Thanks for looking into this!
The issue I think we'd run into with your proposal is that, often,
libraries use non-exported types for context keys. Here is an example
<https://github.com/knative/pkg/blob/d48172451966/logging/logger.go#L45>;
in this case, the non-exported loggerKey{} is used as the key, inside the
exported WithLogger function. The key that would have to be supplied to the
proposed Value and WithValue functions would not be accessible in this case.
Honestly, if *everything *were on the table -- and understand it very well
might not be -- I'd suggest decoupling the Golang context.Context and the
statefun Context, i.e. have two separate parameters to
StatefulFunction.Invoke representing Golang context and statefun
operations. This is actually how things were in an earlier version of the
Golang SDK; the first parameter to Invoke was the plain-vanilla
context.Context and a separate parameter provided the statefun "runtime".
So maybe something like this:
>
> type StatefulFunction interface {
> Invoke(ctx context.Context, runtime Runtime, message Message) error
> }
... instead of the current:
type StatefulFunction interface {
> Invoke(ctx Context, message Message) error
> }
... where Runtime would be everything currently in statefun.Context, except
the context.Context part. This would allow context.Context to be
manipulated and passed around normally.
I think this could potentially be done in a backward-compatible way, with a
new set of types and methods, e.g. StatefulFunctionV2,
StatefufFunctionSpecV2, StatefulFunctions.WithSpecV2, etc. Or it could be
done in an almost backward-compatible way, by changing the existing
StatefulFunction, StatefulFunctionSpec, StatefulFunctions.WithSpec and
providing an adapter for people who want to continue to use the
two-parameter version of Invoke.
If those kinds of changes are a non-starter, then IMO the next best option
would be adding something like:
PrepareContext func(ctx statefun.Context) context.Context
... to StatefulFunctionSpec to allow a one-time customization of the
underlying context at the beginning of a stateful function invocation. That
would cover a lot of use cases.
On Mon, Feb 21, 2022 at 3:06 AM Till Rohrmann <trohrm...@apache.org> wrote:
> Thanks a lot for clarifying the problem. I think I now understand the
> problem. As you've probably figured out, I have no clue about Go and
> its usage of the Context type.
>
> After looking into it a bit I was wondering whether we can't follow a
> similar route as it is done for the Context type. By adding something like
>
> type valueCtx struct {
> Context
> key, val interface{}
> }
>
> func (c *valueCtx) Value(key interface{}) interface{} {
> if c.key == key {
> return c.val
> }
> return c.Context.Value(key)
> }
>
> func WithValue(parent Context, key, val interface{}) Context {
> if parent == nil {
> panic("cannot create context from nil parent")
> }
> if key == nil {
> panic("nil key")
> }
> return &valueCtx{parent, key, val}
> }
>
> to the statefun/context.go we would allow to extend a Statefun context with
> values w/o changing the underlying instance. If statefun.Context is not
> needed, then there is already the option to unwrap the context.Context and
> to extend it with values and then pass on this instance. But maybe this is
> no idiomatic Go. Let me know what you think.
>
> Cheers,
> Till
>
> On Fri, Feb 18, 2022 at 7:01 PM Galen Warren <ga...@cvillewarrens.com>
> wrote:
>
> > Hmm ... a downside to my proposal is that Go contexts are supposed to be
> > immutable, i.e. when adding a custom value to a context, a new context is
> > created with the new value and the old context isn't changed. Changing
> the
> > context.Context associated with the statefun.Context sort of goes against
> > the spirit of that, i.e. a consumer of statefun.Context could see custom
> > values change unexpectedly if another consumer of the same
> statefun.Context
> > modified the underlying context.Context.
> >
> > To avoid that, I think we'd be back to having some mechanism to customize
> > the underlying context.Context once, when the statefun.Context is created
> > at the beginning of a stateful function invocation. Adding a field like:
> >
> > PrepareContext func(ctx statefun.Context) context.Context
> >
> > ... to the StatefulFunctionSpec struct could accomplish that, i.e. if
> > PrepareContext were supplied, the context could be customized once at the
> > start of a function invocation and then left immutable after that point.
> >
> > (Using statefun.Context as the input is deliberate here, in order to
> allow
> > the context.Context to be populated using values from the
> statefun.Context,
> > for example the function id).
> >
> >
> >
> >
> >
> >
> > On Fri, Feb 18, 2022 at 11:34 AM Galen Warren <ga...@cvillewarrens.com>
> > wrote:
> >
> > > An example of passing it around would be:
> > >
> > > func (f *MyFunc) Invoke(ctx statefun.Context, message statefun.Message)
> > > error {
> > >
> > > logger := NewLogger()
> > > ctx.SetContext(ctxzap.ToContext(ctx, logger))
> > >
> > > return SomeOtherFunc(ctx)
> > > }
> > >
> > > func SomeOtherFunc(ctx context.Context) error {
> > >
> > > logger := ctxzap.Extract(ctx)
> > > logger.Info(...)
