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refactor(enginenetx): split generation and mixing (#1591)
As mentioned in #1552 (comment), we want to split the generation of tactics and the mixing of tactics, such that it's easier to compose the desired overall policy. Part of ooni/probe#2704. --------- Co-authored-by: Arturo Filastò <[email protected]>
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,133 @@ | ||
| package enginenetx | ||
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| // | ||
| // Mix policies - ability of mixing from a primary policy and a fallback policy | ||
| // in a more flexible way than strictly falling back | ||
| // | ||
|
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| import ( | ||
| "context" | ||
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| "github.com/ooni/probe-cli/v3/internal/optional" | ||
| ) | ||
|
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| // mixPolicyEitherOr reads from primary and only if primary does | ||
| // not return any tactic, then it reads from fallback. | ||
| type mixPolicyEitherOr struct { | ||
| // Primary is the primary policy. | ||
| Primary httpsDialerPolicy | ||
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| // Fallback is the fallback policy. | ||
| Fallback httpsDialerPolicy | ||
| } | ||
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| var _ httpsDialerPolicy = &mixPolicyEitherOr{} | ||
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| // LookupTactics implements httpsDialerPolicy. | ||
| func (m *mixPolicyEitherOr) LookupTactics(ctx context.Context, domain string, port string) <-chan *httpsDialerTactic { | ||
| // create the output channel | ||
| output := make(chan *httpsDialerTactic) | ||
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| go func() { | ||
| // make sure we eventually close the output channel | ||
| defer close(output) | ||
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| // drain the primary policy | ||
| var count int | ||
| for tx := range m.Primary.LookupTactics(ctx, domain, port) { | ||
| output <- tx | ||
| count++ | ||
| } | ||
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| // if the primary worked, we're good | ||
| if count > 0 { | ||
| return | ||
| } | ||
|
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| // drain the fallback policy | ||
| for tx := range m.Fallback.LookupTactics(ctx, domain, port) { | ||
| output <- tx | ||
| } | ||
| }() | ||
|
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| return output | ||
| } | ||
|
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| // mixPolicyInterleave interleaves policies by a given interleaving | ||
| // factor. Say the interleave factor is N, then we first read N tactics | ||
| // from the primary policy, then N from the fallback one, and we keep | ||
| // going on like this until we've read all the tactics from both. | ||
| type mixPolicyInterleave struct { | ||
| // Primary is the primary policy. We will read N from this | ||
| // policy first, then N from fallback, and so on. | ||
| Primary httpsDialerPolicy | ||
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| // Fallback is the fallback policy. | ||
| Fallback httpsDialerPolicy | ||
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| // Factor is the interleaving factor to use. If this value is | ||
| // zero, we behave like it was set to one. | ||
| Factor uint8 | ||
| } | ||
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| var _ httpsDialerPolicy = &mixPolicyInterleave{} | ||
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| // LookupTactics implements httpsDialerPolicy. | ||
| func (p *mixPolicyInterleave) LookupTactics(ctx context.Context, domain string, port string) <-chan *httpsDialerTactic { | ||
| // create the output channel | ||
| output := make(chan *httpsDialerTactic) | ||
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| go func() { | ||
| // make sure we eventually close the output channel | ||
| defer close(output) | ||
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| // obtain the primary channel | ||
| primary := optional.Some(p.Primary.LookupTactics(ctx, domain, port)) | ||
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| // obtain the fallback channel | ||
| fallback := optional.Some(p.Fallback.LookupTactics(ctx, domain, port)) | ||
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| // loop until both channels are drained | ||
| for !primary.IsNone() || !fallback.IsNone() { | ||
| // take N from primary if possible | ||
| primary = p.maybeTakeN(primary, output) | ||
|
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| // take N from secondary if possible | ||
| fallback = p.maybeTakeN(fallback, output) | ||
| } | ||
| }() | ||
|
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| return output | ||
| } | ||
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| // maybeTakeN takes N entries from input if it's not none. When input is not | ||
| // none and reading from it indicates EOF, this function returns none. Otherwise, | ||
| // it returns the same value given as input. | ||
| func (p *mixPolicyInterleave) maybeTakeN( | ||
| input optional.Value[<-chan *httpsDialerTactic], | ||
| output chan<- *httpsDialerTactic, | ||
| ) optional.Value[<-chan *httpsDialerTactic] { | ||
| // make sure we've not already drained this channel | ||
| if !input.IsNone() { | ||
|
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| // obtain the underlying channel | ||
| ch := input.Unwrap() | ||
|
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| // take N entries from the channel | ||
| for idx := uint8(0); idx < max(1, p.Factor); idx++ { | ||
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| // attempt to get the next tactic | ||
| tactic, good := <-ch | ||
|
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| // handle the case where the channel has been drained | ||
| if !good { | ||
| return optional.None[<-chan *httpsDialerTactic]() | ||
| } | ||
|
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| // emit the tactic | ||
| output <- tactic | ||
| } | ||
| } | ||
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| return input | ||
| } |
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