diff --git a/README.md b/README.md
index 5412937..7a9f39c 100644
--- a/README.md
+++ b/README.md
@@ -187,7 +187,7 @@ int main() {
 
     server.Route("/", std::make_shared<HelloView>());
 
-    server.Start();
+    server.Run();
 
   } catch (const std::exception&) {
     return 1;
@@ -274,8 +274,8 @@ The detailed implementation is out of the scope of this README, but here is an e
 ```cpp
 webcc::ResponsePtr BookDetailView::Get(webcc::RequestPtr request) {
   if (request->args().size() != 1) {
-    // Using kNotFound means the resource specified by the URL cannot be found.
-    // kBadRequest could be another choice.
+    // NotFound means the resource specified by the URL cannot be found.
+    // BadRequest could be another choice.
     return webcc::ResponseBuilder{}.NotFound()();
   }
 
@@ -290,7 +290,8 @@ webcc::ResponsePtr BookDetailView::Get(webcc::RequestPtr request) {
   }
 
   // Convert the book to JSON string and set as response data.
-  return webcc::ResponseBuilder{}.OK().Data(<JsonStringOfTheBook>).Json().Utf8();
+  return webcc::ResponseBuilder{}.OK().Data(<JsonStringOfTheBook>).
+      Json().Utf8()();
 }
 ```
 
diff --git a/autotest/client_autotest.cc b/autotest/client_autotest.cc
index b3caacb..3218504 100644
--- a/autotest/client_autotest.cc
+++ b/autotest/client_autotest.cc
@@ -3,6 +3,7 @@
 #include "gtest/gtest.h"
 
 #include "boost/algorithm/string.hpp"
+#include "boost/filesystem/fstream.hpp"
 #include "boost/filesystem/operations.hpp"
 
 #include "json/json.h"
@@ -10,6 +11,8 @@
 #include "webcc/client_session.h"
 #include "webcc/logger.h"
 
+namespace bfs = boost::filesystem;
+
 // -----------------------------------------------------------------------------
 
 // JSON helper functions (based on jsoncpp).
@@ -30,7 +33,7 @@ static Json::Value StringToJson(const std::string& str) {
 
 // -----------------------------------------------------------------------------
 
-TEST(ClientTest, Head_RequestFunc) {
+TEST(ClientTest, Head) {
   webcc::ClientSession session;
 
   try {
@@ -115,7 +118,7 @@ static void AssertGet(webcc::ResponsePtr r) {
 #endif  // WEBCC_ENABLE_GZIP
 }
 
-TEST(ClientTest, Get_RequestFunc) {
+TEST(ClientTest, Get) {
   webcc::ClientSession session;
 
   try {
@@ -169,127 +172,15 @@ TEST(ClientTest, Get_SSL) {
 }
 #endif  // WEBCC_ENABLE_SSL
 
-// -----------------------------------------------------------------------------
-
-#if WEBCC_ENABLE_GZIP
-
-// Test Gzip compressed response.
-TEST(ClientTest, Compression_Gzip) {
-  webcc::ClientSession session;
-
-  try {
-    auto r = session.Get("http://httpbin.org/gzip");
-
-    Json::Value json = StringToJson(r->data());
-
-    EXPECT_EQ(true, json["gzipped"].asBool());
-
-  } catch (const webcc::Error& error) {
-    std::cerr << error << std::endl;
-  }
-}
-
-// Test Deflate compressed response.
-TEST(ClientTest, Compression_Deflate) {
-  webcc::ClientSession session;
-
-  try {
-    auto r = session.Get("http://httpbin.org/deflate");
-
-    Json::Value json = StringToJson(r->data());
-
-    EXPECT_EQ(true, json["deflated"].asBool());
-
-  } catch (const webcc::Error& error) {
-    std::cerr << error << std::endl;
-  }
-}
-
-// Test trying to compress the request.
-// TODO
-TEST(ClientTest, Compression_Request) {
+// Get a JPEG image (without streaming).
+TEST(ClientTest, Get_Jpeg_NoStream) {
   webcc::ClientSession session;
 
   try {
-    const std::string data = "{'name'='Adam', 'age'=20}";
-
-    // This doesn't really compress the body!
     auto r = session.Request(webcc::RequestBuilder{}.
-                             Post("http://httpbin.org/post").
-                             Body(data).Json().
-                             Gzip()
+                             Get("http://httpbin.org/image/jpeg")
                              ());
 
