Eventline

Causality-aware execution journal for systems-level programs.

Eventline records what happened, when it happened, and in what causal context — without assuming logging, tracing, or telemetry semantics. Built for daemons, CLI tools, and eventually Linux distributions.

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Features

• Append-only journal — never mutates or removes records
• Scoped execution — track outcomes and durations
• Structured data — attach key-value fields to events for rich context
• Runtime log levels — filter events globally (Debug, Info, Warning, Error)
• Dual output mode — journal + optional real-time console printing
• Live logging — automatic, timestamped append to disk
• Unified color control — consistent ANSI colors across console and renderer
• Flexible filtering — by outcome, depth, duration, event kind, message content
• High-throughput batching — JournalBuffer for batch writes
• Async runtime support — fire-and-forget logging and async scopes
• Deterministic replay — safe concurrent reads, reliable audit trails

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Why Eventline?

Eventline is not "better logging" - It's structured execution history.

• Events are append-only and never rewritten
• Work is grouped into scopes with outcomes and durations
• Event != results (warnings can happen in successful work)
• Journals can be replayed deterministically
• Console output is optional - Structure is always preserved

You get:

• human-readable output
• A complete execution record for post-mortem analysis

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Quick Start

Runtime API (Fire-and-Forget Async)

use eventline::runtime;
use eventline::{event_info, event_info_scoped, scoped_eventline};

#[tokio::main]
async fn main() {
    // Initialize runtime
    runtime::init().await;

    // Enable console output
    runtime::enable_console_output(true);
    runtime::enable_console_color(true);

    // Fire-and-forget logging
    event_info!("Application started");

    // Single scoped event
    event_info_scoped!("DatabaseMigration", "Applying schema changes");

    // Multiple events in a scope
    scoped_eventline!("Startup", {
        runtime::info("Loading configuration").await;
        runtime::info("Connecting to database").await;
        runtime::info("Server ready").await;
    });
}

Core Journal API (Explicit Control)

For libraries or embedded systems:

use eventline::Journal;
use eventline::Outcome;
use eventline::JournalWriter;

let mut journal = Journal::new();

let scope = journal.enter_scope(None, Some("Task"));
journal.record(Some(scope), "Starting task");
journal.exit_scope(scope, Outcome::Success);

// Use JournalWriter to output the journal
let writer = JournalWriter::new();
// writer.write_to(&mut std::fs::File::create("events.log")?, &journal)?;

Structured Event Example

use eventline::runtime;
use eventline::{fields, event_info_fields};

#[tokio::main]
async fn main() {
    runtime::init().await;

    // Build structured fields using the helper macro
    let f = fields!({
        "user_id" => 12345,
        "action" => "login",
        "success" => true
    });

    // Fire-and-forget info event with structured fields
    event_info_fields!("User login attempt", f);

    runtime::reset().await;
}

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API Overview

Event Macros (Fire-and-Forget)

Unscoped events:

event_info!("message");
event_debug!("message");
event_warn!("message");
event_error!("message");

Single scoped events:

event_info_scoped!("ScopeName", "message");
event_debug_scoped!("ScopeName", "message");
event_warn_scoped!("ScopeName", "message");
event_error_scoped!("ScopeName", "message");

Structured data:

let f = fields!({ "key" => value });
event_info_fields!("message", f);
event_debug_fields!("message", f);
event_warn_fields!("message", f);
event_error_fields!("message", f);

Complex scopes:

scoped_eventline!("ScopeName", {
    runtime::info("first event").await;
    runtime::debug("second event").await;
});

scoped_eventline_fields!("ScopeName", {
    let f = fields!({ "key" => value });
    runtime::event::info_fields("event", f).await;
});

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Console Output (Simple Format)

Clean, minimal output optimized for watching logs during development:

Starting server
Binding to 0.0.0.0:8080
Server started successfully
warning: cache at 95% capacity

Live Log File (Canonical Format)

Structured output with scope headers, timestamps, and aligned formatting:

[19:04:12.381] Scope startup (id=1) → Success (142ms)
  • info      Starting server
  • info      Binding to 0.0.0.0:8080
  • info      Server started successfully
  • warning   cache at 95% capacity

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Architecture

┌─────────────┐
│   Macros    │  event_info!(), scoped_eventline!()
└──────┬──────┘
       ↓
┌─────────────┐
│   Runtime   │  Global, thread-safe facade (optional)
└──────┬──────┘
       ↓
┌─────────────┐   ┌─────────────┐   ┌─────────────┐
│   Journal   │   │   Console   │   │ LiveLogFile │
└──────┬──────┘   └──────┬──────┘   └──────┬──────┘
       │                 │                 │
       └─────────────────┴─────────────────┘
                         ↓
              ┌─────────────────────┐
              │  Canonical Format   │  Single rendering source
              └─────────────────────┘

Core Layer (always available):

• Journal — Pure data structure
• Scope — Logical units of work
• Record — Individual events
• Filter — Composable criteria

Runtime Layer (optional):

• runtime — Global facade
• console — Dual output control
• live_log — Automatic, timestamped disk logging
• Macros — Zero-overhead convenience
• Log levels — Runtime event filtering

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Live Logging

Live logging is enabled per file path using runtime::enable_live_logging(PathBuf):

use std::path::PathBuf;

runtime::enable_live_logging(PathBuf::from("/tmp/eventline.log"));

event_info!("This event will be written to the live log file automatically");
event_warn!("Timestamped and indented according to scope depth");

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Dual Output Mode

Eventline supports two output modes:

Silent Journaling (Default)

