mesh-host/internal/compose/resolution/seat_into.go

package resolution

import (
	"encoding/json"
	"fmt"
	"regexp"
	"sort"
	"strconv"
	"strings"

	mcat "git.novox.be/novox/mesh-sdk/go/catalogue"
)

// ofSeat is where a module asks about a seat: ${seat:<seat>:<the port its holder's software uses>}.
var ofSeat = regexp.MustCompile(`\$\{seat:([a-z0-9][a-z0-9-]*):([0-9]+)\}`)

// **Where this machine reaches a mesh seat's holder** (novox/hq ADR 0222, issue 190).
//
// `${seat:<mesh-seat>:reach}` is host:port — the address this machine dials to reach whatever holds a
// seat the mesh holds once. The same reasoning as the port above, one step further: nothing is
// required, nothing is granted, no credential is minted, and the answer is an address the mesh
// already holds in the clear and composes into every reference it built. What it is for is a module
// that must *state* where a mesh service is to software it owns — the container runtime trusting
// the mesh's registry is the case — without becoming that service's consumer.
//
// Answered for the seats in reachedSeats only. Another seat is refused by name rather than answered
// with nothing: a module asking where something is that the mesh does not say would otherwise be
// given an empty value and never know the question was not understood.
//
// The answer may be empty: no machine on the private network holds the seat yet (genesis raises
// the store before the network). In a file written into as JSON, an empty member is dropped from
// its list, and a list left with none is dropped, so the runtime is never told to trust "".
var ofSeatReach = regexp.MustCompile(`\$\{seat:([a-z0-9][a-z0-9-]*):reach\}`)

// reachedSeats is every seat ${seat:…:reach} answers for.
var reachedSeats = map[string]bool{"mesh-artifact-store": true}

// seatInto replaces a resource's ${seat:…} placeholders with where this machine put each seat's
// holder — in a file's content, and in a value of a container's or a process's environment. The
// same places portInto fills, for the same reason: they are where a program reads a number from.
func seatInto(resource map[string]any, module string, with mcat.Rendering) error {
	switch fmt.Sprint(resource["type"]) {
	case "file":
		content, ok := resource["content"].(string)
		if !ok || (!ofSeat.MatchString(content) && !ofSeatReach.MatchString(content)) {
			return nil
		}
		where := fmt.Sprintf("%s has a file that", module)
		filled, err := seatsFilledInto(content, where, with)
		if err != nil {
			return err
		}
		if ofSeatReach.MatchString(filled) {
			if filled, err = reachFilledInto(filled, where, with); err != nil {
				return err
			}
			if fmt.Sprint(resource["into"]) == "json" {
				if filled, err = withoutEmptyMembers(filled, where); err != nil {
					return err
				}
			}
		}
		resource["content"] = filled

	case "container", "process":
		env, ok := resource["env"].(map[string]any)
		if !ok {
			return nil
		}
		named := make([]string, 0, len(env))
		for key := range env {
			named = append(named, key)
		}
		sort.Strings(named)

		// A fresh map, and only when something changes — this map is the catalogue's, shared by
		// every node running the module (see portInto).
		var filled map[string]any
		for _, key := range named {
			written, ok := env[key].(string)
			if !ok || (!ofSeat.MatchString(written) && !ofSeatReach.MatchString(written)) {
				continue
			}
			where := fmt.Sprintf("%s's %s %s sets %s to something that",
				module, resource["type"], resource["name"], key)
			value, err := seatsFilledInto(written, where, with)
			if err != nil {
				return err
			}
			if value, err = reachFilledInto(value, where, with); err != nil {
				return err
			}
			if filled == nil {
				filled = map[string]any{}
				for k, v := range env {
					filled[k] = v
				}
			}
			filled[key] = value
		}
		if filled != nil {
			resource["env"] = filled
		}
	}
	return nil
}

// seatsFilledInto answers every ${seat:…} in one written value.
//
// A port the seat's holder does not publish on this machine — or a seat nothing on it holds —
// answers with nothing, for the reason the package comment gives. A port that is not one is
// refused: it was written by a person and it is wrong.
func seatsFilledInto(written, where string, with mcat.Rendering) (string, error) {
	for _, m := range ofSeat.FindAllStringSubmatch(written, -1) {
		seat, port := m[1], m[2]
		wanted, err := strconv.Atoi(port)
		if err != nil || wanted < 1 || wanted > 65535 {
			return "", fmt.Errorf("%s says ${seat:%s:%s}, and %s is not a port", where, seat, port, port)
		}
		answer := ""
		if at, known := with.Seats[seat][wanted]; known {
			answer = strconv.Itoa(at)
		}
		written = strings.ReplaceAll(written, m[0], answer)
	}
	return written, nil
}

// reachFilledInto answers every ${seat:…:reach} in one written value with where this machine
// reaches the seat's holder, or with nothing when no holder is reachable yet. A seat the mesh does
// not answer this for is refused by name.
func reachFilledInto(written, where string, with mcat.Rendering) (string, error) {
	for _, m := range ofSeatReach.FindAllStringSubmatch(written, -1) {
		seat := m[1]
		if !reachedSeats[seat] {
			known := make([]string, 0, len(reachedSeats))
			for s := range reachedSeats {
				known = append(known, s)
			}
			sort.Strings(known)
			return "", fmt.Errorf("%s says ${seat:%s:reach}, and the mesh says where a seat's holder is "+
				"reached only for %s (novox/hq ADR 0222)", where, seat, strings.Join(known, ", "))
		}
		written = strings.ReplaceAll(written, m[0], with.SeatReach[seat])
	}
	return written, nil
}

// withoutEmptyMembers drops every empty string from the lists at the top of a JSON object written
// into a machine's file, and a list left with no members, so an unanswered ${seat:…:reach} adds
// nothing to the machine's list rather than adding "".
func withoutEmptyMembers(content, where string) (string, error) {
	var object map[string]json.RawMessage
	if err := json.Unmarshal([]byte(content), &object); err != nil {
		return "", fmt.Errorf("%s is written into as JSON and is not a JSON object: %w", where, err)
	}
	changed := false
	for key, raw := range object {
		var members []json.RawMessage
		if err := json.Unmarshal(raw, &members); err != nil {
			continue // not a list
		}
		kept := make([]json.RawMessage, 0, len(members))
		for _, member := range members {
			var s string
			if json.Unmarshal(member, &s) == nil && s == "" {
				continue
			}
			kept = append(kept, member)
		}
		if len(kept) == len(members) {
			continue
		}
		changed = true
		if len(kept) == 0 {
			delete(object, key)
			continue
		}
		list, err := json.Marshal(kept)
		if err != nil {
			return "", err
		}
		object[key] = list
	}
	if !changed {
		return content, nil
	}
	out, err := json.Marshal(object)
	if err != nil {
		return "", err
	}
	return string(out) + "\n", nil
}