diff --git a/src/shrpx_client_handler.cc b/src/shrpx_client_handler.cc
index 886b5516..d2947bcd 100644
--- a/src/shrpx_client_handler.cc
+++ b/src/shrpx_client_handler.cc
@@ -135,68 +135,30 @@ int ClientHandler::read_clear() {
 }
 
 int ClientHandler::write_clear() {
+  std::array<iovec, 2> iov;
+
   ev_timer_again(conn_.loop, &conn_.rt);
 
   for (;;) {
-    if (wb_.rleft() > 0) {
-      auto nwrite = conn_.write_clear(wb_.pos, wb_.rleft());
-      if (nwrite == 0) {
-        return 0;
-      }
-      if (nwrite < 0) {
-        return -1;
-      }
-      wb_.drain(nwrite);
-      continue;
-    }
-    wb_.reset();
     if (on_write() != 0) {
       return -1;
     }
-    if (wb_.rleft() == 0) {
+
+    auto iovcnt = upstream_->response_riovec(iov.data(), iov.size());
+    if (iovcnt == 0) {
       break;
     }
-  }
 
-  conn_.wlimit.stopw();
-  ev_timer_stop(conn_.loop, &conn_.wt);
-
-  return 0;
-}
-
-int ClientHandler::writev_clear() {
-  ev_timer_again(conn_.loop, &conn_.rt);
-
-  auto buf = upstream_->get_response_buf();
-  if (!buf) {
-    conn_.wlimit.stopw();
-    ev_timer_stop(conn_.loop, &conn_.wt);
-
-    return 0;
-  }
-
-  for (;;) {
-    if (buf->rleft() > 0) {
-      std::array<iovec, 2> iov;
-      auto iovcnt = buf->riovec(iov.data(), iov.size());
-      auto nwrite = conn_.writev_clear(iov.data(), iovcnt);
-      if (nwrite == 0) {
-        return 0;
-      }
-      if (nwrite < 0) {
-        return -1;
-      }
-      buf->drain(nwrite);
-      continue;
-    }
-    if (on_write() != 0) {
+    auto nwrite = conn_.writev_clear(iov.data(), iovcnt);
+    if (nwrite < 0) {
       return -1;
     }
-    // buf may be destroyed inside on_write()
-    buf = upstream_->get_response_buf();
-    if (!buf || buf->rleft() == 0) {
-      break;
+
+    if (nwrite == 0) {
+      return 0;
     }
+
+    upstream_->response_drain(nwrite);
   }
 
   conn_.wlimit.stopw();
@@ -229,12 +191,7 @@ int ClientHandler::tls_handshake() {
   }
 
   read_ = &ClientHandler::read_tls;
-
-  if (alpn_ == "http/1.1") {
-    write_ = &ClientHandler::writev_tls;
-  } else {
-    write_ = &ClientHandler::write_tls;
-  }
+  write_ = &ClientHandler::write_tls;
 
   return 0;
 }
@@ -271,85 +228,33 @@ int ClientHandler::read_tls() {
 }
 
 int ClientHandler::write_tls() {
+  struct iovec iov;
+
   ev_timer_again(conn_.loop, &conn_.rt);
 
   ERR_clear_error();
 
   for (;;) {
-    if (wb_.rleft() > 0) {
-      auto nwrite = conn_.write_tls(wb_.pos, wb_.rleft());
-
-      if (nwrite == 0) {
-        return 0;
-      }
-
-      if (nwrite < 0) {
-        return -1;
-      }
-
-      wb_.drain(nwrite);
-
-      continue;
-    }
-    wb_.reset();
     if (on_write() != 0) {
       return -1;
     }
-    if (wb_.rleft() == 0) {
+
+    auto iovcnt = upstream_->response_riovec(&iov, 1);
+    if (iovcnt == 0) {
       conn_.start_tls_write_idle();
       break;
     }
-  }
 
