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sys/net/nanocoap: implement observe

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This adds the new `nanocoap_server_observe` module that implements the
server side of the CoAP Observe option. It does require cooperation
from the resource handler to work, though.

Co-Authored-By: mguetschow <mikolai.guetschow@tu-dresden.de>
Co-authored-by: benpicco <benpicco@googlemail.com>
This commit is contained in:
Marian Buschsieweke 2025-01-20 23:50:03 +01:00
parent 1c7ba9e055
commit feeb68470f
No known key found for this signature in database
GPG Key ID: 758BD52517F79C41
9 changed files with 395 additions and 9 deletions
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6
examples/nanocoap_server/Makefile
View File

@ -20,7 +20,7 @@ USEMODULE += gnrc_icmpv6_echo
USEMODULE += nanocoap_sock
USEMODULE += nanocoap_resources
USEMODULE += xtimer
USEMODULE += ztimer_msec
# include this for nicely formatting the returned internal value
USEMODULE += fmt
@ -48,10 +48,12 @@ HIGH_MEMORY_BOARDS := native native64 same54-xpro mcb2388
ifneq (,$(filter $(BOARD),$(HIGH_MEMORY_BOARDS)))
# enable separate response
USEMODULE += nanocoap_server_separate
USEMODULE += event_callback
USEMODULE += event_periodic
USEMODULE += event_thread
USEMODULE += event_timeout_ztimer
USEMODULE += nanocoap_server_observe
USEMODULE += nanocoap_server_separate
# enable fileserver
USEMODULE += nanocoap_fileserver

109
examples/nanocoap_server/coap_handler.c
View File

@ -11,13 +11,13 @@
#include <string.h>
#include "event/callback.h"
#include "event/timeout.h"
#include "event/periodic.h"
#include "event/thread.h"
#include "event/timeout.h"
#include "fmt.h"
#include "net/nanocoap.h"
#include "net/nanocoap_sock.h"
#include "hashes/sha256.h"
#include "kernel_defines.h"
/* internal value that can be read/written via CoAP */
static uint8_t internal_value = 0;
@ -59,7 +59,7 @@ static ssize_t _riot_block2_handler(coap_pkt_t *pkt, uint8_t *buf, size_t len, c
bufpos += coap_put_option_ct(bufpos, 0, COAP_FORMAT_TEXT);
bufpos += coap_opt_put_block2(bufpos, COAP_OPT_CONTENT_FORMAT, &slicer, 1);
*bufpos++ = 0xff;
*bufpos++ = COAP_PAYLOAD_MARKER;
/* Add actual content */
bufpos += coap_blockwise_put_bytes(&slicer, bufpos, block2_intro, sizeof(block2_intro)-1);
@ -196,7 +196,7 @@ static void _send_response(void *ctx)
puts("_separate_handler(): send delayed response");
nanocoap_server_send_separate(ctx, COAP_CODE_CONTENT, COAP_TYPE_NON,
response, sizeof(response));
response, sizeof(response));
}
static ssize_t _separate_handler(coap_pkt_t *pkt, uint8_t *buf, size_t len, coap_request_ctx_t *context)
@ -234,6 +234,107 @@ NANOCOAP_RESOURCE(separate) {
};
#endif /* MODULE_EVENT_THREAD */
#ifdef MODULE_NANOCOAP_SERVER_OBSERVE
static ssize_t _time_handler(coap_pkt_t *pkt, uint8_t *buf, size_t len, coap_request_ctx_t *context)
{
uint32_t obs;
bool registered = false;
if (coap_opt_get_uint(pkt, COAP_OPT_OBSERVE, &obs)) {
/* No (valid) observe option present */
obs = UINT32_MAX;
}
uint32_t now = ztimer_now(ZTIMER_MSEC);
switch (obs) {
case 0:
/* register */
if (nanocoap_register_observer(context, pkt) == 0) {
registered = true;
}
break;
case 1:
/* unregister */
nanocoap_unregister_observer(context, pkt);
break;
default:
/* No (valid) observe option present --> ignore observe and handle
* as regular GET */
break;
}
const size_t estimated_data_len =
4 /* Max Observe Option size */
+ 1 /* payload marker */
+ 10 /* strlen("4294967295"), 4294967295 == UINT32_MAX */
+ 1; /* '\n' */
ssize_t hdr_len = coap_build_reply(pkt, COAP_CODE_CONTENT, buf, len, estimated_data_len);
if (hdr_len < 0) {
/* we undo any potential registration if we cannot reply */
nanocoap_unregister_observer(context, pkt);
return len;
}
if (hdr_len == 0) {
/* no response required, probably because of no-response option matching
* the response class */
return 0;
}
/* coap_build_reply() is a bit goofy: It returns the size of the written
* header + `estiamted_data_len`, so we have to subtract it again to obtain
* the size of data written. */
uint8_t *pos = buf + hdr_len - estimated_data_len;
if (registered) {
uint16_t last_opt = 0;
pos += coap_opt_put_observe(pos, last_opt, now);
}
*pos++ = COAP_PAYLOAD_MARKER;
pos += fmt_u32_dec((void *)pos, now);
*pos++ = '\n';
return (uintptr_t)pos - (uintptr_t)buf;
}
NANOCOAP_RESOURCE(time) {
.path = "/time", .methods = COAP_GET, .handler = _time_handler,
};
static void _notify_observer_handler(event_t *ev)
{
(void)ev;
uint32_t now = ztimer_now(ZTIMER_MSEC);
uint8_t buf[32];
uint8_t *pos = buf;
uint16_t last_opt = 0;
pos += coap_opt_put_observe(pos, last_opt, now);
*pos++ = COAP_PAYLOAD_MARKER;
pos += fmt_u32_dec((void *)pos, now);
*pos++ = '\n';
iolist_t data = {
.iol_base = buf,
.iol_len = (uintptr_t)pos - (uintptr_t)buf,
};
/* `NANOCOAP_RESOURCE(time)` expends to XFA magic adding an entry named
* `coap_resource_time`. */
nanocoap_notify_observers(&coap_resource_time, &data);
}
void setup_observe_event(void)
{
static event_t ev = {
.handler = _notify_observer_handler
};
static event_periodic_t pev;
event_periodic_init(&pev, ZTIMER_MSEC, EVENT_PRIO_MEDIUM, &ev);
event_periodic_start(&pev, MS_PER_SEC);
}
#endif /* MODULE_NANOCOAP_SERVER_OBSERVE */
/* we can also include the fileserver module */
#ifdef MODULE_NANOCOAP_FILESERVER
#include "net/nanocoap/fileserver.h"

