Allow to use a proxy for downloads

This change will make it possible to provide a proxy when downloading.

For that the content of the environment-variable `HTTP_PROXY` is used.
Alternatively one can also use `http_proxy` (as used by curl) can be
used.

For proxy-authentication you can set user and password for basic-
authentication via the environment variable `HTTP_PROXY_AUTH`

phive.xml

@@ -1,6 +1,6 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <phive xmlns="https://phar.io/phive">
-  <phar name="phpunit" version="^9.3" location="./tools/phpunit" copy="false" installed="9.4.2"/>
+  <phar name="phpunit" version="^9.3" location="./tools/phpunit" copy="true" installed="9.5.21"/>
   <phar name="psalm" version="^3.11" location="./tools/psalm" copy="false" installed="3.18.2"/>
   <phar name="php-cs-fixer" version="^2.16" location="./tools/php-cs-fixer" copy="false" installed="2.16.7"/>
 </phive>

src/Service/Download.php

@@ -8,6 +8,8 @@
 use SplFileInfo;
 use function feof;
 use function fwrite;
+use function getenv;
+use function stream_context_create;
 
 final class Download
 {
@@ -20,12 +22,44 @@ public function __construct(Url $url)
 
     public function toLocation(SplFileInfo $downloadLocation) : void
     {
-        $source = fopen($this->url->toString(), 'r');
+        $context = $this->getStreamContext();
+        $source = fopen($this->url->toString(), 'r',false, $context);
         $target = fopen($downloadLocation->getPathname(), 'w');
         while (!feof($source)) {
             fwrite($target, fread($source, 1024));
         }
         fclose($source);
         fclose($target);
     }
+
+    /**
+     * @return resource
+     */
+    private function getStreamContext()
+    {
+        foreach (['http_proxy', 'HTTP_PROXY', 'https_proxy', 'HTTPS_PROXY'] as $envName) {
+            $proxy = getenv($envName);
+            if ($proxy !== '') {
+                break;
+            }
+        }
+
+        if ($proxy === '') {
+            return stream_context_create([]);
+        }
+
+        $context = [
+            'http' => [
+                'proxy' => $proxy,
+                'request_fulluri' => true,
+            ]
+        ];
+
+        $auth = getenv('HTTP_PROXY_AUTH');
+        if ($auth !== '') {
+            $context['http']['header'][] = 'Proxy-Authorization: Basic ' . $auth;
+        }
+
+        return stream_context_create($context);
+    }
 }

tests/unit/Service/DownloadTest.php

@@ -0,0 +1,41 @@
+<?php
+
+namespace PharIo\ComposerDistributorTest\unit\Service;
+
+use PharIo\ComposerDistributor\Service\Download;
+use PharIo\ComposerDistributor\Url;
+use PHPUnit\Framework\TestCase;
+use SplFileInfo;
+use function file_get_contents;
+use function putenv;
+use function sys_get_temp_dir;
+use function tempnam;
+
+class DownloadTest extends TestCase
+{
+    public function testDownloadWithoutProxy(): void
+    {
+        putenv('http_proxy=');
+
+        $temp = new SplFileInfo(tempnam(sys_get_temp_dir(), 'tests'));
+
+        $download = new Download(Url::fromString('https://example.org'));
+
+        $download->toLocation($temp);
+
+        self::assertStringContainsString('example', file_get_contents($temp->getPathname()));
+    }
+
+    public function testDownloadWithProxy(): void
+    {
+        putenv('http_proxy=tcp://172.16.1.184:8888');
+
+        $temp = new SplFileInfo(tempnam(sys_get_temp_dir(), 'tests'));
+
+        $download = new Download(Url::fromString('https://example.org'));
+
+        $this->expectWarning();
+
+        $download->toLocation($temp);
+    }
+}