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server.cpp
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server.cpp
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#include <algorithm>
#include <cctype>
#include <cstddef>
#include <exception>
#include <iostream>
#include <optional>
#include <sstream>
#include <stdexcept>
#include <string>
#include <string_view>
#include <unordered_map>
#include <utility>
#include <vector>
#include "protocol.h"
#include "receive.h"
#include "socket.h"
class Username {
private:
std::string value;
explicit Username(std::string_view s) : value(s) {}
public:
static std::optional<Username> parse(std::string_view s) {
// User names should be of the form [a-z0-9-_]{3,30}.
if (s.size() < 3 || s.size() > 30) {
return std::nullopt;
}
const auto pos_invalid = std::find_if(s.begin(), s.end(), [](int c) {
return !(islower(c) || isdigit(c) || c == '-' || c == '_');
});
if (pos_invalid != s.end()) {
return std::nullopt;
}
// User name also can't be "bc" but that case is handled by the length check.
return Username(s);
}
operator std::string_view() const noexcept { return value; }
};
class Registry {
private:
// INVARIANTS:
// 1. All information in id_to_user_name and user_name_to_client must correspond to a client
// inside m_clients.
// 2. user_name_to_client contains views of Usernames inside id_to_user_name. Handle with care
// to not reference invalid memory.
// 3. Unregistered clients do not have any information in id_to_user_name or
// user_name_to_client.
//
// Note: we do linear searches on m_clients. This should not be a performance issue for our
// use case, given that it is not expected to have a lot of clients, and makes working with
// the server abstraction easier and more performant – if we were to store it in a map,
// we'd have to construct a vector for each call to poll().
std::vector<ServerClient> m_clients;
std::unordered_map<ServerClient::ID, Username> id_to_user_name;
std::unordered_map<std::string_view, ServerClient> user_name_to_client;
auto find_by_id(ServerClient::ID id) const noexcept {
return std::find_if(m_clients.begin(), m_clients.end(), [id](const ServerClient& c) {
return c.id() == id;
});
}
public:
void add_unregistered(ServerClient client) {
const auto it = find_by_id(client.id());
if (it != m_clients.end()) {
throw std::logic_error("tried to add already added client");
}
m_clients.push_back(client);
}
bool is_registered(ServerClient::ID id) { return id_to_user_name.contains(id); }
std::optional<std::reference_wrapper<Username>> get_user_name(ServerClient::ID id) {
const auto it = id_to_user_name.find(id);
if (it == id_to_user_name.end()) {
return std::nullopt;
}
return it->second;
}
std::optional<ServerClient> get_client(const Username& user_name) {
const auto it = user_name_to_client.find(user_name);
if (it == user_name_to_client.end()) {
return std::nullopt;
}
return it->second;
}
bool register_client(ServerClient::ID id, Username user_name) {
if (user_name_to_client.contains(user_name)) {
return false;
}
const auto it = find_by_id(id);
if (it == m_clients.end() || is_registered(it->id())) {
throw std::logic_error("tried to register inexistent or already registered client");
}
id_to_user_name.emplace(std::make_pair(id, std::move(user_name)));
user_name_to_client[id_to_user_name.at(id)] = *it;
return true;
}
void remove(ServerClient::ID id) {
const auto it = find_by_id(id);
if (it == m_clients.end()) {
throw std::logic_error("tried to remove inexistent client");
}
const auto c = *it;
m_clients.erase(it);
if (!is_registered(id)) {
return;
}
const auto& user_name = id_to_user_name.at(id);
user_name_to_client.erase(user_name);
id_to_user_name.erase(id);
}
std::span<ServerClient> clients() noexcept { return m_clients; }
};
static void send_to_all_registered_except(
Registry&, ServerClient::ID, std::string_view, std::vector<std::byte>&);
static void remove_and_broadcast(
ServerClient::ID to_remove, Registry& reg, bool is_unexpected, std::vector<std::byte>& buf) {
const auto user_name = reg.get_user_name(to_remove);
if (!user_name.has_value()) {
// No need to announce if the client was not registered, as no clients can communicate with
// it.
