diff --git a/configure.ac b/configure.ac
index 4001c8b1..16d1324a 100644
--- a/configure.ac
+++ b/configure.ac
@@ -375,6 +375,7 @@ AC_CHECK_HEADERS([argz.h \
                   sys/socket.h \
                   sys/time.h \
                   sys/types.h \
+                  sys/uio.h \
                   termios.h \
                   unistd.h \
 		  utime.h \
diff --git a/src/BtAllowedFastMessage.cc b/src/BtAllowedFastMessage.cc
index 14b53ce0..e0fa3b9b 100644
--- a/src/BtAllowedFastMessage.cc
+++ b/src/BtAllowedFastMessage.cc
@@ -36,6 +36,7 @@
 #include "DlAbortEx.h"
 #include "Peer.h"
 #include "fmt.h"
+#include "SocketBuffer.h"
 
 namespace aria2 {
 
@@ -62,8 +63,24 @@ void BtAllowedFastMessage::doReceivedAction() {
   getPeer()->addPeerAllowedIndex(getIndex());
 }
 
-void BtAllowedFastMessage::onSendComplete() {
-  getPeer()->addAmAllowedIndex(getIndex());
+namespace {
+struct ThisProgressUpdate : public ProgressUpdate {
+  ThisProgressUpdate(const SharedHandle<Peer>& peer, size_t index)
+    : peer(peer), index(index) {}
+  virtual void update(size_t length, bool complete)
+  {
+    if(complete) {
+      peer->addAmAllowedIndex(index);
+    }
+  }
+  SharedHandle<Peer> peer;
+  size_t index;
+};
+} // namespace
+
+ProgressUpdate* BtAllowedFastMessage::getProgressUpdate()
+{
+  return new ThisProgressUpdate(getPeer(), getIndex());
 }
 
 } // namespace aria2
diff --git a/src/BtAllowedFastMessage.h b/src/BtAllowedFastMessage.h
index c32aa0d7..079ca84e 100644
--- a/src/BtAllowedFastMessage.h
+++ b/src/BtAllowedFastMessage.h
@@ -52,8 +52,7 @@ public:
 
   virtual void doReceivedAction();
 
-  virtual void onSendComplete();
-
+  virtual ProgressUpdate* getProgressUpdate();
 };
 
 } // namespace aria2
diff --git a/src/BtChokeMessage.cc b/src/BtChokeMessage.cc
index ed230f5d..ac82bd0a 100644
--- a/src/BtChokeMessage.cc
+++ b/src/BtChokeMessage.cc
@@ -36,6 +36,7 @@
 #include "Peer.h"
 #include "BtMessageDispatcher.h"
 #include "BtRequestFactory.h"
+#include "SocketBuffer.h"
 
 namespace aria2 {
 
@@ -64,10 +65,26 @@ bool BtChokeMessage::sendPredicate() const
   return !getPeer()->amChoking();
 }
 
-void BtChokeMessage::onSendComplete()
+namespace {
+struct ThisProgressUpdate : public ProgressUpdate {
+  ThisProgressUpdate(const SharedHandle<Peer>& peer,
+                     BtMessageDispatcher* disp)
+    : peer(peer), disp(disp) {}
+  virtual void update(size_t length, bool complete)
+  {
+    if(complete) {
+      peer->amChoking(true);
+      disp->doChokingAction();
+    }
+  }
+  SharedHandle<Peer> peer;
+  BtMessageDispatcher* disp;
+};
+} // namespace
+
+ProgressUpdate* BtChokeMessage::getProgressUpdate()
 {
-  getPeer()->amChoking(true);
-  getBtMessageDispatcher()->doChokingAction();
+  return new ThisProgressUpdate(getPeer(), getBtMessageDispatcher());
 }
 
 } // namespace aria2
diff --git a/src/BtChokeMessage.h b/src/BtChokeMessage.h
index 73c357d7..ee02e415 100644
--- a/src/BtChokeMessage.h
+++ b/src/BtChokeMessage.h
@@ -53,7 +53,7 @@ public:
 
   virtual bool sendPredicate() const;
 
-  virtual void onSendComplete();
+  virtual ProgressUpdate* getProgressUpdate();
 };
 
 } // namespace aria2
diff --git a/src/BtInterestedMessage.cc b/src/BtInterestedMessage.cc
index e2391bc1..8fafb399 100644
--- a/src/BtInterestedMessage.cc
+++ b/src/BtInterestedMessage.cc
@@ -35,6 +35,7 @@
 #include "BtInterestedMessage.h"
 #include "Peer.h"
 #include "PeerStorage.h"
+#include "SocketBuffer.h"
 
 namespace aria2 {
 
@@ -66,8 +67,23 @@ bool BtInterestedMessage::sendPredicate() const
   return !getPeer()->amInterested();
 }
 
-void BtInterestedMessage::onSendComplete() {
-  getPeer()->amInterested(true);
+namespace {
+struct ThisProgressUpdate : public ProgressUpdate {
+  ThisProgressUpdate(const SharedHandle<Peer>& peer)
+    : peer(peer) {}
+  virtual void update(size_t length, bool complete)
+  {
+    if(complete) {
+      peer->amInterested(true);
+    }
+  }
+  SharedHandle<Peer> peer;
+};
+} // namespace
+
+ProgressUpdate* BtInterestedMessage::getProgressUpdate()
+{
+  return new ThisProgressUpdate(getPeer());
 }
 
 void BtInterestedMessage::setPeerStorage
diff --git a/src/BtInterestedMessage.h b/src/BtInterestedMessage.h
index 1630db93..bc10b208 100644
--- a/src/BtInterestedMessage.h
+++ b/src/BtInterestedMessage.h
@@ -60,7 +60,7 @@ public:
 
   virtual bool sendPredicate() const;
 
