diff --git a/Cargo.toml b/Cargo.toml
index 63b89ef..e35c75a 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -11,3 +11,4 @@ thiserror = "1.0.22"
 
 [dev-dependencies]
 tempfile = "3.1.0"
+cid = "0.6.0"
diff --git a/examples/fromcarfile/cariter.rs b/examples/fromcarfile/cariter.rs
new file mode 100644
index 0000000..296fe3b
--- /dev/null
+++ b/examples/fromcarfile/cariter.rs
@@ -0,0 +1,95 @@
+use std::convert::TryFrom;
+use std::io::{self, Read};
+
+/// Read and unsigen varint (LEB128) from a reader.
+///
+/// Code is based on the Rust compiler:
+/// https://github.com/rust-lang/rust/blob/0beba9333754ead8febc5101fc5c35f7dcdfaadf/compiler/rustc_serialize/src/leb128.rs
+pub fn read_u64_leb128<R: Read>(reader: &mut R) -> Result<(u64, usize), io::Error> {
+    let mut result = 0;
+    let mut shift = 0;
+    let mut position = 0;
+    let mut buf = [0];
+
+    loop {
+        reader.read_exact(&mut buf)?;
+        let byte = buf[0];
+        position += 1;
+        if (byte & 0x80) == 0 {
+            result |= (byte as u64) << shift;
+            return Ok((result, position));
+        } else {
+            result |= ((byte & 0x7F) as u64) << shift;
+        }
+        shift += 7;
+    }
+}
+
+/// An iterator over a car file.
+#[derive(Debug)]
+pub struct CarIter<R: Read> {
+    /// The data we are iterating over
+    reader: R,
+    /// Position within the reader
+    pos: u64,
+}
+
+impl<R: Read> CarIter<R> {
+    pub fn new(mut reader: R) -> Self {
+        // Ignore the header for now
+        let (_header, bytes_read) = read_data(&mut reader).unwrap();
+        CarIter {
+            reader,
+            pos: bytes_read,
+        }
+    }
+}
+
+/// Read some data prefixed with a varint.
+pub fn read_data<R: Read>(reader: &mut R) -> Result<(Vec<u8>, u64), io::Error> {
+    let (size, bytes_read): (u64, usize) = read_u64_leb128(reader)?;
+    let mut data = Vec::with_capacity(usize::try_from(size).unwrap());
+    reader.take(size).read_to_end(&mut data)?;
+    Ok((data, u64::try_from(bytes_read).unwrap() + size))
+}
+
+/// Read a CID together with some data.
+pub fn read_block(block: &[u8]) -> (Vec<u8>, Vec<u8>) {
+    // A block is a CID together with some data.
+    let (_version, version_offset) = read_u64_leb128(&mut &block[..]).unwrap();
+    let (_codec, codec_offset) = read_u64_leb128(&mut &block[version_offset..]).unwrap();
+    let (_multihash_code, multihash_code_offset) =
+        read_u64_leb128(&mut &block[version_offset + codec_offset..]).unwrap();
+    let (multihash_size, multihash_size_offset) =
+        read_u64_leb128(&mut &block[version_offset + codec_offset + multihash_code_offset..])
+            .unwrap();
+    let cid_size = version_offset
+        + codec_offset
+        + multihash_code_offset
+        + multihash_size_offset
+        + usize::try_from(multihash_size).unwrap();
+    let (cid, data) = block.split_at(cid_size);
+    (cid.to_vec(), data.to_vec())
+}
+
+impl<R: Read> Iterator for CarIter<R> {
+    type Item = (Vec<u8>, Vec<u8>, u64);
+
+    fn next(&mut self) -> Option<Self::Item> {
+        match read_data(&mut self.reader) {
+            Ok((block, bytes_read)) => {
+                let (cid, data) = read_block(&block);
+
+                // Get the current position in order to return it and update it for the next
+                // iteration.