-    //Json::Value json = StringToJson(r->data());
-
-  } catch (const webcc::Error& error) {
-    std::cerr << error << std::endl;
-  }
-}
-#endif  // WEBCC_ENABLE_GZIP
-
-// -----------------------------------------------------------------------------
-
-// Test persistent (keep-alive) connections.
-//
-// NOTE:
-// Boost.org doesn't support persistent connection and always includes
-// "Connection: Close" header in the response.
-// Both Google and GitHub support persistent connection but they don't like
-// to include "Connection: Keep-Alive" header in the responses.
-// URLs:
-//   "http://httpbin.org/get";
-//   "https://www.boost.org/LICENSE_1_0.txt";
-//   "https://www.google.com";
-//   "https://api.github.com/events";
-//
-TEST(ClientTest, KeepAlive) {
-  webcc::ClientSession session;
-
-  std::string url = "http://httpbin.org/get";
-  try {
-
-    // Keep-Alive by default.
-    auto r = session.Get(url);
-
-    using boost::iequals;
-
-    EXPECT_TRUE(iequals(r->GetHeader("Connection"), "Keep-alive"));
-
-    // Close by setting Connection header.
-    r = session.Get(url, {}, { "Connection", "Close" });
-
-    EXPECT_TRUE(iequals(r->GetHeader("Connection"), "Close"));
-
-    // Close by using request builder.
-    r = session.Request(webcc::RequestBuilder{}.
-                        Get(url).KeepAlive(false)
-                        ());
-
-    EXPECT_TRUE(iequals(r->GetHeader("Connection"), "Close"));
-
-    // Keep-Alive explicitly by using request builder.
-    r = session.Request(webcc::RequestBuilder{}.
-                        Get(url).KeepAlive(true)
-                        ());
-
-    EXPECT_TRUE(iequals(r->GetHeader("Connection"), "Keep-alive"));
-
-  } catch (const webcc::Error& error) {
-    std::cerr << error << std::endl;
-  }
-}
-
-// -----------------------------------------------------------------------------
-
-// Get a JPEG image (without streaming).
-TEST(ClientTest, GetImageJpeg_NoStream) {
-  webcc::ClientSession session;
-
-  try {
-
-    auto r = session.Get("http://httpbin.org/image/jpeg");
- 
     // TODO: Verify the response is a valid JPEG image.
     //std::ofstream ofs(<path>, std::ios::binary);
     //ofs << r->data();
@@ -299,16 +190,13 @@ TEST(ClientTest, GetImageJpeg_NoStream) {
   }
 }
 
-// -----------------------------------------------------------------------------
-
-// Streaming
-
-TEST(ClientTest, Stream_GetImageJpeg) {
+TEST(ClientTest, Get_Jpeg_Stream) {
   webcc::ClientSession session;
 
   try {
     auto r = session.Request(webcc::RequestBuilder{}.
-                             Get("http://httpbin.org/image/jpeg")(),
+                             Get("http://httpbin.org/image/jpeg")
+                             (),
                              true);
 
     auto file_body = r->file_body();
@@ -338,7 +226,7 @@ TEST(ClientTest, Stream_GetImageJpeg) {
 
 // Test whether the streamed file will be deleted or not at the end if it's
 // not moved to another path by the user.
-TEST(ClientTest, Stream_GetImageJpeg_NoMove) {
+TEST(ClientTest, Get_Jpeg_Stream_NoMove) {
   webcc::ClientSession session;
 
   try {
@@ -346,7 +234,8 @@ TEST(ClientTest, Stream_GetImageJpeg_NoMove) {
 
     {
       auto r = session.Request(webcc::RequestBuilder{}.
-                               Get("http://httpbin.org/image/jpeg")(),
+                               Get("http://httpbin.org/image/jpeg")
+                               (),
                                true);
 
       auto file_body = r->file_body();
@@ -369,7 +258,49 @@ TEST(ClientTest, Stream_GetImageJpeg_NoMove) {
 
