Adding upstream version 4.2.2.upstream/4.2.2

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 807 insertions, 0 deletions

diff --git a/epan/dissectors/packet-bt-dht.c b/epan/dissectors/packet-bt-dht.c
new file mode 100644
index 00000000..4d442a76
--- /dev/null
+++ b/epan/dissectors/packet-bt-dht.c
@@ -0,0 +1,807 @@
+/******************************************************************************************************/
+/* packet-bt-dht.c
+ * Routines for BT-DHT dissection
+ * Copyright 2011, Xiao Xiangquan <xiaoxiangquan@gmail.com>
+ *
+ * A plugin for BT-DHT packet:
+ *
+ * Wireshark - Network traffic analyzer
+ * By Gerald Combs <gerald@wireshark.org>
+ * Copyright 1999 Gerald Combs
+ *
+ * SPDX-License-Identifier: GPL-2.0-or-later
+ */
+
+#include "config.h"
+
+#include <stdlib.h>
+
+#include <epan/packet.h>
+#include <epan/conversation.h>
+#include <epan/prefs.h>
+#include <epan/to_str.h>
+#include <epan/expert.h>
+
+#include <wsutil/strtoi.h>
+
+#define DHT_MIN_LEN 5
+
+void proto_register_bt_dht(void);
+void proto_reg_handoff_bt_dht(void);
+
+/* Specifications:
+ * https://www.bittorrent.org/beps/bep_0005.html BEP 5 DHT Protocol
+ * https://www.bittorrent.org/beps/bep_0042.html BEP 42 DHT Security extension
+ */
+
+static int proto_bt_dht = -1;
+static dissector_handle_t bt_dht_handle;
+
+/* fields */
+static int hf_bencoded_int = -1;
+static int hf_bencoded_string = -1;
+static int hf_bencoded_list = -1;
+static int hf_bencoded_dict = -1;
+static int hf_bencoded_dict_entry = -1;
+static int hf_bencoded_list_terminator = -1;
+
+static int hf_bt_dht_error = -1;
+static int hf_bt_dht_peers = -1;
+static int hf_bt_dht_peer = -1;
+static int hf_bt_dht_nodes = -1;
+static int hf_bt_dht_node = -1;
+static int hf_bt_dht_id = -1;
+
+static int hf_ip = -1;
+static int hf_ip6 = -1;
+static int hf_port = -1;
+static int hf_truncated_data = -1;
+
+static expert_field ei_int_string = EI_INIT;
+static expert_field ei_invalid_len = EI_INIT;
+
+/* tree types */
+static gint ett_bt_dht = -1;
+static gint ett_bencoded_list = -1;
+static gint ett_bencoded_dict = -1;
+static gint ett_bencoded_dict_entry = -1;
+static gint ett_bt_dht_error = -1;
+static gint ett_bt_dht_peers = -1;
+static gint ett_bt_dht_nodes = -1;
+
+/* some keys use short name in packet */
+static const value_string short_key_name_value_string[] = {
+  { 'a', "Request arguments" },
+  { 'e', "Error" },
+  { 'q', "Request type" },
+  { 'r', "Response values" },
+  { 't', "Transaction ID" },
+  { 'v', "Version" },
+  { 'y', "Message type" },
+  { 0, NULL }
+};
+
+/* some values use short name in packet */
+static const value_string short_val_name_value_string[] = {
+  { 'e', "Error" },
+  { 'q', "Request" },
+  { 'r', "Response" },
+  { 0, NULL }
+};
+
+static const char dict_str[] = "Dictionary...";
+static const char list_str[] = "List...";
+
+
+static inline bool
+bencoded_string_length(packet_info *pinfo, tvbuff_t *tvb, guint *offset_ptr, guint *length)
+{
+  guint offset, start;
+  guint remaining = tvb_captured_length_remaining(tvb, *offset_ptr);
+  if (remaining == 0)
+    return false;
+
+  offset = *offset_ptr;
+  start = offset;
+
+  while(tvb_get_guint8(tvb, offset) != ':' && --remaining)
+    ++offset;
+