-  conn_.wlimit.stopw();
-  ev_timer_stop(conn_.loop, &conn_.wt);
-
-  return 0;
-}
-
-int ClientHandler::writev_tls() {
-  ev_timer_again(conn_.loop, &conn_.rt);
-
-  auto buf = upstream_->get_response_buf();
-  if (!buf) {
-    conn_.wlimit.stopw();
-    ev_timer_stop(conn_.loop, &conn_.wt);
-
-    return 0;
-  }
-
-  ERR_clear_error();
-
-  for (;;) {
-    if (buf->rleft() > 0) {
-      iovec iov;
-      auto iovcnt = buf->riovec(&iov, 1);
-      if (iovcnt == 0) {
-        return 0;
-      }
-
-      auto nwrite = conn_.write_tls(iov.iov_base, iov.iov_len);
-
-      if (nwrite == 0) {
-        return 0;
-      }
-
-      if (nwrite < 0) {
-        return -1;
-      }
-
-      buf->drain(nwrite);
-
-      continue;
-    }
-    if (on_write() != 0) {
+    auto nwrite = conn_.write_tls(iov.iov_base, iov.iov_len);
+    if (nwrite < 0) {
       return -1;
     }
-    buf = upstream_->get_response_buf();
-    if (!buf || buf->rleft() == 0) {
-      conn_.start_tls_write_idle();
-      break;
+
+    if (nwrite == 0) {
+      return 0;
     }
+
+    upstream_->response_drain(nwrite);
   }
 
   conn_.wlimit.stopw();
@@ -374,9 +279,7 @@ int ClientHandler::upstream_write() {
     return -1;
   }
 
-  if (get_should_close_after_write() && wb_.rleft() == 0 &&
-      (!upstream_->get_response_buf() ||
-       upstream_->get_response_buf()->rleft() == 0)) {
+  if (get_should_close_after_write() && upstream_->response_empty()) {
     return -1;
   }
 
@@ -506,7 +409,7 @@ void ClientHandler::setup_upstream_io_callback() {
     upstream_ = make_unique<HttpsUpstream>(this);
     alpn_ = "http/1.1";
     read_ = &ClientHandler::read_clear;
-    write_ = &ClientHandler::writev_clear;
+    write_ = &ClientHandler::write_clear;
     on_read_ = &ClientHandler::upstream_http1_connhd_read;
     on_write_ = &ClientHandler::upstream_noop;
   }
@@ -818,7 +721,6 @@ int ClientHandler::perform_http2_upgrade(HttpsUpstream *http) {
   }
   // http pointer is now owned by upstream.
   upstream_.release();
-  upstream_ = std::move(upstream);
   // TODO We might get other version id in HTTP2-settings, if we
   // support aliasing for h2, but we just use library default for now.
   alpn_ = NGHTTP2_CLEARTEXT_PROTO_VERSION_ID;
@@ -829,7 +731,9 @@ int ClientHandler::perform_http2_upgrade(HttpsUpstream *http) {
                       "Connection: Upgrade\r\n"
                       "Upgrade: " NGHTTP2_CLEARTEXT_PROTO_VERSION_ID "\r\n"
                       "\r\n";
-  wb_.write(res, sizeof(res) - 1);
+  upstream->response_write(res, sizeof(res) - 1);
+  upstream_ = std::move(upstream);
+
   signal_write();
   return 0;
 }
@@ -932,8 +836,6 @@ void ClientHandler::write_accesslog(int major, int minor, unsigned int status,
                      });
 }
 
-ClientHandler::WriteBuf *ClientHandler::get_wb() { return &wb_; }
-
 ClientHandler::ReadBuf *ClientHandler::get_rb() { return &rb_; }
 
 void ClientHandler::signal_write() { conn_.wlimit.startw(); }
diff --git a/src/shrpx_client_handler.h b/src/shrpx_client_handler.h
index 1a243479..b05013c8 100644
--- a/src/shrpx_client_handler.h
+++ b/src/shrpx_client_handler.h
@@ -60,13 +60,11 @@ public:
   // Performs clear text I/O
   int read_clear();
   int write_clear();
-  int writev_clear();
   // Performs TLS handshake
   int tls_handshake();
   // Performs TLS I/O
   int read_tls();
   int write_tls();
-  int writev_tls();
 
   int upstream_noop();
   int upstream_read();
@@ -124,10 +122,8 @@ public:
                        int64_t body_bytes_sent);
   Worker *get_worker() const;
 
