HTTP2 question about setting the initial connection window size

Hi, I'm looking into enhancing the Wireshark HTTP2 dissector to track the connection and session window sizes to investigate flow control bottlenecks. I have a question about RFC9113 6.9.2:

"When an HTTP/2 connection is first established, new streams are created with an initial flow-control window size of 65,535 octets. The connection flow-control window is also 65,535 octets. Both endpoints can adjust the initial window size for new streams by including a value for SETTINGS_INITIAL_WINDOW_SIZE in the SETTINGS frame. The connection flow-control window can only be changed using WINDOW_UPDATE frames."

Does the last sentence mean that the connection flow-control window size can only be changed using a WINDOW_UPDATE frame _after_ the SETTINGS_INITIAL_WINDOW_SIZE?

In other words, does SETTINGS_INITIAL_WINDOW_SIZE also apply to the initial connection flow-control window size?

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Kevin Grigorenko
IBM Automation Portfolio SWAT - App Platform, Software Engineer

Received on Monday, 9 January 2023 21:31:37 UTC