mesh: init ed25519-signed gossip layer; conflict-resolving route store

Signed-off-by: NotAShelf <raf@notashelf.dev>
Change-Id: I92ff256da8e84e86cd9e7c2b511c0ae56a6a6964

go.mod

@@ -3,6 +3,7 @@ module notashelf.dev/ncro
 go 1.25.7
 
 require (
+	github.com/vmihailenco/msgpack/v5 v5.4.1
 	gopkg.in/yaml.v3 v3.0.1
 	modernc.org/sqlite v1.46.1
 )
@@ -13,6 +14,7 @@ require (
 	github.com/mattn/go-isatty v0.0.20 // indirect
 	github.com/ncruces/go-strftime v1.0.0 // indirect
 	github.com/remyoudompheng/bigfft v0.0.0-20230129092748-24d4a6f8daec // indirect
+	github.com/vmihailenco/tagparser/v2 v2.0.0 // indirect
 	golang.org/x/exp v0.0.0-20251023183803-a4bb9ffd2546 // indirect
 	golang.org/x/sys v0.37.0 // indirect
 	modernc.org/libc v1.67.6 // indirect

go.sum

@@ -1,3 +1,5 @@
+github.com/davecgh/go-spew v1.1.0 h1:ZDRjVQ15GmhC3fiQ8ni8+OwkZQO4DARzQgrnXU1Liz8=
+github.com/davecgh/go-spew v1.1.0/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
 github.com/dustin/go-humanize v1.0.1 h1:GzkhY7T5VNhEkwH0PVJgjz+fX1rhBrR7pRT3mDkpeCY=
 github.com/dustin/go-humanize v1.0.1/go.mod h1:Mu1zIs6XwVuF/gI1OepvI0qD18qycQx+mFykh5fBlto=
 github.com/google/pprof v0.0.0-20250317173921-a4b03ec1a45e h1:ijClszYn+mADRFY17kjQEVQ1XRhq2/JR1M3sGqeJoxs=
@@ -10,8 +12,16 @@ github.com/mattn/go-isatty v0.0.20 h1:xfD0iDuEKnDkl03q4limB+vH+GxLEtL/jb4xVJSWWE
 github.com/mattn/go-isatty v0.0.20/go.mod h1:W+V8PltTTMOvKvAeJH7IuucS94S2C6jfK/D7dTCTo3Y=
 github.com/ncruces/go-strftime v1.0.0 h1:HMFp8mLCTPp341M/ZnA4qaf7ZlsbTc+miZjCLOFAw7w=
 github.com/ncruces/go-strftime v1.0.0/go.mod h1:Fwc5htZGVVkseilnfgOVb9mKy6w1naJmn9CehxcKcls=
+github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
+github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
 github.com/remyoudompheng/bigfft v0.0.0-20230129092748-24d4a6f8daec h1:W09IVJc94icq4NjY3clb7Lk8O1qJ8BdBEF8z0ibU0rE=
 github.com/remyoudompheng/bigfft v0.0.0-20230129092748-24d4a6f8daec/go.mod h1:qqbHyh8v60DhA7CoWK5oRCqLrMHRGoxYCSS9EjAz6Eo=
+github.com/stretchr/testify v1.6.1 h1:hDPOHmpOpP40lSULcqw7IrRb/u7w6RpDC9399XyoNd0=
+github.com/stretchr/testify v1.6.1/go.mod h1:6Fq8oRcR53rry900zMqJjRRixrwX3KX962/h/Wwjteg=
+github.com/vmihailenco/msgpack/v5 v5.4.1 h1:cQriyiUvjTwOHg8QZaPihLWeRAAVoCpE00IUPn0Bjt8=
+github.com/vmihailenco/msgpack/v5 v5.4.1/go.mod h1:GaZTsDaehaPpQVyxrf5mtQlH+pc21PIudVV/E3rRQok=
+github.com/vmihailenco/tagparser/v2 v2.0.0 h1:y09buUbR+b5aycVFQs/g70pqKVZNBmxwAhO7/IwNM9g=
+github.com/vmihailenco/tagparser/v2 v2.0.0/go.mod h1:Wri+At7QHww0WTrCBeu4J6bNtoV6mEfg5OIWRZA9qds=
 golang.org/x/exp v0.0.0-20251023183803-a4bb9ffd2546 h1:mgKeJMpvi0yx/sU5GsxQ7p6s2wtOnGAHZWCHUM4KGzY=
 golang.org/x/exp v0.0.0-20251023183803-a4bb9ffd2546/go.mod h1:j/pmGrbnkbPtQfxEe5D0VQhZC6qKbfKifgD0oM7sR70=
 golang.org/x/mod v0.29.0 h1:HV8lRxZC4l2cr3Zq1LvtOsi/ThTgWnUk/y64QSs8GwA=

