Optimize strings

include/util/json_renderer.hpp

@@ -34,7 +34,17 @@ template <typename Out> struct Renderer
     void operator()(const String &string)
     {
         write('"');
-        write(escape_JSON(string.value));
+        auto size = SizeOfEscapedJSONString(string.value);
+        if (size == string.value.size()) {
+            // we don't need to escape anything
+            write(string.value);
+        } else {
+            std::string escaped;
+            escaped.reserve(size);
+            EscapeJSONString(string.value, escaped);
+
+            write(escaped);
+        }
         write('"');
     }
 

include/util/string_util.hpp

@@ -58,11 +58,32 @@ template <int length, int precision> char *printInt(char *buffer, int value)
     return buffer;
 }
 
-inline std::string escape_JSON(const std::string &input)
+inline size_t SizeOfEscapedJSONString(const std::string &string)
+{
+    size_t size = 0;
+    for (const char letter : string)
+    {
+        switch (letter)
+        {
+        case '\\':
+        case '"':
+        case '/':
+        case '\b':
+        case '\f':
+        case '\n':
+        case '\r':
+        case '\t':
+            size += 2;
+            break;
+        default:
+            size += 1;
+        }
+    }
+    return size;
+}
+
+inline void EscapeJSONString(const std::string &input, std::string& output)
 {
-    // escape and skip reallocations if possible
-    std::string output;
-    output.reserve(input.size() + 4); // +4 assumes two backslashes on avg
     for (const char letter : input)
     {
         switch (letter)
@@ -96,7 +117,6 @@ inline std::string escape_JSON(const std::string &input)
             break;
         }
     }
-    return output;
 }
 
 inline std::size_t URIDecode(const std::string &input, std::string &output)