Better memory management for grpc_rb_byte_buffer_to_s.

src/ruby/ext/grpc/rb_byte_buffer.c

@@ -50,24 +50,18 @@ grpc_byte_buffer* grpc_rb_s_to_byte_buffer(char *string, size_t length) {
 }
 
 VALUE grpc_rb_byte_buffer_to_s(grpc_byte_buffer *buffer) {
-  size_t length = 0;
-  char *string = NULL;
   VALUE rb_string;
-  size_t offset = 0;
   grpc_byte_buffer_reader reader;
   gpr_slice next;
   if (buffer == NULL) {
     return Qnil;
   }
-  length = grpc_byte_buffer_length(buffer);
-  string = xmalloc(length + 1);
+  rb_string = rb_str_buf_new(grpc_byte_buffer_length(buffer));
   grpc_byte_buffer_reader_init(&reader, buffer);
   while (grpc_byte_buffer_reader_next(&reader, &next) != 0) {
-    memcpy(string + offset, GPR_SLICE_START_PTR(next), GPR_SLICE_LENGTH(next));
-    offset += GPR_SLICE_LENGTH(next);
+    rb_str_cat(rb_string, (const char *) GPR_SLICE_START_PTR(next),
+               GPR_SLICE_LENGTH(next));
     gpr_slice_unref(next);
   }
-  rb_string = rb_str_new(string, length);
-  xfree(string);
   return rb_string;
 }