 // -----------------------------------------------------------------------------
 
-TEST(ClientTest, Post_RequestFunc) {
+#if WEBCC_ENABLE_GZIP
+// Test Gzip compressed response.
+TEST(ClientTest, Get_Gzip) {
+  webcc::ClientSession session;
+
+  try {
+    auto r = session.Request(webcc::RequestBuilder{}.
+                             Get("http://httpbin.org/gzip")
+                             ());
+
+    Json::Value json = StringToJson(r->data());
+
+    EXPECT_EQ(true, json["gzipped"].asBool());
+
+  } catch (const webcc::Error& error) {
+    std::cerr << error << std::endl;
+  }
+}
+#endif  // WEBCC_ENABLE_GZIP
+
+#if WEBCC_ENABLE_GZIP
+// Test Deflate compressed response.
+TEST(ClientTest, Get_Deflate) {
+  webcc::ClientSession session;
+
+  try {
+    auto r = session.Request(webcc::RequestBuilder{}.
+                             Get("http://httpbin.org/deflate")
+                             ());
+
+    Json::Value json = StringToJson(r->data());
+
+    EXPECT_EQ(true, json["deflated"].asBool());
+
+  } catch (const webcc::Error& error) {
+    std::cerr << error << std::endl;
+  }
+}
+#endif  // WEBCC_ENABLE_GZIP
+
+// -----------------------------------------------------------------------------
+
+TEST(ClientTest, Post) {
   webcc::ClientSession session;
 
   try {
@@ -412,6 +343,80 @@ TEST(ClientTest, Post_Shortcut) {
   }
 }
 
+static bfs::path GenerateTempFile(const std::string& data) {
+  try {
+    bfs::path path = bfs::temp_directory_path() / bfs::unique_path();
+
+    bfs::ofstream ofs;
+    ofs.open(path, std::ios::binary);
+    if (ofs.fail()) {
+      return bfs::path{};
+    }
+
+    ofs << data;
+
+    return path;
+
+  } catch (const bfs::filesystem_error&) {
+    return bfs::path{};
+  }
+}
+
+TEST(ClientTest, Post_FileBody) {
+  webcc::ClientSession session;
+
+  const std::string data = "{'name'='Adam', 'age'=20}";
+
+  auto path = GenerateTempFile(data);
+  if (path.empty()) {
+    return;
+  }
+
+  try {
+    auto r = session.Request(webcc::RequestBuilder{}.
+                             Post("http://httpbin.org/post").
+                             File(path)  // Use the file as body
+                             ());
+
+    EXPECT_EQ(webcc::Status::kOK, r->status());
+    EXPECT_EQ("OK", r->reason());
+
+    Json::Value json = StringToJson(r->data());
+
+    EXPECT_EQ(data, json["data"].asString());
+
+  } catch (const webcc::Error& error) {
+    std::cerr << error << std::endl;
+  }
+
+  // Remove the temp file.
+  boost::system::error_code ec;
+  bfs::remove(path, ec);
+}
+
+#if WEBCC_ENABLE_GZIP
+TEST(ClientTest, Post_Gzip_SmallData) {
+  webcc::ClientSession session;
+
+  try {
+    // This data is too small to be compressed.
+    const std::string data = "{'name'='Adam', 'age'=20}";
+
+    // This doesn't really compress the body!
+    auto r = session.Request(webcc::RequestBuilder{}.
+                             Post("http://httpbin.org/post").
+                             Body(data).Json().
+                             Gzip()
+                             ());
+
+    //Json::Value json = StringToJson(r->data());
+
+  } catch (const webcc::Error& error) {
+    std::cerr << error << std::endl;
+  }
+}
+#endif  // WEBCC_ENABLE_GZIP
+
 #if (WEBCC_ENABLE_GZIP && WEBCC_ENABLE_SSL)
 // NOTE: Most servers don't support compressed requests!
 TEST(ClientTest, Post_Gzip) {
@@ -438,6 +443,63 @@ TEST(ClientTest, Post_Gzip) {
 