+  if (remaining && ws_strtou32(tvb_get_string_enc(pinfo->pool, tvb, start, offset-start, ENC_ASCII),
+      NULL, length)) {
+    ++offset; /* skip the ':' */
+    *offset_ptr = offset;
+    return true;
+  }
+  return false;
+}
+
+
+/*
+ * dissect a bencoded string from tvb, start at offset. it's like "5:abcde"
+ * *result will be the decoded value
+ */
+
+static int
+dissect_bencoded_string(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree, guint offset, const char **result, gboolean tohex, const char *label )
+{
+  guint string_len;
+  if (!bencoded_string_length(pinfo, tvb, &offset, &string_len))
+    return 0;
+
+  const guint remaining = tvb_captured_length_remaining(tvb, offset);
+  if (remaining < string_len)
+    return 0;
+
+  /* fill the return data */
+  if (string_len == 0)
+    *result = "";
+  else if (tohex)
+    *result = tvb_bytes_to_str(pinfo->pool, tvb, offset, string_len );
+  else
+    *result = tvb_get_string_enc( pinfo->pool, tvb, offset, string_len , ENC_ASCII);
+
+  proto_tree_add_string_format( tree, hf_bencoded_string, tvb, offset, string_len, *result, "%s: %s", label, *result );
+  offset += string_len;
+  return offset;
+}
+
+/*
+ * dissect a bencoded integer from tvb, start at offset. it's like "i5673e"
+ * *result will be the decoded value
+ */
+static int
+dissect_bencoded_int(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree, guint offset, const char **result, const char *label )
+{
+  guint start_offset;
+  guint remaining = tvb_captured_length_remaining(tvb, offset);
+
+  /* the shortest valid integer is i0e, so we need at least 3 bytes */
+  if (remaining < 3)
+    return 0;
+
+  if (tvb_get_guint8(tvb, offset) != 'i')
+    return 0;
+
+  offset += 1;
+  remaining -= 1;
+  start_offset = offset;
+  while (tvb_get_guint8(tvb, offset) != 'e' && --remaining)
+    offset += 1;
+
+  if (remaining == 0)
+    return 0;
+
+  proto_tree_add_item(tree, hf_bencoded_list_terminator, tvb, offset, 1, ENC_ASCII);
+
+  *result = tvb_get_string_enc( pinfo->pool, tvb, start_offset, offset-start_offset, ENC_ASCII);
+  proto_tree_add_string_format( tree, hf_bencoded_int, tvb, start_offset, offset-start_offset, *result,
+    "%s: %s", label, *result );
+
+  offset += 1;
+  return offset;
+}
+
+/* pre definition of dissect_bencoded_dict(), which is needed by dissect_bencoded_list() */
+static int dissect_bencoded_dict(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree, guint offset, const char *label );
+
+/* dissect a bencoded list from tvb, start at offset. it's like "lXXXe", "X" is any bencoded thing */
+static int
+dissect_bencoded_list(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree, guint offset, const char *label  )
+{
+  proto_item *ti;
+  proto_tree *sub_tree;
+  guint       one_byte;
+  const char *result;
+
+  /* the shortest valid list is "le", so we need at least 2 bytes */
+  if (tvb_captured_length_remaining(tvb, offset) < 2)
+    return 0;
+
+  ti = proto_tree_add_none_format( tree, hf_bencoded_list, tvb, offset, 0, "%s: list...", label );
+  sub_tree = proto_item_add_subtree( ti, ett_bencoded_list);
+
+  if (tvb_get_guint8(tvb, offset) != 'l')
+    return 0;
+  offset += 1;
+
+  while (tvb_captured_length_remaining(tvb, offset) > 0)
+  {
