removed readme and macos file

forgot to push

Makefile

@@ -10,7 +10,7 @@ BUILD_DIR = build
 SOURCES_CLIENT = client.cpp
 OBJS_CLIENT = $(addprefix $(BUILD_DIR)/,$(SOURCES_CLIENT:.cpp=.o))
 
-SOURCES_SERVER = server.cpp user.cpp user_handler.cpp mail.cpp
+SOURCES_SERVER = server.cpp user.cpp user_handler.cpp mail.cpp ip_ban.cpp
 OBJS_SERVER = $(addprefix $(BUILD_DIR)/,$(SOURCES_SERVER:.cpp=.o))
 
 all: $(BUILD_DIR) $(TARGET)

README.md

@@ -1,9 +0,0 @@
-# Documentation
-
-### File access
-
-Files are stored with their SHA-1 value as their name, with the first two digits being the subfolder name. For each user files belonging to them a represented in a .json file, which is managed by a central process; on runtime contents are stored in memory for thread safety.
-
-Potential issues:
-- Accessing actual files
-- Safing on exit

client/client.cpp

@@ -10,6 +10,8 @@
 #include <string>
 #include <string.h>
 
+#include <termios.h>
+
 ///////////////////////////////////////////////////////////////////////////////
 
 #define BUF 1024
@@ -18,7 +20,8 @@
 ///////////////////////////////////////////////////////////////////////////////
 
 enum commands {
-	SEND = 1,
+	LOGIN = 1,
+	SEND,
 	LIST,
 	READ,
 	DEL,
@@ -27,6 +30,7 @@ enum commands {
 
 inline bool isInteger(const std::string & s);
 void printUsage();
+const std::string getpass();
 
 int main(int argc, char **argv)
 {
@@ -107,10 +111,12 @@ int main(int argc, char **argv)
 	}
 	*/
 
+	bool isLoggedIn = false;
+    std::string loggedInUsername;
+
 	do {
-		printf("Please specify a command (SEND, LIST, READ, DEL, QUIT): ");
-		if (fgets(buffer, BUF - 1, stdin) != NULL)
-		{
+		printf("Please specify a command (%s): ", isLoggedIn ? "SEND, LIST, READ, DEL, QUIT" : "LOGIN, QUIT");
+		if (fgets(buffer, BUF - 1, stdin) != NULL) {
 			size = strlen(buffer);
 			if (buffer[size - 2] == '\r' && buffer[size - 1] == '\n')
 			{
@@ -124,19 +130,39 @@ int main(int argc, char **argv)
 			}
 
 			enum commands cmd;
-			if (strcmp(buffer, "SEND") == 0) cmd = SEND;
+			if (strcmp(buffer, "LOGIN") == 0) cmd = LOGIN;
+			else if (strcmp(buffer, "SEND") == 0) cmd = SEND;
 			else if (strcmp(buffer, "LIST") == 0) cmd = LIST;
 			else if (strcmp(buffer, "READ") == 0) cmd = READ;
 			else if (strcmp(buffer, "DEL") == 0) cmd = DEL;
 			else if (strcmp(buffer, "QUIT") == 0) break;
 
-			char username[BUF], msgNum[10];
+			char msgNum[10];
+			std::string username, password;
 