Events are recorded but not printed:

runtime::init().await;
runtime::enable_console_output(false); // Default

event_info!("Silent"); // Recorded, not printed

// Later, examine the journal
runtime::with_journal(|journal| {
    eventline::render::render_journal_tree(journal, true, None);
}).await;

Dual Output (Traditional Logging Feel)

Events are both journaled AND printed to console:

runtime::init().await;
runtime::enable_console_output(true);
runtime::enable_console_color(true);

event_info!("Starting");  // Journaled + printed
event_warn!("Warning");   // Journaled + printed in yellow
event_error!("Error");    // Journaled + printed to stderr in red

Benefits:

• Get traditional logging behavior when you want it
• Always have structured journal for post-mortem
• Single flag to toggle: enable_console_output(bool)

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Key Concepts

Outcomes vs Events

Event kinds describe what happened:

• Info — routine progress
• Warning — unexpected but recoverable
• Error — something went wrong
• Debug — verbose diagnostics

Scope outcomes describe the result:

• Success — completed normally
• Failure — completed with errors
• Aborted — interrupted by panic

This separation enables:

• Warnings during successful operations
• Errors that don't cause failure
• Clear diagnostics vs results

Filtering at Render Time

Filtering happens when reading the journal, not when writing:

use eventline::Filter;
use eventline::ScopeFilter;
use eventline::Outcome;

let filter = Filter::scope(ScopeFilter::Outcome(Outcome::Failure));
render_journal_tree(&journal, true, Some(&filter));

Benefits:

• Zero overhead when not filtering
• Complete journal always preserved
• Multiple views from same data

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Advanced Usage

Batched Logging

use eventline::Journal;
use eventline::Outcome;

let mut journal = Journal::new();
let mut buffer = journal.create_buffer();

let scope = buffer.enter_scope(None, Some("BatchTask"));
for item in items {
    buffer.record(Some(scope), format!("Processing {}", item));
}
buffer.exit_scope(scope, Outcome::Success);

journal.flush_buffer(buffer); // Atomic ID rebase

Custom Output

use eventline::JournalWriter;
use std::io;

let mut file = std::fs::File::create("output.log")?;

// Customize canonical format
JournalWriter::new()
    .with_color(false)           // Disable colors
    .with_timestamps(true)       // Include timestamps
    .with_bullet("→")            // Custom bullet
    .write_to_all(
        &mut [
            &mut io::stdout() as &mut dyn io::Write,
            &mut file as &mut dyn io::Write,
        ],
        &journal
    )?;

Nested Scopes

scoped_eventline!("Deployment", {
    runtime::info("Starting deployment").await;
    
    scoped_eventline!("BuildImage", {
        runtime::info("Building Docker image").await;
    });
    
    scoped_eventline!("PushRegistry", {
        runtime::info("Pushing to registry").await;
    });
    
    runtime::info("Deployment complete").await;
});

Environment Variable Support

Respect common conventions:

use eventline::runtime::log_level::{set_log_level, LogLevel};

#[tokio::main]
async fn main() {
    runtime::init().await;
    
    // Respect NO_COLOR
    let use_color = std::env::var("NO_COLOR").is_err();
    runtime::enable_console_color(use_color);
    
    // Optional: RUST_LOG compatibility
    let log_level = std::env::var("RUST_LOG")
        .map(|s| match s.to_lowercase().as_str() {
            "debug" => LogLevel::Debug,
            "info" => LogLevel::Info,
            "warn" => LogLevel::Warning,
            "error" => LogLevel::Error,
            _ => LogLevel::Info,
        })
        .unwrap_or(LogLevel::Info);
    
    set_log_level(log_level);
    runtime::enable_console_output(true);
}

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CLI Integration

Typical pattern for command-line tools:

use clap::Parser;
use eventline::runtime::log_level::{set_log_level, LogLevel};

#[derive(Parser)]
struct Args {
    /// Enable verbose output
    #[arg(short, long)]
    verbose: bool,

    /// Suppress console output
    #[arg(short, long)]
    quiet: bool,
    
    /// Disable colored output
    #[arg(long)]
    no_color: bool,
}

#[tokio::main]
async fn main() {
    let args = Args::parse();
    
    runtime::init().await;

    if args.quiet {
        runtime::enable_console_output(false);
        set_log_level(LogLevel::Warning);
    } else {
        runtime::enable_console_output(true);
        runtime::enable_console_color(!args.no_color);
        
        if args.verbose {
            set_log_level(LogLevel::Debug);
        } else {
            set_log_level(LogLevel::Info);
        }
    }

    event_info!("Application started");
    
    // Your application logic here
    
    // At exit, optionally render summary with same color setting
    runtime::with_journal(|journal| {
        let use_color = !args.no_color;
        eventline::render::render_summary(journal, use_color, None, false);
    }).await;
}

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Design Principles

• Append-only by default - safe, auditable, deterministic
• Separation of concerns - data != rendering != runtime
• Human-first output - readable without tooling
• Optional global state - usable in libraries
• Async-safe - fire-and-forget from any task

Test-Friendly

#[tokio::test]
async fn test_task() {
    runtime::init().await;
    runtime::enable_console_output(false); // Quiet in tests
    
    event_info!("test");
    
    runtime::with_journal(|journal| {
        assert_eq!(journal.records().len(), 1);
    }).await;
    
    runtime::reset().await; // Clean up
}

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Installation

[dependencies]
eventline = "0.4.2"
tokio = { version = "1", features = ["full"] }

Optional features:

[dependencies]
eventline = { version = "0.4.2", features = ["colour"] }

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Roadmap

• Custom formatters (JSON, binary)
• Zero-copy query interface
• Tag-based filtering
• systemd journal integration

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License

MIT