Add complete POP3 protocol implementation
Co-authored-by: setoelkahfi <1797197+setoelkahfi@users.noreply.github.com>
copilot-swe-agent[bot] committed
Oct 13, 2025 at 16:08 UTC
991f19be60ce8302c392be3be8705cae71dac017
6 files changed
+417
-7
README.md
+55
-6
@@ -1,35 +1,72 @@
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-# SMTP Server
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+# Mail Server (SMTP + POP3)
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-A basic SMTP server implementation in Rust with TLS/STARTTLS support.
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+A basic mail server implementation in Rust with SMTP and POP3 protocol support, featuring TLS/STARTTLS support.
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## Features
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+### SMTP Server
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- ✅ Basic SMTP protocol support (HELO/EHLO, MAIL FROM, RCPT TO, DATA, QUIT)
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- ✅ STARTTLS support for secure connections
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- ✅ Self-signed certificate generation for TLS
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-- ✅ Async/await with Tokio runtime
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-- ✅ Structured logging with tracing
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- ✅ Multiple recipient support
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- ✅ Command validation and error handling
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+### POP3 Server
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+- ✅ Complete POP3 protocol implementation (RFC 1939)
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+- ✅ User authentication (USER/PASS commands)
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+- ✅ Message retrieval (STAT, LIST, RETR commands)
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+- ✅ Message deletion (DELE, RSET commands)
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+- ✅ Session management (QUIT command with update state)
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+- ✅ Capability advertisement (CAPA command)
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+- ✅ Keep-alive support (NOOP command)
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+
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+### General
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+- ✅ Async/await with Tokio runtime
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+- ✅ Structured logging with tracing
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+- ✅ Shared message storage between protocols
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+- ✅ Concurrent server operation
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+
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## Running the Server
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```bash
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cargo run
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```
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-The server listens on `127.0.0.1:2525` by default.
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+The servers listen on:
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+- SMTP: `127.0.0.1:2525`
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+- POP3: `127.0.0.1:2110`
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## Testing
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-You can test the server using `nc` (netcat) or `telnet`:
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+### SMTP Testing
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+
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+You can test the SMTP server using `nc` (netcat) or `telnet`:
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```bash
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echo -e "EHLO test.com\r\nMAIL FROM: <sender@example.com>\r\nRCPT TO: <recipient@example.com>\r\nDATA\r\nSubject: Test\r\n\r\nTest message\r\n.\r\nQUIT\r\n" | nc localhost 2525
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```
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+### POP3 Testing
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+
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+Test POP3 commands:
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+
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+```bash
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+# List messages
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+echo -e "USER test\r\nPASS password\r\nLIST\r\nQUIT\r\n" | nc localhost 2110
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+
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+# Retrieve a message
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+echo -e "USER test\r\nPASS password\r\nRETR 1\r\nQUIT\r\n" | nc localhost 2110
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+
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+# Check mailbox statistics
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+echo -e "USER test\r\nPASS password\r\nSTAT\r\nQUIT\r\n" | nc localhost 2110
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+
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+# Delete a message
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+echo -e "USER test\r\nPASS password\r\nDELE 1\r\nQUIT\r\n" | nc localhost 2110
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+```
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+
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## Supported Commands
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+### SMTP Commands
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- `HELO/EHLO` - Initiate SMTP session
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- `MAIL FROM` - Specify sender email address
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- `RCPT TO` - Specify recipient email address (supports multiple)
@@ -39,6 +76,18 @@ echo -e "EHLO test.com\r\nMAIL FROM: <sender@example.com>\r\nRCPT TO: <recipient
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- `QUIT` - Close connection
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- `STARTTLS` - Upgrade connection to TLS
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+### POP3 Commands
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+- `USER` - Specify username for authentication
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+- `PASS` - Provide password for authentication
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+- `STAT` - Get mailbox statistics (message count and total size)
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+- `LIST` - List messages with sizes (all or specific message)
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+- `RETR` - Retrieve a specific message
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+- `DELE` - Mark a message for deletion
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+- `NOOP` - No operation (keep-alive)
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+- `RSET` - Reset session (unmark deleted messages)
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+- `QUIT` - End session and apply deletions
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+- `CAPA` - List server capabilities
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+
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## Building
