Add web::json::value::string overload with additional 'has_escaped_chars' parameter. New overload has O(1) performance since it does not try to search for to-be-escaped-characters in provided string. Makes huge performance difference for large enough strings (i.e. images encoded as base64)

Author: kolomiets

Release/include/cpprest/json.h

@@ -200,6 +200,14 @@ namespace web { namespace json
         /// <returns>A JSON string value</returns>
         static _ASYNCRTIMP value __cdecl string(utility::string_t value);
 
+        /// <summary>
+        /// Creates a string value
+        /// </summary>
+        /// <param name="value">The C++ value to create a JSON value from</param>
+        /// <param name="has_escape_chars">Whether <paramref name="value" /> contains characters that should be escaped in JSON value</param>
+        /// <returns>A JSON string value</returns>
+        static _ASYNCRTIMP value __cdecl string(utility::string_t value, bool has_escape_chars);
+
 #ifdef _MS_WINDOWS
 private:
         // Only used internally by JSON parser.

Release/src/json/json.cpp

@@ -184,6 +184,16 @@ web::json::value web::json::value::string(utility::string_t value)
             );
 }
 
+web::json::value web::json::value::string(utility::string_t value, bool has_escape_chars)
+{
+    std::unique_ptr<details::_Value> ptr = utility::details::make_unique<details::_String>(std::move(value), has_escape_chars);
+    return web::json::value(std::move(ptr)
+#ifdef ENABLE_JSON_VALUE_VISUALIZER
+            ,value::String
+#endif
+            );
+}
+
 #ifdef _MS_WINDOWS
 web::json::value web::json::value::string(const std::string &value)
 {

Release/tests/Functional/json/construction_tests.cpp

@@ -186,8 +186,11 @@ TEST(factory_overloads)
     json::value v5 = json::value::string(U("Hello Again!"));
     json::value v6 = json::value::string(U("Hello!"));
     json::value v7 = json::value::string(U("Hello Again!"));
-    json::value v8 = json::value::object();
-    json::value v9 = json::value::array();
+    json::value v8 = json::value::string(U("Hello not-escaped!"), true);
+    json::value v9 = json::value::string(U("Hello not-escaped!"), false);
+    json::value v10 = json::value::object();
+    json::value v11 = json::value::array();
+
 
     VERIFY_ARE_EQUAL(v0.type(), json::value::Null);
     VERIFY_ARE_EQUAL(v1.type(), json::value::Number);
@@ -197,10 +200,12 @@ TEST(factory_overloads)
     VERIFY_ARE_EQUAL(v5.type(), json::value::String);
     VERIFY_ARE_EQUAL(v6.type(), json::value::String);
     VERIFY_ARE_EQUAL(v7.type(), json::value::String);
-    VERIFY_ARE_EQUAL(v8.type(), json::value::Object);
-    VERIFY_IS_TRUE(v8.is_object());
-    VERIFY_ARE_EQUAL(v9.type(), json::value::Array);
-    VERIFY_IS_TRUE(v9.is_array());
+    VERIFY_ARE_EQUAL(v8.type(), json::value::String);
+    VERIFY_ARE_EQUAL(v9.type(), json::value::String);
+    VERIFY_ARE_EQUAL(v10.type(), json::value::Object);
+    VERIFY_IS_TRUE(v10.is_object());
+    VERIFY_ARE_EQUAL(v11.type(), json::value::Array);
+    VERIFY_IS_TRUE(v11.is_array());
 }
 
 TEST(object_construction)

Release/tests/Functional/json/to_as_and_operators_tests.cpp

@@ -124,6 +124,12 @@ void verify_escaped_chars(const utility::string_t& str1, const utility::string_t
     VERIFY_ARE_EQUAL(str2, j1.serialize());
 }
 
+void verify_unescaped_chars(const utility::string_t& str1, const utility::string_t& str2)
+{
+    json::value j1 = json::value::string(str1, false);
+    VERIFY_ARE_EQUAL(str2, j1.serialize());
+}
+
 TEST(to_string_escaped_chars)
 {
     verify_escaped_chars(U(" \" "), U("\" \\\" \""));
@@ -148,6 +154,25 @@ TEST(to_string_escaped_chars)
     VERIFY_ARE_EQUAL(str, obj2.serialize());
 }
 
+TEST(to_string_unescaped_chars)
+{
+    verify_unescaped_chars(U(" \" "), U("\" \" \""));
+    verify_unescaped_chars(U(" \b "), U("\" \b \""));
+    verify_unescaped_chars(U(" \f "), U("\" \f \""));
+    verify_unescaped_chars(U(" \n "), U("\" \n \""));
+    verify_unescaped_chars(U(" \r "), U("\" \r \""));
+    verify_unescaped_chars(U(" \t "), U("\" \t \""));
+
+    json::value obj = json::value::object();
+    obj[U(" \t ")] = json::value::string(U(" \b "), false);
+
+    json::value arr = json::value::array();
+    arr[0] = json::value::string(U(" \f "), false);
+
+    VERIFY_ARE_EQUAL(U("{\" \\t \":\" \b \"}"), obj.serialize());
+    VERIFY_ARE_EQUAL(U("[\" \f \"]"), arr.serialize());
+}
+
 TEST(as_string)
 {
     json::value b(false);