diff --git a/src/asio_client_request_impl.cc b/src/asio_client_request_impl.cc
index ab92333c..10a17e3f 100644
--- a/src/asio_client_request_impl.cc
+++ b/src/asio_client_request_impl.cc
@@ -61,11 +61,15 @@ void request_impl::call_on_close(uint32_t error_code) {
 
 void request_impl::on_read(read_cb cb) { read_cb_ = std::move(cb); }
 
-read_cb::result_type request_impl::call_on_read(uint8_t *buf, std::size_t len) {
+read_cb::result_type request_impl::call_on_read(uint8_t *buf, std::size_t len,
+                                                uint32_t *data_flags) {
   if (read_cb_) {
-    return read_cb_(buf, len);
+    return read_cb_(buf, len, data_flags);
   }
-  return read_cb::result_type{};
+
+  *data_flags |= NGHTTP2_DATA_FLAG_EOF;
+
+  return 0;
 }
 
 void request_impl::header(header_map h) { header_ = std::move(h); }
diff --git a/src/asio_client_request_impl.h b/src/asio_client_request_impl.h
index 5fdf09b7..f9e6b67f 100644
--- a/src/asio_client_request_impl.h
+++ b/src/asio_client_request_impl.h
@@ -55,7 +55,8 @@ public:
   void call_on_close(uint32_t error_code);
 
   void on_read(read_cb cb);
-  read_cb::result_type call_on_read(uint8_t *buf, std::size_t len);
+  read_cb::result_type call_on_read(uint8_t *buf, std::size_t len,
+                                    uint32_t *data_flags);
 
   void header(header_map h);
   header_map &header();
diff --git a/src/asio_client_session_impl.cc b/src/asio_client_session_impl.cc
index 198827ec..edd8557c 100644
--- a/src/asio_client_session_impl.cc
+++ b/src/asio_client_session_impl.cc
@@ -409,18 +409,7 @@ const request *session_impl::submit(boost::system::error_code &ec,
            size_t length, uint32_t *data_flags, nghttp2_data_source *source,
            void *user_data) -> ssize_t {
       auto strm = static_cast<stream *>(source->ptr);
-      auto rv = strm->request().impl().call_on_read(buf, length);
-      if (rv.first < 0) {
-        return NGHTTP2_ERR_TEMPORAL_CALLBACK_FAILURE;
-      }
-
-      if (rv.second) {
-        *data_flags |= NGHTTP2_DATA_FLAG_EOF;
-      } else if (rv.first == 0) {
-        return NGHTTP2_ERR_DEFERRED;
-      }
-
-      return rv.first;
+      return strm->request().impl().call_on_read(buf, length, data_flags);
     };
     prdptr = &prd;
   }
diff --git a/src/asio_common.cc b/src/asio_common.cc
index 34efefa5..2f7548dd 100644
--- a/src/asio_common.cc
+++ b/src/asio_common.cc
@@ -49,11 +49,16 @@ boost::system::error_code make_error_code(nghttp2_error ev) {
 read_cb string_reader(std::string data) {
   auto strio = std::make_shared<std::pair<std::string, size_t>>(std::move(data),
                                                                 data.size());
-  return [strio](uint8_t *buf, size_t len) {
-    auto n = std::min(len, strio->second);
-    std::copy_n(strio->first.c_str(), n, buf);
-    strio->second -= n;
-    return std::make_pair(n, strio->second == 0);
+  return [strio](uint8_t *buf, size_t len, uint32_t *data_flags) {
+    auto &data = strio->first;
+    auto &left = strio->second;
+    auto n = std::min(len, left);
+    std::copy_n(data.c_str() + data.size() - left, n, buf);
+    left -= n;
+    if (left == 0) {
+      *data_flags |= NGHTTP2_DATA_FLAG_EOF;
+    }
+    return n;
   };
 }
 
diff --git a/src/asio_http2_handler.cc b/src/asio_http2_handler.cc
index 8ea9c645..3bf7586e 100644
--- a/src/asio_http2_handler.cc
+++ b/src/asio_http2_handler.cc
@@ -177,13 +177,15 @@ const header_map &response_impl::header() const { return header_; }
 
 void response_impl::stream(http2_stream *s) { stream_ = s; }
 
-std::pair<ssize_t, bool> response_impl::call_read(uint8_t *data,
-                                                  std::size_t len) {
+read_cb::result_type response_impl::call_read(uint8_t *data, std::size_t len,
+                                              uint32_t *data_flags) {
   if (read_cb_) {
-    return read_cb_(data, len);
+    return read_cb_(data, len, data_flags);
   }
 
