Bring mocking ability to other req_perform* functions?

[sckott]

Of the various req_perform* functions (thinking mostly of req_perform_parallel and req_perform_connection) I think mock is only available in req_perform. Is that wrong?

Would you consider adding mocking ability (whether through a parameter or via a with handler like with_mocked_responses) to the other req_perform* functions?

Use case is so that packages like vcr, webmockr, httptest2 can hook into them

[hadley]

I'd consider it 😄

[sckott]

Thanks for considering it!

[hadley]

Ok, I've considered it. I've realised that I would find it personally super useful to mock req_perform_connection() because that way I could easily cache the ellmer vignettes.

[sckott]

Great. Let me know if I can help in any way.

[hadley]

Can you help by implementing it? 😄

[sckott]

I'll have a go at it

[hadley]

I’m also happy to jump on a call and brainstorm how this might work.

[sckott]

Sounds great. Let me get familiar with the package internals and then I'll ping you. Should I email you to schedule? Something else?

[hadley]

Yeah, shoot me an email and I'll send you my meeting invite link.

[sckott]

Notes from a chat w/ Hadley

• functions to mock
  • req_perform_connection() (ignore for the old fxn req_perform_stream() )
    • need to not mock just this function but also the resp_stream* functions
    • most stream fxns are built on resp_stream_raw()
    • most people will want to mock: resp_stream_lines() and resp_stream_sse()
    • different thing about these functions are that the $body returned is a curl connection instead of a normal body (e.g., json, etc) - but we should ask Jeroen to see if there is any way to mock a connection
      • There is not a way said Jeroen
      • Could we just create a connection from scratch? 🤔
  • req_perform_parallel() - didn't talk about this function
  • req_perform_promise() - didn't talk about this function
  • both of _parallel and _promise are very different (AFAICT) from _connection, and so learnings from _connection seem unlikely to help much
• use cases
  • vcr issue Support for streaming requests with httr2 ropensci/vcr#273 -
    • issue mentions req_perform_stream, but req_perform_connection replaces it
  • hadley's ellmer use case: ellmer uses the following httr2 functions that hadley said would be useful to mock for testing purposes:
    • req_perform_parallel
    • req_perform_connection
    • req_perform_promise
• resp_stream* mocking
  • make resp_stream_lines a generic (s3 presumably)?
  • or could handle internally within resp_stream_lines
  • or maybe could mock resp_boundary_pushback? but he said probably not, probably too complicated

Some options to consider

# Option 1
# resp_stream_sse() returns each of these objects in turn 
expect_equal(resp_stream_sse(resp)$type, "message")
expect_equal(resp_stream_sse(resp)$body, "done")

something_mock_sse_something(list(
  list(type = "message", body = "start"),
  list(type = "message", body = "done")
))
  
# Option 2
# take each object and convert it back to its binary representation  
# make resp_stream_raw() return them OR maybe even some sort of  
# special connection object that returns special values from readBin  
# (or make a generic version of readBin?)  
#  
# This would be easiest in terms of recording  
  
# Option 3
# <https://github.com/r-lib/testthat/pull/2061> in github main branch, not on cran yet
local_mocked_bindings(
  resp_stream_sse = mock_output_sequence(
    list(type = "message", body = "start"),
    list(type = "message", body = "done")
  )
)