Prevent race condition in vocabulary cache update

src/Vocab/Loader/DefaultVocabLoader.php

@@ -22,9 +22,12 @@
 use function is_resource;
 use function is_writable;
 use function mkdir;
+use function rename;
 use function sha1;
 use function sprintf;
 use function stream_copy_to_stream;
+use function uniqid;
+use function unlink;
 
 use const DIRECTORY_SEPARATOR;
 
@@ -68,10 +71,11 @@ public function loadFile(string $uri, string|null $checksum = null): string
         }
 
         try {
-            $cacheStream = fopen($cacheFile, 'w+');
+            $tmpFile = $cacheFile . '_' . uniqid('tmp', more_entropy: true);
+            $cacheStream = fopen($tmpFile, 'w+');
 
             if ($cacheStream === false) {
-                throw new IOError(sprintf('Could not open file for write: %s', $cacheFile));
+                throw new IOError(sprintf('Could not open file for write: %s', $tmpFile));
             }
 
             try {
@@ -86,6 +90,17 @@ public function loadFile(string $uri, string|null $checksum = null): string
                     throw new IOError($message);
                 }
 
+                if (rename($tmpFile, $cacheFile) === false) {
+                    $message = 'Could not rename file';
+                    $lastError = error_get_last();
+
+                    if ($lastError !== null) {
+                        $message .= ': ' . $lastError['message'];
+                    }
+
+                    throw new IOError($message);
+                }
+
                 if ($checksum !== null) {
                     if (! $this->checkHash($cacheFile, $checksum)) {
                         throw new IOError(sprintf(
@@ -96,6 +111,10 @@ public function loadFile(string $uri, string|null $checksum = null): string
                 }
             } finally {
                 fclose($cacheStream);
+
+                if (file_exists($tmpFile)) {
+                    unlink($tmpFile);
+                }
             }
         } finally {
             fclose($stream);

tests/EncoderProviderTest.php

@@ -5,6 +5,7 @@
 namespace Yethee\Tiktoken\Tests;
 
 use org\bovigo\vfs\vfsStream;
+use org\bovigo\vfs\vfsStreamFile;
 use PHPUnit\Framework\Attributes\DataProvider;
 use PHPUnit\Framework\TestCase;
 use Yethee\Tiktoken\EncoderProvider;
@@ -46,7 +47,7 @@ public function testUseHashWhenLoadVocab(): void
         $cache = vfsStream::setup('cache');
         $vocabCacheFilename = hash('sha1', EncoderProvider::ENCODINGS['p50k_base']['vocab']);
 
-        $cacheFile = vfsStream::newFile($vocabCacheFilename)
+        vfsStream::newFile($vocabCacheFilename)
             ->withContent('broken cache')
             ->at($cache);
 
@@ -56,6 +57,9 @@ public function testUseHashWhenLoadVocab(): void
 
         $provider->get('p50k_base');
 
+        $cacheFile = $cache->getChild($vocabCacheFilename);
+
+        self::assertInstanceOf(vfsStreamFile::class, $cacheFile);
         self::assertNotEquals('broken cache', $cacheFile->getContent());
     }