CODEWITHSUNDEEP
wiresharkhttp2
BanksySan
BanksySan

Reputation: 28540

Is this Wireshark capture of HTTP/2 showing three frames?

I've got a capture of HTTP/2 fetching https://example.com. The three entries on the initial row of the capture are:

HyperText Transfer Protocol 2
    Stream: Magic
    Stream: SETTINGS, Stream ID: 0, Length 18
    Stream: WINDOW_UPDATE, Stream ID: 0, Length 4

How should I refer to these? Can I say that they're the three initial frames from stream 0 and are the Magic, SETTINGS and WINDOW_UPDATE frames?

Upvotes: 3

Views: 1842

Answers (1)

Barry Pollard
Barry Pollard

Reputation: 46040

The Magic is a not a frame but a special set of bytes, resembling an HTTP/1.1 message. It is sent at the beginning of all HTTP/2 connections to allow HTTP/1.1 servers to reject the connection elegantly with an HTTP/1.1 response so the client knows to revert back to HTTP/1.1. It’s officially known as the Connection Preface but is often referred to as the “Magic” message. As an aside it has an interesting history.

You can see the Magic message is not a frame as it does not have a stream id nor any of the other necessary frame headers which define a frame.

The SETTINGS and WINDOW_UPDATE messages are indeed frames and there are several frame types defined in the HTTP/2 spec and a few more have been added since in extensions.

Upvotes: 5

Related Questions