src/Tweeper.php: add a retry mechanism for cURL sessions

Sometimes the connection to a remote host may stall and a resource
cannot be retrieved. This makes Tweeper hang for a very long time which
can be annoying for users.

Setting a shorter timeout and a retry mechanism usually works around the
problem allowing the resource to be retrieved eventually.

Implement such a mechanism by adding curlExec() method and while at it
move non-curl related messages outside of getUrlContents() and
getUrlInfo() to give the user a better understanding of what actually
failed when even the retry mechanism was not able to retrieve the
resource.

diff --git a/src/Tweeper.php b/src/Tweeper.php
index 7318900..d58b529 100644 (file)
--- a/src/Tweeper.php
+++ b/src/Tweeper.php
@@ -37,6 +37,8 @@ date_default_timezone_set('UTC');
 class Tweeper {
 
   private static $userAgent = "Mozilla/5.0 (Windows NT 6.1; WOW64; rv:60.0) Gecko/20100101 Firefox/60.0";
+  private static $maxConnectionTimeout = 5;
+  private static $maxConnectionRetries = 5;
 
   /**
    * Create a new Tweeper object controlling optional settings.
@@ -86,12 +88,32 @@ class Tweeper {
   }
 
   /**
+   * Perform a cURL session multiple times when it fails with a timeout.
+   *
+   * @param resource $ch
+   *   a cURL session handle.
+   */
+  private static function curlExec($ch) {
+    $ret = FALSE;
+    $attempt = 0;
+    do {
+      $ret = curl_exec($ch);
+      if (FALSE === $ret) {
+        trigger_error(curl_error($ch), E_USER_WARNING);
+      }
+    } while (curl_errno($ch) == CURLE_OPERATION_TIMEDOUT && ++$attempt < Tweeper::$maxConnectionRetries);
+
+    return $ret;
+  }
+
+  /**
    * Get the contents from a URL.
    */
   private static function getUrlContents($url) {
     $ch = curl_init($url);
     curl_setopt_array($ch, array(
       CURLOPT_HEADER => FALSE,
+      CURLOPT_CONNECTTIMEOUT => Tweeper::$maxConnectionTimeout,
       // Follow http redirects to get the real URL.
       CURLOPT_FOLLOWLOCATION => TRUE,
       CURLOPT_RETURNTRANSFER => TRUE,
@@ -100,10 +122,7 @@ class Tweeper {
       CURLOPT_HTTPHEADER => array('Accept-language: en'),
       CURLOPT_USERAGENT => Tweeper::$userAgent,
     ));
-    $contents = curl_exec($ch);
-    if (FALSE === $contents) {
-      trigger_error(curl_error($ch), E_USER_WARNING);
-    }
+    $contents = Tweeper::curlExec($ch);
     curl_close($ch);
 
     return $contents;
@@ -117,6 +136,7 @@ class Tweeper {
     curl_setopt_array($ch, array(
       CURLOPT_HEADER => TRUE,
       CURLOPT_NOBODY => TRUE,
+      CURLOPT_CONNECTTIMEOUT => Tweeper::$maxConnectionTimeout,
       // Follow http redirects to get the real URL.
       CURLOPT_FOLLOWLOCATION => TRUE,
       CURLOPT_RETURNTRANSFER => TRUE,
@@ -125,9 +145,8 @@ class Tweeper {
       CURLOPT_USERAGENT => Tweeper::$userAgent,
     ));
 
-    $ret = curl_exec($ch);
+    $ret = Tweeper::curlExec($ch);
     if (FALSE === $ret) {
-      trigger_error(curl_error($ch), E_USER_WARNING);
       curl_close($ch);
       return FALSE;
     }
@@ -332,6 +351,7 @@ class Tweeper {
 
     $stylesheet_contents = Tweeper::getUrlContents($stylesheet);
     if (FALSE === $stylesheet_contents) {
+      trigger_error("Cannot open $stylesheet", E_USER_WARNING);
       return NULL;
     }
 
@@ -382,6 +402,7 @@ class Tweeper {
 
     $html = Tweeper::getUrlContents($src_url);
     if (FALSE === $html) {
+      trigger_error("Failed to retrieve $src_url", E_USER_WARNING);
       return NULL;
     }