10
examples/nanocoap_server/main.c
View File

@ -20,13 +20,15 @@
#include <stdio.h>
#include "net/nanocoap_sock.h"
#include "xtimer.h"
#include "ztimer.h"
#define COAP_INBUF_SIZE (256U)
#define MAIN_QUEUE_SIZE (8)
static msg_t _main_msg_queue[MAIN_QUEUE_SIZE];
extern void setup_observe_event(void);
int main(void)
{
puts("RIOT nanocoap example application");
@ -35,7 +37,11 @@ int main(void)
msg_init_queue(_main_msg_queue, MAIN_QUEUE_SIZE);
puts("Waiting for address autoconfiguration...");
xtimer_sleep(3);
ztimer_sleep(ZTIMER_MSEC, 3 * MS_PER_SEC);
if (IS_USED(MODULE_NANOCOAP_SERVER_OBSERVE)) {
setup_observe_event();
}
/* print network addresses */
printf("{\"IPv6 addresses\": [\"");

4
sys/Makefile.dep
View File

@ -529,6 +529,10 @@ ifneq (,$(filter nanocoap_server_auto_init,$(USEMODULE)))
USEMODULE += nanocoap_server
endif
ifneq (,$(filter nanocoap_server_observe,$(USEMODULE)))
USEMODULE += nanocoap_server_separate
endif
ifneq (,$(filter nanocoap_server_separate,$(USEMODULE)))
USEMODULE += nanocoap_server
USEMODULE += sock_aux_local

1
sys/include/net/coap.h
View File

@ -519,6 +519,7 @@ typedef enum {
*/
#define COAP_OBS_REGISTER (0)
#define COAP_OBS_DEREGISTER (1)
#define COAP_OBS_MAX_VALUE_MASK (0xffffff) /**< observe value is 24 bits */
/** @} */
/**

