lesavka/client/src/paste.rs

// client/src/paste.rs
#![forbid(unsafe_code)]

use anyhow::{Context, Result};
use chacha20poly1305::aead::{Aead, KeyInit, OsRng, rand_core::RngCore};
use chacha20poly1305::{ChaCha20Poly1305, Key, Nonce};

use lesavka_common::lesavka::PasteRequest;
use lesavka_common::paste::{decode_shared_key, truncate_text};

/// Build an encrypted clipboard request for the server's paste RPC.
///
/// Inputs: the raw clipboard text captured on the desktop client.
/// Outputs: a `PasteRequest` whose payload is truncated to policy, encrypted,
/// and marked as such for the server-side validator.
/// Why: the client owns nonce generation and pre-flight truncation so oversized
/// clipboard content fails predictably before any RPC is attempted.
pub fn build_paste_request(text: &str) -> Result<PasteRequest> {
    let max = std::env::var("LESAVKA_PASTE_MAX")
        .ok()
        .and_then(|v| v.parse::<usize>().ok())
        .unwrap_or(4096);
    let text = truncate_text(text, max);
    let key = load_key()?;
    let cipher = ChaCha20Poly1305::new(Key::from_slice(&key));

    let mut nonce_bytes = [0u8; 12];
    OsRng.fill_bytes(&mut nonce_bytes);
    let nonce = Nonce::from_slice(&nonce_bytes);

    let ciphertext = cipher
        .encrypt(nonce, text.as_bytes())
        .map_err(|e| anyhow::anyhow!("paste encrypt failed: {e}"))?;

    Ok(PasteRequest {
        nonce: nonce_bytes.to_vec(),
        data: ciphertext,
        encrypted: true,
    })
}

fn load_key() -> Result<[u8; 32]> {
    let raw = std::env::var("LESAVKA_PASTE_KEY")
        .context("LESAVKA_PASTE_KEY not set (required for PasteText RPC)")?;
    decode_shared_key(&raw)
}