-  virtual void onSendComplete();
+  virtual ProgressUpdate* getProgressUpdate();
 
   void setPeerStorage(const SharedHandle<PeerStorage>& peerStorage);
 };
diff --git a/src/BtNotInterestedMessage.cc b/src/BtNotInterestedMessage.cc
index 33f3ec3c..60b810a4 100644
--- a/src/BtNotInterestedMessage.cc
+++ b/src/BtNotInterestedMessage.cc
@@ -35,6 +35,7 @@
 #include "BtNotInterestedMessage.h"
 #include "Peer.h"
 #include "PeerStorage.h"
+#include "SocketBuffer.h"
 
 namespace aria2 {
 
@@ -66,8 +67,23 @@ bool BtNotInterestedMessage::sendPredicate() const
   return getPeer()->amInterested();
 }
 
-void BtNotInterestedMessage::onSendComplete() {
-  getPeer()->amInterested(false);
+namespace {
+struct ThisProgressUpdate : public ProgressUpdate {
+  ThisProgressUpdate(const SharedHandle<Peer>& peer)
+    : peer(peer) {}
+  virtual void update(size_t length, bool complete)
+  {
+    if(complete) {
+      peer->amInterested(false);
+    }
+  }
+  SharedHandle<Peer> peer;
+};
+} // namespace
+
+ProgressUpdate* BtNotInterestedMessage::getProgressUpdate()
+{
+  return new ThisProgressUpdate(getPeer());
 }
 
 void BtNotInterestedMessage::setPeerStorage
diff --git a/src/BtNotInterestedMessage.h b/src/BtNotInterestedMessage.h
index c4e47847..fd9a5844 100644
--- a/src/BtNotInterestedMessage.h
+++ b/src/BtNotInterestedMessage.h
@@ -60,7 +60,7 @@ public:
 
   virtual bool sendPredicate() const;
 
-  virtual void onSendComplete();
+  virtual ProgressUpdate* getProgressUpdate();
 
   void setPeerStorage(const SharedHandle<PeerStorage>& peerStorage);
 };
diff --git a/src/BtPieceMessage.cc b/src/BtPieceMessage.cc
index 92f8193b..845493eb 100644
--- a/src/BtPieceMessage.cc
+++ b/src/BtPieceMessage.cc
@@ -71,7 +71,6 @@ BtPieceMessage::BtPieceMessage
     index_(index),
     begin_(begin),
     blockLength_(blockLength),
-    msgHdrLen_(0),
     data_(0)
 {
   setUploading(true);
@@ -180,39 +179,33 @@ size_t BtPieceMessage::getMessageHeaderLength()
   return MESSAGE_HEADER_LENGTH;
 }
 
+namespace {
+struct PieceSendUpdate : public ProgressUpdate {
+  PieceSendUpdate(const SharedHandle<Peer>& peer)
+    : peer(peer) {}
+  virtual void update(size_t length, bool complete)
+  {
+    peer->updateUploadLength(length);
+  }
+  SharedHandle<Peer> peer;
+};
+} // namespace
+
 void BtPieceMessage::send()
 {
   if(isInvalidate()) {
     return;
   }
-  size_t writtenLength;
-  if(!isSendingInProgress()) {
-    A2_LOG_INFO(fmt(MSG_SEND_PEER_MESSAGE,
-                    getCuid(),
-                    getPeer()->getIPAddress().c_str(),
-                    getPeer()->getPort(),
-                    toString().c_str()));
-    unsigned char* msgHdr = createMessageHeader();
-    msgHdrLen_ = getMessageHeaderLength();
-    A2_LOG_DEBUG(fmt("msglength = %lu bytes",
-                     static_cast<unsigned long>(msgHdrLen_+blockLength_)));
-    getPeerConnection()->pushBytes(msgHdr, msgHdrLen_);
-    int64_t pieceDataOffset =
-      static_cast<int64_t>(index_)*downloadContext_->getPieceLength()+begin_;
-    pushPieceData(pieceDataOffset, blockLength_);
-  }
-  writtenLength = getPeerConnection()->sendPendingData();
-  // Subtract msgHdrLen_ from writtenLength to get the uploaded data
-  // size.
-  if(writtenLength > msgHdrLen_) {
-    writtenLength -= msgHdrLen_;
-    msgHdrLen_ = 0;
-    getPeer()->updateUploadLength(writtenLength);
-    downloadContext_->updateUploadLength(writtenLength);
-  } else {
-    msgHdrLen_ -= writtenLength;
-  }
-  setSendingInProgress(!getPeerConnection()->sendBufferIsEmpty());
+  A2_LOG_INFO(fmt(MSG_SEND_PEER_MESSAGE,
+                  getCuid(),
+                  getPeer()->getIPAddress().c_str(),
+                  getPeer()->getPort(),
+                  toString().c_str()));
+  getPeerConnection()->pushBytes(createMessageHeader(),
+                                 getMessageHeaderLength());
+  int64_t pieceDataOffset =
+    static_cast<int64_t>(index_)*downloadContext_->getPieceLength()+begin_;
+  pushPieceData(pieceDataOffset, blockLength_);
 }
 
 void BtPieceMessage::pushPieceData(int64_t offset, int32_t length) const
@@ -224,7 +217,11 @@ void BtPieceMessage::pushPieceData(int64_t offset, int32_t length) const
   if(r == length) {
     unsigned char* dbuf = buf;
     buf.reset(0);
-    getPeerConnection()->pushBytes(dbuf, length);
+    getPeerConnection()->pushBytes(dbuf, length,
+                                   new PieceSendUpdate(getPeer()));
+    // To avoid upload rate overflow, we update the length here at
+    // once.
+    downloadContext_->updateUploadLength(length);
   } else {
     throw DL_ABORT_EX(EX_DATA_READ);
   }
diff --git a/src/BtPieceMessage.h b/src/BtPieceMessage.h
index adcb20ec..26e01ea5 100644
--- a/src/BtPieceMessage.h
+++ b/src/BtPieceMessage.h
@@ -48,7 +48,6 @@ private:
   size_t index_;
   int32_t begin_;
   int32_t blockLength_;
-  size_t msgHdrLen_;
   const unsigned char* data_;
   SharedHandle<DownloadContext> downloadContext_;
   SharedHandle<PeerStorage> peerStorage_;
diff --git a/src/BtUnchokeMessage.cc b/src/BtUnchokeMessage.cc
index 74100689..9dfd4a8e 100644
--- a/src/BtUnchokeMessage.cc
+++ b/src/BtUnchokeMessage.cc
@@ -34,6 +34,7 @@
 /* copyright --> */
 #include "BtUnchokeMessage.h"
 #include "Peer.h"
+#include "SocketBuffer.h"
 
 namespace aria2 {
 
@@ -60,8 +61,23 @@ bool BtUnchokeMessage::sendPredicate() const
   return getPeer()->amChoking();
 }
 
