1 files changed, 95 insertions, 0 deletions
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(_))));
+    }
+}