diff options
Diffstat (limited to 'tvix/nix-compat/src/wire/bytes/writer.rs')
| -rw-r--r-- | tvix/nix-compat/src/wire/bytes/writer.rs | 538 |
1 files changed, 538 insertions, 0 deletions
diff --git a/tvix/nix-compat/src/wire/bytes/writer.rs b/tvix/nix-compat/src/wire/bytes/writer.rs new file mode 100644 index 0000000000..f5632771e9 --- /dev/null +++ b/tvix/nix-compat/src/wire/bytes/writer.rs @@ -0,0 +1,538 @@ +use pin_project_lite::pin_project; +use std::task::{ready, Poll}; + +use tokio::io::AsyncWrite; + +use super::{padding_len, EMPTY_BYTES, LEN_SIZE}; + +pin_project! { + /// Writes a "bytes wire packet" to the underlying writer. + /// The format is the same as in [crate::wire::bytes::write_bytes], + /// however this structure provides a [AsyncWrite] interface, + /// allowing to not having to pass around the entire payload in memory. + /// + /// It internally takes care of writing (non-payload) framing (size and + /// padding). + /// + /// During construction, the expected payload size needs to be provided. + /// + /// After writing the payload to it, the user MUST call flush (or shutdown), + /// which will validate the written payload size to match, and write the + /// necessary padding. + /// + /// In case flush is not called at the end, invalid data might be sent + /// silently. + /// + /// The underlying writer returning `Ok(0)` is considered an EOF situation, + /// which is stronger than the "typically means the underlying object is no + /// longer able to accept bytes" interpretation from the docs. If such a + /// situation occurs, an error is returned. + /// + /// The struct holds three fields, the underlying writer, the (expected) + /// payload length, and an enum, tracking the state. + pub struct BytesWriter<W> + where + W: AsyncWrite, + { + #[pin] + inner: W, + payload_len: u64, + state: BytesPacketPosition, + } +} + +/// Models the position inside a "bytes wire packet" that the writer is in. +/// It can be in three different stages, inside size, payload or padding fields. +/// The number tracks the number of bytes written inside the specific field. +/// There shall be no ambiguous states, at the end of a stage we immediately +/// move to the beginning of the next one: +/// - Size(LEN_SIZE) must be expressed as Payload(0) +/// - Payload(self.payload_len) must be expressed as Padding(0) +/// +/// Padding(padding_len) means we're at the end of the bytes wire packet. +#[derive(Clone, Debug, PartialEq, Eq)] +enum BytesPacketPosition { + Size(usize), + Payload(u64), + Padding(usize), +} + +impl<W> BytesWriter<W> +where + W: AsyncWrite, +{ + /// Constructs a new BytesWriter, using the underlying passed writer. + pub fn new(w: W, payload_len: u64) -> Self { + Self { + inner: w, + payload_len, + state: BytesPacketPosition::Size(0), + } + } +} + +/// Returns an error if the passed usize is 0. +#[inline] +fn ensure_nonzero_bytes_written(bytes_written: usize) -> Result<usize, std::io::Error> { + if bytes_written == 0 { + Err(std::io::Error::new( + std::io::ErrorKind::WriteZero, + "underlying writer accepted 0 bytes", + )) + } else { + Ok(bytes_written) + } +} + +impl<W> AsyncWrite for BytesWriter<W> +where + W: AsyncWrite, +{ + fn poll_write( + self: std::pin::Pin<&mut Self>, + cx: &mut std::task::Context<'_>, + buf: &[u8], + ) -> Poll<Result<usize, std::io::Error>> { + // Use a loop, so we can deal with (multiple) state transitions. + let mut this = self.project(); + + loop { + match *this.state { + BytesPacketPosition::Size(LEN_SIZE) => unreachable!(), + BytesPacketPosition::Size(pos) => { + let size_field = &this.payload_len.to_le_bytes(); + + let bytes_written = ensure_nonzero_bytes_written(ready!(this + .inner + .as_mut() + .poll_write(cx, &size_field[pos..]))?)?; + + let new_pos = pos + bytes_written; + if new_pos == LEN_SIZE { + *this.state = BytesPacketPosition::Payload(0); + } else { + *this.state = BytesPacketPosition::Size(new_pos); + } + } + BytesPacketPosition::Payload(pos) => { + // Ensure we still have space for more payload + if pos + (buf.len() as u64) > *this.payload_len { + return Poll::Ready(Err(std::io::Error::new( + std::io::ErrorKind::InvalidData, + "tried to write excess bytes", + ))); + } + let bytes_written = ready!