How to make REST POST calls in R

Question

I have been using jsonlite to make REST GET calls. The number of parameters have increased and I am wondering how to make a REST POST call using R.

Answer 1

Per your request ...

library(jsonlite)

BLUF

Instead of

fromJSON(myurl, ...)

you need to call httr::POST directly:

txt <- httr::POST(myurl, ...)
fromJSON(txt)

Explanation

The basic mechanism for using jsonlite::fromJSON is to pass it a string. In the special case that you pass an URL (regexpr: ^https?:// ), it does you a courtesy by calling httr::GET and taking its output as your intended input. You can see this intent by looking at its source by typing in jsonlite::fromJSON and finding the line with if(grepl("^https?://" ... ; if you try to find the function download_raw , you'll not find immediately since it is an un-exported function. You can find it as jsonlite:::download_raw (notice the third colon).

Looking at that function's source, you'll see that it makes direct calls to httr::GET . You can mimic how download_raw is calling httr::GET , modifying the arguments as needed. (It might be informative to look at both help(httr::GET) and help(httr::POST) and look for the differences between them. Spoiler: look at the body argument, potentially a list for keys/values. The examples are helpful.)