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
• Event kinds — Info, Warning, Error, Debug (separate from outcomes)
• 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
• Human-readable output — Unicode bullets, optional color coding
• High-throughput batching — JournalBuffer for batch writes
• Dual-layer API — pure core + optional runtime facade
• Async runtime support — fire-and-forget logging and async scopes (scoped_async())
• Deterministic replay — safe concurrent reads, reliable audit trails

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Quick Start

Runtime API (Fire-and-Forget)

For applications and daemons:

use eventline::runtime;
use eventline::runtime::log_level::{set_log_level, LogLevel};
use eventline::{event_info, event_warn, event_error, event_debug, event_scope};
use std::path::PathBuf;

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

    // Enable dual output: journal + console
    runtime::enable_console_output(true).await;
    runtime::enable_console_color(true).await;

    // Enable live logging to disk
    let log_path = PathBuf::from("/tmp/eventline.log");
    runtime::enable_live_logging(log_path).await;

    // Set runtime log level
    set_log_level(LogLevel::Warning).await;

    event_info!("This will NOT be logged").await;
    event_warn!("Cache approaching limit").await;          // Journaled + printed + live
    event_error!("Database connection failed").await;      // Journaled + printed + live
    event_debug!("Verbose debug info").await;              // Filtered out

    event_scope!("RequestHandler", {
        event_info!("Processing request").await;           // Filtered out
        event_warn!("Retry attempt failed").await;         // Journaled + printed + live
    }).await;

    // Journal is now live-appended automatically; no manual flush required
}

Runtime API (Async Scopes)

use eventline::runtime;
use eventline::{event_info, event_scope_async, event_scope_unnamed};

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

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

    // Fire-and-forget logging
    event_info!("Async logging example").await;

    // Named async scope
    event_scope_async!("AsyncTask", {
        event_info!("Inside async scope").await;
        tokio::time::sleep(std::time::Duration::from_millis(100)).await;
    }).await;

    // Unnamed async scope (note: requires 'async' keyword)
    event_scope_unnamed!(async {
        event_info!("Unnamed async work").await;
    }).await;
}

Core Journal API (Explicit Control)

For libraries or embedded systems:

use eventline::journal::Journal;
use eventline::journal::outcome::Outcome;
use eventline::journal::writer::JournalWriter;

let mut journal = Journal::new();

journal.scoped(None, Some("Task"), |journal, scope| {
    journal.record(Some(scope), "Starting task");
    journal.warn(Some(scope), "Low memory");
});

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

---

Architecture

┌─────────────┐
│   Macros    │  event_info!(), event_scope!()
└──────┬──────┘
       ↓
┌─────────────┐
│   Runtime   │  Global, thread-safe facade (optional)
└──────┬──────┘
       ↓
┌─────────────┐  ┌─────────────┐  ┌─────────────┐
│   Journal   │  │   Console   │  │ LiveLogFile │
└─────────────┘  └─────────────┘  └─────────────┘

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

---

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")).await;

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

---

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).await; // Default

event_info!("Silent").await; // 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).await;
runtime::enable_console_color(true).await;

event_info!("Starting").await;  // Journaled + printed
event_warn!("Warning").await;   // Journaled + printed in yellow
event_error!("Error").await;    // 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::journal::filter::{Filter, ScopeFilter, EventFilter};
use eventline::journal::event_kind::EventKind;
use eventline::journal::outcome::Outcome;

// Show only failed scopes
let filter = Filter::scope(ScopeFilter::Outcome(Outcome::Failure));

// Show only warnings and errors
let filter = Filter::event(
    EventFilter::Kind(EventKind::Warning)
        .or(EventFilter::Kind(EventKind::Error))
);

// Complex: failed scopes with deep nesting
let filter = Filter::scope(
    ScopeFilter::Outcome(Outcome::Failure)
        .and(ScopeFilter::MinDepth(2))
);

render_journal_tree(&journal, true, Some(&filter));

Benefits:

• Zero overhead when not filtering
• Complete journal always preserved
• Multiple views from same data
• Composable with AND, OR, NOT

