From 175d986c8a24c779f8d8609796d757772d285e70 Mon Sep 17 00:00:00 2001
From: logkos <65683493+logkos@users.noreply.github.com.>
Date: Fri, 27 Sep 2024 23:46:03 +0300
Subject: [PATCH] Net: Implement SO_LINGER

SO_LINGER allows specifying a timeout interval during which the socket
attempts to send any remaining data before closing. If all data is
ACKed within the specified timeout, the connection is closed
gracefully using a FIN/ACK exchange.

If the timeout expires with unacknowledged data, the socket is
forcefully closed using RST, discarding any unsent data.
---
 Kernel/Net/Socket.cpp    | 13 +++++++++++++
 Kernel/Net/Socket.h      |  1 +
 Kernel/Net/TCPSocket.cpp | 25 ++++++++++++++++++++++++-
 3 files changed, 38 insertions(+), 1 deletion(-)

diff --git a/Kernel/Net/Socket.cpp b/Kernel/Net/Socket.cpp
index b8d9df6f09b45f1..53ea97584b7c1e6 100644
--- a/Kernel/Net/Socket.cpp
+++ b/Kernel/Net/Socket.cpp
@@ -136,6 +136,12 @@ ErrorOr<void> Socket::setsockopt(int level, int option, Userspace<void const*> u
         m_broadcast_allowed = TRY(copy_typed_from_user(static_ptr_cast<int const*>(user_value))) != 0;
         return {};
     }
+    case SO_LINGER: {
+        if (user_value_size != sizeof(linger))
+            return EINVAL;
+        m_linger = TRY(copy_typed_from_user(static_ptr_cast<linger const*>(user_value)));
+        return {};
+    }
     default:
         dbgln("setsockopt({}) at SOL_SOCKET not implemented.", option);
         return ENOPROTOOPT;
@@ -257,6 +263,13 @@ ErrorOr<void> Socket::getsockopt(OpenFileDescription&, int level, int option, Us
         size = sizeof(broadcast_allowed);
         return copy_to_user(value_size, &size);
     }
+    case SO_LINGER: {
+        if (size < sizeof(linger))
+            return EINVAL;
+        TRY(copy_to_user(static_ptr_cast<linger*>(value), &m_linger));
+        size = sizeof(linger);
+        return copy_to_user(value_size, &size);
+    }
     default:
         dbgln("getsockopt({}) at SOL_SOCKET not implemented.", option);
         return ENOPROTOOPT;
diff --git a/Kernel/Net/Socket.h b/Kernel/Net/Socket.h
index 01c154c221a2202..a9511445d7b9bd6 100644
--- a/Kernel/Net/Socket.h
+++ b/Kernel/Net/Socket.h
@@ -157,6 +157,7 @@ class Socket : public File {
     ucred m_acceptor { 0, 0, 0 };
     bool m_routing_disabled { false };
     bool m_broadcast_allowed { false };
+    linger m_linger { 0, 0 };
 
 private:
     virtual bool is_socket() const final { return true; }
diff --git a/Kernel/Net/TCPSocket.cpp b/Kernel/Net/TCPSocket.cpp
index 4414295b7e8ecb1..dbcceae6e1a66c7 100644
--- a/Kernel/Net/TCPSocket.cpp
+++ b/Kernel/Net/TCPSocket.cpp
@@ -664,8 +664,31 @@ ErrorOr<void> TCPSocket::close()
 {
     MutexLocker locker(mutex());
     auto result = IPv4Socket::close();
+    if (m_linger.l_onoff != 0) {
+        if (m_linger.l_linger > 0) {
+            dbgln_if(TCP_SOCKET_DEBUG, "TCPSocket({}) SO_LINGER with {} seconds interval", this, m_linger.l_linger);
+            auto deadline = TimeManagement::the().current_time(CLOCK_MONOTONIC_COARSE) + Duration::from_seconds(m_linger.l_linger);
+            // FIXME: Make this return earlier if all data is acknowledged before end of interval
+            (void)TimerQueue::the().add_timer_without_id(*m_timer, CLOCK_MONOTONIC_COARSE, deadline, [&]() {
+                bool has_unacked_data = m_unacked_packets.with_shared([&](auto const& packets) { return packets.size > 0; });
+                if (has_unacked_data) {
+                    dbgln_if(TCP_SOCKET_DEBUG, "TCPSocket({}) SO_LINGER interval expired. Some data couldn't make it :(", this);
+                    drop_receive_buffer();
+                    (void)send_tcp_packet(TCPFlags::RST);
+                    do_state_closed();
+                    return;
+                }
+                dbgln_if(TCP_SOCKET_DEBUG, "TCPSocket({}) SO_LINGER timeout. All remaining data has been acknowledged, closing gracefully", this);
+            });
+        } else {
+            dbgln_if(TCP_SOCKET_DEBUG, "TCPSocket({}) SO_LINGER without timeout, closing immediately", this);
+            (void)send_tcp_packet(TCPFlags::RST);
+            do_state_closed();
+        }
+    }
+
     if (state() == State::CloseWait) {
-        dbgln_if(TCP_SOCKET_DEBUG, " Sending FIN from CloseWait and moving into LastAck");
+        dbgln_if(TCP_SOCKET_DEBUG, "TCPSocket({}) Sending FIN from CloseWait and moving into LastAck", this);
         [[maybe_unused]] auto rc = send_tcp_packet(TCPFlags::FIN | TCPFlags::ACK);
         set_state(State::LastAck);
     }