transport/http/request: Request.Clone() must take a context. about smithy-go

[jasdel]

Thanks for reaching out with this issue @moriyoshi. The smithyhttp.Request's Clone intentional did not accept a context via its clone method. The intention behind this was that the Request's Build method was the entity that attached the context to the underlying http.Request and returned a constructed http.Request. Prior to Build being called the http.Request would not have a Context associated with it. Build is intended to be the last action performed on the request before it is used with the HTTP Client.

Could you go into more detail and background about the use case for Clone to take a context?

[moriyoshi]

So what is the use of Clone() in the first place? Is it supposed to be used only in a middleware? I guess not, because it's used in RequestCloner, whose comment says it's intended to use in a retrier. Then should the retrier be able to feed a fresh context on a retry? I would say yes.

[jasdel]

Thanks for the update. The intention of the middleware is that a context is only associated with an individual request at the last possible moment. Basically right before the request is passed to the HTTP client's Do method. This is the reason for Build taking the context but not Clone. Clone is intended to create a copy of the smithyhttp.Request, and that request has no reference to the Context used by the middleware.

The retryer is a component of the middleware which will create a clone of the request to ensure the request body stream is reset correctly. Also to ensure that any mutations by the signer do not leak between request attempts. It doesn't need to provide a context because the request is context-less until Build is called when the request is sent to the HTTP client.

The middleware stack it self passes down a context between each layer, and those middleware can mutate the context as needed. Attaching any middleware specific context to the request could cause that context to be invalid by the time the http client's Do method is called. Or each middleware would need to update the request's context. This would create a clone of the request which is not preferred.

[jasdel]

Thanks for reaching out @moriyoshi. I'm going to close this issue. Please reach out and let us know if you have additional questions, feedback, issues, or feature request.