Merge pull request #69 from niluxv/atomic_saves

Add `PathBackend` with atomic saves

Cargo.toml

@@ -16,6 +16,7 @@ all-features = true
 [dependencies]
 failure = "0.1.1"
 serde = "1"
+tempfile = "3"
 
 [dependencies.ron]
 optional = true
@@ -40,7 +41,6 @@ version = "0.6"
 [dev-dependencies]
 lazy_static = "1"
 serde_derive = "1"
-tempfile = "3"
 
 [features]
 default = []

src/backend/mod.rs

@@ -30,6 +30,9 @@ mod mmap;
 #[cfg(feature = "mmap")]
 pub use self::mmap::MmapStorage;
 
+mod path;
+pub use self::path::PathBackend;
+
 /// A backend using a file
 #[derive(Debug)]
 pub struct FileBackend(::std::fs::File);

src/backend/path.rs

@@ -0,0 +1,77 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+//! Module which implements the [`PathBackend`], storing data in a file on the
+//! file system (with a path) and featuring atomic saves.
+
+use super::Backend;
+use ::error;
+use ::error::RustbreakErrorKind as ErrorKind;
+use std::fs::OpenOptions;
+use std::path::{Path, PathBuf};
+use failure::ResultExt;
+use tempfile::NamedTempFile;
+
+/// A [`Backend`] using a file given the path.
+///
+/// Features atomic saves, so that the database file won't be corrupted or
+/// deleted if the program panics during the save.
+#[derive(Debug)]
+pub struct PathBackend {
+    path: PathBuf,
+}
+
+impl PathBackend {
+    /// Opens a new [`PathBackend`] for a given path.
+    pub fn open(path: PathBuf) -> error::Result<Self> {
+        OpenOptions::new().write(true).create(true).open(path.as_path())
+            .context(ErrorKind::Backend)?;
+        Ok(Self {path})
+    }
+}
+
+impl Backend for PathBackend {
+    fn get_data(&mut self) -> error::Result<Vec<u8>> {
+        use ::std::io::Read;
+
+        let mut file = OpenOptions::new().read(true)
+            .open(self.path.as_path()).context(ErrorKind::Backend)?;
+        let mut buffer = vec![];
+        file.read_to_end(&mut buffer).context(ErrorKind::Backend)?;
+        Ok(buffer)
+    }
+
+    /// Write the byte slice to the backend. This uses and atomic save.
+    ///
+    /// This won't corrupt the existing database file if the program panics
+    /// during the save.
+    fn put_data(&mut self, data: &[u8]) -> error::Result<()> {
+        use ::std::io::Write;
+
+        let mut tempf = NamedTempFile::new_in(self.path.parent().unwrap_or(Path::new(".")))
+            .context(ErrorKind::Backend)?;
+        tempf.write_all(data).context(ErrorKind::Backend)?;
+        tempf.as_file().sync_all().context(ErrorKind::Backend)?;
+        tempf.persist(self.path.as_path()).context(ErrorKind::Backend)?;
+        Ok(())
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use tempfile::NamedTempFile;
+    use super::{Backend, PathBackend};
+
+    #[test]
+    fn test_path_backend() {
+        let file = NamedTempFile::new()
+            .expect("could not create temporary file");
+        let mut backend = PathBackend::open(file.path().to_owned())
+            .expect("could not create backend");
+        let data = [4, 5, 1, 6, 8, 1];
+
+        backend.put_data(&data).expect("could not put data");
+        assert_eq!(backend.get_data().expect("could not get data"), data);
+    }
+}

src/lib.rs

@@ -199,7 +199,6 @@ extern crate base64;
 #[cfg(feature = "mmap")]
 extern crate memmap;
 
-#[cfg(test)]
 extern crate tempfile;
 
 /// The rustbreak errors that can be returned
@@ -220,7 +219,7 @@ use serde::Serialize;
 use serde::de::DeserializeOwned;
 use failure::ResultExt;
 
-use backend::{Backend, MemoryBackend, FileBackend};
+use backend::{Backend, MemoryBackend, FileBackend, PathBackend};
 #[cfg(feature = "mmap")]
 use backend::MmapStorage;
 
@@ -671,6 +670,29 @@ impl<Data, DeSer> Database<Data, FileBackend, DeSer>
     }
 }
 
+/// A database backed by a file, using atomic saves.
+pub type PathDatabase<D, DS> = Database<D, PathBackend, DS>;
+
+impl<Data, DeSer> Database<Data, PathBackend, DeSer>
+    where
+        Data: Serialize + DeserializeOwned + Debug + Clone + Send,
+        DeSer: DeSerializer<Data> + Debug + Send + Sync + Clone
+{
+    /// Create new [`PathDatabase`] from a [`Path`](std::path::Path).
+    pub fn from_path<S>(path: S, data: Data)
+        -> error::Result<FileDatabase<Data, DeSer>>
+        where S: AsRef<std::path::Path>
+    {
+        let backend = FileBackend::open(path).context(error::RustbreakErrorKind::Backend)?;
+
+        Ok(Database {
+            data: RwLock::new(data),
+            backend: Mutex::new(backend),
+            deser: DeSer::default(),
+        })
+    }
+}
+
 /// A database backed by a `Vec<u8>`
 pub type MemoryDatabase<D, DS> = Database<D, MemoryBackend, DS>;