From d491e827fb80538cea926dee8ff56a236acaa278 Mon Sep 17 00:00:00 2001
From: Martine Lenders <m.lenders@fu-berlin.de>
Date: Mon, 12 Oct 2020 15:21:22 +0200
Subject: [PATCH] gnrc_pkt: introduce packet list operations

Up until now `utlist.h` is used to manipulate the packet list within a
GNRC pkt snip. Since I always wanted to see if there would be an
advantage when using `core`'s `list.h`, I provide this
`gnrc_pktsnip_t`-specific API to manipulate the packet list. It has the
additional advantage of type safety and that future steps could
encapsulate those operations.
---
 sys/include/net/gnrc/pkt.h | 64 ++++++++++++++++++++++++++++++++++++++
 1 file changed, 64 insertions(+)

diff --git a/sys/include/net/gnrc/pkt.h b/sys/include/net/gnrc/pkt.h
index efa363003c..ffa57fbf24 100644
--- a/sys/include/net/gnrc/pkt.h
+++ b/sys/include/net/gnrc/pkt.h
@@ -27,6 +27,7 @@
 
 #include "kernel_types.h"
 #include "net/gnrc/nettype.h"
+#include "utlist.h"
 
 #ifdef __cplusplus
 extern "C" {
@@ -122,6 +123,23 @@ typedef struct gnrc_pktsnip {
 #endif
 } gnrc_pktsnip_t;
 
+/**
+ * @brief   Returns the snip before a given snip in a packet
+ *
+ * @param[in] pkt   A packet.
+ * @param[in] snip  The snip for which the predecessor in @p pkt is searched for.
+ *
+ * @return  The snip before @p snip in @p pkt if @p snip is in @p pkt.
+ * @return  `NULL`, if @p snip is not in @p pkt.
+ */
+static inline gnrc_pktsnip_t *gnrc_pkt_prev_snip(gnrc_pktsnip_t *pkt,
+                                                 gnrc_pktsnip_t *snip)
+{
+    gnrc_pktsnip_t *prev;
+    LL_SEARCH_SCALAR(pkt, prev, next, snip);
+    return prev;
+}
+
 /**
  * @brief Calculates length of a packet in byte.
  *
@@ -141,6 +159,52 @@ static inline size_t gnrc_pkt_len(const gnrc_pktsnip_t *pkt)
     return len;
 }
 
+/**
+ * @brief   Appends a snip to a packet.
+ *
+ * @param[in] pkt   A packet.
+ * @param[in] snip  A snip.
+ *
+ * @return  The new head of @p pkt.
+ */
+static inline gnrc_pktsnip_t *gnrc_pkt_append(gnrc_pktsnip_t *pkt,
+                                              gnrc_pktsnip_t *snip)
+{
+    LL_APPEND(pkt, snip);
+    return pkt;
+}
+
+/**
+ * @brief   Prepends a snip to a packet.
+ *
+ * @param[in] pkt   A packet.
+ * @param[in] snip  A snip.
+ *
+ * @return  The new head of @p pkt.
+ */
+static inline gnrc_pktsnip_t *gnrc_pkt_prepend(gnrc_pktsnip_t *pkt,
+                                               gnrc_pktsnip_t *snip)
+{
+    LL_PREPEND(pkt, snip);
+    return pkt;
+}
+
+/**
+ * @brief   Deletes a snip from a packet.
+ *
+ * @param[in] pkt   A packet.
+ * @param[in] snip  A snip.
+ *
+ * @return  The new head of @p pkt.
+ */
+static inline gnrc_pktsnip_t *gnrc_pkt_delete(gnrc_pktsnip_t *pkt,
+                                              gnrc_pktsnip_t *snip)
+{
+    LL_DELETE(pkt, snip);
+    return pkt;
+}
+
+
 /**
  * @brief Calculates length of a packet in byte up to (including) a snip with the given type.
  *