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Restore message context in Timeout middleware #517

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Restore message context in Timeout middleware #517

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Restore message's original context before exiting the Timeout middlew…
zanvd Nov 21, 2024
9f12134
Use orgCtx as a parent context.
zanvd Nov 21, 2024
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7 changes: 6 additions & 1 deletion message/router/middleware/timeout.go
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Original file line number Diff line number Diff line change
Expand Up @@ -9,11 +9,16 @@ import (

// Timeout makes the handler cancel the incoming message's context after a specified time.
// Any timeout-sensitive functionality of the handler should listen on msg.Context().Done() to know when to fail.
// Before exiting this middleware, message's original context is restored to not disrupt the logic of possible
// enveloping handlers (e.g. Retry) that also rely on message context.
func Timeout(timeout time.Duration) func(message.HandlerFunc) message.HandlerFunc {
return func(h message.HandlerFunc) message.HandlerFunc {
return func(msg *message.Message) ([]*message.Message, error) {
ctx, cancel := context.WithTimeout(msg.Context(), timeout)
orgCtx := msg.Context()

ctx, cancel := context.WithTimeout(orgCtx, timeout)
defer func() {
msg.SetContext(orgCtx)
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@zanvd how about we use context.WithoutCancel(ctx) here? This way the cancellation won't be propagated while the values stored in the context can be. Would that also solve the root issue? 🤔

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context.WithoutCancel was a great addition to context lately, but here if we use it, it means the context stored again won't be canceled if orgCtx is canceled. It doesn't a good move

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Ah, you're right.

My point is that restoring the context will also remove all context values. If someone uses middleware that uses the context after the handler is executed, it will be lost this way.

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@ccoVeille ccoVeille Nov 24, 2024 •
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Here is the way then

orgCtx := msg.Context() 
ctx, cancel := context.WithTimeout(orgCtx, timeout)

defer func() {
   cancel()
   ctx, cancel2 := context.WithCancelWithCause(context.WithoutCancel(ctx))
   msg.SetContext(ctx)
   go func() {
        <- ctx.Done()
        cancel2(ctx.Err())
   }
}()

But I find it ugly

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I'd have to test it out, but this is more or less why I was asking on Discord about usage of context within Message - makes it sort of a global object that anyone can modify. Since the blueprint for this was the net/http package, I'd follow its logic and not even allow changing of the Message's context. Not something to solve in this PR, though.

What would be an example of values stored in the context that we should be vary of? Perhaps copying them to the original context might be a temporary solution.

cancel()
}()

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6 changes: 5 additions & 1 deletion message/router/middleware/timeout_test.go
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Expand Up @@ -5,6 +5,7 @@ import (
"testing"
"time"

"github.com/stretchr/testify/assert"
"github.com/stretchr/testify/require"

"github.com/ThreeDotsLabs/watermill/message"
Expand All @@ -25,6 +26,9 @@ func TestTimeout(t *testing.T) {
}
})

_, err := h(message.NewMessage("any-uuid", nil))
msg := message.NewMessage("any-uuid", nil)

_, err := h(msg)
require.NoError(t, err)
assert.Nil(t, msg.Context().Err())
}