preproxy: renamed what was added as SOCKS_PROXY

CURLOPT_SOCKS_PROXY -> CURLOPT_PRE_PROXY

Added the corresponding --preroxy command line option. Sets a SOCKS
proxy to connect to _before_ connecting to a HTTP(S) proxy.

1 files changed, 21 insertions, 0 deletions

diff --git a/docs/cmdline-opts/preproxy.d b/docs/cmdline-opts/preproxy.d
new file mode 100644
index 000000000..ebef4ab07
--- /dev/null
+++ b/docs/cmdline-opts/preproxy.d
@@ -0,0 +1,21 @@
+Long: preproxy
+Arg: [protocol://]host[:port]
+Help: Use this proxy first
+Added: 7.52.0
+---
+Use the specified proxy before connecting to the ordinary proxy. Hence pre
+proxy. A pre proxy must be a SOCKS speaking proxy.
+
+The pre proxy string should be specified with a protocol:// prefix to specify
+alternative proxy protocols. Use socks4://, socks4a://, socks5:// or
+socks5h:// to request the specific SOCKS version to be used. No protocol
+specified will make curl default to SOCKS4.
+
+If the port number is not specified in the proxy string, it is assumed to be
+1080.
+
+User and password that might be provided in the proxy string are URL decoded
+by curl. This allows you to pass in special characters such as @ by using %40
+or pass in a colon with %3a.
+
+If this option is used several times, the last one will be used.