Logger

The log package provides structured logging functionality with context support, built on top of Go’s standard log/slog package.

Logger Overview

Platforma’s logger automatically extracts and logs context values like trace IDs, service names, and user IDs. It supports both JSON and text output formats with structured key-value pairs.

Global Logger

The package provides a default global logger:

var Logger logger = New(os.Stdout, "text", slog.LevelInfo, nil)

SetDefault

void

Sets the default logger used by package-level logging functions.

customLogger := log.New(os.Stdout, "json", slog.LevelDebug, nil)
log.SetDefault(customLogger)

Creating Loggers

New

*slog.Logger

Creates a new slog.Logger with the specified configuration.Parameters:

w (io.Writer): Output destination (e.g., os.Stdout, file)
loggerType (string): Logger format - “json” or “text”
level (slog.Level): Minimum log level (LevelDebug, LevelInfo, LevelWarn, LevelError)
contextKeys (map[string]any): Additional context keys to extract from context

logger := log.New(os.Stdout, "json", slog.LevelInfo, nil)

Logging Methods

The logger provides both context-aware and simple logging methods. Always prefer context-aware methods for better traceability.

Context-Aware Methods

void

Logs a debug-level message with context values.

log.DebugContext(ctx, "processing request", "user_id", 123)

void

Logs an info-level message with context values.

log.InfoContext(ctx, "user created", "id", user.ID, "email", user.Email)

void

Logs a warning-level message with context values.

log.WarnContext(ctx, "rate limit approaching", "remaining", 10)

void

Logs an error-level message with context values.

log.ErrorContext(ctx, "database error", "error", err, "query", sql)

Simple Methods

These methods don’t use context values:

log.Debug(msg, args...)
log.Info(msg, args...)
log.Warn(msg, args...)
log.Error(msg, args...)

Context Keys

The logger automatically extracts these context keys:

contextKey

Domain name for domain-driven architecture.

ctx = context.WithValue(ctx, log.DomainNameKey, "auth")
log.InfoContext(ctx, "domain action")
// Output includes: domainName=auth

contextKey

Unique trace ID for request tracking.

ctx = context.WithValue(ctx, log.TraceIDKey, uuid.NewString())
log.InfoContext(ctx, "request started")
// Output includes: traceId=abc-123-def

contextKey

Name of the service handling the request.

ctx = context.WithValue(ctx, log.ServiceNameKey, "api")
log.InfoContext(ctx, "service started")
// Output includes: serviceName=api

contextKey

Name of the startup task being executed.

ctx = context.WithValue(ctx, log.StartupTaskKey, "migrations")
log.InfoContext(ctx, "task running")
// Output includes: startupTask=migrations

contextKey

User ID for user-specific operations.

ctx = context.WithValue(ctx, log.UserIDKey, "user_123")
log.InfoContext(ctx, "user action")
// Output includes: userId=user_123

contextKey

Worker ID for queue processor workers.

ctx = context.WithValue(ctx, log.WorkerIDKey, uuid.NewString())
log.InfoContext(ctx, "processing job")
// Output includes: workerId=worker-abc-123

TraceIDMiddleware

HTTP middleware that adds trace IDs to requests.

type TraceIDMiddleware struct {
    contextKey any
    header     string
}

Constructor

*TraceIDMiddleware

Creates a new TraceID middleware.Parameters:

contextKey (any): Context key to store trace ID (nil = use TraceIDKey)
header (string): HTTP header name (empty = use “Platforma-Trace-Id”)

traceMiddleware := log.NewTraceIDMiddleware(nil, "")
server.Use(traceMiddleware)

Wrap

http.Handler

Wraps an HTTP handler to add trace IDs to requests.The middleware:

Generates a unique trace ID (UUID)
Adds it to the request context
Sets it in the response header
Passes the request to the next handler

wrapped := traceMiddleware.Wrap(handler)

Example Usage

Basic Logging

package main

import (
    "context"
    "github.com/platforma-dev/platforma/log"
)

func main() {
    ctx := context.Background()
    
    // Simple info log
    log.InfoContext(ctx, "application started")
    
    // Structured logging with key-value pairs
    log.InfoContext(ctx, "user logged in",
        "user_id", 123,
        "email", "user@example.com",
        "ip", "192.168.1.1",
    )
    
    // Error logging
    err := doSomething()
    if err != nil {
        log.ErrorContext(ctx, "operation failed",
            "error", err,
            "operation", "doSomething",
        )
    }
}

