Go dispatcher: Add SCMP ID tracking tables

[scrye]

This is a stepping stone to implementing SCMP Echo, TraceRoute, and RecordPath support in the Go dispatcher.

---

This change is 

[lukedirtwalker]

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

---

go/godispatcher/internal/registration/iatable_test.go, line 149 at r1 (raw file):

		err = ref.RegisterID(42)
		xtest.FailOnErr(t, err)
		Convey("Performing SCMP lookup now succeeds", func() {

Nit: the now doesn't really make sense (only with the Test above, but that is in a different function)

---

go/godispatcher/internal/registration/scmp_table.go, line 34 at r1 (raw file):

func (t *SCMPTable) Lookup(id uint64) (interface{}, bool) {
	value, ok := t.m[id]
	return value, ok

This could be collapsed into return t.m[id]

---

go/godispatcher/internal/registration/scmp_table.go, line 50 at r1 (raw file):

func (t *SCMPTable) Remove(id uint64) error {
	if _, ok := t.m[id]; !ok {
		return common.NewBasicError("element not found", nil, "id", id)

Why is the error needed? Default go delete also doesn't complain if an entry is deleted that isn't there?

[scrye]

Reviewable status: 1 of 5 files reviewed, 2 unresolved discussions (waiting on @lukedirtwalker)

---

go/godispatcher/internal/registration/scmp_table.go, line 34 at r1 (raw file):

Previously, lukedirtwalker (Lukas Vogel) wrote…

This could be collapsed into return t.m[id]

Sadly, it can't. The compiler assumes the one return value variant of map access if used in the return, so it complains that it's returning only one value instead of two.

---

go/godispatcher/internal/registration/scmp_table.go, line 50 at r1 (raw file):

Previously, lukedirtwalker (Lukas Vogel) wrote…

Why is the error needed? Default go delete also doesn't complain if an entry is deleted that isn't there?

I was thinking it's useful to catch double frees, but it leads to some awkward untestable branches. I dropped the return value, it's more elegant.

[lukedirtwalker]

Reviewed 4 of 4 files at r2.
Reviewable status: complete! all files reviewed, all discussions resolved

---

go/godispatcher/internal/registration/scmp_table.go, line 34 at r1 (raw file):

Previously, scrye (Sergiu Costea) wrote…

Sadly, it can't. The compiler assumes the one return value variant of map access if used in the return, so it complains that it's returning only one value instead of two.

wow TIL