fix(mint): avoid failing large HTTP/2 uploads

[yordis]

• Large HTTP/2 uploads currently fail once the request body exceeds Mint's flow-control window.
• Streamed HTTP/2 uploads can crash instead of recovering when window updates arrive mid-request.
• Tesla should handle larger HTTP/2 request bodies without forcing callers to fall back to HTTP/1.

[cursor]

PR Summary

Medium Risk
Changes request-body streaming logic for HTTP/2 (chunking, window-update handling, and header tweaks), which can affect upload behavior and error handling across protocols. Coverage is improved with new integration tests for large bodies and early server responses.

Overview
Fixes large HTTP/2 uploads in Tesla.Adapter.Mint by switching non-empty HTTP/2 request bodies into a controlled streaming path, ensuring content-length is set, and chunking request data with flow-control/window-update aware retries when Mint reports :exceeds_window_size.

Also propagates any response data received during upload into format_response/4, so callers can return :plain, :chunks, or :stream bodies even when the server responds early. Adds new Cowboy-based test coverage for large HTTP/2 bodies and early-response scenarios, plus a small test support handler.

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[Copilot]

Pull request overview

This PR updates the Mint adapter to support large HTTP/2 request bodies by streaming uploads and respecting HTTP/2 flow-control windows, preventing failures/crashes on large or streamed uploads.

Changes:

• Add HTTP/2-aware request-body streaming that waits for flow-control window updates and splits chunks accordingly.
• Thread an accumulated “early response” accumulator through the request/response pipeline so window updates (and any early response frames) can be processed mid-upload.
• Add regression tests for large HTTP/2 uploads (binary body and streamed body).

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 3 comments.

File	Description
lib/tesla/adapter/mint.ex	Streams HTTP/2 request bodies (including previously non-streaming iodata) and waits for flow-control window before writing chunks.
test/tesla/adapter/mint_test.exs	Adds tests covering large HTTP/2 uploads and helpers to generate/verify posted payloads.

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[Copilot]

Pull request overview

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

Comments suppressed due to low confidence (2)

lib/tesla/adapter/mint.ex:322

• receive_headers_and_status/4 always calls receive_packet/4 before checking whether acc already contains :status and :headers. Since acc can now be pre-populated from request-body streaming (e.g., while waiting for HTTP/2 window updates), this can cause an unnecessary extra receive and potentially block/timeout even though the headers/status are already available. Add a fast-path that returns immediately when acc already has both keys.

    defp receive_headers_and_status(conn, ref, opts, acc) do
      with {:ok, conn, acc} <- receive_packet(conn, ref, opts, acc) do
        case acc do
          %{status: _status, headers: _headers} -> {:ok, conn, acc}
          # if we don't have status or headers we try to get them in next packet
          _ -> receive_headers_and_status(conn, ref, opts, acc)
        end

lib/tesla/adapter/mint.ex:300

• receive_responses/4 now accepts an initial acc, but it still unconditionally calls receive_packet/4 first. If acc already contains :done (or all response data) from earlier receives during HTTP/2 upload flow-control handling, this will wait for an extra packet and may block/timeout. Consider checking acc[:done] (and running check_data_size/3) before attempting another receive_packet/4 call.

    defp receive_responses(conn, ref, opts, acc) do
      with {:ok, conn, acc} <- receive_packet(conn, ref, opts, acc),
           :ok <- check_data_size(acc, conn, opts) do
        if acc[:done] do
          if opts[:close_conn], do: {:ok, _conn} = close(conn)
          {:ok, acc}
        else
          receive_responses(conn, ref, opts, acc)
        end

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[cursor]

Cursor Bugbot has reviewed your changes and found 1 potential issue.

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