fix: handle empty api responses more gracefully

src/BusProNet/ApiClient.php

@@ -688,6 +688,14 @@ class ApiClient
         // message length (10 bytes) is prepended to actual message
         $xml = substr($response, 10);
 
+        if ('' === $xml) {
+            $this->logger->error('Empty response body received from API (header-only response)', [
+                'request_id' => $requestId,
+                'raw_length' => strlen($response),
+            ]);
+            throw new ApiClientException('Empty response body received from API');
+        }
+
         if (true === $debug || true === $this->config['debug']) {
             $this->dumpXmlToFile('response', $requestId, $xml);
         }
@@ -898,6 +906,15 @@ class ApiClient
             $response .= $chunk;
         }
 
+        if (0 === strlen($response)) {
+            $elapsedTime = microtime(true) - $this->operationStartTime;
+            $this->logger->warning('Server closed connection without sending data', [
+                'elapsed_time' => $elapsedTime,
+                'read_attempts' => $readAttempts,
+            ]);
+            throw new ImmediateConnectionCloseException('Server closed connection without sending data');
+        }
+
         return $response;
     }
 

tests/BusProNet/ApiClientReceiveTest.php

@@ -0,0 +1,78 @@
+<?php
+
+declare(strict_types=1);
+
+namespace App\Tests\BusProNet;
+
+use App\BusProNet\ApiClient;
+use App\BusProNet\DataProcessor\BookingDataProcessor;
+use App\BusProNet\Exception\ImmediateConnectionCloseException;
+use App\BusProNet\XmlParser\ApiResponseParser;
+use League\Flysystem\FilesystemOperator;
+use PHPUnit\Framework\TestCase;
+use Psr\Log\LoggerInterface;
+use Symfony\Component\HttpFoundation\RequestStack;
+use Symfony\Component\Serializer\SerializerInterface;
+
+class ApiClientReceiveTest extends TestCase
+{
+    private ApiClient $apiClient;
+
+    protected function setUp(): void
+    {
+        $this->apiClient = new ApiClient(
+            $this->createMock(SerializerInterface::class),
+            $this->createMock(ApiResponseParser::class),
+            $this->createMock(FilesystemOperator::class),
+            $this->createMock(LoggerInterface::class),
+            $this->createMock(BookingDataProcessor::class),
+            new RequestStack(),
+            [
+                'bpn_username' => 'test',
+                'bpn_password' => 'test',
+                'bpn_api_ip' => '127.0.0.1',
+                'bpn_api_ports' => [9000],
+            ],
+        );
+    }
+
+    public function testEmptyResponseThrowsImmediateConnectionCloseException(): void
+    {
+        $stream = fopen('php://memory', 'r+');
+        // Write nothing — stream is immediately at EOF
+        rewind($stream);
+
+        $this->setOperationStartTime();
+
+        $this->expectException(ImmediateConnectionCloseException::class);
+        $this->expectExceptionMessage('Server closed connection without sending data');
+
+        $this->invokeReceive($stream);
+    }
+
+    public function testNonEmptyResponseReturnsData(): void
+    {
+        $stream = fopen('php://memory', 'r+');
+        fwrite($stream, '0000000005Hello');
+        rewind($stream);
+
+        $this->setOperationStartTime();
+
+        $result = $this->invokeReceive($stream);
+
+        self::assertSame('0000000005Hello', $result);
+    }
+
+    private function invokeReceive($socket): string
+    {
+        $method = new \ReflectionMethod(ApiClient::class, 'receive');
+
+        return $method->invoke($this->apiClient, $socket);
+    }
+
+    private function setOperationStartTime(): void
+    {
+        $property = new \ReflectionProperty(ApiClient::class, 'operationStartTime');
+        $property->setValue($this->apiClient, microtime(true));
+    }
+}