-void BtUnchokeMessage::onSendComplete() {
-  getPeer()->amChoking(false);
+namespace {
+struct ThisProgressUpdate : public ProgressUpdate {
+  ThisProgressUpdate(const SharedHandle<Peer>& peer)
+    : peer(peer) {}
+  virtual void update(size_t length, bool complete)
+  {
+    if(complete) {
+      peer->amChoking(false);
+    }
+  }
+  SharedHandle<Peer> peer;
+};
+} // namespace
+
+ProgressUpdate* BtUnchokeMessage::getProgressUpdate()
+{
+  return new ThisProgressUpdate(getPeer());
 }
 
 } // namespace aria2
diff --git a/src/BtUnchokeMessage.h b/src/BtUnchokeMessage.h
index b5474a84..710e0a23 100644
--- a/src/BtUnchokeMessage.h
+++ b/src/BtUnchokeMessage.h
@@ -56,7 +56,7 @@ public:
 
   virtual bool sendPredicate() const;
 
-  virtual void onSendComplete();
+  virtual ProgressUpdate* getProgressUpdate();
 };
 
 } // namespace aria2
diff --git a/src/DefaultBtMessageDispatcher.cc b/src/DefaultBtMessageDispatcher.cc
index 1d1dee50..56b1c6c7 100644
--- a/src/DefaultBtMessageDispatcher.cc
+++ b/src/DefaultBtMessageDispatcher.cc
@@ -56,6 +56,7 @@
 #include "RequestGroup.h"
 #include "util.h"
 #include "fmt.h"
+#include "PeerConnection.h"
 
 namespace aria2 {
 
@@ -87,7 +88,8 @@ void DefaultBtMessageDispatcher::addMessageToQueue
   }
 }
 
-void DefaultBtMessageDispatcher::sendMessages() {
+void DefaultBtMessageDispatcher::sendMessagesInternal()
+{
   std::vector<SharedHandle<BtMessage> > tempQueue;
   while(!messageQueue_.empty()) {
     SharedHandle<BtMessage> msg = messageQueue_.front();
@@ -100,10 +102,6 @@ void DefaultBtMessageDispatcher::sendMessages() {
       }
     }
     msg->send();
-    if(msg->isSendingInProgress()) {
-      messageQueue_.push_front(msg);
-      break;
-    }
   }
   if(!tempQueue.empty()) {
     // Insert pending message to the front, so that message is likely sent in
@@ -118,6 +116,16 @@ void DefaultBtMessageDispatcher::sendMessages() {
   }
 }
 
+void DefaultBtMessageDispatcher::sendMessages() {
+  // First flush any pending data in the buffer.
+  peerConnection_->sendPendingData();
+  if(!peerConnection_->sendBufferIsEmpty()) {
+    return;
+  }
+  sendMessagesInternal();
+  peerConnection_->sendPendingData();
+}
+
 // Cancel sending piece message to peer.
 void DefaultBtMessageDispatcher::doCancelSendingPieceAction
 (size_t index, int32_t begin, int32_t length)
diff --git a/src/DefaultBtMessageDispatcher.h b/src/DefaultBtMessageDispatcher.h
index 00069fdc..7a8c44e1 100644
--- a/src/DefaultBtMessageDispatcher.h
+++ b/src/DefaultBtMessageDispatcher.h
@@ -52,6 +52,7 @@ class BtMessageFactory;
 class Peer;
 class Piece;
 class RequestGroupMan;
+class PeerConnection;
 
 class DefaultBtMessageDispatcher : public BtMessageDispatcher {
 private:
@@ -61,6 +62,7 @@ private:
   SharedHandle<DownloadContext> downloadContext_;
   SharedHandle<PeerStorage> peerStorage_;
   SharedHandle<PieceStorage> pieceStorage_;
+  SharedHandle<PeerConnection> peerConnection_;
   BtMessageFactory* messageFactory_;
   SharedHandle<Peer> peer_;
   RequestGroupMan* requestGroupMan_;
@@ -77,6 +79,9 @@ public:
 
   virtual void sendMessages();
 
+  // For unit tests without PeerConnection
+  void sendMessagesInternal();
+
   virtual void doCancelSendingPieceAction
   (size_t index, int32_t begin, int32_t length);
 
@@ -143,6 +148,11 @@ public:
   {
     requestTimeout_ = requestTimeout;
   }
+
+  void setPeerConnection(const SharedHandle<PeerConnection>& peerConnection)
+  {
+    peerConnection_ = peerConnection;
+  }
 };
 
 } // namespace aria2
diff --git a/src/DefaultPeerStorage.cc b/src/DefaultPeerStorage.cc
index 469f044e..ff596076 100644
--- a/src/DefaultPeerStorage.cc
+++ b/src/DefaultPeerStorage.cc
@@ -322,7 +322,7 @@ void DefaultPeerStorage::returnPeer(const SharedHandle<Peer>& peer)
 
 bool DefaultPeerStorage::chokeRoundIntervalElapsed()
 {
-  const time_t CHOKE_ROUND_INTERVAL = 10;
+  const time_t CHOKE_ROUND_INTERVAL = 1;//10;
   if(pieceStorage_->downloadFinished()) {
     return seederStateChoke_->getLastRound().
       difference(global::wallclock()) >= CHOKE_ROUND_INTERVAL;
diff --git a/src/PeerConnection.cc b/src/PeerConnection.cc
index 1039f9ec..c0c6c999 100644
--- a/src/PeerConnection.cc
+++ b/src/PeerConnection.cc
@@ -85,12 +85,13 @@ PeerConnection::~PeerConnection()
   delete [] resbuf_;
 }
 