 			switch (cmd) {
+			case LOGIN: 
+                if (isLoggedIn) {
+                    printf("Already logged in as %s\n", loggedInUsername.c_str());
+                    continue;
+                }
+                printf("LDAP Username: ");
+                fgets(buffer, BUF - 1, stdin);
+                username = buffer;
+                username.pop_back(); 
+
+                printf("Password: ");
+                password = getpass();
+
+                snprintf(buffer, sizeof(buffer), "LOGIN\n%s\n%s\n", username.c_str(), password.c_str());
+                break;
+
 			case SEND:
-				char sender[BUF], receiver[BUF], subject[81], message[BUF * 10];
-				printf("Sender: ");
-				fgets(sender, BUF - 1, stdin);
+				if (!isLoggedIn) {
+					printf("Please login first.\n\n");
+					continue;;
+				}
+				char receiver[BUF], subject[81], message[BUF * 10];
 				printf("Receiver: ");
 				fgets(receiver, BUF - 1, stdin);
 				printf("Subject: ");
@@ -144,37 +170,42 @@ int main(int argc, char **argv)
 				printf("Message (send by typing \".\" in a seperate line): ");
 				char line[BUF];
 				message[0] = '\0';
-				while (true)
-				{
+				while (true) {
 					fgets(line, BUF - 1, stdin);
 					if (strcmp(line, ".\n") == 0)
 						break;
 					strcat(message, line);
 				}
-				snprintf(buffer, sizeof(buffer), "SEND\n%s%s%s%s.\n", sender, receiver, subject, message);
-				break;
+				snprintf(buffer, sizeof(buffer), "SEND\n%s%s%s.\n",  receiver, subject, message);
+       			break;
 			case LIST:
-				char username[BUF];
-				printf("Username: ");
-				fgets(username, BUF - 1, stdin);
-				snprintf(buffer, sizeof(buffer), "LIST\n%s", username);
-				break;
+				if (!isLoggedIn) {
+            		printf("Please login first.\n");
+            		continue;
+            	}
+            	snprintf(buffer, sizeof(buffer), "LIST\n");
+				printf("%s", buffer);
+        		break;
 			case READ:
-				printf("Username: ");
-				fgets(username, BUF - 1, stdin);
-				printf("Message Number: ");
-				fgets(msgNum, 9, stdin);
-				snprintf(buffer, sizeof(buffer), "READ\n%s%s", username, msgNum);
-				break;
+				if (!isLoggedIn) {
+            		printf("Please login first.\n");
+            		continue;
+            	}
+            	printf("Message Number: ");
+            	fgets(msgNum, 9, stdin);
+            	snprintf(buffer, sizeof(buffer), "READ\n%s", msgNum);
+        		break;
 			case DEL:
-				printf("Username: ");
-				fgets(username, BUF - 1, stdin);
-				printf("Message Number: ");
-				fgets(msgNum, 9, stdin);
-				snprintf(buffer, sizeof(buffer), "DEL\n%s%s", username, msgNum);
-				break;
+				if (!isLoggedIn) {
+            		printf("Please login first.\n");
+            		continue;
+            	}
+            	printf("Message Number: ");
+            	fgets(msgNum, 9, stdin);
+            	snprintf(buffer, sizeof(buffer), "DEL\n%s", msgNum);
+       			break;
 			case QUIT:
-				// will break out of loop before quit
+				// should never be reached;
 				break;
 			}
 		
