Fix ComposerRepository handling of offline state to allow resolution as long as everything is present in the cache, fixes #10116

src/Composer/Repository/ComposerRepository.php

@@ -1178,6 +1178,14 @@ class ComposerRepository extends ArrayRepository implements ConfigurableReposito
                     throw $e;
                 }
 
+                // try to detect offline state (if dns resolution fails it is pretty likely to keep failing) and avoid retrying in that case
+                if ($e instanceof TransportException && $e->getStatusCode() === null) {
+                    $responseInfo = $e->getResponseInfo();
+                    if (isset($responseInfo['namelookup_time']) && $responseInfo['namelookup_time'] == 0) {
+                        $retries = 0;
+                    }
+                }
+
                 if ($retries) {
                     usleep(100000);
                     continue;
@@ -1349,7 +1357,7 @@ class ComposerRepository extends ArrayRepository implements ConfigurableReposito
             return $data;
         };
 
-        $reject = function ($e) use (&$retries, $httpDownloader, $filename, $options, &$reject, $accept, $io, $url, &$degradedMode, $repo) {
+        $reject = function ($e) use (&$retries, $httpDownloader, $filename, $options, &$reject, $accept, $io, $url, &$degradedMode, $repo, $lastModifiedTime) {
             if ($e instanceof TransportException && $e->getStatusCode() === 404) {
                 $repo->packagesNotFoundCache[$filename] = true;
 
@@ -1361,6 +1369,14 @@ class ComposerRepository extends ArrayRepository implements ConfigurableReposito
                 $retries = 0;
             }
 
+            // try to detect offline state (if dns resolution fails it is pretty likely to keep failing) and avoid retrying in that case
+            if ($e instanceof TransportException && $e->getStatusCode() === null) {
+                $responseInfo = $e->getResponseInfo();
+                if (isset($responseInfo['namelookup_time']) && $responseInfo['namelookup_time'] == 0) {
+                    $retries = 0;
+                }
+            }
+
             if (--$retries > 0) {
                 usleep(100000);
 
@@ -1372,6 +1388,11 @@ class ComposerRepository extends ArrayRepository implements ConfigurableReposito
             }
             $degradedMode = true;
 
+            // if the file is in the cache, we fake a 304 Not Modified to allow the process to continue
+            if ($lastModifiedTime) {
+                return $accept(new Response(array('url' => $url), 304, array(), ''));
+            }
+
             // special error code returned when network is being artificially disabled
             if ($e instanceof TransportException && $e->getStatusCode() === 499) {
                 return $accept(new Response(array('url' => $url), 404, array(), ''));

src/Composer/Util/Http/CurlDownloader.php

@@ -341,6 +341,7 @@ class CurlDownloader
                     if (!$error && function_exists('curl_strerror')) {
                         $error = curl_strerror($errno);
                     }
+                    $progress['error_code'] = $errno;
                     throw new TransportException('curl error '.$errno.' while downloading '.Url::sanitize($progress['url']).': '.$error);
                 }
                 $statusCode = $progress['http_code'];