path: root/libtorrent-extended/magnet_uri.patch

diff --git a/src/download/download_constructor.cc b/src/download/download_constructor.cc
index f37f848..86e5351 100644
--- a/src/download/download_constructor.cc
+++ b/src/download/download_constructor.cc
@@ -81,7 +81,10 @@ struct download_constructor_encoding_match :
 };
 
 void
-DownloadConstructor::initialize(const Object& b) {
+DownloadConstructor::initialize(Object& b) {
+  if (!b.has_key_map("info") && b.has_key_string("magnet-uri"))
+    parse_magnet_uri(b, b.get_key_string("magnet-uri"));
+
   if (b.has_key_string("encoding"))
     m_defaultEncoding = b.get_key_string("encoding");
 
@@ -136,10 +139,24 @@ DownloadConstructor::parse_info(const Object& b) {
   if (b.flags() & Object::flag_unordered)
     throw input_error("Download has unordered info dictionary.");
 
-  uint32_t chunkSize = b.get_key_value("piece length");
+  uint32_t chunkSize;
+
+  if (b.has_key_value("meta_download") && b.get_key_value("meta_download"))
+    m_download->info()->set_meta_download(true);
+
+  if (m_download->info()->is_meta_download()) {
+    if (b.get_key_string("pieces").length() != HashString::size_data)
+      throw input_error("Meta-download has invalid piece data.");
+
+    chunkSize = 1;
+    parse_single_file(b, chunkSize);
+
+  } else {
+    chunkSize = b.get_key_value("piece length");
 
-  if (chunkSize <= (1 << 10) || chunkSize > (128 << 20))
-    throw input_error("Torrent has an invalid \"piece length\".");
+    if (chunkSize <= (1 << 10) || chunkSize > (128 << 20))
+      throw input_error("Torrent has an invalid \"piece length\".");
+  }
 
   if (b.has_key("length")) {
     parse_single_file(b, chunkSize);
@@ -148,11 +165,11 @@ DownloadConstructor::parse_info(const Object& b) {
     parse_multi_files(b.get_key("files"), chunkSize);
     fileList->set_root_dir("./" + m_download->info()->name());
 
-  } else {
+  } else if (!m_download->info()->is_meta_download()) {
     throw input_error("Torrent must have either length or files entry.");
   }
 
-  if (fileList->size_bytes() == 0)
+  if (fileList->size_bytes() == 0 && !m_download->info()->is_meta_download())
     throw input_error("Torrent has zero length.");
 
   // Set chunksize before adding files to make sure the index range is
@@ -239,7 +256,7 @@ DownloadConstructor::parse_single_file(const Object& b, uint32_t chunkSize) {
     throw input_error("Bad torrent file, \"name\" is an invalid path name.");
 
   FileList* fileList = m_download->main()->file_list();
-  fileList->initialize(b.get_key_value("length"), chunkSize);
+  fileList->initialize(chunkSize == 1 ? 1 : b.get_key_value("length"), chunkSize);
   fileList->set_multi_file(false);
 
   std::list<Path> pathList;
@@ -343,4 +360,132 @@ DownloadConstructor::choose_path(std::list<Path>* pathList) {
   return pathList->front();
 }
 
+static const char*
+parse_base32_sha1(const char* pos, HashString& hash) {
+  HashString::iterator hashItr = hash.begin();
+
+  static const int base_shift = 8+8-5;
+  int shift = base_shift;
+  uint16_t decoded = 0;
+
+  while (*pos) {
+    char c = *pos++;
+    uint16_t value;
+
+    if (c >= 'A' && c <= 'Z')
+      value = c - 'A';
+    else if (c >= 'a' && c <= 'z')
+      value = c - 'a';
+    else if (c >= '2' && c <= '7')
+      value = 26 + c - '2';
+    else if (c == '&')
+      break;
+    else
+      return NULL;
+
+    decoded |= (value << shift);
+    if (shift <= 8) {
+      // Too many characters for a base32 SHA1.
+      if (hashItr == hash.end())
+        return NULL;
+
+      *hashItr++ = (decoded >> 8);
+      decoded <<= 8;
+      shift += 3;
+    } else {
+      shift -= 5;
+    }
+  }
+
+  return hashItr != hash.end() || shift != base_shift ? NULL : pos;
+}
+
+void
+DownloadConstructor::parse_magnet_uri(Object& b, const std::string& uri) {
+  if (std::strncmp(uri.c_str(), "magnet:?", 8))
+    throw input_error("Invalid magnet URI.");
+
+  const char* pos = uri.c_str() + 8;
+
+  Object trackers(Object::create_list());
+  HashString hash;
+  bool hashValid = false;
+
+  while (*pos) {
+    const char* tagStart = pos;
+    while (*pos != '=')
+      if (!*pos++)
+        break;
+
+    SimpleString tag(tagStart, pos - tagStart);
+    pos++;
+
+    // hash may be base32 encoded (optional in BEP 0009 and common practice)
+    if (tag == "xt") {
+      if (strncmp(pos, "urn:btih:", 9))
+        throw input_error("Invalid magnet URI.");
+
+      pos += 9;
+
+      const char* nextPos = parse_base32_sha1(pos, hash);
+      if (nextPos != NULL) {
+        pos = nextPos;
+        hashValid = true;
+        continue;
+      }
+    }
+
+    // everything else, including sometimes the hash, is url encoded.
+    std::string decoded;
+    while (*pos) {
+      char c = *pos++;
+      if (c == '%') {
+        if (sscanf(pos, "%02hhx", &c) != 1)
+          throw input_error("Invalid magnet URI.");
+
+        pos += 2;
+
+      } else if (c == '&') {
+        break;
+      }
+
+      decoded.push_back(c);
+    }
+
+    if (tag == "xt") {
+      // url-encoded hash as per magnet URN specs
+      if (decoded.length() == hash.size_data) {
+        hash = *HashString::cast_from(decoded);
+        hashValid = true;
+
+      // hex-encoded hash as per BEP 0009
+      } else if (decoded.length() == hash.size_data * 2) {
+        std::string::iterator hexItr = decoded.begin();
+        for (HashString::iterator itr = hash.begin(), last = hash.end(); itr != last; itr++, hexItr += 2)
+          *itr = (rak::hexchar_to_value(*hexItr) << 4) + rak::hexchar_to_value(*(hexItr + 1));
+        hashValid = true;
+
+      } else {
+        throw input_error("Invalid magnet URI.");
+      }
+    } else if (tag == "tr") {
+      trackers.insert_back(Object::create_list()).insert_back(decoded);
+    }
+    // could also handle "dn" = display name (torrent name), but we can't really use that
+  }
+
+  if (!hashValid)
+    throw input_error("Invalid magnet URI.");
+
+  Object& info = b.insert_key("info", Object::create_map());
+  info.insert_key("pieces", hash.str());
+  info.insert_key("name", rak::transform_hex(hash.str()) + ".meta");
+  info.insert_key("meta_download", (int64_t)1);
+
+  if (!trackers.as_list().empty()) {
+    b.insert_preserve_copy("announce", trackers.as_list().begin()->as_list().begin()->as_string());
+    b.insert_preserve_type("announce-list", trackers);
+  }
+}
+
 }
diff --git a/src/download/download_constructor.h b/src/download/download_constructor.h
index 7192f90..8af520f 100644
--- a/src/download/download_constructor.h
+++ b/src/download/download_constructor.h
@@ -55,7 +55,7 @@ class DownloadConstructor {
 public:
   DownloadConstructor() : m_download(NULL), m_encodingList(NULL) {}
 
