move everything to the same directory.

event.go

@@ -0,0 +1,129 @@
+package nostr
+
+import (
+	"bytes"
+	"crypto/rand"
+	"crypto/sha256"
+	"encoding/hex"
+	"encoding/json"
+	"fmt"
+
+	"github.com/fiatjaf/bip340"
+)
+
+const (
+	KindSetMetadata            int = 0
+	KindTextNote               int = 1
+	KindRecommendServer        int = 2
+	KindContactList            int = 3
+	KindEncryptedDirectMessage int = 4
+	KindDeletion               int = 5
+)
+
+type Event struct {
+	ID string `json:"id"` // it's the hash of the serialized event
+
+	PubKey    string `json:"pubkey"`
+	CreatedAt uint32 `json:"created_at"`
+
+	Kind int `json:"kind"`
+
+	Tags    Tags   `json:"tags"`
+	Content string `json:"content"`
+	Sig     string `json:"sig"`
+}
+
+// Serialize outputs a byte array that can be hashed/signed to identify/authenticate
+func (evt *Event) Serialize() []byte {
+	// the serialization process is just putting everything into a JSON array
+	// so the order is kept
+	arr := make([]interface{}, 6)
+
+	// version: 0
+	arr[0] = 0
+
+	// pubkey
+	arr[1] = evt.PubKey
+
+	// created_at
+	arr[2] = int64(evt.CreatedAt)
+
+	// kind
+	arr[3] = int64(evt.Kind)
+
+	// tags
+	if evt.Tags != nil {
+		arr[4] = evt.Tags
+	} else {
+		arr[4] = make([]bool, 0)
+	}
+
+	// content
+	arr[5] = evt.Content
+
+	serialized := new(bytes.Buffer)
+
+	enc := json.NewEncoder(serialized)
+	enc.SetEscapeHTML(false)
+	_ = enc.Encode(arr)
+	return serialized.Bytes()[:serialized.Len()-1] // Encode add new line char
+}
+
+// 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
+	pubkey, err := bip340.ParsePublicKey(evt.PubKey)
+	if err != nil {
+		return false, fmt.Errorf("Event has invalid pubkey '%s': %w", evt.PubKey, err)
+	}
+
+	// check tags
+	for _, tag := range evt.Tags {
+		for _, item := range tag {
+			switch item.(type) {
+			case string, int64, float64, int, bool:
+				// fine
+			default:
+				// not fine
+				return false, fmt.Errorf("tag contains an invalid value %v", item)
+			}
+		}
+	}
+
+	s, err := hex.DecodeString(evt.Sig)
+	if err != nil {
+		return false, fmt.Errorf("signature is invalid hex: %w", err)
+	}
+	if len(s) != 64 {
+		return false, fmt.Errorf("signature must be 64 bytes, not %d", len(s))
+	}
+
+	var sig [64]byte
+	copy(sig[:], s)
+
+	hash := sha256.Sum256(evt.Serialize())
+	return bip340.Verify(pubkey, hash, sig)
+}
+
+// Sign signs an event with a given privateKey
+func (evt *Event) Sign(privateKey string) error {
+	h := sha256.Sum256(evt.Serialize())
+
+	s, err := bip340.ParsePrivateKey(privateKey)
+	if err != nil {
+		return fmt.Errorf("Sign called with invalid private key '%s': %w", privateKey, err)
+	}
+
+	aux := make([]byte, 32)
+	rand.Read(aux)
+	sig, err := bip340.Sign(s, h, aux)
+	if err != nil {
+		return err
+	}
+
+	evt.ID = hex.EncodeToString(h[:])
+	evt.Sig = hex.EncodeToString(sig[:])
+	return nil
+}