mesh-controller/internal/catalogue/bound_into_files.go

package catalogue

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

// The half of a connection that is not secret, put where the program reading it can find it.
//
// **The asymmetry this removes was backwards** (novox/hq 04-ISSUES/023). A sealed credential can
// be placed inside any configuration file a module writes: the module leaves a hole, the mesh
// delivers the value sealed beside it, and the host — the only thing that sees both — fills it in.
// The host and the port and the name to present are ordinary facts the mesh holds in the clear,
// and they were the ones stuck: readable only inside a JSON binding, which a program reading
// `KEY=value` cannot use.
//
// So the same shape, and simpler. These values are not secret, so **the control plane substitutes
// them itself** before the declaration is sent. Nothing new reaches the host, which learns no
// formats and gains no fields.
//
// **It stays name-agnostic** ([ADR 0027]). The mesh does not learn what a `postgres-database` is:
// `at`, `as` and `from` are facts about any provision at all, and everything else comes from what
// the provider said it serves — whose keys are agreed by the requirement's name, not by this file.

// bound is where a module says a value from one of its bindings belongs:
// ${bound:<provision>.<key>}.
var bound = regexp.MustCompile(`\$\{bound:([a-z0-9][a-z0-9.-]*[a-z0-9]):([a-z0-9][a-z0-9_-]*)\}`)

// boundUsed are the (provision, key) pairs a file's content asks for, first appearance first.
func boundUsed(content string) [][2]string {
	var used [][2]string
	seen := map[string]bool{}
	for _, m := range bound.FindAllStringSubmatch(content, -1) {
		if key := m[1] + ":" + m[2]; !seen[key] {
			seen[key] = true
			used = append(used, [2]string{m[1], m[2]})
		}
	}
	return used
}

// knownFor is everything a module may name from one of its bindings.
//
// Three facts the mesh states about any provision, plus whatever the provider said it serves. A
// module may not reach a binding it does not have — the same boundary as a secret, for the same
// reason.
func knownFor(m Manifest, needs []Needed, node string) map[string]map[string]string {
	out := map[string]map[string]string{}
	for _, want := range m.Wants() {
		for i := range needs {
			n := needs[i]
			if n.Name != want || n.For != m.Module {
				continue
			}
			values := map[string]string{
				"at":   n.At,
				"from": n.From,
				"as":   ConsumerIdentity(node, IdentitySource(m.Slug, m.Module)),
			}
			for key, value := range n.Serves {
				// The provider's own vocabulary. Rendered plainly: a port is 5432, not 5432.000000,
				// which is what a float would write and what a connection string would refuse.
				values[key] = plainly(value)
			}
			out[want] = values
		}
	}
	return out
}

// plainly renders a served value as a program would expect to read it.
func plainly(value any) string {
	switch v := value.(type) {
	case string:
		return v
	case float64:
		if v == float64(int64(v)) {
			return fmt.Sprintf("%d", int64(v))
		}
		return strings.TrimRight(strings.TrimRight(fmt.Sprintf("%f", v), "0"), ".")
	case bool:
		return fmt.Sprintf("%t", v)
	case nil:
		return ""
	default:
		return fmt.Sprint(v)
	}
}

// boundInto replaces a file's ${bound:…} placeholders with what the mesh knows.
//
// A placeholder naming something the module does not require, or a key the provider does not
// serve, is refused. Left as it was, the literal `${bound:x:y}` would be written into a
// configuration file and read as a value — a connection to a host called `${bound:x:y}`, failing
// somewhere that names neither the module nor the mesh.
func boundInto(resource map[string]any, known map[string]map[string]string, module string) error {
	if fmt.Sprint(resource["type"]) != "file" {
		return nil
	}
	content, ok := resource["content"].(string)
	if !ok {
		return nil
	}
	for _, pair := range boundUsed(content) {
		provision, key := pair[0], pair[1]
		values, has := known[provision]
		if !has {
			return fmt.Errorf(
				"%s has a file that says ${bound:%s:%s}, and %s does not require %q. It may name %s",
				module, provision, key, module, provision, orNothing(namesOfBindings(known)))
		}
		value, said := values[key]
		if !said {
			return fmt.Errorf(
				"%s asks its %s binding for %q, and what answers it says %s",
				module, provision, key, orNothing(namesOfKeys(values)))
		}
		resource["content"] = strings.ReplaceAll(
			content, fmt.Sprintf("${bound:%s:%s}", provision, key), value)
		content = resource["content"].(string)
	}
	return nil
}

func namesOfBindings(known map[string]map[string]string) []string {
	var names []string
	for name := range known {
		names = append(names, fmt.Sprintf("%q", name))
	}
	sort.Strings(names)
	return names
}

func namesOfKeys(values map[string]string) []string {
	var names []string
	for key := range values {
		names = append(names, fmt.Sprintf("%q", key))
	}
	sort.Strings(names)
	return names
}

func orNothing(names []string) string {
	if len(names) == 0 {
		return "nothing"
	}
	return join(names)
}