-  return std::make_pair(0, true);
+  *data_flags |= NGHTTP2_DATA_FLAG_EOF;
+
+  return 0;
 }
 
 http2_stream::http2_stream(http2_handler *h, int32_t stream_id)
@@ -481,18 +483,7 @@ int http2_handler::start_response(http2_stream &stream) {
          size_t length, uint32_t *data_flags, nghttp2_data_source *source,
          void *user_data) -> ssize_t {
     auto &stream = *static_cast<http2_stream *>(source->ptr);
-    auto rv = stream.response().impl().call_read(buf, length);
-    if (rv.first < 0) {
-      return NGHTTP2_ERR_TEMPORAL_CALLBACK_FAILURE;
-    }
-
-    if (rv.second) {
-      *data_flags |= NGHTTP2_DATA_FLAG_EOF;
-    } else if (rv.first == 0) {
-      return NGHTTP2_ERR_DEFERRED;
-    }
-
-    return rv.first;
+    return stream.response().impl().call_read(buf, length, data_flags);
   };
 
   rv = nghttp2_submit_response(session_, stream.get_stream_id(), nva.data(),
diff --git a/src/asio_http2_handler.h b/src/asio_http2_handler.h
index 055fbac6..febf0bf3 100644
--- a/src/asio_http2_handler.h
+++ b/src/asio_http2_handler.h
@@ -91,7 +91,8 @@ public:
   const header_map &header() const;
   bool started() const;
   void stream(http2_stream *s);
-  read_cb::result_type call_read(uint8_t *data, std::size_t len);
+  read_cb::result_type call_read(uint8_t *data, std::size_t len,
+                                 uint32_t *data_flags);
 
 private:
   http2_stream *stream_;
diff --git a/src/asio_http2_impl.cc b/src/asio_http2_impl.cc
index 4d2c5ddf..17236744 100644
--- a/src/asio_http2_impl.cc
+++ b/src/asio_http2_impl.cc
@@ -139,20 +139,21 @@ read_cb file_reader(const std::string &path) {
 read_cb file_reader_from_fd(int fd) {
   auto d = defer_shared(close, fd);
 
-  return [fd, d](uint8_t *buf, size_t len) -> read_cb::result_type {
-    int rv;
-    while ((rv = read(fd, buf, len)) == -1 && errno == EINTR)
+  return [fd, d](uint8_t *buf, size_t len, uint32_t *data_flags)
+      -> read_cb::result_type {
+    ssize_t n;
+    while ((n = read(fd, buf, len)) == -1 && errno == EINTR)
       ;
 
-    if (rv == -1) {
-      return std::make_pair(-1, false);
+    if (n == -1) {
+      return NGHTTP2_ERR_TEMPORAL_CALLBACK_FAILURE;
     }
 
-    if (rv == 0) {
-      return std::make_pair(rv, true);
+    if (n == 0) {
+      *data_flags |= NGHTTP2_DATA_FLAG_EOF;
     }
 
-    return std::make_pair(rv, false);
+    return n;
   };
 }
 
diff --git a/src/includes/nghttp2/asio_http2.h b/src/includes/nghttp2/asio_http2.h
index 6934f00b..2382fe75 100644
--- a/src/includes/nghttp2/asio_http2.h
+++ b/src/includes/nghttp2/asio_http2.h
@@ -76,18 +76,9 @@ typedef std::function<void(void)> void_cb;
 typedef std::function<void(const boost::system::error_code &ec)> error_cb;
 typedef std::function<void(uint32_t)> close_cb;
 
-// Callback function to generate response body.  The implementation of
-// this callback must fill at most |len| bytes data to |buf|.  The
-// return value is pair of written bytes and bool value indicating
-// that this is the end of the body.  If the end of the body was
-// reached, return true.  If there is error and application wants to
-// terminate stream, return std::make_pair(-1, false).  Returning
-// std::make_pair(0, false) tells the library that don't call this
-// callback until application calls response::resume().  This is
-// useful when there is no data to send at the moment but there will
-// be more to come in near future.
-typedef std::function<std::pair<ssize_t, bool>(uint8_t *buf, std::size_t len)>
-    read_cb;
+// Callback function to generate response body.  TBD
+typedef std::function<
+    ssize_t(uint8_t *buf, std::size_t len, uint32_t *data_flags)> read_cb;
 
 // Convenient function to create function to read file denoted by
 // |path|.  This can be passed to response::end().