asterix: special processing for field item I021/150

There is a problem where one field decodes differently
depending on another fields content.

A code has been added to save information for 021_150_IM field.
When the next field 021_150_ASPD is decoded, the
stored information determines how it shall be scaled.
This is a special case for I021/150 only.

The same way as this change, other changes shall be done for
fields that are dependent on other fields.

Bug: 14076
Change-Id: I51f2c8f79bc6bde9efc0429e54fbea36818e9b36
Reviewed-on: https://code.wireshark.org/review/24734
Reviewed-by: Martin Kaiser <wireshark@kaiser.cx>
Petri-Dish: Martin Kaiser <wireshark@kaiser.cx>
Petri-Dish: Graham Bloice <graham.bloice@trihedral.com>
Tested-by: Petri Dish Buildbot
Reviewed-by: Anders Broman <a.broman58@gmail.com>

1 files changed, 40 insertions, 18 deletions

diff --git a/epan/dissectors/packet-asterix.c b/epan/dissectors/packet-asterix.c
index b7d58ae370..b23538895a 100644
--- a/epan/dissectors/packet-asterix.c
+++ b/epan/dissectors/packet-asterix.c
@@ -33,6 +33,7 @@
 
 #include <epan/packet.h>
 #include <epan/prefs.h>
+#include <epan/proto_data.h>
 
 void proto_register_asterix(void);
 void proto_reg_handoff_asterix(void);
@@ -2760,11 +2761,11 @@ struct AsterixField_s {
 };
 DIAG_ON(pedantic)
 
-static void dissect_asterix_packet (tvbuff_t *, proto_tree *);
-static void dissect_asterix_data_block (tvbuff_t *tvb, guint, proto_tree *, guint8, gint);
-static gint dissect_asterix_fields (tvbuff_t *, guint, proto_tree *, guint8, const AsterixField *[]);
+static void dissect_asterix_packet (tvbuff_t *, packet_info *pinfo, proto_tree *);
+static void dissect_asterix_data_block (tvbuff_t *tvb, packet_info *pinfo, guint, proto_tree *, guint8, gint);
+static gint dissect_asterix_fields (tvbuff_t *, packet_info *pinfo, guint, proto_tree *, guint8, const AsterixField *[]);
 
-static void asterix_build_subtree (tvbuff_t *, guint, proto_tree *, const AsterixField *);
+static void asterix_build_subtree (tvbuff_t *, packet_info *pinfo, guint, proto_tree *, const AsterixField *);
 static void twos_complement (gint64 *, guint8);
 static guint8 byte_length (guint8);
 static guint8 asterix_bit (guint8, guint8);
@@ -8425,13 +8426,13 @@ static int dissect_asterix (tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree,
     col_clear (pinfo->cinfo, COL_INFO);
 
     if (tree) { /* we are being asked for details */
-        dissect_asterix_packet (tvb, tree);
+        dissect_asterix_packet (tvb, pinfo, tree);
     }
 
     return tvb_captured_length(tvb);
 }
 
-static void dissect_asterix_packet (tvbuff_t *tvb, proto_tree *tree)
+static void dissect_asterix_packet (tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree)
 {
     guint i;
     guint8 category;
@@ -8449,11 +8450,11 @@ static void dissect_asterix_packet (tvbuff_t *tvb, proto_tree *tree)
         proto_tree_add_item (asterix_packet_tree, hf_asterix_category, tvb, i, 1, ENC_BIG_ENDIAN);
         proto_tree_add_item (asterix_packet_tree, hf_asterix_length, tvb, i + 1, 2, ENC_BIG_ENDIAN);
 
-        dissect_asterix_data_block (tvb, i + 3, asterix_packet_tree, category, length);
+        dissect_asterix_data_block (tvb, pinfo, i + 3, asterix_packet_tree, category, length);
     }
 }
 
-static void dissect_asterix_data_block (tvbuff_t *tvb, guint offset, proto_tree *tree, guint8 category, gint length)
+static void dissect_asterix_data_block (tvbuff_t *tvb, packet_info *pinfo, guint offset, proto_tree *tree, guint8 category, gint length)
 {
     guint8 active_uap;
     int fspec_len, inner_offset, size, counter;
@@ -8471,7 +8472,7 @@ static void dissect_asterix_data_block (tvbuff_t *tvb, guint offset, proto_tree
             /*show_fspec (tvb, asterix_message_tree, offset + inner_offset, fspec_len);*/
             proto_tree_add_item (asterix_message_tree, hf_asterix_fspec, tvb, offset + inner_offset, fspec_len, ENC_NA);
 
