From d114c5e17bc4311776c77d3dc67eee642dc93795 Mon Sep 17 00:00:00 2001
From: Jaymz Julian <jaymzjulian@meta.com>
Date: Tue, 12 Dec 2023 14:29:47 -0800
Subject: [PATCH] Adjust the buffer write function to clear the buffer once,
 rather than piece by piece.  This avoids a case where a large write (in our
 case, around 70mbytes) will consume 100% of CPU.  This takes a webrick GET
 request via SSL from around 200kbyts/sec and consuming 100% of a core, to
 line speed on gigabit ethernet and 6% cpu utlization.

---
 lib/openssl/buffering.rb | 17 +++++++++++------
 1 file changed, 11 insertions(+), 6 deletions(-)

diff --git a/lib/openssl/buffering.rb b/lib/openssl/buffering.rb
index 9570f14f3..50308e9b9 100644
--- a/lib/openssl/buffering.rb
+++ b/lib/openssl/buffering.rb
@@ -345,13 +345,18 @@ def do_write(s)
     @wbuffer << s
     @wbuffer.force_encoding(Encoding::BINARY)
     @sync ||= false
-    if @sync or @wbuffer.size > BLOCK_SIZE
-      until @wbuffer.empty?
-        begin
-          nwrote = syswrite(@wbuffer)
-        rescue Errno::EAGAIN
-          retry
+    buffer_size = @wbuffer.size
+    if @sync or buffer_size > BLOCK_SIZE
+      nwrote = 0
+      begin
+        while nwrote < buffer_size do
+          begin
+            nwrote += syswrite(@wbuffer)
+          rescue Errno::EAGAIN
+            retry
+          end
         end
+      ensure
         @wbuffer[0, nwrote] = ""
       end
     end