event.go

package nostr

import (
	"crypto/sha256"
	"encoding/hex"
	"fmt"

	"github.com/btcsuite/btcd/btcec/v2"
	"github.com/btcsuite/btcd/btcec/v2/schnorr"
	"github.com/mailru/easyjson"
)

type Event struct {
	ID        string    `json:"id"`
	PubKey    string    `json:"pubkey"`
	CreatedAt Timestamp `json:"created_at"`
	Kind      int       `json:"kind"`
	Tags      Tags      `json:"tags"`
	Content   string    `json:"content"`
	Sig       string    `json:"sig"`

	// anything here will be mashed together with the main event object when serializing
	extra map[string]any
}

const (
	KindSetMetadata              int = 0
	KindTextNote                 int = 1
	KindRecommendServer          int = 2
	KindContactList              int = 3
	KindEncryptedDirectMessage   int = 4
	KindDeletion                 int = 5
	KindBoost                    int = 6
	KindReaction                 int = 7
	KindChannelCreation          int = 40
	KindChannelMetadata          int = 41
	KindChannelMessage           int = 42
	KindChannelHideMessage       int = 43
	KindChannelMuteUser          int = 44
	KindFileMetadata             int = 1063
	KindZapRequest               int = 9734
	KindZap                      int = 9735
	KindMuteList                 int = 10000
	KindPinList                  int = 10001
	KindRelayListMetadata        int = 10002
	KindNWCWalletInfo            int = 13194
	KindClientAuthentication     int = 22242
	KindNWCWalletRequest         int = 23194
	KindNWCWalletResponse        int = 23195
	KindNostrConnect             int = 24133
	KindCategorizedPeopleList    int = 30000
	KindCategorizedBookmarksList int = 30001
	KindProfileBadges            int = 30008
	KindBadgeDefinition          int = 30009
	KindStallDefinition          int = 30017
	KindProductDefinition        int = 30018
	KindArticle                  int = 30023
	KindApplicationSpecificData  int = 30078
)

// Event Stringer interface, just returns the raw JSON as a string
func (evt Event) String() string {
	j, _ := easyjson.Marshal(evt)
	return string(j)
}

// GetID serializes and returns the event ID as a string
func (evt *Event) GetID() string {
	h := sha256.Sum256(evt.Serialize())
	return hex.EncodeToString(h[:])
}

// Serialize outputs a byte array that can be hashed/signed to identify/authenticate.
// JSON encoding as defined in RFC4627.
func (evt *Event) Serialize() []byte {
	// the serialization process is just putting everything into a JSON array
	// so the order is kept. See NIP-01
	dst := make([]byte, 0)

	// the header portion is easy to serialize
	// [0,"pubkey",created_at,kind,[
	dst = append(dst, []byte(
		fmt.Sprintf(
			"[0,\"%s\",%d,%d,",
			evt.PubKey,
			evt.CreatedAt,
			evt.Kind,
		))...)

	// tags
	dst = evt.Tags.marshalTo(dst)
	dst = append(dst, ',')

	// content needs to be escaped in general as it is user generated.
	dst = escapeString(dst, evt.Content)
	dst = append(dst, ']')

	return dst
}

// CheckSignature checks if the signature is valid for the id
// (which is a hash of the serialized event content).
// returns an error if the signature itself is invalid.
func (evt Event) CheckSignature() (bool, error) {
	// read and check pubkey
	pk, err := hex.DecodeString(evt.PubKey)
	if err != nil {
		return false, fmt.Errorf("event pubkey '%s' is invalid hex: %w", evt.PubKey, err)
	}

	pubkey, err := schnorr.ParsePubKey(pk)
	if err != nil {
		return false, fmt.Errorf("event has invalid pubkey '%s': %w", evt.PubKey, err)
	}

	// read signature
	s, err := hex.DecodeString(evt.Sig)
	if err != nil {
		return false, fmt.Errorf("signature '%s' is invalid hex: %w", evt.Sig, err)
	}
	sig, err := schnorr.ParseSignature(s)
	if err != nil {
		return false, fmt.Errorf("failed to parse signature: %w", err)
	}

	// check signature
	hash := sha256.Sum256(evt.Serialize())
	return sig.Verify(hash[:], pubkey), nil
}

// Sign signs an event with a given privateKey
func (evt *Event) Sign(privateKey string) error {
	s, err := hex.DecodeString(privateKey)
	if err != nil {
		return fmt.Errorf("Sign called with invalid private key '%s': %w", privateKey, err)
	}

	sk, pk := btcec.PrivKeyFromBytes(s)
	pkBytes := pk.SerializeCompressed()
	evt.PubKey = hex.EncodeToString(pkBytes[1:])

	h := sha256.Sum256(evt.Serialize())
	sig, err := schnorr.Sign(sk, h[:])
	if err != nil {
		return err
	}

	evt.ID = hex.EncodeToString(h[:])
	evt.Sig = hex.EncodeToString(sig.Serialize())
	return nil
}