---

Scoped Macros

Named Scopes

// Standard named scope
event_scope!("TaskName", {
    event_info!("Work happening").await;
}).await;

// Async variant (explicit async support)
event_scope_async!("AsyncTask", {
    event_info!("Async work").await;
    tokio::time::sleep(Duration::from_millis(10)).await;
}).await;

Unnamed Scopes

// Unnamed scope - requires 'async' keyword
event_scope_unnamed!(async {
    event_info!("Anonymous work").await;
}).await;

// Async variant
event_scope_unnamed_async!({
    event_info!("Anonymous async work").await;
}).await;

Try Scopes (No-Panic)

// Named scope without panicking if runtime uninitialized
try_scope!("OptionalScope", {
    event_info!("Safe logging").await;
}).await;

// Unnamed scope without panicking
try_scope_unnamed!(async {
    event_info!("Safe anonymous logging").await;
}).await;

Single-Line Scoped Events

For IPC handlers and event callbacks where you want scope context without wrapping a block:

// These create a scope and log a single event
event_info_scoped!("ProfileSwitch", "Switched to profile: {}", profile_name).await;
event_warn_scoped!("CacheCheck", "Cache at {}% capacity", 95).await;
event_error_scoped!("IpcHandler", "Failed to process: {}", error).await;
event_debug_scoped!("Trigger", "Window {} focused", window_id).await;

---

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

    event_info!("Application started").await;
    
    // 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);
    }).await;
}

---

Advanced Usage

Batched Logging

use eventline::journal::Journal;
use eventline::journal::outcome::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::journal::writer::JournalWriter;
use std::io;

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

JournalWriter::new()
    .with_bullet("→")
    .write_to_all(
        &mut [
            &mut io::stdout() as &mut dyn io::Write,
            &mut file as &mut dyn io::Write,
        ],
        &journal
    )?;

Nested Scopes

event_scope!("Deployment", {
    event_info!("Starting deployment").await;
    
    event_scope!("BuildImage", {
        event_info!("Building Docker image").await;
    }).await;
    
    event_scope!("PushRegistry", {
        event_info!("Pushing to registry").await;
    }).await;
    
    event_info!("Deployment complete").await;
}).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).await;
    
    // 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).await;
    runtime::enable_console_output(true).await;
}

---

Design Principles

Append-Only Invariant

Once written, entries are never modified or removed:

• Deterministic replay
• Safe concurrent reads
• Reliable audit trails

Separation of Concerns

• Journal — Pure data
• JournalWriter — Rendering policy
• JournalBuffer — Batching mechanism
• Filter — Selection criteria
• Runtime — Optional global facade
• Console — Dual output control

Test-Friendly

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

---

Installation

[dependencies]
eventline = "0.3.1"
tokio = { version = "1", features = ["full"] }

Optional features:

[dependencies]
eventline = { version = "0.3.1", features = ["colour"] }

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Roadmap

• Custom formatters (JSON, binary)
• Structured data (key-value pairs)
• Zero-copy query interface
• Tag-based filtering
• systemd journal integration

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Philosophy

Eventline is designed to:

• Be intuitive for humans reading logs
• Enable deterministic replay of execution
• Support both traditional logging and structured journaling
• Serve as foundation for distribution-wide logging
• Make debugging and monitoring pleasant

It is not:

• A metrics system (use Prometheus)
• A distributed tracing backend
• A replacement for structured logging (yet)

Focuses on local, human-readable execution traces with optional runtime log filtering and dual output modes.

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Version 0.3.0 — Highlights

• Async runtime support — init().await, scoped_async(), fire-and-forget logging from async tasks
• Live logging — automatic timestamped file append
• Runtime output formatting — indentation by scope depth, bullets, colors
• Dual output mode — console + journal, fully async-safe
• Scoped event macros — single-line events with scope context (event_info_scoped!, etc.)
• Removed unnecessary manual flush — runtime manages output automatically
• Improved CLI integration — verbose, quiet, color flags respected
• Internal cleanup — simpler, safer, maintainable runtime code

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License

MIT