Add file abstraction function to check whether path exists

lib/core/libimagstore/src/file_abstraction/fs.rs

@@ -133,6 +133,10 @@ impl FileAbstraction for FSFileAbstraction {
         create_dir_all(path).chain_err(|| SEK::DirNotCreated)
     }
 
+    fn exists(&self, path: &PathBuf) -> Result<bool, SE> {
+        Ok(path.exists())
+    }
+
     fn new_instance(&self, p: PathBuf) -> Box<FileAbstractionInstance> {
         Box::new(FSFileAbstractionInstance::Absent(p))
     }

lib/core/libimagstore/src/file_abstraction/inmemory.rs

@@ -152,6 +152,13 @@ impl FileAbstraction for InMemoryFileAbstraction {
         Ok(())
     }
 
+    fn exists(&self, pb: &PathBuf) -> Result<bool, SE> {
+        let mut mtx = self.backend().lock().expect("Locking Mutex failed");
+        let backend = mtx.get_mut();
+
+        Ok(backend.contains_key(pb))
+    }
+
     fn new_instance(&self, p: PathBuf) -> Box<FileAbstractionInstance> {
         Box::new(InMemoryFileAbstractionInstance::new(self.backend().clone(), p))
     }

lib/core/libimagstore/src/file_abstraction/mod.rs

@@ -43,6 +43,8 @@ pub trait FileAbstraction : Debug {
     fn rename(&self, from: &PathBuf, to: &PathBuf) -> Result<(), SE>;
     fn create_dir_all(&self, _: &PathBuf) -> Result<(), SE>;
 
+    fn exists(&self, &PathBuf) -> Result<bool, SE>;
+
     fn new_instance(&self, p: PathBuf) -> Box<FileAbstractionInstance>;
 
     fn drain(&self) -> Result<Drain, SE>;

lib/core/libimagstore/src/file_abstraction/stdio/mod.rs

@@ -115,6 +115,10 @@ impl<W: Write, M: Mapper> FileAbstraction for StdIoFileAbstraction<W, M> {
         self.0.new_instance(p)
     }
 
+    fn exists(&self, p: &PathBuf) -> Result<bool, SE> {
+        self.0.exists(p)
+    }
+
     fn drain(&self) -> Result<Drain, SE> {
         self.0.drain()
     }

lib/core/libimagstore/src/file_abstraction/stdio/out.rs

@@ -136,6 +136,10 @@ impl<W: Write, M: Mapper> FileAbstraction for StdoutFileAbstraction<W, M> {
         self.mem.new_instance(p)
     }
 
+    fn exists(&self, p: &PathBuf) -> Result<bool, SE> {
+        self.mem.exists(p)
+    }
+
     fn drain(&self) -> Result<Drain, SE> {
         self.backend_cloned().map(Drain::new)
     }