FWIW I received a lot of early feedback explicitly asking me to couple the statefun specific operations with the Context (why the runtime type went away).
Seth On Mon, Feb 21, 2022 at 10:32 AM Galen Warren <ga...@cvillewarrens.com> wrote: > 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. > > > >>> >> > > > > > >> > > > > >>> >> > > > > > >> > > > >>> >> > > > > > > > > > >>> >> > > > > > > > > >>> >> > > > > > > > >>> >> > > > > > > >>> >> > > > > > >>> >> > > > > >>> >> > > > >>> > > > > >>> > > > >> > > > > > >
