coap_cache: initial caching code

include/coap2/coap.h.in

@@ -40,6 +40,7 @@ extern "C" {
 #include "async.h"
 #include "bits.h"
 #include "block.h"
+#include "coap_cache.h"
 #include "coap_dtls.h"
 #include "coap_event.h"
 #include "coap_io.h"

include/coap2/coap_cache.h

@@ -0,0 +1,89 @@
+/* coap_cache.h -- Caching of CoAP requests
+*
+* Copyright (C) 2020 Olaf Bergmann <bergmann@tzi.org>
+*
+* This file is part of the CoAP library libcoap. Please see
+* README for terms of use.
+*/
+
+/**
+ * @file coap_cache.h
+ * @brief Provides a simple request storage for CoAP requests
+ */
+
+#ifndef COAP_CACHE_H_
+#define COAP_CACHE_H_
+
+#include <limits.h>
+
+#include "coap_forward_decls.h"
+
+typedef enum {
+              COAP_CACHE_INVALID=-1,
+              COAP_CACHE_MAXKEY=INT_MAX
+} coap_cache_key_t;
+
+/**
+ * Calculates a cache key for the given CoAP PDU. See
+ * https://tools.ietf.org/html/rfc7252#section-5.6
+ * for an explanation of CoAP cache keys.
+ *
+ * @param pdu The CoAP PDU for which a cache key is to be
+ *            calculated.
+ *
+ * @return The calculcated cache key.
+ */
+coap_cache_key_t coap_cache_key(const coap_pdu_t *pdu);
+
+/**
+ * Marks a request for permanent storage. The request may be retrieved
+ * through its cache-key.
+ *
+ * @param ctx     The context to use.
+ * @param request The request to be stored.
+ *
+ * @return The cache key that corresponds to the newly stored
+ *         request or @c COAP_CACHE_INVALID if the request could
+ *         not be stored.
+ */
+coap_cache_key_t coap_cache_mark_request(coap_context_t *ctx,
+                                         const coap_pdu_t *request);
+
+/**
+ * Clears a mark from a request.
+ *
+ * @param ctx        The context to use.
+ * @param cache_key  The cache key for the request which can be
+ *                   unmarked.
+ */
+void coap_cache_unmark_request(coap_context_t *ctx,
+                               coap_cache_key_t cache_key);
+
+/**
+ * Searches for a cache entry identified by @p cache_key. This
+ * function returns the corresponding cache entry or @c NULL
+ * if not found.
+ *
+ * @param ctx        The context to use.
+ * @param cache_key  The cache key to look up.
+ *
+ * @return The cache entry for @p cache_key or @c NULL if not found.
+ */
+struct coap_cache_entry_t *coap_cache_lookup_key(coap_context_t *ctx,
+                                                 coap_cache_key_t cache_key);
+
+/**
+ * Searches for a cache entry corresponding to @p request. This
+ * function returns the corresponding cache entry or @c NULL if not
+ * found.
+ *
+ * @param ctx        The context to use.
+ * @param request    The CoAP request to search for.
+ *
+ * @return The cache entry for @p request or @c NULL if not found.
+ */
+struct coap_cache_entry_t *coap_cache_lookup_request(coap_context_t *ctx,
+                                                     const coap_pdu_t *request);
+
+
+#endif  /* COAP_CACHE_H */

include/coap2/coap_forward_decls.h

@@ -28,6 +28,7 @@ struct coap_queue_t;
 struct coap_session_t;
 struct coap_string_t;
 struct coap_subscription_t;
+struct coap_cache_entry_t;
 
 /*
  * typedef all the structures that are defined in coap_*_internal.h

include/coap2/net.h

@@ -209,6 +209,7 @@ typedef struct coap_context_t {
   unsigned int csm_timeout;           /**< Timeout for waiting for a CSM from the remote side. 0 means disabled. */
   int observe_pending;             /**< Observe response pending */
 
+  struct coap_cache_entry_t *cache; /**< CoAP message cache */
   void *app;                       /**< application-specific data */
 #ifdef COAP_EPOLL_SUPPORT
   int epfd;                        /**< External FD for epoll */