structured_logging_example.cpp

This example covers:

• Basic structured logging with key-value fields
• Context propagation (trace ID, correlation ID)
• Thread-local context scopes
• JSON and Logfmt formatters
• Template-based custom formatters

// BSD 3-Clause License
// Copyright (c) 2025, 🍀☀🌕🌥 🌊
// See the LICENSE file in the project root for full license information.
 
#include <kcenon/logger/core/logger.h>
#include <kcenon/logger/core/structured_log_builder.h>
#include <kcenon/logger/core/log_context_scope.h>
#include <kcenon/logger/writers/console_writer.h>
#include <kcenon/logger/formatters/json_formatter.h>
#include <kcenon/logger/formatters/logfmt_formatter.h>
#include <kcenon/logger/formatters/template_formatter.h>
 
#include <iostream>
#include <thread>
#include <chrono>
 
using namespace kcenon::logger;
 
void basic_structured_logging() {
    std::cout << "\n=== Basic Structured Logging ===\n" << std::endl;
 
    auto logger_instance = std::make_shared<logger>(false);  // Synchronous mode
    logger_instance->add_writer(std::make_unique<console_writer>());
    logger_instance->start();
 
    // Basic structured log with various field types using canonical API
    logger_instance->log_structured(log_level::info)
        .message("User login successful")
        .field("user_id", 12345)
        .field("username", "john_doe")
        .field("ip_address", "192.168.1.100")
        .field("login_time_ms", 42.5)
        .field("mfa_enabled", true)
        .emit();
 
    // Error with structured details
    logger_instance->log_structured(log_level::error)
        .message("Database connection failed")
        .field("host", "db.example.com")
        .field("port", 5432)
        .field("retry_count", 3)
        .field("timeout_ms", 30000)
        .emit();
 
    // Debug with technical details
    logger_instance->log_structured(log_level::debug)
        .message("Cache lookup performed")
        .field("cache_key", "user:12345:profile")
        .field("hit", false)
        .field("latency_us", 150)
        .emit();
 
    logger_instance->stop();
}
 
void context_propagation_example() {
    std::cout << "\n=== Context Propagation Example ===\n" << std::endl;
 
    auto logger_instance = std::make_shared<logger>(false);
    logger_instance->add_writer(std::make_unique<console_writer>());
    logger_instance->start();
 
    // Set distributed tracing context using unified context API
    logger_instance->context()
        .set("trace_id", std::string("0af7651916cd43dd8448eb211c80319c"), context_category::trace)
        .set("span_id", std::string("b7ad6b7169203331"), context_category::trace)
        .set("correlation_id", std::string("req-abc-123"), context_category::trace);
 
    // All subsequent logs will include trace context
    logger_instance->log_structured(log_level::info)
        .message("Processing API request")
        .field("endpoint", "/api/v1/users")
        .field("method", "GET")
        .emit();
 
    logger_instance->log_structured(log_level::info)
        .message("Database query executed")
        .field("query_type", "SELECT")
        .field("rows_returned", 42)
        .emit();
 
    // Clear all trace context IDs when request is complete
    logger_instance->context().clear(context_category::trace);
 
    logger_instance->stop();
}
 
void context_scope_example() {
    std::cout << "\n=== Context Scope Example ===\n" << std::endl;
 
    auto logger_instance = std::make_shared<logger>(false);
    logger_instance->add_writer(std::make_unique<console_writer>());
    logger_instance->start();
 
    // Outer scope: request-level context
    {
        log_context_scope request_scope({
            {"request_id", std::string("req-12345")},
            {"user_id", static_cast<int64_t>(1001)},
            {"tenant", std::string("acme-corp")}
        });
 
        logger_instance->log_structured(log_level::info)
            .message("Request processing started")
            .emit();
 
        // Inner scope: operation-specific context
        {
            log_context_scope db_scope({
                {"operation", std::string("user_lookup")},
                {"database", std::string("users_db")}
            });
 
            logger_instance->log_structured(log_level::debug)
                .message("Executing database query")
                .field("query_time_ms", 15.3)
                .emit();
        }
        // db_scope ended - "operation" and "database" removed
 
        logger_instance->log_structured(log_level::info)
            .message("Request processing completed")
            .field("total_time_ms", 45.7)
            .emit();
    }
    // request_scope ended - all context cleared
 
    logger_instance->stop();
}
 
void scoped_context_single_field() {
    std::cout << "\n=== Scoped Context (Single Field) ===\n" << std::endl;
 
    auto logger_instance = std::make_shared<logger>(false);
    logger_instance->add_writer(std::make_unique<console_writer>());
    logger_instance->start();
 
    // Using scoped_context for single fields
    {
        scoped_context order_ctx("order_id", static_cast<int64_t>(98765));
 
        logger_instance->log_structured(log_level::info)
            .message("Processing order")
            .field("status", "pending")
            .emit();
 
