commit 64a88a417ce3e2912964279c150677fcd8dd5745
author Alexei Frolov <frolv@google.com> Fri Aug 12 20:52:49 2022 +0000
committer CQ Bot Account <pigweed-scoped@luci-project-accounts.iam.gserviceaccount.com> Fri Aug 12 20:52:49 2022 +0000
tree 0ec5c6a310477210bd8dd9de96e8b6c2250789ae
parent 400c0f3bdb19675e885f99f744f9d953b786015d

pw_transfer: Version 2 opening handshake in C++

This implements the opening handshake of pw_transfer's version 2
protocol within the C++ transfer client and server. The handshake
consists of protocol version negotiation and ephemeral session ID
assignment.

The protocol version used for a transfer session is controlled by the
client when it starts a new transfer. By default, this still remains the
legacy protocol for now, though the client API is extended to allow
specifying the desired version.

If the START chunk a transfer service receives is configured for version
2, the service will assign a transfer session ID and proceed with the
handshake. Otherwise, it will fall back to the legacy protocol.

The version 2 START chunk sent by a client retains all of the chunk
proto fields set by the legacy protocol, allowing it to be understood
by a server which is not version 2 aware. In such a case, the server
will process the chunk per the legacy protocol and send a non-handshake
response. The client will recognize the legacy response and revert to
running the legacy protocol.

As a result of this, version 2 capable transfer clients and servers
remain fully backwards-compatible with older code that only runs the
legacy protocol.

Change-Id: Ie0a295509e754b963d3a78593ba1c43bbe13c977
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/99500
Reviewed-by: Wyatt Hepler <hepler@google.com>
Commit-Queue: Alexei Frolov <frolv@google.com>