At some point, we stopped ever constructing invalid messages. This makes
that clearer, and will allow us to stop requiring that IPC arguments be
default-constructible.
The Linux IPC uses SCM_RIGHTS to transfer fds to another process
(see TransportSocket::transfer, which calls LocalSocket::send_message).
File descriptors are handled separately from regular data.
On Windows handles are embedded in regular data. They are duplicated
in the sender process.
Socket handles need special code both on sender side (because they
require using WSADuplicateSocket instead of DuplicateHandle, see
TransportSocketWindows::duplicate_handles) and on receiver side
(because they require WSASocket, see FileWindows.cpp).
TransportSocketWindows::ReadResult::fds vector is always empty, it is
kept the same as Linux version to avoid OS #ifdefs in Connection.h/.cpp
and Web::HTML::MessagePort::read_from_transport. Separate handling of
fds permeates all IPC code, it doesn't make sense to #ifdef out all this
code on Windows. In other words, the Linux code is more generic -
it handles both regular data and fds. On Windows, we need only the
regular data portion of it, and we just use that.
Duplicating handles on Windows requires pid of target (receiver)
process (see TransportSocketWindows::m_peer_pid). This pid is received
during special TransportSocketWindows initialization, which is performed
only on Windows. It is handled in a separate PR #3179.
Note: ChatGPT and [stackoverflow](https://stackoverflow.com/questions/25429887/getting-pid-of-peer-socket-on-windows) suggest using GetExtendedTcpTable/GetTcpTable2
to get peer pid, but this doesn't work because [MIB_TCPROW2::dwOwningPid](https://learn.microsoft.com/en-us/windows/win32/api/tcpmib/ns-tcpmib-mib_tcprow2)
is "The PID of the process that issued a context bind for this TCP
connection.", so for both ends it will return the pid of the process
that called socketpair.
Co-Authored-By: Andrew Kaster <andrew@ladybird.org>
It is now possible to use the special IPC::File type in message arguments. In
C++, the type is nothing more than a wrapper over a file descriptor. But when
serializing/deserializing IPC::File arguments, LibIPC will use the sendfd/recvfd
kernel APIs instead of sending the integer inline.
This makes it quite convenient to pass files over IPC, and will allow us to
significantly tighten sandboxes in the future :^)
Closes https://github.com/SerenityOS/serenity/issues/3643
You can now #include <AK/Forward.h> to get most of the AK types as
forward declarations.
Header dependency explosion is one of the main contributors to compile
times at the moment, so this is a step towards smaller include graphs.
