gcoap: Observe extension server

examples/gcoap/README.md

@@ -14,13 +14,14 @@ Build with `Makefile.slip`. Follow the setup instructions in README-slip.md, whi
 ## Current Status
 gcoap includes server and client capability. Available features include:
 
+* Message Type: Supports non-confirmable (NON) messaging. Additionally provides a callback on timeout.
+* Observe extension: Provides server-side registration and notifications.
 * Server and Client provide helper functions for writing the response/request. See the CoAP topic in the source documentation for details. See the gcoap example for sample implementations.
 * Server allows an application to register a 'listener', which includes an array of endpoint paths and function callbacks used to write a response.
 * Server listens on a port at startup; defaults to 5683.
-* Client operates asynchronously; sends request and then handles response in a user provided callback. Also executes callback on timeout.
+* Client operates asynchronously; sends request and then handles response in a user provided callback.
 * Client generates token; length defined at compile time.
-* Message Type: Supports non-confirmable (NON) messaging.
-* Options: Supports Content-Format for response payload.
+* Options: Supports Content-Format for payload.
 
 
 ## Example Use

examples/gcoap/gcoap_cli.c

@@ -26,6 +26,9 @@
 #include "od.h"
 #include "fmt.h"
 
+#define ENABLE_DEBUG (0)
+#include "debug.h"
+
 static void _resp_handler(unsigned req_state, coap_pkt_t* pdu);
 static ssize_t _stats_handler(coap_pkt_t* pdu, uint8_t *buf, size_t len);
 
@@ -149,15 +152,33 @@ int gcoap_cli_cmd(int argc, char **argv)
  argv[4]);
  }
  printf("gcoap_cli: sending msg ID %u, %u bytes\n", coap_get_id(&pdu),
-  (unsigned) len);
+ (unsigned) len);
  if (!_send(&buf[0], len, argv[2], argv[3])) {
  puts("gcoap_cli: msg send failed");
  }
+ else {
+ /* send Observe notification for /cli/stats */
+ switch (gcoap_obs_init(&pdu, &buf[0], GCOAP_PDU_BUF_SIZE,
+ &_resources[0])) {
+ case GCOAP_OBS_INIT_OK:
+ DEBUG("gcoap_cli: creating /cli/stats notification\n");
+ size_t payload_len = fmt_u16_dec((char *)pdu.payload, req_count);
+ len = gcoap_finish(&pdu, payload_len, COAP_FORMAT_TEXT);
+ gcoap_obs_send(&buf[0], len, &_resources[0]);
+ break;
+ case GCOAP_OBS_INIT_UNUSED:
+ DEBUG("gcoap_cli: no observer for /cli/stats\n");
+ break;
+ case GCOAP_OBS_INIT_ERR:
+ DEBUG("gcoap_cli: error initializing /cli/stats notification\n");
+ break;
+ }
+ }
  return 0;
  }
  else {
  printf("usage: %s <get|post|put> <addr> <port> <path> [data]\n",
-  argv[0]);
+ argv[0]);
  return 1;
  }
  }

pkg/nanocoap/Makefile

@@ -1,6 +1,6 @@
 PKG_NAME=nanocoap
 PKG_URL=https:/kaspar030/sock
-PKG_VERSION=4035239dce751216038bb2dc8632aa4a734d68a7
+PKG_VERSION=1bba8bb16463914266dd5a04fe2a3eac4ee129ae
 PKG_LICENSE=LGPL-2.1
 
