docs: clarify FTP over HTTP proxy functionality somewhat

Reported-by: newfunction
Closes #15417

diff --git a/docs/cmdline-opts/proxy.md b/docs/cmdline-opts/proxy.md
index 529d3369fb2b1dc65afa72f29638b58283e939cc..afaa29837eeb85a1a7421ea804892a9d460c3930 100644 (file)
--- a/docs/cmdline-opts/proxy.md
+++ b/docs/cmdline-opts/proxy.md
@@ -56,3 +56,7 @@ password.
 
 When a proxy is used, the active FTP mode as set with --ftp-port, cannot be
 used.
+
+Doing FTP over an HTTP proxy without --proxytunnel makes curl do HTTP with an
+FTP URL over the proxy. For such transfers, common FTP specific options do not
+work, including --ftp-ssl-reqd and --ftp-ssl-control.

diff --git a/docs/libcurl/opts/CURLOPT_PROXY.md b/docs/libcurl/opts/CURLOPT_PROXY.md
index c414f4f512968618e49fc6654a1f55e6dd2dd7c1..7c8455602452603d836258cdd942d73a98c19b08 100644 (file)
--- a/docs/libcurl/opts/CURLOPT_PROXY.md
+++ b/docs/libcurl/opts/CURLOPT_PROXY.md
@@ -102,6 +102,10 @@ single port number used widely for proxies. Specify it.
 When a proxy is used, the active FTP mode as set with *CUROPT_FTPPORT(3)*,
 cannot be used.
 
+Doing FTP over an HTTP proxy without CURLOPT_HTTPPROXYTUNNEL(3) set makes
+libcurl do HTTP with an FTP URL over the proxy. For such transfers, common FTP
+specific options do not work, for example CURLOPT_USE_SSL(3).
+
 # Environment variables
 
 libcurl respects the proxy environment variables named **http_proxy**,