16
sys/include/net/nanocoap.h
View File

@ -1790,6 +1790,22 @@ static inline size_t coap_opt_put_block2_control(uint8_t *buf, uint16_t lastonum
(block->blknum << 4) | block->szx);
}
/**
* @brief Insert an CoAP Observe Option into the buffer
*
* @param[out] buf Buffer to write to
* @param[in] lastonum last option number (must be < 6)
* @param[in] obs observe number to write
*
* @returns amount of bytes written to @p buf
*/
static inline size_t coap_opt_put_observe(uint8_t *buf, uint16_t lastonum,
uint32_t obs)
{
obs &= COAP_OBS_MAX_VALUE_MASK; /* trim obs down to 24 bit */
return coap_opt_put_uint(buf, lastonum, COAP_OPT_OBSERVE, obs);
}
/**
* @brief Encode the given string as multi-part option into buffer
*

93
sys/include/net/nanocoap_sock.h
View File

@ -352,6 +352,99 @@ ssize_t nanocoap_server_build_separate(const nanocoap_server_response_ctx_t *ctx
int nanocoap_server_sendv_separate(const nanocoap_server_response_ctx_t *ctx,
const iolist_t *reply);
/**
* @brief Register an observer
* @param[in] req_ctx Request context belonging to @p req_pkt
* @param[in,out] req_pkt Request that contained the observe registration request
*
* @warning This depends on module `nanocoap_server_observe`
*
* @note If the same endpoint already was registered on the same resource,
* it will just update the token and keep the existing entry. This
* way duplicate detection is not needed and we eagerly can reclaim
* resources when a client lost state.
*
* @warning Preventing the same endpoint to registers more than once (using
* different tokens) to the same resource deviates from RFC 7641.
*
* The deviation here is intentional. A server can receive a second registration
* from the same endpoint for the same resource for one of the following
* reasons:
*
* 1. Reaffirming the registration by using the same token again.
* 2. Losing state on the client side.
* 3. A malicious client trying to exhaust resources.
* 4. The same resource has different representations depending on the
* request. (E.g. `/.well-known/core` can yield a wildly different response
* depending on filters provided via URI-Query Options.)
*
* For case 1 updating the registration is matching what the spec mandates.
* For two the old registration will not be of value for the client, and
* overwriting it makes more efficient use of network bandwidth and RAM.
* For 3 the deviation forces the adversary to send observe requests from
* different ports to exhaust resources, which is a very minor improvement.
* For 4 the deviation is a problem. However, the observe API does not allow to
* send out different notification messages for the same resource anyway, so
* case 4 cannot occur here.
*
* @retval 0 Success
* @retval -ENOMEM Not enough resources to register another observer
* @retval <0 Negative errno code indicating error
*/
int nanocoap_register_observer(const coap_request_ctx_t *req_ctx, coap_pkt_t *req_pkt);
/**
* @brief Unregister an observer
* @param req_ctx Request context belonging to @p req_pkt
* @param req_pkt Received request for unregistration
*
* @warning This depends on module `nanocoap_server_observe`
*
* @note It is safe to call this multiple times, e.g. duplicate detection
* is not needed for this.
*/
void nanocoap_unregister_observer(const coap_request_ctx_t *req_ctx,
const coap_pkt_t *req_pkt);
/**
* @brief Unregister a stale observation due to a reset message received
* @param[in] ep Endpoint to wipe from the observer list
* @param[in] msg_id Message ID of the notification send.
*/
void nanocoap_unregister_observer_due_to_reset(const sock_udp_ep_t *ep,
uint16_t msg_id);
/**
* @brief Notify all currently registered observers of the given resource
*
* @param[in] res Resource to send updates for
* @param[in] iol I/O list containing the CoAP Options, payload marker,
* and payload of the update to send up
*
* @pre @p iol contains everything but the CoAP header needed to send out.
* This will at least be a CoAP observe option, a payload marker,
* and a payload
*
* @post For each registered observer a CoAP packet header is generated and
* the concatenation of that header and the provided list is sent
*/
void nanocoap_notify_observers(const coap_resource_t *res, const iolist_t *iol);
/**
* @brief Build and send notification to observers registered to a specific
* resource.
*
* @note Use @ref nanocoap_notify_observers for more control (such
* as adding custom options) over the notification(s) to send.
*
* @param[in] res Resource to send updates for
* @param[in] obs 24-bit number to add as observe option
* @param[in] payload Payload to send out
* @param[in] payload_len Length of @p payload in bytes
*/
void nanocoap_notify_observers_simple(const coap_resource_t *res, uint32_t obs,
const void *payload, size_t payload_len);
/**
* @brief Get next consecutive message ID for use when building a new
* CoAP request.

