feat: implement download

Signed-off-by: Sebastian Krupinski <krupinski01@gmail.com>

lib/Client/Transport/ConnectionInterface.php

@@ -20,5 +20,13 @@ interface ConnectionInterface
 
     public function readBytes(int $length): string;
 
+    /**
+     * Yield the literal payload in chunks without buffering the full content.
+     * Reads exactly $length bytes from the socket, never crossing the literal boundary.
+     *
+     * @return \Generator<string>
+     */
+    public function readBytesChunked(int $length, int $chunkSize = 8192): \Generator;
+
     public function upgradeToTls(): void;
 }

lib/Client/Transport/SocketConnection.php

@@ -135,6 +135,26 @@ final class SocketConnection implements ConnectionInterface
         return $buffer;
     }
 
+    public function readBytesChunked(int $length, int $chunkSize = 8192): \Generator
+    {
+        if ($length < 0) {
+            throw new ImapException('IMAP socket cannot read a negative number of bytes.');
+        }
+
+        $remaining = $length;
+
+        while ($remaining > 0) {
+            $chunk = fread($this->stream(), min($chunkSize, $remaining));
+
+            if ($chunk === false || $chunk === '') {
+                throw new ImapException('Failed to read literal payload from IMAP socket.');
+            }
+
+            $remaining -= strlen($chunk);
+            yield $chunk;
+        }
+    }
+
     public function upgradeToTls(): void
     {
         $stream = $this->stream();