-  void                initialize(const Object& b);
+  void                initialize(Object& b);
 
   void                set_download(DownloadWrapper* d)         { m_download = d; }
   void                set_encoding_list(const EncodingList* e) { m_encodingList = e; }
@@ -64,6 +64,7 @@ private:
   void                parse_name(const Object& b);
   void                parse_tracker(const Object& b);
   void                parse_info(const Object& b);
+  void                parse_magnet_uri(Object& b, const std::string& uri);
 
   void                add_tracker_group(const Object& b);
   void                add_tracker_single(const Object& b, int group);
diff --git a/src/download/download_info.h b/src/download/download_info.h
index 0a3c0e8..68fb178 100644
--- a/src/download/download_info.h
+++ b/src/download/download_info.h
@@ -76,6 +76,7 @@ public:
     m_isCompact(true),
     m_isAcceptingNewPeers(true),
     m_isPrivate(false),
+    m_isMetaDownload(false),
     m_pexEnabled(true),
     m_pexActive(true),
 
@@ -86,7 +87,8 @@ public:
     m_uploadedBaseline(0),
     m_completedBaseline(0),
     m_sizePex(0),
-    m_maxSizePex(8) {
+    m_maxSizePex(8),
+    m_metadataSize(0) {
   }
 
   const std::string&  name() const                                 { return m_name; }
@@ -116,6 +118,9 @@ public:
   bool                is_private() const                           { return m_isPrivate; }
   void                set_private(bool p)                          { m_isPrivate = p; if (p) m_pexEnabled = false; }
 
+  bool                is_meta_download() const                     { return m_isMetaDownload; }
+  void                set_meta_download(bool m)                    { m_isMetaDownload = m; }
+
   bool                is_pex_enabled() const                       { return m_pexEnabled; }
   void                set_pex_enabled(bool enabled)                { m_pexEnabled = enabled && !m_isPrivate; }
 
@@ -134,6 +139,9 @@ public:
   uint64_t            completed_adjusted() const                   { return std::max<int64_t>(m_slotStatCompleted() - completed_baseline(), 0); }
   void                set_completed_baseline(uint64_t b)           { m_completedBaseline = b; }
 
+  size_t              metadata_size() const                        { return m_metadataSize; }
+  void                set_metadata_size(size_t size)               { m_metadataSize = size; }
+
   uint32_t            size_pex() const                             { return m_sizePex; }
   void                set_size_pex(uint32_t b)                     { m_sizePex = b; }
 
@@ -165,6 +173,7 @@ private:
   bool                m_isCompact;
   bool                m_isAcceptingNewPeers;
   bool                m_isPrivate;
+  bool                m_isMetaDownload;
   bool                m_pexEnabled;
   bool                m_pexActive;
 
@@ -176,6 +185,7 @@ private:
   uint64_t            m_completedBaseline;
   uint32_t            m_sizePex;
   uint32_t            m_maxSizePex;
+  size_t              m_metadataSize;
 
   slot_stat_type      m_slotStatCompleted;
   slot_stat_type      m_slotStatLeft;
diff --git a/src/download/download_main.cc b/src/download/download_main.cc
index 1dd5f98..5691021 100644
--- a/src/download/download_main.cc
+++ b/src/download/download_main.cc
@@ -455,4 +455,19 @@ DownloadMain::do_peer_exchange() {
   }
 }
 
+void
+DownloadMain::set_metadata_size(size_t size) {
+  if (m_info->is_meta_download()) {
+    if (m_fileList.size_bytes() < 2)
+      file_list()->reset_filesize(size);
+    else if (size != m_fileList.size_bytes())
+      throw communication_error("Peer-supplied metadata size mismatch.");
+
+  } else if (m_info->metadata_size() && m_info->metadata_size() != size) {
+      throw communication_error("Peer-supplied metadata size mismatch.");
+  }
+
+  m_info->set_metadata_size(size);
+}
+
 }
diff --git a/src/download/download_main.h b/src/download/download_main.h
index 5d0090b..700f41e 100644
--- a/src/download/download_main.h
+++ b/src/download/download_main.h
@@ -116,6 +116,8 @@ public:
 
   bool                want_pex_msg()                             { return m_info->is_pex_active() && m_peerList.available_list()->want_more(); }; 
 
+  void                set_metadata_size(size_t s);
+
   // Carefull with these.
   void                setup_delegator();
   void                setup_tracker();
diff --git a/src/net/data_buffer.h b/src/net/data_buffer.h
index a26ca36..e3d9e38 100644
--- a/src/net/data_buffer.h
+++ b/src/net/data_buffer.h
@@ -48,6 +48,7 @@ struct DataBuffer {
   DataBuffer(char* data, char* end)   : m_data(data), m_end(end),  m_owned(true) {}
 
   DataBuffer          clone() const        { DataBuffer d = *this; d.m_owned = false; return d; }
+  DataBuffer          release()            { DataBuffer d = *this; set(NULL, NULL, false); return d; }
 
   char*               data() const         { return m_data; }
   char*               end() const          { return m_end; }
@@ -70,7 +71,7 @@ private:
 
 inline void
 DataBuffer::clear() {
-  if (!empty())
+  if (!empty() && m_owned)
     delete[] m_data;
 
   m_data = m_end = NULL;
diff --git a/src/net/socket_base.cc b/src/net/socket_base.cc
index 90457dc..13a9c8b 100644
--- a/src/net/socket_base.cc
+++ b/src/net/socket_base.cc
@@ -47,7 +47,7 @@
 
 namespace torrent {
 
-char* SocketBase::m_nullBuffer = new char[1 << 17];
+char* SocketBase::m_nullBuffer = new char[SocketBase::null_buffer_size];
 
 SocketBase::~SocketBase() {
   if (get_fd().is_valid())
diff --git a/src/net/socket_base.h b/src/net/socket_base.h
index 9340a23..0f0f424 100644
--- a/src/net/socket_base.h
+++ b/src/net/socket_base.h
@@ -68,6 +68,8 @@ protected:
   SocketBase(const SocketBase&);
   void operator = (const SocketBase&);
 
+  static const size_t null_buffer_size = 1 << 17;
+
   static char*        m_nullBuffer;
 };
 
diff --git a/src/protocol/Makefile.am b/src/protocol/Makefile.am
index 6171d06..18f671d 100644
--- a/src/protocol/Makefile.am
+++ b/src/protocol/Makefile.am
@@ -17,6 +17,8 @@ libsub_protocol_la_SOURCES = \
 	peer_connection_base.h \
 	peer_connection_leech.cc \
 	peer_connection_leech.h \
+	peer_connection_metadata.cc \
+	peer_connection_metadata.h \
 	peer_factory.cc \
 	peer_factory.h \
 	protocol_base.h \
diff --git a/src/protocol/extensions.cc b/src/protocol/extensions.cc
index 7cbf6e3..3e0cf60 100644
--- a/src/protocol/extensions.cc
+++ b/src/protocol/extensions.cc
@@ -43,6 +43,8 @@
 
 #include "download/available_list.h"
 #include "download/download_main.h"
+#include "download/download_manager.h"
+#include "download/download_wrapper.h"
 #include "protocol/peer_connection_base.h"
 #include "torrent/connection_manager.h"
 #include "torrent/object.h"
@@ -58,7 +60,9 @@ namespace torrent {
 
 enum ext_handshake_keys {
   key_e,
+  key_m_utMetadata,
   key_m_utPex,
+  key_metadataSize,
   key_p,
   key_reqq,
   key_v,
@@ -70,6 +74,13 @@ enum ext_pex_keys {
   key_pex_LAST
 };
 