-void PeerConnection::pushBytes(unsigned char* data, size_t len)
+void PeerConnection::pushBytes(unsigned char* data, size_t len,
+                               ProgressUpdate* progressUpdate)
 {
   if(encryptionEnabled_) {
     encryptor_->encrypt(len, data, data);
   }
-  socketBuffer_.pushBytes(data, len);
+  socketBuffer_.pushBytes(data, len, progressUpdate);
 }
 
 bool PeerConnection::receiveMessage(unsigned char* data, size_t& dataLength)
diff --git a/src/PeerConnection.h b/src/PeerConnection.h
index beb7f3ff..c852db5b 100644
--- a/src/PeerConnection.h
+++ b/src/PeerConnection.h
@@ -96,7 +96,8 @@ public:
 
   // Pushes data into send buffer. After this call, this object gets
   // ownership of data, so caller must not delete or alter it.
-  void pushBytes(unsigned char* data, size_t len);
+  void pushBytes(unsigned char* data, size_t len,
+                 ProgressUpdate* progressUpdate = 0);
 
   void pushStr(const std::string& data);
 
diff --git a/src/PeerInteractionCommand.cc b/src/PeerInteractionCommand.cc
index 2a84d38d..5fcc8faf 100644
--- a/src/PeerInteractionCommand.cc
+++ b/src/PeerInteractionCommand.cc
@@ -200,6 +200,7 @@ PeerInteractionCommand::PeerInteractionCommand
   dispatcherPtr->setBtMessageFactory(factoryPtr);
   dispatcherPtr->setRequestGroupMan
     (getDownloadEngine()->getRequestGroupMan().get());
+  dispatcherPtr->setPeerConnection(peerConnection);
   SharedHandle<BtMessageDispatcher> dispatcher(dispatcherPtr);
 
   DefaultBtMessageReceiver* receiverPtr(new DefaultBtMessageReceiver());
diff --git a/src/SimpleBtMessage.cc b/src/SimpleBtMessage.cc
index 565eab29..c7aa670a 100644
--- a/src/SimpleBtMessage.cc
+++ b/src/SimpleBtMessage.cc
@@ -48,29 +48,19 @@ SimpleBtMessage::SimpleBtMessage(uint8_t id, const char* name)
 {}
 
 void SimpleBtMessage::send() {
-  if(isInvalidate()) {
+  if(isInvalidate() || !sendPredicate()) {
     return;
   }
-  if(!sendPredicate() && !isSendingInProgress()) {
-    return;
-  }
-  if(!isSendingInProgress()) {
-    A2_LOG_INFO(fmt(MSG_SEND_PEER_MESSAGE,
-                    getCuid(),
-                    getPeer()->getIPAddress().c_str(),
-                    getPeer()->getPort(),
-                    toString().c_str()));
-    unsigned char* msg = createMessage();
-    size_t msgLength = getMessageLength();
-    A2_LOG_DEBUG(fmt("msglength = %lu bytes",
-                     static_cast<unsigned long>(msgLength)));
-    getPeerConnection()->pushBytes(msg, msgLength);
-  }
-  getPeerConnection()->sendPendingData();
-  setSendingInProgress(!getPeerConnection()->sendBufferIsEmpty());
-  if(!isSendingInProgress()) {
-    onSendComplete();
-  }
+  A2_LOG_INFO(fmt(MSG_SEND_PEER_MESSAGE,
+                  getCuid(),
+                  getPeer()->getIPAddress().c_str(),
+                  getPeer()->getPort(),
+                  toString().c_str()));
+  unsigned char* msg = createMessage();
+  size_t msgLength = getMessageLength();
+  A2_LOG_DEBUG(fmt("msglength = %lu bytes",
+                   static_cast<unsigned long>(msgLength)));
+  getPeerConnection()->pushBytes(msg, msgLength, getProgressUpdate());
 }
 
 } // namespace aria2
diff --git a/src/SimpleBtMessage.h b/src/SimpleBtMessage.h
index c3dc6419..eefc9466 100644
--- a/src/SimpleBtMessage.h
+++ b/src/SimpleBtMessage.h
@@ -39,6 +39,8 @@
 
 namespace aria2 {
 
+class ProgressUpdate;
+
 class SimpleBtMessage : public AbstractBtMessage {
 public:
   SimpleBtMessage(uint8_t id, const char* name);
@@ -49,7 +51,7 @@ public:
 
   virtual size_t getMessageLength() = 0;
 
-  virtual void onSendComplete() {};
+  virtual ProgressUpdate* getProgressUpdate() { return 0; };
 
   virtual bool sendPredicate() const { return true; };
 
diff --git a/src/SocketBuffer.cc b/src/SocketBuffer.cc
index 35cd2419..ae3972a4 100644
--- a/src/SocketBuffer.cc
+++ b/src/SocketBuffer.cc
@@ -41,12 +41,13 @@
 #include "DlAbortEx.h"
 #include "message.h"
 #include "fmt.h"
+#include "LogFactory.h"
 
 namespace aria2 {
 
 SocketBuffer::ByteArrayBufEntry::ByteArrayBufEntry
-(unsigned char* bytes, size_t length)
-  : bytes_(bytes), length_(length)
+(unsigned char* bytes, size_t length, ProgressUpdate* progressUpdate)
+  : BufEntry(progressUpdate), bytes_(bytes), length_(length)
 {}
 
 SocketBuffer::ByteArrayBufEntry::~ByteArrayBufEntry()
@@ -65,11 +66,22 @@ bool SocketBuffer::ByteArrayBufEntry::final(size_t offset) const
   return length_ <= offset;
 }
 
-SocketBuffer::StringBufEntry::StringBufEntry(const std::string& s)
-  : str_(s)
+size_t SocketBuffer::ByteArrayBufEntry::getLength() const
+{
+  return length_;
+}
+
+const unsigned char* SocketBuffer::ByteArrayBufEntry::getData() const
+{
+  return bytes_;
+}
+
+SocketBuffer::StringBufEntry::StringBufEntry(const std::string& s,
+                                             ProgressUpdate* progressUpdate)
+  : BufEntry(progressUpdate), str_(s)
 {}
 
