Protocol negotiation and ambiguity of network.protocol.version

[lmolkova]

Related to dotnet/docs#39223 (comment) and dotnet/runtime#97395 (comment)

During network protocol negotiation there are two protocol versions:

• one that client requested originally
• one that was agreed upon during negotiation

If response was received at all, then it makes total sense to set network.protocol.version to the final version.
If response was not received, we can set the network.protocol.version to the request version (which might be misleading or not useful since it's at least sometimes per-client configuration)

So we:

• need to update network.protocol.version description to clarify that it's the negotiated version
• need to decide if we want to fallback to request/initial version if no response was received

[trask]

since it's at least sometimes per-client configuration

I didn't follow this part, can you explain a bit more?

[lmolkova]

I didn't follow this part, can you explain a bit more?

On the request side, protocol is frequently a client property:

• .NET HttpClient
• okhttp
• Reactor-netty

It's interesting that okhttp and netty allow to pass an array of supported protocols reiterating the point that request protocol version is somewhat useless.

The only benefit of falling back to request protocol version I see is when the client sends bad protocol version and/or server fails to respond to it. Then having requested version would be interesting.

[joaopgrassi]

The only benefit of falling back to request protocol version I see is when the client sends bad protocol version and/or server fails to respond to it. Then having requested version would be interesting.

Wouldn't the HTTP client log a message/exception, maybe containing the requested protocol version? I feel this is more a job of a log than recording this info in a span or somewhere else 🤔

[trask]

It definitely simplifies things if we simply clarify that network.protocol.version is the negotiated version

[joaopgrassi]

Who will do the honors with a PR? ✨

[lmolkova]

Adding it here so we don't forget

When addressing #520 we this text needs to be manually updated in dotnet-http-metrics.md.

#801 (comment)

I can do the PR after #801 is merged.