internal/mesh/mesh.go

@@ -1 +1,161 @@
 package mesh
+
+import (
+	"crypto/ed25519"
+	"crypto/rand"
+	"encoding/hex"
+	"errors"
+	"fmt"
+	"os"
+	"sync"
+	"time"
+
+	"github.com/vmihailenco/msgpack/v5"
+	"notashelf.dev/ncro/internal/cache"
+)
+
+// Gossip message types.
+type MsgType uint8
+
+const (
+	MsgAnnounce    MsgType = 1
+	MsgSyncRequest MsgType = 2
+	MsgSyncReply   MsgType = 3
+)
+
+// Wire format for gossip messages.
+type Message struct {
+	Type      MsgType
+	NodeID    string
+	Timestamp int64
+	Routes    []cache.RouteEntry
+}
+
+// Cryptographic identity of an ncro node.
+type Node struct {
+	pubKey  ed25519.PublicKey
+	privKey ed25519.PrivateKey
+	store   *RouteStore
+}
+
+// Loads or generates an ed25519 keypair from keyPath.
+// Pass "" for an ephemeral in-memory key.
+func NewNode(keyPath string, store *RouteStore) (*Node, error) {
+	if store == nil {
+		store = NewRouteStore()
+	}
+	if keyPath == "" {
+		pub, priv, err := ed25519.GenerateKey(rand.Reader)
+		if err != nil {
+			return nil, fmt.Errorf("generate key: %w", err)
+		}
+		return &Node{pubKey: pub, privKey: priv, store: store}, nil
+	}
+	data, err := os.ReadFile(keyPath)
+	if err == nil && len(data) == ed25519.PrivateKeySize {
+		priv := ed25519.PrivateKey(data)
+		return &Node{pubKey: priv.Public().(ed25519.PublicKey), privKey: priv, store: store}, nil
+	}
+	pub, priv, err := ed25519.GenerateKey(rand.Reader)
+	if err != nil {
+		return nil, fmt.Errorf("generate key: %w", err)
+	}
+	if err := os.WriteFile(keyPath, priv, 0600); err != nil {
+		return nil, fmt.Errorf("write key: %w", err)
+	}
+	return &Node{pubKey: pub, privKey: priv, store: store}, nil
+}
+
+// Returns the hex-encoded public key fingerprint.
+func (n *Node) ID() string {
+	return hex.EncodeToString(n.pubKey[:8])
+}
+
+// Returns the node's public key.
+func (n *Node) PublicKey() ed25519.PublicKey {
+	return n.pubKey
+}
+
+// Serializes msg with msgpack and signs it; returns (data, signature, error).
+func (n *Node) Sign(msg Message) ([]byte, []byte, error) {
+	data, err := msgpack.Marshal(msg)
+	if err != nil {
+		return nil, nil, err
+	}
+	return data, ed25519.Sign(n.privKey, data), nil
+}
+
+// Checks that sig is a valid ed25519 signature of data under pubKey.
+func Verify(pubKey ed25519.PublicKey, data, sig []byte) error {
+	if !ed25519.Verify(pubKey, data, sig) {
+		return errors.New("invalid signature")
+	}
+	return nil
+}
+
+// In-memory route table with merge-conflict resolution for gossip.
+type RouteStore struct {
+	mu     sync.RWMutex
+	routes map[string]*cache.RouteEntry
+}
+
+// Creates an empty RouteStore.
+func NewRouteStore() *RouteStore {
+	return &RouteStore{routes: make(map[string]*cache.RouteEntry)}
+}
+
+// Applies incoming routes: lower latency wins; newer LastVerified wins on tie.
+func (rs *RouteStore) Merge(incoming []cache.RouteEntry) {
+	rs.mu.Lock()
+	defer rs.mu.Unlock()
+	now := time.Now()
+	for _, r := range incoming {
+		r := r
+		if r.TTL.Before(now) {
+			continue
+		}
+		existing, ok := rs.routes[r.StorePath]
+		if !ok {
+			rs.routes[r.StorePath] = &r
+			continue
+		}
+		if r.LatencyEMA < existing.LatencyEMA {
+			rs.routes[r.StorePath] = &r
+		} else if r.LatencyEMA == existing.LatencyEMA && r.LastVerified.After(existing.LastVerified) {
+			rs.routes[r.StorePath] = &r
+		}
+	}
+}
+
+// Returns a copy of the stored route, or nil.
+func (rs *RouteStore) Get(storePath string) *cache.RouteEntry {
+	rs.mu.RLock()
+	defer rs.mu.RUnlock()
+	e, ok := rs.routes[storePath]
+	if !ok {
+		return nil
+	}
+	cp := *e
+	return &cp
+}
+
+// Returns up to n routes for sync batching.
+func (rs *RouteStore) Top(n int) []cache.RouteEntry {
+	rs.mu.RLock()
+	defer rs.mu.RUnlock()
+	result := make([]cache.RouteEntry, 0, min(n, len(rs.routes)))
+	for _, e := range rs.routes {
+		result = append(result, *e)
+		if len(result) >= n {
+			break
+		}
+	}
+	return result
+}
+
+func min(a, b int) int {
+	if a < b {
+		return a
+	}
+	return b
+}