+enum ext_metadata_keys {
+  key_msgType,
+  key_piece,
+  key_totalSize,
+  key_metadata_LAST
+};
+
 class ExtHandshakeMessage : public StaticMap<ext_handshake_keys, key_handshake_LAST> {
 public:
   typedef StaticMap<ext_handshake_keys, key_handshake_LAST> base_type;
@@ -82,9 +93,17 @@ public:
   typedef StaticMapKeys::mapping_type   mapping_type;
 };
 
+class ExtMetadataMessage : public StaticMap<ext_metadata_keys, key_metadata_LAST> {
+public:
+  typedef StaticMap<ext_metadata_keys, key_metadata_LAST> base_type;
+  typedef StaticMapKeys::mapping_type   mapping_type;
+};
+
 ExtHandshakeMessage::mapping_type ext_handshake_key_names[ExtHandshakeMessage::length] = {
   { key_e,            "e" },
+  { key_m_utMetadata, "m::ut_metadata" },
   { key_m_utPex,      "m::ut_pex" },
+  { key_metadataSize, "metadata_size" },
   { key_p,            "p" },
   { key_reqq,         "reqq" },
   { key_v,            "v" },
@@ -94,9 +113,16 @@ ExtPEXMessage::mapping_type ext_pex_key_names[ExtPEXMessage::length] = {
   { key_pex_added,    "added" },
 };
 
+ExtMetadataMessage::mapping_type ext_metadata_key_names[ExtMetadataMessage::length] = {
+  { key_msgType,      "msg_type" },
+  { key_piece,        "piece" },
+  { key_totalSize,    "total_size" },
+};
+
 ext_handshake_keys message_keys[ProtocolExtension::FIRST_INVALID] = {
   key_handshake_LAST,     // Handshake, not actually used.
   key_m_utPex,
+  key_m_utMetadata,
 };
 
 template<>
@@ -105,6 +131,9 @@ const ExtHandshakeMessage::key_map_init ExtHandshakeMessage::base_type::keyMap(e
 template<>
 const ExtPEXMessage::key_map_init ExtPEXMessage::base_type::keyMap(ext_pex_key_names);
 
+template<>
+const ExtMetadataMessage::key_map_init ExtMetadataMessage::base_type::keyMap(ext_metadata_key_names);
+
 void
 ProtocolExtension::cleanup() {
 //   if (is_default())
@@ -160,7 +189,11 @@ ProtocolExtension::generate_handshake_message() {
   message[key_v] = SimpleString("libTorrent " VERSION);
   message[key_reqq] = 2048;  // maximum request queue size
 
+  if (!m_download->info()->is_meta_download())
+    message[key_metadataSize] = m_download->info()->metadata_size();
+
   message[key_m_utPex] = is_local_enabled(UT_PEX) ? UT_PEX : 0;
+  message[key_m_utMetadata] = UT_METADATA;
 
   char buffer[1024];
   object_buffer_t result = staticMap_write_bencode_c(object_write_to_buffer, NULL, std::make_pair(buffer, buffer + sizeof(buffer)), message);
@@ -224,7 +257,7 @@ ProtocolExtension::generate_ut_pex_message(const PEXList& added, const PEXList&
 
 void
 ProtocolExtension::read_start(int type, uint32_t length, bool skip) {
-  if (is_default() || (type >= FIRST_INVALID) || length > (1 << 14))
+  if (is_default() || (type >= FIRST_INVALID) || length > (1 << 15))
     throw communication_error("Received invalid extension message.");
 
   if (m_read != NULL || length < 0)
@@ -244,19 +277,25 @@ ProtocolExtension::read_start(int type, uint32_t length, bool skip) {
   m_readPos = m_read = new char[length];
 }
 
-void
+bool
 ProtocolExtension::read_done() {
+  bool blocked = false;
+
   try {
     switch(m_readType) {
     case SKIP_EXTENSION:
       break;
 
     case HANDSHAKE:
-      parse_handshake();
+      blocked = parse_handshake();
       break;
 
     case UT_PEX:
-      parse_ut_pex();
+      blocked = parse_ut_pex();
+      break;
+
+    case UT_METADATA:
+      blocked = parse_ut_metadata();
       break;
 
     default:
@@ -272,6 +311,8 @@ ProtocolExtension::read_done() {
 
   m_readType = FIRST_INVALID;
   m_flags |= flag_received_ext;
+
+  return !blocked;
 }
 
 // Called whenever peer enables or disables an extension.
@@ -285,7 +326,7 @@ ProtocolExtension::peer_toggle_remote(int type, bool active) {
   }
 }
 
-void
+bool
 ProtocolExtension::parse_handshake() {
   ExtHandshakeMessage message;
   staticMap_read_bencode(m_read, m_readPos, message);
@@ -323,10 +364,15 @@ ProtocolExtension::parse_handshake() {
   if (message[key_reqq].is_value())
     m_maxQueueLength = message[key_reqq].as_value();
 
+  if (message[key_metadataSize].is_value())
+    m_download->set_metadata_size(message[key_metadataSize].as_value());
+
   m_flags &= ~flag_initial_handshake;
+
+  return false;
 }
 
-void
+bool
 ProtocolExtension::parse_ut_pex() {
   // Ignore message if we're still in the handshake (no connection
   // yet), or no peers are present.
@@ -336,11 +382,11 @@ ProtocolExtension::parse_ut_pex() {
 
   // TODO: Check if pex is enabled?
   if (!message[key_pex_added].is_sstring())
-    return;
+    return false;
 
   SimpleString peers = message[key_pex_added].as_sstring();
   if (peers.empty())
-    return;
+    return false;
 
   AddressList l;
   l.parse_address_compact(peers);
@@ -348,6 +394,82 @@ ProtocolExtension::parse_ut_pex() {
   l.erase(std::unique(l.begin(), l.end()), l.end());
  