(this.inner.as_mut().poll_write(cx, buf))?; + ensure_nonzero_bytes_written(bytes_written)?; + let new_pos = pos + (bytes_written as u64); + if new_pos == *this.payload_len { + *this.state = BytesPacketPosition::Padding(0) + } else { + *this.state = BytesPacketPosition::Payload(new_pos) + } + + return Poll::Ready(Ok(bytes_written)); + } + // If we're already in padding state, there should be no more payload left to write! + BytesPacketPosition::Padding(_pos) => { + return Poll::Ready(Err(std::io::Error::new( + std::io::ErrorKind::InvalidData, + "tried to write excess bytes", + ))) + } + } + } + } + + fn poll_flush( + self: std::pin::Pin<&mut Self>, + cx: &mut std::task::Context<'_>, + ) -> Poll<Result<(), std::io::Error>> { + let mut this = self.project(); + + loop { + match *this.state { + BytesPacketPosition::Size(LEN_SIZE) => unreachable!(), + BytesPacketPosition::Size(pos) => { + // More bytes to write in the size field + let size_field = &this.payload_len.to_le_bytes()[..]; + let bytes_written = ensure_nonzero_bytes_written(ready!(this + .inner + .as_mut() + .poll_write(cx, &size_field[pos..]))?)?; + let new_pos = pos + bytes_written; + if new_pos == LEN_SIZE { + // Size field written, now ready to receive payload + *this.state = BytesPacketPosition::Payload(0); + } else { + *this.state = BytesPacketPosition::Size(new_pos); + } + } + BytesPacketPosition::Payload(_pos) => { + // If we're at position 0 and want to write 0 bytes of payload + // in total, we can transition to padding. + // Otherwise, break, as we're expecting more payload to + // be written. + if *this.payload_len == 0 { + *this.state = BytesPacketPosition::Padding(0); + } else { + break; + } + } + BytesPacketPosition::Padding(pos) => { + // Write remaining padding, if there is padding to write. + let total_padding_len = padding_len(*this.payload_len) as usize; + + if pos != total_padding_len { + let bytes_written = ensure_nonzero_bytes_written(ready!(this + .inner + .as_mut() + .poll_write(cx, &EMPTY_BYTES[pos..total_padding_len]))?)?; + *this.state = BytesPacketPosition::Padding(pos + bytes_written); + } else { + // everything written, break + break; + } + } + } + } + // Flush the underlying writer. + this.inner.as_mut().poll_flush(cx) + } + + fn poll_shutdown( + mut self: std::pin::Pin<&mut Self>, + cx: &mut std::task::Context<'_>, + ) -> Poll<Result<(), std::io::Error>> { + // Call flush. + ready!(self.as_mut().poll_flush(cx))?; + + let this = self.project(); + + // After a flush, being inside the padding state, and at the end of the padding + // is the only way to prevent a dirty shutdown. + if let BytesPacketPosition::Padding(pos) = *this.state { + let padding_len = padding_len(*this.payload_len) as usize; + if padding_len == pos { + // Shutdown the underlying writer + return this.inner.poll_shutdown(cx); + } + } + + // Shutdown the underlying writer, bubbling up any errors. + ready!(this.inner.poll_shutdown(cx))?; + + // return an error about unclean shutdown + Poll::Ready(Err(std::io::Error::new( + std::io::ErrorKind::BrokenPipe, + "unclean shutdown", + ))) + } +} + +#[cfg(test)] +mod tests { + use std::time::Duration; + + use crate::wire::bytes::write_bytes; + use hex_literal::hex; + use lazy_static::lazy_static; + use tokio::io::AsyncWriteExt; + use tokio_test::{assert_err, assert_ok, io::Builder}; + + use super::*; + + lazy_static! { + pub static ref LARGE_PAYLOAD: Vec<u8> = (0..255).collect::<Vec<u8>>().repeat(4 * 1024); + } + + /// Helper function, calling the (simpler) write_bytes with the payload. + /// We use this to create data we want to see on the wire. + async fn produce_exp_bytes(payload: &[u8]) -> Vec<u8> { + let mut exp = vec![]; + write_bytes(&mut exp, payload).await.unwrap(); + exp + } + + /// Write an empty bytes packet. + #[tokio::test] + async fn write_empty() { + let payload = &[]; + let mut mock = Builder::new() + .write(&produce_exp_bytes(payload).await) + .build(); + + let mut w = BytesWriter::new(&mut mock, 0); + assert_ok!(w.write_all(&[]).await, "write all data"); + assert_ok!