# logViewer

**[中文文档](README-zh.md)**

A high-performance terminal log file viewer built in Rust, designed to handle multi-gigabyte files with minimal memory overhead.

Uses memory-mapped I/O with a sparse line index and progressive background loading to open files instantly — even 5GB+ logs scroll smoothly from the first keystroke.

## Features

- **Instant file open** — mmap-backed reader with background progressive indexing; start scrolling before indexing finishes
- **Handles huge files** — sparse line index (1 entry per 256 lines) keeps memory usage at ~8MB even for 5GB files
- **Live file tracking** — watches for appends, truncations, and log rotation via `notify`
- **JSON log support** — NDJSON parsing with BOM handling, duplicate key detection, and toggleable pretty-printing
- **Unicode-aware wrapping** — correct line wrapping for CJK, emoji, and tabs
- **Persistent index cache** — line indexes saved to disk with xxh3 content hashing; re-opens are near-instant
- **Vim-like keybindings** — familiar navigation for terminal users
- **Customizable colors** — per-log-level colors via TOML config, adjustable from within the TUI

## Quick Start

```bash
# Build and run
cargo run -p log-viewer-tui -- path/to/logfile.log

# Or build first
cargo build --release -p log-viewer-tui
./target/release/log-viewer-tui path/to/logfile.log
```

Requires Rust 1.92+ (see `rust-toolchain.toml`).

## Keybindings

| Key | Action |
|-----|--------|
| `j` / `↓` | Scroll down one line |
| `k` / `↑` | Scroll up one line |
| `Ctrl+d` | Scroll down half page |
| `Ctrl+u` | Scroll up half page |
| `Ctrl+f` / `PgDn` | Scroll down full page |
| `Ctrl+b` / `PgUp` | Scroll up full page |
| `G` / `End` | Jump to end of file |
| `gg` / `Home` | Jump to start of file |
| `Tab` | Toggle JSON pretty-printing |
| `S` | Open color settings |
| `q` / `Esc` | Quit |

Settings panel: use `j`/`k` to select a log level, `←`/`→` to cycle colors, `Enter` to save, `Esc` to cancel.

## Workspace Structure

```
crates/core  — Shared library: I/O, parsing, types, config, file watching
crates/tui   — Terminal UI (ratatui + crossterm)
crates/gui   — GUI (egui + eframe) — placeholder, not yet functional
crates/bench — mmap vs pread benchmark harness
```

## Development

```bash
# Check, test, lint
cargo check --workspace
cargo test --workspace
cargo fmt --check --all
cargo clippy --workspace -- -D warnings

# Run benchmarks (requires a pre-generated ~5GB test file)
mkdir -p /tmp/test-logviewer
dd if=/dev/urandom of=/tmp/test-logviewer/extreme.log bs=1M count=5000
cargo run -p log-viewer-bench
cargo run -p log-viewer-bench -- --quick --suites startup,render --output results.md

# Test a single crate
cargo test -p log-viewer-core
cargo test -p log-viewer-tui
```

### CI

The CI gate runs on ubuntu-latest and windows-latest:
1. `cargo fmt --check --all`
2. `cargo check --workspace`
3. `cargo test --workspace`
4. `cargo clippy --workspace -- -D warnings`

No custom rustfmt or clippy config — uses toolchain defaults.

## Architecture

The core library (`log-viewer-core`) owns all I/O, parsing, and data types. Key design decisions:

- **Sparse line index** — samples every 256 lines using memchr SIMD acceleration. A 1M-line file produces a ~32KB index instead of ~8MB.
- **Progressive loading** — `ProgressiveFileReader` starts with a quick head+tail sample for instant line estimates, then builds the full index in a background thread via crossbeam-channel.
- **mmap with TOCTOU mitigation** — post-mmap stat check to detect file changes. `read_cache` module exists as a future pread-based alternative to eliminate SIGBUS risk entirely.
- **Persistent cache** — line indexes are serialized to disk with xxh3 content hashing for invalidation. Atomic writes via temp files.
- **Visual height index** — prefix-sum over wrapped-line heights, enabling O(log n) scroll-to-line mapping for long wrapped lines.

Planned but not yet built: filtering, bookmarks, sessions, search engine (stub modules exist).

## Benchmarks

Custom harness comparing mmap vs pread backends across 7 suites (startup, render, jump, memory, growth, rotation, concurrent). Uses wall-clock timing with `/proc/self/` RSS and page fault metrics. Results are written as markdown tables to `benchmark-report.md`.

The harness expects `/tmp/test-logviewer/extreme.log` to already exist. It does not generate the primary 5GB test file automatically; create it first with the `dd` command shown above.

The benchmark binary includes ~75 unit tests for the reader backends and metrics collection.