go.uber.org/zap v1.28.0: zapcore.AddSync

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 go.uber.org/zap/zapcore.AddSync in pkg:golang/go.uber.org/zap@v1.28.0
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:golang/go.uber.org/zap@v1.28.0
Demonstrate these symbols/APIs:
  - go.uber.org/zap/zapcore.AddSync

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:c107176304c9aa290e21e7e0dd20e687f9b124642b98ebac94b0d215d3484651","contract":["WrapWriter wraps an io.Writer into a zapcore.WriteSyncer with a no-op Sync method","WrapWriter preserves an existing WriteSyncer delegating Sync to the underlying implementation","CreateLoggerWithSyncer builds a functional zap.Logger that writes and flushes through an AddSync WriteSyncer"],"goal":"verify go.uber.org/zap/zapcore.AddSync in pkg:golang/go.uber.org/zap@v1.28.0","kind":"HOW","packages":["pkg:golang/go.uber.org/zap@v1.28.0"],"schemaVersion":1,"symbols":["go.uber.org/zap/zapcore.AddSync"]},"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@v1.28.0"],"schemaVersion":1,"subject":"pkg:golang/go.uber.org/zap@v1.28.0","symbols":["go.uber.org/zap/zapcore.AddSync"],"verifierAdapter":"golang@1"}

module example.com/sample

go 1.22.0

require go.uber.org/zap v1.28.0

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

github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c=
github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
github.com/stretchr/testify v1.8.1 h1:w7B6lhMri9wdJUVmEZPGGhZzrYTPvgJArz7wNPgYKsk=
github.com/stretchr/testify v1.8.1/go.mod h1:w2LPCIKwWwSfY2zedu0+kehJoqGctiVI29o6fzry7u4=
go.uber.org/goleak v1.3.0 h1:2K3zAYmnTNqV73imy9J1T3WC+gmCePx2hEGkimedGto=
go.uber.org/goleak v1.3.0/go.mod h1:CoHD4mav9JJNrW/WLlf7HGZPjdw8EucARQHekz1X6bE=
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 v1.28.0 h1:IZzaP1Fv73/T/pBMLk4VutPl36uNC+OSUh3JLG3FIjo=
go.uber.org/zap v1.28.0/go.mod h1:rDLpOi171uODNm/mxFcuYWxDsqWSAVkFdX4XojSKg/Q=
go.yaml.in/yaml/v3 v3.0.4 h1:tfq32ie2Jv2UxXFdLJdh3jXuOzWiL1fo0bu/FbuKpbc=
go.yaml.in/yaml/v3 v3.0.4/go.mod h1:DhzuOOF2ATzADvBadXxruRBLzYTpT36CKvDb3+aBEFg=
gopkg.in/yaml.v3 v3.0.1 h1:fxVm/GzAzEWqLHuvctI91KS9hhNmmWOoWu0XTYJS7CA=
gopkg.in/yaml.v3 v3.0.1/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=

package sample

import (
	"bytes"
	"io"

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

// SyncingBuffer wraps a bytes.Buffer and tracks calls to Sync.
type SyncingBuffer struct {
	bytes.Buffer
	SyncCalled bool
}

// Sync records that the buffer was synchronized.
func (s *SyncingBuffer) Sync() error {
	s.SyncCalled = true
	return nil
}

// WrapWriter converts an io.Writer into a zapcore.WriteSyncer using zapcore.AddSync.
func WrapWriter(w io.Writer) zapcore.WriteSyncer {
	return zapcore.AddSync(w)
}

// CreateLoggerWithSyncer creates a zap.Logger configured to write to the provided WriteSyncer.
func CreateLoggerWithSyncer(ws zapcore.WriteSyncer) *zap.Logger {
	encoderCfg := zapcore.EncoderConfig{
		MessageKey:     "msg",
		LevelKey:       "level",
		NameKey:        "logger",
		EncodeLevel:    zapcore.LowercaseLevelEncoder,
		EncodeTime:     zapcore.ISO8601TimeEncoder,
		EncodeDuration: zapcore.StringDurationEncoder,
	}
	core := zapcore.NewCore(
		zapcore.NewJSONEncoder(encoderCfg),
		ws,
		zapcore.InfoLevel,
	)
	return zap.New(core)
}