-SocketBuffer::StringBufEntry::StringBufEntry() {}
+// SocketBuffer::StringBufEntry::StringBufEntry() {}
 
 ssize_t SocketBuffer::StringBufEntry::send
 (const SharedHandle<SocketCore>& socket, size_t offset)
@@ -82,6 +94,16 @@ bool SocketBuffer::StringBufEntry::final(size_t offset) const
   return str_.size() <= offset;
 }
 
+size_t SocketBuffer::StringBufEntry::getLength() const
+{
+  return str_.size();
+}
+
+const unsigned char* SocketBuffer::StringBufEntry::getData() const
+{
+  return reinterpret_cast<const unsigned char*>(str_.c_str());
+}
+
 void SocketBuffer::StringBufEntry::swap(std::string& s)
 {
   str_.swap(s);
@@ -92,38 +114,82 @@ SocketBuffer::SocketBuffer(const SharedHandle<SocketCore>& socket):
 
 SocketBuffer::~SocketBuffer() {}
 
-void SocketBuffer::pushBytes(unsigned char* bytes, size_t len)
+void SocketBuffer::pushBytes(unsigned char* bytes, size_t len,
+                             ProgressUpdate* progressUpdate)
 {
   if(len > 0) {
-    bufq_.push_back(SharedHandle<BufEntry>(new ByteArrayBufEntry(bytes, len)));
+    bufq_.push_back(SharedHandle<BufEntry>
+                    (new ByteArrayBufEntry(bytes, len, progressUpdate)));
   }
 }
 
-void SocketBuffer::pushStr(const std::string& data)
+void SocketBuffer::pushStr(const std::string& data,
+                           ProgressUpdate* progressUpdate)
 {
   if(data.size() > 0) {
-    bufq_.push_back(SharedHandle<BufEntry>(new StringBufEntry(data)));
+    bufq_.push_back(SharedHandle<BufEntry>
+                    (new StringBufEntry(data, progressUpdate)));
   }
 }
 
 ssize_t SocketBuffer::send()
 {
+  a2iovec iov[A2_IOV_MAX];
   size_t totalslen = 0;
   while(!bufq_.empty()) {
-    const SharedHandle<BufEntry>& buf = bufq_[0];
-    ssize_t slen = buf->send(socket_, offset_);
+    size_t num;
+    ssize_t amount = 16*1024;
+    ssize_t firstlen = bufq_[0]->getLength() - offset_;
+    amount -= firstlen;
+    iov[0].A2IOVEC_BASE =
+      reinterpret_cast<char*>(const_cast<unsigned char*>
+                              (bufq_[0]->getData() + offset_));
+    iov[0].A2IOVEC_LEN = firstlen;
+
+    for(num = 1; num < A2_IOV_MAX && num < bufq_.size() && amount > 0; ++num) {
+      const SharedHandle<BufEntry>& buf = bufq_[num];
+      ssize_t len = buf->getLength();
+      if(amount >= len) {
+        amount -= len;
+        iov[num].A2IOVEC_BASE =
+          reinterpret_cast<char*>(const_cast<unsigned char*>(buf->getData()));
+        iov[num].A2IOVEC_LEN = len;
+      } else {
+        break;
+      }
+    }
+    ssize_t slen = socket_->writeVector(iov, num);
     if(slen == 0 && !socket_->wantRead() && !socket_->wantWrite()) {
       throw DL_ABORT_EX(fmt(EX_SOCKET_SEND, "Connection closed."));
     }
+    //A2_LOG_NOTICE(fmt("SEND=%d", slen));
     totalslen += slen;
-    offset_ += slen;
-    if(buf->final(offset_)) {
+
+    if(firstlen > slen) {
+      offset_ += slen;
+      bufq_[0]->progressUpdate(slen, false);
+    } else {
+      slen -= firstlen;
+      bufq_[0]->progressUpdate(firstlen, true);
       bufq_.pop_front();
       offset_ = 0;
-    } else {
-      break;
+      for(size_t i = 1; i < num; ++i) {
+        const SharedHandle<BufEntry>& buf = bufq_[0];
+        ssize_t len = buf->getLength();
+        if(len > slen) {
+          offset_ = slen;
+          bufq_[0]->progressUpdate(slen, false);
+          goto fin;
+          break;
+        } else {
+          slen -= len;
+          bufq_[0]->progressUpdate(len, true);
+          bufq_.pop_front();
+        }
+      }
     }
   }
+ fin:
   return totalslen;
 }
 
diff --git a/src/SocketBuffer.h b/src/SocketBuffer.h
index c433d8d0..1f0a32df 100644
--- a/src/SocketBuffer.h
+++ b/src/SocketBuffer.h
@@ -46,23 +46,46 @@ namespace aria2 {
 
 class SocketCore;
 
+struct ProgressUpdate {
+  virtual ~ProgressUpdate() {}
+  virtual void update(size_t length, bool complete) = 0;
+};
+
 class SocketBuffer {
 private:
   class BufEntry {
   public:
-    virtual ~BufEntry() {}
+    BufEntry(ProgressUpdate* progressUpdate)
+    : progressUpdate_(progressUpdate) {}
+    virtual ~BufEntry()
+    {
+      delete progressUpdate_;
+    }
     virtual ssize_t send
     (const SharedHandle<SocketCore>& socket, size_t offset) = 0;
     virtual bool final(size_t offset) const = 0;
+    virtual size_t getLength() const = 0;
+    virtual const unsigned char* getData() const = 0;
+    void progressUpdate(size_t length, bool complete)
+    {
+      if(progressUpdate_) {
+        progressUpdate_->update(length, complete);
+      }
+    }
+  private:
+    ProgressUpdate* progressUpdate_;
   };
 
