feat: Add optional HTTP Middleware function to StartSettings for serverimpl

[gdfast]

Problem

Traces for HTTP requests to the opamp-go server break, see #253

Solution

• Add an HTTP Handler middleware function to StartSettings
• If this function is configured, apply it in serverimpl's Start where the HTTP Handler is set
• (add unit tests)

Code review notes

• This is a step in addressing opamp-go server impl is breaking traces #253 but mostly just for HTTP clients and requests. There is likely more to do for maintaining trace linkage through requests that come over websocket connections
• I figured if users are using Attach instead of Start, they might have their own middleware configured for their HTTP server, so it makes more sense to hook this into StartSettings and the Start function

[linux-foundation-easycla]

The committers listed above are authorized under a signed CLA.

• ✅ login: gdfast / name: Greg F (213856b, ab39e09, 929e0d0, bdd080a, dca2076, c186aab, 7608e11, a098362)

[andykellr]

I was curious why we weren't running into this and realized that we're using Attach. I'm fine with adding this, but I would expect most users to use Attach. @tigrannajaryan @evan-bradley please have a look.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 74.98%. Comparing base (d1d6081) to head (929e0d0).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #263      +/-   ##
==========================================
+ Coverage   74.70%   74.98%   +0.27%     
==========================================
  Files          25       25              
  Lines        1625     1631       +6     
==========================================
+ Hits         1214     1223       +9     
+ Misses        299      297       -2     
+ Partials      112      111       -1     

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[tigrannajaryan]

• This is a step in addressing opamp-go server impl is breaking traces #253 but mostly just for HTTP clients and requests. There is likely more to do for maintaining trace linkage through requests that come over websocket connections

@gdfast Can you please post the outline of the full plan with all the steps? I want to see the big picture before we merge this PR.

[tigrannajaryan]

• ❌ - login: @gdfast / name: Greg F . The commit (bdd080a) is not authorized under a signed CLA. Please click here to be authorized. For further assistance with EasyCLA, please submit a support request ticket.

Please sign the CLA.

[gdfast]

• ❌ - login: @gdfast / name: Greg F . The commit (bdd080a) is not authorized under a signed CLA. Please click here to be authorized. For further assistance with EasyCLA, please submit a support request ticket.

Please sign the CLA.

Working on it, it's in progress. I'm signing on as a Corprorate Contributor and am waiting for my company's CLA Manager

[gdfast]

• This is a step in addressing opamp-go server impl is breaking traces #253 but mostly just for HTTP clients and requests. There is likely more to do for maintaining trace linkage through requests that come over websocket connections

@gdfast Can you please post the outline of the full plan with all the steps? I want to see the big picture before we merge this PR.

My company/team has some HTTP Middleware code that adds OTel instrumentation that I'm planning to use in our OpAMP service that is built around opamp-go. I'm planning to follow up with my leads/management about contributing some version of this middleware in a separate, public Go module as you recommended, but I don't know what they'll say. I think giving users the ability to add their own HTTP Middleware is net good though, right?

Meanwhile, I'll need to start looking into how to propagate context for the messages that come in on a websocket connection. I imagine we may need some similar hook to add middleware in order to facilitate Otel Go SDK instrumentation, but I'm not sure.

I think I mentioned that I'm pretty new to Go and OTel instrumentation, so I'm learning as I go

[tigrannajaryan]

My company/team has some HTTP Middleware code that adds OTel instrumentation that I'm planning to use in our OpAMP service that is built around opamp-go. I'm planning to follow up with my leads/management about contributing some version of this middleware in a separate, public Go module as you recommended, but I don't know what they'll say. I think giving users the ability to add their own HTTP Middleware is net good though, right?

If you end up not contributing your implementation to Otel I would still want to see some example showing how the new capability can be used. It can be a very minimal example, just to demonstrate the idea.

[gdfast]

My company/team has some HTTP Middleware code that adds OTel instrumentation that I'm planning to use in our OpAMP service that is built around opamp-go. I'm planning to follow up with my leads/management about contributing some version of this middleware in a separate, public Go module as you recommended, but I don't know what they'll say. I think giving users the ability to add their own HTTP Middleware is net good though, right?

If you end up not contributing your implementation to Otel I would still want to see some example showing how the new capability can be used. It can be a very minimal example, just to demonstrate the idea.

Sure thing. Where did you have in mind for this? I could add to https://github.com/open-telemetry/opamp-go/blob/main/internal/examples/server/opampsrv/opampsrv.go but I want to be careful not to add the OTel Go SDK to the repo unnecessarily. I guess adding to the examples directory is fine though?

[tigrannajaryan]

If you end up not contributing your implementation to Otel I would still want to see some example showing how the new capability can be used. It can be a very minimal example, just to demonstrate the idea.

Sure thing. Where did you have in mind for this? I could add to https://github.com/open-telemetry/opamp-go/blob/main/internal/examples/server/opampsrv/opampsrv.go but I want to be careful not to add the OTel Go SDK to the repo unnecessarily. I guess adding to the examples directory is fine though?

Yes, it is fine to add to opampsrv in the examples directory since it is a separate Go module. The example can use the Otel Go SDK.

[gdfast]

If you end up not contributing your implementation to Otel I would still want to see some example showing how the new capability can be used. It can be a very minimal example, just to demonstrate the idea.

Sure thing. Where did you have in mind for this? I could add to https://github.com/open-telemetry/opamp-go/blob/main/internal/examples/server/opampsrv/opampsrv.go but I want to be careful not to add the OTel Go SDK to the repo unnecessarily. I guess adding to the examples directory is fine though?

Yes, it is fine to add to opampsrv in the examples directory since it is a separate Go module. The example can use the Otel Go SDK.

@tigrannajaryan I went with a very minimal example of using otelhttp.NewMiddleware to create the HTTP middleware, which I think should actually be a good idea for users who want to add OTel tracing!

[tigrannajaryan]

Mostly LGTM, just one small comment to reduce the public API surface.

[gdfast]

Hoping this is good to go now @tigrannajaryan . Thanks for your guidance and feedback!

[tigrannajaryan]

Thank you @gdfast