-            size = dissect_asterix_fields (tvb, offset + inner_offset, asterix_message_tree, category, categories[category][global_categories_version[category]][active_uap]);
+            size = dissect_asterix_fields (tvb, pinfo, offset + inner_offset, asterix_message_tree, category, categories[category][global_categories_version[category]][active_uap]);
 
             inner_offset += size + fspec_len;
         }
@@ -8481,7 +8482,7 @@ static void dissect_asterix_data_block (tvbuff_t *tvb, guint offset, proto_tree
     }
 }
 
-static gint dissect_asterix_fields (tvbuff_t *tvb, guint offset, proto_tree *tree, guint8 category, const AsterixField *current_uap[])
+static gint dissect_asterix_fields (tvbuff_t *tvb, packet_info *pinfo, guint offset, proto_tree *tree, guint8 category, const AsterixField *current_uap[])
 {
     guint i, j, size, start, len, inner_offset, fspec_len;
     guint64 counter;
@@ -8503,7 +8504,7 @@ static gint dissect_asterix_fields (tvbuff_t *tvb, guint offset, proto_tree *tre
                 asterix_field_tree = proto_item_add_subtree (asterix_field_item, ett_asterix_subtree);
                 fspec_len = asterix_fspec_len (tvb, offset + start);
                 proto_tree_add_item (asterix_field_tree, hf_asterix_fspec, tvb, offset + start, fspec_len, ENC_NA);
-                dissect_asterix_fields (tvb, offset + start, asterix_field_tree, category, (const AsterixField **)current_uap[i]->field);
+                dissect_asterix_fields (tvb, pinfo, offset + start, asterix_field_tree, category, (const AsterixField **)current_uap[i]->field);
             }
             else if (current_uap[i]->type & REPETITIVE) {
                 asterix_field_item = proto_tree_add_item (tree, *current_uap[i]->hf, tvb, offset + start, len, ENC_NA);
@@ -8515,7 +8516,7 @@ static gint dissect_asterix_fields (tvbuff_t *tvb, guint offset, proto_tree *tre
                 for (j = 0, inner_offset = 0; j < counter; j++, inner_offset += current_uap[i]->length) {
                     asterix_field_item2 = proto_tree_add_item (asterix_field_tree, *current_uap[i]->hf, tvb, offset + start + current_uap[i]->repetition_counter_size + inner_offset, current_uap[i]->length, ENC_NA);
                     asterix_field_tree2 = proto_item_add_subtree (asterix_field_item2, ett_asterix_subtree);
-                    asterix_build_subtree (tvb, offset + start + current_uap[i]->repetition_counter_size + inner_offset, asterix_field_tree2, current_uap[i]);
+                    asterix_build_subtree (tvb, pinfo, offset + start + current_uap[i]->repetition_counter_size + inner_offset, asterix_field_tree2, current_uap[i]);
                 }
             }
             else if (current_uap[i]->type & RE) {
@@ -8525,24 +8526,26 @@ static gint dissect_asterix_fields (tvbuff_t *tvb, guint offset, proto_tree *tre
                 start++;
                 fspec_len = asterix_fspec_len (tvb, offset + start);
                 proto_tree_add_item (asterix_field_tree, hf_asterix_fspec, tvb, offset + start, fspec_len, ENC_NA);
-                dissect_asterix_fields (tvb, offset + start, asterix_field_tree, category, (const AsterixField **)current_uap[i]->field);
+                dissect_asterix_fields (tvb, pinfo, offset + start, asterix_field_tree, category, (const AsterixField **)current_uap[i]->field);
             }
             else {
                 asterix_field_item = proto_tree_add_item (tree, *current_uap[i]->hf, tvb, offset + start, len, ENC_NA);
                 asterix_field_tree = proto_item_add_subtree (asterix_field_item, ett_asterix_subtree);
-                asterix_build_subtree (tvb, offset + start, asterix_field_tree, current_uap[i]);
+                asterix_build_subtree (tvb, pinfo, offset + start, asterix_field_tree, current_uap[i]);
             }
         }
     }
     return size;
 }
 
