Refactor: modular architecture with shared packages

Major code reorganization to eliminate duplication and improve maintainability:

- Created pkg/crypto: shared cryptographic functions (padding, AES-GCM, ECDH, HMAC auth)
- Created pkg/protocol: unified message structures and JSON serialization
- Created pkg/identity: persistent identity management (load/save/generate)
- Created pkg/tor: Tor SOCKS5 proxy connection utilities

- Refactored server to use shared packages (cmd/server)
- Refactored CLI client with shared packages (cmd/cli-client)
- Refactored GUI client with shared packages (cmd/gui-client)
- Refactored web client with embedded HTML template (cmd/web-client)

Security improvements:
- Replaced math/rand with crypto/rand for randomDelay()
- Added proper error handling for crypto operations

Code reduction: eliminated ~500+ lines of duplicated code

1 files changed, 206 insertions, 0 deletions

diff --git a/pkg/protocol/messages.go b/pkg/protocol/messages.go
new file mode 100644
index 0000000..c8f6398
--- /dev/null
+++ b/pkg/protocol/messages.go
@@ -0,0 +1,206 @@
+// Package protocol defines the message structures and types for NoshiTalk communication.
+package protocol
+
+import (
+	"encoding/json"
+	"time"
+)
+
+// Message types
+const (
+	TypeMessage      = "message"
+	TypePrivate      = "private"
+	TypeSystem       = "system"
+	TypeError        = "error"
+	TypeUserList     = "user_list"
+	TypeUserJoin     = "user_join"
+	TypeUserLeave    = "user_leave"
+	TypeHandshake    = "handshake"
+	TypePublic       = "public"
+	TypeKeyRotation  = "key_rotation"
+	TypeFileOffer    = "file_offer"
+	TypeFileChunk    = "file_chunk"
+	TypeFileAccept   = "file_accept"
+	TypeFileReject   = "file_reject"
+	TypeFileComplete = "file_complete"
+)
+
+// Message represents a chat message.
+type Message struct {
+	From    string `json:"from"`
+	To      string `json:"to,omitempty"`
+	Content string `json:"content"`
+	Time    string `json:"time"`
+	Type    string `json:"type"`
+}
+
+// UserListMessage represents a list of online users.
+type UserListMessage struct {
+	Type  string   `json:"type"`
+	Users []string `json:"users"`
+	Time  string   `json:"time"`
+}
+
+// FileOfferMessage represents a file transfer offer.
+type FileOfferMessage struct {
+	Type        string `json:"type"`
+	From        string `json:"from"`
+	To          string `json:"to"`
+	FileID      string `json:"file_id"`
+	Filename    string `json:"filename"`
+	Size        int64  `json:"size"`
+	TotalChunks int    `json:"total_chunks"`
+	SHA256      string `json:"sha256"`
+	Compressed  bool   `json:"compressed"`
+	Time        string `json:"time"`
+}
+
+// FileChunkMessage represents a chunk of file data.
+type FileChunkMessage struct {
+	Type        string `json:"type"`
+	FileID      string `json:"file_id"`
+	ChunkIndex  int    `json:"chunk_index"`
+	TotalChunks int    `json:"total_chunks"`
+	Data        string `json:"data"`
+	Time        string `json:"time"`
+}
+
+// FileResponseMessage represents a response to a file transfer.
+type FileResponseMessage struct {
+	Type    string `json:"type"`
+	FileID  string `json:"file_id"`
+	From    string `json:"from"`
+	Status  string `json:"status"`
+	Message string `json:"message"`
+	SHA256  string `json:"sha256,omitempty"`
+	Time    string `json:"time"`
+}
+
+// KeyRotationMessage represents a key rotation request.
+type KeyRotationMessage struct {
+	Type      string `json:"type"`