+                let pos = self.pos;
+                self.pos += bytes_read;
+
+                Some((cid, data, pos))
+            }
+            // We might have hit the end of the file => stop iterating
+            Err(error) if error.kind() == std::io::ErrorKind::UnexpectedEof => None,
+            Err(error) => panic!(error),
+        }
+    }
+}
diff --git a/examples/fromcarfile/main.rs b/examples/fromcarfile/main.rs
new file mode 100644
index 0000000..8fd148d
--- /dev/null
+++ b/examples/fromcarfile/main.rs
@@ -0,0 +1,76 @@
+mod cariter;
+
+use std::convert::TryFrom;
+use std::env;
+use std::fs::File;
+use std::io::{BufReader, Read, Seek, SeekFrom};
+
+use cid::Cid;
+use storethehash::index::Index;
+use storethehash::primary::{PrimaryError, PrimaryStorage};
+
+use cariter::CarIter;
+
+/// CAR file storage implementation.
+///
+/// The primary storage is a CAR file.
+#[derive(Debug)]
+struct CarFile(File);
+
+impl CarFile {
+    pub fn new(file: File) -> Self {
+        Self(file)
+    }
+}
+
+impl PrimaryStorage for CarFile {
+    fn get_key(&mut self, pos: u64) -> Result<Vec<u8>, PrimaryError> {
+        let file_size = self.0.seek(SeekFrom::End(0))?;
+        if pos > file_size {
+            return Err(PrimaryError::OutOfBounds);
+        }
+
+        self.0.seek(SeekFrom::Start(pos))?;
+        let (block, _bytes_read) = cariter::read_data(&mut self.0)?;
+        let (cid_bytes, _data) = cariter::read_block(&block);
+        let cid =
+            Cid::try_from(&cid_bytes[..]).map_err(|error| PrimaryError::Other(Box::new(error)))?;
+        let digest = cid.hash().digest();
+        Ok(digest.to_vec())
+    }
+}
+
+fn insert_into_index<R: Read>(car_file: CarFile, car_iter: CarIter<R>) {
+    const BUCKETS_BITS: u8 = 24;
+    let temp_dir = tempfile::tempdir().unwrap();
+    let index_path = temp_dir.path().join("storethehash.index");
+    let mut index = Index::<_, BUCKETS_BITS>::open(index_path, car_file).unwrap();
+
+    let mut counter = 0;
+    for (cid_bytes, _, pos) in car_iter {
+        if counter % 100000 == 0 {
+            println!("{} keys inserted", counter);
+        }
+        let cid = Cid::try_from(&cid_bytes[..]).unwrap();
+        let digest = cid.hash().digest();
+        index.put(&digest, pos).unwrap();
+
+        counter += 1;
+    }
+}
+
+fn main() {
+    let car_path = env::args().skip(1).next();
+    match car_path {
+        Some(path) => {
+            let car_file_for_iter = File::open(&path).unwrap();
+            let car_file_for_iter_reader = BufReader::new(car_file_for_iter);
+            let car_iter = CarIter::new(car_file_for_iter_reader);
+
+            let car_file_for_index = File::open(&path).unwrap();
+            let primary_storage = CarFile::new(car_file_for_index);
+            insert_into_index(primary_storage, car_iter);
+        }
+        None => println!("usage: fromcarfile <path-to-car-file>"),
+    }
+}
diff --git a/src/primary.rs b/src/primary.rs
index 0f6d7c7..6642cb9 100644
--- a/src/primary.rs
+++ b/src/primary.rs
@@ -11,6 +11,9 @@ pub enum PrimaryError {
     OutOfBounds,
     #[error("IO error.")]
     Io(#[from] std::io::Error),
+    // Catch-all for errors that could happen within the primary storage.
+    #[error(transparent)]
+    Other(Box<dyn std::error::Error>),
 }
 
 pub trait PrimaryStorage {