 // -----------------------------------------------------------------------------
 
+// Test persistent (keep-alive) connections.
+//
+// NOTE:
+// Boost.org doesn't support persistent connection and always includes
+// "Connection: Close" header in the response.
+// Both Google and GitHub support persistent connection but they don't like
+// to include "Connection: Keep-Alive" header in the responses.
+// URLs:
+//   "http://httpbin.org/get";
+//   "https://www.boost.org/LICENSE_1_0.txt";
+//   "https://www.google.com";
+//   "https://api.github.com/events";
+//
+TEST(ClientTest, KeepAlive) {
+  webcc::ClientSession session;
+
+  const std::string url = "http://httpbin.org/get";
+
+  try {
+    // Keep-Alive by default.
+    auto r = session.Request(webcc::RequestBuilder{}.Get(url)());
+
+    using boost::iequals;
+
+    EXPECT_TRUE(iequals(r->GetHeader("Connection"), "Keep-alive"));
+
+    // Close by setting Connection header directly.
+    r = session.Request(webcc::RequestBuilder{}.
+                        Get(url).
+                        Header("Connection", "Close")
+                        ());
+
+    EXPECT_TRUE(iequals(r->GetHeader("Connection"), "Close"));
+
+    // Close by using request builder.
+    r = session.Request(webcc::RequestBuilder{}.
+                        Get(url).
+                        KeepAlive(false)
+                        ());
+
+    EXPECT_TRUE(iequals(r->GetHeader("Connection"), "Close"));
+
+    // Keep-Alive explicitly by using request builder.
+    r = session.Request(webcc::RequestBuilder{}.
+                        Get(url).
+                        KeepAlive(true)
+                        ());
+
+    EXPECT_TRUE(iequals(r->GetHeader("Connection"), "Keep-alive"));
+
+  } catch (const webcc::Error& error) {
+    std::cerr << error << std::endl;
+  }
+}
+
+// -----------------------------------------------------------------------------
+
 int main(int argc, char* argv[]) {
   // Set webcc::LOG_CONSOLE to enable logging.
   WEBCC_LOG_INIT("", 0);
diff --git a/examples/file_downloader.cc b/examples/file_downloader.cc
index aa800ee..df9ad3d 100644
--- a/examples/file_downloader.cc
+++ b/examples/file_downloader.cc
@@ -6,18 +6,15 @@
 #include "webcc/client_session.h"
 #include "webcc/logger.h"
 
-void Help(const char* argv0) {
-  std::cout << "Usage: file_downloader <url> <path>" << std::endl;
-  std::cout << "E.g.," << std::endl;
-  std::cout << "    file_downloader http://httpbin.org/image/jpeg D:/test.jpg"
-            << std::endl;
-  std::cout << "    file_downloader https://www.google.com/favicon.ico"
-            << " D:/test.ico" << std::endl;
-}
-
 int main(int argc, char* argv[]) {
   if (argc != 3) {
-    Help(argv[0]);
+    std::cout << "usage: file_downloader <url> <path>" << std::endl;
+    std::cout << std::endl;
+    std::cout << "examples:" << std::endl;
+    std::cout << "  $ file_downloader http://httpbin.org/image/jpeg D:/test.jpg"
+              << std::endl;
+    std::cout << "  $ file_downloader https://www.google.com/favicon.ico"
+              << " D:/test.ico" << std::endl;
     return 1;
   }
 
diff --git a/examples/file_server.cc b/examples/file_server.cc
index facbd05..76fcf66 100644
--- a/examples/file_server.cc
+++ b/examples/file_server.cc
@@ -6,17 +6,14 @@
 #include "webcc/logger.h"
 #include "webcc/server.h"
 
-void Help() {
-  std::cout << "Usage:" << std::endl;
-  std::cout << "    file_server <port> <doc_root> [chunk_size]" << std::endl;
-  std::cout << "E.g.," << std::endl;
-  std::cout << "    file_server 8080 D:/www" << std::endl;
-  std::cout << "    file_server 8080 D:/www 10000" << std::endl;
-}
-
 int main(int argc, char* argv[]) {
   if (argc < 3) {
-    Help();
+    std::cout << "usage: file_server <port> <doc_root> [chunk_size]"
+              << std::endl;
+    std::cout << std::endl;
+    std::cout << "examples:" << std::endl;
+    std::cout << "  $ file_server 8080 D:/www" << std::endl;
+    std::cout << "  $ file_server 8080 D:/www 10000" << std::endl;
     return 1;
   }
 
diff --git a/examples/file_upload_client.cc b/examples/file_upload_client.cc
index d281dad..17dee71 100644
--- a/examples/file_upload_client.cc
+++ b/examples/file_upload_client.cc
@@ -5,20 +5,17 @@
 #include "webcc/client_session.h"
 #include "webcc/logger.h"
 