return;
}
std::ostringstream out;
out << "\n"
<< std::string_view(user_name->get()) << " has "
<< (is_unexpected ? "been disconnected" : "left") << ".\n> ";
send_to_all_registered_except(reg, to_remove, out.str(), buf);
reg.remove(to_remove);
}
static bool
send_or_remove(ServerClient& c, Registry& reg, std::string_view msg, std::vector<std::byte>& buf) {
buf.resize(0);
proto::pack(msg, buf);
try {
c.send(buf);
return true;
} catch (const SocketError&) {
remove_and_broadcast(c.id(), reg, true, buf);
return false;
}
}
static void send_to_all_registered_except(
Registry& reg, ServerClient::ID omit, std::string_view msg, std::vector<std::byte>& buf) {
buf.resize(0);
proto::pack(msg, buf);
std::vector<ServerClient::ID> failed;
for (auto& client : reg.clients()) {
if (client.id() == omit || !reg.is_registered(client.id())) {
continue;
}
try {
client.send(buf);
} catch (const SocketError&) {
failed.push_back(client.id());
}
}
for (auto id : failed) {
remove_and_broadcast(id, reg, true, buf);
}
}
class ServerClientNonBlockGuard {
private:
ServerClient client;
public:
ServerClientNonBlockGuard(ServerClient& c) : client(c) { client.set_blocking(false); }
~ServerClientNonBlockGuard() { client.set_blocking(true); }
};
static std::optional<std::string>
recv_or_remove(ServerClient& client, Registry& reg, std::vector<std::byte>& buf) try {
ReceiveResult recv;
{
ServerClientNonBlockGuard g(client);
recv = receive(client, buf);
}
if (!recv.is_connected) {
remove_and_broadcast(client.id(), reg, true, buf);
return std::nullopt;
}
if (!recv.message.has_value()) {
send_or_remove(client, reg, "I couldn't quite get that. Can you say it again?\n> ", buf);
return std::nullopt;
}
if (recv.message == "") { // disconnect
remove_and_broadcast(client.id(), reg, false, buf);
return std::nullopt;
}
return std::move(recv.message);
} catch (const SocketError& e) {
if (e.would_block()) {
return std::nullopt;
}
throw e;
}
static void handle_new_client(ServerClient& client, Registry& reg, std::vector<std::byte>& buf) {
reg.add_unregistered(client);
send_or_remove(client, reg, "Hi there! Please give us your username.\n> ", buf);
}
static void
handle_unregistered_client_data(ServerClient& client, Registry& reg, std::vector<std::byte>& buf) {
auto recv = recv_or_remove(client, reg, buf);
if (!recv.has_value()) {
return;
}
auto maybe_user_name = Username::parse(*recv);
if (!maybe_user_name.has_value()) {
send_or_remove(client, reg, "That's not a valid user name. Try again!\n> ", buf);
return;
}
if (!reg.register_client(client.id(), std::move(*maybe_user_name))) {
send_or_remove(client, reg, "This user name is taken. Try again!\n> ", buf);
return;
}
std::ostringstream out;
out << "Registered!\nCurrently active users:\n";
for (const auto& c : reg.clients()) {
const auto user_name = reg.get_user_name(c.id());
if (!user_name.has_value()) {
continue;
}
out << " - " << std::string_view(user_name->get());
if (c.id() == client.id()) {
out << " (you)";
}
out << '\n';
}
out << "To send a message to someone, type \"<username> <your message>\"\n"
"To send a message to everyone, type \"bc <your message>\"\n"
"Happy chatting!\n\n"
"> ";
if (!send_or_remove(client, reg, out.str(), buf)) {
return;
}
out.str("");
out << '\n' << std::string_view(reg.get_user_name(client.id())->get()) << " is here!\n> ";
send_to_all_registered_except(reg, client.id(), out.str(), buf);
}
class indent {
private:
std::string_view s;
public:
explicit indent(std::string_view s) : s(s) {}
friend std::ostream& operator<<(std::ostream& os, const indent& i) {
std::string_view s = i.s;
for (std::size_t pos_lf; (pos_lf = s.find('\n')) != std::string::npos;) {
os << " " << s.substr(0, pos_lf + 1);
s = s.substr(pos_lf + 1);
}
return os << " " << s;
}
};
static void handle_broadcast(
ServerClient& from, Registry& reg, std::string_view msg, std::vector<std::byte>& buf) {
const auto user_name = reg.get_user_name(from.id());
std::ostringstream out;
out << '\n' << std::string_view(user_name->get()) << " to everyone:\n" << indent(msg) << "\n> ";
send_to_all_registered_except(reg, from.id(), out.str(), buf);
send_or_remove(from, reg, "> ", buf);
}
static void handle_private(
ServerClient& from, ServerClient& to, Registry& reg, std::string_view msg,
std::vector<std::byte>& buf) {
const auto user_name = reg.get_user_name(from.id());
std::ostringstream out("\n");
if (from.id() == to.id()) {
out << "Note to self:";
} else {
out << std::string_view(user_name->get()) << " to you:";
}
out << '\n' << indent(msg) << "\n> ";
send_or_remove(to, reg, out.str(), buf);
if (from.id() != to.id()) {
send_or_remove(from, reg, "> ", buf);
}
}
static void
handle_registered_client_data(ServerClient& client, Registry& reg, std::vector<std::byte>& buf) {
auto recv = recv_or_remove(client, reg, buf);
if (!recv.has_value()) {
return;
}
const auto pos_blank = recv->find(' ');
if (pos_blank == std::string::npos) {
send_or_remove(client, reg, "Can't send empty message. Try again!\n> ", buf);
return;
}
std::string_view user_name_in(recv->data(), pos_blank);
std::string_view msg(recv->data() + pos_blank + 1, recv->size() - pos_blank - 1);
if (user_name_in == "bc") {
handle_broadcast(client, reg, msg, buf);
return;
}
const auto maybe_user_name = Username::parse(user_name_in);
if (!maybe_user_name.has_value()) {
send_or_remove(client, reg, "Invalid user name. Try again!\n> ", buf);
return;
}
auto maybe_to = reg.get_client(*maybe_user_name);
if (!maybe_to.has_value()) {
send_or_remove(client, reg, "This user doesn't exist. Misspelled?\n> ", buf);
return;
}
handle_private(client, *maybe_to, reg, msg, buf);
}
int main(int argc, char** argv) try {
if (argc < 2) {
std::cerr << "termchat: no port specified\n";
return 1;
}
const unsigned short port = std::stoul(argv[1]);
Server server(port);
Registry registry;
std::vector<ServerPollResult> polled;
std::vector<std::byte> buf;
while (true) {
server.poll(registry.clients(), polled);
for (auto& [client, status] : polled) {
switch (status) {
case ServerClientStatus::New:
handle_new_client(client, registry, buf);
case ServerClientStatus::PendingData:
if (registry.is_registered(client.id())) {
handle_registered_client_data(client, registry, buf);
} else {
handle_unregistered_client_data(client, registry, buf);
}
}
}
}
} catch (const std::exception& e) {
std::cerr << e.what() << '\n';
}