8.7 Explain how you would design a chat server. In particular, provide details about the various backend components, classes, and methods. What would be the hardest problems to solve?

這個簡易的聊天服務(wù)器功能十分的有限，畢竟只是針對面試題的，誰也無法在面試的有限時間內(nèi)設(shè)計出像QQ那樣強(qiáng)大的聊天工具，所以只是實現(xiàn)一些基本的功能即可，根據(jù)書上所述，包括如下功能：

1. 登陸和登出

2. 添加請求（發(fā)送，接受，和拒絕）

3. 更顯一個狀態(tài)消息

4. 建立私聊和群聊

5. 添加信息到私聊和群聊

enum UserStatusType { Offline, Away, Idle, Available, Busy }; enum RequestStatus { Unread, Read, Accepted, Rejected };class Date { public:Date() {}Date(int m, int d, int y): _month(m), _day(d), _year(y) {}private:int _month, _day, _year; };class Message { public:Message(string content, Date *date): _content(content), _date(date) {} string getContent() { return _content; }Date* getDate() { return _date; }private:string _content;Date *_date; };class Conversation { public:vector<Message*> getMessages() { return _messages; }bool addMessage(Message *m) { _messages.push_back(m);return true;} int getId() { return _id; }protected:vector<User*> _participants;int _id;vector<Message*> _messages; };class GroupChat: public Conversation { public:void removeParticipant(User *user) {for (vector<User*>::iterator it = _participants.begin(); it != _participants.end(); ++it) {if (*it == user) _participants.erase(it);}} void addParticipant(User *user) {_participants.push_back(user);} };class PrivateChat: public Conversation { public:PrivateChat(User *user1, User *user2) {_participants.push_back(user1);_participants.push_back(user2);} User* getOtherParticipant(User *primary) {if (_participants[0] == primary) {return _participants[1];} else if (_participants[1] == primary) {return _participants[0];}return nullptr;} };class AddRequest { public:AddRequest(User *from, User *to, Date *date): _fromUser(from), _toUser(to), _date(date) {_status = RequestStatus::Unread;} void setStatus(RequestStatus status) { _status = status; }RequestStatus getStatus() { return _status; }User* getFromUser() { return _fromUser; }User* getToUser() { return _toUser; }Date* getDate() { return _date; }private:User *_fromUser;User *_toUser;Date *_date;RequestStatus _status; };class UserStatus{ public:UserStatus(UserStatusType type, string message): _type(type), _message(message) {} UserStatusType getStatusType() { return _type; }string getMessage() { return _message; }private:string _message;UserStatusType _type; };class UserManager;class User { public:User(int id, string accountName, string fullName): _id(id), _accountName(accountName), _fullName(fullName) {}bool sendMessageToUser(User *to, string content) {PrivateChat *chat = _privateChats[to->getId()];if (chat == nullptr) {chat = new PrivateChat(this, to);_privateChats[to->getId()] = chat;}Message *message = new Message(content, new Date());return chat->addMessage(message);} bool sendMessageToGroupChat(int id, string content) {GroupChat *chat = _groupChats[id];if (chat != nullptr) {Message *message = new Message(content, new Date());return chat->addMessage(message);}return false;} void setStatus(UserStatus *status) { _status = status; }UserStatus* getStatus() { return _status; };bool addContact(User *user) {if (_contacts.find(user->getId()) != _contacts.end()) {return false;} else {_contacts[user->getId()] = user;return true;}} void receivedAddRequest(AddRequest *req) {int senderId = req->getFromUser()->getId();if (_receivedAddRequests.find(senderId) == _receivedAddRequests.end()) {_receivedAddRequests[senderId] = req;}} void sentAddRequest(AddRequest *req) {int receiverId = req->getFromUser()->getId();if (_sentAddRequests.find(receiverId) == _sentAddRequests.end()) {_sentAddRequests[receiverId] = req;}} void removeAddRequest(AddRequest *req) {if (req->getToUser() == this) {for (unordered_map<int, AddRequest*>::iterator it = _receivedAddRequests.begin(); it != _receivedAddRequests.end(); ++it) {if (it->second == req) _receivedAddRequests.erase(it);}} else if (req->getFromUser() == this) {for (unordered_map<int, AddRequest*>::iterator it = _sentAddRequests.begin(); it != _sentAddRequests.end(); ++it) {if (it->second == req) _sentAddRequests.erase(it);}}} void requestAddUser(string accountName) {UserManager::getInstance()->addUser(this, accountName);} void addConversation(PrivateChat *conversation) {User *otherUser = conversation->getOtherParticipant(this);_privateChats[otherUser->getId()] = conversation;}void addConversation(GroupChat *conversation) {_groupChats.push_back(conversation);}int getId() { return _id; }string getAccountName() { return _accountName; };string getFullName() { return _fullName; }private:int _id;UserStatus *_status = nullptr;unordered_map<int, PrivateChat*> _privateChats;vector<GroupChat*> _groupChats;unordered_map<int, AddRequest*> _receivedAddRequests;unordered_map<int, AddRequest*> _sentAddRequests;unordered_map<int, User*> _contacts;string _accountName;string _fullName; }; class UserManager { public:static UserManager* getInstance() {if (_instance == nullptr) _instance = new UserManager();return _instance;}void addUser(User *fromUser, string toAcountName) {User *toUser = _usersByAccountName[toAcountName];AddRequest *req = new AddRequest(fromUser, toUser, new Date());toUser->receivedAddRequest(req);fromUser->sentAddRequest(req);} void approveAddRequest(AddRequest *req) {req->setStatus(RequestStatus::Accepted);User *from = req->getFromUser();User *to = req->getToUser();from->addContact(to);to->addContact(from);} void rejectAddRequest(AddRequest *req) {req->setStatus(RequestStatus::Rejected);User *from = req->getFromUser();User *to = req->getToUser();from->removeAddRequest(req);to->removeAddRequest(req);}void userSignedOn(string accountName) {User *user = _usersByAccountName[accountName];if (user != nullptr) {user->setStatus(new UserStatus(UserStatusType::Available, ""));_onlineUsers[user->getId()] = user;}} void userSignedOff(string accountName) {User *user = _usersByAccountName[accountName];if (user != nullptr) {user->setStatus(new UserStatus(UserStatusType::Offline, ""));for (unordered_map<int, User*>::iterator it = _onlineUsers.begin(); it != _onlineUsers.end(); ++it) {if (it->first == user->getId()) _onlineUsers.erase(it);}}} private:static UserManager *_instance;unordered_map<int, User*> _usersById;unordered_map<string, User*> _usersByAccountName;unordered_map<int, User*> _onlineUsers; };

本文轉(zhuǎn)自博客園Grandyang的博客，原文鏈接：聊天服務(wù)器[CareerCup] 8.7 Chat Server ，如需轉(zhuǎn)載請自行聯(lián)系原博主。

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