So, upon further fiddling, I think it would be possible to keep full backward compatibility and add the option for someone to use an Invoke method with a separate context.Context and statefun.Runtime, via an adapter, if direct manipulation of the context.Context is needed. So, basically, the idea would be to let the user choose the form of the Invoke method, with the default behavior remaining the same as now.
This would require: - Recreating the Runtime interface (all methods currently defined on Context except not embedding context.Context) and embedding it in the statefun.Context interface, so that statefun.Context remains effectively unchanged - Add StatefulFunctionV2 and StatefunFunctionV2Pointer to support the new signature with separate context and runtime - Add StatefulFunctionV2Adapter to wrap a StatefulFunctionV2 and expose it as a StatefulFunction. The statefun.Context would get split into a context.Context and a statefun.Runtime here in order to call the new signature. Thoughts? I'd be happy to take a crack at it. On Mon, Feb 21, 2022 at 12:06 PM Galen Warren <ga...@cvillewarrens.com> wrote: > Was the reason to combine them the desire to have two parameters vs. > three, or was there another motivation? > > On Mon, Feb 21, 2022 at 12:02 PM Seth Wiesman <sjwies...@gmail.com> wrote: > >> 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. >> > > > >>> >> > > > > > >> > >> > > > >>> >> > > > > > >> >> > > > >>> >> > > > > > > >> > > > >>> >> > > > > > >> > > > >>> >> > > > > >> > > > >>> >> > > > >> > > > >>> >> > > >> > > > >>> >> > >> > > > >>> >> >> > > > >>> > >> > > > >>> >> > > > >> >> > > > >> > > >> > >> >
