1 files changed, 71 insertions, 0 deletions
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
+    }
+}