-void Help() {
-  std::cout << "Usage:" << std::endl;
-  std::cout << "    file_upload_client <upload_dir> [url]" << std::endl;
-  std::cout << "Default Url: http://httpbin.org/post" << std::endl;
-  std::cout << "E.g.," << std::endl;
-  std::cout << "    file_upload_client E:/github/webcc/data/upload"
-            << std::endl;
-  std::cout << "    file_upload_client E:/github/webcc/data/upload"
-            << " http://httpbin.org/post" << std::endl;
-}
-
 int main(int argc, char* argv[]) {
   if (argc < 2) {
-    Help();
+    std::cout << "usage: file_upload_client <upload_dir> [url]" << std::endl;
+    std::cout << std::endl;
+    std::cout << "default url: http://httpbin.org/post" << std::endl;
+    std::cout << std::endl;
+    std::cout << "examples:" << std::endl;
+    std::cout << "  $ file_upload_client E:/github/webcc/data/upload"
+              << std::endl;
+    std::cout << "  $ file_upload_client E:/github/webcc/data/upload "
+              << "http://httpbin.org/post" << std::endl;
     return 1;
   }
 
@@ -45,8 +42,8 @@ int main(int argc, char* argv[]) {
   try {
     auto r = session.Request(webcc::RequestBuilder{}.
                              Post(url).
-                             File("file", upload_dir / "remember.txt").
-                             Form("json", "{}", "application/json")
+                             FormFile("file", upload_dir / "remember.txt").
+                             FormData("json", "{}", "application/json")
                              ());
 
     std::cout << r->status() << std::endl;
diff --git a/examples/file_upload_server.cc b/examples/file_upload_server.cc
index 160b297..502cbf7 100644
--- a/examples/file_upload_server.cc
+++ b/examples/file_upload_server.cc
@@ -32,15 +32,9 @@ private:
 
 // -----------------------------------------------------------------------------
 
-void Help(const char* argv0) {
-  std::cout << "Usage: " << argv0 << " <port>" << std::endl;
-  std::cout << "  E.g.," << std::endl;
-  std::cout << "    " << argv0 << " 8080" << std::endl;
-}
-
 int main(int argc, char* argv[]) {
   if (argc < 2) {
-    Help(argv[0]);
+    std::cout << "usage: file_upload_server <port>" << std::endl;
     return 1;
   }
 
diff --git a/examples/rest_book_client.cc b/examples/rest_book_client.cc
index 6ab0478..dc35f55 100644
--- a/examples/rest_book_client.cc
+++ b/examples/rest_book_client.cc
@@ -188,17 +188,13 @@ void PrintBookList(const std::list<Book>& books) {
 
 // -----------------------------------------------------------------------------
 
-void Help() {
-  std::cout << "Usage:" << std::endl;
-  std::cout << "    rest_book_client <url> [timeout]" << std::endl;
-  std::cout << "E.g.," << std::endl;
-  std::cout << "    rest_book_client http://localhost:8080" << std::endl;
-  std::cout << "    rest_book_client http://localhost:8080 2" << std::endl;
-}
-
 int main(int argc, char* argv[]) {
   if (argc < 2) {
-    Help();
+    std::cout << "usage: rest_book_client <url> [timeout]" << std::endl;
+    std::cout << std::endl;
+    std::cout << "examples:" << std::endl;
+    std::cout << "  $ rest_book_client http://localhost:8080" << std::endl;
+    std::cout << "  $ rest_book_client http://localhost:8080 2" << std::endl;
     return 1;
   }
 
diff --git a/examples/rest_book_server.cc b/examples/rest_book_server.cc
index e24acad..cd80dc7 100644
--- a/examples/rest_book_server.cc
+++ b/examples/rest_book_server.cc
@@ -145,8 +145,8 @@ webcc::ResponsePtr BookDetailView::Get(webcc::RequestPtr request) {
   Sleep(sleep_seconds_);
 
   if (request->args().size() != 1) {
-    // Using kNotFound means the resource specified by the URL cannot be found.
-    // kBadRequest could be another choice.
+    // NotFound means the resource specified by the URL cannot be found.
+    // BadRequest could be another choice.
     return webcc::ResponseBuilder{}.NotFound()();
   }
 
@@ -157,8 +157,8 @@ webcc::ResponsePtr BookDetailView::Get(webcc::RequestPtr request) {
     return webcc::ResponseBuilder{}.NotFound()();
   }
 
