6 files changed, 408 insertions, 0 deletions
diff --git a/iroh-car/src/error.rs b/iroh-car/src/error.rs
new file mode 100644
index 0000000..3579413
--- /dev/null
+++ b/iroh-car/src/error.rs
@@ -0,0 +1,28 @@
+use thiserror::Error;
+
+/// Car utility error
+#[derive(Debug, Error)]
+pub enum Error {
+    #[error("Failed to parse CAR file: {0}")]
+    Parsing(String),
+    #[error("Invalid CAR file: {0}")]
+    InvalidFile(String),
+    #[error("Io error: {0}")]
+    Io(#[from] std::io::Error),
+    #[error("Cbor encoding error: {0}")]
+    Cbor(#[from] ipld::error::Error),
+    #[error("ld read too large {0}")]
+    LdReadTooLarge(usize),
+}
+
+impl From<cid::Error> for Error {
+    fn from(err: cid::Error) -> Error {
+        Error::Parsing(err.to_string())
+    }
+}
+
+impl From<cid::multihash::Error> for Error {
+    fn from(err: cid::multihash::Error) -> Error {
+        Error::Parsing(err.to_string())
+    }
+}
diff --git a/iroh-car/src/header.rs b/iroh-car/src/header.rs
new file mode 100644
index 0000000..c004e35
--- /dev/null
+++ b/iroh-car/src/header.rs
@@ -0,0 +1,104 @@
+use cid::Cid;
+use ipld::codec::Codec;
+use ipld_cbor::DagCborCodec;
+
+use crate::error::Error;
+
+/// A car header.
+#[derive(Debug, Clone, PartialEq, Eq)]
+#[non_exhaustive]
+pub enum CarHeader {
+    V1(CarHeaderV1),
+}
+
+impl CarHeader {
+    pub fn new_v1(roots: Vec<Cid>) -> Self {
+        Self::V1(roots.into())
+    }
+
+    pub fn decode(buffer: &[u8]) -> Result<Self, Error> {
+        let header: CarHeaderV1 = DagCborCodec
+            .decode(buffer)
+            .map_err(|e| Error::Parsing(e.to_string()))?;
+
+        if header.roots.is_empty() {
+            return Err(Error::Parsing("empty CAR file".to_owned()));
+        }
+
+        if header.version != 1 {
+            return Err(Error::InvalidFile(
+                "Only CAR file version 1 is supported".to_string(),
+            ));
+        }
+
+        Ok(CarHeader::V1(header))
+    }
+
+    pub fn encode(&self) -> Result<Vec<u8>, Error> {
+        match self {
+            CarHeader::V1(ref header) => {
+                let res = DagCborCodec.encode(header)?;
+                Ok(res)
+            }
+        }
+    }
+
+    pub fn roots(&self) -> &[Cid] {
+        match self {
+            CarHeader::V1(header) => &header.roots,
+        }
+    }
+
+    pub fn version(&self) -> u64 {
+        match self {
+            CarHeader::V1(_) => 1,
+        }
+    }
+}
+
+/// CAR file header version 1.
+#[derive(Debug, Clone, Default, ipld::DagCbor, PartialEq, Eq)]
+pub struct CarHeaderV1 {
+    #[ipld]
+    pub roots: Vec<Cid>,
+    #[ipld]
+    pub version: u64,
+}
+
+impl CarHeaderV1 {
+    /// Creates a new CAR file header
+    pub fn new(roots: Vec<Cid>, version: u64) -> Self {
+        Self { roots, version }
+    }
+}
+
+impl From<Vec<Cid>> for CarHeaderV1 {
+    fn from(roots: Vec<Cid>) -> Self {
+        Self { roots, version: 1 }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use ipld::codec::{Decode, Encode};
+    use ipld_cbor::DagCborCodec;
+    use multihash::MultihashDigest;
+
+    use super::*;
+
+    #[test]
+    fn symmetric_header_v1() {
+        let digest = multihash::Code::Blake2b256.digest(b"test");
+        let cid = Cid::new_v1(DagCborCodec.into(), digest);
+
+        let header = CarHeaderV1::from(vec![cid]);
+
+        let mut bytes = Vec::new();
+        header.encode(DagCborCodec, &mut bytes).unwrap();
+
+        assert_eq!(
+            CarHeaderV1::decode(DagCborCodec, &mut std::io::Cursor::new(&bytes)).unwrap(),
+            header
+        );
+    }
+}
diff --git a/iroh-car/src/lib.rs b/iroh-car/src/lib.rs
new file mode 100644
index 0000000..d4e5f66
--- /dev/null
+++ b/iroh-car/src/lib.rs
@@ -0,0 +1,11 @@
+//! Implementation of the [car](https://ipld.io/specs/transport/car/) format.
