add chapter about data repositories, and start work on perfomance chapter

implementation/15-adding-content/src/Http/BasicEmitter.php

@@ -0,0 +1,38 @@
+<?php declare(strict_types=1);
+
+namespace Lubian\NoFramework\Http;
+
+use Psr\Http\Message\ResponseInterface;
+
+use function header;
+use function sprintf;
+use function strtolower;
+
+final class BasicEmitter implements Emitter
+{
+    public function emit(ResponseInterface $response, bool $withoutBody = false): void
+    {
+        foreach ($response->getHeaders() as $name => $values) {
+            $first = strtolower($name) !== 'set-cookie';
+            foreach ($values as $value) {
+                $header = sprintf('%s: %s', $name, $value);
+                header($header, $first);
+                $first = false;
+            }
+        }
+
+        $statusLine = sprintf(
+            'HTTP/%s %s %s',
+            $response->getProtocolVersion(),
+            $response->getStatusCode(),
+            $response->getReasonPhrase()
+        );
+        header($statusLine, true, $response->getStatusCode());
+
+        if ($withoutBody) {
+            return;
+        }
+
+        echo $response->getBody();
+    }
+}