Fix slowdown when sending large data over HTTP/2 (mitmproxy#6873) (mi…

…tmproxy#6875)

* Do not mutate data when splitting into chunks (mitmproxy#6873)

* [autofix.ci] apply automated fixes

---------

Co-authored-by: autofix-ci[bot] <114827586+autofix-ci[bot]@users.noreply.github.com>

CHANGELOG.md

@@ -15,6 +15,8 @@
   ([#6821](https://github.com/mitmproxy/mitmproxy/pull/6821), @Prinzhorn)
 * Fix a bug where client replay would not work with proxyauth.
   ([#6866](https://github.com/mitmproxy/mitmproxy/pull/6866), @mhils)
+* Fix slowdown when sending large data over HTTP/2
+  ([#6875](https://github.com/mitmproxy/mitmproxy/pull/6875), @aib)
 
 
 ## 17 April 2024: mitmproxy 10.3.0

mitmproxy/proxy/layers/http/_http_h2.py

@@ -68,12 +68,12 @@ def send_data(
         frame_size = len(data)
         assert pad_length is None
 
-        while frame_size > self.max_outbound_frame_size:
-            chunk_data = data[: self.max_outbound_frame_size]
-            self.send_data(stream_id, chunk_data, end_stream=False)
+        if frame_size > self.max_outbound_frame_size:
+            for start in range(0, frame_size, self.max_outbound_frame_size):
+                chunk = data[start : start + self.max_outbound_frame_size]
+                self.send_data(stream_id, chunk, end_stream=False)
 
-            data = data[self.max_outbound_frame_size :]
-            frame_size -= len(chunk_data)
+            return
 
         if self.stream_buffers.get(stream_id, None):
             # We already have some data buffered, let's append.