internal/mesh/mesh_test.go

@@ -0,0 +1,75 @@
+package mesh_test
+
+import (
+	"testing"
+	"time"
+
+	"notashelf.dev/ncro/internal/cache"
+	"notashelf.dev/ncro/internal/mesh"
+)
+
+func TestSignVerify(t *testing.T) {
+	node, err := mesh.NewNode("", nil)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	msg := mesh.Message{
+		Type:      mesh.MsgAnnounce,
+		NodeID:    node.ID(),
+		Timestamp: time.Now().UnixNano(),
+		Routes:    []cache.RouteEntry{{StorePath: "abc123", UpstreamURL: "https://cache.nixos.org"}},
+	}
+
+	data, sig, err := node.Sign(msg)
+	if err != nil {
+		t.Fatalf("Sign: %v", err)
+	}
+	if err := mesh.Verify(node.PublicKey(), data, sig); err != nil {
+		t.Errorf("Verify: %v", err)
+	}
+}
+
+func TestVerifyFailsOnTamper(t *testing.T) {
+	node, _ := mesh.NewNode("", nil)
+	msg := mesh.Message{Type: mesh.MsgAnnounce, NodeID: node.ID()}
+	data, sig, _ := node.Sign(msg)
+	data[0] ^= 0xFF
+	if err := mesh.Verify(node.PublicKey(), data, sig); err == nil {
+		t.Error("expected verification failure on tampered data")
+	}
+}
+
+func TestMergeLowerLatencyWins(t *testing.T) {
+	store := mesh.NewRouteStore()
+	store.Merge([]cache.RouteEntry{
+		{StorePath: "pkg-a", UpstreamURL: "https://slow.example.com", LatencyEMA: 200, TTL: time.Now().Add(time.Hour)},
+	})
+	store.Merge([]cache.RouteEntry{
+		{StorePath: "pkg-a", UpstreamURL: "https://fast.example.com", LatencyEMA: 10, TTL: time.Now().Add(time.Hour)},
+	})
+
+	entry := store.Get("pkg-a")
+	if entry == nil {
+		t.Fatal("entry is nil")
+	}
+	if entry.UpstreamURL != "https://fast.example.com" {
+		t.Errorf("expected fast upstream, got %q", entry.UpstreamURL)
+	}
+}
+
+func TestMergeNewerTimestampWinsOnTie(t *testing.T) {
+	store := mesh.NewRouteStore()
+	now := time.Now()
+	store.Merge([]cache.RouteEntry{
+		{StorePath: "pkg-b", UpstreamURL: "https://a.example.com", LatencyEMA: 50, LastVerified: now.Add(-time.Minute), TTL: time.Now().Add(time.Hour)},
+	})
+	store.Merge([]cache.RouteEntry{
+		{StorePath: "pkg-b", UpstreamURL: "https://b.example.com", LatencyEMA: 50, LastVerified: now, TTL: time.Now().Add(time.Hour)},
+	})
+
+	entry := store.Get("pkg-b")
+	if entry.UpstreamURL != "https://b.example.com" {
+		t.Errorf("expected newer upstream, got %q", entry.UpstreamURL)
+	}
+}