 .PHONY: all

sys/include/net/gcoap.h

@@ -25,6 +25,10 @@
  * port, which supports RFC 6282 compression. Internally, gcoap depends on the
  * nanocoap package for base level structs and functionality.
  *
+ * gcoap also supports the Observe extension (RFC 7641) for a server. gcoap
+ * provides functions to generate and send an observe notification that are
+ * similar to the functions to send a client request.
+ *
  * ## Server Operation ##
  *
  * gcoap listens for requests on GCOAP_PORT, 5683 by default. You can redefine
@@ -75,7 +79,7 @@
  *
  * ### Creating a request ###
  *
- * Here is the expected sequence for preparing and sending a request:
+ * Here is the expected sequence to prepare and send a request:
  *
  * Allocate a buffer and a coap_pkt_t for the request.
  *
@@ -109,6 +113,43 @@
  * _content_type_ attributes.
  * -# Read the payload, if any.
  *
+ * ## Observe Server Operation
+ *
+ * A CoAP client may register for Observe notifications for any resource that
+ * an application has registered with gcoap. An application does not need to
+ * take any action to support Observe client registration. However, gcoap
+ * limits registration for a given resource to a _single_ observer.
+ *
+ * An Observe notification is considered a response to the original client
+ * registration request. So, the Observe server only needs to create and send
+ * the notification -- no further communication or callbacks are required.
+ *
+ * ### Creating a notification ###
+ *
+ * Here is the expected sequence to prepare and send a notification:
+ *
+ * Allocate a buffer and a coap_pkt_t for the notification, then follow the
+ * steps below.
+ *
+ * -# Call gcoap_obs_init() to initialize the notification for a resource.
+ * Test the return value, which may indicate there is not an observer for
+ * the resource. If so, you are done.
+ * -# Write the notification payload, starting at the updated _payload_ pointer
+ * in the coap_pkt_t.
+ * -# Call gcoap_finish(), which updates the packet for the payload.
+ *
+ * Finally, call gcoap_obs_send() for the resource.
+ *
+ * ### Other considerations ###
+ *
+ * By default, the value for the Observe option in a notification is three
+ * bytes long. For resources that change slowly, this length can be reduced via
+ * GCOAP_OBS_VALUE_WIDTH.
+ *
+ * To cancel a notification, the server expects to receive a GET request with
+ * the Observe option value set to 1. The server does not support cancellation
+ * via a reset (RST) response to a non-confirmable notification.
+ *
  * ## Implementation Notes ##
  *
  * ### Building a packet ###
@@ -175,6 +216,13 @@ extern "C" {
  */
 #define GCOAP_RESP_OPTIONS_BUF (8)
 
+/**
+ * @brief Size of the buffer used to write options in an Observe notification.
+ *
+ * Accommodates Content-Format and Observe.
+ */
+#define GCOAP_OBS_OPTIONS_BUF (8)
+
 /** @brief Maximum number of requests awaiting a response */
 #define GCOAP_REQ_WAITING_MAX (2)
 
@@ -225,6 +273,69 @@ extern "C" {
  */
 #define GCOAP_MSG_TYPE_INTR (0x1502)
 
+/** @brief Maximum number of Observe clients; use 2 if not defined */
+#ifndef GCOAP_OBS_CLIENTS_MAX
+#define GCOAP_OBS_CLIENTS_MAX (2)
+#endif
+
+/**
+ * @brief Maximum number of registrations for Observable resources; use 2 if
+ * not defined
+ */
+#ifndef GCOAP_OBS_REGISTRATIONS_MAX
+#define GCOAP_OBS_REGISTRATIONS_MAX (2)
+#endif
+
+/**
+ * @name States for the memo used to track Observe registrations
+ * @{
+ */
+#define GCOAP_OBS_MEMO_UNUSED (0) /**< This memo is unused */
+#define GCOAP_OBS_MEMO_IDLE (1) /**< Registration OK; no current activity */
+#define GCOAP_OBS_MEMO_PENDING (2) /**< Resource changed; notification pending */
+/** @} */
+
+/**
+ * @brief Width in bytes of the Observe option value for a notification.
+ *
+ * This width is used to determine the length of the 'tick' used to measure
+ * the time between observable changes to a resource. A tick is expressed
+ * internally as GCOAP_OBS_TICK_EXPONENT, which is the base-2 log value of the
+ * tick length in microseconds.
+ *
+ * The canonical setting for the value width is 3 (exponent 5), which results
+ * in a tick length of 32 usec, per sec. 3.4, 4.4 of the RFC. Width 2
+ * (exponent 16) results in a tick length of ~65 msec, and width 1 (exponent
+ * 24) results in a tick length of ~17 sec.
+ *
+ * The tick length must be short enough so that the Observe value strictly
+ * increases for each new notification. The purpose of the value is to allow a
+ * client to detect message reordering within the network latency period (128
+ * sec). For resources that change only slowly, the reduced message length is
+ * useful when packet size is limited.
+ */
+#ifndef GCOAP_OBS_VALUE_WIDTH
+#define GCOAP_OBS_VALUE_WIDTH (3)
+#endif
+
+/** @brief See GCOAP_OBS_VALUE_WIDTH. */
+#if (GCOAP_OBS_VALUE_WIDTH == 3)
+#define GCOAP_OBS_TICK_EXPONENT (5)
+#elif (GCOAP_OBS_VALUE_WIDTH == 2)
+#define GCOAP_OBS_TICK_EXPONENT (16)
+#elif (GCOAP_OBS_VALUE_WIDTH == 1)
+#define GCOAP_OBS_TICK_EXPONENT (24)
+#endif
+
+/**
+ * @name Return values for gcoap_obs_init()
+ * @{
+ */
+#define GCOAP_OBS_INIT_OK (0)
+#define GCOAP_OBS_INIT_ERR (-1)
+#define GCOAP_OBS_INIT_UNUSED (-2)
+/** @} */
+
 /**
  * @brief A modular collection of resources for a server
  */
@@ -255,16 +366,29 @@ typedef struct {
  msg_t timeout_msg; /**< For response timer */
 } gcoap_request_memo_t;
 
