netreg: add multiplexer for checksum calculation

sys/include/net/ng_netreg.h

@@ -127,6 +127,22 @@ int ng_netreg_num(ng_nettype_t type, uint32_t demux_ctx);
  */
 ng_netreg_entry_t *ng_netreg_getnext(ng_netreg_entry_t *entry);
 
+/**
+ * @brief   Calculates the checksum for a header.
+ *
+ * @param[in] hdr           The header the checksum should be calculated
+ *                          for.
+ * @param[in] pseudo_hdr    The header the pseudo header shall be generated
+ *                          from. NULL if none is needed.
+ *
+ * @return  0, on success.
+ * @return  -EINVAL, if @p pseudo_hdr is NULL but a pseudo header was required.
+ * @return  -ENOENT, if @ref net_netreg does not know how to calculate checksum
+ *          for ng_pktsnip_t::type of @p hdr.
+ */
+
+int ng_netreg_calc_csum(ng_pktsnip_t *hdr, ng_pktsnip_t *pseudo_hdr);
+
 /**
  * @brief   Builds a header for sending and adds it to the packet buffer.
  *

sys/net/crosslayer/ng_netreg/ng_netreg.c

@@ -19,6 +19,7 @@
 #include "utlist.h"
 #include "net/ng_netreg.h"
 #include "net/ng_nettype.h"
+#include "net/ng_pkt.h"
 #include "net/ng_ipv6.h"
 
 #define _INVALID_TYPE(type) (((type) < NG_NETTYPE_UNDEF) || ((type) >= NG_NETTYPE_NUMOF))
@@ -102,6 +103,33 @@ ng_netreg_entry_t *ng_netreg_getnext(ng_netreg_entry_t *entry)
     return entry;
 }
 
+int ng_netreg_calc_csum(ng_pktsnip_t *hdr, ng_pktsnip_t *pseudo_hdr)
+{
+    if (pseudo_hdr == NULL) {
+        /* XXX: Might be allowed for future checksums.
+         *      If this is the case: move this to the branches were it
+         *      is needed. */
+        return -EINVAL;
+    }
+
+    switch (hdr->type) {
+#ifdef MODULE_NG_ICMPV6
+        case NG_NETTYPE_ICMPV6:
+            return ng_icmpv6_calc_csum(hdr, pseudo_hdr);
+#endif
+#ifdef MODULE_NG_TCP
+        case NG_NETTYPE_TCP:
+            return ng_tcp_calc_csum(hdr, pseudo_hdr);
+#endif
+#ifdef MODULE_NG_UDP
+        case NG_NETTYPE_UDP:
+            return ng_udp_calc_csum(hdr, pseudo_hdr);
+#endif
+        default:
+            return -ENOENT;
+    }
+}
+
 ng_pktsnip_t *ng_netreg_hdr_build(ng_nettype_t type, ng_pktsnip_t *payload,
                                   uint8_t *src, uint8_t src_len,
                                   uint8_t *dst, uint8_t dst_len)