RTPS: Added an analysis field to the ACKNACK dissection

A lot of people fail when interpreting ACKNACKs. I added a new field
that interprets the numeric values and shows a brief sentence with
the analysis.

Bug: 12312

Change-Id: I89a33f04c52ebd5ca486d2e23bddb7a6646945e7
Reviewed-on: https://code.wireshark.org/review/14724
Petri-Dish: Michael Mann <mmann78@netscape.net>
Tested-by: Petri Dish Buildbot <buildbot-no-reply@wireshark.org>
Reviewed-by: Michael Mann <mmann78@netscape.net>

1 files changed, 57 insertions, 37 deletions

diff --git a/epan/dissectors/packet-rtps.c b/epan/dissectors/packet-rtps.c
index 41208faec1..9a9c4d7902 100644
--- a/epan/dissectors/packet-rtps.c
+++ b/epan/dissectors/packet-rtps.c
@@ -276,6 +276,7 @@ static int hf_rtps_encapsulation_kind                           = -1;
 static int hf_rtps_octets_to_inline_qos                         = -1;
 static int hf_rtps_filter_signature                             = -1;
 static int hf_rtps_bitmap                                       = -1;
+static int hf_rtps_acknack_analysis                             = -1;
 static int hf_rtps_property_name                                = -1;
 static int hf_rtps_property_value                               = -1;
 static int hf_rtps_union                                        = -1;
@@ -2756,27 +2757,49 @@ static int rtps_util_add_bitmap(proto_tree *tree,
                         tvbuff_t *tvb,
                         gint       offset,
                         gboolean   little_endian,
-                        const char *label _U_) {
+                        const char *label) {
   gint32 num_bits;
   guint32 data;
   wmem_strbuf_t *temp_buff = wmem_strbuf_new_label(wmem_packet_scope());
-  int i, j, idx;
+  wmem_strbuf_t *analysis_buff = wmem_strbuf_new_label(wmem_packet_scope());
+  gint i, j, idx;
   gchar *last_one;
-  proto_item *ti;
+  proto_item *ti = NULL, *ti_tree = NULL;
   proto_tree *bitmap_tree;
   const gint original_offset = offset;
   guint32 datamask;
+  guint64 first_seq_number;
+  gboolean first_nack = TRUE;
 
-  bitmap_tree = proto_tree_add_subtree(tree, tvb, original_offset, offset-original_offset, ett_rtps_bitmap, &ti, label);
+  bitmap_tree = proto_tree_add_subtree(tree, tvb, original_offset, offset-original_offset,
+          ett_rtps_bitmap, &ti_tree, label);
 
   /* Bitmap base sequence number */
-  rtps_util_add_seq_number(bitmap_tree, tvb, offset, little_endian, "bitmapBase");
+  first_seq_number = rtps_util_add_seq_number(bitmap_tree, tvb, offset, little_endian, "bitmapBase");
   offset += 8;
 
   /* Reads the bitmap size */
   num_bits = NEXT_guint32(tvb, offset, little_endian);
   proto_tree_add_uint(bitmap_tree, hf_rtps_bitmap_num_bits, tvb, offset, 4, num_bits);
   offset += 4;
+  /* bitmap base 0 means that this is a preemptive ACKNACK */
+  if (first_seq_number == 0) {
+    ti = proto_tree_add_uint_format(bitmap_tree, hf_rtps_acknack_analysis, tvb, 0, 0,
+        1, "Acknack Analysis: Preemptive ACKNACK");
+    PROTO_ITEM_SET_GENERATED(ti);
+  }
+
+  if (first_seq_number > 0 && num_bits == 0) {
+    ti = proto_tree_add_uint_format(bitmap_tree, hf_rtps_acknack_analysis, tvb, 0, 0,
+            2, "Acknack Analysis: Expecting sample %" G_GINT64_MODIFIER "u", first_seq_number);
+    PROTO_ITEM_SET_GENERATED(ti);
+  }
+
+  if (num_bits > 0) {
+    ti = proto_tree_add_uint_format(bitmap_tree, hf_rtps_acknack_analysis, tvb, 0, 0,
+            3, "Acknack Analysis: Lost samples");
+    PROTO_ITEM_SET_GENERATED(ti);
+  }
 
