From 4aabee2443b8a1650679a733e861935801bd3754 Mon Sep 17 00:00:00 2001
From: Niklas Keller <me@kelunik.com>
Date: Sun, 3 Sep 2023 19:16:37 +0200
Subject: [PATCH] Fix window size if body size limit is large

Fixes #355.
---
 src/Driver/Http2Driver.php | 13 ++++++++-----
 1 file changed, 8 insertions(+), 5 deletions(-)

diff --git a/src/Driver/Http2Driver.php b/src/Driver/Http2Driver.php
index fa758238..0188f689 100644
--- a/src/Driver/Http2Driver.php
+++ b/src/Driver/Http2Driver.php
@@ -175,7 +175,7 @@ public function initializeWriting(
                 \pack(
                     "nNnNnNnN",
                     Http2Parser::INITIAL_WINDOW_SIZE,
-                    $this->bodySizeLimit,
+                    $this->initialWindowSize,
                     Http2Parser::MAX_CONCURRENT_STREAMS,
                     $this->concurrentStreamLimit,
                     Http2Parser::MAX_HEADER_LIST_SIZE,
@@ -727,7 +727,7 @@ private function readPreface(): string
                 \pack(
                     "nNnNnNnN",
                     Http2Parser::INITIAL_WINDOW_SIZE,
-                    $this->bodySizeLimit,
+                    $this->initialWindowSize,
                     Http2Parser::MAX_CONCURRENT_STREAMS,
                     $this->concurrentStreamLimit,
                     Http2Parser::MAX_HEADER_LIST_SIZE,
@@ -1055,9 +1055,12 @@ function (int $bodySize) use ($streamId) {
         $bodySizeLimit = $this->bodySizeLimit;
 
         if ($this->serverWindow <= $bodySizeLimit >> 1) {
-            $increment = $bodySizeLimit - $this->serverWindow;
-            $this->serverWindow = $bodySizeLimit;
-            $this->writeFrame(\pack("N", $increment), Http2Parser::WINDOW_UPDATE, Http2Parser::NO_FLAG);
+            $increment = \min($bodySizeLimit - $this->serverWindow, self::MAX_INCREMENT);
+
+            if ($increment > 0) {
+                $this->serverWindow += $increment;
+                $this->writeFrame(\pack("N", $increment), Http2Parser::WINDOW_UPDATE, Http2Parser::NO_FLAG);
+            }
         }
 
         if (isset($headers["content-length"])) {