gnrc_sixlowpan_iphc: refactor reception for RIOT-OS#8511

This refactors reception/decoding part of `gnrc_sixlowpan_iphc` to the
more layered approach modeled in RIOT-OS#8511. Since the reception part is
already complicated enough I decided to divide send and receive up into
separate changes.

sys/include/net/gnrc/sixlowpan/iphc.h

@@ -32,23 +32,17 @@ extern "C" {
 /**
  * @brief   Decompresses a received 6LoWPAN IPHC frame.
  *
- * @pre (dec_hdr != NULL) && (*dec_hdr != NULL) && ((*dec_hdr)->size >= sizeof(gnrc_ipv6_hdr_t))
- *
- * @param[out] dec_hdr      A pre-allocated IPv6 header. Will not be inserted into
- *                          @p pkt. May change due to next headers being added in NHC.
- * @param[in] pkt           A received 6LoWPAN IPHC frame. IPHC dispatch will not
- *                          be marked.
- * @param[in] datagram_size Size of the full uncompressed IPv6 datagram. May be 0, if @p pkt
- *                          contains the full (unfragmented) IPv6 datagram.
- * @param[in] offset        Offset of the IPHC dispatch in 6LoWPaN frame.
- * @param[in, out] nh_len   Pointer to next header length
+ * @pre (pkt != NULL)
  *
- * @return  length of the HC dispatches + inline values on success.
- * @return  0 on error.
+ * @param[in] pkt           A received 6LoWPAN IPHC frame. The first snip is to
+ *                          be expected to start with the IPHC dispatch.
+ * @param[in,out] ctx       Context for the packet. May be NULL. If not NULL it
+ *                          is expected to be of type
+ *                          @ref gnrc_sixlowpan_rbuf_t. This function might
+ *                          change the content of that.
+ * @param[in] page          Current 6Lo dispatch parsing page.
  */
-size_t gnrc_sixlowpan_iphc_decode(gnrc_pktsnip_t **dec_hdr, gnrc_pktsnip_t *pkt,
-                                  size_t datagram_size, size_t offset,
-                                  size_t *nh_len);
+void gnrc_sixlowpan_iphc_recv(gnrc_pktsnip_t *pkt, void *ctx, unsigned page);
 
 /**
  * @brief   Compresses a 6LoWPAN for IPHC.

sys/net/gnrc/network_layer/sixlowpan/frag/gnrc_sixlowpan_frag.c

@@ -312,8 +312,6 @@ void gnrc_sixlowpan_frag_recv(gnrc_pktsnip_t *pkt, void *ctx, unsigned page)
     }
 
     rbuf_add(hdr, pkt, offset, page);
-
-    gnrc_pktbuf_release(pkt);
 }
 
 void gnrc_sixlowpan_frag_rbuf_gc(void)

