pytest: add SOCKS tests and scoring

Configure curl with `--with-test-sockd=<path to sockd>` for a locally
installed dante sockd server and new `test_40_*` will verify that
down- and uploads work via SOCKS.

Invoke scorecard.py with `--socks4` or `--socks5` to run performance
tests with SOCKS. Note that SOCKS is not supported for HTTP/3.

Ref: #17969
Closes #17986

docs/INSTALL-CMAKE.md

@@ -463,6 +463,7 @@ Details via CMake
 - `CADDY`:                                  Default: `caddy`
 - `HTTPD_NGHTTPX`:                          Default: `nghttpx`
 - `HTTPD`:                                  Default: `apache2`
+- `SOCKD`:                                  Default: `sockd`
 - `TEST_NGHTTPX`:                           Default: `nghttpx`
 - `VSFTPD`:                                 Default: `vsftps`
 

docs/internals/SCORECARD.md

@@ -52,6 +52,13 @@ curl> python3 tests/http/scorecard.py -d --download-sizes=1mb --download-count=1
 
 Similar options are available for uploads and requests scenarios.
 
+## sockd
+
+If you have configured curl with `--with-test-sockd=<sockd-path>` for a
+`dante sockd` server installed on your system, you can provide the scorecard
+with arguments `--socks4` or `--socks5` to test performance with a SOCKS proxy
+involved. (Note: this does not work for HTTP/3)
+
 ## dtrace
 
 With the `--dtrace` option, scorecard produces a dtrace sample of the user stacks in `tests/http/gen/curl/curl.user_stacks`. On many platforms, `dtrace` requires **special permissions**. It is therefore invoked via `sudo` and you should make sure that sudo works for the run without prompting for a password.

docs/tests/HTTP.md

@@ -52,6 +52,7 @@ Via curl's `configure` script you may specify:
   * `--with-test-httpd=<httpd-install-path>` if you have an Apache httpd installed somewhere else. On Debian/Ubuntu it will otherwise look into `/usr/bin` and `/usr/sbin` to find those.
   * `--with-test-caddy=<caddy-install-path>` if you have a Caddy web server installed somewhere else.
   * `--with-test-vsftpd=<vsftpd-install-path>` if you have a vsftpd ftp  server installed somewhere else.
+  * `--with-test-sockd=<dante-sockd-path>` if you have `dante sockd` server installed
 
 ## Usage Tips