@@ -258,12 +258,26 @@
  end
  defp build_acknowledgments(_repo, [], _done) do
    # No haves = initial clone, no acknowledgments section needed.
    # Client sent no haves at all (initial clone). The acknowledgments
    # section is optional per protocol v2 and the client does not expect
    # one in that case, so omit it.
    <<>>
  end
  defp build_acknowledgments(repo, haves, done) do
    # Client sent at least one have. Per protocol v2 the client enters its
    # `process_acks` state after sending haves and expects an
    # Check which haves we have in common.
    # `acknowledgments` section from us — even if none of the haves match.
    # Omitting the section here causes the client to error with
    #   fatal: expected 'acknowledgments', received 'packfile'
    # and emitting a section that ends with `NAK` before a packfile causes
    #   fatal: expected no other sections to be sent after no 'ready'
    #
    # Grammar (Documentation/technical/protocol-v2.txt):
    #   acknowledgments = PKT-LINE("acknowledgments" LF) (nak | *ack) [ready]
    # When `done` is in the request we must end with `ready` (packfile
    # follows); otherwise we end with `NAK` / `ACK`s and a flush (client
    # sends another round of haves).
    acks =
      haves
      |> Enum.filter(fn sha ->
@@ -274,33 +288,21 @@
      end)
      |> Enum.map(fn sha -> PktLine.encode("ACK #{sha}") end)
    # Per protocol v2 (Documentation/technical/protocol-v2.txt):
    #   acknowledgments = PKT-LINE("acknowledgments" LF) (nak | *ack) [ready]
    # and: if the client sent `done` the server MUST be "ready" — either by
    # emitting a `ready` line at the end of the acks section, or by omitting
    # the section entirely. Sending `NAK` followed by a packfile is a
    # protocol violation; real git clients reject it with
    #   fatal: expected no other sections to be sent after no 'ready'
    cond do
      # Client sent `done` but nothing matched — omit the acks section.
    header = PktLine.encode("acknowledgments")
      # A packfile will follow unconditionally.
      done and acks == [] ->
        <<>>
      # Client sent `done` — end the acks section with `ready` so the
      # following packfile section is expected by the client.
    cond do
      # Client sent `done` — packfile follows, so end with `ready`.
      # `ready` is valid with zero ACKs (spec allows `*ack [ready]` where
      # `*ack` is zero or more).
      done ->
        header = PktLine.encode("acknowledgments")
        IO.iodata_to_binary([header | acks] ++ [PktLine.encode("ready"), PktLine.delim()])
      # Multi-round negotiation: client hasn't sent `done` yet. No matches
      # Multi-round negotiation: client hasn't sent `done` yet.
      # No matches found — tell the client to send more haves.
      # found — tell the client to send more haves.
      acks == [] ->
        header = PktLine.encode("acknowledgments")
        IO.iodata_to_binary([header, PktLine.encode("NAK"), PktLine.flush()])
      true ->
        header = PktLine.encode("acknowledgments")
        IO.iodata_to_binary([header | acks] ++ [PktLine.flush()])
    end
  end