disconnect context in a dedicated middleware

[butonic]

Move disconnecting the context to a separate middleware. Deprecates #309

This allows customizing the context that is used for the request handlers by implementing a custom middleware that can eg also add opentracing or other context information.

requires go 1.13 to do a deep copy of the request: https://golang.org/pkg/net/http/#Request.Clone see golang/go#23544 for duscussion and golang/go@f5c43b9 for the commit

[Acconut]

To be honest, I am not a huge fan of since since it complicates the request flow even more. Instead, I could think of a creating a new background context which inherits the values from the request's context. Something like this:

type contextWithValues struct {
  context.Context
  valueHolder context.Context
}

func (c contextWithValues) Value(key interface{}) interface{} {
  return c.valueHolder.Value(key)
}

ctxForStorage := contextWithValues{
  // Use background to not get cancel event
  Context: context.Background(),
  // Use request context to get stored values
  valueHolder: request.Context(),
}

requires go 1.13 to do a deep copy of the request: https://golang.org/pkg/net/http/#Request.Clone see golang/go#23544 for duscussion and golang/go@f5c43b9 for the commit

This would also be a problem since we promised to support Go 1.12 until Go 1.14 has been released: https://github.com/tus/tusd/blob/master/docs/installation.md

[Acconut]

Thanks you for your contribution! In tusd v2, the request context will be accessible in the hooks and stores. Please see #986 for more details and #672 for the development of v2.