@@ -227,6 +258,12 @@ int main(int argc, char **argv)
 			{
 				buffer[size] = '\0';
 				printf("<< %s\n", buffer); // ignore error
+
+				if (cmd == LOGIN && strcmp("OK\n", buffer) == 0) {
+					loggedInUsername = username;
+             	    isLoggedIn = true;
+				}
+
 				/*if (strcmp("OK", buffer) != 0) // needs proper verification, since responses vary between commands
 				{
 					fprintf(stderr, "<< Server error occured, abort\n");
@@ -270,3 +307,75 @@ void printUsage()
 {
 	printf("Usage: <twmailer-server [host/ip (default: 127.0.0.1)] [port]>\n");
 }
+
+int getch()
+{
+    int ch;
+    // https://man7.org/linux/man-pages/man3/termios.3.html
+    struct termios t_old, t_new;
+
+    // https://man7.org/linux/man-pages/man3/termios.3.html
+    // tcgetattr() gets the parameters associated with the object referred
+    //   by fd and stores them in the termios structure referenced by
+    //   termios_p
+    tcgetattr(STDIN_FILENO, &t_old);
+    
+    // copy old to new to have a base for setting c_lflags
+    t_new = t_old;
+
+    // https://man7.org/linux/man-pages/man3/termios.3.html
+    //
+    // ICANON Enable canonical mode (described below).
+    //   * Input is made available line by line (max 4096 chars).
+    //   * In noncanonical mode input is available immediately.
+    //
+    // ECHO   Echo input characters.
+    t_new.c_lflag &= ~(ICANON | ECHO);
+    
+    // sets the attributes
+    // TCSANOW: the change occurs immediately.
+    tcsetattr(STDIN_FILENO, TCSANOW, &t_new);
+
+    ch = getchar();
+
+    // reset stored attributes
+    tcsetattr(STDIN_FILENO, TCSANOW, &t_old);
+
+    return ch;
+}
+
+const std::string getpass()
+{
+    int show_asterisk = 0;
+
+    const char BACKSPACE = 127;
+    const char RETURN = 10;
+
+    unsigned char ch = 0;
+    std::string password;
+
+    while ((ch = getch()) != RETURN)
+    {
+        if (ch == BACKSPACE)
+        {
+            if (password.length() != 0)
+            {
+                if (show_asterisk)
+                {
+                    printf("\b \b"); // backslash: \b
+                }
+                password.resize(password.length() - 1);
+            }
+        }
+        else
+        {
+            password += ch;
+            if (show_asterisk)
+            {
+                printf("*");
+            }
+        }
+    }
+    printf("\n");
+    return password;
+}

server/ip_ban.cpp

@@ -0,0 +1,59 @@
+#include "ip_ban.h"
+
+#include <chrono>
+#include <filesystem>
+#include <iterator>
+#include <fstream>
+
+ip_ban::ip_ban() : m_ban()
+{
+	this->file = fs::path();
+}
+
+ip_ban::~ip_ban()
+{
+	if (this->file.empty())
+		return;
+
+	json jsonfile = this->ban_list;
+
+	std::ofstream ofs(this->file, std::ofstream::out | std::ofstream::trunc);
+	ofs << jsonfile.dump();
+}
+
+void ip_ban::loadFile(fs::path file)
+{
+	this->file = file;
+
+	if (fs::exists(file)) {
+		std::ifstream ifs(file);
+		this->ban_list = json::parse(ifs);
+	}
+}
+
+void ip_ban::failedAttempt(std::string username, std::string ip)
+{
+	std::unique_lock<std::shared_mutex> lock(this->m_ban);
+
+	std::map<std::string, std::pair<std::map<std::string, ushort>, time_t>>::iterator it = this->ban_list.insert({ip, {{}, 0}}).first;
+	if (++it->second.first.insert({username, 0}).first->second >= MAX_ATTEMPTS) { // increase attempt count && check if reached MAX_ATTEMPTS
+		for (auto& pair : it->second.first ) { // reset attempts to 0 for all names
+			pair.second = 0;
+		}
+		(*it).second.second = std::chrono::system_clock::to_time_t(std::chrono::system_clock::now()) + BAN_TIME; // set unban time to current time + BAN_TIME seconds
+	}
+}
+
+void ip_ban::success(std::string ip)
+{
+	std::unique_lock<std::shared_mutex> lock(this->m_ban);
+	this->ban_list.erase(ip);
+}
+
+bool ip_ban::checkBanned(std::string ip)
+{
+	std::shared_lock<std::shared_mutex> lock(this->m_ban);
+
+	std::map<std::string, std::pair<std::map<std::string, ushort>, time_t>>::iterator it;
+	return (it = this->ban_list.find(ip)) != this->ban_list.end() && (*it).second.second > std::chrono::system_clock::to_time_t(std::chrono::system_clock::now());
+}