+    one_byte = tvb_get_guint8(tvb, offset);
+    if (one_byte == 'e')
+      break;
+
+    guint start_offset = offset;
+    switch( one_byte )
+    {
+    /* a integer */
+    case 'i':
+      offset = dissect_bencoded_int( tvb, pinfo, sub_tree, offset, &result, "Integer" );
+      break;
+    /* a sub-list */
+    case 'l':
+      offset = dissect_bencoded_list( tvb, pinfo, sub_tree, offset, "Sub-list" );
+      break;
+    /* a dictionary */
+    case 'd':
+      offset = dissect_bencoded_dict( tvb, pinfo, sub_tree, offset, "Sub-dict" );
+      break;
+    /* a string */
+    default:
+      offset = dissect_bencoded_string( tvb, pinfo, sub_tree, offset, &result, FALSE, "String" );
+      break;
+    }
+    if (offset <= start_offset)
+    {
+      proto_tree_add_expert(sub_tree, pinfo, &ei_int_string, tvb, offset, -1);
+      /* if offset is not going on, there is no chance to exit the loop, then return*/
+      return 0;
+    }
+  }
+
+  if (tvb_captured_length_remaining(tvb, offset) == 0)
+    return 0;
+
+  proto_tree_add_item(sub_tree, hf_bencoded_list_terminator, tvb, offset, 1, ENC_ASCII);
+  offset += 1;
+  return offset;
+}
+
+/* dissect a bt dht error from tvb, start at offset. it's like "li201e9:error msge" */
+static int
+dissect_bt_dht_error(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree, guint offset, const char **result, const char *label )
+{
+  proto_item *ti;
+  proto_tree *sub_tree;
+  const char *error_no, *error_msg;
+
+  error_no  = NULL;
+  error_msg = NULL;
+
+  ti       = proto_tree_add_item( tree, hf_bt_dht_error, tvb, offset, 0, ENC_NA );
+  sub_tree = proto_item_add_subtree( ti, ett_bt_dht_error);
+
+  /* we have confirmed that the first byte is 'l' */
+  offset += 1;
+
+  /* dissect bt-dht error number and message */
+  offset = dissect_bencoded_int( tvb, pinfo, sub_tree, offset, &error_no, "Error ID" );
+  if (offset == 0) {
+    return 0;
+  }
+  offset = dissect_bencoded_string( tvb, pinfo, sub_tree, offset, &error_msg, FALSE, "Error Message" );
+  if (offset == 0) {
+    return 0;
+  }
+
+  proto_item_set_text( ti, "%s: error %s, %s", label, error_no, error_msg );
+  col_append_fstr( pinfo->cinfo, COL_INFO, " No=%s Msg=%s", error_no, error_msg );
+  *result = wmem_strdup_printf(pinfo->pool, "error %s, %s", error_no, error_msg );
+
+  return offset + 1;
+}
+
+/* dissect a bt dht values list from tvb, start at offset. it's like "l6:....6:....e" */
+static int
+dissect_bt_dht_values(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree, guint offset, const char **result, const char *label )
+{
+  proto_item *ti;
+  proto_tree *sub_tree;
+  proto_item *value_ti;
+  proto_tree *value_tree;
+
+  guint       peer_index;
+  guint       string_len;
+
+  ti = proto_tree_add_item( tree, hf_bt_dht_peers, tvb, offset, 0, ENC_NA );
+  sub_tree = proto_item_add_subtree( ti, ett_bt_dht_peers);
+
+  peer_index = 0;
+  /* we has confirmed that the first byte is 'l' */
+  offset += 1;
+
+  /* dissect bt-dht values */
+  while( tvb_get_guint8(tvb,offset)!='e' )
+  {
+    if (!bencoded_string_length(pinfo, tvb, &offset, &string_len))
+    {
+      expert_add_info(pinfo, ti, &ei_invalid_len);
+      // Fail hard here rather than potentially looping excessively.