   m_download->peer_list()->insert_available(&l);
+
+  return false;
+}
+
+bool
+ProtocolExtension::parse_ut_metadata() {
+  ExtMetadataMessage message;
+
+  // Piece data comes after bencoded extension message.
+  const char* dataStart = staticMap_read_bencode(m_read, m_readPos, message);
+
+  switch(message[key_msgType].as_value()) {
+  case 0:
+    // Can't process new request while still having data to send.
+    if (has_pending_message())
+      return true;
+
+    send_metadata_piece(message[key_piece].as_value());
+    break;
+
+  case 1:
+    if (m_connection == NULL)
+      break;
+
+    m_connection->receive_metadata_piece(message[key_piece].as_value(), dataStart, m_readPos - dataStart);
+    break;
+
+  case 2:
+    if (m_connection != NULL)
+      m_connection->receive_metadata_piece(message[key_piece].as_value(), NULL, 0);
+    break;
+  };
+
+  return false;
+}
+
+void
+ProtocolExtension::send_metadata_piece(size_t piece) {
+  // Reject out-of-range piece, or if we don't have the complete metadata yet.
+  size_t metadataSize = m_download->info()->metadata_size();
+  size_t pieceEnd = (metadataSize + metadata_piece_size - 1) >> metadata_piece_shift;
+
+  if (m_download->info()->is_meta_download() || piece >= pieceEnd) {
+    // reject: { "msg_type" => 2, "piece" => ... }
+    m_pendingType = UT_METADATA;
+    m_pending = build_bencode(40, "d8:msg_typei2e5:piecei%zuee", piece);
+    return;
+  }
+
+  // These messages will be rare, so we'll just build the
+  // metadata here instead of caching it uselessly.
+  char* buffer = new char[metadataSize];
+  object_buffer_t result = object_write_bencode_c(object_write_to_buffer, NULL, object_buffer_t(buffer, buffer + metadataSize), 
+                                                 &(*manager->download_manager()->find(m_download->info()))->bencode()->get_key("info"));
+
+  // data: { "msg_type" => 1, "piece" => ..., "total_size" => ... } followed by piece data (outside of dictionary)
+  size_t length = piece == pieceEnd - 1 ? m_download->info()->metadata_size() % metadata_piece_size : metadata_piece_size;
+  m_pendingType = UT_METADATA;
+  m_pending = build_bencode(length + 128, "d8:msg_typei1e5:piecei%zue10:total_sizei%zuee", piece, metadataSize);
+
+  memcpy(m_pending.end(), buffer + (piece << metadata_piece_shift), length);
+  m_pending.set(m_pending.data(), m_pending.end() + length, m_pending.owned());
+  delete [] buffer;
+}
+
+bool
+ProtocolExtension::request_metadata_piece(const Piece* p) {
+  if (p->offset() % metadata_piece_size)
+    throw internal_error("ProtocolExtension::request_metadata_piece got misaligned piece offset.");
+
+  if (has_pending_message())
+    return false;
+
+  m_pendingType = UT_METADATA;
+  m_pending = build_bencode(40, "d8:msg_typei0e5:piecei%uee", (unsigned)(p->offset() >> metadata_piece_shift));
+  return true;
 }
 
 }
diff --git a/src/protocol/extensions.h b/src/protocol/extensions.h
index 96ed652..485e7d7 100644
--- a/src/protocol/extensions.h
+++ b/src/protocol/extensions.h
@@ -60,6 +60,7 @@ public:
   typedef enum {
     HANDSHAKE = 0,
     UT_PEX,
+    UT_METADATA,
 
     FIRST_INVALID,    // first invalid message ID
 
@@ -81,6 +82,10 @@ public:
   // Number of extensions we support, not counting handshake.
   static const int    extension_count = FIRST_INVALID - HANDSHAKE - 1;
 
+  // Fixed size of a metadata piece (16 KB).
+  static const size_t metadata_piece_shift = 14;
+  static const size_t metadata_piece_size  = 1 << metadata_piece_shift;
+
   ProtocolExtension();
   ~ProtocolExtension() { delete [] m_read; }
 
@@ -91,6 +96,7 @@ public:
   static ProtocolExtension make_default();
 
   void                set_info(PeerInfo* peerInfo, DownloadMain* download) { m_peerInfo = peerInfo; m_download = download; }
+  void                set_connection(PeerConnectionBase* c)                { m_connection = c; }
 
   DataBuffer          generate_handshake_message();
   static DataBuffer   generate_toggle_message(MessageType t, bool on);
@@ -112,7 +118,7 @@ public:
 
   // Handle reading extension data from peer.
   void                read_start(int type, uint32_t length, bool skip);
-  void                read_done();
+  bool                read_done();
 
   char*               read_position()                  { return m_readPos; }
   bool                read_move(uint32_t v)            { m_readPos += v; return (m_readLeft -= v) == 0; }
@@ -132,13 +138,23 @@ public:
   void                clear_initial_pex()              { m_flags &= ~flag_initial_pex; }
   void                reset()                          { std::memset(&m_idMap, 0, sizeof(m_idMap)); }
 
+  bool                request_metadata_piece(const Piece* p);
+
+  // To handle cases where the extension protocol needs to send a reply.
+  bool                has_pending_message() const      { return m_pendingType != HANDSHAKE; }
+  MessageType         pending_message_type() const     { return m_pendingType; }
+  DataBuffer          pending_message_data()           { return m_pending.release(); }
+  void                clear_pending_message()          { if (m_pending.empty()) m_pendingType = HANDSHAKE; }
+
 private:
-  void                parse_handshake();
-  void                parse_ut_pex();
+  bool                parse_handshake();
+  bool                parse_ut_pex();
+  bool                parse_ut_metadata();
 
   static DataBuffer   build_bencode(size_t maxLength, const char* format, ...) ATTRIBUTE_PRINTF(2);
 
   void                peer_toggle_remote(int type, bool active);
+  void                send_metadata_piece(size_t piece);
 
   // Map of IDs peer uses for each extension message type, excluding
   // HANDSHAKE. 
@@ -149,11 +165,15 @@ private:
   int                 m_flags;
   PeerInfo*           m_peerInfo;
   DownloadMain*       m_download;
+  PeerConnectionBase* m_connection;
 
   uint8_t             m_readType;
   uint32_t            m_readLeft;
   char*               m_read;
   char*               m_readPos;
+
+  MessageType         m_pendingType;
+  DataBuffer          m_pending;
 };
 
 inline
@@ -163,10 +183,13 @@ ProtocolExtension::ProtocolExtension() :
   m_flags(flag_local_enabled_base | flag_remote_supported_base | flag_initial_handshake),
   m_peerInfo(NULL),
   m_download(NULL),
+  m_connection(NULL),
   m_readType(FIRST_INVALID),
-  m_read(NULL) {
+  m_read(NULL),
+  m_pendingType(HANDSHAKE) {
 
   reset();
+  set_local_enabled(UT_METADATA);
 }
 
 inline ProtocolExtension
diff --git a/src/protocol/handshake.cc b/src/protocol/handshake.cc
index d863f7b..7fb389b 100644
--- a/src/protocol/handshake.cc
+++ b/src/protocol/handshake.cc
@@ -723,6 +723,17 @@ restart:
 
     case READ_MESSAGE:
     case POST_HANDSHAKE:
+      // For meta-downloads, we aren't interested in the bitfield or
+      // extension messages here, PCMetadata handles all that. The
+      // bitfield only refers to the single-chunk meta-data, so fake that.
+      if (m_download->info()->is_meta_download()) {
+        m_bitfield.set_size_bits(1);
+        m_bitfield.allocate();
+        m_bitfield.set(0);
+        read_done();
+        break;
+      }
+
       fill_read_buffer(5);
 
       // Received a keep-alive message which means we won't be
@@ -1022,6 +1033,10 @@ Handshake::prepare_peer_info() {
   std::memcpy(m_peerInfo->set_options(), m_options, 8);
   m_peerInfo->mutable_id().assign((const char*)m_readBuffer.position());
   m_readBuffer.consume(20);
+
+  // For meta downloads, we require support of the extension protocol.
+  if (m_download->info()->is_meta_download() && !m_peerInfo->supports_extensions())
+    throw handshake_error(ConnectionManager::handshake_dropped, e_handshake_unwanted_connection);
 }
 
 void
diff --git a/src/protocol/peer_connection_base.cc b/src/protocol/peer_connection_base.cc
index ab043a6..815ea93 100644
--- a/src/protocol/peer_connection_base.cc
+++ b/src/protocol/peer_connection_base.cc
@@ -93,8 +93,7 @@ PeerConnectionBase::~PeerConnectionBase() {
   if (m_extensions != NULL && !m_extensions->is_default())
     delete m_extensions;
 
-  if (m_extensionMessage.owned())
-    m_extensionMessage.clear();
+  m_extensionMessage.clear();
 }
 
 void
@@ -116,6 +115,8 @@ PeerConnectionBase::initialize(DownloadMain* download, PeerInfo* peerInfo, Socke
   m_encryption = *encryptionInfo;
   m_extensions = extensions;
 
