Before this patch `accept4()`, `socket()`, `socketpair()`, `send()` and
`recv()` system symbols were remapped via macros, using the same name,
to local curl debug wrappers. This patch replaces these overrides by
introducing curl-namespaced macros that map either to the system symbols
or to their curl debug wrappers in `CURLDEBUG` (TrackMemory) builds.
This follows a patch that implemented the same for `accept()`.
The old method required tricks to make these redefines work in unity
builds, and avoid them interfering with system headers. These tricks
did not work for system symbols implemented as macros.
The new method allows to setup these mappings once, without interfering
with system headers, upstream macros, or unity builds. It makes builds
more robust.
Also:
- checksrc: ban all mapped functions.
- docs/examples: tidy up checksrc rules.
Follow-up to 9863599d69#18502
Follow-up to 3bb5e58c10#17827Closes#18503
Multipath TCP (MPTCP), standardized in RFC8684 [1], is a TCP extension
that enables a TCP connection to use different paths.
Multipath TCP has been used for several use cases. On smartphones, MPTCP
enables seamless handovers between cellular and Wi-Fi networks while
preserving established connections. This use-case is what pushed Apple
to use MPTCP since 2013 in multiple applications [2]. On dual-stack
hosts, Multipath TCP enables the TCP connection to automatically use the
best performing path, either IPv4 or IPv6. If one path fails, MPTCP
automatically uses the other path.
To benefit from MPTCP, both the client and the server have to support
it. Multipath TCP is a backward-compatible TCP extension that is enabled
by default on recent Linux distributions (Debian, Ubuntu, Redhat, ...).
Multipath TCP is included in the Linux kernel since version 5.6 [3]. To
use it on Linux, an application must explicitly enable it when creating
the socket. No need to change anything else in the application.
This attached patch adds an --mptcp option which allows the creation of
an MPTCP socket instead of TCP on Linux. If Multipath TCP is not
supported on the system, an error will be reported. It is important to
note that if the end server doesn't support MPTCP, the connection will
continue after a seamless fallback to TCP.
Link: https://www.rfc-editor.org/rfc/rfc8684.html [1]
Link: https://www.tessares.net/apples-mptcp-story-so-far/ [2]
Link: https://www.mptcp.dev [3]
Co-developed-by: Dorian Craps (@CrapsDorian) <doriancraps@gmail.com>
Co-developed-by: Olivier Bonaventure (@obonaventure) <Olivier.Bonaventure@uclouvain.be>
Co-developed-by: Matthieu Baerts (@matttbe) <matttbe@kernel.org>
Signed-off-by: Dorian Craps <dorian.craps@student.vinci.be>
Closes#13278