server/ip_ban.h

@@ -0,0 +1,48 @@
+#pragma once
+
+#include <filesystem>
+#include <map>
+#include <mutex>
+#include <shared_mutex>
+#include <string>
+#include <chrono>
+
+#include <nlohmann/json.hpp>
+
+#define BAN_TIME 60
+#define MAX_ATTEMPTS 3
+
+namespace fs = std::filesystem;
+
+using json = nlohmann::json;
+
+class ip_ban {
+public:
+
+	static ip_ban& getInstance() {
+		static ip_ban instance;
+		return instance;
+	};
+
+	ip_ban(ip_ban const&) = delete;
+	ip_ban(ip_ban&&) = delete;
+	ip_ban& operator=(ip_ban const&) = delete;
+	ip_ban& operator=(ip_ban &&) = delete;
+
+	void loadFile(fs::path file);
+
+	void failedAttempt(std::string username, std::string ip);
+	void success(std::string ip);
+	bool checkBanned(std::string ip);
+
+protected:
+
+	ip_ban();
+	~ip_ban();
+
+	std::shared_mutex m_ban;
+
+	fs::path file;
+	std::map<std::string, std::pair<std::map<std::string, ushort>, time_t>> ban_list;
+	
+};

server/mail.cpp

@@ -1,5 +1,4 @@
 #include "mail.h"
-#include <mutex>
 
 mail::mail(std::string filename, std::string subject, std::string sender) :
 	filename(filename),

server/server.cpp

@@ -1,8 +1,15 @@
+#include "ip_ban.h"
 #include "user.h"
 #include "user_handler.h"
 
 #include "mail.h"
 
+
+#include <ldap.h>
+
+
+#include <algorithm>
+#include <ranges>
 #include <cstddef>
 #include <cstdio>
 #include <cstdlib>
@@ -21,7 +28,6 @@
 #include <string>
 #include <thread>
 #include <vector>
-#include <algorithm>
 
 #include <locale>
 
@@ -31,6 +37,9 @@
 #include <arpa/inet.h>
 #include <signal.h>
 #include <openssl/sha.h>
+#include <sys/socket.h>
+#include <sys/types.h>
+#include <unistd.h>
 
 #define BUF 1024
 
@@ -49,7 +58,7 @@ bool abortRequested = false;
 int create_socket = -1;
 int new_socket = -1;
 
-std::vector<pthread_t> threads;
+// std::vector<pthread_t> threads;
 
 void printUsage();
 inline bool isInteger(const std::string & s);
@@ -63,15 +72,23 @@ std::string getSha1(const std::string& p_arg);
 void *clientCommunication(void *data);
 void signalHandler(int sig);
 
-std::string cmdLOGIN(std::vector<std::string>& received);
-std::string cmdSEND(std::vector<std::string>& received);
-std::string cmdLIST(std::vector<std::string>& received);
-std::string cmdREAD(std::vector<std::string>& received);
-std::string cmdDEL(std::vector<std::string>& received);
+std::string cmdLOGIN(std::vector<std::string>& received, std::string& loggedInUsername, const std::string& ip);
+std::string cmdSEND(std::vector<std::string>& received, const std::string& loggedInUsername);
+std::string cmdLIST(std::vector<std::string>& received, const std::string& loggedInUsername);
+std::string cmdREAD(std::vector<std::string>& received, const std::string& loggedInUsername);
+std::string cmdDEL(std::vector<std::string>& received, const std::string& loggedInUsername);
+
 
 inline void exiting();
 inline std::string read_file(std::string_view path);
 
+struct args
+{
+    int socket;
+    std::string ip;
+    fs::path spool_dir;
+};
+
 int main (int argc, char* argv[])
 {
 	if (argc < 3 ||	
@@ -97,6 +114,8 @@ int main (int argc, char* argv[])
 
 	user_handler::getInstance().setSpoolDir(spool_dir);
 
+	ip_ban::getInstance().loadFile(spool_dir / "bans.json");
+
 	std::atexit(exiting);
 
 	char* p;
@@ -172,8 +191,9 @@ int main (int argc, char* argv[])
 				 ntohs(cliaddress.sin_port));
 		// clientCommunication(&new_socket); // returnValue can be ignored
 		pthread_t tid;
-		pthread_create(&tid, NULL, clientCommunication, (void *)new int(new_socket));
-		threads.push_back(tid);
+		pthread_create(&tid, NULL, clientCommunication, static_cast<void *>(new args{new_socket, inet_ntoa(cliaddress.sin_addr), spool_dir}));
+		// threads.push_back(tid);
+		pthread_detach(tid);
 		new_socket = -1;
 	}
 