+      return 0;
+    }
+    else if (string_len == 6)
+    {
+      /* 4 bytes ip, 2 bytes port */
+      peer_index += 1;
+
+      value_ti = proto_tree_add_item( sub_tree, hf_bt_dht_peer, tvb, offset, 6, ENC_NA );
+      proto_item_append_text(value_ti, " %d", peer_index);
+      value_tree = proto_item_add_subtree( value_ti, ett_bt_dht_peers);
+
+      proto_tree_add_item( value_tree, hf_ip, tvb, offset, 4, ENC_BIG_ENDIAN);
+      proto_item_append_text(value_ti, " (IP/Port: %s", tvb_ip_to_str(pinfo->pool, tvb, offset));
+      proto_tree_add_item( value_tree, hf_port, tvb, offset+4, 2, ENC_BIG_ENDIAN);
+      proto_item_append_text(value_ti, ":%u)", tvb_get_ntohs( tvb, offset+4 ));
+    }
+    else if (string_len == 18)
+    {
+      /* 16 bytes ip, 2 bytes port */
+      peer_index += 1;
+
+      value_ti = proto_tree_add_item( sub_tree, hf_bt_dht_peer, tvb, offset, 18, ENC_NA );
+      proto_item_append_text(value_ti, " %d", peer_index);
+      value_tree = proto_item_add_subtree( value_ti, ett_bt_dht_peers);
+
+      proto_tree_add_item( value_tree, hf_ip6, tvb, offset, 16, ENC_NA);
+      proto_item_append_text(value_ti, " (IPv6/Port: [%s]", tvb_ip6_to_str(pinfo->pool, tvb, offset));
+      proto_tree_add_item( value_tree, hf_port, tvb, offset+16, 2, ENC_BIG_ENDIAN);
+      proto_item_append_text(value_ti, ":%u)", tvb_get_ntohs( tvb, offset+16 ));
+    }
+    else
+    {
+      /* truncated data */
+      proto_tree_add_item( tree, hf_truncated_data, tvb, offset, string_len, ENC_NA );
+    }
+
+    offset += string_len;
+  }
+
+  if (tvb_get_guint8(tvb,offset)=='e') { /* list ending delimiter */
+    proto_tree_add_item(sub_tree, hf_bencoded_list_terminator, tvb, offset, 1, ENC_ASCII);
+    offset++;
+  }
+
+  proto_item_set_text( ti, "%s: %d peers", label, peer_index );
+  col_append_fstr( pinfo->cinfo, COL_INFO, " Peers=%d", peer_index );
+  *result = wmem_strdup_printf(pinfo->pool, "%d peers", peer_index);
+
+  return offset;
+}
+
+static int
+dissect_bt_dht_nodes(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree, guint offset, const char **result, const char *label, gboolean is_ipv6 )
+{
+  proto_item *ti;
+  proto_tree *sub_tree;
+  proto_item *node_ti;
+  proto_tree *node_tree;
+
+  guint       node_index;
+  guint       string_len;
+  guint       node_byte_length;
+
+  if (!bencoded_string_length(pinfo, tvb, &offset, &string_len))
+    return 0;
+
+  ti = proto_tree_add_item( tree, hf_bt_dht_nodes, tvb, offset, string_len, ENC_NA );
+  sub_tree = proto_item_add_subtree( ti, ett_bt_dht_nodes);
+  node_index = 0;
+
+  /* 26 bytes = 20 bytes id + 4 bytes ipv4 address + 2 bytes port */
+  node_byte_length = 26;
+
+  if ( is_ipv6 )
+  {
+    /* 38 bytes = 20 bytes id + 16 bytes ipv6 address + 2 bytes port */
+    node_byte_length = 38;
+  }
+
+  for( ; string_len>=node_byte_length; string_len-=node_byte_length, offset+=node_byte_length )
+  {
+    node_index += 1;
+
+    node_ti = proto_tree_add_item( sub_tree, hf_bt_dht_node, tvb, offset, node_byte_length, ENC_NA);
+    proto_item_append_text(node_ti, " %d", node_index);
+    node_tree = proto_item_add_subtree( node_ti, ett_bt_dht_peers);
+
+    proto_tree_add_item( node_tree, hf_bt_dht_id, tvb, offset, 20, ENC_NA);
+    proto_item_append_text(node_ti, " (id: %s", tvb_bytes_to_str(pinfo->pool, tvb, offset, 20));
+
+    if ( is_ipv6 )
+    {
+      proto_tree_add_item( node_tree, hf_ip6, tvb, offset+20, 16, ENC_NA);
+      proto_item_append_text(node_ti, ", IPv6/Port: [%s]", tvb_ip6_to_str(pinfo->pool, tvb, offset+20));
+
+      proto_tree_add_item( node_tree, hf_port, tvb, offset+36, 2, ENC_BIG_ENDIAN);
+      proto_item_append_text(node_ti, ":%u)", tvb_get_ntohs( tvb, offset+36 ));
+    }
+    else
+    {