+
+mod error;
+mod header;
+mod reader;
+mod util;
+mod writer;
+
+pub use crate::header::CarHeader;
+pub use crate::reader::CarReader;
+pub use crate::writer::CarWriter;
diff --git a/iroh-car/src/reader.rs b/iroh-car/src/reader.rs
new file mode 100644
index 0000000..c0209be
--- /dev/null
+++ b/iroh-car/src/reader.rs
@@ -0,0 +1,99 @@
+use cid::Cid;
+use futures::Stream;
+use tokio::io::AsyncRead;
+
+use crate::{
+    error::Error,
+    header::CarHeader,
+    util::{ld_read, read_node},
+};
+
+/// Reads CAR files that are in a BufReader
+pub struct CarReader<R> {
+    reader: R,
+    header: CarHeader,
+    buffer: Vec<u8>,
+}
+
+impl<R> CarReader<R>
+where
+    R: AsyncRead + Send + Unpin,
+{
+    /// Creates a new CarReader and parses the CarHeader
+    pub async fn new(mut reader: R) -> Result<Self, Error> {
+        let mut buffer = Vec::new();
+
+        match ld_read(&mut reader, &mut buffer).await? {
+            Some(buf) => {
+                let header = CarHeader::decode(buf)?;
+
+                Ok(CarReader {
+                    reader,
+                    header,
+                    buffer,
+                })
+            }
+            None => Err(Error::Parsing(
+                "failed to parse uvarint for header".to_string(),
+            )),
+        }
+    }
+
+    /// Returns the header of this car file.
+    pub fn header(&self) -> &CarHeader {
+        &self.header
+    }
+
+    /// Returns the next IPLD Block in the buffer
+    pub async fn next_block(&mut self) -> Result<Option<(Cid, Vec<u8>)>, Error> {
+        read_node(&mut self.reader, &mut self.buffer).await
+    }
+
+    pub fn stream(self) -> impl Stream<Item = Result<(Cid, Vec<u8>), Error>> {
+        futures::stream::try_unfold(self, |mut this| async move {
+            let maybe_block = read_node(&mut this.reader, &mut this.buffer).await?;
+            Ok(maybe_block.map(|b| (b, this)))
+        })
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use std::io::Cursor;
+
+    use cid::Cid;
+    use futures::TryStreamExt;
+    use ipld_cbor::DagCborCodec;
+    use multihash::MultihashDigest;
+
+    use crate::{header::CarHeaderV1, writer::CarWriter};
+
+    use super::*;
+
+    #[tokio::test]
+    async fn car_write_read() {
+        let digest_test = multihash::Code::Blake2b256.digest(b"test");
+        let cid_test = Cid::new_v1(DagCborCodec.into(), digest_test);
+
+        let digest_foo = multihash::Code::Blake2b256.digest(b"foo");
+        let cid_foo = Cid::new_v1(DagCborCodec.into(), digest_foo);
+
+        let header = CarHeader::V1(CarHeaderV1::from(vec![cid_foo]));
+
+        let mut buffer = Vec::new();
+        let mut writer = CarWriter::new(header, &mut buffer);
+        writer.write(cid_test, b"test").await.unwrap();
+        writer.write(cid_foo, b"foo").await.unwrap();
+        writer.finish().await.unwrap();
+
+        let reader = Cursor::new(&buffer);
+        let car_reader = CarReader::new(reader).await.unwrap();
+        let files: Vec<_> = car_reader.stream().try_collect().await.unwrap();
+
+        assert_eq!(files.len(), 2);
+        assert_eq!(files[0].0, cid_test);
+        assert_eq!(files[0].1, b"test");
+        assert_eq!(files[1].0, cid_foo);
+        assert_eq!(files[1].1, b"foo");
+    }
+}
diff --git a/iroh-car/src/util.rs b/iroh-car/src/util.rs
new file mode 100644
index 0000000..25be761
--- /dev/null
+++ b/iroh-car/src/util.rs
@@ -0,0 +1,95 @@
+use cid::Cid;
+use integer_encoding::VarIntAsyncReader;
+use tokio::io::{AsyncRead, AsyncReadExt};
+
+use super::error::Error;
+
+/// Maximum size that is used for single node.
