use std::io::{self, Cursor, Read, Write};
use data_encoding::BASE64;
use crate::{chunkservice::ChunkService, proto};
/// BlobReader implements reading of a blob, by querying individual chunks.
///
/// It doesn't talk to BlobService, but assumes something has already fetched
/// blob_meta already.
pub struct BlobReader<'a, CS: ChunkService> {
// used to look up chunks
chunk_service: &'a CS,
// internal iterator over chunk hashes and their sizes
chunks_iter: std::vec::IntoIter<proto::blob_meta::ChunkMeta>,
// If a chunk was partially read (if buf.len() < chunk.size),
// a cursor to its contents are stored here.
current_chunk: Option<Cursor<Vec<u8>>>,
}
impl<'a, CS: ChunkService> BlobReader<'a, CS> {
pub fn open(chunk_service: &'a CS, blob_meta: proto::BlobMeta) -> Self {
Self {
chunk_service,
chunks_iter: blob_meta.chunks.into_iter(),
current_chunk: None,
}
}
/// reads (up to n bytes) from the current chunk into buf (if there is
/// a chunk).
///
/// If it arrives at the end of the chunk, sets it back to None.
/// Returns a io::Result<usize> of the bytes read from the chunk.
fn read_from_current_chunk<W: std::io::Write>(
&mut self,
m: usize,
buf: &mut W,
) -> std::io::Result<usize> {
// If there's still something in partial_chunk, read from there
// (up to m: usize bytes) and return the number of bytes read.
if let Some(current_chunk) = &mut self.current_chunk {
let result = io::copy(&mut current_chunk.take(m as u64), buf);
match result {
Ok(n) => {
// if we were not able to read all off m bytes,
// this means we arrived at the end of the chunk.
if n < m as u64 {
self.current_chunk = None
}
// n can never be > m, so downcasting this to usize is ok.
Ok(n as usize)
}
Err(e) => Err(e),
}
} else {
Ok(0)
}
}
}
impl<CS: ChunkService> std::io::Read for BlobReader<'_, CS> {
fn read(&mut self, buf: &mut [u8]) -> std::io::Result<usize> {
let read_max = buf.len();
let mut bytes_read = 0_usize;
let mut buf_w = std::io::BufWriter::new(buf);
// read up to buf.len() bytes into buf, by reading from the current
// chunk and subsequent ones.
loop {
// try to fill buf with bytes from the current chunk
// (if there's still one)
let n = self.read_from_current_chunk(read_max - bytes_read, &mut buf_w)?;
bytes_read += n;
// We want to make sure we don't accidentially read past more than
// we're allowed to.
assert!(bytes_read <= read_max);
// buf is entirerly filled, we're done.
if bytes_read == read_max {
buf_w.flush()?;
break Ok(bytes_read);
}
// Otherwise, bytes_read is < read_max, so we could still write
// more to buf.
// Check if we have more chunks to read from.
match self.chunks_iter.next() {
// No more chunks, we're done.
None => {
buf_w.flush()?;
return Ok(bytes_read);
}
// There's another chunk to visit, fetch its contents
Some(chunk_meta) => match self.chunk_service.get(&chunk_meta.digest) {
// Fetch successful, put it into `self.current_chunk` and restart the loop.
Ok(Some(chunk_data)) => {
// make sure the size matches what chunk_meta says as well.
if chunk_data.len() as u32 != chunk_meta.size {
break Err(std::io::Error::new(
io::ErrorKind::InvalidData,
format!(
"chunk_service returned chunk with wrong size for {}, expected {}, got {}",
BASE64.encode(&chunk_meta.digest), chunk_meta.size, chunk_data.len()
)
));
}
self.current_chunk = Some(Cursor::new(chunk_data));
}
// Chunk requested does not exist
Ok(None) => {
break Err(std::io::Error::new(
io::ErrorKind::NotFound,
format!("chunk {} not found", BASE64.encode(&chunk_meta.digest)),
))
}
// Error occured while fetching the next chunk, propagate the error from the chunk service
Err(e) => {
break Err(std::io::Error::new(io::ErrorKind::InvalidData, e));
}
},
}
}
}
}
#[cfg(test)]
mod tests {
use super::BlobReader;
use crate::chunkservice::ChunkService;
use crate::proto;
use crate::tests::fixtures::DUMMY_DATA_1;
use crate::tests::fixtures::DUMMY_DATA_2;
use crate::tests::fixtures::DUMMY_DIGEST;
use crate::tests::utils::gen_chunk_service;
use std::io::Cursor;
use std::io::Read;
use std::io::Write;
use tempfile::TempDir;
#[test]
/// reading from a blobmeta with zero chunks should produce zero bytes.
