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//! A simple example showing how to crate size-sealed memfd.
//!
//! It creates a new memfd and seals to on a fixed 1K size.
//!
//! This is an example ONLY: do NOT panic/unwrap/assert
//! in production code!
extern crate memfd;
use std::io::{Seek, SeekFrom, Write};
fn main() {
// Create a sealable memfd.
let opts = memfd::MemfdOptions::default().allow_sealing(true);
let mfd = opts.create("sized-1K").unwrap();
// Resize to 1024B.
mfd.as_file().set_len(1024).unwrap();
// Add seals to prevent further resizing.
mfd.add_seals(&[
memfd::FileSeal::SealShrink,
memfd::FileSeal::SealGrow
]).unwrap();
// Prevent further sealing changes.
mfd.add_seal(memfd::FileSeal::SealSeal).unwrap();
// Write 1K of data, allowed by size seals.
let data_1k = vec![0x00; 1024];
let r = mfd.as_file().write_all(&data_1k);
assert!(r.is_ok());
mfd.as_file().seek(SeekFrom::Start(0)).unwrap();
// Write 2K of data, now allowed by size seals.
let data_2k = vec![0x11; 2048];
let r = mfd.as_file().write_all(&data_2k);
assert!(r.is_err());
mfd.as_file().seek(SeekFrom::Start(0)).unwrap();
// Try to resize to 2048B, not allowed by size seals.
let r = mfd.as_file().set_len(2048);
assert!(r.is_err());
// Overwrite 1K of data, allowed by size seals.
let data_1k = vec![0x22; 1024];
let r = mfd.as_file().write_all(&data_1k);
assert!(r.is_ok());
}
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