   class ByteArrayBufEntry:public BufEntry {
   public:
-    ByteArrayBufEntry(unsigned char* bytes, size_t length);
+    ByteArrayBufEntry(unsigned char* bytes, size_t length,
+                      ProgressUpdate* progressUpdate);
     virtual ~ByteArrayBufEntry();
     virtual ssize_t send
     (const SharedHandle<SocketCore>& socket, size_t offset);
     virtual bool final(size_t offset) const;
+    virtual size_t getLength() const;
+    virtual const unsigned char* getData() const;
   private:
     unsigned char* bytes_;
     size_t length_;
@@ -70,11 +93,14 @@ private:
 
   class StringBufEntry:public BufEntry {
   public:
-    StringBufEntry(const std::string& s);
+    StringBufEntry(const std::string& s,
+                   ProgressUpdate* progressUpdate);
     StringBufEntry();
     virtual ssize_t send
     (const SharedHandle<SocketCore>& socket, size_t offset);
     virtual bool final(size_t offset) const;
+    virtual size_t getLength() const;
+    virtual const unsigned char* getData() const;
     void swap(std::string& s);
   private:
     std::string str_;
@@ -99,11 +125,18 @@ public:
 
   // Feeds data pointered by bytes with length len into queue.  This
   // object gets ownership of bytes, so caller must not delete or
-  // later bytes after this call. This function doesn't send data.
-  void pushBytes(unsigned char* bytes, size_t len);
+  // later bytes after this call. This function doesn't send data.  If
+  // progressUpdate is not null, its update() function will be called
+  // each time the data is sent. It will be deleted by this object. It
+  // can be null.
+  void pushBytes(unsigned char* bytes, size_t len,
+                 ProgressUpdate* progressUpdate = 0);
 
-  // Feeds data into queue. This function doesn't send data.
-  void pushStr(const std::string& data);
+  // Feeds data into queue. This function doesn't send data.  If
+  // progressUpdate is not null, its update() function will be called
+  // each time the data is sent. It will be deleted by this object. It
+  // can be null.
+  void pushStr(const std::string& data, ProgressUpdate* progressUpdate = 0);
 
   // Sends data in queue.  Returns the number of bytes sent.
   ssize_t send();
diff --git a/src/SocketCore.cc b/src/SocketCore.cc
index 1be9010b..d8596009 100644
--- a/src/SocketCore.cc
+++ b/src/SocketCore.cc
@@ -738,14 +738,57 @@ void SocketCore::gnutlsRecordCheckDirection()
 }
 #endif // HAVE_LIBGNUTLS
 
-ssize_t SocketCore::writeData(const char* data, size_t len)
+ssize_t SocketCore::writeVector(a2iovec *iov, size_t iovcnt)
+{
+  ssize_t ret = 0;
+  wantRead_ = false;
+  wantWrite_ = false;
+  if(!secure_) {
+#ifdef __MINGW32__
+    DWORD nsent;
+    int rv = WSASend(sockfd_, iov, iovcnt, &nsent, 0, 0, 0);
+    if(rv == 0) {
+      ret = nsent;
+    } else {
+      ret = -1;
+    }
+#else // !__MINGW32__
+    while((ret = writev(sockfd_, iov, iovcnt)) == -1 &&
+          SOCKET_ERRNO == A2_EINTR);
+#endif // !__MINGW32__
+    int errNum = SOCKET_ERRNO;
+    if(ret == -1) {
+      if(A2_WOULDBLOCK(errNum)) {
+        wantWrite_ = true;
+        ret = 0;
+      } else {
+        throw DL_RETRY_EX(fmt(EX_SOCKET_SEND, errorMsg(errNum).c_str()));
+      }
+    }
+  } else {
+    // For SSL/TLS, we could not use writev, so just iterate vector
+    // and write the data in normal way.
+    for(size_t i = 0; i < iovcnt; ++i) {
+      ssize_t rv = writeData(iov[i].A2IOVEC_BASE, iov[i].A2IOVEC_LEN);
+      if(rv == 0) {
+        break;
+      }
+      ret += rv;
+    }
+  }
+  return ret;
+}
+
+ssize_t SocketCore::writeData(const void* data, size_t len)
 {
   ssize_t ret = 0;
   wantRead_ = false;
   wantWrite_ = false;
 
   if(!secure_) {
-    while((ret = send(sockfd_, data, len, 0)) == -1 && SOCKET_ERRNO == A2_EINTR);
+    // Cast for Windows send()
+    while((ret = send(sockfd_, reinterpret_cast<const char*>(data),
+                      len, 0)) == -1 && SOCKET_ERRNO == A2_EINTR);
     int errNum = SOCKET_ERRNO;
     if(ret == -1) {
       if(A2_WOULDBLOCK(errNum)) {
@@ -1166,7 +1209,7 @@ bool SocketCore::tlsHandshake(TLSContext* tlsctx, const std::string& hostname)
 
 #endif // ENABLE_SSL
 
-ssize_t SocketCore::writeData(const char* data, size_t len,
+ssize_t SocketCore::writeData(const void* data, size_t len,
                               const std::string& host, uint16_t port)
 {
   wantRead_ = false;
@@ -1184,7 +1227,9 @@ ssize_t SocketCore::writeData(const char* data, size_t len,
   ssize_t r = -1;
   int errNum = 0;
   for(rp = res; rp; rp = rp->ai_next) {
-    while((r = sendto(sockfd_, data, len, 0, rp->ai_addr, rp->ai_addrlen)) == -1
+    // Cast for Windows sendto()
+    while((r = sendto(sockfd_, reinterpret_cast<const char*>(data), len, 0,
+                      rp->ai_addr, rp->ai_addrlen)) == -1
           && A2_EINTR == SOCKET_ERRNO);
     errNum = SOCKET_ERRNO;
     if(r == static_cast<ssize_t>(len)) {
diff --git a/src/SocketCore.h b/src/SocketCore.h
index 2c943c3b..470921a6 100644
--- a/src/SocketCore.h
+++ b/src/SocketCore.h
@@ -252,25 +252,16 @@ public:
    * @param data data to write
    * @param len length of data
    */
-  ssize_t writeData(const char* data, size_t len);
+  ssize_t writeData(const void* data, size_t len);
   ssize_t writeData(const std::string& msg)
   {
     return writeData(msg.c_str(), msg.size());
   }
-  ssize_t writeData(const unsigned char* data, size_t len)
-  {
-    return writeData(reinterpret_cast<const char*>(data), len);
-  }
 