-  using WriteBuf = Buffer<32768>;
   using ReadBuf = Buffer<8_k>;
 
-  WriteBuf *get_wb();
   ReadBuf *get_rb();
 
   RateLimit *get_rlimit();
@@ -153,7 +149,6 @@ private:
   // The number of bytes of HTTP/2 client connection header to read
   size_t left_connhd_len_;
   bool should_close_after_write_;
-  WriteBuf wb_;
   ReadBuf rb_;
 };
 
diff --git a/src/shrpx_http2_upstream.cc b/src/shrpx_http2_upstream.cc
index bcffba14..c885f2e7 100644
--- a/src/shrpx_http2_upstream.cc
+++ b/src/shrpx_http2_upstream.cc
@@ -852,9 +852,8 @@ int Http2Upstream::on_read() {
     rlimit->startw();
   }
 
-  auto wb = handler_->get_wb();
   if (nghttp2_session_want_read(session_) == 0 &&
-      nghttp2_session_want_write(session_) == 0 && wb->rleft() == 0) {
+      nghttp2_session_want_write(session_) == 0 && wb_.rleft() == 0) {
     if (LOG_ENABLED(INFO)) {
       ULOG(INFO, this) << "No more read/write for this HTTP2 session";
     }
@@ -867,11 +866,13 @@ int Http2Upstream::on_read() {
 
 // After this function call, downstream may be deleted.
 int Http2Upstream::on_write() {
-  auto wb = handler_->get_wb();
+  if (wb_.rleft() == 0) {
+    wb_.reset();
+  }
 
   if (data_pending_) {
-    auto n = std::min(wb->wleft(), data_pendinglen_);
-    wb->write(data_pending_, n);
+    auto n = std::min(wb_.wleft(), data_pendinglen_);
+    wb_.write(data_pending_, n);
     if (n < data_pendinglen_) {
       data_pending_ += n;
       data_pendinglen_ -= n;
@@ -894,7 +895,7 @@ int Http2Upstream::on_write() {
     if (datalen == 0) {
       break;
     }
-    auto n = wb->write(data, datalen);
+    auto n = wb_.write(data, datalen);
     if (n < static_cast<decltype(n)>(datalen)) {
       data_pending_ = data + n;
       data_pendinglen_ = datalen - n;
@@ -903,7 +904,7 @@ int Http2Upstream::on_write() {
   }
 
   if (nghttp2_session_want_read(session_) == 0 &&
-      nghttp2_session_want_write(session_) == 0 && wb->rleft() == 0) {
+      nghttp2_session_want_write(session_) == 0 && wb_.rleft() == 0) {
     if (LOG_ENABLED(INFO)) {
       ULOG(INFO, this) << "No more read/write for this HTTP2 session";
     }
@@ -1755,4 +1756,23 @@ int Http2Upstream::initiate_push(Downstream *downstream, const char *uri,
   return 0;
 }
 
+int Http2Upstream::response_riovec(struct iovec *iov, int iovcnt) const {
+  if (iovcnt == 0 || wb_.rleft() == 0) {
+    return 0;
+  }
+
+  iov->iov_base = wb_.pos;
+  iov->iov_len = wb_.rleft();
+
+  return 1;
+}
+
+void Http2Upstream::response_drain(size_t n) { wb_.drain(n); }
+
+bool Http2Upstream::response_empty() const { return wb_.rleft() == 0; }
+
+void Http2Upstream::response_write(void *data, size_t len) {
+  wb_.write(data, len);
+}
+
 } // namespace shrpx
diff --git a/src/shrpx_http2_upstream.h b/src/shrpx_http2_upstream.h
index cc877f5c..11be767c 100644
--- a/src/shrpx_http2_upstream.h
+++ b/src/shrpx_http2_upstream.h
@@ -36,6 +36,7 @@
 #include "shrpx_upstream.h"
 #include "shrpx_downstream_queue.h"
 #include "memchunk.h"
+#include "buffer.h"
 
 using namespace nghttp2;
 