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```bash
src/handle_pop3_session.rs
new
+204
@@ -0,0 +1,204 @@
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+use crate::pop3_storage::Pop3Mailbox;
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+use crate::send_commands::send_commands;
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+use futures::StreamExt;
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+use tokio::io::{AsyncRead, AsyncWrite};
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+use tokio_util::codec::{Framed, LinesCodec};
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+
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+#[derive(Debug, Clone, PartialEq)]
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+enum Pop3State {
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+ Authorization,
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+ Transaction,
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+ Update,
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+}
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+
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+pub async fn handle_pop3_session<S>(stream: S, mailbox: Pop3Mailbox) -> anyhow::Result<()>
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+where
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+ S: AsyncRead + AsyncWrite + Unpin,
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+{
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+ let mut state = Pop3State::Authorization;
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+ let mut username: Option<String> = None;
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+ let mut authenticated_user: Option<String> = None;
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+
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+ let mut framed = Framed::new(stream, LinesCodec::new());
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+
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+ // Send greeting
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+ send_commands(&mut framed, vec!["+OK POP3 server ready".to_string()]).await?;
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+
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+ while let Some(line_str) = framed.next().await {
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+ let line = line_str?;
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+ let parts: Vec<&str> = line.trim().split_whitespace().collect();
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+
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+ if parts.is_empty() {
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+ send_commands(&mut framed, vec!["-ERR Invalid command".to_string()]).await?;
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+ continue;
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+ }
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+
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+ let command = parts[0].to_uppercase();
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+
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+ match state {
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+ Pop3State::Authorization => {
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+ match command.as_str() {
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+ "USER" => {
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+ if parts.len() < 2 {
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+ send_commands(&mut framed, vec!["-ERR Username required".to_string()]).await?;
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+ } else {
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+ username = Some(parts[1].to_string());
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+ send_commands(&mut framed, vec![format!("+OK User {} accepted", parts[1])]).await?;
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+ }
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+ }
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+ "PASS" => {
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+ if username.is_none() {
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+ send_commands(&mut framed, vec!["-ERR No username given".to_string()]).await?;
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+ } else if parts.len() < 2 {
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+ send_commands(&mut framed, vec!["-ERR Password required".to_string()]).await?;
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+ } else {
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+ // Simple authentication - accept any password for now
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+ let user = username.clone().unwrap();
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+ authenticated_user = Some(user.clone());
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+
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+ let (count, size) = mailbox.get_stats(&user);
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+ send_commands(&mut framed, vec![format!("+OK {} messages ({} octets)", count, size)]).await?;
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+ state = Pop3State::Transaction;
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+ }
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+ }
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+ "CAPA" => {
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+ send_commands(&mut framed, vec![
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+ "+OK Capability list follows".to_string(),
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+ "USER".to_string(),
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+ "UIDL".to_string(),
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+ "TOP".to_string(),
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+ ".".to_string(),
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+ ]).await?;
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+ }
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+ "QUIT" => {
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+ send_commands(&mut framed, vec!["+OK Goodbye".to_string()]).await?;
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+ break;
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+ }
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+ _ => {
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+ send_commands(&mut framed, vec!["-ERR Unknown command".to_string()]).await?;
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+ }
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+ }
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+ }
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+ Pop3State::Transaction => {
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+ match command.as_str() {
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+ "STAT" => {
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+ if let Some(ref user) = authenticated_user {
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+ let (count, size) = mailbox.get_stats(user);
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+ send_commands(&mut framed, vec![format!("+OK {} {}", count, size)]).await?;
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+ } else {
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+ send_commands(&mut framed, vec!["-ERR Not authenticated".to_string()]).await?;
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+ }