(w.flush().await, "flush"); + } + + /// Write an empty bytes packet, not calling write. + #[tokio::test] + async fn write_empty_only_flush() { + let payload = &[]; + let mut mock = Builder::new() + .write(&produce_exp_bytes(payload).await) + .build(); + + let mut w = BytesWriter::new(&mut mock, 0); + assert_ok!(w.flush().await, "flush"); + } + + /// Write an empty bytes packet, not calling write or flush, only shutdown. + #[tokio::test] + async fn write_empty_only_shutdown() { + let payload = &[]; + let mut mock = Builder::new() + .write(&produce_exp_bytes(payload).await) + .build(); + + let mut w = BytesWriter::new(&mut mock, 0); + assert_ok!(w.shutdown().await, "shutdown"); + } + + /// Write a 1 bytes packet + #[tokio::test] + async fn write_1b() { + let payload = &[0xff]; + + let mut mock = Builder::new() + .write(&produce_exp_bytes(payload).await) + .build(); + + let mut w = BytesWriter::new(&mut mock, payload.len() as u64); + assert_ok!(w.write_all(payload).await); + assert_ok!(w.flush().await, "flush"); + } + + /// Write a 8 bytes payload (no padding) + #[tokio::test] + async fn write_8b() { + let payload = &hex!("0001020304050607"); + + let mut mock = Builder::new() + .write(&produce_exp_bytes(payload).await) + .build(); + + let mut w = BytesWriter::new(&mut mock, payload.len() as u64); + assert_ok!(w.write_all(payload).await); + assert_ok!(w.flush().await, "flush"); + } + + /// Write a 9 bytes payload (7 bytes padding) + #[tokio::test] + async fn write_9b() { + let payload = &hex!("000102030405060708"); + + let mut mock = Builder::new() + .write(&produce_exp_bytes(payload).await) + .build(); + + let mut w = BytesWriter::new(&mut mock, payload.len() as u64); + assert_ok!(w.write_all(payload).await); + assert_ok!(w.flush().await, "flush"); + } + + /// Write a 9 bytes packet very granularly, with a lot of flushing in between, + /// and a shutdown at the end. + #[tokio::test] + async fn write_9b_flush() { + let payload = &hex!("000102030405060708"); + let exp_bytes = produce_exp_bytes(payload).await; + + let mut mock = Builder::new().write(&exp_bytes).build(); + + let mut w = BytesWriter::new(&mut mock, payload.len() as u64); + assert_ok!(w.flush().await); + + assert_ok!(w.write_all(&payload[..4]).await); + assert_ok!(w.flush().await); + + // empty write, cause why not + assert_ok!(w.write_all(&[]).await); + assert_ok!(w.flush().await); + + assert_ok!(w.write_all(&payload[4..]).await); + assert_ok!(w.flush().await); + assert_ok!(w.shutdown().await); + } + + /// Write a 9 bytes packet, but cause the sink to only accept half of the + /// padding, ensuring we correctly write (only) the rest of the padding later. + /// We write another 2 bytes of "bait", where a faulty implementation (pre + /// cl/11384) would put too many null bytes. + #[tokio::test] + async fn write_9b_write_padding_2steps() { + let payload = &hex!("000102030405060708"); + let exp_bytes = produce_exp_bytes(payload).await; + + let mut mock = Builder::new() + .write(&exp_bytes[0..8]) // size + .write(&exp_bytes[8..17]) // payload + .write(&exp_bytes[17..19]) // padding (2 of 7 bytes) + // insert a wait to prevent Mock from merging the two writes into one + .wait(Duration::from_nanos(1)) + .write(&hex!("0000000000ffff")) // padding (5 of 7 bytes, plus 2 bytes of "bait") + .build(); + + let mut w = BytesWriter::new(&mut mock, payload.len() as u64); + assert_ok!(w.write_all(&payload[..]).await); + assert_ok!(w.flush().await); + // Write bait + assert_ok!(mock.write_all(&hex!("ffff")).await); + } + + /// Write a larger bytes packet + #[tokio::test] + async fn write_1m() { + let payload = LARGE_PAYLOAD.as_slice(); + let exp_bytes = produce_exp_bytes(payload).await; + + let mut mock = Builder::new().write(&exp_bytes).build(); + let mut w = BytesWriter::new(&mut mock, payload.len() as u64); + + assert_ok!(w.write_all(payload).await); + assert_ok!(w.flush().await, "flush"); + } + + /// Not calling flush at the end, but shutdown is also ok if we wrote all + /// bytes we promised to write (as shutdown implies flush) + #[tokio::test] + async fn write_shutdown_without_flush_end() { + let payload = &[0xf0, 0xff]; + let exp_bytes = produce_exp_bytes(payload).await; + + let mut mock = Builder::new().write(&exp_bytes).build(); + let mut w = BytesWriter::new(&mut mock, payload.len() as u64); + + // call flush to write the size field + assert_ok!