R/Shiny app similar to Google Translate whole page translation (when you paste a URL)

app.R

#### Prerequisites -- in Linux terminal: 
# Once:
#    pipx install libretranslate
# Run in the background:
#    libretranslate

#### Test:
# Open the following page in a web browser
# (but first modify  your.shiny-server.domain  and  your_translate_app_name):
#    https://your.shiny-server.domain/your_translate_app_name/?url=https://example.com/&from=en&to=fr
# equivalent of:
#    https://translate.google.com/?sl=en&tl=fr&text=https%3A%2F%2Fexample.com&op=translate
# which provides the link:
#    https://example-com.translate.goog/?_x_tr_sl=en&_x_tr_tl=fr

library(shiny)
library(curl)
library(jsonlite)
library(magrittr)

INTERNAL_URL <- "http://localhost:5000/translate"

fetch_and_transform <- function(URL,from,to) {
  con <- 
    url(URL, "rb")
  on.exit(close(con), add = TRUE)
  json_data <-
    readLines(con, warn=FALSE, encoding="UTF-8") %>% 
    paste(collapse="") %>% 
    list(q=.,
         source=from,
         target=to,
         format="html") %>% 
    toJSON(auto_unbox = TRUE)
  h <-
    new_handle()
  handle_setheaders(h, "Content-Type"="application/json")
  handle_setopt(h, postfields=json_data)
  curl_fetch_memory(INTERNAL_URL, handle=h) %>% 
    .$content %>% 
    rawToChar %>% 
    fromJSON %>% 
    .$translatedText %>% 
    substr(5,nchar(.)) # remove string "html" from the beginning
}

ui <- function(request) {
  query <-
    parseQueryString(request$QUERY_STRING)
  URL <-
    URLdecode(query$url)
  from <-
    tolower(query$from) %>% 
    `if`(length(.)==0,'en',.)
  to <-
    tolower(query$to) %>% 
    `if`(length(.)==0,'pl',.)
  content <- 
    tryCatch(fetch_and_transform(URL,from,to),
             error = function(e) e)
  if (inherits(content, "error")) 
    httpResponse(
      status = 502,
      content_type = "text/plain; charset=UTF-8",
      content = paste0("Upstream fetch failed: ", conditionMessage(content))
    ) else
    httpResponse(
      status = 200,
      content_type = "text/html; charset=UTF-8",
      content = content
    )
}

server <- function(input, output, session) {}

shinyApp(ui, server)