sys/net/nanocoap: Add CoAP over TCP support #21048
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Area: network
This changes the API of nanocoap with the goal to reduce the expose of
UDP specifics in the API. The plan is to eventually support transports
such as CoAP over TCP and CoAP over WebSocket directly in nanocoap
while sharing most of the code, as e.g. the CoAP Option processing
remains identical. Specifically, the plan is to unlock a transport with
modules and introduce overhead for dispatching to specific transport
only when multiple transports are actually in use.
Support for OSCORE directly in nanocoap is probably not sensible, as
the serialization is very much unlike the other transports. A unified
CoAP API for multiple transports including OSCORE is probably best
implemented on top. But when limited to the boring set of CoAP
transports, we probably can support them well with nanocoap with less
overhead.
Breaking API Changes:
=====================
- `coap_parse()` now returns `ssize_t` instead of `int`
- This function is not really user facing, so the impact should
be limited
- This is useful for stream transports where the buffer may
contain data of more than one packet. The return value contains
the number of bytes actually consumed, which will match the
buffer size for non-stream transports.
API Changes:
============
- `coap_pkt_t` now contains a `uint8_t *buf` pointer instead of a
`coap_hdr_t *hdr` pointer to the beginning of the buffer
- This will also work when the buffer is used by non-UDP
transports
- A deprecated `coap_udp_hdr_t *hdr` has been crammed into
an unnamed `union` with `uint8_t *buf`. For architectures
where pointers have the same memory layout regardless of type
(e.g. all of the supported ones), this will make `hdr` an
alias for `buf`.
- The alias will only be provided if no transport besides UDP is
used in nanocoap. So existing apps will continue to work, new
apps that want to support other transports need to move to
adapt.
- `coap_hdr_t` has been renamed to `coap_udp_hdr_t`
- A deprecated alias was created for deprecation
- `coap_hdr*()` functions have been deprecated
- Equivalent `coap_pkt*()` functions have been created that work
on `coap_pkt_t *` instead of `coap_hdr_t *`
- If non-UDP transports are used, the deprecated `coap_hdr*()`
will probably not be exposed to avoid footguns.
- `coap_build_hdr()` has been renamed to `coap_build_udp_hdr()` and
that works on an `uint8_t *` buffer with a given length, rather than
on a `coap_hdr_t *` with a *figers crossed* length
- a deprecated `coap_build_hdr()` function was added that calls
to `coap_build_udp_hdr()` and has the same signature, so that
users have time to update
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In TCP server mode, the sock_tcp_t sockets are managed by the network stack and can be reused if a previous connection is no longer in used. However, an event may still be posted in the event queue when the socket is reused. Wiping it will result in the `next` pointer in that event to be NULL, which will cause the event handler fetching that event to crash. This adds an `event_cancel()` at two places: 1. Just before reusing the socket 2. During sock_tcp_disconnect() The former catches issues in server mode e.g. when a connect has been closed (e.g. due to timeout) and is reused before a pending event (e.g. a timeout event) has been processed. The letter may be an issue on client side. E.g. when `sock_tcp_t` was allocated on stack and goes out of scope after `sock_tcp_disconnect` but before the event handler was run.
This changes the Makefile to easily setup lwIP as network stack, while keeping GNRC as the default. If lwIP is used on one of the larger boards, the app will be build with CoAP over TCP support enabled.
We need to clear `event->next` while IRQs are still disabled to avoid another thread from calling `event_cancel()` just in-between.
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Contribution description
This PR adds CoAP over TCP support to nanocoap. It is still work in progress, with many rough edges. This will get updated and filled in with more details as the PR evolves.
Testing procedure
Run
sudo ./dist/tools/tapsetup/tapsetupServer
Wait for the IPv6 address to show up
Client
Then in the RIOT shell run e.g.
Issues/PRs references
Depends on and includes: #20900