DynamicBuffer: Add function for moves to String

Allow moving a DynamicBuffer's buffer in to a String object.  Requires
that the buffer hold a null-terminated string.

Author: willmmiles

src/DynamicBuffer.cpp

@@ -2,29 +2,42 @@
 #include <numeric>
 
 // Helper class - lets us move the buffer out of a String
-class ReleasableString : public String {
-  public:
-  // Inherit constructors
-  using String::String;
-  ReleasableString(String&& s) : String(std::move(s)) {};
-
-  // Special feature: releease the buffer to the caller without deallocating
-  char* release() {
-    if (isSSO()) return nullptr;
-    auto result = wbuffer();
-    init();
-    return result;
-  }
-};
+namespace {
+  class DynamicBufferString : public String {
+    public:
+    // Inherit constructors
+    using String::String;
+    DynamicBufferString(String&& s) : String(std::move(s)) {};
+    DynamicBufferString(DynamicBuffer&& d) : String() {
+      setSSO(false);
+      setCapacity(d.size() - 1);
+      setBuffer(d.release());
+      setLen(strlen(ptr.buff));
+    }
+
+    // Special feature: releease the buffer to the caller without deallocating
+    char* release() {
+      if (isSSO()) return nullptr;
+      auto result = wbuffer();
+      init();
+      return result;
+    }
+  };
+}
 
 DynamicBuffer::DynamicBuffer(String&& s) : _data(nullptr), _len(s.length()) {
-  auto rb = ReleasableString(std::move(s));
+  auto rb = DynamicBufferString(std::move(s));
   _data = rb.release();
   if (!_data) {
     *this = DynamicBuffer(rb);  // use const-ref constructor to copy string
   }
 }
 
+String toString(DynamicBuffer buf) {  
+  auto dbstr = DynamicBufferString(std::move(buf));
+  return std::move(*static_cast<String*>(&dbstr));  // Move-construct the result string from dbstr
+}
+
 template<typename list_type>
 static inline list_type allocateList(size_t total, size_t max_buffer_size) {
   list_type buffers;

src/DynamicBuffer.h

@@ -39,10 +39,12 @@ class DynamicBuffer {
 
   explicit operator bool() const { return (_data != nullptr) && (_len > 0); }
 
+  // Release the buffer without freeing it
+  char* release() { char* temp = _data; _data = nullptr; _len = 0; return temp; }
+
   // TODO, if it ever matters - resizing
 };
 
-
 // Same interface as DynamicBuffer, but with shared_ptr semantics: buffer is held until last copy releases it.
 class SharedBuffer {
   std::shared_ptr<DynamicBuffer> _buf;
@@ -65,6 +67,9 @@ class SharedBuffer {
   DynamicBuffer copy() const { return *_buf; }; // Make a copy of the buffer
 };
 
+// Utility functions
+String toString(DynamicBuffer buf);   // Move a buffer in to a string.  Buffer will be moved if buf is an rvalue, copied otherwise.
+
 
 // DynamicBufferList - an RAII list of DynamicBuffers
 // This structure can be used to create a chain of buffers, useful when the heap could get fragmented