mesh-host/cmd/mesh-host/userlist.go

package main

import (
	"context"
	"encoding/json"
	"errors"
	"fmt"
	"os"
	"path/filepath"

	"git.novox.be/novox/mesh-sdk/go/declaration"
	"git.novox.be/novox/mesh-sdk/go/delivery"
	"git.novox.be/novox/mesh-sdk/go/seal"
	"github.com/novox/mesh-host/internal/apply"
	"github.com/novox/mesh-host/internal/identity"
	"github.com/novox/mesh-host/internal/link"
	"github.com/novox/mesh-host/internal/store"
	"github.com/novox/mesh-host/internal/system"
	"github.com/novox/mesh-host/internal/userlist"
)

// The bridge of novox/hq ADR 0547 §8, wired: the bus node's engine writes the grants part's user list alone into the file
// the bus module's composition declares, under the apply's two locks as a filled file is written (filling.go), and says what
// it wrote in the bus module's have.

// userListFollower is the follower of the bus's user list for one link: the node's composition bucket, the keys the
// agent trusts, the write alone, and the have.
func userListFollower(opts options, session *link.Session, running func() []delivery.Composed,
	say link.Announce, wrote func()) *userlist.Follower {
	return userlist.New(userlist.Env{
		Node:    session.Membership.Node,
		Running: running,
		OnDisk:  userListOnDisk,
		Write: func(ctx context.Context, module string, raw json.RawMessage, body []byte) (string, bool, error) {
			digest, changed, err := writeUserListAlone(session.WithLink(ctx), opts, raw, body, say)
			if changed && wrote != nil {
				wrote()
			}
			return digest, changed, err
		},
		Report: func(ctx context.Context, module string, w userlist.Written) {
			session.NoteUserList(ctx, module, w)
		},
		// From take-over, the grants part's list (ADR 0547 clauses 7, 8): its one key watched, its object read by name and
		// opened with this machine's sealing key, the key's public half said in the have so the grants part seals to it.
		Grants: bucketWatch{session, delivery.GrantsUserListBucket},
		Fetch: func(ctx context.Context, name string) ([]byte, error) {
			return session.GrantsObject(ctx, name, grantsListLimit)
		},
		Open: func(b seal.Box) ([]byte, error) {
			key, err := identity.LoadSealingKey(identity.SealingKeyPath(opts.state))
			if err != nil {
				return nil, err
			}
			return key.OpenVaultBox(b)
		},
		Key: func() string {
			key, err := identity.LoadSealingKey(identity.SealingKeyPath(opts.state))
			if err != nil {
				return ""
			}
			pem, err := key.PublicPEM()
			if err != nil {
				return ""
			}
			return pem
		},
		// The grants part's key as last heard, kept beside the node's state, followed while it cannot be watched; its
		// watch tried again as a passing failure of the bus is (ADR 0547 clause 8).
		Kept:    func() ([]byte, uint64) { return keptGrantsKey(opts) },
		Keep:    func(value []byte, rev uint64) { keepGrantsKey(opts, value, rev, say) },
		Backoff: link.Backoff,
		Say:     announceOr(say),
	})
}

// grantsListLimit is the largest sealed list the bus node reads: the live list is about a hundred kilobytes.
const grantsListLimit = 16 << 20

// userListFile is a user-list resource as the file it declares.
func userListFile(raw []byte) (*declaration.File, error) {
	r, err := declaration.ParseResource(raw)
	if err != nil {
		return nil, fmt.Errorf("the user list is not a resource: %w", err)
	}
	f, ok := r.(*declaration.File)
	if !ok {
		return nil, fmt.Errorf("the user list is a %s, not a file", r.Kind())
	}
	return f, nil
}

// userListOnDisk is what the user list's file holds on this machine now; nil when there is none.
func userListOnDisk(raw json.RawMessage) ([]byte, error) {
	f, err := userListFile(raw)
	if err != nil {
		return nil, err
	}
	body, err := os.ReadFile(f.Path)
	if errors.Is(err, os.ErrNotExist) {
		return nil, nil
	}
	return body, err
}

// writeUserListAlone writes one user-list resource alone (apply.WriteAlone) with body as its content, the node's state
// read and saved under the apply's locks, and answers the digest of the file on the machine after.
func writeUserListAlone(ctx context.Context, opts options, raw []byte, body []byte, say link.Announce) (string, bool, error) {
	declared, err := userListFile(raw)
	if err != nil {
		return "", false, err
	}
	file := *declared
	file.Content, file.Digest, file.Size = string(body), "", 0

	applying.Lock()
	defer applying.Unlock()
	unlock, err := store.Lock(opts.state, nil)
	if err != nil {
		return "", false, err
	}
	defer unlock()
	known, err := store.Load(opts.state)
	if err != nil {
		return "", false, err
	}
	built, err := system.For(builtFor)
	if err != nil {
		return "", false, err
	}
	out, updated, writeErr := apply.WriteAlone(ctx, built, &file, known, apply.ExecRunner, announceOr(say))
	// Saved whichever way it went, as an apply's: what was written is on the machine either way.
	if err := store.Save(opts.state, updated); err != nil {
		writeErr = errors.Join(writeErr, errors.New("written, and the node's state could not be saved: "+err.Error()))
	}
	digest := ""
	if body, err := os.ReadFile(file.Path); err == nil {
		digest = userlist.Digest(body)
	}
	return digest, writeErr == nil && out.Action != "unchanged", writeErr
}

// grantsKeyPath is where the grants part's user-list key last heard is kept, beside the node's state.
func grantsKeyPath(opts options) string {
	return filepath.Join(filepath.Dir(opts.state), "grants-user-list.json")
}

type keptKey struct {
	Revision uint64          `json:"revision"`
	Value    json.RawMessage `json:"value"`
}

func keptGrantsKey(opts options) ([]byte, uint64) {
	raw, err := os.ReadFile(grantsKeyPath(opts))
	if err != nil {
		return nil, 0
	}
	var k keptKey
	if json.Unmarshal(raw, &k) != nil || len(k.Value) == 0 {
		return nil, 0
	}
	return k.Value, k.Revision
}

func keepGrantsKey(opts options, value []byte, rev uint64, say link.Announce) {
	path := grantsKeyPath(opts)
	if value == nil {
		if err := os.Remove(path); err != nil && !errors.Is(err, os.ErrNotExist) {
			announceOr(say)("the grants part's user-list key kept on this machine could not be taken away: " + err.Error())
		}
		return
	}
	raw, _ := json.Marshal(keptKey{Revision: rev, Value: value})
	tmp := path + ".new"
	err := os.WriteFile(tmp, raw, 0o600)
	if err == nil {
		err = os.Rename(tmp, path)
	}
	if err != nil {
		announceOr(say)("the grants part's user-list key could not be kept on this machine: " + err.Error())
	}
}