{
  "schemaVersion": 1,
  "goal": "verify go.uber.org/zap/zapcore.AddSync in pkg:golang/go.uber.org/zap@v1.28.0",
  "kind": "HOW",
  "packages": [
    "pkg:golang/go.uber.org/zap@v1.28.0"
  ],
  "symbols": [
    "go.uber.org/zap/zapcore.AddSync"
  ]
}

package main

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

	"go.uber.org/zap"

	"example.com/sample"
)

type logEntry struct {
	Level  string `json:"level"`
	Msg    string `json:"msg"`
	Action string `json:"action,omitempty"`
}

func main() {
	// 1. Verify WrapWriter wraps a plain io.Writer into a WriteSyncer with a no-op Sync
	var plainBuf bytes.Buffer
	plainWS := sample.WrapWriter(&plainBuf)
	if plainWS == nil {
		fmt.Fprintf(os.Stderr, "expected non-nil WriteSyncer from plain writer\n")
		os.Exit(1)
	}
	if n, err := plainWS.Write([]byte("plain payload")); err != nil || n != 13 {
		fmt.Fprintf(os.Stderr, "failed writing to wrapped plain writer: n=%d err=%v\n", n, err)
		os.Exit(1)
	}
	if plainBuf.String() != "plain payload" {
		fmt.Fprintf(os.Stderr, "expected buffer content 'plain payload', got %q\n", plainBuf.String())
		os.Exit(1)
	}
	if err := plainWS.Sync(); err != nil {
		fmt.Fprintf(os.Stderr, "expected no-op Sync to succeed on plain writer, got: %v\n", err)
		os.Exit(1)
	}

	// 2. Verify WrapWriter preserves an existing WriteSyncer without double wrapping
	syncingBuf := &sample.SyncingBuffer{}
	syncWS := sample.WrapWriter(syncingBuf)
	if syncWS == nil {
		fmt.Fprintf(os.Stderr, "expected non-nil WriteSyncer from syncing buffer\n")
		os.Exit(1)
	}
	if err := syncWS.Sync(); err != nil {
		fmt.Fprintf(os.Stderr, "Sync failed on syncing buffer: %v\n", err)
		os.Exit(1)
	}
	if !syncingBuf.SyncCalled {
		fmt.Fprintf(os.Stderr, "expected SyncCalled to be true on underlying SyncingBuffer\n")
		os.Exit(1)
	}

	// 3. Verify CreateLoggerWithSyncer writes and flushes logs using the AddSync WriteSyncer
	var logBuf bytes.Buffer
	logWS := sample.WrapWriter(&logBuf)
	logger := sample.CreateLoggerWithSyncer(logWS)
	if logger == nil {
		fmt.Fprintf(os.Stderr, "expected non-nil zap.Logger\n")
		os.Exit(1)
	}
	logger.Info("sync-verified", zap.String("action", "test"))
	if err := logger.Sync(); err != nil {
		fmt.Fprintf(os.Stderr, "logger.Sync failed: %v\n", err)
		os.Exit(1)
	}

	var entry logEntry
	if err := json.Unmarshal(logBuf.Bytes(), &entry); err != nil {
		fmt.Fprintf(os.Stderr, "failed to unmarshal log entry: %v, raw: %s\n", err, logBuf.String())
		os.Exit(1)
	}
	if entry.Level != "info" {
		fmt.Fprintf(os.Stderr, "expected level 'info', got %q\n", entry.Level)
		os.Exit(1)
	}
	if entry.Msg != "sync-verified" {
		fmt.Fprintf(os.Stderr, "expected msg 'sync-verified', got %q\n", entry.Msg)
		os.Exit(1)
	}
	if entry.Action != "test" {
		fmt.Fprintf(os.Stderr, "expected action 'test', got %q\n", entry.Action)
		os.Exit(1)
	}

	fmt.Println("All contracts passed successfully.")
}