@@ -210,12 +230,17 @@ void printUsage()
 
 void *clientCommunication(void *data)
 {
+	args* args = (struct args*) data;
+
 	char buffer[BUF];
 	int size;
-	int *current_socket = (int *)data;
+	int *current_socket = &args->socket;
+	std::string ip = args->ip;
 
 	std::string incomplete_message = "";
 
+	std::string loggedInUsername;
+
 	do {
 		std::string response;
 
@@ -251,7 +276,6 @@ void *clientCommunication(void *data)
 			lines.push_back(line);
 		}
 
-
 		enum commands cmd;
 
 		// can't wait for reflections (maybe c++26?)
@@ -265,27 +289,29 @@ void *clientCommunication(void *data)
 
 		switch (cmd) {
 		case LOGIN:
-			response = cmdLOGIN(lines);
+			response = cmdLOGIN(lines, loggedInUsername, ip);
 			break;
 		case SEND:
 			if (lines.size() < 5 || lines.back().compare(".") != 0) {
-				incomplete_message = buffer;
-				continue; // issues if command end is never received
-			}
-
-			response = cmdSEND(lines);
-			break;
+            	incomplete_message = buffer;
+            	continue; 
+        		}
+        	response = cmdSEND(lines, loggedInUsername);
+        	break;
 		case LIST:
-			response = cmdLIST(lines);
+			response = cmdLIST(lines, loggedInUsername);
 			break;
 		case READ:
-			response = cmdREAD(lines);
+			response = cmdREAD(lines, loggedInUsername);
 			break;
 		case DEL:
-			response = cmdDEL(lines);
+			response = cmdDEL(lines, loggedInUsername);
 			break;
 		case QUIT:
 			break;
+		default:
+			// invalid command
+			response = "ERR\n";
 		}
 
 		if (send(*current_socket, response.c_str(), response.size(), 0) == -1) {
@@ -308,7 +334,7 @@ void *clientCommunication(void *data)
 		*current_socket = -1;
 	}
 
-	delete(current_socket);
+	delete(args);
 	return NULL;
 }
 
@@ -374,104 +400,157 @@ std::string getSha1(const std::string& str)
 
 inline void exiting()
 {
-    for (auto& thread : threads) {
+    /*for (auto& thread : threads) {
     	pthread_join(thread, NULL);
-    }
+    }*/
 
 	user_handler::getInstance().saveAll();
 	printf("Saving...	\n");
 }
 
-std::string cmdLOGIN(std::vector<std::string>& received)
+std::string cmdLOGIN(std::vector<std::string>& received, std::string& loggedInUsername, const std::string& ip)
 {
-	// code
-	return "";
-}	
+	if (received.size() < 3) {
+        return "ERR\n";
+    }
 