+  m_extensions->set_connection(this);
+
   m_peerChunks.set_peer_info(m_peerInfo);
   m_peerChunks.bitfield()->swap(*bitfield);
 
@@ -581,8 +582,12 @@ PeerConnectionBase::down_extension() {
     m_extensions->read_move(bytes);
   }
 
-  if (m_extensions->is_complete())
-    m_extensions->read_done();
+  // If extension can't be processed yet (due to a pending write),
+  // disable reads until the pending message is completely sent.
+  if (m_extensions->is_complete() && !m_extensions->is_invalid() && !m_extensions->read_done()) {
+    manager->poll()->remove_read(this);
+    return false;
+  }
 
   return m_extensions->is_complete();
 }
@@ -693,12 +698,15 @@ PeerConnectionBase::up_extension() {
   if (m_extensionOffset < m_extensionMessage.length())
     return false;
 
-  // clear() deletes the buffer, only do that if we made a copy,
-  // otherwise the buffer is shared among all connections.
-  if (m_extensionMessage.owned())
-    m_extensionMessage.clear();
-  else 
-    m_extensionMessage.set(NULL, NULL, false);
+  m_extensionMessage.clear();
+
+  // If we have an unprocessed message, process it now and enable reads again.
+  if (m_extensions->is_complete() && !m_extensions->is_invalid()) {
+    if (!m_extensions->read_done())
+      throw internal_error("PeerConnectionBase::up_extension could not process complete extension message.");
+
+    manager->poll()->insert_read(this);
+  }
 
   return true;
 }
@@ -857,4 +865,16 @@ PeerConnectionBase::send_pex_message() {
   return true;
 }
 
+// Extension protocol needs to send a reply.
+bool
+PeerConnectionBase::send_ext_message() {
+  write_prepare_extension(m_extensions->pending_message_type(), m_extensions->pending_message_data());
+  m_extensions->clear_pending_message();
+  return true;
+}
+
+void
+PeerConnectionBase::receive_metadata_piece(uint32_t piece, const char* data, uint32_t length) {
+}
+
 }
diff --git a/src/protocol/peer_connection_base.h b/src/protocol/peer_connection_base.h
index 2994963..d131341 100644
--- a/src/protocol/peer_connection_base.h
+++ b/src/protocol/peer_connection_base.h
@@ -140,6 +140,9 @@ public:
   void                read_insert_poll_safe();
   void                write_insert_poll_safe();
 
+  // Communication with the protocol extensions
+  virtual void        receive_metadata_piece(uint32_t piece, const char* data, uint32_t length);
+
 protected:
   static const uint32_t extension_must_encrypt = ~uint32_t();
 
@@ -179,6 +182,7 @@ protected:
   bool                try_request_pieces();
 
   bool                send_pex_message();
+  bool                send_ext_message();
 
   DownloadMain*       m_download;
 
diff --git a/src/protocol/peer_connection_leech.cc b/src/protocol/peer_connection_leech.cc
index a75d333..36c6d7a 100644
--- a/src/protocol/peer_connection_leech.cc
+++ b/src/protocol/peer_connection_leech.cc
@@ -333,9 +333,13 @@ PeerConnection<type>::read_message() {
       m_down->set_state(ProtocolRead::READ_EXTENSION);
     }
 
-    if (down_extension())
-      m_down->set_state(ProtocolRead::IDLE);
+    if (!down_extension())
+      return false;
 
+    if (m_extensions->has_pending_message())
+      write_insert_poll_safe();
+
+    m_down->set_state(ProtocolRead::IDLE);
     return true;
 
   default:
@@ -433,6 +437,9 @@ PeerConnection<type>::event_read() {
         if (!down_extension())
           return;
 
+        if (m_extensions->has_pending_message())
+          write_insert_poll_safe();
+
         m_down->set_state(ProtocolRead::IDLE);
         break;
 
@@ -546,6 +553,10 @@ PeerConnection<type>::fill_write_buffer() {
       send_pex_message()) {
     // Don't do anything else if send_pex_message() succeeded.
 
