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use anyhow::Result;
use async_trait::async_trait;
use std::io::{Cursor, SeekFrom};
use tokio::fs::File;
use tokio::io::{AsyncSeekExt, AsyncWrite, AsyncWriteExt};
#[async_trait]
pub trait AsyncWriterFactory {
async fn get_writer<'a>(&'a mut self) -> Result<Box<dyn AsyncWrite + Unpin + 'a>>;
}
pub struct CursorWriterFactory<T>(Cursor<T>);
#[async_trait]
impl AsyncWriterFactory for CursorWriterFactory<Vec<u8>> {
async fn get_writer<'a>(&'a mut self) -> Result<Box<dyn AsyncWrite + Unpin + 'a>> {
self.0.get_mut().clear();
self.0.set_position(0);
Ok(Box::new(&mut self.0))
}
}
#[async_trait]
impl AsyncWriterFactory for CursorWriterFactory<&mut [u8]> {
async fn get_writer<'a>(&'a mut self) -> Result<Box<dyn AsyncWrite + Unpin + 'a>> {
self.0.set_position(0);
Ok(Box::new(&mut self.0))
}
}
impl Default for CursorWriterFactory<Vec<u8>> {
fn default() -> Self {
Self(Cursor::new(Vec::new()))
}
}
impl CursorWriterFactory<Vec<u8>> {
pub fn new() -> Self {
Self::default()
}
pub fn into_inner(self) -> Vec<u8> {
self.0.into_inner()
}
}
impl<'a> CursorWriterFactory<&'a mut [u8]> {
pub fn for_buf(inner: &'a mut [u8]) -> Self {
Self(Cursor::new(inner))
}
pub fn size(self) -> usize {
self.0.position() as usize
}
}
pub struct FileWriterFactory(File);
#[async_trait]
impl AsyncWriterFactory for FileWriterFactory {
async fn get_writer<'a>(&'a mut self) -> Result<Box<dyn AsyncWrite + Unpin + 'a>> {
let mut file = self.0.try_clone().await?;
file.set_len(0).await?;
file.seek(SeekFrom::Start(0)).await?;
Ok(Box::new(file))
}
}
impl FileWriterFactory {
pub fn new(file: File) -> Self {
Self(file)
}
pub async fn into_inner(mut self) -> Result<File> {
self.0.flush().await?;
Ok(self.0)
}
}
#[cfg(test)]
mod test {
use super::*;
use anyhow::Result;
use tempfile::tempfile;
use tokio::io::{copy, AsyncReadExt, AsyncSeekExt};
const DATA: &[u8] = b"HELLO/WORLD";
async fn copy_to_factory<F: AsyncWriterFactory>(
data: &[u8],
factory: &mut F,
) -> std::io::Result<()> {
let mut reader = Cursor::new(data);
let mut writer = factory.get_writer().await.unwrap();
copy(&mut reader, &mut writer).await?;
Ok(())
}
#[tokio::test]
async fn vec_cursor_writer_twice() -> Result<()> {
let mut factory = CursorWriterFactory::new();
copy_to_factory(b"wrong data, shouldn't see this", &mut factory).await?;
copy_to_factory(DATA, &mut factory).await?;
assert_eq!(&factory.into_inner(), DATA);
Ok(())
}
#[tokio::test]
async fn buf_cursor_writer_twice() -> Result<()> {
let mut buf = [0u8; 256];
let mut factory = CursorWriterFactory::for_buf(&mut buf[..]);
copy_to_factory(b"nobody should see this", &mut factory).await?;
copy_to_factory(DATA, &mut factory).await?;
let size = factory.size();
assert_eq!(&buf[..size], DATA);
Ok(())
}
#[tokio::test]
async fn buf_cursor_writer_too_small() -> Result<()> {
let mut buf = [0u8; 5];
let mut factory = CursorWriterFactory::for_buf(&mut buf[..]);
let err = copy_to_factory(DATA, &mut factory).await.unwrap_err();
assert_eq!(err.kind(), std::io::ErrorKind::WriteZero);
Ok(())
}
#[tokio::test]
async fn file_writer_twice() -> Result<()> {
let mut factory = FileWriterFactory::new(tempfile()?.into());
copy_to_factory(b"wrong data, shouldn't see this", &mut factory).await?;
copy_to_factory(DATA, &mut factory).await?;
let mut file = factory.into_inner().await?;
file.seek(SeekFrom::Start(0)).await?;
let mut res = Vec::new();
file.read_to_end(&mut res).await?;
assert_eq!(&res, DATA);
Ok(())
}
}