mailsis-utils 0.2.2

//! Async file I/O helpers for large payloads.
//!
//! Email attachments can be arbitrarily large, so file reads and writes
//! go through async, chunked helpers here to avoid blocking the Tokio
//! runtime. Also includes random-file generation for test fixtures.

use std::{io::Error, path::Path};

use rand::Rng;
use tokio::{
    fs::File,
    io::{AsyncReadExt, AsyncWriteExt},
};

/// Reads a large file from the given path.
///
/// The file is read in an async manner.
pub async fn read_large_file(path: impl AsRef<Path>) -> Result<Vec<u8>, Error> {
    let mut file = File::open(path).await?;
    let mut buffer = Vec::new();
    file.read_to_end(&mut buffer).await?;
    Ok(buffer)
}

/// Generates a random file with the given size in MB.
///
/// The file is created in the path provided and in an
/// async manner.
pub async fn generate_random_file(path: impl AsRef<Path>, size_mb: usize) -> Result<(), Error> {
    let mut file = File::create(path).await?;
    let mut rng = rand::thread_rng();
    let chunk_size = 1024 * 1024;
    let total_chunks = size_mb;

    for _ in 0..total_chunks {
        let mut chunk = vec![0u8; chunk_size];
        rng.fill(&mut chunk[..]);
        AsyncWriteExt::write_all(&mut file, &chunk).await?;
    }

    file.flush().await?;
    Ok(())
}

/// Generates random bytes that can be used to test the file system.
///
/// The generated bytes are not guaranteed to be unique, but it
/// uses a good random number generator.
pub async fn generate_random_bytes(size: usize) -> Result<Vec<u8>, Error> {
    let mut rng = rand::thread_rng();
    let mut bytes = vec![0u8; size];
    rng.fill(&mut bytes[..]);
    Ok(bytes)
}

#[cfg(test)]
mod tests {
    use tempfile::TempDir;

    use super::*;

    #[tokio::test]
    async fn test_read_large_file_success() {
        let temp_dir = TempDir::new().unwrap();
        let file_path = temp_dir.path().join("test.txt");
        tokio::fs::write(&file_path, b"Hello, World!")
            .await
            .unwrap();

        let content = read_large_file(&file_path).await.unwrap();
        assert_eq!(content, b"Hello, World!");
    }

    #[tokio::test]
    async fn test_read_large_file_empty() {
        let temp_dir = TempDir::new().unwrap();
        let file_path = temp_dir.path().join("empty.txt");
        tokio::fs::write(&file_path, b"").await.unwrap();

        let content = read_large_file(&file_path).await.unwrap();
        assert!(content.is_empty());
    }

    #[tokio::test]
    async fn test_read_large_file_not_found() {
        let result = read_large_file("/nonexistent/path/file.txt").await;
        assert!(result.is_err());
    }

    #[tokio::test]
    async fn test_generate_random_file_creates_file() {
        let temp_dir = TempDir::new().unwrap();
        let file_path = temp_dir.path().join("random.bin");

        generate_random_file(&file_path, 1).await.unwrap();

        let content = tokio::fs::read(&file_path).await.unwrap();
        assert_eq!(content.len(), 1024 * 1024);
    }

    #[tokio::test]
    async fn test_generate_random_file_zero_size() {
        let temp_dir = TempDir::new().unwrap();
        let file_path = temp_dir.path().join("empty_random.bin");

        generate_random_file(&file_path, 0).await.unwrap();

        let content = tokio::fs::read(&file_path).await.unwrap();
        assert!(content.is_empty());
    }

    #[tokio::test]
    async fn test_generate_random_bytes_size() {
        let bytes = generate_random_bytes(256).await.unwrap();
        assert_eq!(bytes.len(), 256);
    }

    #[tokio::test]
    async fn test_generate_random_bytes_zero_size() {
        let bytes = generate_random_bytes(0).await.unwrap();
        assert!(bytes.is_empty());
    }

    #[tokio::test]
    async fn test_generate_random_bytes_not_all_zeros() {
        let bytes = generate_random_bytes(1024).await.unwrap();
        assert!(bytes.iter().any(|&byte| byte != 0));
    }

    #[tokio::test]
    async fn test_read_large_file_roundtrip() {
        let temp_dir = TempDir::new().unwrap();
        let file_path = temp_dir.path().join("roundtrip.bin");

        generate_random_file(&file_path, 1).await.unwrap();
        let content = read_large_file(&file_path).await.unwrap();
        assert_eq!(content.len(), 1024 * 1024);
    }
}