With Trace IDs

import (
    "context"
    "github.com/google/uuid"
    "github.com/platforma-dev/platforma/log"
)

func handleRequest(ctx context.Context) {
    // Add trace ID to context
    traceID := uuid.NewString()
    ctx = context.WithValue(ctx, log.TraceIDKey, traceID)
    
    log.InfoContext(ctx, "request started")
    // Output: time=... level=INFO msg="request started" traceId=abc-123-def
    
    processRequest(ctx)
    
    log.InfoContext(ctx, "request completed")
    // Output: time=... level=INFO msg="request completed" traceId=abc-123-def
}

HTTP Server with Trace Middleware

package main

import (
    "net/http"
    "time"
    "github.com/platforma-dev/platforma/application"
    "github.com/platforma-dev/platforma/httpserver"
    "github.com/platforma-dev/platforma/log"
)

func main() {
    app := application.New()
    
    // Create HTTP server
    api := httpserver.New("8080", 3*time.Second)
    
    // Add trace ID middleware
    api.Use(log.NewTraceIDMiddleware(nil, ""))
    
    // Add handler
    api.HandleFunc("/users", func(w http.ResponseWriter, r *http.Request) {
        // Context already has trace ID from middleware
        log.InfoContext(r.Context(), "listing users")
        
        // Trace ID is also in response header: Platforma-Trace-Id
        w.Write([]byte("users"))
    })
    
    app.RegisterService("api", api)
    app.Run(context.Background())
}

Custom Logger Configuration

import (
    "log/slog"
    "os"
    "github.com/platforma-dev/platforma/log"
)

// JSON logger with debug level
jsonLogger := log.New(os.Stdout, "json", slog.LevelDebug, nil)
log.SetDefault(jsonLogger)

// Custom context keys
customKeys := map[string]any{
    "request_id": requestIDKey,
    "session_id": sessionIDKey,
}
logger := log.New(os.Stdout, "json", slog.LevelInfo, customKeys)

Output Formats

Text format:

time=2024-01-15T10:30:00.000Z level=INFO msg="user created" traceId=abc-123 userId=user_456 email=user@example.com

JSON format:

{
  "time": "2024-01-15T10:30:00.000Z",
  "level": "INFO",
  "msg": "user created",
  "traceId": "abc-123",
  "userId": "user_456",
  "email": "user@example.com"
}

Multiple Context Values

func processUserRequest(ctx context.Context, userID string) {
    // Add multiple context values
    ctx = context.WithValue(ctx, log.TraceIDKey, uuid.NewString())
    ctx = context.WithValue(ctx, log.UserIDKey, userID)
    ctx = context.WithValue(ctx, log.DomainNameKey, "auth")
    
    log.InfoContext(ctx, "processing user request")
    // Output includes: traceId=... userId=... domainName=auth
    
    if err := validateUser(ctx, userID); err != nil {
        log.ErrorContext(ctx, "validation failed", "error", err)
        return
    }
    
    log.InfoContext(ctx, "request completed successfully")
}

Best Practices

Always use context-aware methods (e.g., InfoContext) instead of simple methods
Add trace IDs to all requests for distributed tracing
Use structured logging with key-value pairs instead of string interpolation
Include relevant context like user IDs, request IDs, and error details
Use appropriate log levels: Debug for detailed info, Info for normal operations, Warn for concerning situations, Error for actual errors

Core Packages

Domain Modules

Logger Overview

Global Logger

SetDefault

Creating Loggers

New

Logging Methods

Context-Aware Methods

Simple Methods

Context Keys

TraceIDMiddleware

Constructor

Wrap

Example Usage

Basic Logging

With Trace IDs

HTTP Server with Trace Middleware

Custom Logger Configuration

Output Formats

Multiple Context Values

Best Practices

​Logger Overview

​Global Logger

​SetDefault

​Creating Loggers

​New

​Logging Methods

​Context-Aware Methods

​Simple Methods

​Context Keys

​TraceIDMiddleware

​Constructor

​Wrap

​Example Usage

​Basic Logging

​With Trace IDs

​HTTP Server with Trace Middleware

​Custom Logger Configuration

​Output Formats

​Multiple Context Values

​Best Practices

Logger Overview

Global Logger

SetDefault

Creating Loggers

New

Logging Methods

Context-Aware Methods

Simple Methods

Context Keys

TraceIDMiddleware

Constructor

Wrap

Example Usage

Basic Logging

With Trace IDs

HTTP Server with Trace Middleware

Custom Logger Configuration

Output Formats

Multiple Context Values

Best Practices