Swift Log

SwiftLog - Level-Based Swift Logging

When to Use

• Adding log statements to Swift code
• Debugging network requests with Unicode payload support
• Configuring log output levels (trace/debug/net/info/warning/error/fault)
• Writing logs to files with automatic expiration
• Replacing print() statements with structured logging

Quick Start

Import

import SwiftLog
// or if using CocoaPods:
import Swift_Log

Configuration (App Delegate / Entry Point)

// Set minimum log level (logs below this are ignored)
SLog.defaultLogDegree = .debug

// Toggle network logs independently
SLog.showNetLog = false

// Set max log file age in seconds (default: 7 days)
// Must be set BEFORE enabling addFileLog
SLog.maxLogAge = 60 * 60 * 24 * 7

// Enable file logging
SLog.addFileLog = true

// Get log file URL for upload/sharing
let logURL = SLog.getLogFileURL

Log Levels (Lowest → Highest)

Global Functions (Recommended)

SLogTrace("User tapped button, current state: \(state)")
SLogDebug("Parsing JSON response: \(jsonString)")
SLogNet("POST /api/users | Body: {\"name\":\"John\"} | \\u8bf7\\u6c42\\u6210\\u529f")
SLogInfo("User logged in successfully: \(userId)")
SLogWarning("Disk space running low: \(availableSpace)MB")
SLogError("Failed to fetch data: \(error.localizedDescription)")
SLogFault("Database corruption detected in table: \(tableName)")

Class Methods (Alternative)

SLog.trace("Trace message")
SLog.debug("Debug message")
SLog.net("Network message")
SLog.info("Info message")
SLog.warning("Warning message")
SLog.error("Error message")
SLog.fault("Fault message")

LogDegree Enum

public enum LogDegree: Int {
    case trace = 0   // Track program execution
    case debug = 1   // Debugging information
    case net = 2     // Network requests/responses
    case info = 3    // Important information
    case warning = 4 // Warning messages
    case error = 5   // Error messages
    case fault = 6   // Critical/fatal errors
}

Key Features

Unicode Decoding

Network logs automatically decode Unicode escape sequences:

SLogNet("\\u6253\\u5370\\u6d88\\u606f")
// Output: 打印消息

File Logging

• Logs written to Caches directory (SLog.txt)
• Automatic LRU expiration (default: 7 days)
• Access via SLog.getLogFileURL

DEBUG-Only Output

Logs only print to console in DEBUG builds. Release builds skip console output but can still write to files.

Auto-Captured Context

Every log automatically captures:

• Source file name
• Function name
• Line number

Output Format

🌐 Network 🌐 | 2021-03-05 15:27:33:609 
 所在类:ViewController.swift 
 方法名:viewDidLoad() 
 所在行:31 
<<<<<<<<<<<<<<<<信息>>>>>>>>>>>>>>>>

 POST /api/users | Body: {"name":"John"}

<<<<<<<<<<<<<<<<END>>>>>>>>>>>>>>>>

Common Patterns

Error Handling

do {
    let data = try fetchData()
    SLogInfo("Fetched \(data.count) records")
} catch {
    SLogError("Fetch failed: \(error.localizedDescription)")
    SLogFault("Critical: Data fetch failed at \(#function)")
}

Network Requests

SLogNet("Request: \(request.httpMethod ?? "GET") \(url)")
SLogNet("Response: \(response.statusCode) | Body: \\(responseBody)")

State Transitions

SLogTrace("State transition: \(oldState) -> \(newState)")
SLogDebug("ViewModel updated with \(items.count) items")

Warnings & Errors

guard let user = currentUser else {
    SLogWarning("No current user found, using guest session")
    return
}

SLogError("Failed to save user: \(error)")

Best Practices

1. Use appropriate levels: Don't use .error for informational messages
2. Network logs: Use SLogNet() for all API traffic; toggle with showNetLog
3. File logging: Enable in production for crash reporting; set maxLogAge appropriately
4. Unicode: Network logs auto-decode \uXXXX sequences - no manual conversion needed
5. Performance: @autoclosure ensures message is only evaluated if log level passes

Source: zjinhu/SwiftLog — distributed by TomeVault.