+  } else if (m_extensions->has_pending_message() && m_up->can_write_extension() &&
+             send_ext_message()) {
+    // Same.
+
   } else if (!m_upChoke.choked() &&
              !m_peerChunks.upload_queue()->empty() &&
              m_up->can_write_piece() &&
diff --git a/src/protocol/peer_connection_metadata.cc b/src/protocol/peer_connection_metadata.cc
new file mode 100644
index 0000000..24f13ca
--- /dev/null
+++ b/src/protocol/peer_connection_metadata.cc
@@ -0,0 +1,461 @@
+// libTorrent - BitTorrent library
+// Copyright (C) 2005-2007, Jari Sundell
+//
+// This program is free software; you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation; either version 2 of the License, or
+// (at your option) any later version.
+// 
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+// 
+// You should have received a copy of the GNU General Public License
+// along with this program; if not, write to the Free Software
+// Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
+//
+// In addition, as a special exception, the copyright holders give
+// permission to link the code of portions of this program with the
+// OpenSSL library under certain conditions as described in each
+// individual source file, and distribute linked combinations
+// including the two.
+//
+// You must obey the GNU General Public License in all respects for
+// all of the code used other than OpenSSL.  If you modify file(s)
+// with this exception, you may extend this exception to your version
+// of the file(s), but you are not obligated to do so.  If you do not
+// wish to do so, delete this exception statement from your version.
+// If you delete this exception statement from all source files in the
+// program, then also delete it here.
+//
+// Contact:  Jari Sundell <jaris@ifi.uio.no>
+//
+//           Skomakerveien 33
+//           3185 Skoppum, NORWAY
+
+#include "config.h"
+
+#include <cstring>
+#include <sstream>
+
+#include "data/chunk_list_node.h"
+#include "download/choke_manager.h"
+#include "download/chunk_selector.h"
+#include "download/chunk_statistics.h"
+#include "download/download_info.h"
+#include "download/download_main.h"
+#include "torrent/dht_manager.h"
+#include "torrent/peer/connection_list.h"
+#include "torrent/peer/peer_info.h"
+
+#include "extensions.h"
+#include "peer_connection_metadata.h"
+
+namespace torrent {
+
+PeerConnectionMetadata::~PeerConnectionMetadata() {
+}
+
+void
+PeerConnectionMetadata::initialize_custom() {
+}
+
+void
+PeerConnectionMetadata::update_interested() {
+}
+
+bool
+PeerConnectionMetadata::receive_keepalive() {
+  if (cachedTime - m_timeLastRead > rak::timer::from_seconds(240))
+    return false;
+
+  m_tryRequest = true;
+
+  // There's no point in adding ourselves to the write poll if the
+  // buffer is full, as that will already have been taken care of.
+  if (m_up->get_state() == ProtocolWrite::IDLE &&
+      m_up->can_write_keepalive()) {
+
+    write_insert_poll_safe();
+
+    ProtocolBuffer<512>::iterator old_end = m_up->buffer()->end();
+    m_up->write_keepalive();
+
+    if (is_encrypted())
+      m_encryption.encrypt(old_end, m_up->buffer()->end() - old_end);
+  }
+
+  return true;
+}
+
+// We keep the message in the buffer if it is incomplete instead of
+// keeping the state and remembering the read information. This
+// shouldn't happen very often compared to full reads.
+inline bool
+PeerConnectionMetadata::read_message() {
+  ProtocolBuffer<512>* buf = m_down->buffer();
+
+  if (buf->remaining() < 4)
+    return false;
+
+  // Remember the start of the message so we may reset it if we don't
+  // have the whole message.
+  ProtocolBuffer<512>::iterator beginning = buf->position();
+
+  uint32_t length = buf->read_32();
+
+  if (length == 0) {
+    // Keepalive message.
+    m_down->set_last_command(ProtocolBase::KEEP_ALIVE);
+
+    return true;
+
+  } else if (buf->remaining() < 1) {
+    buf->set_position_itr(beginning);
+    return false;
+
+  } else if (length > (1 << 20)) {
+    throw communication_error("PeerConnection::read_message() got an invalid message length.");
+  }
+    
+  m_down->set_last_command((ProtocolBase::Protocol)buf->peek_8());
+
+  // Ignore most messages, they aren't relevant for a metadata download.
+  switch (buf->read_8()) {
+  case ProtocolBase::CHOKE:
+  case ProtocolBase::UNCHOKE:
+  case ProtocolBase::INTERESTED:
+  case ProtocolBase::NOT_INTERESTED:
+    return true;
+
+  case ProtocolBase::HAVE:
+    if (!m_down->can_read_have_body())
+      break;
+
+    buf->read_32();
+    return true;
+
+  case ProtocolBase::REQUEST:
+    if (!m_down->can_read_request_body())
+      break;
+
+    m_down->read_request();
+    return true;
+
+  case ProtocolBase::PIECE:
+    throw communication_error("Received a piece but the connection is strictly for meta data.");
+
+  case ProtocolBase::CANCEL:
+    if (!m_down->can_read_cancel_body())
+      break;
+
+    m_down->read_request();
+    return true;
+
+  case ProtocolBase::PORT:
+    if (!m_down->can_read_port_body())
+      break;
+
+    manager->dht_manager()->add_node(m_peerInfo->socket_address(), m_down->buffer()->read_16());
+    return true;
+
+  case ProtocolBase::EXTENSION_PROTOCOL:
+    if (!m_down->can_read_extension_body())
+      break;
+
+    if (m_extensions->is_default()) {
+      m_extensions = new ProtocolExtension();
+      m_extensions->set_info(m_peerInfo, m_download);
+    }
+
+    {
+      int extension = m_down->buffer()->read_8();
+      m_extensions->read_start(extension, length - 2, (extension == ProtocolExtension::UT_PEX) && !m_download->want_pex_msg());
+      m_down->set_state(ProtocolRead::READ_EXTENSION);
+    }
+
+    if (!down_extension())
+      return false;
+
+    // Drop peer if it disabled the metadata extension.
+    if (!m_extensions->is_remote_supported(ProtocolExtension::UT_METADATA))
+      throw close_connection();
+
+    m_down->set_state(ProtocolRead::IDLE);
+    m_tryRequest = true;
+    write_insert_poll_safe();
+
+    return true;
+
+  case ProtocolBase::BITFIELD:
+    // Discard the bitfield sent by the peer.
+    m_skipLength = length - 1;
+    m_down->set_state(ProtocolRead::READ_SKIP_PIECE);
+    return false;
+
+  default:
+    throw communication_error("Received unsupported message type.");
+  }
+
+  // We were unsuccessfull in reading the message, need more data.
+  buf->set_position_itr(beginning);
+  return false;
+}
+
+void
+PeerConnectionMetadata::event_read() {
+  m_timeLastRead = cachedTime;
+
+  // Need to make sure ProtocolBuffer::end() is pointing to the end of
+  // the unread data, and that the unread data starts from the
+  // beginning of the buffer. Or do we use position? Propably best,
+  // therefor ProtocolBuffer::position() points to the beginning of
+  // the unused data.
+
+  try {
+    
+    // Normal read.
+    //
+    // We rarely will read zero bytes as the read of 64 bytes will
+    // almost always either not fill up or it will require additional
+    // reads.
+    //
+    // Only loop when end hits 64.
+
+    do {
+      switch (m_down->get_state()) {
+      case ProtocolRead::IDLE:
+        if (m_down->buffer()->size_end() < read_size) {
+          unsigned int length = read_stream_throws(m_down->buffer()->end(), read_size - m_down->buffer()->size_end());
+          m_down->throttle()->node_used_unthrottled(length);
+
+          if (is_encrypted())
+            m_encryption.decrypt(m_down->buffer()->end(), length);
+
+          m_down->buffer()->move_end(length);
+        }
+
+        while (read_message());
+        
+        if (m_down->buffer()->size_end() == read_size) {
+          m_down->buffer()->move_unused();
+          break;
+        } else {
+          m_down->buffer()->move_unused();
+          return;
+        }
+
+      case ProtocolRead::READ_EXTENSION:
+        if (!down_extension())
+          return;
+
+        // Drop peer if it disabled the metadata extension.
+        if (!m_extensions->is_remote_supported(ProtocolExtension::UT_METADATA))
+          throw close_connection();
+
+        m_down->set_state(ProtocolRead::IDLE);
+        m_tryRequest = true;
+        write_insert_poll_safe();
+        break;
+
+      // Actually skipping the bitfield.
+      // We never receive normal piece messages anyway.
+      case ProtocolRead::READ_SKIP_PIECE:
+        if (!read_skip_bitfield())
+          return;
+
+        m_down->set_state(ProtocolRead::IDLE);
+        break;
+
+      default:
+        throw internal_error("PeerConnection::event_read() wrong state.");
+      }
+
+      // Figure out how to get rid of the shouldLoop boolean.