-std::string cmdSEND(std::vector<std::string>& received)
-{
-	// TODO: change sender to be implicit from currently logged in; replace received.at(1) and move all other received one forward
-	if (received.at(3).length() > 80)
+	const char* ldapUri = "ldap://ldap.technikum-wien.at:389";
+    const int ldapVersion = LDAP_VERSION3;
+    LDAP* ldapHandle;
+    int rc = ldap_initialize(&ldapHandle, ldapUri);
+    if (rc != LDAP_SUCCESS) {
+        return "ERR\n";
+    }
+
+	rc = ldap_set_option(ldapHandle, LDAP_OPT_PROTOCOL_VERSION, &ldapVersion);
+    if (rc != LDAP_OPT_SUCCESS) {
+        ldap_unbind_ext_s(ldapHandle, NULL, NULL);
+        return "ERR\n"; 
+    }
+
+	rc = ldap_start_tls_s(ldapHandle, NULL, NULL);
+    if (rc != LDAP_SUCCESS) {
+        ldap_unbind_ext_s(ldapHandle, NULL, NULL);
+        return "ERR\n";
+    }
+
+	std::string ldapBindUser = "uid=" + received.at(1) + ",ou=people,dc=technikum-wien,dc=at";
+    std::string ldapBindPassword = received.at(2);
+
+	BerValue bindCredentials;
+    bindCredentials.bv_val = (char*) ldapBindPassword.c_str();
+    bindCredentials.bv_len = ldapBindPassword.length();
+    rc = ldap_sasl_bind_s(ldapHandle, ldapBindUser.c_str(), LDAP_SASL_SIMPLE, &bindCredentials, NULL, NULL, NULL);
+    if (rc != LDAP_SUCCESS) {
+    	ip_ban::getInstance().failedAttempt(received.at(1), ip);
+        ldap_unbind_ext_s(ldapHandle, NULL, NULL);
+        return "ERR\n";
+    }
+
+    if (ip_ban::getInstance().checkBanned(ip)) {
+		ldap_unbind_ext_s(ldapHandle, NULL, NULL);
 		return "ERR\n";
+    }
 
-	if (received.size() > 5) {
-		for (std::vector<std::string>::iterator it = received.begin() + 5; it != received.end() && *it != "."; it++) {
-			received.at(4).append("\n").append(*it);
-		}
-	}
-
-	user_handler::getInstance().getOrCreateUser(received.at(2))->addMail(
-		new struct mail(saveToFile(user_handler::getInstance().getSpoolDir()/"messages", received.at(4)), received.at(3), received.at(1))
-	);
-
-	return "OK\n"; // TODO: error handling
-}
-
-std::string cmdLIST(std::vector<std::string>& received)
-{
-	// TODO: change user to be implicit from currently logged in; replace received.at(1)
-	maillist inbox;
-	user* user;
-
-	if (received.size() < 2 || (user = user_handler::getInstance().getUser(received.at(1))) == nullptr)
-		return "0\n";
-		
-	inbox = user->getMails();
-	std::string response = std::to_string(std::count_if(inbox.begin(), inbox.end(), [](auto& mail) { return !mail->deleted; })) + "\n";
-	for ( auto mail : inbox ) {
-		if (mail->deleted)
-			continue;
-		response.append(std::to_string(mail->id)).append(": ").append(mail->subject).append("\n");
-	}
-
-	return response;
-}
-
-std::string cmdREAD(std::vector<std::string>& received)
-{
-	// TODO: change user to be implicit from currently logged in; replace received.at(1) and move received.at(2) one forward
-	std::string response = "OK\n";
-
-	user* user;
-	mail* mail;
-
-	char* p;
-
-	if(received.size() < 3 ||
-		!isInteger(received.at(2)) ||
-		(user = user_handler::getInstance().getUser(received.at(1))) == nullptr ||
-		(mail = user->getMail(strtoul(received.at(2).c_str(), &p, 10))) == nullptr ||
-		mail->deleted)
-		return "ERR\n";
-
-	try {
-		std::string path_str = user_handler::getInstance().getSpoolDir()/"messages"/mail->filename;
-		std::unique_lock<std::mutex> lock(mail->m_file);
-		response.append(read_file(path_str)).append("\n");
-	}
-	catch (...) { // TODO: more specific error handling - then again, it will respond with ERR either way
-		return "ERR\n";
-	}
-
-	return response;
-}
-
-std::string cmdDEL(std::vector<std::string>& received)
-{
-	// TODO: change user to be implicit from currently logged in; replace received.at(1) and move received.at(2) one forward
-	user* user;
-
-	char* p;
-
-	if(received.size() < 3 ||
-		!isInteger(received.at(2)) ||
-		(user = user_handler::getInstance().getUser(received.at(1))) == nullptr ||
-		(user->delMail(strtoul(received.at(2).c_str(), &p, 10))) == false)
-		return "ERR\n";
+    loggedInUsername = received.at(1);
+    ip_ban::getInstance().success(ip);
+	ldap_unbind_ext_s(ldapHandle, NULL, NULL);
 	
