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

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.NewJSONEncoder 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.NewJSONEncoder
Constraints:
  - executionContext: node
Required runtime conditions:
  - ecosystem: npm
  - language: javascript
  - moduleSystem: cjs
  - packageManager: npm@10.9.8
  - runtime: node@22.23.2

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:sha256:93e5d16489039f392c0e638d743320a2529dfe014984fa2909a1548a23be09b7","contract":["CreateJSONEncoder constructs a zapcore.Encoder using NewJSONEncoder that formats log entries with custom EncoderConfig settings","EncodeLogEntry formats log metadata and structured fields into a valid JSON string with configured timestamp and level keys","NewJSONLogger creates a zap.Logger configured with NewJSONEncoder and writes structured JSON logs to the destination buffer"],"goal":"verify go.uber.org/zap/zapcore.NewJSONEncoder 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.NewJSONEncoder"]},"contractCommand":["go","run","./test"],"environment":{"arch":"x64","ecosystem":"golang","language":"go","os":"linux","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.NewJSONEncoder"],"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"
	"time"

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

// DefaultJSONEncoderConfig returns a standard EncoderConfig for JSON formatting.
func DefaultJSONEncoderConfig() zapcore.EncoderConfig {
	return zapcore.EncoderConfig{
		TimeKey:        "ts",
		LevelKey:       "level",
		NameKey:        "logger",
		CallerKey:      "caller",
		MessageKey:     "msg",
		StacktraceKey:  "stacktrace",
		LineEnding:     zapcore.DefaultLineEnding,
		EncodeLevel:    zapcore.LowercaseLevelEncoder,
		EncodeTime:     zapcore.ISO8601TimeEncoder,
		EncodeDuration: zapcore.StringDurationEncoder,
		EncodeCaller:   zapcore.ShortCallerEncoder,
	}
}

// CreateJSONEncoder creates a zapcore.Encoder configured with JSON formatting via NewJSONEncoder.
func CreateJSONEncoder(cfg zapcore.EncoderConfig) zapcore.Encoder {
	return zapcore.NewJSONEncoder(cfg)
}

// EncodeLogEntry encodes a single log entry and fields directly using the JSON encoder.
func EncodeLogEntry(enc zapcore.Encoder, level zapcore.Level, msg string, t time.Time, fields ...zapcore.Field) (string, error) {
	entry := zapcore.Entry{
		Level:      level,
		Time:       t,
		Message:    msg,
		LoggerName: "json-test",
	}
	buf, err := enc.EncodeEntry(entry, fields)
	if err != nil {
		return "", err
	}
	defer buf.Free()
	return buf.String(), nil
}

// NewJSONLogger creates a zap.Logger configured with NewJSONEncoder writing to the provided buffer.
func NewJSONLogger(cfg zapcore.EncoderConfig, buf *bytes.Buffer, level zapcore.Level) *zap.Logger {
	encoder := zapcore.NewJSONEncoder(cfg)
	core := zapcore.NewCore(encoder, zapcore.AddSync(buf), level)
	return zap.New(core)
}

{
  "schemaVersion": 1,
  "goal": "verify go.uber.org/zap/zapcore.NewJSONEncoder 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.NewJSONEncoder"
  ],
  "constraints": {
    "executionContext": "node"
  },
  "runtimeConditions": {
    "ecosystem": "npm",
    "language": "javascript",
    "moduleSystem": "cjs",
    "packageManager": "npm@10.9.8",
    "runtime": "node@22.23.2"
  }
}

package main

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

	"example.com/sample"
	"go.uber.org/zap"
	"go.uber.org/zap/zapcore"
)

type defaultLogEntry struct {
	Level   string `json:"level"`
	Ts      string `json:"ts"`
	Logger  string `json:"logger"`
	Msg     string `json:"msg"`
	Service string `json:"service,omitempty"`
	Attempt int    `json:"attempt,omitempty"`
}

type customLogEntry struct {
	Severity string `json:"severity"`
	Message  string `json:"message"`
	Code     int    `json:"code"`
}

func main() {
	// Test 1: Verify direct encoding using NewJSONEncoder
	cfg := sample.DefaultJSONEncoderConfig()
	enc := sample.CreateJSONEncoder(cfg)
	if enc == nil {
		fmt.Fprintf(os.Stderr, "expected non-nil encoder\n")
		os.Exit(1)
	}

	fixedTime := time.Date(2026, 9, 4, 12, 0, 0, 0, time.UTC)
	output, err := sample.EncodeLogEntry(
		enc,
		zapcore.InfoLevel,
		"direct encode test",
		fixedTime,
		zap.String("service", "auth"),
		zap.Int("attempt", 1),
	)
	if err != nil {
		fmt.Fprintf(os.Stderr, "EncodeLogEntry failed: %v\n", err)
		os.Exit(1)
	}

	var entry defaultLogEntry
	if err := json.Unmarshal([]byte(output), &entry); err != nil {
		fmt.Fprintf(os.Stderr, "failed to parse JSON from EncodeLogEntry: %v, raw: %s\n", err, output)
		os.Exit(1)
	}

	if entry.Level != "info" || entry.Msg != "direct encode test" || entry.Service != "auth" || entry.Attempt != 1 {
		fmt.Fprintf(os.Stderr, "unexpected field values in encoded entry: %+v\n", entry)
		os.Exit(1)
	}

	// Test 2: Verify NewJSONEncoder integrated into zap.Logger via zapcore.NewCore
	var buf bytes.Buffer
	logger := sample.NewJSONLogger(cfg, &buf, zapcore.InfoLevel)
	if logger == nil {
		fmt.Fprintf(os.Stderr, "expected non-nil logger\n")
		os.Exit(1)
	}

	logger.Info("pipeline operational", zap.String("service", "indexer"), zap.Int("attempt", 3))

	var loggerEntry defaultLogEntry
	if err := json.Unmarshal(buf.Bytes(), &loggerEntry); err != nil {
		fmt.Fprintf(os.Stderr, "failed to parse JSON from logger: %v, raw: %s\n", err, buf.String())
		os.Exit(1)
	}

	if loggerEntry.Level != "info" || loggerEntry.Msg != "pipeline operational" || loggerEntry.Service != "indexer" || loggerEntry.Attempt != 3 {
		fmt.Fprintf(os.Stderr, "unexpected field values from logger: %+v\n", loggerEntry)
		os.Exit(1)
	}

	// Test 3: Verify custom EncoderConfig key mapping
	buf.Reset()
	customCfg := zapcore.EncoderConfig{
		LevelKey:       "severity",
		MessageKey:     "message",
		EncodeLevel:    zapcore.LowercaseLevelEncoder,
		EncodeTime:     zapcore.ISO8601TimeEncoder,
		EncodeDuration: zapcore.StringDurationEncoder,
	}
	customLogger := sample.NewJSONLogger(customCfg, &buf, zapcore.WarnLevel)
	customLogger.Warn("rate limit exceeded", zap.Int("code", 429))

	var customEntry customLogEntry
	if err := json.Unmarshal(buf.Bytes(), &customEntry); err != nil {
		fmt.Fprintf(os.Stderr, "failed to parse custom JSON: %v, raw: %s\n", err, buf.String())
		os.Exit(1)
	}

	if customEntry.Severity != "warn" || customEntry.Message != "rate limit exceeded" || customEntry.Code != 429 {
		fmt.Fprintf(os.Stderr, "unexpected custom log values: %+v\n", customEntry)
		os.Exit(1)
	}

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