fn empty_blobmeta() -> anyhow::Result<()> {
let tmpdir = TempDir::new()?;
let chunk_service = gen_chunk_service(tmpdir.path());
let blobmeta = proto::BlobMeta {
chunks: vec![],
inline_bao: vec![],
};
let mut blob_reader = BlobReader::open(&chunk_service, blobmeta);
let mut buf = Cursor::new(Vec::new());
let res = std::io::copy(&mut blob_reader, &mut buf);
assert_eq!(0, res.unwrap());
Ok(())
}
#[test]
/// trying to read something where the chunk doesn't exist should fail
fn missing_chunk_fail() -> anyhow::Result<()> {
let tmpdir = TempDir::new()?;
let chunk_service = gen_chunk_service(tmpdir.path());
let blobmeta = proto::BlobMeta {
chunks: vec![proto::blob_meta::ChunkMeta {
digest: DUMMY_DIGEST.to_vec(),
size: 42,
}],
inline_bao: vec![],
};
let mut blob_reader = BlobReader::open(&chunk_service, blobmeta);
let mut buf = Cursor::new(Vec::new());
let res = std::io::copy(&mut blob_reader, &mut buf);
assert!(res.is_err());
Ok(())
}
#[test]
/// read something containing the single (empty) chunk
fn empty_chunk() -> anyhow::Result<()> {
let tmpdir = TempDir::new()?;
let chunk_service = gen_chunk_service(tmpdir.path());
// insert a single chunk
let dgst = chunk_service.put(vec![]).expect("must succeed");
// assemble a blobmeta
let blobmeta = proto::BlobMeta {
chunks: vec![proto::blob_meta::ChunkMeta {
digest: dgst,
size: 0,
}],
inline_bao: vec![],
};
let mut blob_reader = BlobReader::open(&chunk_service, blobmeta);
let mut buf: Vec<u8> = Vec::new();
let res =
std::io::copy(&mut blob_reader, &mut Cursor::new(&mut buf)).expect("must succeed");
assert_eq!(res, 0, "number of bytes read must match");
assert!(buf.is_empty(), "buf must be empty");
Ok(())
}
/// read something which contains a single chunk
#[test]
fn single_chunk() -> anyhow::Result<()> {
let tmpdir = TempDir::new()?;
let chunk_service = gen_chunk_service(tmpdir.path());
// insert a single chunk
let dgst = chunk_service
.put(DUMMY_DATA_1.clone())
.expect("must succeed");
// assemble a blobmeta
let blobmeta = proto::BlobMeta {
chunks: vec![proto::blob_meta::ChunkMeta {
digest: dgst,
size: 3,
}],
inline_bao: vec![],
};
let mut blob_reader = BlobReader::open(&chunk_service, blobmeta);
let mut buf: Vec<u8> = Vec::new();
let res =
std::io::copy(&mut blob_reader, &mut Cursor::new(&mut buf)).expect("must succeed");
assert_eq!(res, 3, "number of bytes read must match");
assert_eq!(DUMMY_DATA_1[..], buf[..], "data read must match");
Ok(())
}
/// read something referring to a chunk, but with wrong size
#[test]
fn wrong_size_fail() -> anyhow::Result<()> {
let tmpdir = TempDir::new()?;
let chunk_service = gen_chunk_service(tmpdir.path());
// insert chunks
let dgst_1 = chunk_service
.put(DUMMY_DATA_1.clone())
.expect("must succeed");
// assemble a blobmeta
let blobmeta = proto::BlobMeta {
chunks: vec![proto::blob_meta::ChunkMeta {
digest: dgst_1,
size: 42,
}],
inline_bao: vec![],
};
let mut blob_reader = BlobReader::open(&chunk_service, blobmeta);
let mut buf: Vec<u8> = Vec::new();
let res = std::io::copy(&mut blob_reader, &mut Cursor::new(&mut buf));
assert!(res.is_err(), "reading must fail");
Ok(())
}
/// read something referring to multiple chunks
#[test]
fn multiple_chunks() -> anyhow::Result<()> {
let tmpdir = TempDir::new()?;
let chunk_service = gen_chunk_service(tmpdir.path());
// insert chunks
let dgst_1 = chunk_service
.put(DUMMY_DATA_1.clone())
.expect("must succeed");
let dgst_2 = chunk_service
.put(DUMMY_DATA_2.clone())
.expect("must succeed");
// assemble a blobmeta
let blobmeta = proto::BlobMeta {
chunks: vec![
proto::blob_meta::ChunkMeta {
digest: dgst_1.clone(),
size: 3,
},
proto::blob_meta::ChunkMeta {
digest: dgst_2,
size: 2,
},
proto::blob_meta::ChunkMeta {
digest: dgst_1,
size: 3,
},
],
inline_bao: vec![],
};
// assemble ecpected data
let mut expected_data: Vec<u8> = Vec::new();
expected_data.extend_from_slice(&DUMMY_DATA_1[..]);
expected_data.extend_from_slice(&DUMMY_DATA_2[..]);
expected_data.extend_from_slice(&DUMMY_DATA_1[..]);
// read via io::copy
{
let mut blob_reader = BlobReader::open(&chunk_service, blobmeta.clone());
let mut buf: Vec<u8> = Vec::new();
let res =
std::io::copy(&mut blob_reader, &mut Cursor::new(&mut buf)).expect("must succeed");
assert_eq!(8, res, "number of bytes read must match");
assert_eq!(expected_data[..], buf[..], "data read must match");
}
// now read the same thing again, but not via io::copy, but individually
{
let mut blob_reader = BlobReader::open(&chunk_service, blobmeta);
let mut buf: Vec<u8> = Vec::new();
let mut cursor = Cursor::new(&mut buf);
let mut bytes_read = 0;
loop {
let mut smallbuf = [0xff; 1];
match blob_reader.read(&mut smallbuf) {
Ok(n) => {
if n == 0 {
break;
}
let w_b = cursor.write(&smallbuf).unwrap();
assert_eq!(n, w_b);
bytes_read += w_b;
}
Err(_) => {
panic!("error occured during read");
}
}
}
assert_eq!(8, bytes_read, "number of bytes read must match");
assert_eq!(expected_data[..], buf[..], "data read must match");
}
Ok(())
}
}
