Add response trailers

src/ResponseTrailers.php

@@ -0,0 +1,73 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Spiral\RoadRunner\GRPC;
+
+use Spiral\RoadRunner\GRPC\Internal\Json;
+
+/**
+ * @psalm-type THeaderKey = non-empty-string
+ * @psalm-type THeaderValue = string
+ * @implements \IteratorAggregate<THeaderKey, string>
+ */
+final class ResponseTrailers implements \IteratorAggregate, \Countable
+{
+    /**
+     * @var array<THeaderKey, THeaderValue>
+     */
+    private array $trailers = [];
+
+    /**
+     * @param iterable<THeaderKey, THeaderValue> $trailers
+     */
+    public function __construct(iterable $trailers = [])
+    {
+        foreach ($trailers as $key => $value) {
+            $this->set($key, $value);
+        }
+    }
+
+    /**
+     * @param THeaderKey $key
+     * @param THeaderValue $value
+     */
+    public function set(string $key, string $value): void
+    {
+        $this->trailers[$key] = $value;
+    }
+
+    /**
+     * @param THeaderKey $key
+     * @param string|null $default
+     * @return THeaderValue|null
+     */
+    public function get(string $key, string $default = null): ?string
+    {
+        return $this->trailers[$key] ?? $default;
+    }
+
+    public function getIterator(): \Traversable
+    {
+        return new \ArrayIterator($this->trailers);
+    }
+
+    public function count(): int
+    {
+        return \count($this->trailers);
+    }
+
+    /**
+     * @throws \JsonException
+     */
+    public function packTrailers(): string
+    {
+        // If an empty array is serialized, it is cast to the string "[]"
+        // instead of object string "{}"
+        if ($this->trailers === []) {
+            return '{}';
+        }
+
+        return Json::encode($this->trailers);
+    }
+}

src/Server.php

@@ -74,19 +74,28 @@ public function serve(WorkerInterface $worker = null, callable $finalize = null)
             }
 
             $responseHeaders = new ResponseHeaders();
+            $responseTrailers = new ResponseTrailers();
 
             try {
                 $call = CallContext::decode($request->header);
 
-                $context = (new Context($call->context))
-                    ->withValue(ResponseHeaders::class, $responseHeaders);
+                $context = new Context(array_merge(
+                    $call->context,
+                    [
+                        ResponseHeaders::class => $responseHeaders,
+                        ResponseTrailers::class => $responseTrailers
+                    ]
+                ));
 
                 $response = $this->invoke($call->service, $call->method, $context, $request->body);
 
                 $this->workerSend(
                     worker: $worker,
                     body: $response,
-                    headers: $responseHeaders->packHeaders()
+                    headers: Json::encode([
+                        'headers' => $responseHeaders->packHeaders(),
+                        'trailers' => $responseTrailers->packTrailers(),
+                    ]),
                 );
             } catch (GRPCExceptionInterface $e) {
                 $this->workerSend(
@@ -95,6 +104,7 @@ public function serve(WorkerInterface $worker = null, callable $finalize = null)
                     headers: Json::encode([
                         'error' => $this->createGrpcError($e),
                         'headers' => $responseHeaders->packHeaders(),
+                        'trailers' => $responseTrailers->packTrailers(),
                     ]),
                 );
             } catch (\Throwable $e) {