@@ -82,6 +83,11 @@ public:
                          size_t bodylen);
   virtual int initiate_push(Downstream *downstream, const char *uri,
                             size_t len);
+  virtual int response_riovec(struct iovec *iov, int iovcnt) const;
+  virtual void response_drain(size_t n);
+  virtual bool response_empty() const;
+
+  void response_write(void *data, size_t len);
 
   bool get_flow_control() const;
   // Perform HTTP/2 upgrade from |upstream|. On success, this object
@@ -106,7 +112,10 @@ public:
 
   int on_request_headers(Downstream *downstream, const nghttp2_frame *frame);
 
+  using WriteBuffer = Buffer<32_k>;
+
 private:
+  WriteBuffer wb_;
   std::unique_ptr<HttpsUpstream> pre_upstream_;
   DownstreamQueue downstream_queue_;
   ev_timer settings_timer_;
diff --git a/src/shrpx_https_upstream.cc b/src/shrpx_https_upstream.cc
index 3e11c7ea..7e5398ef 100644
--- a/src/shrpx_https_upstream.cc
+++ b/src/shrpx_https_upstream.cc
@@ -1160,12 +1160,34 @@ int HttpsUpstream::initiate_push(Downstream *downstream, const char *uri,
   return 0;
 }
 
-DefaultMemchunks *HttpsUpstream::get_response_buf() const {
+int HttpsUpstream::response_riovec(struct iovec *iov, int iovcnt) const {
   if (!downstream_) {
-    return nullptr;
+    return 0;
   }
 
-  return downstream_->get_response_buf();
+  auto buf = downstream_->get_response_buf();
+
+  return buf->riovec(iov, iovcnt);
+}
+
+void HttpsUpstream::response_drain(size_t n) {
+  if (!downstream_) {
+    return;
+  }
+
+  auto buf = downstream_->get_response_buf();
+
+  buf->drain(n);
+}
+
+bool HttpsUpstream::response_empty() const {
+  if (!downstream_) {
+    return true;
+  }
+
+  auto buf = downstream_->get_response_buf();
+
+  return buf->rleft() == 0;
 }
 
 } // namespace shrpx
diff --git a/src/shrpx_https_upstream.h b/src/shrpx_https_upstream.h
index df390e3f..6f3b5742 100644
--- a/src/shrpx_https_upstream.h
+++ b/src/shrpx_https_upstream.h
@@ -78,7 +78,9 @@ public:
                          size_t bodylen);
   virtual int initiate_push(Downstream *downstream, const char *uri,
                             size_t len);
-  virtual DefaultMemchunks *get_response_buf() const;
+  virtual int response_riovec(struct iovec *iov, int iovcnt) const;
+  virtual void response_drain(size_t n);
+  virtual bool response_empty() const;
 
   void reset_current_header_length();
   void log_response_headers(DefaultMemchunks *buf) const;
diff --git a/src/shrpx_spdy_upstream.cc b/src/shrpx_spdy_upstream.cc
index 0be56597..6b45a2e6 100644
--- a/src/shrpx_spdy_upstream.cc
+++ b/src/shrpx_spdy_upstream.cc
@@ -53,8 +53,7 @@ namespace {
 ssize_t send_callback(spdylay_session *session, const uint8_t *data, size_t len,
                       int flags, void *user_data) {
   auto upstream = static_cast<SpdyUpstream *>(user_data);
-  auto handler = upstream->get_client_handler();
-  auto wb = handler->get_wb();
+  auto wb = upstream->get_response_buf();
 
   if (wb->wleft() == 0) {
     return SPDYLAY_ERR_WOULDBLOCK;
@@ -555,6 +554,10 @@ int SpdyUpstream::on_read() {
 int SpdyUpstream::on_write() {
   int rv = 0;
 
