labelize 0.5.0

Fast Rust engine to parse ZPL & EPL label data and render to PNG/PDF. CLI, HTTP microservice, or library. Open-source Labelary alternative.
Documentation 
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use sha2::{Digest, Sha256};
use std::path::PathBuf;
use std::sync::Mutex;
use std::time::Instant;

static RATE_LIMITER: Mutex<Option<Instant>> = Mutex::new(None);

/// Minimum interval between Labelary API requests (~333ms = 3 req/sec).
const MIN_INTERVAL_MS: u128 = 334;

fn cache_dir() -> PathBuf {
    let dir = PathBuf::from("testdata/labelary_cache");
    std::fs::create_dir_all(&dir).ok();
    dir
}

fn cache_key(zpl: &str, dpmm: u8, width_inches: f64, height_inches: f64) -> String {
    let mut hasher = Sha256::new();
    hasher.update(zpl.as_bytes());
    hasher.update(dpmm.to_le_bytes());
    hasher.update(width_inches.to_le_bytes());
    hasher.update(height_inches.to_le_bytes());
    format!("{:x}", hasher.finalize())
}

fn rate_limit() {
    let mut last = RATE_LIMITER.lock().unwrap();
    if let Some(prev) = *last {
        let elapsed = prev.elapsed().as_millis();
        if elapsed < MIN_INTERVAL_MS {
            std::thread::sleep(std::time::Duration::from_millis(
                (MIN_INTERVAL_MS - elapsed) as u64,
            ));
        }
    }
    *last = Some(Instant::now());
}

/// Fetch a reference PNG from the Labelary API with caching and rate limiting.
/// Returns None if the API is unreachable or returns an error.
pub fn labelary_render(
    zpl: &str,
    dpmm: u8,
    width_inches: f64,
    height_inches: f64,
) -> Option<Vec<u8>> {
    let key = cache_key(zpl, dpmm, width_inches, height_inches);
    let cache_path = cache_dir().join(format!("{}.png", key));

    // Check cache first
    if cache_path.exists() {
        return std::fs::read(&cache_path).ok();
    }

    rate_limit();

    let url = format!(
        "http://api.labelary.com/v1/printers/{}/labels/{}x{}/0/",
        dpmm, width_inches, height_inches
    );

    let client = reqwest::blocking::Client::new();
    let resp = client
        .post(&url)
        .header("Accept", "image/png")
        .header("Content-Type", "application/x-www-form-urlencoded")
        .body(zpl.to_string())
        .send()
        .ok()?;

    if !resp.status().is_success() {
        eprintln!("Labelary API returned status {} for {}", resp.status(), url);
        return None;
    }

    let bytes = resp.bytes().ok()?.to_vec();
    // Cache the response
    std::fs::write(&cache_path, &bytes).ok();
    Some(bytes)
}