sys/net/gnrc/network_layer/sixlowpan/frag/rbuf.c

@@ -69,9 +69,6 @@ void rbuf_add(gnrc_netif_hdr_t *netif_hdr, gnrc_pktsnip_t *pkt,
               size_t offset, unsigned page)
 {
     rbuf_t *entry;
-    /* cppcheck-suppress variableScope
-     * (reason: cppcheck is clearly wrong here) */
-    unsigned int data_offset = 0;
     sixlowpan_frag_t *frag = pkt->data;
     rbuf_int_t *ptr;
     uint8_t *data = ((uint8_t *)pkt->data) + sizeof(sixlowpan_frag_t);
@@ -96,27 +93,6 @@ void rbuf_add(gnrc_netif_hdr_t *netif_hdr, gnrc_pktsnip_t *pkt,
         if (data[0] == SIXLOWPAN_UNCOMP) {
             frag_size--;
         }
-#ifdef MODULE_GNRC_SIXLOWPAN_IPHC
-        else if (sixlowpan_iphc_is(data)) {
-            size_t iphc_len, nh_len = 0;
-            iphc_len = gnrc_sixlowpan_iphc_decode(&entry->super.pkt, pkt,
-                                                  entry->super.pkt->size,
-                                                  sizeof(sixlowpan_frag_t),
-                                                  &nh_len);
-            if (iphc_len == 0) {
-                DEBUG("6lo rfrag: could not decode IPHC dispatch\n");
-                gnrc_pktbuf_release(entry->super.pkt);
-                rbuf_rm(entry);
-                return;
-            }
-            data += iphc_len;       /* take remaining data as data */
-            frag_size -= iphc_len;  /* and reduce frag size by IPHC dispatch length */
-            /* but add IPv6 header + next header lengths */
-            frag_size += sizeof(ipv6_hdr_t) + nh_len;
-            /* start copying after IPv6 header and next headers */
-            data_offset += sizeof(ipv6_hdr_t) + nh_len;
-        }
-#endif
     }
     else {
         frag_size = pkt->size - sizeof(sixlowpan_frag_n_t);
@@ -153,11 +129,30 @@ void rbuf_add(gnrc_netif_hdr_t *netif_hdr, gnrc_pktsnip_t *pkt,
     if (_rbuf_update_ints(entry, offset, frag_size)) {
         DEBUG("6lo rbuf: add fragment data\n");
         entry->super.current_size += (uint16_t)frag_size;
-        memcpy(((uint8_t *)entry->super.pkt->data) + offset + data_offset, data,
-               frag_size - data_offset);
+        if (offset == 0) {
+#ifdef MODULE_GNRC_SIXLOWPAN_IPHC
+            if (sixlowpan_iphc_is(data)) {
+                gnrc_pktsnip_t *frag_hdr = gnrc_pktbuf_mark(pkt,
+                        sizeof(sixlowpan_frag_t), GNRC_NETTYPE_SIXLOWPAN);
+                if (frag_hdr == NULL) {
+                    gnrc_pktbuf_release(entry->super.pkt);
+                    rbuf_rm(entry);
+                    return;
+                }
+                gnrc_sixlowpan_iphc_recv(pkt, &entry->super, 0);
+                return;
+            }
+            else
+#endif
+            if (data[0] == SIXLOWPAN_UNCOMP) {
+                data++;
+            }
+        }
+        memcpy(((uint8_t *)entry->super.pkt->data) + offset, data,
+               frag_size);
     }
-
     gnrc_sixlowpan_frag_rbuf_dispatch_when_complete(&entry->super, netif_hdr);
+    gnrc_pktbuf_release(pkt);
 }
 
 static inline bool _rbuf_int_overlap_partially(rbuf_int_t *i, uint16_t start, uint16_t end)

sys/net/gnrc/network_layer/sixlowpan/gnrc_sixlowpan.c

@@ -211,32 +211,9 @@ static void _receive(gnrc_pktsnip_t *pkt)
 #endif
 #ifdef MODULE_GNRC_SIXLOWPAN_IPHC
     else if (sixlowpan_iphc_is(dispatch)) {
-        size_t dispatch_size, nh_len;
-        gnrc_pktsnip_t *sixlowpan;
-        gnrc_pktsnip_t *dec_hdr = gnrc_pktbuf_add(NULL, NULL, sizeof(ipv6_hdr_t),
-                                                  GNRC_NETTYPE_IPV6);
-        if ((dec_hdr == NULL) ||
-            (dispatch_size = gnrc_sixlowpan_iphc_decode(&dec_hdr, pkt, 0, 0,
-                                                        &nh_len)) == 0) {
-            DEBUG("6lo: error on IPHC decoding\n");
-            if (dec_hdr != NULL) {
-                gnrc_pktbuf_release(dec_hdr);
-            }
-            gnrc_pktbuf_release(pkt);
-            return;
-        }
-        sixlowpan = gnrc_pktbuf_mark(pkt, dispatch_size, GNRC_NETTYPE_SIXLOWPAN);
-        if (sixlowpan == NULL) {
-            DEBUG("6lo: error on marking IPHC dispatch\n");
-            gnrc_pktbuf_release(dec_hdr);
-            gnrc_pktbuf_release(pkt);
-            return;
-        }
-
-        /* Remove IPHC dispatches */
-        /* Insert decoded header instead */
-        pkt = gnrc_pktbuf_replace_snip(pkt, sixlowpan, dec_hdr);
-        payload->type = GNRC_NETTYPE_UNDEF;
+        DEBUG("6lo: received 6LoWPAN IPHC comressed datagram\n");
+        gnrc_sixlowpan_iphc_recv(pkt, NULL, 0);
+        return;
     }
 #endif
     else {