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use rusoto_core::RusotoError;
use rusoto_s3::{GetObjectError, GetObjectRequest, S3Client, S3};
use std::convert::TryFrom;
use std::io::{Error, ErrorKind, Read, Seek};
use std::pin::Pin;
use tokio::io::AsyncRead;
use tokio::io::AsyncReadExt;
pub struct SeekableS3Object<'a, A> {
client: A,
req: GetObjectRequest,
position: u64,
// Updated when we first read the object.
length: u64,
body: Option<Pin<Box<dyn AsyncRead + Send>>>,
runtime: &'a tokio::runtime::Runtime,
}
impl<A: std::fmt::Debug> std::fmt::Debug for SeekableS3Object<'_, A> {
fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
f.debug_struct("SeekableS3Object")
.field("client", &self.client)
.field("req", &self.req)
.field("position", &self.position)
.field("length", &self.length)
.field("runtime", &self.runtime)
.finish()
}
}
impl<'a, A> SeekableS3Object<'a, A> {
pub fn new(
client: A,
runtime: &'a tokio::runtime::Runtime,
mut req: GetObjectRequest,
) -> Result<Self, RusotoError<GetObjectError>>
where
A: S3,
{
// If for some reason we get request with range field filled, get rid of
// it or we will end up with the wrong content length returned.
// Alternatively we may want to use HeadObject request instead.
req.range = None;
let object = runtime.block_on(client.get_object(req.to_owned()))?;
let body = object
.body
// I don't understand why the cast is needed but otherwise we get
//
// note: expected enum `Option<Box<(dyn tokio::io::AsyncRead + Sync + std::marker::Send + 'static)>>`
// found enum `Option<Box<impl std::marker::Send+Sync+tokio::io::AsyncRead>>`
//
// https://stackoverflow.com/questions/61259521/struct-with-boxed-impl-trait
.map(|bs| Box::pin(bs.into_async_read()) as Pin<Box<dyn AsyncRead + Send>>);
let length = match object.content_length {
None => Err(RusotoError::Validation(
"Content length not set in response.".to_owned(),
)),
Some(length) => match u64::try_from(length) {
Ok(length) => Ok(length),
Err(_e) => Err(RusotoError::Validation(format!(
"Content length didn't fit into a u64, got {}",
length
))),
},
}?;
Ok(SeekableS3Object {
client,
req,
position: 0,
length,
body,
runtime,
})
}
// Sets current position. If the position actually changes, invalidates the
// current object body.
//
// You should only use this if you're not consuming the body. If the body is
// being consumed, you just want to update the position directly based on
// how much you've consumed.
fn set_position(&mut self, new_position: u64) {
if self.position != new_position {
self.position = new_position;
self.body = None;
}
}
// Reads some data from the body while remebering to update the position.
fn read_body(&mut self, buf: &mut [u8]) -> std::io::Result<usize> {
if let Some(body) = &mut self.body {
let bytes_read = self.runtime.block_on(body.read(buf))?;
// If we managed to read something, make sure to update position.
// This saves us work if we something calls seek into the new
// position.
self.position += bytes_read as u64;
Ok(bytes_read)
} else {
// No body.
Ok(0)
}
}
}
impl<'a, A> Read for SeekableS3Object<'_, A>
where
A: S3,
{
fn read(&mut self, buf: &mut [u8]) -> std::io::Result<usize> {
// We're done reading, AWS API throws a fit for out-of-range range
// requests so we exit early.
if self.position >= self.length {
return Ok(0);
}
// We may have a body already present in which case we just read from
// it. Only if we don't have the body (for example, we performed a seek)
// do we issue any new requests.
if self.body.is_some() {
return self.read_body(buf);
}
// We didn't have existing body to read from: probably we have done a
// seek. Get the body at the new position, read some data and store the
// new body for the future.
self.req.range = Some(format!("bytes={}-", self.position));
let object = self
.runtime
.block_on(self.client.get_object(self.req.to_owned()))
.map_err(|e| Error::new(ErrorKind::Other, e))?;
self.body = object
.body
.map(|bs| Box::pin(bs.into_async_read()) as Pin<Box<dyn AsyncRead + Send>>);
self.read_body(buf)
}
}
impl<A> Seek for SeekableS3Object<'_, A> {
fn seek(&mut self, pos: std::io::SeekFrom) -> std::io::Result<u64> {
// Implementation roughly lifted from std::io::cursor Seek trait
// implementation.
let (base_pos, offset) = match pos {
std::io::SeekFrom::Start(pos) => {
self.set_position(pos);
return Ok(pos);
}
std::io::SeekFrom::End(pos) => (self.length, pos),
std::io::SeekFrom::Current(pos) => (self.position, pos),
};
let new_pos = if offset >= 0 {
base_pos.checked_add(offset as u64)
} else {
base_pos.checked_sub((offset.wrapping_neg()) as u64)
};
match new_pos {
Some(n) => {
self.set_position(n);
Ok(self.position)
}
None => Err(Error::new(
ErrorKind::InvalidInput,
"invalid seek to a negative or overflowing position",
)),
}
}
}
// Allows to simply say `s3.get_seekable_object` to be consistent with rest of
// rusoto API.
pub trait GetSeekableObject: Sized {
fn get_seekable_object(
self,
runtime: &tokio::runtime::Runtime,
input: GetObjectRequest,
) -> Result<SeekableS3Object<'_, Self>, RusotoError<GetObjectError>>;
}
impl GetSeekableObject for S3Client {
fn get_seekable_object(
self,
runtime: &tokio::runtime::Runtime,
input: GetObjectRequest,
) -> Result<SeekableS3Object<'_, Self>, RusotoError<GetObjectError>> {
SeekableS3Object::new(self, runtime, input)
}
}