[SIP]Parse out the individual feature cap(s).

Change-Id: Ie834da60a2d389d33e1a5b6cc897e13ae1522fb9
Reviewed-on: https://code.wireshark.org/review/18742
Petri-Dish: Anders Broman <a.broman58@gmail.com>
Tested-by: Petri Dish Buildbot <buildbot-no-reply@wireshark.org>
Reviewed-by: Michael Mann <mmann78@netscape.net>

epan/dissectors/packet-sip.c

@@ -219,6 +219,7 @@ static gint hf_sip_session_id_param       = -1;
 static gint hf_sip_session_id_local_uuid  = -1;
 static gint hf_sip_session_id_remote_uuid = -1;
 static gint hf_sip_continuation           = -1;
+static gint hf_sip_feature_cap            = -1;
 
 static gint hf_sip_p_acc_net_i_acc_type   = -1;
 static gint hf_sip_p_acc_net_i_ucid_3gpp  = -1;
@@ -255,6 +256,7 @@ static gint ett_sip_ppi_uri               = -1;
 static gint ett_sip_tc_uri                = -1;
 static gint ett_sip_session_id            = -1;
 static gint ett_sip_p_access_net_info     = -1;
+static gint ett_sip_feature_caps          = -1;
 
 static expert_field ei_sip_unrecognized_header = EI_INIT;
 static expert_field ei_sip_header_no_colon = EI_INIT;
@@ -2801,6 +2803,56 @@ static void dissect_sip_p_access_network_info_header(tvbuff_t *tvb, proto_tree *
     }
 }
 
+/*
+https://tools.ietf.org/html/rfc6809
+The ABNF for the Feature-Caps header fields is:
+
+Feature-Caps = "Feature-Caps" HCOLON fc-value
+*(COMMA fc-value)
+fc-value     = "*" *(SEMI feature-cap)
+
+The ABNF for the feature-capability indicator is:
+
+feature-cap       =  "+" fcap-name [EQUAL LDQUOT (fcap-value-list
+/ fcap-string-value ) RDQUOT]
+fcap-name         =  ftag-name
+fcap-value-list   =  tag-value-list
+fcap-string-value =  string-value
+;; ftag-name, tag-value-list, string-value defined in RFC 3840
+
+NOTE: In comparison with media feature tags, the "+" sign in front of
+the feature-capability indicator name is mandatory.
+
+*/
+static void
+dissect_sip_p_feature_caps(tvbuff_t *tvb, proto_tree *tree, gint start_offset, gint line_end_offset)
+{
+    gint current_offset, next_offset, length;
+    guint16 semi_plus = 0x3b2b;
+
+    /* skip Spaces and Tabs */
+    next_offset = tvb_skip_wsp(tvb, start_offset, line_end_offset - start_offset);
+
+    if (next_offset >= line_end_offset) {
+        /* Nothing to parse */
+        return;
+    }
+
+    while (next_offset < line_end_offset) {
+        /* Find the end of feature cap or start of feature cap parameter, ";+" should indicate the start of a new feature-cap */
+        current_offset = next_offset;
+        next_offset = tvb_find_guint16(tvb, current_offset, line_end_offset - current_offset, semi_plus);
+        if (next_offset == -1) {
+            length = line_end_offset - current_offset;
+            next_offset = line_end_offset;
+        }
+        else {
+            length = next_offset - current_offset;
+            next_offset += 2;
+        }
+        proto_tree_add_item(tree, hf_sip_feature_cap, tvb, current_offset, length, ENC_UTF_8 | ENC_NA);
+    }
+}
 
 /* Code to actually dissect the packets */
 static int
@@ -4035,6 +4087,19 @@ dissect_sip_common(tvbuff_t *tvb, int offset, int remaining_length, packet_info
                             dissect_sip_p_access_network_info_header(tvb, p_access_net_info_tree, value_offset, line_end_offset);
                         }
                         break;
+                    case POS_FEATURE_CAPS:
+                        if (hdr_tree) {
+                            proto_tree *feature_caps_tree;
+
+                            sip_element_item = sip_proto_tree_add_string(hdr_tree,
+                                hf_header_array[hf_index], tvb,
+                                offset, next_offset - offset,
+                                value_offset, value_len);
+                            sip_proto_set_format_text(hdr_tree, sip_element_item, tvb, offset, linelen);
+                            feature_caps_tree = proto_item_add_subtree(sip_element_item, ett_sip_feature_caps);
+                            dissect_sip_p_feature_caps(tvb, feature_caps_tree, value_offset, line_end_offset);
+                        }
+                        break;
                     default :
                         /* Default case is to assume it's an FT_STRING field */
                         sip_element_item = sip_proto_tree_add_string(hdr_tree,
@@ -6589,6 +6654,12 @@ void proto_register_sip(void)
           { "Continuation data",  "sip.continuation",
             FT_BYTES, BASE_NONE, NULL, 0x0,
             NULL, HFILL}
+        },
+        {
+            &hf_sip_feature_cap,
+            { "Feature Cap",  "sip.feature_cap",
+                FT_STRING, BASE_NONE, NULL, 0x0,
+                NULL, HFILL }
         }
     };
 
@@ -6632,7 +6703,8 @@ void proto_register_sip(void)
         &ett_sip_from_uri,
         &ett_sip_curi,
         &ett_sip_session_id,
-        &ett_sip_p_access_net_info
+        &ett_sip_p_access_net_info,
+        &ett_sip_feature_caps
     };
     static gint *ett_raw[] = {
         &ett_raw_text,