nak/gift.go

package main

import (
	"context"
	"fmt"
	"math/rand"
	"time"

	"fiatjaf.com/nostr"
	"fiatjaf.com/nostr/nip44"
	"github.com/mailru/easyjson"
	"github.com/urfave/cli/v3"
)

var gift = &cli.Command{
	Name:  "gift",
	Usage: "gift-wraps (or unwraps) an event according to NIP-59",
	Description: `example:
  nak event | nak gift wrap --sec <sec-a> -p <sec-b> | nak gift unwrap --sec <sec-b> --from <pub-a>`,
	DisableSliceFlagSeparator: true,
	Commands: []*cli.Command{
		{
			Name: "wrap",
			Flags: append(
				defaultKeyFlags,
				&PubKeyFlag{
					Name:     "recipient-pubkey",
					Aliases:  []string{"p", "tgt", "target", "pubkey", "to"},
					Required: true,
				},
			),
			Usage: "turns an event into a rumor (unsigned) then gift-wraps it to the recipient",
			Description: `example:
  nak event -c 'hello' | nak gift wrap --sec <my-secret-key> -p <target-public-key>`,
			Action: func(ctx context.Context, c *cli.Command) error {
				kr, _, err := gatherKeyerFromArguments(ctx, c)
				if err != nil {
					return err
				}

				recipient := getPubKey(c, "recipient-pubkey")

				// get sender pubkey
				sender, err := kr.GetPublicKey(ctx)
				if err != nil {
					return fmt.Errorf("failed to get sender pubkey: %w", err)
				}

				// read event from stdin
				for eventJSON := range getJsonsOrBlank() {
					if eventJSON == "{}" {
						continue
					}

					var originalEvent nostr.Event
					if err := easyjson.Unmarshal([]byte(eventJSON), &originalEvent); err != nil {
						return fmt.Errorf("invalid event JSON: %w", err)
					}

					// turn into rumor (unsigned event)
					rumor := originalEvent
					rumor.Sig = [64]byte{} // remove signature
					rumor.PubKey = sender
					rumor.ID = rumor.GetID() // compute ID

					// create seal
					rumorJSON, _ := easyjson.Marshal(rumor)
					encryptedRumor, err := kr.Encrypt(ctx, string(rumorJSON), recipient)
					if err != nil {
						return fmt.Errorf("failed to encrypt rumor: %w", err)
					}
					seal := &nostr.Event{
						Kind:      13,
						Content:   encryptedRumor,
						PubKey:    sender,
						CreatedAt: randomNow(),
						Tags:      nostr.Tags{},
					}
					if err := kr.SignEvent(ctx, seal); err != nil {
						return fmt.Errorf("failed to sign seal: %w", err)
					}

					// create gift wrap
					ephemeral := nostr.Generate()
					sealJSON, _ := easyjson.Marshal(seal)
					convkey, err := nip44.GenerateConversationKey(recipient, ephemeral)
					if err != nil {
						return fmt.Errorf("failed to generate conversation key: %w", err)
					}
					encryptedSeal, err := nip44.Encrypt(string(sealJSON), convkey)
					if err != nil {
						return fmt.Errorf("failed to encrypt seal: %w", err)
					}
					wrap := &nostr.Event{
						Kind:      1059,
						Content:   encryptedSeal,
						CreatedAt: randomNow(),
						Tags:      nostr.Tags{{"p", recipient.Hex()}},
					}
					wrap.Sign(ephemeral)

					// print the gift-wrap
					wrapJSON, err := easyjson.Marshal(wrap)
					if err != nil {
						return fmt.Errorf("failed to marshal gift wrap: %w", err)
					}
					stdout(string(wrapJSON))
				}

				return nil
			},
		},
		{
			Name:  "unwrap",
			Usage: "decrypts a gift-wrap event sent by the sender to us and exposes its internal rumor (unsigned event).",
			Description: `example:
  nak req -p <my-public-key> -k 1059 dmrelay.com | nak gift unwrap --sec <my-secret-key> --from <sender-public-key>`,
			Flags: append(
				defaultKeyFlags,
				&PubKeyFlag{
					Name:     "sender-pubkey",
					Aliases:  []string{"p", "src", "source", "pubkey", "from"},
					Required: true,
				},
			),
			Action: func(ctx context.Context, c *cli.Command) error {
				kr, _, err := gatherKeyerFromArguments(ctx, c)
				if err != nil {
					return err
				}

				sender := getPubKey(c, "sender-pubkey")

				// read gift-wrapped event from stdin
				for wrapJSON := range getJsonsOrBlank() {
					if wrapJSON == "{}" {
						continue
					}

					var wrap nostr.Event
					if err := easyjson.Unmarshal([]byte(wrapJSON), &wrap); err != nil {
						return fmt.Errorf("invalid gift wrap JSON: %w", err)
					}

					if wrap.Kind != 1059 {
						return fmt.Errorf("not a gift wrap event (kind %d)", wrap.Kind)
					}

					ephemeralPubkey := wrap.PubKey

					// decrypt seal
					sealJSON, err := kr.Decrypt(ctx, wrap.Content, ephemeralPubkey)
					if err != nil {
						return fmt.Errorf("failed to decrypt seal: %w", err)
					}

					var seal nostr.Event
					if err := easyjson.Unmarshal([]byte(sealJSON), &seal); err != nil {
						return fmt.Errorf("invalid seal JSON: %w", err)
					}

					if seal.Kind != 13 {
						return fmt.Errorf("not a seal event (kind %d)", seal.Kind)
					}

					// decrypt rumor
					rumorJSON, err := kr.Decrypt(ctx, seal.Content, sender)
					if err != nil {
						return fmt.Errorf("failed to decrypt rumor: %w", err)
					}

					var rumor nostr.Event
					if err := easyjson.Unmarshal([]byte(rumorJSON), &rumor); err != nil {
						return fmt.Errorf("invalid rumor JSON: %w", err)
					}

					// output the unwrapped event (rumor)
					stdout(rumorJSON)
				}

				return nil
			},
		},
	},
}

func randomNow() nostr.Timestamp {
	const twoDays = 2 * 24 * 60 * 60
	now := time.Now().Unix()
	randomOffset := rand.Int63n(twoDays)
	return nostr.Timestamp(now - randomOffset)
}