        {
            scoped_context item_ctx("item_id", static_cast<int64_t>(42));
 
            logger_instance->log_structured(log_level::debug)
                .message("Validating item")
                .field("quantity", 3)
                .emit();
        }
 
        logger_instance->log_structured(log_level::info)
            .message("Order completed")
            .field("status", "completed")
            .emit();
    }
 
    logger_instance->stop();
}
 
void json_formatter_example() {
    std::cout << "\n=== JSON Formatter Example ===\n" << std::endl;
 
    // Create a log entry with structured fields
    log_entry entry(log_level::info, "User profile updated");
    entry.fields = log_fields{
        {"user_id", static_cast<int64_t>(12345)},
        {"fields_changed", static_cast<int64_t>(3)},
        {"notification_sent", true}
    };
 
    // Format with JSON formatter
    json_formatter formatter;
    std::string output = formatter.format(entry);
 
    std::cout << "JSON formatted output:\n" << output << std::endl;
}
 
void logfmt_formatter_example() {
    std::cout << "\n=== Logfmt Formatter Example ===\n" << std::endl;
 
    // Create a log entry with structured fields
    log_entry entry(log_level::info, "HTTP request completed");
    entry.fields = log_fields{
        {"method", std::string("POST")},
        {"path", std::string("/api/orders")},
        {"status_code", static_cast<int64_t>(201)},
        {"duration_ms", 125.5}
    };
 
    // Format with logfmt formatter
    logfmt_formatter formatter;
    std::string output = formatter.format(entry);
 
    std::cout << "Logfmt formatted output:\n" << output << std::endl;
}
 
void template_formatter_example() {
    std::cout << "\n=== Template Formatter Example ===\n" << std::endl;
 
    // Create a log entry with structured fields
    log_entry entry(log_level::info, "Session created");
    entry.fields = log_fields{
        {"user_id", static_cast<int64_t>(12345)},
        {"session_id", std::string("sess-abc-123")}
    };
 
    // Format with custom template
    template_formatter formatter("[{timestamp_local}] [{level:8}] {message} | user={user_id}");
    std::string output = formatter.format(entry);
 
    std::cout << "Template formatted output:\n" << output << std::endl;
 
    // Try different templates
    formatter.set_template("{level}: {message} (session={session_id})");
    std::string output2 = formatter.format(entry);
    std::cout << "Alternative template:\n" << output2 << std::endl;
}
 
void multithreaded_context_example() {
    std::cout << "\n=== Multithreaded Context Example ===\n" << std::endl;
 
    auto logger_instance = std::make_shared<logger>(true);  // Async mode for MT
    logger_instance->add_writer(std::make_unique<console_writer>());
    logger_instance->start();
 
    auto worker = [&](int thread_id) {
        // Each thread has its own context (thread-local storage)
        log_context_scope scope({
            {"thread_id", static_cast<int64_t>(thread_id)},
            {"worker", std::string("processor-" + std::to_string(thread_id))}
        });
 
        for (int i = 0; i < 3; ++i) {
            logger_instance->log_structured(log_level::info)
                .message("Processing item")
                .field("item_number", i)
                .emit();
 
            std::this_thread::sleep_for(std::chrono::milliseconds(10));
        }
    };
 
    std::thread t1(worker, 1);
    std::thread t2(worker, 2);
 
    t1.join();
    t2.join();
 
    logger_instance->stop();
}
 
void logger_context_example() {
    std::cout << "\n=== Logger Context Example ===\n" << std::endl;
 
    auto logger_instance = std::make_shared<logger>(false);
    logger_instance->add_writer(std::make_unique<console_writer>());
    logger_instance->start();
 
    // Set logger-level context (applies to all logs)
    logger_instance->context()
        .set("service", std::string("order-service"))
        .set("version", std::string("1.2.3"))
        .set("environment", std::string("production"));
 
    // All logs will include service, version, and environment
    logger_instance->log_structured(log_level::info)
        .message("Service started")
        .emit();
 
    logger_instance->log_structured(log_level::info)
        .message("Processing request")
        .field("request_id", "req-001")
        .emit();
 
    // Check if context exists
    if (!logger_instance->context().empty()) {
        auto ctx = logger_instance->context().to_fields();
        std::cout << "Current context has " << ctx.size() << " fields" << std::endl;
    }
 
    // Remove specific context
    logger_instance->context().remove("environment");
 
    // Clear all context
    logger_instance->context().clear();
 
    logger_instance->stop();
}
 
int main() {
    try {
        basic_structured_logging();
        context_propagation_example();
        context_scope_example();
        scoped_context_single_field();
        json_formatter_example();
        logfmt_formatter_example();
        template_formatter_example();
        multithreaded_context_example();
        logger_context_example();
 
        std::cout << "\n=== All structured logging examples completed! ===" << std::endl;
 
    } catch (const std::exception& e) {
        std::cerr << "Error: " << e.what() << std::endl;
        return 1;
    }
 
    return 0;
}