+    } while (true);
+
+  // Exception handlers:
+
+  } catch (close_connection& e) {
+    m_download->connection_list()->erase(this, 0);
+
+  } catch (blocked_connection& e) {
+    m_download->info()->signal_network_log().emit("Momentarily blocked read connection.");
+    m_download->connection_list()->erase(this, 0);
+
+  } catch (network_error& e) {
+    m_download->connection_list()->erase(this, 0);
+
+  } catch (storage_error& e) {
+    m_download->info()->signal_storage_error().emit(e.what());
+    m_download->connection_list()->erase(this, 0);
+
+  } catch (base_error& e) {
+    std::stringstream s;
+    s << "Connection read fd(" << get_fd().get_fd() << ',' << m_down->get_state() << ',' << m_down->last_command() << ") \"" << e.what() << '"';
+
+    throw internal_error(s.str());
+  }
+}
+
+inline void
+PeerConnectionMetadata::fill_write_buffer() {
+  ProtocolBuffer<512>::iterator old_end = m_up->buffer()->end();
+
+  if (m_tryRequest)
+    m_tryRequest = try_request_metadata_pieces();
+
+  if (m_sendPEXMask && m_up->can_write_extension() &&
+      send_pex_message()) {
+    // Don't do anything else if send_pex_message() succeeded.
+
+  } else if (m_extensions->has_pending_message() && m_up->can_write_extension() &&
+             send_ext_message()) {
+    // Same.
+  }
+
+  if (is_encrypted())
+    m_encryption.encrypt(old_end, m_up->buffer()->end() - old_end);
+}
+
+void
+PeerConnectionMetadata::event_write() {
+  try {
+  
+    do {
+
+      switch (m_up->get_state()) {
+      case ProtocolWrite::IDLE:
+
+        fill_write_buffer();
+
+        if (m_up->buffer()->remaining() == 0) {
+          manager->poll()->remove_write(this);
+          return;
+        }
+
+        m_up->set_state(ProtocolWrite::MSG);
+
+      case ProtocolWrite::MSG:
+        if (!m_up->buffer()->consume(m_up->throttle()->node_used_unthrottled(write_stream_throws(m_up->buffer()->position(), m_up->buffer()->remaining()))))
+          return;
+
+        m_up->buffer()->reset();
+
+        if (m_up->last_command() != ProtocolBase::EXTENSION_PROTOCOL) {
+          m_up->set_state(ProtocolWrite::IDLE);
+          break;
+        }
+
+        m_up->set_state(ProtocolWrite::WRITE_EXTENSION);
+
+      case ProtocolWrite::WRITE_EXTENSION:
+        if (!up_extension())
+          return;
+
+        m_up->set_state(ProtocolWrite::IDLE);
+        break;
+
+      default:
+        throw internal_error("PeerConnection::event_write() wrong state.");
+      }
+
+    } while (true);
+
+  } catch (close_connection& e) {
+    m_download->connection_list()->erase(this, 0);
+
+  } catch (blocked_connection& e) {
+    m_download->info()->signal_network_log().emit("Momentarily blocked write connection.");
+    m_download->connection_list()->erase(this, 0);
+
+  } catch (network_error& e) {
+    m_download->connection_list()->erase(this, 0);
+
+  } catch (storage_error& e) {
+    m_download->info()->signal_storage_error().emit(e.what());
+    m_download->connection_list()->erase(this, 0);
+
+  } catch (base_error& e) {
+    std::stringstream s;
+    s << "Connection write fd(" << get_fd().get_fd() << ',' << m_up->get_state() << ',' << m_up->last_command() << ") \"" << e.what() << '"';
+
+    throw internal_error(s.str());
+  }
+}
+
+bool
+PeerConnectionMetadata::read_skip_bitfield() {
+  if (m_down->buffer()->remaining()) {
+    uint32_t length = std::min(m_skipLength, (uint32_t)m_down->buffer()->remaining());
+    m_down->buffer()->consume(length);
+    m_skipLength -= length;
+  }
+
+  if (m_skipLength) {
+    uint32_t length = std::min(m_skipLength, (uint32_t)null_buffer_size);
+    length = read_stream_throws(m_nullBuffer, length);
+    if (!length)
+      return false;
+    m_skipLength -= length;
+  }
+
+  return !m_skipLength;
+}
+
+// Same as the PCB code, but only one at a time and with the extension protocol.
+bool
+PeerConnectionMetadata::try_request_metadata_pieces() {
+  if (m_download->file_list()->chunk_size() == 1 || !m_extensions->is_remote_supported(ProtocolExtension::UT_METADATA))
+    return false;
+
+  if (download_queue()->queued_empty())
+    m_downStall = 0;
+
+  uint32_t pipeSize = download_queue()->calculate_pipe_size(m_peerChunks.download_throttle()->rate()->rate());
+
+  // Don't start requesting if we can't do it in large enough chunks.
+  if (download_queue()->queued_size() >= (pipeSize + 10) / 2)
+    return false;
+
+  if (!download_queue()->queued_size() < pipeSize || !m_up->can_write_extension() ||
+      m_extensions->has_pending_message())
+    return false;
+
+  const Piece* p = download_queue()->delegate();
+
+  if (p == NULL)
+    return false;
+
+  if (!m_download->file_list()->is_valid_piece(*p) || !m_peerChunks.bitfield()->get(p->index()))
+    throw internal_error("PeerConnectionMetadata::try_request_metadata_pieces() tried to use an invalid piece.");
+
+  return m_extensions->request_metadata_piece(p);
+}
+
+void
+PeerConnectionMetadata::receive_metadata_piece(uint32_t piece, const char* data, uint32_t length) {
+  if (data == NULL) {
+    // Length is not set in a reject message.
+    length = ProtocolExtension::metadata_piece_size;
+    if ((piece << ProtocolExtension::metadata_piece_shift) + ProtocolExtension::metadata_piece_size >= m_download->file_list()->size_bytes())
+      length = m_download->file_list()->chunk_size() % ProtocolExtension::metadata_piece_size;
+    m_tryRequest = false;
+    read_cancel_piece(Piece(0, piece << ProtocolExtension::metadata_piece_shift, length));
+    return;
+  }
+
+  if (!down_chunk_start(Piece(0, piece << ProtocolExtension::metadata_piece_shift, length)))
+    down_chunk_skip_process(data, length);
+  else
+    down_chunk_process(data, length);
+
+  if (!m_downloadQueue.transfer()->is_finished())
+    throw internal_error("PeerConnectionMetadata::receive_metadata_piece did not have complete piece.");
+
+  m_tryRequest = true;
+  down_chunk_finished();
+}
+
+}
diff --git a/src/protocol/peer_connection_metadata.h b/src/protocol/peer_connection_metadata.h
new file mode 100644
index 0000000..127700a
--- /dev/null
+++ b/src/protocol/peer_connection_metadata.h
@@ -0,0 +1,73 @@
+// libTorrent - BitTorrent library
+// Copyright (C) 2005-2007, Jari Sundell
+//
+// This program is free software; you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation; either version 2 of the License, or
+// (at your option) any later version.
+// 
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+// 
+// You should have received a copy of the GNU General Public License
+// along with this program; if not, write to the Free Software
+// Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
+//
+// In addition, as a special exception, the copyright holders give
+// permission to link the code of portions of this program with the
+// OpenSSL library under certain conditions as described in each
+// individual source file, and distribute linked combinations
+// including the two.
+//
+// You must obey the GNU General Public License in all respects for
+// all of the code used other than OpenSSL.  If you modify file(s)
+// with this exception, you may extend this exception to your version
+// of the file(s), but you are not obligated to do so.  If you do not
+// wish to do so, delete this exception statement from your version.
+// If you delete this exception statement from all source files in the
+// program, then also delete it here.
+//
+// Contact:  Jari Sundell <jaris@ifi.uio.no>
+//
+//           Skomakerveien 33
+//           3185 Skoppum, NORWAY
+
+#ifndef LIBTORRENT_PROTOCOL_PEER_CONNECTION_METADATA_H
+#define LIBTORRENT_PROTOCOL_PEER_CONNECTION_METADATA_H
+
+#include "peer_connection_base.h"
+
+#include "torrent/download.h"
+
+namespace torrent {
+
+class PeerConnectionMetadata : public PeerConnectionBase {
+public:
+  ~PeerConnectionMetadata();
+
+  virtual void        initialize_custom();
+  virtual void        update_interested();
+  virtual bool        receive_keepalive();
+
+  virtual void        event_read();
+  virtual void        event_write();
+
+  virtual void        receive_metadata_piece(uint32_t piece, const char* data, uint32_t length);
+
+private:
+  inline bool         read_message();
+
+  bool                read_skip_bitfield();
+
+  bool                try_request_metadata_pieces();
+
+  inline void         fill_write_buffer();
+
+  uint32_t   m_skipLength;
+};
+
+}
+
+#endif
diff --git a/src/protocol/peer_factory.cc b/src/protocol/peer_factory.cc
index 7ab9fe8..cfe6a1e 100644
--- a/src/protocol/peer_factory.cc
+++ b/src/protocol/peer_factory.cc
@@ -38,6 +38,7 @@
 
