nanocoap: add coap_request_ctx_init()

sys/include/net/nanocoap.h

@@ -322,6 +322,33 @@ typedef const struct {
     const size_t resources_numof;       /**< number of entries in array */
 } coap_resource_subtree_t;
 
+/**
+ * @brief   Size of the CoAP request context struct
+ */
+#define COAP_REQUEST_CTX_SIZE   (2 * sizeof(void *) + \
+                                 IS_USED(MODULE_GCOAP) * sizeof(uint32_t))
+
+/**
+ * @brief   Define and initialize CoAP request context struct
+ *
+ * @param[in] ctx    Name of the request context variable
+ * @param[in] remote Remote endpoint that made the request
+ */
+#define COAP_REQUEST_CTX_INIT(ctx, remote)                      \
+            uint8_t ctx ## _buffer[COAP_REQUEST_CTX_SIZE];      \
+            coap_request_ctx_t *ctx = (void *)ctx ## _buffer;   \
+            coap_request_ctx_init(ctx, remote)
+
+/**
+ * @brief   Initialize CoAP request context
+ *          Called by @ref COAP_REQUEST_CTX_INIT
+ * @internal
+ *
+ * @param[in] ctx    Pointer to the request context to initialize
+ * @param[in] remote Remote endpoint that made the request
+ */
+void coap_request_ctx_init(coap_request_ctx_t *ctx, sock_udp_ep_t *remote);
+
 /**
  * @brief   Get resource path associated with a CoAP request
  *

sys/net/application_layer/nanocoap/nanocoap.c

@@ -1260,6 +1260,15 @@ unsigned coap_get_len(coap_pkt_t *pkt)
     return pktlen;
 }
 
+void coap_request_ctx_init(coap_request_ctx_t *ctx, sock_udp_ep_t *remote)
+{
+    static_assert(COAP_REQUEST_CTX_SIZE == sizeof(coap_request_ctx_t),
+                  "COAP_REQUEST_CTX_SIZE define does not match actual size");
+
+    memset(ctx, 0, sizeof(*ctx));
+    ctx->remote = remote;
+}
+
 const char *coap_request_ctx_get_path(const coap_request_ctx_t *ctx)
 {
     return ctx->resource->path;