`check_content_type` causes error in `resp_body_json` for cached requests (status 304)

[jemus42]

When making an API request that has a cached response, resp_body_json throws an error unless check_type = FALSE.

Reprex using a boiled down version of my API wrapper:

library(httr2)

req <- request("https://api.trakt.tv/users/jemus42/comments/all/episodes?include_replies=false") |>
  req_headers(
    # Additional headers required by the API
    "trakt-api-key" = "12fc1de7671c7f2fb4a8ac08ba7c9f45b447f4d5bad5e11e3490823d629afdf2",
    "Content-Type" = "application/json",
    "trakt-api-version" = 2
  ) |>
  httr2::req_retry(max_tries = 2) |>
  httr2::req_cache(path = tempdir(), use_on_error = TRUE, debug = TRUE)

httr2::req_dry_run(req)
#> GET /users/jemus42/comments/all/episodes?include_replies=false HTTP/1.1
#> Host: api.trakt.tv
#> User-Agent: httr2/0.2.3.9000 r-curl/5.0.2 libcurl/7.88.1
#> Accept: */*
#> Accept-Encoding: deflate, gzip
#> trakt-api-key: 12fc1de7671c7f2fb4a8ac08ba7c9f45b447f4d5bad5e11e3490823d629afdf2
#> Content-Type: application/json
#> trakt-api-version: 2
resp_first <- httr2::req_perform(req)
#> Saving response to cache "b2b3e9120f4a602db8b46ba633aa8027"

response_parsed <- httr2::resp_body_json(resp_first)

resp_second <- httr2::req_perform(req)
#> Found url in cache "b2b3e9120f4a602db8b46ba633aa8027"
#> Cached value is stale; checking for updates
#> Cached value still ok; retrieving body from cache
response_parsed <- httr2::resp_body_json(resp_second)
#> Error in if (!is.null(suffix) && endsWith(content_type, suffix)) {: missing value where TRUE/FALSE needed

# Current workaround: disabling content type check
response_parsed <- httr2::resp_body_json(resp_second, check_type = FALSE)

^{Created on 2023-08-11 with reprex v2.0.2}

I found that resp_content_type(resp) can return NA_character here:

httr2/R/resp-headers.R

Lines 101 to 107 in d789827

	resp_content_type <- function(resp) {
	if (resp_header_exists(resp, "content-type")) {
	parse_media(resp_header(resp, "content-type"))$type
	} else {
	NA_character_
	}
	}

which causes a missing value where TRUE/FALSE needed error in the if condition here:

httr2/R/resp-body.R

Lines 130 to 133 in d789827

	content_type <- resp_content_type(resp)
	if (content_type %in% types) {
	return()
	}

I'm not sure I'm doing caching correctly (I'm in the process of migrating from httr to httr2 and did no caching previously), but I assume that at least this particular error is not the result of me holding it wrong or the trakt.tv API being weird (which is unfortunately the case when it comes to OAuth, but that's a different issue).

[mgirlich]

Thanks for the issue report. This was actually a bug in httr2 and you did things correctly.