+	PublicKey []byte `json:"public_key"`
+	Nonce     []byte `json:"nonce"`
+	Signature []byte `json:"signature"`
+	Time      string `json:"time"`
+}
+
+// NewMessage creates a new message with the current timestamp.
+func NewMessage(from, to, content, msgType string) *Message {
+	return &Message{
+		From:    from,
+		To:      to,
+		Content: content,
+		Time:    time.Now().Format("15:04:05"),
+		Type:    msgType,
+	}
+}
+
+// NewSystemMessage creates a new system message.
+func NewSystemMessage(content string) *Message {
+	return NewMessage("System", "", content, TypeSystem)
+}
+
+// NewErrorMessage creates a new error message.
+func NewErrorMessage(content string) *Message {
+	return NewMessage("System", "", content, TypeError)
+}
+
+// NewUserListMessage creates a new user list message.
+func NewUserListMessage(users []string) *UserListMessage {
+	return &UserListMessage{
+		Type:  TypeUserList,
+		Users: users,
+		Time:  time.Now().Format("15:04:05"),
+	}
+}
+
+// ToJSON marshals the message to JSON.
+func (m *Message) ToJSON() ([]byte, error) {
+	return json.Marshal(m)
+}
+
+// ToJSON marshals the user list message to JSON.
+func (m *UserListMessage) ToJSON() ([]byte, error) {
+	return json.Marshal(m)
+}
+
+// ToJSON marshals the file offer message to JSON.
+func (m *FileOfferMessage) ToJSON() ([]byte, error) {
+	return json.Marshal(m)
+}
+
+// ToJSON marshals the file chunk message to JSON.
+func (m *FileChunkMessage) ToJSON() ([]byte, error) {
+	return json.Marshal(m)
+}
+
+// ToJSON marshals the file response message to JSON.
+func (m *FileResponseMessage) ToJSON() ([]byte, error) {
+	return json.Marshal(m)
+}
+
+// ToJSON marshals the key rotation message to JSON.
+func (m *KeyRotationMessage) ToJSON() ([]byte, error) {
+	return json.Marshal(m)
+}
+
+// ParseMessage parses a JSON message and returns its type and raw data.
+func ParseMessage(data []byte) (string, map[string]interface{}, error) {
+	var generic map[string]interface{}
+	if err := json.Unmarshal(data, &generic); err != nil {
+		return "", nil, err
+	}
+
+	msgType, ok := generic["type"].(string)
+	if !ok {
+		msgType = TypeMessage
+	}
+
+	return msgType, generic, nil
+}
+
+// ParseAsMessage parses JSON data as a Message.
+func ParseAsMessage(data []byte) (*Message, error) {
+	var msg Message
+	if err := json.Unmarshal(data, &msg); err != nil {
+		return nil, err
+	}
+	return &msg, nil
+}
+
+// ParseAsUserList parses JSON data as a UserListMessage.
+func ParseAsUserList(data []byte) (*UserListMessage, error) {
+	var msg UserListMessage
+	if err := json.Unmarshal(data, &msg); err != nil {
+		return nil, err
+	}
+	return &msg, nil
+}
+
+// ParseAsFileOffer parses JSON data as a FileOfferMessage.
+func ParseAsFileOffer(data []byte) (*FileOfferMessage, error) {
+	var msg FileOfferMessage
+	if err := json.Unmarshal(data, &msg); err != nil {
+		return nil, err
+	}
+	return &msg, nil
+}
+
+// ParseAsFileChunk parses JSON data as a FileChunkMessage.
+func ParseAsFileChunk(data []byte) (*FileChunkMessage, error) {
+	var msg FileChunkMessage
+	if err := json.Unmarshal(data, &msg); err != nil {
+		return nil, err
+	}
+	return &msg, nil
+}
+
+// ParseAsFileResponse parses JSON data as a FileResponseMessage.
+func ParseAsFileResponse(data []byte) (*FileResponseMessage, error) {
+	var msg FileResponseMessage
+	if err := json.Unmarshal(data, &msg); err != nil {
+		return nil, err
+	}
+	return &msg, nil
+}