-static void asterix_build_subtree (tvbuff_t *tvb, guint offset, proto_tree *parent, const AsterixField *field)
+static void asterix_build_subtree (tvbuff_t *tvb, packet_info *pinfo, guint offset, proto_tree *parent, const AsterixField *field)
 {
     gint i, inner_offset;
     guint8 go_on;
     gint64 value;
     char *str_buffer = NULL;
+    double scaling_factor = 1.0;
+    guint8 *set_im_021_150, *get_im_021_150;
 
     if (field->part != NULL) {
         for (i = 0, inner_offset = 0, go_on = 1; go_on && field->part[i] != NULL; i++) {
@@ -8554,6 +8557,14 @@ static void asterix_build_subtree (tvbuff_t *tvb, guint offset, proto_tree *pare
                         /* Fall through */
                     case FIELD_PART_INT:
                     case FIELD_PART_UINT:
+                        /* special processing for I021/150 because ASPD depends on IM subfield */
+                        if (field->part[i] == &I021_150_IM) {
+                            set_im_021_150 = wmem_new (wmem_packet_scope (), guint8);
+                            *set_im_021_150 = (tvb_get_guint8 (tvb, offset + inner_offset / 8) & 0x80) >> 7;
+                            /* Save IAS info for the packet. Cat 21 and field number 150 used for key = 21150. */
+                            p_add_proto_data (pinfo->pool, pinfo, proto_asterix, 21150, set_im_021_150);
+                        }
+                        /* Fall through */
                     case FIELD_PART_HEX:
                     case FIELD_PART_ASCII:
                     case FIELD_PART_SQUAWK:
@@ -8563,10 +8574,21 @@ static void asterix_build_subtree (tvbuff_t *tvb, guint offset, proto_tree *pare
                         twos_complement (&value, field->part[i]->bit_length);
                         /* Fall through */
                     case FIELD_PART_UFLOAT:
+                        /* Special processing for I021/150 depends on another field, which stores the value in static variable im_021_150 */
+                        if (field->part[i] == &I021_150_ASPD) {
+                            get_im_021_150 = (guint8 *)p_get_proto_data (pinfo->pool, pinfo, proto_asterix, 21150);
+                            if (*get_im_021_150 == 0)
+                                scaling_factor = 1.0/16384.0;
+                            else
+                                scaling_factor = 0.001;
+                        }
+                        else
+                            scaling_factor = field->part[i]->scaling_factor;
+
                         if (field->part[i]->format_string != NULL)
-                            proto_tree_add_double_format_value (parent, *field->part[i]->hf, tvb, offset + inner_offset / 8, byte_length (field->part[i]->bit_length), value * field->part[i]->scaling_factor, field->part[i]->format_string, value * field->part[i]->scaling_factor);
+                            proto_tree_add_double_format_value (parent, *field->part[i]->hf, tvb, offset + inner_offset / 8, byte_length (field->part[i]->bit_length), value * scaling_factor, field->part[i]->format_string, value * scaling_factor);
                         else
-                            proto_tree_add_double (parent, *field->part[i]->hf, tvb, offset + inner_offset / 8, byte_length (field->part[i]->bit_length), value * field->part[i]->scaling_factor);
+                            proto_tree_add_double (parent, *field->part[i]->hf, tvb, offset + inner_offset / 8, byte_length (field->part[i]->bit_length), value * scaling_factor);
                         break;
                     case FIELD_PART_CALLSIGN:
                         str_buffer = (char *)wmem_alloc (wmem_packet_scope (), 9);
@@ -9155,7 +9177,7 @@ void proto_register_asterix (void)
         { &hf_021_148_ALT, { "Altitude [ft]", "asterix.021_148_ALT", FT_DOUBLE, BASE_NONE, NULL, 0x0, NULL, HFILL } },
         { &hf_021_150, { "150, Air Speed", "asterix.021_150", FT_NONE, BASE_NONE, NULL, 0x0, NULL, HFILL } },
         { &hf_021_150_IM, { "IM", "asterix.021_150_IM", FT_UINT8, BASE_DEC, VALS (valstr_021_150_IM), 0x80, NULL, HFILL } },
-        { &hf_021_150_ASPD, { "ASPD [2^-14NM/s or 0.001Mach]", "asterix.021_150_ASPD", FT_DOUBLE, BASE_NONE, NULL, 0x0, NULL, HFILL } },
+        { &hf_021_150_ASPD, { "ASPD [IAS (0) => NM/s or IAS (1) => Mach]", "asterix.021_150_ASPD", FT_DOUBLE, BASE_NONE, NULL, 0x0, NULL, HFILL } },
         { &hf_021_151, { "151 True Airspeed", "asterix.021_151", FT_NONE, BASE_NONE, NULL, 0x0, NULL, HFILL } },
         { &hf_021_151_RE, { "RE", "asterix.021_151_RE", FT_UINT8, BASE_DEC, VALS (valstr_021_151_RE), 0x80, NULL, HFILL } },
         { &hf_021_151_TASPD, { "TASPD [knot]", "asterix.021_151_TASPD", FT_DOUBLE, BASE_NONE, NULL, 0x0, NULL, HFILL } },