Cannot capture 4xx response bodies with req_perform_stream

[jwimberl]

I'm finding a difference in behavior between req_perform and req_perform_stream when it comes to capturing HTTP errors and translating them to R errors, and moreover in capturing 4xx response bodies. Both occur straightforwardly with req_perform, following the documented instructions:

req <- ...
req <- req_error(req, body = \(resp) resp_body_string(resp)
resp <- req_perform(req)

This will throw an R error that includes the text body from the error message.

However, error responses are not handled and converted to R errors in the same way using req_perform_stream:

> req <- ...
> req <- req_error(req, body = \(resp) resp_body_string(resp)
> req_perform(req)
<httr2_response>
POST http://obfuscated
Status: 400 Bad Request
Content-Type: text/plain
Body: None

This returns a response object with an error status code is returned, but does not throw an R error. It also does not include any body. This is true even when setting is_error to a lambda returning FALSE. In the req_perform case, that successfully turns off the http-to-R error handling and yields a 4xx response with a body, but for req_perform_stream the response body is still empty. The following obfuscated example uses a private API and so is not a reprex:

> request <- ...
> request <- httr2::req_error(request, is_error = \(z) FALSE)
> httr2::req_perform(request)
<httr2_response>
POST http://obfuscated
Status: 400 Bad Request
Content-Type: text/plain
Body: In memory (147 bytes)

> httr2::req_perform_stream(request, cb, buffer_kb = buffer_kb)
<httr2_response>
POST http://obfuscated
Status: 400 Bad Request
Content-Type: text/plain
Body: None

My current workaround is to repeat the request using req_perform when req_perform_stream returns an error status, but this can mean repeating large POST requests. Is there a way to get the 400 response's along with the single req_perform_stream request?