 #include "peer_factory.h"
 #include "peer_connection_leech.h"
+#include "peer_connection_metadata.h"
 
 namespace torrent {
 
@@ -62,4 +63,11 @@ createPeerConnectionInitialSeed(bool encrypted) {
   return pc;
 }
 
+PeerConnectionBase*
+createPeerConnectionMetadata(bool encrypted) {
+  PeerConnectionBase* pc = new PeerConnectionMetadata;
+
+  return pc;
+}
+
 }
diff --git a/src/protocol/peer_factory.h b/src/protocol/peer_factory.h
index 363a5c3..f22d76f 100644
--- a/src/protocol/peer_factory.h
+++ b/src/protocol/peer_factory.h
@@ -44,6 +44,7 @@ class PeerConnectionBase;
 PeerConnectionBase* createPeerConnectionDefault(bool encrypted);
 PeerConnectionBase* createPeerConnectionSeed(bool encrypted);
 PeerConnectionBase* createPeerConnectionInitialSeed(bool encrypted);
+PeerConnectionBase* createPeerConnectionMetadata(bool encrypted);
 
 }
 
diff --git a/src/torrent/data/file_list.cc b/src/torrent/data/file_list.cc
index 2f5d8d2..7208612 100644
--- a/src/torrent/data/file_list.cc
+++ b/src/torrent/data/file_list.cc
@@ -466,6 +466,18 @@ FileList::open(int flags) {
 
   m_isOpen = true;
   m_frozenRootDir = m_rootDir;
+
+  // For meta-downloads, if the file exists, we have to assume that
+  // it is either 0 or 1 length or the correct size. If the size
+  // turns out wrong later, a communication_error will be thrown elsewhere
+  // to alert the user in this (unlikely) case.
+  if (size_bytes() < 2) {
+    rak::file_stat stat;
+
+    // This probably recurses into open() once, but that is harmless.
+    if (stat.update((*begin())->frozen_path()) && stat.size() > 1)
+      return reset_filesize(stat.size());
+  }
 }
 
 void
@@ -661,4 +673,14 @@ FileList::update_completed() {
   }
 }
 
+void
+FileList::reset_filesize(int64_t size) {
+  close();
+  m_chunkSize = size;
+  m_torrentSize = size;
+  (*begin())->set_size_bytes(size);
+  (*begin())->set_range(m_chunkSize);
+  open(open_no_create);
+}
+
 }
diff --git a/src/torrent/data/file_list.h b/src/torrent/data/file_list.h
index bcc8939..60d418a 100644
--- a/src/torrent/data/file_list.h
+++ b/src/torrent/data/file_list.h
@@ -167,6 +167,10 @@ protected:
   iterator            inc_completed(iterator firstItr, uint32_t index) LIBTORRENT_NO_EXPORT;
   void                update_completed() LIBTORRENT_NO_EXPORT;
 
+  // Used for meta downloads; we only know the
+  // size after the first extension handshake.
+  void                reset_filesize(int64_t) LIBTORRENT_NO_EXPORT;
+
 private:
   bool                open_file(File* node, const Path& lastPath, int flags) LIBTORRENT_NO_EXPORT;
   void                make_directory(Path::const_iterator pathBegin, Path::const_iterator pathEnd, Path::const_iterator startItr) LIBTORRENT_NO_EXPORT;
diff --git a/src/torrent/download.cc b/src/torrent/download.cc
index d6cc199..49daad9 100644
--- a/src/torrent/download.cc
+++ b/src/torrent/download.cc
@@ -225,6 +225,11 @@ Download::set_pex_enabled(bool enabled) {
   m_ptr->info()->set_pex_enabled(enabled);
 }
 
+bool
+Download::is_meta_download() const {
+  return m_ptr->info()->is_meta_download();
+}
+
 const std::string&
 Download::name() const {
   if (m_ptr == NULL)
@@ -504,6 +509,11 @@ Download::connection_type() const {
 
 void
 Download::set_connection_type(ConnectionType t) {
+  if (m_ptr->info()->is_meta_download()) {
+    m_ptr->main()->connection_list()->slot_new_connection(&createPeerConnectionMetadata);
+    return;
+  }
+
   switch (t) {
   case CONNECTION_LEECH:
     m_ptr->main()->connection_list()->slot_new_connection(&createPeerConnectionDefault);
diff --git a/src/torrent/download.h b/src/torrent/download.h
index 5e9700e..5d16d4e 100644
--- a/src/torrent/download.h
+++ b/src/torrent/download.h
@@ -100,6 +100,8 @@ public:
   bool                is_pex_enabled() const;
   void                set_pex_enabled(bool enabled);
 
+  bool                is_meta_download() const;
+
   // Returns "" if the object is not valid.
   const std::string&  name() const;
 
@@ -184,6 +186,7 @@ public:
     CONNECTION_LEECH,
     CONNECTION_SEED,
     CONNECTION_INITIAL_SEED,
+    CONNECTION_METADATA,
   } ConnectionType;
 
   ConnectionType      connection_type() const;
diff --git a/src/torrent/object_stream.cc b/src/torrent/object_stream.cc
index 73c816b..9d9a962 100644
--- a/src/torrent/object_stream.cc
+++ b/src/torrent/object_stream.cc
@@ -600,4 +600,11 @@ object_write_to_stream(void* data, object_buffer_t buffer) {
   return buffer;
 }
 
+object_buffer_t
+object_write_to_size(void* data, object_buffer_t buffer) {
+  *reinterpret_cast<uint64_t*>(data) += std::distance(buffer.first, buffer.second);
+
+  return buffer;
+}
+
 }
diff --git a/src/torrent/object_stream.h b/src/torrent/object_stream.h
index b399bf7..3de5d82 100644
--- a/src/torrent/object_stream.h
+++ b/src/torrent/object_stream.h
@@ -91,6 +91,9 @@ object_buffer_t staticMap_write_bencode_c_wrap(object_write_t writeFunc, void* d
 object_buffer_t object_write_to_buffer(void* data, object_buffer_t buffer) LIBTORRENT_EXPORT;
 object_buffer_t object_write_to_sha1(void* data, object_buffer_t buffer) LIBTORRENT_EXPORT;
 object_buffer_t object_write_to_stream(void* data, object_buffer_t buffer) LIBTORRENT_EXPORT;
+
+// Measures bencode size, 'data' is uint64_t*.
+object_buffer_t object_write_to_size(void* data, object_buffer_t buffer) LIBTORRENT_EXPORT;
 }
 
 #endif
diff --git a/src/torrent/torrent.cc b/src/torrent/torrent.cc
index e8ffbac..47027cc 100644
--- a/src/torrent/torrent.cc
+++ b/src/torrent/torrent.cc
@@ -350,11 +350,22 @@ download_add(Object* object) {
 
   ctor.initialize(*object);
 
-  std::string infoHash = object_sha1(&object->get_key("info"));
+  std::string infoHash;
+  if (download->info()->is_meta_download())
+    infoHash = object->get_key("info").get_key("pieces").as_string();
+  else
+    infoHash = object_sha1(&object->get_key("info"));
 
   if (manager->download_manager()->find(infoHash) != manager->download_manager()->end())
     throw input_error("Info hash already used by another torrent.");
 
+  if (!download->info()->is_meta_download()) {
+    char buffer[1024];
+    uint64_t metadata_size = 0;
+    object_write_bencode_c(&object_write_to_size, &metadata_size, object_buffer_t(buffer, buffer + sizeof(buffer)), &object->get_key("info"));
+    download->main()->set_metadata_size(metadata_size);
+  }
+
   download->set_hash_queue(manager->hash_queue());
   download->initialize(infoHash, PEER_NAME + rak::generate_random<std::string>(20 - std::string(PEER_NAME).size()));