+      proto_tree_add_item( node_tree, hf_ip, tvb, offset+20, 4, ENC_BIG_ENDIAN);
+      proto_item_append_text(node_ti, ", IPv4/Port: %s", tvb_ip_to_str(pinfo->pool, tvb, offset+20));
+
+      proto_tree_add_item( node_tree, hf_port, tvb, offset+24, 2, ENC_BIG_ENDIAN);
+      proto_item_append_text(node_ti, ":%u)", tvb_get_ntohs( tvb, offset+24 ));
+    }
+  }
+
+  if( string_len>0 )
+  {
+    proto_tree_add_item( tree, hf_truncated_data, tvb, offset, string_len, ENC_NA );
+    offset += string_len;
+  }
+  proto_item_set_text( ti, "%s: %d nodes", label, node_index );
+  col_append_fstr( pinfo->cinfo, COL_INFO, " Nodes=%d", node_index );
+  *result = wmem_strdup_printf(pinfo->pool, "%d", node_index);
+
+  return offset;
+}
+
+static int
+dissect_bencoded_dict_entry(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree, guint offset )
+{
+  proto_item *ti;
+  proto_tree *sub_tree;
+  gboolean    tohex;
+  const char *key;
+  const char *val;
+  guint       orig_offset = offset;
+
+  key = NULL;
+  val = NULL;
+
+  ti       = proto_tree_add_item( tree, hf_bencoded_dict_entry, tvb, offset, 0, ENC_NA );
+  sub_tree = proto_item_add_subtree( ti, ett_bencoded_dict_entry);
+
+  /* dissect the key, it must be a string */
+  offset   = dissect_bencoded_string( tvb, pinfo, sub_tree, offset, &key, FALSE, "Key" );
+  if (offset == 0)
+  {
+    proto_tree_add_expert_format(sub_tree, pinfo, &ei_int_string, tvb, offset, -1, "Invalid string for Key");
+    return 0;
+  }
+
+  if (tvb_captured_length_remaining(tvb, offset) == 0)
+    return 0;
+
+  /* If it is a dict, then just do recursion */
+  switch( tvb_get_guint8(tvb,offset) )
+  {
+  case 'd':
+    offset = dissect_bencoded_dict( tvb, pinfo, sub_tree, offset, "Value" );
+    val    = dict_str;
+    break;
+  case 'l':
+    if( strcmp(key,"e")==0 )
+      offset = dissect_bt_dht_error( tvb, pinfo, sub_tree, offset, &val, "Value" );
+    else if( strcmp(key,"values")==0 )
+      offset = dissect_bt_dht_values( tvb, pinfo, sub_tree, offset, &val, "Value" );
+    /* other unfamiliar lists */
+    else
+    {
+      offset = dissect_bencoded_list( tvb, pinfo, sub_tree, offset, "Value" );
+      val = list_str;
+    }
+    break;
+  case 'i':
+    offset = dissect_bencoded_int( tvb, pinfo, sub_tree, offset, &val, "Value" );
+    break;
+  /* it's a string */
+  default:
+    /* special process */
+    if( strcmp(key,"nodes")==0 )
+    {
+      offset = dissect_bt_dht_nodes( tvb, pinfo, sub_tree, offset, &val, "Value", 0 );
+    }
+    else if( strcmp(key,"nodes6")==0 )
+    {
+      offset = dissect_bt_dht_nodes( tvb, pinfo, sub_tree, offset, &val, "Value", 1 );
+    }
+    else if( strcmp(key,"ip")==0 )
+    {
+      /*
+       * BEP 42 DHT Security extension
+       * https://www.bittorrent.org/beps/bep_0042.html
+       * https://www.rasterbar.com/products/libtorrent/dht_sec.html
+       */
+
+      guint len;
+      int old_offset = offset;
+      if (!bencoded_string_length(pinfo, tvb, &offset, &len)) {
+        proto_tree_add_expert_format(sub_tree, pinfo, &ei_int_string, tvb, offset, -1, "Invalid string for value");
+        return 0;
+      }
+
+      if(len == 6) {
+        proto_tree_add_item(sub_tree, hf_ip, tvb, offset, 4, ENC_BIG_ENDIAN);
+        val = tvb_ip_to_str(pinfo->pool, tvb, offset);
+        offset += 4;
+        proto_tree_add_item(sub_tree, hf_port, tvb, offset, 2, ENC_BIG_ENDIAN);
+        offset += 2;
+      }
+      else {
+        /* XXX: BEP 42 doesn't mention IPv6 and predates the IPv6 DHT;
+         * it doesn't make sense for IPv6 because the purpose is to tell
+         * the requestor its own publicly routable IP address and port
+         * (working around NAT). So any other length than 6 is unexpected.
