`req_body_raw` blocks setting the Content-Type header

[colmanhumphrey]

NOTE: LOW PRIORITY

I could have this wrong, and/or this could be intended behaviour.

In trying to send a top-level empty list (see #115), I figured I could create the required JSON myself and use req_body_raw. I didn't see at first that this function takes a type, and I first set the header, that is:

library(httr2)

url <- "http://httpbin.org/"
req <- request(url)

body <- req |>
    req_body_raw("{\"empty_list\":[]}") |>
    req_headers("Content-Type" = "application/json") |>
    req_dry_run()

#> POST / HTTP/1.1
#> Host: httpbin.org
#> User-Agent: httr2/0.1.1 r-curl/4.3.2 libcurl/7.77.0
#> Accept: */*
#> Accept-Encoding: deflate, gzip
#> Content-Length: 17
#> 
#> {"empty_list":[]}

But this doesn't set Content-Type: application/json. I am a little surprised that the header call coming after the body doesn't "win" the header battle.

This also isn't resolved by setting the header before the req_body_raw call (or by setting both).

As expected, all works if the type parameter of req_body_raw is used instead of setting the header:

library(httr2)

url <- "http://httpbin.org/"
req <- request(url)

body <- req |>
    req_body_raw("{\"empty_list\":[]}", type = "application/json") |>
    req_dry_run()
#> POST / HTTP/1.1
#> Host: httpbin.org
#> User-Agent: httr2/0.1.1 r-curl/4.3.2 libcurl/7.77.0
#> Accept: */*
#> Accept-Encoding: deflate, gzip
#> Content-Type: application/json
#> Content-Length: 17
#> 
#> {"empty_list":[]}

Session Info

> sessionInfo()
R version 4.1.2 (2021-11-01)
Platform: aarch64-apple-darwin20 (64-bit)
Running under: macOS Monterey 12.1

Matrix products: default
BLAS:   /Library/Frameworks/R.framework/Versions/4.1-arm64/Resources/lib/libRblas.0.dylib
LAPACK: /Library/Frameworks/R.framework/Versions/4.1-arm64/Resources/lib/libRlapack.dylib

locale:
[1] en_US.UTF-8/en_US.UTF-8/en_US.UTF-8/C/en_US.UTF-8/en_US.UTF-8

attached base packages:
[1] stats     graphics  grDevices utils     datasets  methods   base     

other attached packages:
[1] jsonlite_1.7.2   httr2_0.1.1      conflicted_1.0.4

loaded via a namespace (and not attached):
 [1] Rcpp_1.0.8.3     crayon_1.4.2     later_1.3.0      rappdirs_0.3.3  
 [5] R6_2.5.1         magrittr_2.0.1   rlang_1.0.2      cachem_1.0.6    
 [9] cli_3.1.0        curl_4.3.2       promises_1.2.0.1 tools_4.1.2     
[13] glue_1.5.1       httpuv_1.6.5     fastmap_1.1.0    compiler_4.1.2  

[hadley]

I think this is a bug — req_body_apply() should prefer a header set in the request before using it's default.