@@ -63,6 +63,60 @@
  end
  @doc """
  Generate a packfile by streaming bytes through a write callback.
  `write_fn` is invoked with each piece of the pack as it's produced:
  first the 12-byte pack header, then one zlib-compressed entry per
  object, then the trailing 20-byte SHA-1 checksum. SHA-1 is computed
  incrementally so no intermediate full-pack binary is held in memory —
  peak heap is bounded by the largest single object.
  Two arities are exposed:
    * `generate_stream/2` — `write_fn` is `(binary -> any)`, side-effecting.
      Convenient for tests / simple sinks.
    * `generate_stream/3` — `write_fn` is `(binary, acc -> acc)`, threading
      caller state through each chunk. Used by the protocol layer so a
      sideband chunker can accumulate buffered bytes between calls.
  Returns `{pack_sha, count}` for `/2`, `{pack_sha, count, final_acc}` for `/3`.
  """
  @spec generate_stream([object_entry()], (binary() -> any())) ::
          {String.t(), non_neg_integer()}
  def generate_stream(objects, write_fn) when is_list(objects) and is_function(write_fn, 1) do
    {sha, count, nil} =
      generate_stream(objects, nil, fn bytes, _acc ->
        write_fn.(bytes)
        nil
      end)
    {sha, count}
  end
  @spec generate_stream([object_entry()], acc, (binary(), acc -> acc)) ::
          {String.t(), non_neg_integer(), acc}
        when acc: var
  def generate_stream(objects, acc, write_fn)
      when is_list(objects) and is_function(write_fn, 2) do
    count = length(objects)
    header = <<@pack_signature, @pack_version::unsigned-big-32, count::unsigned-big-32>>
    hasher = :crypto.hash_init(:sha)
    acc = write_fn.(header, acc)
    hasher = :crypto.hash_update(hasher, header)
    {hasher, acc} =
      Enum.reduce(objects, {hasher, acc}, fn {type, content, _sha}, {h, a} ->
        entry = IO.iodata_to_binary(encode_entry(type_to_num(type), content))
        a = write_fn.(entry, a)
        {:crypto.hash_update(h, entry), a}
      end)
    checksum = :crypto.hash_final(hasher)
    acc = write_fn.(checksum, acc)
    {Base.encode16(checksum, case: :lower), count, acc}
  end
  @doc """
  Generate both a packfile and its .idx v2 index.
  Returns `{pack_data, idx_data, pack_sha}`.
  """