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+ }
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+ "LIST" => {
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+ if let Some(ref user) = authenticated_user {
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+ let messages = mailbox.get_messages(user);
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+ let non_deleted: Vec<_> = messages.iter().filter(|m| !m.deleted).collect();
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+
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+ if parts.len() == 1 {
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+ // List all messages
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+ let (count, size) = mailbox.get_stats(user);
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+ let mut response = vec![format!("+OK {} messages ({} octets)", count, size)];
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+ for msg in non_deleted {
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+ response.push(format!("{} {}", msg.id, msg.size));
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+ }
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+ response.push(".".to_string());
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+ send_commands(&mut framed, response).await?;
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+ } else if let Ok(msg_id) = parts[1].parse::<usize>() {
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+ // List specific message
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+ if let Some(msg) = non_deleted.iter().find(|m| m.id == msg_id) {
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+ send_commands(&mut framed, vec![format!("+OK {} {}", msg.id, msg.size)]).await?;
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+ } else {
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+ send_commands(&mut framed, vec!["-ERR No such message".to_string()]).await?;
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+ }
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+ } else {
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+ send_commands(&mut framed, vec!["-ERR Invalid message number".to_string()]).await?;
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+ }
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+ } else {
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+ send_commands(&mut framed, vec!["-ERR Not authenticated".to_string()]).await?;
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+ }
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+ }
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+ "RETR" => {
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+ if let Some(ref user) = authenticated_user {
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+ if parts.len() < 2 {
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+ send_commands(&mut framed, vec!["-ERR Message number required".to_string()]).await?;
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+ } else if let Ok(msg_id) = parts[1].parse::<usize>() {
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+ let messages = mailbox.get_messages(user);
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+ if let Some(msg) = messages.iter().find(|m| m.id == msg_id && !m.deleted) {
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+ let mut response = vec![format!("+OK {} octets", msg.size)];
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+ response.extend(msg.content.lines().map(|l| l.to_string()));
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+ response.push(".".to_string());
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+ send_commands(&mut framed, response).await?;
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+ } else {
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+ send_commands(&mut framed, vec!["-ERR No such message".to_string()]).await?;
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+ }
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+ } else {
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+ send_commands(&mut framed, vec!["-ERR Invalid message number".to_string()]).await?;
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+ }
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+ } else {
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+ send_commands(&mut framed, vec!["-ERR Not authenticated".to_string()]).await?;
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+ }
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+ }
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+ "DELE" => {
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+ if let Some(ref user) = authenticated_user {
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+ if parts.len() < 2 {
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+ send_commands(&mut framed, vec!["-ERR Message number required".to_string()]).await?;
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+ } else if let Ok(msg_id) = parts[1].parse::<usize>() {
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+ if mailbox.mark_deleted(user, msg_id) {
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+ send_commands(&mut framed, vec![format!("+OK Message {} deleted", msg_id)]).await?;
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+ } else {
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+ send_commands(&mut framed, vec!["-ERR No such message".to_string()]).await?;
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+ }
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+ } else {
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+ send_commands(&mut framed, vec!["-ERR Invalid message number".to_string()]).await?;
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+ }
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+ } else {
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+ send_commands(&mut framed, vec!["-ERR Not authenticated".to_string()]).await?;
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+ }
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+ }
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+ "NOOP" => {
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+ send_commands(&mut framed, vec!["+OK".to_string()]).await?;
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+ }
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+ "RSET" => {
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+ if let Some(ref user) = authenticated_user {
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+ mailbox.reset_deleted(user);
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+ let (count, size) = mailbox.get_stats(user);
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+ send_commands(&mut framed, vec![format!("+OK {} messages ({} octets)", count, size)]).await?;
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+ } else {
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+ send_commands(&mut framed, vec!["-ERR Not authenticated".to_string()]).await?;
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+ }
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+ }
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+ "QUIT" => {
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+ state = Pop3State::Update;
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+ break;
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+ }
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+ "CAPA" => {
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+ send_commands(&mut framed, vec![