-  ssize_t writeData(const char* data, size_t len,
+  ssize_t writeData(const void* data, size_t len,
                     const std::string& host, uint16_t port);
 
-  ssize_t writeData(const unsigned char* data, size_t len,
-                    const std::string& host,
-                    uint16_t port)
-  {
-    return writeData(reinterpret_cast<const char*>(data), len, host, port);
-  }
+  ssize_t writeVector(a2iovec *iov, size_t iovcnt);
 
   /**
    * Reads up to len bytes from this socket.
diff --git a/src/a2netcompat.h b/src/a2netcompat.h
index 41378307..46af621b 100644
--- a/src/a2netcompat.h
+++ b/src/a2netcompat.h
@@ -87,6 +87,10 @@
 # include <netinet/in.h>
 #endif // HAVE_NETINET_IN_H
 
+#ifdef HAVE_SYS_UIO_H
+# include <sys/uio.h>
+#endif // HAVE_SYS_UIO_H
+
 #ifndef HAVE_GETADDRINFO
 # include "getaddrinfo.h"
 # define HAVE_GAI_STRERROR
@@ -141,4 +145,22 @@ union sockaddr_union {
   sockaddr_in in;
 };
 
+#define A2_DEFAULT_IOV_MAX 128
+
+#if defined(IOV_MAX) && IOV_MAX < A2_DEFAULT_IOV_MAX
+#  define A2_IOV_MAX IOV_MAX
+#else
+#  define A2_IOV_MAX A2_DEFAULT_IOV_MAX
+#endif
+
+#ifdef __MINGW32__
+typedef WSABUF a2iovec;
+#  define A2IOVEC_BASE buf
+#  define A2IOVEC_LEN len
+#else // !__MINGW32__
+typedef struct iovec a2iovec;
+#  define A2IOVEC_BASE iov_base
+#  define A2IOVEC_LEN iov_len
+#endif // !__MINGW32__
+
 #endif // D_A2NETCOMPAT_H
diff --git a/test/BtAllowedFastMessageTest.cc b/test/BtAllowedFastMessageTest.cc
index 5e996660..e8d1fa4d 100644
--- a/test/BtAllowedFastMessageTest.cc
+++ b/test/BtAllowedFastMessageTest.cc
@@ -6,6 +6,7 @@
 #include "bittorrent_helper.h"
 #include "util.h"
 #include "Peer.h"
+#include "SocketBuffer.h"
 
 namespace aria2 {
 
@@ -98,7 +99,8 @@ void BtAllowedFastMessageTest::testOnSendComplete() {
   peer->setFastExtensionEnabled(true);
   msg.setPeer(peer);
   CPPUNIT_ASSERT(!peer->isInAmAllowedIndexSet(1));
-  msg.onSendComplete();
+  SharedHandle<ProgressUpdate> pu(msg.getProgressUpdate());
+  pu->update(0, true);
   CPPUNIT_ASSERT(peer->isInAmAllowedIndexSet(1));
 }
 
diff --git a/test/BtChokeMessageTest.cc b/test/BtChokeMessageTest.cc
index 83465df5..31e8bfe8 100644
--- a/test/BtChokeMessageTest.cc
+++ b/test/BtChokeMessageTest.cc
@@ -9,6 +9,7 @@
 #include "MockBtRequestFactory.h"
 #include "Peer.h"
 #include "FileEntry.h"
+#include "SocketBuffer.h"
 
 namespace aria2 {
 
@@ -123,7 +124,8 @@ void BtChokeMessageTest::testOnSendComplete() {
   SharedHandle<MockBtMessageDispatcher2> dispatcher(new MockBtMessageDispatcher2());
   msg.setBtMessageDispatcher(dispatcher.get());
 
-  msg.onSendComplete();
+  SharedHandle<ProgressUpdate> pu(msg.getProgressUpdate());
+  pu->update(0, true);
 
   CPPUNIT_ASSERT(dispatcher->doChokingActionCalled);
   CPPUNIT_ASSERT(peer->amChoking());
diff --git a/test/BtInterestedMessageTest.cc b/test/BtInterestedMessageTest.cc
index e0accffe..ccb6b8b2 100644
--- a/test/BtInterestedMessageTest.cc
+++ b/test/BtInterestedMessageTest.cc
@@ -7,6 +7,7 @@
 #include "bittorrent_helper.h"
 #include "Peer.h"
 #include "MockPeerStorage.h"
+#include "SocketBuffer.h"
 
 namespace aria2 {
 
@@ -90,7 +91,8 @@ void BtInterestedMessageTest::testOnSendComplete() {
   peer->allocateSessionResource(1024, 1024*1024);
   msg.setPeer(peer);
   CPPUNIT_ASSERT(!peer->amInterested());
-  msg.onSendComplete();
+  SharedHandle<ProgressUpdate> pu(msg.getProgressUpdate());
+  pu->update(0, true);
   CPPUNIT_ASSERT(peer->amInterested());
 }
 
diff --git a/test/BtNotInterestedMessageTest.cc b/test/BtNotInterestedMessageTest.cc
index d9a8e5f1..1bd204d0 100644
--- a/test/BtNotInterestedMessageTest.cc
+++ b/test/BtNotInterestedMessageTest.cc
@@ -7,6 +7,7 @@
 #include "bittorrent_helper.h"
 #include "Peer.h"
 #include "MockPeerStorage.h"
+#include "SocketBuffer.h"
 
 namespace aria2 {
 
@@ -92,7 +93,8 @@ void BtNotInterestedMessageTest::testOnSendComplete() {
   BtNotInterestedMessage msg;
   msg.setPeer(peer);
   CPPUNIT_ASSERT(peer->amInterested());
-  msg.onSendComplete();
+  SharedHandle<ProgressUpdate> pu(msg.getProgressUpdate());
+  pu->update(0, true);
   CPPUNIT_ASSERT(!peer->amInterested());
 }
 
diff --git a/test/BtUnchokeMessageTest.cc b/test/BtUnchokeMessageTest.cc
index 639a8406..17b7fe50 100644
--- a/test/BtUnchokeMessageTest.cc
+++ b/test/BtUnchokeMessageTest.cc
@@ -1,9 +1,12 @@
 #include "BtUnchokeMessage.h"
-#include "bittorrent_helper.h"
-#include "Peer.h"
+
 #include <cstring>
 #include <cppunit/extensions/HelperMacros.h>
 
