mesh-controller/internal/catalogue/names_served.go

package catalogue

import (
	"sort"
	"strings"
)

// Which machine serves each routed name (novox/hq ADR 0066, issue 178).
//
// A routed name is a label the mesh composed for a consumer's endpoint, and it is *served* by the
// provider that answers requests for it — the proxy the consumer's route reaches. The same name is
// composed into every labelled contribution the consumer makes, because a provider that must know
// the consumer's public name (an identity provider composing a redirect) is told it the same way
// (04-ISSUES/122). Attributing the name to whichever of those providers a map happened to yield
// last sent a public name to the identity provider's machine on one plan and to the proxy's on the
// next (forge issue 227), and the whole names region flipped with it.
//
// **The terminus serves the name.** Among the providers a name reaches, the one that serves it is
// the one that is not itself routed: a provider that contributes a labelled name of its own to some
// requirement is published through another provider, and is a consumer of names, not their end.
// Name-agnostic — nothing here knows what "route" means — and structural: it reads the graph the
// modules declared. Deterministic: names, requirements and nodes are walked in order, so two
// plans of one mesh yield one region.

// NamesServed is every routed name across the mesh and the node that serves it, from every node's
// resolution and settings. A name several termini claim goes to the first node in name order, so
// the answer is stable; a name nothing terminal claims is left out.
func NamesServed(plans map[string]Resolution, settings map[string]SettingsBy) (map[string]string, error) {
	nodes := make([]string, 0, len(plans))
	for n := range plans {
		nodes = append(nodes, n)
	}
	sort.Strings(nodes)

	out := map[string]string{}
	for _, node := range nodes {
		plan := plans[node]
		all, err := plan.contributions(settings[node], nil, nil)
		if err != nil {
			return nil, err
		}
		requirements := make([]string, 0, len(all))
		for to := range all {
			requirements = append(requirements, to)
		}
		sort.Strings(requirements)
		for _, to := range requirements {
			for _, given := range all[to] {
				if given.Node != "" {
					// Said from another machine; that machine's own resolution carries it.
					continue
				}
				// A routed name, and only that: a contribution the mesh composed a name for from a
				// label it was given. A grant that happens to carry a `name` of its own — a database
				// name — carries no label and is left alone.
				if _, labelled := given.Values["label"]; !labelled {
					continue
				}
				name, _ := given.Values["name"].(string)
				if name == "" {
					continue
				}
				serving := servingNodeOf(plan, to, given.From, node)
				if !servesNames(plans[serving], to) {
					continue
				}
				name = strings.ToLower(name)
				if held, taken := out[name]; !taken || serving < held {
					out[name] = serving
				}
			}
		}
	}
	return out, nil
}

// servingNodeOf is the node answering one consumer's requirement: whoever the plan needs it from,
// or this same node when the provider is beside the consumer.
func servingNodeOf(plan Resolution, requirement, consumer, self string) string {
	for _, need := range plan.Needs {
		if need.Name == requirement && need.For == consumer && need.From != "" {
			return need.From
		}
	}
	return self
}

// servesNames says whether the module providing a requirement on a node is a terminus: it is not
// itself published under a labelled name through some other provider. A node whose plan is not
// known (it did not resolve) serves nothing.
func servesNames(plan Resolution, requirement string) bool {
	for _, m := range plan.Modules {
		if !offers(m, requirement) {
			continue
		}
		return !contributesALabel(m)
	}
	return false
}

func offers(m Manifest, requirement string) bool {
	for _, o := range m.Offers() {
		if o == requirement {
			return true
		}
	}
	return false
}

func contributesALabel(m Manifest) bool {
	for _, values := range m.Contributes {
		if _, labelled := values["label"]; labelled {
			return true
		}
	}
	for _, locals := range m.ContributesMany {
		for _, values := range locals {
			if _, labelled := values["label"]; labelled {
				return true
			}
		}
	}
	return false
}