6
sys/net/application_layer/nanocoap/nanocoap.c
View File

@ -28,6 +28,7 @@
#include "bitarithm.h"
#include "net/nanocoap.h"
#include "net/nanocoap_sock.h"
#define ENABLE_DEBUG 0
#include "debug.h"
@ -494,6 +495,11 @@ ssize_t coap_handle_req(coap_pkt_t *pkt, uint8_t *resp_buf, unsigned resp_buf_le
{
assert(ctx);
if (IS_USED(MODULE_NANOCOAP_SERVER_OBSERVE) && (coap_get_type(pkt) == COAP_TYPE_RST)) {
nanocoap_unregister_observer_due_to_reset(coap_request_ctx_get_remote_udp(ctx),
coap_get_id(pkt));
}
if (coap_get_code_class(pkt) != COAP_REQ) {
DEBUG("coap_handle_req(): not a request.\n");
return -EBADMSG;

159
sys/net/application_layer/nanocoap/sock.c
View File

@ -25,6 +25,7 @@
#include <string.h>
#include <stdio.h>
#include "container.h"
#include "net/credman.h"
#include "net/nanocoap.h"
#include "net/nanocoap_sock.h"
@ -48,6 +49,10 @@
# define CONFIG_NANOCOAP_DTLS_HANDSHAKE_BUF_SIZE (160)
#endif
#ifndef CONFIG_NANOCOAP_MAX_OBSERVERS
# define CONFIG_NANOCOAP_MAX_OBSERVERS 4
#endif
enum {
STATE_REQUEST_SEND, /**< request was just sent or will be sent again */
STATE_STOP_RETRANSMIT, /**< stop retransmissions due to a matching empty ACK */
@ -64,6 +69,35 @@ typedef struct {
#endif
} _block_ctx_t;
/**
* @brief Structure to track the state of an observation
*/
typedef struct {
/**
* @brief Context needed to build notifications (e.g. Token, endpoint
* to send to)
*
* @details To safe ROM, we reuse the separate response code to also
* send notifications, as the functionality is almost identical.
*/
nanocoap_server_response_ctx_t response;
/**
* @brief The resource the client has subscribed to
*
* @details This is `NULL` when the slot is free
*/
const coap_resource_t *resource;
/**
* @brief Message ID used in the last notification
*/
uint16_t msg_id;
} _observer_t;
#if MODULE_NANOCOAP_SERVER_OBSERVE
static _observer_t _observer_pool[CONFIG_NANOCOAP_MAX_OBSERVERS];
static mutex_t _observer_pool_lock;
#endif
int nanocoap_sock_dtls_connect(nanocoap_sock_t *sock, sock_udp_ep_t *local,
const sock_udp_ep_t *remote, credman_tag_t tag)
{
@ -1150,7 +1184,13 @@ int nanocoap_server_sendv_separate(const nanocoap_server_response_ctx_t *ctx,
if (!sock_udp_ep_is_multicast(&ctx->local)) {
aux_out_ptr = &aux_out;
}
return sock_udp_sendv_aux(NULL, reply, &ctx->remote, aux_out_ptr);
ssize_t retval = sock_udp_sendv_aux(NULL, reply, &ctx->remote, aux_out_ptr);
if (retval < 0) {
return retval;
}
return 0;
}
int nanocoap_server_send_separate(const nanocoap_server_response_ctx_t *ctx,
@ -1184,3 +1224,120 @@ int nanocoap_server_send_separate(const nanocoap_server_response_ctx_t *ctx,
return nanocoap_server_sendv_separate(ctx, &head);
}
#endif
#if MODULE_NANOCOAP_SERVER_OBSERVE
int nanocoap_register_observer(const coap_request_ctx_t *req_ctx, coap_pkt_t *req_pkt)
{
mutex_lock(&_observer_pool_lock);
_observer_t *free = NULL;
const coap_resource_t *resource = req_ctx->resource;
for (size_t i = 0; i < CONFIG_NANOCOAP_MAX_OBSERVERS; i++) {
if (_observer_pool[i].resource == NULL) {
free = &_observer_pool[i];
}
if ((_observer_pool[i].resource == resource)
&& sock_udp_ep_equal(&_observer_pool[i].response.remote,
coap_request_ctx_get_remote_udp(req_ctx)))
