ansi-rs

ANSI/VT terminal output as data, built entirely on the Rust standard library. Zero dependencies.

The TUI ecosystem's answer to "put styled text on a terminal" is a 30-crate dependency tree. This crate is the pure-bytes core of that job: build escape sequences, parse them, and diff screen frames, with no I/O at all: no raw mode, no stdin/stdout, no PTY. Feed it bytes from anywhere; write its bytes to anywhere.

Philosophy

See nativelite-philosophy for the broader engineering standards and attack surface reduction strategy behind all nativelite packages.

Three capabilities, one concern

Build styled output. Style + Color (default / 256-indexed / RGB) render to SGR sequences: absolutely, or as a minimal transition from a previous style:

use ansi::{Color, Style};

let warn = Style { bold: true, fg: Color::Indexed(1), ..Style::default() };
assert_eq!(warn.sgr(), "\x1b[0;1;31m");

let plain = Style::default();
assert_eq!(plain.transition_to(&warn), "\x1b[0;1;31m");

Parse a terminal byte stream, incrementally. Parser::feed accepts chunks split at any byte boundary (mid-escape, mid-UTF-8) and yields tokens: text runs, C0 controls, CSI/ESC/OSC sequences, and raw DCS/APC strings. The state machine follows the classic VT500-series design: C0 controls execute even inside sequences, CAN/SUB abort, a stray ESC restarts, malformed sequences are dropped rather than leaked as text, and invalid UTF-8 becomes U+FFFD without desyncing the stream.

let mut p = ansi::Parser::new();
for token in p.feed(b"\x1b[1;31mred\x1b[0m") {
    // Csi { params: [1, 31], final_byte: 'm', .. }, Text("red"), Csi { .. }
}

Render by diff. Screen is a grid of styled Cells. Screen::diff emits only the bytes that change what the terminal already shows: cursor moves, minimal SGR transitions, changed characters, and render_full repaints from scratch. Equal frames emit zero bytes.

use ansi::{Screen, Style};

let mut prev = Screen::new(24, 80);
let mut next = prev.clone();
next.write_str(0, 0, "hello", Style::default());
stdout_write(&prev.diff(&next)); // your I/O, not ours

What's deliberately out of scope

• I/O and raw mode: the rawterm crate's concern. This crate never touches a file descriptor.
• Full terminal emulation: the parser tokenizes; it does not maintain scrollback, tabs, or modes. apply_sgr is provided because the renderer and any output-interpreter need it.
• East Asian double-width: every char is one cell in Screen.
• Scroll-region diff tricks: the diff is cell-precise but does not emit scroll commands.

Correctness

SGR goldens are asserted byte-exact, then round-tripped: every built sequence is fed back through the parser and re-applied with apply_sgr, which must reproduce the original style, for a spread of styles and all transitions between them. Tokenizer fixtures (xterm/ECMA-48 sequences, private modes, both OSC terminators, aborts, mid-sequence C0, invalid UTF-8) are each verified twice: fed one-shot and fed byte-at-a-time, which must yield identical tokens. The screen renderer is verified end-to-end: every diff is replayed through the parser onto an interpreted screen, and the result must equal the target frame exactly, including a byte-exact golden for the minimal-update case.

Development

python dev.py check   # zero-dependency guard + cargo test (the pre-push gate)
python dev.py test    # cargo test
python dev.py fmt     # cargo fmt --check
python dev.py guard   # zero-dependency guard

dev.py is a stdlib-only runner, so python dev.py check is the same one-command local gate used across every nativelite package. The guard fails if Cargo.toml declares any dependency: runtime, build, or dev.