> > >
> > > return nil
> > > }
> > >
> > > This would also work with further nested calls, so long as the context
> is
> > > passed to them.
> > >
> > > On Fri, Feb 18, 2022 at 11:23 AM Galen Warren <ga...@cvillewarrens.com
> >
> > > wrote:
> > >
> > >> Ha, our emails keep passing.
> > >>
> > >> I've been playing around with options locally, and the SetContext
> option
> > >> seems to be the most flexible (and non-breaking), imo.
> > >>
> > >> The implementation would be trivial, just add:
> > >>
> > >> SetContext(ctx context.Context)
> > >>
> > >> ... to the statefun.Context interface, which is implemented as:
> > >>
> > >> func (s *statefunContext) SetContext(ctx context.Context) {
> > >> s.Context = ctx
> > >> }
> > >>
> > >>
> > >>
> > >>
> > >> On Fri, Feb 18, 2022 at 11:18 AM Austin Cawley-Edwards <
> > >> austin.caw...@gmail.com> wrote:
> > >>
> > >>> It would be helpful to have a small example though, if you have on
> > Galen,
> > >>> to see how you're passing it around.
> > >>>
> > >>> On Fri, Feb 18, 2022 at 11:10 AM Austin Cawley-Edwards <
> > >>> austin.caw...@gmail.com> wrote:
> > >>>
> > >>> > Looking through the statefun Context interface, it indeed doesn't
> > give
> > >>> > access to the underlying context.Context and the only
> implementation
> > is
> > >>> > package-private [1]. I don't think there would be a way to update
> the
> > >>> > statfun.Context interface without introducing breaking changes, but
> > if
> > >>> we
> > >>> > were to make that implementation public, that might be a stopgap
> > >>> solution.
> > >>> > e.g.,
> > >>> >
> > >>> > ```
> > >>> > type StatefunContext struct {
> > >>> > // expose embedded context
> > >>> > context.Context
> > >>> >
> > >>> > // make the mutext private
> > >>> > mu sync.Mutex
> > >>> >
> > >>> > // keep internals private
> > >>> > self Address
> > >>> > caller *Address
> > >>> > storage *storage
> > >>> > response *protocol.FromFunction_InvocationResponse
> > >>> > }
> > >>> > ```
> > >>> >
> > >>> > You could then do a type assertion in the handlers for this type of
> > >>> > context, and modify the context on it directly. It would be a bit
> > >>> ugly, but
> > >>> > may work.
> > >>> >
> > >>> > ```
> > >>> > func (s aFunc) Invoke(ctx Context, message Message) error {
> > >>> > if sCtx, ok := ctx.(*statefun.StatefunContext); ok {
> > >>> > sCtx.Context = context.WithValue(sCtx.Context, "logger",
> aLogger)
> > >>> > }
> > >>> > // ...
> > >>> > }
> > >>> > ```
> > >>> >
> > >>> > Let me know what you all think,
> > >>> > Austin
> > >>> >
> > >>> >
> > >>> > [1]:
> > >>> >
> > >>>
> >
> https://github.com/apache/flink-statefun/blob/1dfe226d85fea05a46c8ffa688175b4c0f2d4900/statefun-sdk-go/v3/pkg/statefun/context.go#L66-L73
> > >>> >
> > >>> >
> > >>> > On Fri, Feb 18, 2022 at 11:03 AM Galen Warren <
> > ga...@cvillewarrens.com
> > >>> >
> > >>> > wrote:
> > >>> >
> > >>> >> Sorry Austin, I didn't see your response before I replied. Yes,
> > we're
> > >>> >> saying the same thing.
> > >>> >>
> > >>> >> On Fri, Feb 18, 2022 at 10:56 AM Austin Cawley-Edwards <
> > >>> >> austin.caw...@gmail.com> wrote:
> > >>> >>
> > >>> >> > Hey all, jumping in. This makes sense to me – for instance to
> > >>> attach a
> > >>> >> > logger with some common metadata, e.g trace ID for the request?
> > >>> This is
> > >>> >> > common in go to add arbitrary items without updating the method
> > >>> >> signatures,
> > >>> >> > similar to thread local storage in Java.
> > >>> >> >
> > >>> >> > On Fri, Feb 18, 2022 at 10:53 AM Till Rohrmann <
> > >>> trohrm...@apache.org>
> > >>> >> > wrote:
> > >>> >> >
> > >>> >> > > Thanks for the clarification Galen. If you call the other Go
> > >>> >> functions,
> > >>> >> > > then you could also pass the other values as separate
> arguments
> > to
> > >>> >> these
> > >>> >> > > functions, can't you?
