Mint adapter cannot upload more than 65535 bytes on HTTP/2

[jayjun]

• tesla 1.3.3
• mint 1.1.0

To reproduce,

client = Tesla.client([], Tesla.Adapter.Mint)
Tesla.post(client, "https://httpbin.org/post", String.duplicate("0", 65536))

returns :exceeds_window_size error.

%Mint.HTTPError{
  module: Mint.HTTP2,
  reason: {:exceeds_window_size, :connection, 65535}
}

Full error

```elixir {:error, %Mint.HTTP2{ buffer: <<0, 0, 4, 8, 0, 0, 0, 0, 0, 127, 255, 0, 0>>, client_settings: %{ enable_push: true, max_concurrent_streams: 100, max_frame_size: 16384 }, client_settings_queue: {[[]], []}, decode_table: %Mint.HTTP2.HPACK.Table{ entries: [], length: 0, max_table_size: 4096, size: 0 }, encode_table: %Mint.HTTP2.HPACK.Table{ entries: [], length: 0, max_table_size: 4096, size: 0 }, headers_being_processed: nil, hostname: "httpbin.org", mode: :active, next_stream_id: 5, open_client_stream_count: 1, open_server_stream_count: 0, ping_queue: {[], []}, port: 443, private: %{}, ref_to_stream_id: %{#Reference<0.4203460067.3989045250.44202> => 3}, scheme: "https", server_settings: %{ enable_push: true, initial_window_size: 65536, max_concurrent_streams: 128, max_frame_size: 16777215, max_header_list_size: :infinity }, socket: {:sslsocket, {:gen_tcp, #Port<0.2811>, :tls_connection, :undefined}, [#PID<0.1699.0>, #PID<0.1698.0>]}, state: :open, streams: %{ 3 => %{ id: 3, received_first_headers?: false, ref: #Reference<0.4203460067.3989045250.44202>, state: :open, window_size: 65536 } }, transport: Mint.Core.Transport.SSL, window_size: 65535 }, %Mint.HTTPError{ module: Mint.HTTP2, reason: {:exceeds_window_size, :connection, 65535} }} ```

That is because window_size: 65535 is set initially, according to standard, but is not updated when the server sends WINDOW_UPDATE frames.

Each time Tesla sends data using Mint.HTTP.stream_request_body, the window size is decremented by data’s size. When the window size gets low, the server sends WINDOW_UPDATE frames to increment the connection’s window size. Calling Mint.HTTP.stream to read responses will automatically do this.

https://github.com/teamon/tesla/blob/754d4a6ffe41ff508fc7fa460508a40e965b2960/lib/tesla/adapter/mint.ex#L178-L187

However, the adapter repeatedly calls Mint.HTTP.stream_request_body without calling Mint.HTTP.stream so the window size hits zero and Mint errors.

[teamon]

Hi @jayjun, thanks for reporting the issue. Would you be able to provide the fix as a PR?

[jayjun]

Unfortunately not at the moment because I don’t have the bandwidth to learn Tesla internals, Mint and HTTP/2 enough to do a good job.

[slapers]

If someone hits this error until this is solved, as a temporary solution you can force the connection to be http1 by adding some options for the adapter:

Tesla.post(client, url, content, [opts: [adapter: [protocols: [:http1]]]])

[sheharyarn]

Bumping this since this is a serious issue!

Thank you for all the work on Tesla!

[yordis]

@sheharyarn do you have some bandwidth to tackle the issue?

[sheharyarn]

@yordis I can definitely try, but would need someone to push me in the right direction. While I have a good amount of experience with Tesla in general, I don't have enough experience with Mint's internals.