Fix handling empty HTTP headers in parser_v1.hpp

This patch rectifies flush() of beast::http::parser_v1
to properly handle the case when an HTTP header has
empty value.

Without the fix an empty-valued HTTP header is being
concatenated with the header directly following it.
This situation can be replicated using eg. curl:

  curl <url> -H "X-First;" -H "X-Second: bla"

What Beast's client would see is a single header named
as "X-FirstX-Second".

CHANGELOG.md

@@ -6,6 +6,7 @@
 * Fix message_v1 constructor
 * Tidy up DynamicBuffer requirements
 * Tidy up error types and headers
+* Fix handling empty HTTP headers in parser_v1
 
 --------------------------------------------------------------------------------
 

include/beast/http/parser_v1.hpp

@@ -12,6 +12,7 @@
 #include <beast/http/concepts.hpp>
 #include <beast/http/message_v1.hpp>
 #include <beast/core/error.hpp>
+#include <boost/assert.hpp>
 #include <functional>
 #include <string>
 #include <type_traits>
@@ -94,6 +95,7 @@ private:
     message_type m_;
     typename message_type::body_type::reader r_;
     std::uint8_t skip_body_ = 0;
+    bool flush_ = false;
 
 public:
     parser_v1(parser_v1&&) = default;
@@ -161,13 +163,14 @@ private:
 
     void flush()
     {
-        if(! value_.empty())
+        if(! flush_)
-        {
+            return;
+        flush_ = false;
+        BOOST_ASSERT(! field_.empty());
         m_.headers.insert(field_, value_);
         field_.clear();
         value_.clear();
     }
-    }
 
     void on_start(error_code&)
     {
@@ -197,6 +200,7 @@ private:
     void on_value(boost::string_ref const& s, error_code&)
     {
         value_.append(s.data(), s.size());
+        flush_ = true;
     }
 
     void set(std::true_type)

test/websocket/stream.cpp

@@ -263,7 +263,7 @@ public:
                     }
                     catch(system_error const& se)
                     {
-                        BEAST_EXPECT(se.code() == ev);
+                        BEAST_EXPECTS(se.code() == ev, se.what());
                     }
                 }
             };