> > >>> >> > >
> > >>> >> > > Cheers,
> > >>> >> > > Till
> > >>> >> > >
> > >>> >> > > On Fri, Feb 18, 2022 at 3:31 PM Galen Warren <
> > >>> ga...@cvillewarrens.com
> > >>> >> >
> > >>> >> > > wrote:
> > >>> >> > >
> > >>> >> > > > The former.
> > >>> >> > > >
> > >>> >> > > > I think there's potential for confusion here because we're
> > >>> using the
> > >>> >> > > > word *function
> > >>> >> > > > *in a couple of senses. One sense is a *stateful function*;
> > >>> another
> > >>> >> > sense
> > >>> >> > > > is a *Go function*.
> > >>> >> > > >
> > >>> >> > > > What I'm looking to do is to put values in the Context so
> that
> > >>> >> > downstream
> > >>> >> > > > Go functions that receive the context can access those
> values.
> > >>> Those
> > >>> >> > > > downstream Go functions would be called during one
> invocation
> > >>> of the
> > >>> >> > > > stateful function.
> > >>> >> > > >
> > >>> >> > > > On Fri, Feb 18, 2022 at 6:48 AM Till Rohrmann <
> > >>> trohrm...@apache.org
> > >>> >> >
> > >>> >> > > > wrote:
> > >>> >> > > >
> > >>> >> > > > > Hi Galen,
> > >>> >> > > > >
> > >>> >> > > > > Am I understanding it correctly, that you would like to
> set
> > >>> some
> > >>> >> > values
> > >>> >> > > > in
> > >>> >> > > > > the Context of function A that is then accessible in a
> > >>> downstream
> > >>> >> > call
> > >>> >> > > of
> > >>> >> > > > > function B? Or would you like to set a value that is
> > >>> accessible
> > >>> >> once
> > >>> >> > > > > function A is called again (w/ or w/o the same id)?
> > >>> >> > > > >
> > >>> >> > > > > Cheers,
> > >>> >> > > > > Till
> > >>> >> > > > >
> > >>> >> > > > > On Thu, Feb 17, 2022 at 10:59 PM Galen Warren <
> > >>> >> > ga...@cvillewarrens.com
> > >>> >> > > >
> > >>> >> > > > > wrote:
> > >>> >> > > > >
> > >>> >> > > > > > Also, a potentially simpler way to support this would be
> > to
> > >>> add
> > >>> >> a
> > >>> >> > > > > > SetContext method to the statefun.Context interface, and
> > >>> have it
> > >>> >> > > assign
> > >>> >> > > > > the
> > >>> >> > > > > > wrapped context. This would not require changes to the
> > >>> function
> > >>> >> > spec,
> > >>> >> > > > or
> > >>> >> > > > > > anything else, and would be more flexible.
> > >>> >> > > > > >
> > >>> >> > > > > > On Thu, Feb 17, 2022 at 1:05 PM Galen Warren <
> > >>> >> > > ga...@cvillewarrens.com>
> > >>> >> > > > > > wrote:
> > >>> >> > > > > >
> > >>> >> > > > > > > Thanks for the quick reply!
> > >>> >> > > > > > >
> > >>> >> > > > > > > What I'm trying to do is put some things into the
> > context
> > >>> so
> > >>> >> that
> > >>> >> > > > > they're
> > >>> >> > > > > > > available in downstream calls, perhaps in methods with
> > >>> pointer
> > >>> >> > > > > receivers
> > >>> >> > > > > > to
> > >>> >> > > > > > > the function struct (MyFunc) but also perhaps in
> methods
> > >>> that
> > >>> >> are
> > >>> >> > > > > further
> > >>> >> > > > > > > downstream that don't have access to MyFunc. If I'm
> > >>> >> understanding
> > >>> >> > > > > > > correctly, your proposal would work for the former but
> > >>> not the
> > >>> >> > > > latter.
> > >>> >> > > > > > >
> > >>> >> > > > > > > An example would be to put a configured Logger into
> the
> > >>> >> context
> > >>> >> > > via a
> > >>> >> > > > > > > WithLogger method (logging package -
> > >>> knative.dev/pkg/logging
> > >>> >> -
> > >>> >> > > > > > pkg.go.dev
> > >>> >> > > > > > > <
> https://pkg.go.dev/knative.dev/pkg/logging#WithLogger
> > >)
> > >>> and
> > >>> >> > then
> > >>> >> > > > pull
> > >>> >> > > > > > it
> > >>> >> > > > > > > out downstream via FromContext (logging package -
> > >>> >> > > > > > knative.dev/pkg/logging
> > >>> >> > > > > > > - pkg.go.dev <
> > >>> >> > > https://pkg.go.dev/knative.dev/pkg/logging#FromContext
> > >>> >> > > > > >).