{
/* Deviation from the standard: Subscribing twice makes no
* sense with our CoAP implementation, so either this is a
* reaffirmation of an existing subscription (same token) or the
* client lost state (different token). We just update the
* subscription in either case */
DEBUG("nanocoap: observe slot %" PRIuSIZE " reused\n", i);
uint8_t tkl = coap_get_token_len(req_pkt);
_observer_pool[i].response.tkl = tkl;
memcpy(_observer_pool[i].response.token, coap_get_token(req_pkt), tkl);
mutex_unlock(&_observer_pool_lock);
return 0;
}
}
if (!free) {
DEBUG_PUTS("nanocoap: observe registration failed, no free slot");
mutex_unlock(&_observer_pool_lock);
return -ENOMEM;
}
int retval = nanocoap_server_prepare_separate(&free->response, req_pkt, req_ctx);
if (retval) {
DEBUG("nanocoap: observe registration failed: %d\n", retval);
mutex_unlock(&_observer_pool_lock);
return retval;
}
free->resource = req_ctx->resource;
free->msg_id = random_uint32();
mutex_unlock(&_observer_pool_lock);
DEBUG("nanocoap: new observe registration at slot %" PRIuSIZE "\n",
index_of(_observer_pool, free));
return 0;
}
void nanocoap_unregister_observer(const coap_request_ctx_t *req_ctx,
const coap_pkt_t *req_pkt)
{
mutex_lock(&_observer_pool_lock);
for (size_t i = 0; i < CONFIG_NANOCOAP_MAX_OBSERVERS; i++) {
if ((_observer_pool[i].resource == req_ctx->resource)
&& (_observer_pool[i].response.tkl == coap_get_token_len(req_pkt))
&& !memcmp(_observer_pool[i].response.token, coap_get_token(req_pkt),
_observer_pool[i].response.tkl)
&& sock_udp_ep_equal(&_observer_pool[i].response.remote, coap_request_ctx_get_remote_udp(req_ctx))) {
DEBUG("nanocoap: observer at index %" PRIuSIZE " unregistered\n", i);
_observer_pool[i].resource = NULL;
}
}
mutex_unlock(&_observer_pool_lock);
}
void nanocoap_unregister_observer_due_to_reset(const sock_udp_ep_t *ep,
uint16_t msg_id)
{
mutex_lock(&_observer_pool_lock);
for (size_t i = 0; i < CONFIG_NANOCOAP_MAX_OBSERVERS; i++) {
if ((_observer_pool[i].resource != NULL)
&& (_observer_pool[i].msg_id == msg_id)
&& sock_udp_ep_equal(&_observer_pool[i].response.remote, ep)) {
DEBUG("nanocoap: observer at index %" PRIuSIZE " unregistered due to RST\n", i);
_observer_pool[i].resource = NULL;
return;
}
}
mutex_unlock(&_observer_pool_lock);
}
void nanocoap_notify_observers(const coap_resource_t *res, const iolist_t *iol)
{
mutex_lock(&_observer_pool_lock);
for (size_t i = 0; i < CONFIG_NANOCOAP_MAX_OBSERVERS; i++) {
if (_observer_pool[i].resource == res) {
uint8_t rbuf[sizeof(coap_hdr_t) + COAP_TOKEN_LENGTH_MAX + 1];
ssize_t hdr_len = nanocoap_server_build_separate(&_observer_pool[i].response, rbuf, sizeof(rbuf),
COAP_CODE_CONTENT, COAP_TYPE_NON,
++_observer_pool[i].msg_id);
if (hdr_len < 0) {
/* no need to keep the observer in the pool, if we cannot
* send anyway */
_observer_pool[i].resource = NULL;
continue;
}
const iolist_t msg = {
.iol_base = rbuf,
.iol_len = hdr_len,
.iol_next = (iolist_t *)iol
};
if (nanocoap_server_sendv_separate(&_observer_pool[i].response, &msg)) {
/* no need to keep the observer in the pool, if we cannot
* send anyway */
_observer_pool[i].resource = NULL;
}
}
}
mutex_unlock(&_observer_pool_lock);
}
#endif