Inverted control flow, engine as library

luprex/core/cpp/streambuffer.hpp

@@ -266,6 +266,11 @@ public:
     // Frees up as much space as possible.
     void clear();
 
+    // Attempt to do a "readline".  If there is no newline in
+    // the buffer, returns empty string.  If there is a newline,
+    // returns a block of text that ends in newline.
+    std::string readline();
+
     // Write block of bytes into the buffer.
     //
     // Caution: this function doesn't write the length!