Fix repeated web server error log failures

tests/Unit/WebServerTest.php

@@ -0,0 +1,115 @@
+<?php
+
+namespace DDTrace\Tests\Unit;
+
+use DDTrace\Tests\Common\BaseTestCase;
+use DDTrace\Tests\Sapi\Sapi;
+use DDTrace\Tests\WebServer;
+
+final class WebServerTest extends BaseTestCase
+{
+    private $temporaryDirectory;
+
+    protected function ddTearDown()
+    {
+        if ($this->temporaryDirectory) {
+            @unlink($this->temporaryDirectory . '/index.php');
+            @unlink($this->temporaryDirectory . '/' . WebServer::ERROR_LOG_NAME);
+            @rmdir($this->temporaryDirectory);
+        }
+
+        parent::ddTearDown();
+    }
+
+    public function testCheckErrorsConsumesLogEntriesOnce()
+    {
+        $server = $this->createWebServer();
+        $errorLog = $this->temporaryDirectory . '/' . WebServer::ERROR_LOG_NAME;
+
+        file_put_contents($errorLog, "[ddtrace] [error] first error\n");
+
+        $this->assertSame('[ddtrace] [error] first error', $server->checkErrors());
+        $this->assertNull($server->checkErrors());
+
+        file_put_contents($errorLog, "[ddtrace] [warn] second error\n", FILE_APPEND);
+
+        $this->assertSame('[ddtrace] [warn] second error', $server->checkErrors());
+        $this->assertNull($server->checkErrors());
+    }
+
+    public function testCheckErrorsHandlesTruncatedLog()
+    {
+        $server = $this->createWebServer();
+        $errorLog = $this->temporaryDirectory . '/' . WebServer::ERROR_LOG_NAME;
+
+        file_put_contents($errorLog, "[ddtrace] [error] a deliberately long error\n");
+        $server->checkErrors();
+
+        file_put_contents($errorLog, "[ddtrace] [error] new\n");
+
+        $this->assertSame('[ddtrace] [error] new', $server->checkErrors());
+        $this->assertNull($server->checkErrors());
+    }
+
+    public function testCheckErrorsHandlesReplacedLogGrownPastPreviousOffset()
+    {
+        $server = $this->createWebServer();
+        $errorLog = $this->temporaryDirectory . '/' . WebServer::ERROR_LOG_NAME;
+
+        // Long enough that a naive size-only comparison would not detect the
+        // replacement once the new file grows to at least this offset.
+        $padding = str_repeat('x', 4096);
+        file_put_contents($errorLog, "[ddtrace] [error] first error $padding\n");
+        $server->checkErrors();
+
+        // Simulate rotation: create a new file elsewhere and rename it over the
+        // old path, guaranteeing a new inode, already containing more bytes than
+        // the previous offset.
+        $replacement = $errorLog . '.1';
+        file_put_contents($replacement, "[ddtrace] [error] early marker in replacement\n$padding\n");
+        rename($replacement, $errorLog);
+
+        $this->assertSame('[ddtrace] [error] early marker in replacement', $server->checkErrors());
+        $this->assertNull($server->checkErrors());
+    }
+
+    private function createWebServer()
+    {
+        $temporaryFile = tempnam(sys_get_temp_dir(), 'ddtrace-webserver-test-');
+        @unlink($temporaryFile);
+        mkdir($temporaryFile);
+        $this->temporaryDirectory = $temporaryFile;
+
+        $indexFile = $this->temporaryDirectory . '/index.php';
+        touch($indexFile);
+
+        $server = new WebServer($indexFile);
+        $sapi = new WebServerTestSapi();
+        $property = new \ReflectionProperty($server, 'sapi');
+        $property->setAccessible(true);
+        $property->setValue($server, $sapi);
+
+        return $server;
+    }
+}
+
+final class WebServerTestSapi implements Sapi
+{
+    public function start()
+    {
+    }
+
+    public function stop()
+    {
+    }
+
+    public function isFastCgi()
+    {
+        return false;
+    }
+
+    public function checkErrors()
+    {
+        return null;
+    }
+}

tests/WebServer.php

@@ -93,6 +93,7 @@ final class WebServer
     ];
 
     private $errorLogSize = 0;
+    private $errorLogInode = 0;
 
     /**
      * Persisted apache instance for the lifetime of the testsuite - we use reload instead of restart to apply changes.
@@ -184,6 +185,7 @@ public function start()
         }
 
         $this->errorLogSize = (int)@filesize($this->defaultInis['error_log']);
+        $this->errorLogInode = (int)@fileinode($this->defaultInis['error_log']);
 
         if ($this->roadrunnerVersion) {
             $this->sapi = new RoadrunnerServer(
@@ -358,7 +360,30 @@ public function mergeInis($inis)
      */
     public function checkErrors()
     {
-        $diff = @file_get_contents($this->defaultInis['error_log'], false, null, $this->errorLogSize);
+        $errorLog = $this->defaultInis['error_log'];
+
+        // Only inspect log entries written since the previous check. Without
+        // advancing the offset, one transient error is reported again by every
+        // retry and every subsequent test that shares this web server.
+        clearstatcache(true, $errorLog);
+        $currentSize = (int) @filesize($errorLog);
+        $currentInode = (int) @fileinode($errorLog);
+        if ($currentSize < $this->errorLogSize || $currentInode !== $this->errorLogInode) {
+            // The log may have been truncated, rotated, or replaced while the
+            // server was running. Comparing the inode detects a replacement that
+            // has already grown to at least the previous offset, which a size-only
+            // check would miss. Start reading from the beginning of the new file.
+            $this->errorLogSize = 0;
+        }
+        $this->errorLogInode = $currentInode;
+
+        $diff = @file_get_contents($errorLog, false, null, $this->errorLogSize);
+        if ($diff === false) {
+            $diff = "";
+        } else {
+            $this->errorLogSize += strlen($diff);
+        }
+
         $out = "";
         foreach (explode("\n", $diff) as $line) {
             // Ignore sidecar retry errors for known-invalid test hostnames — these are