2 files changed, 58 insertions, 4 deletions

diff --git a/src/PhpBB3.php b/src/PhpBB3.php
index b12841f..5a60712 100644
--- a/src/PhpBB3.php
+++ b/src/PhpBB3.php
@@ -81,6 +81,39 @@ class PhpBB3 {
     }
   }
 
+  public function topicExists($topicId) {
+    global $db;
+
+    if (!is_int($topicId)) {
+      trigger_error('topic id is not an integer', E_USER_ERROR);
+    }
+
+    if ($topicId < 0) {
+      trigger_error('topic id is negative', E_USER_ERROR);
+    }
+
+    $sql = 'SELECT 1 FROM ' . TOPICS_TABLE . ' ' .
+           'WHERE topic_id = ' . $topicId . ' LIMIT 1';
+
+    $result = $db->sql_query($sql);
+  
+    $rows = $db->sql_fetchrowset($result);
+    $db->sql_freeresult($result);
+
+    switch (count($rows)) {
+    case 0:
+      return false;
+    
+    case 1:
+      return true;
+    
+    default:
+      # Should be impossible due to LIMIT 1.
+      trigger_error("Too many rows returned: $sql", E_USER_ERROR);
+      break;
+    }
+  }
+
   public function postMessage($postType, $forumId, $topicId, $msg) {
     if ($postType != 'post' && $postType != 'reply') {
       trigger_error('bad post type: ' . $postType, E_USER_ERROR);
@@ -94,10 +127,12 @@ class PhpBB3 {
       trigger_error('forum does not exist: ' . $forumId, E_USER_ERROR);
     } 
 
-    if ($topicId !== null) {
-      if (!is_int($topicId) || $topicId < 0) {
-        trigger_error('bad topic id: ' . $topicId, E_USER_ERROR);
-      }
+    if (!is_int($topicId)) {
+      trigger_error('bad topic id: ' . $topicId, E_USER_ERROR);
+    }
+
+    if ($postType == 'reply' && !$this->topicExists($topicId)) {
+      trigger_error('topic does not exist: ' . $topicId, E_USER_ERROR);
     }
 
     if ($msg === null) {
diff --git a/test/PhpBB3Test.php b/test/PhpBB3Test.php
index a853b8b..1ff9b88 100644
--- a/test/PhpBB3Test.php
+++ b/test/PhpBB3Test.php
@@ -99,4 +99,23 @@ EOF;
       array(2, true, null)
     );
   }
+
+  /**
+   * @dataProvider providerTopicExists
+   */
+  public function testTopicExists($topic_id, $expected, $ex) {
+    if ($ex) $this->setExpectedException($ex);
+    $run = 'topicExists(' . $topic_id . ')';
+    $this->assertEquals($expected, $this->exec_kludge($run));
+  }
+
+  public function providerTopicExists() {
+    return array(
+      array('bogus', null, 'PHPUnit_Framework_Error'),
+      array(3.5, null, 'PHPUnit_Framework_Error'),
+      array(-1, null, 'PHPUnit_Framework_Error'),
+      array(0, false, null),
+      array(1, true, null)
+    );
+  }
 }