implement more primitives

chord/client.go

@@ -22,6 +22,15 @@ type Client interface {
 // considering we can sort by increasing distance from the origin and then do
 // the query in linear time.
 
+// Find finds the first node in the network preceding id.
+func Find(ctx context.Context, cl Client, n *Node, id ID) (Peer, error) {
+	if n.IsLocal(id) {
+		return n.self, nil
+	}
+	p, err := cl.FindSuccessor(ctx, n.Closest(id), id)
+	return p, err
+}
+
 // Join creates a new node joining an existing Chord network by communicating
 // with any peer already in the network.
 func Join(ctx context.Context, cl Client, addr netip.AddrPort, np Peer) (*Node, error) {

chord/id.go

@@ -4,6 +4,7 @@ import (
 	"bytes"
 	"crypto/sha1"
 	"encoding/hex"
+	"errors"
 	"net/netip"
 )
 
@@ -49,3 +50,12 @@ func (id ID) String() string {
 	b = hex.AppendEncode(b, id[:])
 	return string(b)
 }
+
+func ParseID(s string) (ID, error) {
+	if len(s) != len(ID{})*2 {
+		return ID{}, errors.New("invalid ID")
+	}
+	var id ID
+	_, err := hex.AppendDecode(id[:], []byte(s))
+	return id, err
+}

chord/topology.go

@@ -26,16 +26,19 @@ func (n *Node) Successor() Peer {
 	return n.succ[0]
 }
 
+// Neighbors returns the node's predecessor and appends its successor list to s.
+func (n *Node) Neighbors(s []Peer) (Peer, []Peer) {
+	return n.pred, append(s, n.succ...)
+}
+
 // IsLocal reports whether this node owns the given key.
-func (n *Node) IsLocal(key string) bool {
-	id := keyID(key)
+func (n *Node) IsLocal(id ID) bool {
 	return contains(n.self.id, n.Successor().id, id)
 }
 
 // Closest finds the locally known peer which is the closest predecessor of key.
-func (n *Node) Closest(key string) Peer {
+func (n *Node) Closest(id ID) Peer {
 	self := n.self.id
-	id := keyID(key)
 	l := n.fingers
 	for i := len(l) - 1; i >= 0; i-- {
 		f := l[i]