Add RAII class for atomic overwrites

diff --git a/source/fs/redirectedpath.cpp b/source/fs/redirectedpath.cpp
new file mode 100644 (file)
index 0000000..6ca59cc
--- /dev/null
+++ b/source/fs/redirectedpath.cpp
@@ -0,0 +1,38 @@
+#include <exception>
+#include "redirectedpath.h"
+#include "stat.h"
+#include "utils.h"
+
+using namespace std;
+
+namespace Msp {
+namespace FS {
+
+RedirectedPath::RedirectedPath(const Path &p, const char *ext):
+       Path(p.str()+ext),
+       original(p)
+{ }
+
+RedirectedPath::RedirectedPath(const Path &p, const string &ext):
+       Path(p.str()+ext),
+       original(p)
+{ }
+
+RedirectedPath::RedirectedPath(const Path &p, const Path &r):
+       Path(r),
+       original(p)
+{ }
+
+RedirectedPath::~RedirectedPath()
+{
+       if(exists(*this))
+       {
+               if(uncaught_exception())
+                       unlink(*this);
+               else
+                       rename(*this, original);
+       }
+}
+
+} // namespace FS
+} // namespace Msp

diff --git a/source/fs/redirectedpath.h b/source/fs/redirectedpath.h
new file mode 100644 (file)
index 0000000..50a3609
--- /dev/null
+++ b/source/fs/redirectedpath.h
@@ -0,0 +1,30 @@
+#ifndef MSP_FS_REDIRECTEDPATH_H_
+#define MSP_FS_REDIRECTEDPATH_H_
+
+#include "path.h"
+
+namespace Msp {
+namespace FS {
+
+/**
+Provides a redirected path for the lifetime of the object.  When RedirectedPath
+goes out of scope, it is renamed to the original path.  If destruction happens
+due to an exception, it is unlinked instead.  The primary use for this is to
+atomically overwrite a file with a new version.
+*/
+class RedirectedPath: public Path
+{
+private:
+       Path original;
+
+public:
+       explicit RedirectedPath(const Path &, const char * = ".tmp");
+       RedirectedPath(const Path &, const std::string &);
+       RedirectedPath(const Path &, const Path &);
+       ~RedirectedPath();
+};
+
+} // namespace FS
+} // namespace Msp
+
+#endif