curl's verbose=TRUE argument not working on Windows

[allanvc]

Hi Jeroen. Thanks for this nice and useful package.
I currently have a package built on top of curl. It is called mRpostman. The idea is to implement several IMAP functionalities so that R users can easily manipulate mail folders and messages from inside R.
A few weeks ago, I noticed that the curl's verbose=TRUE argument is not working properly on Windows. Sometimes the communication with the server appears in the console, sometimes it doesn’t .

I test it regularly on Linux and everything works fine. So, the problem seems to be restricted to Windows.

The code below may allow you to replicate the problem:

conn_params <- list(username="user@gmail.com",
                    password="pass",
                    verbose = TRUE)

h <- curl::new_handle()

do.call(curl::handle_setopt, c(h, conn_params))

curl::handle_setopt(h, customrequest = paste0('SELECT ', "INBOX"))

curl::curl_fetch_memory("imaps://imap.gmail.com", handle = h)

In mRpostman, the equivalent would be:

library(mRpostman)
imapconf <- configure_imap(url="imaps://imap.gmail.com",
                           username="user",
                           password="pass",
                           verbose = TRUE
)

imapconf %>%
  select_mailbox(mbox = "INBOX")

This is my libcurl version on Windows:

curl::curl_version()

$version
[1] "7.64.1"

$ssl_version
[1] "(OpenSSL/1.1.1a) Schannel"

$libz_version
[1] "1.2.11"

$libssh_version
[1] "libssh2/1.8.2"

$libidn_version
[1] NA

$host
[1] "x86_64-w64-mingw32"

$protocols
 [1] "dict"   "file"   "ftp"    "ftps"   "gopher" "http"   "https"  "imap"   "imaps"  "ldap"   "ldaps" 
[12] "pop3"   "pop3s"  "rtsp"   "scp"    "sftp"   "smtp"   "smtps"  "telnet" "tftp"  

$ipv6
[1] TRUE

$http2
[1] FALSE

$idn
[1] TRUE

R version 4.0.2 (2020-06-22)
Platform: x86_64-w64-mingw32/x64 (64-bit)
Running under: Windows 10 x64 (build 18362)

Matrix products: default

locale:
[1] LC_COLLATE=Portuguese_Brazil.1252  LC_CTYPE=Portuguese_Brazil.1252    LC_MONETARY=Portuguese_Brazil.1252
[4] LC_NUMERIC=C                       LC_TIME=Portuguese_Brazil.1252    

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

other attached packages:
[1] mRpostman_0.3.1

loaded via a namespace (and not attached):
[1] compiler_4.0.2   assertthat_0.2.1 magrittr_1.5     tools_4.0.2      rstudioapi_0.11  curl_4.3        
[7] stringi_1.4.6    stringr_1.4.0