+pub(crate) const MAX_ALLOC: usize = 4 * 1024 * 1024;
+
+pub(crate) async fn ld_read<R>(mut reader: R, buf: &mut Vec<u8>) -> Result<Option<&[u8]>, Error>
+where
+    R: AsyncRead + Send + Unpin,
+{
+    let length: usize = match VarIntAsyncReader::read_varint_async(&mut reader).await {
+        Ok(len) => len,
+        Err(e) => {
+            if e.kind() == std::io::ErrorKind::UnexpectedEof {
+                return Ok(None);
+            }
+            return Err(Error::Parsing(e.to_string()));
+        }
+    };
+
+    if length > MAX_ALLOC {
+        return Err(Error::LdReadTooLarge(length));
+    }
+    if length > buf.len() {
+        buf.resize(length, 0);
+    }
+
+    reader
+        .read_exact(&mut buf[..length])
+        .await
+        .map_err(|e| Error::Parsing(e.to_string()))?;
+
+    Ok(Some(&buf[..length]))
+}
+
+pub(crate) async fn read_node<R>(
+    buf_reader: &mut R,
+    buf: &mut Vec<u8>,
+) -> Result<Option<(Cid, Vec<u8>)>, Error>
+where
+    R: AsyncRead + Send + Unpin,
+{
+    if let Some(buf) = ld_read(buf_reader, buf).await? {
+        let mut cursor = std::io::Cursor::new(buf);
+        let c = Cid::read_bytes(&mut cursor)?;
+        let pos = cursor.position() as usize;
+
+        return Ok(Some((c, buf[pos..].to_vec())));
+    }
+    Ok(None)
+}
+
+#[cfg(test)]
+mod tests {
+    use integer_encoding::VarIntAsyncWriter;
+    use tokio::io::{AsyncWrite, AsyncWriteExt};
+
+    use super::*;
+
+    async fn ld_write<'a, W>(writer: &mut W, bytes: &[u8]) -> Result<(), Error>
+    where
+        W: AsyncWrite + Send + Unpin,
+    {
+        writer.write_varint_async(bytes.len()).await?;
+        writer.write_all(bytes).await?;
+        writer.flush().await?;
+        Ok(())
+    }
+
+    #[tokio::test]
+    async fn ld_read_write_good() {
+        let mut buffer = Vec::<u8>::new();
+        ld_write(&mut buffer, b"test bytes").await.unwrap();
+        let reader = std::io::Cursor::new(buffer);
+
+        let mut buffer = vec![1u8; 1024];
+        let read = ld_read(reader, &mut buffer).await.unwrap().unwrap();
+        assert_eq!(read, b"test bytes");
+    }
+
+    #[tokio::test]
+    async fn ld_read_write_fail() {
+        let mut buffer = Vec::<u8>::new();
+        let size = MAX_ALLOC + 1;
+        ld_write(&mut buffer, &vec![2u8; size]).await.unwrap();
+        let reader = std::io::Cursor::new(buffer);
+
+        let mut buffer = vec![1u8; 1024];
+        let read = ld_read(reader, &mut buffer).await;
+        assert!(matches!(read, Err(Error::LdReadTooLarge(_))));
+    }
+}
diff --git a/iroh-car/src/writer.rs b/iroh-car/src/writer.rs
new file mode 100644
index 0000000..9f17eb9
--- /dev/null
+++ b/iroh-car/src/writer.rs
@@ -0,0 +1,71 @@
+use cid::Cid;
+use integer_encoding::VarIntAsyncWriter;
+use tokio::io::{AsyncWrite, AsyncWriteExt};
+
+use crate::{error::Error, header::CarHeader};
+
+#[derive(Debug)]
+pub struct CarWriter<W> {
+    header: CarHeader,
+    writer: W,
+    cid_buffer: Vec<u8>,
+    is_header_written: bool,
+}
+
+impl<W> CarWriter<W>
+where
+    W: AsyncWrite + Send + Unpin,
+{
+    pub fn new(header: CarHeader, writer: W) -> Self {
+        CarWriter {
+            header,
+            writer,
+            cid_buffer: Vec::new(),
+            is_header_written: false,
+        }
+    }
+
+    /// Writes header and stream of data to writer in Car format.
+    pub async fn write<T>(&mut self, cid: Cid, data: T) -> Result<(), Error>
+    where
+        T: AsRef<[u8]>,
+    {
+        if !self.is_header_written {
+            // Write header bytes
+            let header_bytes = self.header.encode()?;
+            self.writer.write_varint_async(header_bytes.len()).await?;
+            self.writer.write_all(&header_bytes).await?;
+            self.is_header_written = true;
+        }
+
+        // Write the given block.
+        self.cid_buffer.clear();
+        cid.write_bytes(&mut self.cid_buffer).expect("vec write");
+
+        let data = data.as_ref();
+        let len = self.cid_buffer.len() + data.len();
+
+        self.writer.write_varint_async(len).await?;
+        self.writer.write_all(&self.cid_buffer).await?;
+        self.writer.write_all(data).await?;
+
+        Ok(())
+    }
+
+    /// Finishes writing, including flushing and returns the writer.
+    pub async fn finish(mut self) -> Result<W, Error> {
+        self.flush().await?;
+        Ok(self.writer)
+    }
+
+    /// Flushes the underlying writer.
+    pub async fn flush(&mut self) -> Result<(), Error> {
+        self.writer.flush().await?;
+        Ok(())
+    }
+
+    /// Consumes the [`CarWriter`] and returns the underlying writer.
+    pub fn into_inner(self) -> W {
+        self.writer
+    }
+}