io/fs: add new module with filesystem access helpers

Wrappers around std::fs with error messages, as well as a
create_with_tmpfile() helper.

src/io/fs.rs

@@ -0,0 +1,61 @@
+use std::{
+	fs::{self, File},
+	io::{BufWriter, Write},
+	path::{Path, PathBuf},
+};
+
+use anyhow::{Context, Ok, Result};
+
+fn tmpfile_name(path: &Path) -> PathBuf {
+	let mut file_name = path.file_name().unwrap_or_default().to_os_string();
+	file_name.push(".tmp");
+
+	let mut ret = path.to_path_buf();
+	ret.set_file_name(file_name);
+	ret
+}
+
+pub fn create_dir_all(path: &Path) -> Result<()> {
+	fs::create_dir_all(path)
+		.with_context(|| format!("Failed to create directory {}", path.display(),))
+}
+
+pub fn rename(from: &Path, to: &Path) -> Result<()> {
+	fs::rename(from, to)
+		.with_context(|| format!("Failed to rename {} to {}", from.display(), to.display()))
+}
+
+pub fn create<T, F>(path: &Path, f: F) -> Result<T>
+where
+	F: FnOnce(&mut BufWriter<File>) -> Result<T>,
+{
+	(|| {
+		let file = File::create(path)?;
+		let mut writer = BufWriter::new(file);
+
+		let ret = f(&mut writer)?;
+		writer.flush()?;
+
+		Ok(ret)
+	})()
+	.with_context(|| format!("Failed to write file {}", path.display()))
+}
+
+pub fn create_with_tmpfile<T, F>(path: &Path, f: F) -> Result<T>
+where
+	F: FnOnce(&mut BufWriter<File>) -> Result<T>,
+{
+	let tmp_path = tmpfile_name(path);
+
+	let ret = (|| {
+		let ret = create(&tmp_path, f)?;
+		rename(&tmp_path, path)?;
+		Ok(ret)
+	})();
+
+	if ret.is_err() {
+		let _ = fs::remove_file(&tmp_path);
+	}
+
+	ret
+}

src/io/mod.rs

@@ -1,3 +1,4 @@
 pub mod data;
+pub mod fs;
 pub mod region;
 pub mod storage;