---
name: zap-logging-3340da197532
description: Blazing fast structured logging from Uber.
metadata:
  labels: [golang, zap, logging, observability]
  triggers:
    files: ['**/logger.go', '**/main.go']
    keywords: [zap, Logger, SugaredLogger, zapcore]
---

# Zap Logging Standards

## Setup

```go
import "go.uber.org/zap"

// Development (human readable)
func NewDevelopmentLogger() *zap.Logger {
    logger, _ := zap.NewDevelopment()
    return logger
}

// Production (JSON, optimized)
func NewProductionLogger() *zap.Logger {
    logger, _ := zap.NewProduction()
    return logger
}

// With options
func NewLogger() *zap.Logger {
    cfg := zap.NewProductionConfig()
    cfg.Level = zap.NewAtomicLevelAt(zap.InfoLevel)
    cfg.OutputPaths = []string{"stdout", "/var/log/app.log"}
    cfg.EncoderConfig.TimeKey = "timestamp"
    cfg.EncoderConfig.EncodeTime = zapcore.ISO8601TimeEncoder

    logger, _ := cfg.Build()
    return logger
}
```

## Logger vs SugaredLogger

```go
// Logger - faster, type-safe
logger := zap.NewProduction()
logger.Info("User logged in",
    zap.String("user_id", "123"),
    zap.Int("attempt", 1),
    zap.Duration("latency", time.Millisecond*50),
)

// SugaredLogger - convenient, slower
sugar := logger.Sugar()
sugar.Infow("User logged in",
    "user_id", "123",
    "attempt", 1,
    "latency", time.Millisecond*50,
)
sugar.Infof("User %s logged in", userID)
```

## Structured Fields

```go
logger.Info("Request completed",
    zap.String("method", "GET"),
    zap.String("path", "/users"),
    zap.Int("status", 200),
    zap.Duration("latency", latency),
    zap.String("client_ip", clientIP),
    zap.Any("headers", headers),     // Any type
    zap.Error(err),                   // Error field
    zap.Stack("stacktrace"),          // Stack trace
)

// Namespaced fields
logger.Info("Request",
    zap.Namespace("http"),
    zap.String("method", "GET"),
    zap.Int("status", 200),
)
// Output: {"http": {"method": "GET", "status": 200}}
```

## Log Levels

```go
logger.Debug("Debug message")   // -1
logger.Info("Info message")     // 0
logger.Warn("Warning message")  // 1
logger.Error("Error message")   // 2
logger.DPanic("DPanic message") // 3 (panics in development)
logger.Panic("Panic message")   // 4 (always panics)
logger.Fatal("Fatal message")   // 5 (calls os.Exit(1))

// Check level before expensive operations
if logger.Core().Enabled(zap.DebugLevel) {
    logger.Debug("Expensive", zap.Any("data", computeExpensiveData()))
}
```

## Child Loggers

```go
// Add fields to all subsequent logs
requestLogger := logger.With(
    zap.String("request_id", requestID),
    zap.String("user_id", userID),
)

requestLogger.Info("Processing request")
requestLogger.Info("Request completed")
// Both logs include request_id and user_id

// Named logger
dbLogger := logger.Named("database")
dbLogger.Info("Query executed")
// Output: {"logger": "database", "msg": "Query executed"}
```

## Gin Integration

```go
import (
    "github.com/gin-gonic/gin"
    "go.uber.org/zap"
)

func GinLogger(logger *zap.Logger) gin.HandlerFunc {
    return func(c *gin.Context) {
        start := time.Now()
        path := c.Request.URL.Path

        c.Next()

        logger.Info("Request",
            zap.String("method", c.Request.Method),
            zap.String("path", path),
            zap.Int("status", c.Writer.Status()),
            zap.Duration("latency", time.Since(start)),
            zap.String("client_ip", c.ClientIP()),
        )
    }
}

r := gin.New()
r.Use(GinLogger(logger))
```

## Custom Encoder

```go
cfg := zap.NewProductionConfig()
cfg.EncoderConfig = 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.MillisDurationEncoder,
    EncodeCaller:   zapcore.ShortCallerEncoder,
}
```

## Sampling

```go
// Sample logs to reduce volume in production
cfg := zap.NewProductionConfig()
cfg.Sampling = &zap.SamplingConfig{
    Initial:    100,  // First 100 per second logged
    Thereafter: 100,  // Then every 100th message
}
```

## Global Logger

```go
// Replace global logger
logger := zap.NewProduction()
zap.ReplaceGlobals(logger)

// Use global
zap.L().Info("Using global logger")
zap.S().Infow("Using global sugar")

// Always sync before exit
defer logger.Sync()
```

## Best Practices

1. **Production**: Use `zap.NewProduction()` for JSON output
2. **Sync**: Always call `logger.Sync()` before exit
3. **Fields**: Prefer `zap.String()` etc. over SugaredLogger
4. **Child loggers**: Add request context with `With()`
5. **Sampling**: Enable in high-throughput production


---
Source attribution: ngxtm
Original project: https://github.com/ngxtm/devkit/blob/9439f27ce3fa7fe53ff9278a1ee9a44bffa70eba/rules/golang/zap-logging/SKILL.md
License: MIT
License information: https://opensource.org/license/mit
Original upstream instructions; downloaded from Mega AI Hub.

## Upstream license notice

MIT License

Copyright (c) 2024

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
SOFTWARE.



# Mega AI Hub resource metadata

Creator / publisher: ngxtm
Original project: https://github.com/ngxtm/devkit/blob/9439f27ce3fa7fe53ff9278a1ee9a44bffa70eba/rules/golang/zap-logging/SKILL.md
Attribution basis: Source repository record

Fields of work: Development & Engineering
Roles: Backend Developer, Data Engineer, DevOps / SRE
Specialties: Backend
Tools: Zap
Country applicability: Country not specified
Classification basis: Source catalog labels
Instruction SHA-256: 1179ef99c7ac92a15db6bb31fcbf323fdd5e158523045082b7a3f49f8632528e