+         */
+        offset = dissect_bencoded_string( tvb, pinfo, sub_tree, old_offset, &val, TRUE, "Value" );
+      }
+    }
+    else
+    {
+      /* some need to return hex string */
+      tohex = strcmp(key,"id")==0 || strcmp(key,"target")==0
+           || strcmp(key,"info_hash")==0 || strcmp(key,"t")==0
+           || strcmp(key,"v")==0 || strcmp(key,"token")==0;
+      offset = dissect_bencoded_string( tvb, pinfo, sub_tree, offset, &val, tohex, "Value" );
+    }
+  }
+
+  if (offset == 0)
+  {
+    proto_tree_add_expert_format(sub_tree, pinfo, &ei_int_string, tvb, offset, -1, "Invalid string for value");
+    return 0;
+  }
+
+  if(key && strcmp(key,"q")==0 && strlen(val)>1 )
+    col_prepend_fstr(pinfo->cinfo, COL_INFO, "%c%s", g_ascii_toupper(val[0]), val + 1);
+  if(key && strcmp(key,"r")==0 )
+    col_prepend_fstr(pinfo->cinfo, COL_INFO, "Response");
+  if(key && strcmp(key,"e")==0 )
+    col_prepend_fstr(pinfo->cinfo, COL_INFO, "Error");
+  if(key && (strcmp(key,"info_hash")==0 || strcmp(key,"target")==0) )
+    col_append_fstr(pinfo->cinfo, COL_INFO, " %c%s=%s", g_ascii_toupper(key[0]), key + 1, val);
+
+  if(key && strlen(key)==1 )
+    key = val_to_str_const( key[0], short_key_name_value_string, key );
+  if(val && strlen(val)==1 )
+    val = val_to_str_const( val[0], short_val_name_value_string, val );
+
+  proto_item_set_text( ti, "%s: %s", key, val );
+  proto_item_set_len( ti, offset-orig_offset );
+
+  return offset;
+}
+
+/* dict = d...e */
+static int
+dissect_bencoded_dict(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree, guint offset, const char *label )
+{
+  proto_item *ti;
+  proto_tree *sub_tree;
+  guint       orig_offset = offset;
+
+  /* the shortest valid dictionary is "de", so we need at least 2 bytes */
+  if (tvb_captured_length_remaining(tvb, offset) < 2)
+    return 0;
+
+  if(offset == 0)
+  {
+    ti = proto_tree_add_item(tree, proto_bt_dht, tvb, 0, -1, ENC_NA);
+    sub_tree = proto_item_add_subtree(ti, ett_bt_dht);
+  }
+  else
+  {
+    ti = proto_tree_add_none_format( tree, hf_bencoded_dict, tvb, offset, -1, "%s: Dictionary...", label );
+    sub_tree = proto_item_add_subtree( ti, ett_bencoded_dict);
+  }
+
+  if (tvb_get_guint8(tvb, offset) != 'd')
+    return 0;
+  offset += 1;
+
+  while (tvb_captured_length_remaining(tvb, offset) > 0) {
+    if (tvb_get_guint8(tvb, offset) == 'e')
+      break;
+
+    offset = dissect_bencoded_dict_entry( tvb, pinfo, sub_tree, offset );
+    if (offset == 0)
+    {
+      proto_tree_add_expert(sub_tree, pinfo, &ei_int_string, tvb, offset, -1);
+      return 0;
+    }
+  }
+
+  if (tvb_captured_length_remaining(tvb, offset) == 0)
+    return 0;
+
+  proto_tree_add_item(sub_tree, hf_bencoded_list_terminator, tvb, offset, 1, ENC_ASCII);
+  offset += 1;
+  proto_item_set_len( ti, offset-orig_offset );
+
+  return offset;
+}
+
+static gboolean
+test_bt_dht(packet_info *pinfo _U_, tvbuff_t *tvb, int offset, void *data _U_)
+{
+
+  /* The DHT KRPC protocol sends packets that are bencoded dictionaries.
