Introduce request splitter

[lukedirtwalker]

This is the first part of the new path lookup strategy.
It splits up a request into up, core, and down parts.

Contributes #2454

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This change is 

[oncilla]

Reviewed 4 of 7 files at r1.
Reviewable status: 4 of 7 files reviewed, all discussions resolved (waiting on @oncilla)

[oncilla]

Reviewed 3 of 7 files at r1.
Reviewable status: all files reviewed, 5 unresolved discussions (waiting on @lukedirtwalker)

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go/lib/infra/modules/segfetcher/request.go, line 39 at r1 (raw file):

// IsEmpty returns whether the request set is empty.
func (r RequestSet) IsEmpty() bool {
	return r.Up.IsZero() && len(r.Cores) == 0 && r.Down.IsZero()

add method Requests.IsEmpty

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go/lib/infra/modules/segfetcher/request.go, line 59 at r1 (raw file):

	var ias []addr.IA
	addrs := make(map[addr.IA]struct{})
	for _, req := range r {

I think the following is easier to understand: (plus, probably faster anyway)

set := make(map[addr.IA]struct{})
for _, req := range r {
  set[extract(ia)] = struct{}{}
}
ias := make([]addr.IA, 0, len(set))
for ia := range set {
  ias = append(ias, ia)
}
return ias

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go/lib/infra/modules/segfetcher/splitter.go, line 41 at r1 (raw file):

	ctx, cancelF := context.WithTimeout(context.Background(), time.Second)
	defer cancelF()
	trc, err := trcProvider.GetTRC(ctx, localIA.I, scrypto.LatestVer)

instead of fetching trc here, you can simply call baseSplitter.IsCore(ctx, localIA)

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go/lib/infra/modules/segfetcher/splitter.go, line 76 at r1 (raw file):

}

func (s *baseRequestSplitter) isLocal(dst addr.IA) bool {

isLocalISD or isISDLocal

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go/lib/infra/modules/segfetcher/splitter.go, line 99 at r1 (raw file):

}

func (s *coreRequestSplitter) Split(ctx context.Context, r Request) (RequestSet, error) {

This does not check that r.Src is core.

[oncilla]

Reviewed 2 of 2 files at r2.
Reviewable status: all files reviewed, 1 unresolved discussion (waiting on @lukedirtwalker)

[lukedirtwalker]

Reviewable status: all files reviewed, 1 unresolved discussion (waiting on @oncilla)

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go/lib/infra/modules/segfetcher/request.go, line 39 at r1 (raw file):

Previously, Oncilla wrote…

add method Requests.IsEmpty

Done.

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go/lib/infra/modules/segfetcher/request.go, line 59 at r1 (raw file):

Previously, Oncilla wrote…

I think the following is easier to understand: (plus, probably faster anyway)

set := make(map[addr.IA]struct{})
for _, req := range r {
  set[extract(ia)] = struct{}{}
}
ias := make([]addr.IA, 0, len(set))
for ia := range set {
  ias = append(ias, ia)
}
return ias

Done.

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go/lib/infra/modules/segfetcher/splitter.go, line 41 at r1 (raw file):

Previously, Oncilla wrote…

instead of fetching trc here, you can simply call baseSplitter.IsCore(ctx, localIA)

Done.

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go/lib/infra/modules/segfetcher/splitter.go, line 76 at r1 (raw file):

Previously, Oncilla wrote…

isLocalISD or isISDLocal

Done.

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go/lib/infra/modules/segfetcher/splitter.go, line 99 at r1 (raw file):

Previously, Oncilla wrote…

This does not check that r.Src is core.

Validation will happen in a separate function outside of this.

[oncilla]

Reviewable status: complete! all files reviewed, all discussions resolved