Detect and hint for solutions for common curl errors, fixes #9376

src/Composer/Command/DiagnoseCommand.php

@@ -224,6 +224,12 @@ EOT
         try {
             $this->httpDownloader->get($proto . '://repo.packagist.org/packages.json');
         } catch (TransportException $e) {
+            if ($hints = HttpDownloader::getExceptionHints($e)) {
+                foreach ($hints as $hint) {
+                    $result[] = $hint;
+                }
+            }
+
             $result[] = '<error>[' . get_class($e) . '] ' . $e->getMessage() . '</error>';
         }
 

src/Composer/Console/Application.php

@@ -30,6 +30,7 @@ use Composer\IO\IOInterface;
 use Composer\IO\ConsoleIO;
 use Composer\Json\JsonValidationException;
 use Composer\Util\ErrorHandler;
+use Composer\Util\HttpDownloader;
 use Composer\EventDispatcher\ScriptExecutionException;
 use Composer\Exception\NoSslException;
 
@@ -382,6 +383,12 @@ class Application extends BaseApplication
             $io->writeError('<error>The following exception is caused by a lack of memory or swap, or not having swap configured</error>', true, IOInterface::QUIET);
             $io->writeError('<error>Check https://getcomposer.org/doc/articles/troubleshooting.md#proc-open-fork-failed-errors for details</error>', true, IOInterface::QUIET);
         }
+
+        if ($hints = HttpDownloader::getExceptionHints($exception)) {
+            foreach ($hints as $hint) {
+                $io->writeError($hint, true, IOInterface::QUIET);
+            }
+        }
     }
 
     /**

src/Composer/Util/Http/CurlDownloader.php

@@ -157,7 +157,6 @@ class CurlDownloader
 
         curl_setopt($curlHandle, CURLOPT_URL, $url);
         curl_setopt($curlHandle, CURLOPT_FOLLOWLOCATION, false);
-        //curl_setopt($curlHandle, CURLOPT_DNS_USE_GLOBAL_CACHE, false);
         curl_setopt($curlHandle, CURLOPT_CONNECTTIMEOUT, 10);
         curl_setopt($curlHandle, CURLOPT_TIMEOUT, 300);
         curl_setopt($curlHandle, CURLOPT_WRITEHEADER, $headerHandle);

src/Composer/Util/HttpDownloader.php

@@ -378,4 +378,32 @@ class HttpDownloader
             $io->writeError('<'.$type.'>'.ucfirst($type).' from '.$url.': '.$data[$type].'</'.$type.'>');
         }
     }
+
+    public static function getExceptionHints(\Exception $e)
+    {
+        if (!$e instanceof TransportException) {
+            return;
+        }
+
+        if (
+            false !== strpos($e->getMessage(), 'Resolving timed out')
+            || false !== strpos($e->getMessage(), 'Could not resolve host')
+        ) {
+            Silencer::suppress();
+            $testConnectivity = file_get_contents('https://8.8.8.8', false, stream_context_create(array(
+                'ssl' => array('verify_peer' => false),
+                'http' => array('follow_location' => false, 'ignore_errors' => true)
+            )));
+            Silencer::restore();
+            if (false !== $testConnectivity) {
+                return array(
+                    '<error>The following exception probably indicates you have misconfigured DNS resolver(s)</error>'
+                );
+            }
+
+            return array(
+                '<error>The following exception probably indicates you are offline or have misconfigured DNS resolver(s)</error>'
+            );
+        }
+    }
 }