   /* Reads the bits (and format the print buffer) */
   idx = 0;
@@ -2786,6 +2809,12 @@ static int rtps_util_add_bitmap(proto_tree *tree,
     for (j = 0; j < 32; ++j) {
       datamask = (1U << (31-j));
       wmem_strbuf_append_c(temp_buff, ((data & datamask) == datamask) ? '1':'0');
+      if ((data & datamask) == datamask) {
+        proto_item_append_text(ti,
+                first_nack ? " %" G_GINT64_MODIFIER "u" : ", %" G_GINT64_MODIFIER "u",
+                first_seq_number + idx);
+        first_nack = FALSE;
+      }
       ++idx;
       if ((idx >= num_bits) || (wmem_strbuf_get_len(temp_buff) >= (ITEM_LABEL_LENGTH - 1))) {
         break;
@@ -2800,11 +2829,19 @@ static int rtps_util_add_bitmap(proto_tree *tree,
   }
 
   if (wmem_strbuf_get_len(temp_buff) > 0) {
-    proto_tree_add_bytes_format_value(bitmap_tree, hf_rtps_bitmap, tvb, original_offset + 12, offset - original_offset - 12,
-                                       NULL, "%s", wmem_strbuf_get_str(temp_buff));
+    proto_tree_add_bytes_format_value(bitmap_tree, hf_rtps_bitmap, tvb,
+            original_offset + 12, offset - original_offset - 12,
+            NULL, "%s", wmem_strbuf_get_str(temp_buff));
+  }
+
+  proto_item_set_len(ti_tree, offset-original_offset);
+
+  /* Add analysis of the information */
+  if (num_bits > 0) {
+    proto_item_append_text(ti, "%s in range [%" G_GINT64_MODIFIER "u,%" G_GINT64_MODIFIER "u]",
+        wmem_strbuf_get_str(analysis_buff), first_seq_number, first_seq_number + num_bits - 1);
   }
 
-  proto_item_set_len(ti, offset-original_offset);
   return offset;
 }
 
@@ -5921,11 +5958,7 @@ static void dissect_ACKNACK(tvbuff_t *tvb, packet_info *pinfo, gint offset, guin
 
   proto_tree_add_bitmask_value(tree, tvb, offset + 1, hf_rtps_sm_flags, ett_rtps_flags, ACKNACK_FLAGS, flags);
 
-  octet_item = proto_tree_add_item(tree,
-                        hf_rtps_sm_octets_to_next_header,
-                        tvb,
-                        offset + 2,
-                        2,
+  octet_item = proto_tree_add_item(tree, hf_rtps_sm_octets_to_next_header, tvb, offset + 2, 2,
                         little_endian ? ENC_LITTLE_ENDIAN : ENC_BIG_ENDIAN);
 
   if (octets_to_next_header < 20) {
@@ -5937,36 +5970,17 @@ static void dissect_ACKNACK(tvbuff_t *tvb, packet_info *pinfo, gint offset, guin
   original_offset = offset;
 
   /* readerEntityId */
-  rtps_util_add_entity_id(tree,
-                        tvb,
-                        offset,
-                        hf_rtps_sm_rdentity_id,
-                        hf_rtps_sm_rdentity_id_key,
-                        hf_rtps_sm_rdentity_id_kind,
-                        ett_rtps_rdentity,
-                        "readerEntityId",
-                        NULL);
+  rtps_util_add_entity_id(tree, tvb, offset, hf_rtps_sm_rdentity_id, hf_rtps_sm_rdentity_id_key,
+                        hf_rtps_sm_rdentity_id_kind, ett_rtps_rdentity, "readerEntityId", NULL);
   offset += 4;
 
   /* writerEntityId */
-  rtps_util_add_entity_id(tree,
-                        tvb,
-                        offset,
-                        hf_rtps_sm_wrentity_id,
-                        hf_rtps_sm_wrentity_id_key,
-                        hf_rtps_sm_wrentity_id_kind,
-                        ett_rtps_wrentity,
-                        "writerEntityId",
-                        NULL);
+  rtps_util_add_entity_id(tree, tvb, offset, hf_rtps_sm_wrentity_id, hf_rtps_sm_wrentity_id_key,
+                        hf_rtps_sm_wrentity_id_kind, ett_rtps_wrentity, "writerEntityId", NULL);
   offset += 4;
 
   /* Bitmap */
-  offset = rtps_util_add_bitmap(tree,
-                        tvb,
-                        offset,
-                        little_endian,
-                        "readerSNState");
-
+  offset = rtps_util_add_bitmap(tree, tvb, offset, little_endian, "readerSNState");
 
   /* RTPS 1.0 didn't have count: make sure we don't decode it wrong
    * in this case
@@ -9297,6 +9311,12 @@ void proto_register_rtps(void) {
         NULL, HFILL }
     },
 
+    { &hf_rtps_acknack_analysis,
+      { "Acknack Analysis", "rtps.sm.acknack_analysis",
+        FT_UINT32, BASE_DEC, NULL, 0,
+        NULL, HFILL }
+    },
+
     { &hf_rtps_param_partition_num,
       { "Size", "rtps.param.partition_num",
         FT_INT32, BASE_DEC, NULL, 0,