(w.flush().await); + + // write payload + assert_ok!(w.write_all(payload).await); + + // call shutdown + assert_ok!(w.shutdown().await); + } + + /// Writing more bytes than previously signalled should fail. + #[tokio::test] + async fn write_more_than_signalled_fail() { + let mut buf = Vec::new(); + let mut w = BytesWriter::new(&mut buf, 2); + + assert_err!(w.write_all(&hex!("000102")).await); + } + /// Writing more bytes than previously signalled, but in two parts + #[tokio::test] + async fn write_more_than_signalled_split_fail() { + let mut buf = Vec::new(); + let mut w = BytesWriter::new(&mut buf, 2); + + // write two bytes + assert_ok!(w.write_all(&hex!("0001")).await); + + // write the excess byte. + assert_err!(w.write_all(&hex!("02")).await); + } + + /// Writing more bytes than previously signalled, but flushing after the + /// signalled amount should fail. + #[tokio::test] + async fn write_more_than_signalled_flush_fail() { + let mut buf = Vec::new(); + let mut w = BytesWriter::new(&mut buf, 2); + + // write two bytes, then flush + assert_ok!(w.write_all(&hex!("0001")).await); + assert_ok!(w.flush().await); + + // write the excess byte. + assert_err!(w.write_all(&hex!("02")).await); + } + + /// Calling shutdown while not having written all bytes that were promised + /// returns an error. + /// Note there's still cases of silent corruption if the user doesn't call + /// shutdown explicitly (only drops). + #[tokio::test] + async fn premature_shutdown() { + let payload = &[0xf0, 0xff]; + let mut buf = Vec::new(); + let mut w = BytesWriter::new(&mut buf, payload.len() as u64); + + // call flush to write the size field + assert_ok!(w.flush().await); + + // write half of the payload (!) + assert_ok!(w.write_all(&payload[0..1]).await); + + // call shutdown, ensure it fails + assert_err!(w.shutdown().await); + } + + /// Write to a Writer that fails to write during the size packet (after 4 bytes). + /// Ensure this error gets propagated on the first call to write. + #[tokio::test] + async fn inner_writer_fail_during_size_firstwrite() { + let payload = &[0xf0]; + + let mut mock = Builder::new() + .write(&1u32.to_le_bytes()) + .write_error(std::io::Error::new(std::io::ErrorKind::Other, "๐ฟ")) + .build(); + let mut w = BytesWriter::new(&mut mock, payload.len() as u64); + + assert_err!(w.write_all(payload).await); + } + + /// Write to a Writer that fails to write during the size packet (after 4 bytes). + /// Ensure this error gets propagated during an initial flush + #[tokio::test] + async fn inner_writer_fail_during_size_initial_flush() { + let payload = &[0xf0]; + + let mut mock = Builder::new() + .write(&1u32.to_le_bytes()) + .write_error(std::io::Error::new(std::io::ErrorKind::Other, "๐ฟ")) + .build(); + let mut w = BytesWriter::new(&mut mock, payload.len() as u64); + + assert_err!(w.flush().await); + } + + /// Write to a writer that fails to write during the payload (after 9 bytes). + /// Ensure this error gets propagated when we're writing this byte. + #[tokio::test] + async fn inner_writer_fail_during_write() { + let payload = &hex!("f0ff"); + + let mut mock = Builder::new() + .write(&2u64.to_le_bytes()) + .write(&hex!("f0")) + .write_error(std::io::Error::new(std::io::ErrorKind::Other, "๐ฟ")) + .build(); + let mut w = BytesWriter::new(&mut mock, payload.len() as u64); + + assert_ok!(w.write(&hex!("f0")).await); + assert_err!(w.write(&hex!("ff")).await); + } + + /// Write to a writer that fails to write during the padding (after 10 bytes). + /// Ensure this error gets propagated during a flush. + #[tokio::test] + async fn inner_writer_fail_during_padding_flush() { + let payload = &hex!("f0"); + + let mut mock = Builder::new() + .write(&1u64.to_le_bytes()) + .write(&hex!("f0")) + .write(&hex!("00")) + .write_error(std::io::Error::new(std::io::ErrorKind::Other, "๐ฟ")) + .build(); + let mut w = BytesWriter::new(&mut mock, payload.len() as u64); + + assert_ok!(w.write(&hex!("f0")).await); + assert_err!(w.flush().await); + } +} |