How to check if an FTP file exists

Question

I am trying to check if a file exists on my ftp server.

I've tried using the packages httr and httr2 but haven't gotten it to work. Below are my attempts:

my_file_url <- "sftp://my_server/my_file.txt"

With httr

httr::HEAD(my_file_url, httr::authenticate(my_username, my_password))

Fails with the below message

Error in x$headers$`content-type` : 
  $ operator is invalid for atomic vectors

With httr2

request(my_file_url) %>% 
  req_method("HEAD") %>% 
  req_auth_basic( my_username, my_password) %>% 
  req_perform()

Fails with the following message (I checked my credentials):

Error:
! Authentication failure

• What am I doing wrong in these two attempts?
• How do I do it directly through the curl package?

P.S. I tried the following, but this downloads the file:

curl::curl_fetch_memory(my_file_url, handle = my_curl_handle)

Answer 1

I don't believe you can pass HTTP methods (HEAD) or authenticate headers to (s)ftp service, but if your permissions allow you to get a directory listing, this might work:

library(curl)
#> Using libcurl 8.3.0 with Schannel
# https://test.rebex.net/ demo server
SFTP_DEMO <- "sftp://demo:password@test.rebex.net:22/"

file_list <- 
  curl(url = SFTP_DEMO, handle = new_handle(dirlistonly = TRUE)) |> 
  readLines()

file_list
#> [1] "."          ".."         "pub"        "readme.txt"

"readme.txt" %in% file_list
#> [1] TRUE

"im-not-here" %in% file_list
#> [1] FALSE

^{Created on 2023-11-29 with reprex v2.0.2}