> > >>> >> > > > > > >
> > >>> >> > > > > > >
> > >>> >> > > > > > >
> > >>> >> > > > > > >
> > >>> >> > > > > > > On Wed, Feb 16, 2022 at 5:50 PM Seth Wiesman <
> > >>> >> > sjwies...@gmail.com>
> > >>> >> > > > > > wrote:
> > >>> >> > > > > > >
> > >>> >> > > > > > >> Hi Galen,
> > >>> >> > > > > > >>
> > >>> >> > > > > > >> No, that is not currently supported, the current
> > >>> idiomatic
> > >>> >> way
> > >>> >> > > would
> > >>> >> > > > > be
> > >>> >> > > > > > to
> > >>> >> > > > > > >> pass those values to the struct implementing the
> > Statefun
> > >>> >> > > interface.
> > >>> >> > > > > > >>
> > >>> >> > > > > > >>
> > >>> >> > > > > > >> type MyFunc struct { someRuntimeInfo string } func (m
> > >>> >> *MyFunc)
> > >>> >> > > > > > Invoke(ctx
> > >>> >> > > > > > >> statefun.Context, message statefun.Message) error { }
> > >>> func
> > >>> >> > main()
> > >>> >> > > {
> > >>> >> > > > > > >> builder
> > >>> >> > > > > > >> := statefun.StatefulFunctionsBuilder()
> > >>> >> > > > > > >> f := MyFunc { someRuntimeInfo: "runtime-provided" }
> > >>> >> > > builder.WithSpec
> > >>> >> > > > > > >> (statefun.StatefulFunctionSpec{ FunctionType:
> > >>> >> > > statefun.TypeNameFrom(
> > >>> >> > > > > > >> "example/my-func"), Function: f })
> > >>> >> > > > > > >> http.Handle("/statefun", builder.AsHandler())
> > >>> >> > > > > > >> _ = http.ListenAndServe(":8000", nil) }
> > >>> >> > > > > > >>
> > >>> >> > > > > > >> Would this work for you? Or what is the context (pun
> > >>> >> intended)
> > >>> >> > you
> > >>> >> > > > are
> > >>> >> > > > > > >> looking for?
> > >>> >> > > > > > >>
> > >>> >> > > > > > >> Seth
> > >>> >> > > > > > >>
> > >>> >> > > > > > >> On Wed, Feb 16, 2022 at 4:35 PM Galen Warren <
> > >>> >> > > > ga...@cvillewarrens.com
> > >>> >> > > > > >
> > >>> >> > > > > > >> wrote:
> > >>> >> > > > > > >>
> > >>> >> > > > > > >> > When stateful functions are invoked, they are
> passed
> > an
> > >>> >> > instance
> > >>> >> > > > of
> > >>> >> > > > > > >> > statefun.Context, which wraps the context.Context
> > >>> received
> > >>> >> by
> > >>> >> > > the
> > >>> >> > > > > HTTP
> > >>> >> > > > > > >> > request. Is there any way to customize that
> > >>> context.Context
> > >>> >> > to,
> > >>> >> > > > say,
> > >>> >> > > > > > >> hold
> > >>> >> > > > > > >> > custom values, using ctx.WithValue()? I don't see a
> > way
> > >>> >> but I
> > >>> >> > > > wanted
> > >>> >> > > > > > to
> > >>> >> > > > > > >> > ask.
> > >>> >> > > > > > >> >
> > >>> >> > > > > > >> > If not, would you be interested in a PR to add this
> > >>> >> > > > functionality? A
> > >>> >> > > > > > >> simple
> > >>> >> > > > > > >> > way might be to add a property to
> > StatefulFunctionSpec,
> > >>> >> say:
> > >>> >> > > > > > >> >
> > >>> >> > > > > > >> > TransformContext func(ctx context.Context)
> > >>> context.Context
> > >>> >> > > > > > >> >
> > >>> >> > > > > > >> > ... that, if supplied, would be called to create a
> > >>> >> customized
> > >>> >> > > > > context
> > >>> >> > > > > > >> that
> > >>> >> > > > > > >> > would be used downstream?
> > >>> >> > > > > > >> >
> > >>> >> > > > > > >> > Thanks.
> > >>> >> > > > > > >> >
> > >>> >> > > > > > >>
> > >>> >> > > > > > >
> > >>> >> > > > > >
> > >>> >> > > > >
> > >>> >> > > >
> > >>> >> > >
> > >>> >> >
> > >>> >>
> > >>> >
> > >>>
> > >>
> >
>
