From 943069b2a3eb6fb78dd91ed9bd0cfadd572626fb Mon Sep 17 00:00:00 2001
From: Bananymous <oskari.alaranta@bananymous.com>
Date: Tue, 3 Jun 2025 10:24:44 +0300
Subject: [PATCH] Kernel: Socket EPIPE and send SIGPIPE on write after hang up

---
 kernel/kernel/Networking/TCPSocket.cpp  |  8 ++++++++
 kernel/kernel/OpenFileDescriptorSet.cpp | 19 +++++++++++++++----
 2 files changed, 23 insertions(+), 4 deletions(-)

diff --git a/kernel/kernel/Networking/TCPSocket.cpp b/kernel/kernel/Networking/TCPSocket.cpp
index 0ca588c1..1514b82f 100644
--- a/kernel/kernel/Networking/TCPSocket.cpp
+++ b/kernel/kernel/Networking/TCPSocket.cpp
@@ -439,6 +439,8 @@ namespace Kernel
 
 		LockGuard _(m_mutex);
 
+		const bool hungup_before = has_hungup_impl();
+
 		auto& header = buffer.as<const TCPHeader>();
 		dprintln_if(DEBUG_TCP, "receiving {} {8b}", (uint8_t)m_state, header.flags);
 		dprintln_if(DEBUG_TCP, "  {}", (uint32_t)header.ack_number);
@@ -609,6 +611,9 @@ namespace Kernel
 			}
 		}
 
+		if (!hungup_before && has_hungup_impl())
+			epoll_notify(EPOLLHUP);
+
 		m_thread_blocker.unblock();
 	}
 
@@ -690,9 +695,12 @@ namespace Kernel
 					auto target_address_len = m_connection_info->address_len;
 					if (auto ret = m_network_layer.sendto(*this, {}, target_address, target_address_len); ret.is_error())
 						dwarnln("{}", ret.error());
+					const bool hungup_before = has_hungup_impl();
 					m_state = m_next_state;
 					if (m_state == State::Established)
 						m_has_connected = true;
+					if (!hungup_before && has_hungup_impl())
+						epoll_notify(EPOLLHUP);
 					continue;
 				}
 
diff --git a/kernel/kernel/OpenFileDescriptorSet.cpp b/kernel/kernel/OpenFileDescriptorSet.cpp
index fd71238a..309f69f7 100644
--- a/kernel/kernel/OpenFileDescriptorSet.cpp
+++ b/kernel/kernel/OpenFileDescriptorSet.cpp
@@ -476,14 +476,25 @@ namespace Kernel
 
 		LockGuard _(inode->m_mutex);
 
-		if (is_nonblock && !inode->can_write())
-			return BAN::Error::from_errno(EWOULDBLOCK);
+		const auto check_errors =
+			[&inode, is_nonblock]() -> BAN::ErrorOr<void>
+			{
+				if (inode->has_hungup())
+				{
+					Thread::current().add_signal(SIGPIPE);
+					return BAN::Error::from_errno(EPIPE);
+				}
+				if (is_nonblock && !inode->can_write())
+					return BAN::Error::from_errno(EWOULDBLOCK);
+				return {};
+			};
+
+		TRY(check_errors());
 
 		size_t total_sent = 0;
 		while (total_sent < buffer.size())
 		{
-			if (is_nonblock && !inode->can_write())
-				return total_sent;
+			TRY(check_errors());
 			const size_t nsend = TRY(inode->sendto(buffer.slice(total_sent), address, address_len));
 			if (nsend == 0)
 				return 0;