-  return webcc::ResponseBuilder{}.OK().Body(BookToJsonString(book)).Json().
-      Utf8()();
+  return webcc::ResponseBuilder{}.OK().Body(BookToJsonString(book)).
+      Json().Utf8()();
 }
 
 webcc::ResponsePtr BookDetailView::Put(webcc::RequestPtr request) {
@@ -199,19 +199,17 @@ webcc::ResponsePtr BookDetailView::Delete(webcc::RequestPtr request) {
 
 // -----------------------------------------------------------------------------
 
-void Help(const char* argv0) {
-  std::cout << "Usage: " << argv0 << " <port> [seconds]" << std::endl;
-  std::cout << "If |seconds| is provided, the server will sleep these seconds "
-               "before sending back each response."
-            << std::endl;
-  std::cout << "  E.g.," << std::endl;
-  std::cout << "    " << argv0 << " 8080" << std::endl;
-  std::cout << "    " << argv0 << " 8080 3" << std::endl;
-}
-
 int main(int argc, char* argv[]) {
   if (argc < 2) {
-    Help(argv[0]);
+    std::cout << "usage: rest_book_server <port> [seconds]" << std::endl;
+    std::cout << std::endl;
+    std::cout << "If |seconds| is provided, the server will sleep, for testing "
+              << "timeout, before " << std::endl
+              << "send back each response." << std::endl;
+    std::cout << std::endl;
+    std::cout << "examples:" << std::endl;
+    std::cout << "  $ rest_book_server 8080" << std::endl;
+    std::cout << "  $ rest_book_server 8080 3" << std::endl;
     return 1;
   }
 
diff --git a/webcc/request_builder.cc b/webcc/request_builder.cc
index ea5eda0..546c812 100644
--- a/webcc/request_builder.cc
+++ b/webcc/request_builder.cc
@@ -51,20 +51,29 @@ RequestPtr RequestBuilder::operator()() {
   return request;
 }
 
-RequestBuilder& RequestBuilder::File(const std::string& name,
-                                     const Path& path,
-                                     const std::string& media_type) {
-  assert(!name.empty());
-  form_parts_.push_back(FormPart::NewFile(name, path, media_type));
+RequestBuilder& RequestBuilder::File(const Path& path, bool infer_media_type,
+                                     std::size_t chunk_size) {
+  body_.reset(new FileBody{ path, chunk_size });
+
+  if (infer_media_type) {
+    media_type_ = media_types::FromExtension(path.extension().string());
+  }
+
   return *this;
 }
 
-RequestBuilder& RequestBuilder::Form(const std::string& name,
-                                     std::string&& data,
-                                     const std::string& media_type) {
+RequestBuilder& RequestBuilder::FormFile(const std::string& name,
+                                         const Path& path,
+                                         const std::string& media_type) {
   assert(!name.empty());
-  form_parts_.push_back(FormPart::New(name, std::move(data), media_type));
-  return *this;
+  return Form(FormPart::NewFile(name, path, media_type));
+}
+
+RequestBuilder& RequestBuilder::FormData(const std::string& name,
+                                         std::string&& data,
+                                         const std::string& media_type) {
+  assert(!name.empty());
+  return Form(FormPart::New(name, std::move(data), media_type));
 }
 
 RequestBuilder& RequestBuilder::Auth(const std::string& type,
diff --git a/webcc/request_builder.h b/webcc/request_builder.h
index 244a8ce..26787d6 100644
--- a/webcc/request_builder.h
+++ b/webcc/request_builder.h
@@ -95,17 +95,23 @@ public:
     return *this;
   }
 
-  // Add a file to upload.
-  RequestBuilder& File(const std::string& name, const Path& path,
-                       const std::string& media_type = "");
+  // Use the file content as body.
+  RequestBuilder& File(const Path& path, bool infer_media_type = true,
+                       std::size_t chunk_size = 1024);
 
+  // Add a form part.
   RequestBuilder& Form(FormPartPtr part) {
     form_parts_.push_back(part);
     return *this;
   }
 
-  RequestBuilder& Form(const std::string& name, std::string&& data,
-                       const std::string& media_type = "");
+  // Add a form part of file.
+  RequestBuilder& FormFile(const std::string& name, const Path& path,
+                           const std::string& media_type = "");
+
+  // Add a form part of string data.
+  RequestBuilder& FormData(const std::string& name, std::string&& data,
+                           const std::string& media_type = "");
 
   RequestBuilder& Header(const std::string& key, const std::string& value) {
     headers_.push_back(key);