mesh-controller/internal/catalogue/zones.go

package catalogue

import (
	"fmt"
	"sort"
	"strings"
)

// Zones: names a module answers itself (novox/hq ADR 0199).
//
// The mesh's resolver holds each node's internal domain and nothing else (ADR 0191, 0194). A module
// whose names are its own — the lab's scenario machines, known only while a scenario runs — declares
// the zone it answers and the listen that answers it; the controller hands the resolver's holder every
// zone with the declaring node's private address and the port that listen is published on, and the
// holder forwards the zone there. **A definition names no address** (ADR 0112): the zone is a setting,
// the listen is the module's own, and where they are is the mesh's fact.

// Zone is the manifest's declaration that a module answers the names in one zone.
type Zone struct {
	// Name is the zone: a label or a dotted name, normally `${setting:<key>}`, so the operator chooses
	// it and the definition does not.
	Name string `json:"name"`
	// Listen names one of the module's listens: the DNS answerer for the zone.
	Listen string `json:"listen"`
}

// ZoneAt is a declared zone where the mesh placed it: what the resolver's holder forwards, and where.
type ZoneAt struct {
	Zone    string
	Node    string
	Module  string
	Address string
	Port    int
}

// zoneProblems is what is wrong with a module's zone declaration on its own, before any node.
func zoneProblems(m Manifest) []string {
	if m.Zone == nil {
		return nil
	}
	var problems []string
	if strings.TrimSpace(m.Zone.Name) == "" {
		problems = append(problems, fmt.Sprintf("%s declares a zone with no name", m.Module))
	}
	if !m.hasListen(m.Zone.Listen) {
		problems = append(problems, fmt.Sprintf(
			"%s declares zone %q answered by listen %q, and has no listen of that name",
			m.Module, m.Zone.Name, m.Zone.Listen))
	}
	return problems
}

func (m Manifest) hasListen(name string) bool {
	if name == "" {
		return false
	}
	for _, l := range m.Listens {
		if l.Name == name {
			return true
		}
	}
	return false
}

// ZoneOn is one module's zone as one node places it: the name settled from the node's settings, the
// port its answering listen is published on there. Nothing when the module declares no zone.
func ZoneOn(m Manifest, layers []Layer, published map[int]int, node, address string) (*ZoneAt, error) {
	if m.Zone == nil {
		return nil, nil
	}
	settled, err := Settle(map[string]any{"zone": m.Zone.Name}, layers)
	if err != nil {
		return nil, fmt.Errorf("%s's zone on %s: %w", m.Module, node, err)
	}
	zone := strings.Trim(strings.ToLower(fmt.Sprint(settled["zone"])), ".")
	var port int
	for _, l := range m.Listens {
		if l.Name == m.Zone.Listen {
			port = l.Port
			if at, given := published[l.Port]; given {
				port = at
			}
		}
	}
	return &ZoneAt{Zone: zone, Node: node, Module: m.Module, Address: address, Port: port}, nil
}

// ZonesProblems is what the mesh refuses about its zones together: one zone declared twice, a zone
// that is the mesh's suffix or under it, a zone that is a node's public domain or under one. A module
// may not shadow names the mesh's resolver or the public DNS answers.
func ZonesProblems(zones []ZoneAt, suffix string, publicDomains []string) []string {
	var problems []string
	under := func(zone, domain string) bool {
		domain = strings.Trim(strings.ToLower(domain), ".")
		return domain != "" && (zone == domain || strings.HasSuffix(zone, "."+domain))
	}
	seen := map[string]ZoneAt{}
	for _, z := range zones {
		if other, twice := seen[z.Zone]; twice && (other.Node != z.Node || other.Module != z.Module) {
			problems = append(problems, fmt.Sprintf("zone %q is declared by %s on %s and by %s on %s; one module answers a zone",
				z.Zone, other.Module, other.Node, z.Module, z.Node))
		}
		seen[z.Zone] = z
		if under(z.Zone, suffix) {
			problems = append(problems, fmt.Sprintf("%s on %s declares zone %q, which is the mesh's own suffix or under it",
				z.Module, z.Node, z.Zone))
		}
		for _, d := range publicDomains {
			if under(z.Zone, d) {
				problems = append(problems, fmt.Sprintf("%s on %s declares zone %q, which is the public domain %q or under it",
					z.Module, z.Node, z.Zone, d))
			}
		}
	}
	sort.Strings(problems)
	return problems
}