UI function that handles GET or POST requests

app.R

ui <- function(req) {
  if (identical(req$REQUEST_METHOD, "GET")) {  
    
    htmlTemplate("index.html")
    
  } else if (identical(req$REQUEST_METHOD, "POST")) {
    body <- rawToChar(req$rook.input$read(-1))
    url <- stringr::str_interp("${CPD_URL}/ml/v4/deployments/${DEPLOYMENT_ID}/predictions")
    query <- list(version=VERSION)
    r <- POST(
      url,
      add_headers(
        .headers = getHeaders()
      ),
      query=query,
      body=body,
      encode="raw"
    )

    content <- jsonlite::toJSON(
      list(
        fields = unlist(httr::content(r)$predictions[[1]]$fields),
        values = lapply(httr::content(r)$predictions[[1]]$values, unlist)
      )
    )
    
    httpResponse(
      status = 200L,
      content_type = "application/json",
      content = content
    )

  }
}