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+ "+OK Capability list follows".to_string(),
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+ "USER".to_string(),
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+ "UIDL".to_string(),
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+ "TOP".to_string(),
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+ ".".to_string(),
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+ ]).await?;
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+ }
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+ _ => {
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+ send_commands(&mut framed, vec!["-ERR Unknown command".to_string()]).await?;
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+ }
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+ }
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+ }
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+ Pop3State::Update => {
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+ break;
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+ }
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+ }
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+ }
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+
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+ // Update state - delete marked messages
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+ if state == Pop3State::Update {
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+ if let Some(ref user) = authenticated_user {
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+ mailbox.delete_marked(user);
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+ tracing::info!("POP3 session ended for user: {}", user);
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+ }
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+ send_commands(&mut framed, vec!["+OK Goodbye".to_string()]).await?;
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+ }
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+
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+ Ok(())
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+}
src/lib.rs
+3
@@ -1,6 +1,9 @@
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pub mod generate_certificate;
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+pub mod handle_pop3_session;
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pub mod handle_session;
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pub mod handle_starttls;
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pub mod handle_unsecured_session;
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pub mod listen;
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+pub mod listen_pop3;
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+pub mod pop3_storage;
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pub mod send_commands;
src/listen_pop3.rs
new
+27
@@ -0,0 +1,27 @@
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+use crate::handle_pop3_session::handle_pop3_session;
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+use crate::pop3_storage::Pop3Mailbox;
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+use std::net::SocketAddr;
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+use tokio::net::TcpListener;
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+
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+pub async fn listen_pop3(mailbox: Pop3Mailbox) -> anyhow::Result<()> {
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+ let addr = SocketAddr::from(([127, 0, 0, 1], 2110));
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+ let listener = TcpListener::bind(addr).await?;
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+
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+ tracing::info!("POP3 server listening on {}", addr);
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+
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+ loop {
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+ match listener.accept().await {
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+ Ok((stream, _)) => {
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+ let mailbox_clone = mailbox.clone();
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+ tokio::spawn(async move {
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+ if let Err(err) = handle_pop3_session(stream, mailbox_clone).await {
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+ tracing::error!("Error handling POP3 connection: {:?}", err);
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+ }
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+ });
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+ }
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+ Err(err) => {
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+ tracing::error!("Error establishing POP3 connection: {:?}", err);
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+ }
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+ }
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+ }
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+}
src/main.rs
+29
-1
@@ -1,10 +1,38 @@
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use anyhow::Result;
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use smbcloud_mail::listen::listen;
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+use smbcloud_mail::listen_pop3::listen_pop3;
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+use smbcloud_mail::pop3_storage::Pop3Mailbox;
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#[tokio::main]
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async fn main() -> Result<()> {
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// Initialize tracing subscriber for logging
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tracing_subscriber::fmt::init();
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- listen().await
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+ // Create shared POP3 mailbox
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+ let mailbox = Pop3Mailbox::new();
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+
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+ // Add some sample messages for testing
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+ mailbox.add_message("test", "From: sender@example.com\r\nTo: test@example.com\r\nSubject: Test Message 1\r\n\r\nThis is the first test message.".to_string());
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+ mailbox.add_message("test", "From: sender@example.com\r\nTo: test@example.com\r\nSubject: Test Message 2\r\n\r\nThis is the second test message.".to_string());
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+
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+ // Run both SMTP and POP3 servers concurrently
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+ let smtp_server = tokio::spawn(async move {
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+ if let Err(e) = listen().await {
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+ tracing::error!("SMTP server error: {:?}", e);
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+ }
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+ });
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+
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+ let pop3_server = tokio::spawn(async move {
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+ if let Err(e) = listen_pop3(mailbox).await {