+   * Bencoded dictionaries always have the keys in sorted (raw string)
+   * order. There are three possible message types, query, which has "a" and
+   * "q" keys that map to dictionaries, response, which has an "r" key
+   * that maps to a dictionary, and error, which has an "e" key that maps
+   * to a list.
+   *
+   * Conveniently, those keys appear in sort order before all other possible
+   * top level keys, with the exception of the "ip" key added in BEP-0042.
+   *
+   * Thus, there are only four possible initial sets of bytes, corresponding
+   * to beginning with an "a" dictionary, "r" dictionary, "ip" string, or an
+   * "e" list.
+   */
+
+  if (tvb_captured_length_remaining(tvb, offset) < DHT_MIN_LEN)
+    return FALSE;
+
+  if (tvb_memeql(tvb, offset, (const guint8*)"d1:ad", 5) == 0) {
+    return TRUE;
+  } else if (tvb_memeql(tvb, offset, (const guint8*)"d1:rd", 5) == 0) {
+    return TRUE;
+  } else if (tvb_memeql(tvb, offset, (const guint8*)"d2:ip", 5) == 0) {
+    return TRUE;
+  } else if (tvb_memeql(tvb, offset, (const guint8*)"d1:el", 5) == 0) {
+    return TRUE;
+  }
+
+  return FALSE;
+}
+
+static int
+dissect_bt_dht(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree, void *data)
+{
+  /* BitTorrent clients use the same UDP connection for DHT as for uTP.
+   * So even if this has been set as the dissector for this conversation
+   * or port, test it and reject it if not BT-DHT in order to give other
+   * dissectors, especially BT-uTP, a chance.
+   */
+  if (!test_bt_dht(pinfo, tvb, 0, data)) {
+    return 0;
+  }
+
+  col_set_str(pinfo->cinfo, COL_PROTOCOL, "BT-DHT");
+  col_clear(pinfo->cinfo, COL_INFO);
+
+  /* XXX: There is a separate "bencode" dissector. Would it be possible
+   * to use it, at least to move some functions into a shared header?
+   * DHT has some keys with special meanings, and some values that
+   * are supposed to be interpreted specially (e.g., IP/port combinations),
+   * so maybe it's more trouble than it's worth.
+   */
+  return dissect_bencoded_dict(tvb, pinfo, tree, 0, "BitTorrent DHT Protocol");
+}
+
+static
+gboolean dissect_bt_dht_heur (tvbuff_t *tvb, packet_info *pinfo,
+                                        proto_tree *tree, void *data)
+{
+  conversation_t *conversation;
+
+  if (!test_bt_dht(pinfo, tvb, 0, data)) {
+    return FALSE;
+  }
+
+  conversation = find_or_create_conversation(pinfo);
+  conversation_set_dissector_from_frame_number(conversation, pinfo->num, bt_dht_handle);
+
+  dissect_bt_dht(tvb, pinfo, tree, NULL);
+  return TRUE;
+}
+
+void
+proto_register_bt_dht(void)
+{
+  expert_module_t* expert_bt_dht;
+
+  static hf_register_info hf[] = {
+    { &hf_bencoded_string,
+      { "String", "bt-dht.bencoded.string",
+        FT_STRING, BASE_NONE, NULL, 0x0, NULL, HFILL }
+    },
+    { &hf_bencoded_list,
+      { "List", "bt-dht.bencoded.list",
+        FT_NONE, BASE_NONE, NULL, 0x0, NULL, HFILL }
+    },
+    { &hf_bencoded_int,
+      { "Int", "bt-dht.bencoded.int",
+        FT_STRING, BASE_NONE, NULL, 0x0, NULL, HFILL }
+    },
+    { &hf_bencoded_dict,
+      { "Dictionary", "bt-dht.bencoded.dict",