+/** @brief Memo for Observe registration and notifications */
+typedef struct {
+ sock_udp_ep_t *observer; /**< Client endpoint; unused if null */
+ coap_resource_t *resource; /**< Entity being observed */
+ uint8_t token[GCOAP_TOKENLEN_MAX]; /**< Client token for notifications */
+ unsigned token_len; /**< Actual length of token attribute */
+} gcoap_observe_memo_t;
+
 /**
  * @brief Container for the state of gcoap itself
  */
 typedef struct {
- gcoap_listener_t *listeners; /**< List of registered listeners */
+ gcoap_listener_t *listeners;  /**< List of registered listeners */
  gcoap_request_memo_t open_reqs[GCOAP_REQ_WAITING_MAX];
- /**< Storage for open requests; if first
- byte of an entry is zero, the entry
- is available */
- uint16_t last_message_id; /**< Last message ID used */
+ /**< Storage for open requests; if first
+ byte of an entry is zero, the entry
+ is available */
+ uint16_t last_message_id; /**< Last message ID used */
+ sock_udp_ep_t observers[GCOAP_OBS_CLIENTS_MAX];
+ /**< Observe clients; allows reuse for
+ observe memos */
+ gcoap_observe_memo_t observe_memos[GCOAP_OBS_REGISTRATIONS_MAX];
+ /**< Observed resource registrations */
 } gcoap_state_t;
 
 /**
@@ -402,6 +526,39 @@ static inline ssize_t gcoap_response(coap_pkt_t *pdu, uint8_t *buf, size_t len,
  : -1;
 }
 
+/**
+ * @brief Initializes a CoAP Observe notification packet on a buffer, for the
+ * observer registered for a resource.
+ *
+ * First verifies that an observer has been registered for the resource.
+ *
+ * @param[in] pdu Notification metadata
+ * @param[in] buf Buffer containing the PDU
+ * @param[in] len Length of the buffer
+ * @param[in] resource Resource for the notification
+ *
+ * @return GCOAP_OBS_INIT_OK on success
+ * @return GCOAP_OBS_INIT_ERR on error
+ * @return GCOAP_OBS_INIT_UNUSED if no observer for resource
+ */
+int gcoap_obs_init(coap_pkt_t *pdu, uint8_t *buf, size_t len,
+ const coap_resource_t *resource);
+
+/**
+ * @brief Sends a buffer containing a CoAP Observe notification to the
+ * observer registered for a resource.
+ *
+ * Assumes a single observer for a resource.
+ *
+ * @param[in] buf Buffer containing the PDU
+ * @param[in] len Length of the buffer
+ * @param[in] resource Resource to send
+ *
+ * @return length of the packet
+ * @return 0 if cannot send
+ */
+size_t gcoap_obs_send(uint8_t *buf, size_t len, const coap_resource_t *resource);
+
 /**
  * @brief Provides important operational statistics.
  *