Fix payload iteration issue of FormBody; Log form body; ignore body for response of HEAD.

unittest/CMakeLists.txt

@@ -2,6 +2,7 @@
 
 set(UT_SRCS
     base64_unittest.cc
+    body_unittest.cc
     request_parser_unittest.cc
     url_unittest.cc
     utility_unittest.cc

unittest/body_unittest.cc

@@ -0,0 +1,19 @@
+#include "gtest/gtest.h"
+
+#include "webcc/body.h"
+
+TEST(FormBodyTest, Payload) {
+  std::vector<webcc::FormPartPtr> parts{
+    std::make_shared<webcc::FormPart>("json", "{}", "application/json")
+  };
+
+  webcc::FormBody form_body{ parts, "123456" };
+
+  form_body.InitPayload();
+
+  auto payload = form_body.NextPayload();
+  EXPECT_EQ(false, payload.empty());
+
+  payload = form_body.NextPayload();
+  EXPECT_EQ(true, payload.empty());
+}