Kernel: Add MSG_PEEK support for the IPv4Socket

This commit will add MSG_PEEK support, which allows a package to be
seen without taking it from the buffer, so that a subsequent recv()
without the MSG_PEEK flag can pick it up.

Kernel/Net/IPv4Socket.cpp

@@ -217,7 +217,7 @@ KResultOr<size_t> IPv4Socket::sendto(FileDescription&, const UserOrKernelBuffer&
  return nsent_or_error;
 }
 
-KResultOr<size_t> IPv4Socket::receive_byte_buffered(FileDescription& description, UserOrKernelBuffer& buffer, size_t buffer_length, int, Userspace<sockaddr*>, Userspace<socklen_t*>)
+KResultOr<size_t> IPv4Socket::receive_byte_buffered(FileDescription& description, UserOrKernelBuffer& buffer, size_t buffer_length, int flags, Userspace<sockaddr*>, Userspace<socklen_t*>)
 {
  Locker locker(lock());
  if (m_receive_buffer.is_empty()) {
@@ -241,8 +241,14 @@ KResultOr<size_t> IPv4Socket::receive_byte_buffered(FileDescription& description
  }
 
  VERIFY(!m_receive_buffer.is_empty());
- int nreceived = m_receive_buffer.read(buffer, buffer_length);
- if (nreceived > 0)
+
+ int nreceived;
+ if (flags & MSG_PEEK)
+ nreceived = m_receive_buffer.peek(buffer, buffer_length);
+ else
+ nreceived = m_receive_buffer.read(buffer, buffer_length);
+
+ if (nreceived > 0 && !(flags & MSG_PEEK))
  Thread::current()->did_ipv4_socket_read((size_t)nreceived);
 
  set_can_read(!m_receive_buffer.is_empty());
@@ -264,7 +270,11 @@ KResultOr<size_t> IPv4Socket::receive_packet_buffered(FileDescription& descripti
  }
 
  if (!m_receive_queue.is_empty()) {
- packet = m_receive_queue.take_first();
+ if (flags & MSG_PEEK)
+ packet = m_receive_queue.first();
+ else
+ packet = m_receive_queue.take_first();
+
  set_can_read(!m_receive_queue.is_empty());
 
  dbgln_if(IPV4_SOCKET_DEBUG, "IPv4Socket({}): recvfrom without blocking {} bytes, packets in queue: {}",
@@ -293,7 +303,12 @@ KResultOr<size_t> IPv4Socket::receive_packet_buffered(FileDescription& descripti
  }
  VERIFY(m_can_read);
  VERIFY(!m_receive_queue.is_empty());
- packet = m_receive_queue.take_first();
+
+ if (flags & MSG_PEEK)
+ packet = m_receive_queue.first();
+ else
+ packet = m_receive_queue.take_first();
+
  set_can_read(!m_receive_queue.is_empty());
 
  dbgln_if(IPV4_SOCKET_DEBUG, "IPv4Socket({}): recvfrom with blocking {} bytes, packets in queue: {}",

Kernel/UnixTypes.h

@@ -496,6 +496,7 @@ struct pollfd {
 
 #define MSG_TRUNC 0x1
 #define MSG_CTRUNC 0x2
+#define MSG_PEEK 0x4
 #define MSG_DONTWAIT 0x40
 
 #define SOL_SOCKET 1

Userland/Libraries/LibC/sys/socket.h

@@ -46,6 +46,7 @@ __BEGIN_DECLS
 
 #define MSG_TRUNC 0x1
 #define MSG_CTRUNC 0x2
+#define MSG_PEEK 0x4
 #define MSG_DONTWAIT 0x40
 
 typedef uint16_t sa_family_t;