PHP CURL with proxy causes CLOSE_WAIT on socket - php

Question

I'm using PHP curl library to establish connection and retrieve content from WEB - the usual.
I have multiple SOCKS5 proxy servers running on localhost on ports from 10300 to 10350 and PHP selects a port randomly.
My code:
$ch = curl_init();
curl_setopt($ch, CURLOPT_URL, $url);
curl_setopt($ch, CURLOPT_PROXY, "localhost:".mt_rand(10300, 10350));
curl_setopt($ch, CURLOPT_PROXYTYPE, CURLPROXY_SOCKS5);
curl_setopt($ch, CURLOPT_FOLLOWLOCATION, 1);
curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);
$curl_resp = curl_exec($ch);
curl_close($ch);
/// ... whatever logic
But if I put this code into loop for long time, I get error telling that no more files can be opened. I read online that is because filehandler limit being reached, so I debugged with lsof -p and I noticed that the process has hundreds and even thousands of these lines:
... TCP localhost:43030->localhost:10303 (CLOSE_WAIT)
... TCP localhost:40982->localhost:10341 (CLOSE_WAIT)
... TCP localhost:48718->localhost:10304 (CLOSE_WAIT)
... TCP localhost:41655->localhost:10350 (CLOSE_WAIT)
... TCP localhost:41915->localhost:10310 (CLOSE_WAIT)
... TCP localhost:49746->localhost:10322 (ESTABLISHED)
I was researching why is this that way, but I don't understand, because I am calling curl_close and I would assume that CURL would close PROXY connection as well, or am I missing something?
Versions:
PHP 7.1.4-1+deb.sury.org~trusty+1 (cli) (built: Apr 11 2017 22:45:20) (NTS)
curl 7.52.1 (x86_64-pc-linux-gnu) libcurl/7.52.1 OpenSSL/1.0.1f zlib/1.2.8 libidn2/0.9 libpsl/0.11.0 (+libicu/52.1) libssh2/1.4.3 nghttp2/1.19.0 librtmp/2.3

Answer 1

I also came across this issue. The work around is add
curl_setopt($ch, CURLOPT_HTTPHEADER, array("Connection: close"));
At first I thought is was related with php7, because i can reproduce it on a php7 box, but on php5, it will not happen. Unfortunately, I tried this on another php7 box, it also did not happen again. So I am still confused about the root cause.