context-logger

A lightweight, ergonomic library for adding structured context to your logs.

context-logger enhances the standard Rust log crate ecosystem by allowing you to attach rich contextual information to your log messages without changing your existing logging patterns.

Usage

Basic Example

Add context-logger to your Cargo.toml:

[dependencies]
context-logger = "0.1.0"
log = { version = "0.4", features = ["kv_serde"] }
env_logger = "0.10"

Then, you can use it in your code:

use context_logger::{ContextLogger, LogContext};
use log::info;

fn main() {
    // Create a logger.
    let env_logger = env_logger::builder().build();
    let max_level = env_logger.filter();
    // Wrap it with ContextLogger to enable context propagation.
    let context_logger = ContextLogger::new(env_logger)
        // Add version default record.
        .default_record("version", "1.0.0");
    // Initialize the resulting logger.
    context_logger.init(max_level);   

    // Create a context
    let ctx = LogContext::new()
        .record("request_id", "req-123")
        .record("user_id", 42);
    
    // Use the context
    let _guard = ctx.enter();
    
    // Log with context automatically attached
    info!("Processing request"); // Will include version=1.0.0 request_id=req-123 and user_id=42
}

Async Context Propagation

Context logger supports async functions and can propagate log context across .await points.

use context_logger::{ContextLogger, LogContext, FutureExt};
use log::info;

async fn process_user_data(user_id: &str) {
    let context = LogContext::new().record("user_id", user_id);
    
    async {
        info!("Processing user data"); // Includes user_id
        
        // Context automatically propagates through .await points
        fetch_user_preferences().await;
        
        info!("User data processed"); // Still includes user_id
    }
    .in_log_context(context)
    .await;
}

async fn fetch_user_preferences() {
    // Add additional context for this specific operation
    LogContext::add_record("operation", "fetch_preferences");
    info!("Fetching preferences"); // Includes both user_id and operation
}

License

This project is licensed under the MIT License. See the LICENSE file for details.