Proxy handling docs and tweaks (#9735)

src/Composer/Util/Http/CurlDownloader.php

@@ -183,7 +183,6 @@ class CurlDownloader
         }
 
         $options['http']['header'] = $this->authHelper->addAuthenticationHeader($options['http']['header'], $origin, $url);
-        // Merge in headers - we don't get any proxy values
         $options = StreamContextFactory::initOptions($url, $options, true);
 
         foreach (self::$options as $type => $curlOptions) {

src/Composer/Util/Http/ProxyHelper.php

@@ -131,12 +131,14 @@ class ProxyHelper
         $error = sprintf('malformed %s url', $envName);
         $proxy = parse_url($proxyUrl);
 
+        // We need parse_url to have identified a host
         if (!isset($proxy['host'])) {
             throw new \RuntimeException($error);
         }
 
         $proxyUrl = self::formatParsedUrl($proxy, true);
 
+        // We need a port because streams and curl use different defaults
         if (!parse_url($proxyUrl, PHP_URL_PORT)) {
             throw new \RuntimeException($error);
         }

src/Composer/Util/RemoteFilesystem.php

@@ -254,7 +254,7 @@ class RemoteFilesystem
 
         $ctx = StreamContextFactory::getContext($fileUrl, $options, array('notification' => array($this, 'callbackGet')));
 
-        $proxy = ProxyManager::getInstance()->getProxyForRequest($fileUrl);
+        $proxy = $this->proxyManager->getProxyForRequest($fileUrl);
         $usingProxy = $proxy->getFormattedUrl(' using proxy (%s)');
         $this->io->writeError((strpos($origFileUrl, 'http') === 0 ? 'Downloading ' : 'Reading ') . Url::sanitize($origFileUrl) . $usingProxy, true, IOInterface::DEBUG);
         unset($origFileUrl, $proxy, $usingProxy);