 	return "OK\n";
 }	
 
+
+std::string cmdSEND(std::vector<std::string>& received, const std::string& loggedInUsername) {
+
+    if (loggedInUsername.empty() || received.size() < 4) {
+        return "ERR\n";
+    }
+
+	std::string receiver = received.at(1);
+    std::string subject = received.at(2);
+    std::string message = received.at(3);
+
+	if (subject.length() > 80) {
+        return "ERR\n";
+    }
+
+	user_handler::getInstance().getOrCreateUser(receiver)->addMail(
+        new struct mail(saveToFile(user_handler::getInstance().getSpoolDir()/"messages", message), subject, loggedInUsername)
+    );
+
+	return "OK\n"; // TODO: error handling
+
+}
+
+std::string cmdLIST(std::vector<std::string>& received, const std::string& loggedInUsername) {
+    if (loggedInUsername.empty()) {
+    	printf("%s %zu\n", loggedInUsername.c_str(), received.size());
+        return "ERR\n";
+    }
+
+    user* currentUser = user_handler::getInstance().getUser(loggedInUsername);
+    if (currentUser == nullptr) {
+        return "0\n";
+    }
+
+    maillist inbox = currentUser->getMails();
+    std::string response = std::to_string(std::count_if(inbox.begin(), inbox.end(), [](auto& mail) { return !mail->deleted; })) + "\n";
+    for (auto& mail : inbox) {
+        if (!mail->deleted) {
+            response.append(std::to_string(mail->id)).append(": ").append(mail->subject).append("\n");
+        }
+    }
+
+    return response;
+}
+
+std::string cmdREAD(std::vector<std::string>& received, const std::string& loggedInUsername) {
+    if (loggedInUsername.empty() || received.size() < 2) {
+    	printf("%s %zu\n", loggedInUsername.c_str(), received.size());
+        return "ERR\n";
+    }
+
+    char* p;
+    long mailId = strtol(received.at(1).c_str(), &p, 10);
+    if (*p != 0) { 
+        return "ERR\n";
+    }
+
+    user* currentUser = user_handler::getInstance().getUser(loggedInUsername);
+    if (currentUser == nullptr) {
+        return "ERR\n";
+    }
+
+    mail* selectedMail = currentUser->getMail(mailId);
+    if (selectedMail == nullptr || selectedMail->deleted) {
+        return "ERR\n";
+    }
+
+    std::string mailContent = read_file((user_handler::getInstance().getSpoolDir() / "messages" / selectedMail->filename).string());
+    return "OK\n" + mailContent;
+}
+
+std::string cmdDEL(std::vector<std::string>& received, const std::string& loggedInUsername) {
+    if (loggedInUsername.empty() || received.size() < 2) {
+    	printf("%s %zu\n", loggedInUsername.c_str(), received.size());
+        return "ERR\n";
+    }
+
+    char* p;
+    long mailId = strtol(received.at(1).c_str(), &p, 10);
+    if (*p != 0) { 
+        return "ERR\n";
+    }
+
+    user* currentUser = user_handler::getInstance().getUser(loggedInUsername);
+    if (currentUser == nullptr) {
+        return "ERR\n";
+    }
+
+    bool deleteResult = currentUser->delMail(mailId);
+    return deleteResult ? "OK\n" : "ERR\n";
+}
+
 // https://stackoverflow.com/a/116220
 inline std::string read_file(std::string_view path)
 {
@@ -500,5 +579,6 @@ bool ichar_equals(char a, char b)
 
 bool iequals(std::string_view lhs, std::string_view rhs)
 {
-    return std::ranges::equal(lhs, rhs, ichar_equals);
+    // return std::ranges::equal(lhs, rhs, ichar_equals);
+    return std::equal(lhs.begin(), lhs.end(), rhs.begin(), ichar_equals);
 }