+        FT_NONE, BASE_NONE, NULL, 0x0, NULL, HFILL }
+    },
+    { &hf_bencoded_dict_entry,
+      { "Dictionary Entry", "bt-dht.bencoded.dict_entry",
+        FT_NONE, BASE_NONE, NULL, 0x0, NULL, HFILL }
+    },
+    { &hf_bencoded_list_terminator,
+      { "Terminator", "bt-dht.bencoded.list.terminator",
+        FT_STRING, BASE_NONE, NULL, 0x0, NULL, HFILL }
+    },
+    { &hf_bt_dht_error,
+      { "Error", "bt-dht.error",
+        FT_NONE, BASE_NONE, NULL, 0x0, NULL, HFILL }
+    },
+    { &hf_bt_dht_peer,
+      { "Peer", "bt-dht.peer",
+        FT_NONE, BASE_NONE, NULL, 0x0, NULL, HFILL }
+    },
+    { &hf_bt_dht_peers,
+      { "Peers", "bt-dht.peers",
+        FT_NONE, BASE_NONE, NULL, 0x0, NULL, HFILL }
+    },
+    { &hf_bt_dht_node,
+      { "Node", "bt-dht.node",
+        FT_NONE, BASE_NONE, NULL, 0x0, NULL, HFILL }
+    },
+    { &hf_bt_dht_nodes,
+      { "Nodes", "bt-dht.nodes",
+        FT_NONE, BASE_NONE, NULL, 0x0, NULL, HFILL }
+    },
+    { &hf_bt_dht_id,
+      { "ID", "bt-dht.id",
+        FT_BYTES, BASE_NONE, NULL, 0x0, NULL, HFILL }
+    },
+    { &hf_ip,
+      { "IP", "bt-dht.ip",
+        FT_IPv4, BASE_NONE, NULL, 0x0, NULL, HFILL }
+    },
+    { &hf_ip6,
+      { "IP", "bt-dht.ip6",
+        FT_IPv6, BASE_NONE, NULL, 0x0, NULL, HFILL }
+    },
+    { &hf_port,
+      { "Port", "bt-dht.port",
+        FT_UINT16, BASE_DEC, NULL, 0x0, NULL, HFILL }
+    },
+    { &hf_truncated_data,
+      { "Truncated data", "bt-dht.truncated_data",
+        FT_BYTES, BASE_NONE, NULL, 0x0, NULL, HFILL }
+    }
+  };
+
+  static ei_register_info ei[] = {
+    { &ei_int_string, { "bt-dht.invalid_string", PI_MALFORMED, PI_ERROR,
+    "String must contain an integer", EXPFILL }},
+    { &ei_invalid_len, { "bt-dht.invalid_length", PI_MALFORMED, PI_ERROR,
+    "Invalid length", EXPFILL }},
+  };
+
+  /* Setup protocol subtree array */
+  static gint *ett[] = {
+    &ett_bt_dht,
+    &ett_bencoded_list,
+    &ett_bencoded_dict,
+    &ett_bt_dht_error,
+    &ett_bt_dht_peers,
+    &ett_bt_dht_nodes,
+    &ett_bencoded_dict_entry
+  };
+
+  module_t *bt_dht_module;
+
+  proto_bt_dht = proto_register_protocol ("BitTorrent DHT Protocol", "BT-DHT", "bt-dht");
+
+  bt_dht_module = prefs_register_protocol(proto_bt_dht, NULL);
+  prefs_register_obsolete_preference(bt_dht_module, "enable");
+
+  proto_register_field_array(proto_bt_dht, hf, array_length(hf));
+  proto_register_subtree_array(ett, array_length(ett));
+
+  expert_bt_dht = expert_register_protocol(proto_bt_dht);
+  expert_register_field_array(expert_bt_dht, ei, array_length(ei));
+
+  bt_dht_handle = register_dissector("bt-dht", dissect_bt_dht, proto_bt_dht);
+}
+
+void
+proto_reg_handoff_bt_dht(void)
+{
+  heur_dissector_add("udp", dissect_bt_dht_heur, "BitTorrent DHT over UDP", "bittorrent_dht_udp", proto_bt_dht, HEURISTIC_ENABLE);
+
+  dissector_add_for_decode_as_with_preference("udp.port", bt_dht_handle);
+}
+
+/*
+ * Editor modelines
+ *
+ * Local Variables:
+ * c-basic-offset: 2
+ * tab-width: 8
+ * indent-tabs-mode: nil
+ * End:
+ *
+ * ex: set shiftwidth=2 tabstop=8 expandtab:
+ * :indentSize=2:tabSize=8:noTabs=true:
+ */