Take advantage of unique_ptr and move construction for Buffer

Since Buffer has always implemented its copy constructor with a deep
copy, its Members object will never have multiple owners. Change to unique_ptr.

Also implement move constructors for Buffer, since there may be cases
where a deep copy is not needed.

include/qpdf/Buffer.hh

@@ -49,6 +49,10 @@ class Buffer
     QPDF_DLL
     Buffer& operator=(Buffer const&);
     QPDF_DLL
+    Buffer(Buffer &&) noexcept;
+    QPDF_DLL
+    Buffer& operator=(Buffer &&) noexcept;
+    QPDF_DLL
     size_t getSize() const;
     QPDF_DLL
     unsigned char const* getBuffer() const;
@@ -75,7 +79,7 @@ class Buffer
 
     void copy(Buffer const&);
 
-    std::shared_ptr<Members> m;
+    std::unique_ptr<Members> m;
 };
 
 #endif // BUFFER_HH

libqpdf/Buffer.cc

@@ -48,12 +48,24 @@ Buffer::operator=(Buffer const& rhs)
     return *this;
 }
 
+Buffer::Buffer(Buffer&& rhs) noexcept :
+    m(std::move(rhs.m))
+{
+}
+
+Buffer&
+Buffer::operator=(Buffer&& rhs) noexcept
+{
+    std::swap(this->m, rhs.m);
+    return *this;
+}
+
 void
 Buffer::copy(Buffer const& rhs)
 {
     if (this != &rhs) {
         this->m =
-            std::shared_ptr<Members>(new Members(rhs.m->size, nullptr, true));
+            std::unique_ptr<Members>(new Members(rhs.m->size, nullptr, true));
         if (this->m->size) {
             memcpy(this->m->buf, rhs.m->buf, this->m->size);
         }

libtests/buffer.cc

@@ -37,6 +37,23 @@ main()
         assert(bc2p[1] == 'W');
     }
 
+    {
+        // Test that buffers can be moved.
+        Buffer bm1(2);
+        unsigned char* bm1p = bm1.getBuffer();
+        bm1p[0] = 'Q';
+        bm1p[1] = 'W';
+        Buffer bm2(std::move(bm1));
+        bm1p[0] = 'R';
+        unsigned char* bm2p = bm2.getBuffer();
+        assert(bm2p == bm1p);
+        assert(bm2p[0] == 'R');
+
+        Buffer bm3 = std::move(bm2);
+        unsigned char* bm3p = bm3.getBuffer();
+        assert(bm3p == bm2p);
+    }
+
     try {
         Pl_Discard discard;
         Pl_Count count("count", &discard);