+#include "bittorrent_helper.h"
+#include "Peer.h"
+#include "SocketBuffer.h"
+
 namespace aria2 {
 
 class BtUnchokeMessageTest:public CppUnit::TestFixture {
@@ -83,7 +86,8 @@ void BtUnchokeMessageTest::testOnSendComplete() {
   msg.setPeer(peer);
 
   CPPUNIT_ASSERT(peer->amChoking());
-  msg.onSendComplete();
+  SharedHandle<ProgressUpdate> pu(msg.getProgressUpdate());
+  pu->update(0, true);
   CPPUNIT_ASSERT(!peer->amChoking());
 }
 
diff --git a/test/DefaultBtMessageDispatcherTest.cc b/test/DefaultBtMessageDispatcherTest.cc
index 9ca5a434..71cb3ed8 100644
--- a/test/DefaultBtMessageDispatcherTest.cc
+++ b/test/DefaultBtMessageDispatcherTest.cc
@@ -19,6 +19,7 @@
 #include "RequestGroup.h"
 #include "DownloadContext.h"
 #include "bittorrent_helper.h"
+#include "PeerConnection.h"
 
 namespace aria2 {
 
@@ -30,7 +31,6 @@ class DefaultBtMessageDispatcherTest:public CppUnit::TestFixture {
   CPPUNIT_TEST(testSendMessages_underUploadLimit);
   // See the comment on the definition
   //CPPUNIT_TEST(testSendMessages_overUploadLimit);
-  CPPUNIT_TEST(testSendMessages_sendingInProgress);
   CPPUNIT_TEST(testDoCancelSendingPieceAction);
   CPPUNIT_TEST(testCheckRequestSlotAndDoNecessaryThing);
   CPPUNIT_TEST(testCheckRequestSlotAndDoNecessaryThing_timeout);
@@ -58,7 +58,6 @@ public:
   void testSendMessages();
   void testSendMessages_underUploadLimit();
   void testSendMessages_overUploadLimit();
-  void testSendMessages_sendingInProgress();
   void testDoCancelSendingPieceAction();
   void testCheckRequestSlotAndDoNecessaryThing();
   void testCheckRequestSlotAndDoNecessaryThing_timeout();
@@ -188,7 +187,7 @@ void DefaultBtMessageDispatcherTest::testSendMessages() {
   msg2->setUploading(false);
   btMessageDispatcher->addMessageToQueue(msg1);
   btMessageDispatcher->addMessageToQueue(msg2);
-  btMessageDispatcher->sendMessages();
+  btMessageDispatcher->sendMessagesInternal();
 
   CPPUNIT_ASSERT(msg1->isSendCalled());
   CPPUNIT_ASSERT(msg2->isSendCalled());
@@ -203,7 +202,7 @@ void DefaultBtMessageDispatcherTest::testSendMessages_underUploadLimit() {
   msg2->setUploading(true);
   btMessageDispatcher->addMessageToQueue(msg1);
   btMessageDispatcher->addMessageToQueue(msg2);
-  btMessageDispatcher->sendMessages();
+  btMessageDispatcher->sendMessagesInternal();
 
   CPPUNIT_ASSERT(msg1->isSendCalled());
   CPPUNIT_ASSERT(msg2->isSendCalled());
@@ -232,7 +231,7 @@ void DefaultBtMessageDispatcherTest::testSendMessages_underUploadLimit() {
 //   btMessageDispatcher->addMessageToQueue(msg1);
 //   btMessageDispatcher->addMessageToQueue(msg2);
 //   btMessageDispatcher->addMessageToQueue(msg3);
-//   btMessageDispatcher->sendMessages();
+//   btMessageDispatcher->sendMessagesInternal();
 
 //   CPPUNIT_ASSERT(!msg1->isSendCalled());
 //   CPPUNIT_ASSERT(!msg2->isSendCalled());
@@ -242,31 +241,6 @@ void DefaultBtMessageDispatcherTest::testSendMessages_underUploadLimit() {
 //                     btMessageDispatcher->getMessageQueue().size());
 // }
 
-void DefaultBtMessageDispatcherTest::testSendMessages_sendingInProgress() {
-  SharedHandle<MockBtMessage2> msg1(new MockBtMessage2());
-  msg1->setSendingInProgress(false);
-  msg1->setUploading(false);
-  SharedHandle<MockBtMessage2> msg2(new MockBtMessage2());
-  msg2->setSendingInProgress(true);
-  msg2->setUploading(false);
-  SharedHandle<MockBtMessage2> msg3(new MockBtMessage2());
-  msg3->setSendingInProgress(false);
-  msg3->setUploading(false);
-
-  btMessageDispatcher->addMessageToQueue(msg1);
-  btMessageDispatcher->addMessageToQueue(msg2);
-  btMessageDispatcher->addMessageToQueue(msg3);
-
-  btMessageDispatcher->sendMessages();
-
-  CPPUNIT_ASSERT(msg1->isSendCalled());
-  CPPUNIT_ASSERT(msg2->isSendCalled());
-  CPPUNIT_ASSERT(!msg3->isSendCalled());
-
-  CPPUNIT_ASSERT_EQUAL((size_t)2,
-                       btMessageDispatcher->getMessageQueue().size());
-}
-
 void DefaultBtMessageDispatcherTest::testDoCancelSendingPieceAction() {
   SharedHandle<MockBtMessage2> msg1(new MockBtMessage2());
   SharedHandle<MockBtMessage2> msg2(new MockBtMessage2());