a6536d74c08bfcf6f14ce978a6157c17","contract":["zap.RedirectStdLog redirects standard library log output to the zap logger at InfoLevel","invoking the returned restore function reinstates original log routing","zap.RedirectStdLog output is filtered when the zap logger level threshold is configured above InfoLevel"],"goal":"verify zap.RedirectStdLog in pkg:golang/go.uber.org/zap@v1.26.0","kind":"HOW","packages":["pkg:golang/go.uber.org/zap@v1.26.0"],"schemaVersion":1,"symbols":["zap.RedirectStdLog"]},"contractCommand":["go","run","./test"],"environment":{"arch":"x64","distro":"ubuntu","ecosystem":"golang","libc":"glibc","libcVersion":"2.39","os":"linux","osVersionBucket":"24","packageManager":"go","schemaVersion":1},"license":"MIT-0","packages":["pkg:golang/go.uber.org/zap@v1.26.0"],"schemaVersion":1,"subject":"pkg:golang/go.uber.org/zap@v1.26.0","symbols":["zap.RedirectStdLog"],"verifierAdapter":"golang@1"}

module example.com/zapredirect

go 1.22.0

require go.uber.org/zap v1.26.0

require go.uber.org/multierr v1.10.0 // indirect

go.uber.org/multierr v1.10.0 h1:S0h4aNzvfcFsC3dRF1jLoaov7oRaKqRGC/pUEJ2yvPQ=
go.uber.org/multierr v1.10.0/go.mod h1:20+QtiLqy0Nd6FdQB9TLXag12DsQkrbs3htMFfDN80Y=
go.uber.org/zap v1.26.0 h1:sI7k6L95XOKS281NhVKOFCUNIvv9e0w4BF8N3u+tCRo=
go.uber.org/zap v1.26.0/go.mod h1:dtElttAiwGvoJ/vj4IwHBS/gXsEu/pZ50mUIRWuG0so=

package zapredirect

import (
	"go.uber.org/zap"
)

// RedirectStandardLog redirects standard library log output to the provided zap logger at InfoLevel.
// It returns a restore function that reinstates original standard library log settings.
func RedirectStandardLog(logger *zap.Logger) func() {
	return zap.RedirectStdLog(logger)
}

{
  "schemaVersion": 1,
  "goal": "verify zap.RedirectStdLog in pkg:golang/go.uber.org/zap@v1.26.0",
  "kind": "HOW",
  "packages": [
    "pkg:golang/go.uber.org/zap@v1.26.0"
  ],
  "symbols": [
    "zap.RedirectStdLog"
  ]
}

package main

import (
	"bytes"
	"encoding/json"
	"fmt"
	"log"
	"os"
	"strings"

	"go.uber.org/zap"
	"go.uber.org/zap/zapcore"

	zapredirect "example.com/zapredirect"
)

type syncer struct {
	buf bytes.Buffer
}

func (s *syncer) Write(p []byte) (n int, err error) {
	return s.buf.Write(p)
}

func (s *syncer) Sync() error {
	return nil
}

func (s *syncer) Reset() {
	s.buf.Reset()
}

func (s *syncer) Lines() []string {
	raw := strings.TrimSpace(s.buf.String())
	if raw == "" {
		return nil
	}
	return strings.Split(raw, "\n")
}

func newLogger(level zapcore.LevelEnabler) (*zap.Logger, *syncer) {
	sink := &syncer{}
	encCfg := zapcore.EncoderConfig{
		MessageKey:     "msg",
		LevelKey:       "level",
		EncodeLevel:    zapcore.LowercaseLevelEncoder,
		EncodeDuration: zapcore.StringDurationEncoder,
	}
	core := zapcore.NewCore(
		zapcore.NewJSONEncoder(encCfg),
		sink,
		level,
	)
	return zap.New(core), sink
}

func parseLine(raw string) (map[string]interface{}, error) {
	var entry map[string]interface{}
	if err := json.Unmarshal([]byte(raw), &entry); err != nil {
		return nil, fmt.Errorf("failed to parse JSON log %q: %w", raw, err)
	}
	return entry, nil
}

func main() {
	// Assertion 1: zap.RedirectStdLog redirects standard library log output to the zap logger at InfoLevel
	logger, sink := newLogger(zapcore.DebugLevel)
	restore := zapredirect.RedirectStandardLog(logger)
	if restore == nil {
		fmt.Fprintln(os.Stderr, "FAIL: expected non-nil restore func from RedirectStdLog")
		os.Exit(1)
	}

	log.Print("contract test redirected message")

	lines := sink.Lines()
	if len(lines) != 1 {
		fmt.Fprintf(os.Stderr, "FAIL: expected 1 log line in sink, got %d\n", len(lines))
		os.Exit(1)
	}
	entry, err := parseLine(lines[0])
	if err != nil {
		fmt.Fprintf(os.Stderr, "FAIL: parsing log entry: %v\n", err)
		os.Exit(1)
	}
	if entry["level"] != "info" {
		fmt.Fprintf(os.Stderr, "FAIL: expected level 'info', got %v\n", entry["level"])
		os.Exit(1)
	}
	msg, _ := entry["msg"].(string)
	if !strings.Contains(msg, "contract test redirected message") {
		fmt.Fprintf(os.Stderr, "FAIL: expected msg to contain 'contract test redirected message', got %q\n", msg)
		os.Exit(1)
	}

	// Assertion 2: invoking the returned restore function reinstates original log routing
	restore()
	sink.Reset()

	var customBuf bytes.Buffer
	log.SetOutput(&customBuf)
	log.Print("message after restoration")

	if len(sink.Lines()) != 0 {
		fmt.Fprintf(os.Stderr, "FAIL: zap sink received log after restore: %s\n", sink.buf.String())
		os.Exit(1)
	}
	if !strings.Contains(customBuf.String(), "message after restoration") {
		fmt.Fprintf(os.Stderr, "FAIL: customBuf did not receive standard log output: %s\n", customBuf.String())
		os.Exit(1)
	}

	// Assertion 3: zap.RedirectStdLog output is filtered when the zap logger level threshold is configured above InfoLevel
	warnLogger, warnSink := newLogger(zapcore.WarnLevel)
	restoreWarn := zapredirect.RedirectStandardLog(warnLogger)
	defer restoreWarn()

	log.Print("info level message should be filtered out by WarnLevel threshold")
	if len(warnSink.Lines()) != 0 {
		fmt.Fprintf(os.Stderr, "FAIL: expected 0 logs when zap logger is WarnLevel, got %d\n", len(warnSink.Lines()))
		os.Exit(1)
	}

	fmt.Println("PASS: zap.RedirectStdLog contract passed")
}