session: add utility function for interacting with the session_t object

These functions were mostly added to make it easier to provide a ruby
FFI for tinydtls. This is also the reason why `dtls_session_addr`
dynamically allocates memory for a `struct sockaddr` instead of
receiving a pointer to a memory location for a `struct sockaddr` as an
argument.

Change-Id: I91c3ee0ab03f5e8ed50e8e309c08b2436536496a
Signed-off-by: Sören Tempel <tempel@uni-bremen.de>
Signed-off-by: Olaf Bergmann <bergmann@tzi.org>

session.c

@@ -71,6 +71,52 @@ dtls_session_init(session_t *sess) {
   sess->size = sizeof(sess->addr);
 }
 
+/* These functions are primarly needed for the tinydtls ruby gem.
+ *
+ * They are not implemented on Contiki and RIOT because these operating
+ * system don't supply malloc(3). This could be fixed by fixed by using
+ * memory pools on these operating system as in `peer.c`. However, the
+ * downside of this approach is that the memory pools reserve memory
+ * even if the `dtls_new_session` isn't used and usually memory for the
+ * `session_t` type is already resevered in the `peer_t` struct.
+ * Therefore it would introduces quite some overhead on these
+ * constrained platforms.
+ *
+ * In the long run we probably want to create two seperate memory pools
+ * for sessions and peers and store a pointer to a session in the peer
+ * struct.
+ */
+#if !(defined (WITH_CONTIKI)) && !(defined (RIOT_VERSION))
+session_t*
+dtls_new_session(struct sockaddr *addr, socklen_t addrlen) {
+  session_t *sess;
+
+  sess = malloc(sizeof(session_t));
+  if (!sess)
+    return NULL;
+  dtls_session_init(sess);
+
+  sess->size = addrlen;
+  memcpy(&sess->addr.sa, addr, sess->size);
+
+  return sess;
+}
+
+void
+dtls_free_session(session_t *sess) {
+  free(sess);
+}
+#endif
+
+struct sockaddr*
+dtls_session_addr(session_t *sess, socklen_t *addrlen) {
+  if (!sess)
+    return NULL;
+
+  *addrlen = sess->size;
+  return &sess->addr.sa;
+}
+
 int
 dtls_session_equals(const session_t *a, const session_t *b) {
   assert(a); assert(b);

session.h

@@ -66,6 +66,35 @@ typedef struct {
  */
 void dtls_session_init(session_t *sess);
 
+#if !(defined (WITH_CONTIKI)) && !(defined (RIOT_VERSION))
+/**
+ * Creates a new ::session_t for the given address.
+ *
+ * @param addr Address which should be stored in the ::session_t.
+ * @param addrlen Length of the @p addr.
+ * @return The new session or @c NULL on error.
+ */
+session_t* dtls_new_session(struct sockaddr *addr, socklen_t addrlen);
+
+/**
+ * Frees memory allocated for a session using ::dtls_new_session.
+ *
+ * @param sess Pointer to a session for which allocated memory should be
+ *     freed.
+ */
+void dtls_free_session(session_t *sess);
+#endif
+
+/**
+ * Extracts the address of the given ::session_t.
+ *
+ * @param sess Session to extract address for.
+ * @param addrlen Pointer to memory location where the address
+ *     length should be stored.
+ * @return The address or @c NULL if @p sess was @c NULL.
+ */
+struct sockaddr* dtls_session_addr(session_t *sess, socklen_t *addrlen);
+
 /**
  * Compares the given session objects. This function returns @c 0
  * when @p a and @p b differ, @c 1 otherwise.