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+ tracing::error!("POP3 server error: {:?}", e);
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+ }
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+ });
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+
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+ // Wait for both servers (they run indefinitely)
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+ tokio::select! {
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+ _ = smtp_server => {},
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+ _ = pop3_server => {},
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+ }
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+
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+ Ok(())
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}
src/pop3_storage.rs
new
+99
@@ -0,0 +1,99 @@
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+use std::collections::HashMap;
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+use std::sync::{Arc, Mutex};
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+
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+#[derive(Debug, Clone)]
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+pub struct Pop3Message {
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+ pub id: usize,
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+ pub content: String,
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+ pub size: usize,
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+ pub deleted: bool,
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+}
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+
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+impl Pop3Message {
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+ pub fn new(id: usize, content: String) -> Self {
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+ let size = content.len();
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+ Self {
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+ id,
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+ content,
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+ size,
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+ deleted: false,
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+ }
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+ }
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+}
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+
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+#[derive(Debug, Clone)]
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+pub struct Pop3Mailbox {
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+ messages: Arc<Mutex<HashMap<String, Vec<Pop3Message>>>>,
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+}
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+
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+impl Pop3Mailbox {
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+ pub fn new() -> Self {
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+ Self {
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+ messages: Arc::new(Mutex::new(HashMap::new())),
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+ }
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+ }
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+
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+ pub fn add_message(&self, username: &str, content: String) {
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+ let mut messages = self.messages.lock().unwrap();
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+ let user_messages = messages.entry(username.to_string()).or_insert_with(Vec::new);
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+ let id = user_messages.len() + 1;
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+ user_messages.push(Pop3Message::new(id, content));
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+ }
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+
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+ pub fn get_messages(&self, username: &str) -> Vec<Pop3Message> {
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+ let messages = self.messages.lock().unwrap();
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+ messages
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+ .get(username)
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+ .map(|m| m.clone())
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+ .unwrap_or_default()
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+ }
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+
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+ pub fn mark_deleted(&self, username: &str, msg_id: usize) -> bool {
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+ let mut messages = self.messages.lock().unwrap();
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+ if let Some(user_messages) = messages.get_mut(username) {
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+ if let Some(msg) = user_messages.iter_mut().find(|m| m.id == msg_id) {
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+ msg.deleted = true;
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+ return true;
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+ }
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+ }
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+ false
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+ }
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+
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+ pub fn reset_deleted(&self, username: &str) {
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+ let mut messages = self.messages.lock().unwrap();
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+ if let Some(user_messages) = messages.get_mut(username) {
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+ for msg in user_messages.iter_mut() {
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+ msg.deleted = false;
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+ }
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+ }
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+ }
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+
71
+ pub fn delete_marked(&self, username: &str) {
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+ let mut messages = self.messages.lock().unwrap();
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+ if let Some(user_messages) = messages.get_mut(username) {
74
+ user_messages.retain(|m| !m.deleted);
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+ // Re-index messages after deletion
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+ for (idx, msg) in user_messages.iter_mut().enumerate() {
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+ msg.id = idx + 1;
78
+ }
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+ }
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+ }
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+
82
+ pub fn get_stats(&self, username: &str) -> (usize, usize) {
83
+ let messages = self.messages.lock().unwrap();
84
+ if let Some(user_messages) = messages.get(username) {
85
+ let non_deleted: Vec<_> = user_messages.iter().filter(|m| !m.deleted).collect();
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+ let count = non_deleted.len();
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+ let total_size = non_deleted.iter().map(|m| m.size).sum();
88
+ (count, total_size)
89
+ } else {
90
+ (0, 0)
91
+ }
92
+ }
93
+}
94
+
95
+impl Default for Pop3Mailbox {
96
+ fn default() -> Self {
97
+ Self::new()
98
+ }
99
+}