+  if (wb_.rleft() == 0) {
+    wb_.reset();
+  }
+
   rv = spdylay_session_send(session_);
   if (rv != 0) {
     ULOG(ERROR, this) << "spdylay_session_send() returned error: "
@@ -563,8 +566,7 @@ int SpdyUpstream::on_write() {
   }
 
   if (spdylay_session_want_read(session_) == 0 &&
-      spdylay_session_want_write(session_) == 0 &&
-      handler_->get_wb()->rleft() == 0) {
+      spdylay_session_want_write(session_) == 0 && wb_.rleft() == 0) {
     if (LOG_ENABLED(INFO)) {
       ULOG(INFO, this) << "No more read/write for this SPDY session";
     }
@@ -1213,4 +1215,21 @@ int SpdyUpstream::initiate_push(Downstream *downstream, const char *uri,
   return 0;
 }
 
+int SpdyUpstream::response_riovec(struct iovec *iov, int iovcnt) const {
+  if (iovcnt == 0 || wb_.rleft() == 0) {
+    return 0;
+  }
+
+  iov->iov_base = wb_.pos;
+  iov->iov_len = wb_.rleft();
+
+  return 1;
+}
+
+void SpdyUpstream::response_drain(size_t n) { wb_.drain(n); }
+
+bool SpdyUpstream::response_empty() const { return wb_.rleft() == 0; }
+
+SpdyUpstream::WriteBuffer *SpdyUpstream::get_response_buf() { return &wb_; }
+
 } // namespace shrpx
diff --git a/src/shrpx_spdy_upstream.h b/src/shrpx_spdy_upstream.h
index b39f885f..7d509340 100644
--- a/src/shrpx_spdy_upstream.h
+++ b/src/shrpx_spdy_upstream.h
@@ -36,7 +36,7 @@
 #include "shrpx_upstream.h"
 #include "shrpx_downstream_queue.h"
 #include "memchunk.h"
-#include "util.h"
+#include "buffer.h"
 
 namespace shrpx {
 
@@ -78,6 +78,9 @@ public:
                          size_t bodylen);
   virtual int initiate_push(Downstream *downstream, const char *uri,
                             size_t len);
+  virtual int response_riovec(struct iovec *iov, int iovcnt) const;
+  virtual void response_drain(size_t n);
+  virtual bool response_empty() const;
 
   bool get_flow_control() const;
 
@@ -86,7 +89,12 @@ public:
   void start_downstream(Downstream *downstream);
   void initiate_downstream(Downstream *downstream);
 
+  using WriteBuffer = Buffer<32_k>;
+
+  WriteBuffer *get_response_buf();
+
 private:
+  WriteBuffer wb_;
   DownstreamQueue downstream_queue_;
   ClientHandler *handler_;
   spdylay_session *session_;
diff --git a/src/shrpx_upstream.h b/src/shrpx_upstream.h
index 8d80097f..92fe5190 100644
--- a/src/shrpx_upstream.h
+++ b/src/shrpx_upstream.h
@@ -71,9 +71,11 @@ public:
   virtual int initiate_push(Downstream *downstream, const char *uri,
                             size_t len) = 0;
 
-  // Returns response buffer of Downstream directly.  This exists for
-  // optimization purpose for cleartext HttpsUpstream.
-  virtual DefaultMemchunks *get_response_buf() const { return nullptr; }
+  // Fills response data in |iov| whose capacity is |iovcnt|.  Returns
+  // the number of iovs filled.
+  virtual int response_riovec(struct iovec *iov, int iovcnt) const = 0;
+  virtual void response_drain(size_t n) = 0;
+  virtual bool response_empty() const = 0;
 };
 
 } // namespace shrpx