mount_fstab/
write.rs

1//! fstab serialization and file writing.
2//!
3//! Provides `Display` implementations for `Fstab` and `Entry` with proper
4//! escape encoding, plus safe file writing (overwrite and atomic via
5//! tempfile + fsync + rename).
6
7use crate::escape::encode_escapes;
8use crate::types::{Entry, Fstab};
9use std::fmt;
10use std::io;
11use std::path::Path;
12
13/// Format an [`Fstab`] for display / serialization.
14///
15/// Outputs the intro comment (if any), each entry with its preceding
16/// comment (if any), and the trailing comment (if any).
17impl fmt::Display for Fstab {
18    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
19        if let Some(ref intro) = self.intro_comment {
20            f.write_str(intro)?;
21        }
22        for entry in &self.entries {
23            if let Some(ref comment) = entry.comment {
24                f.write_str(comment)?;
25            }
26            write!(f, "{entry}")?;
27        }
28        if let Some(ref trailing) = self.trailing_comment {
29            f.write_str(trailing)?;
30        }
31        Ok(())
32    }
33}
34
35/// Format an [`Entry`] as an fstab data line.
36///
37/// The output includes the spec (with escape encoding), mount point
38/// (with escape encoding), filesystem type, and options. If either
39/// `freq` or `passno` is non-zero, both are included.
40impl fmt::Display for Entry {
41    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
42        write!(
43            f,
44            "{} {} {} {}",
45            encode_escapes(&self.spec.to_string()),
46            encode_escapes(&self.file.to_string()),
47            self.vfstype,
48            self.options,
49        )?;
50        if self.freq != 0 || self.passno != 0 {
51            write!(f, " {} {}", self.freq, self.passno)?;
52        }
53        writeln!(f)?;
54        Ok(())
55    }
56}
57
58impl Fstab {
59    /// Write the fstab to a file, overwriting if it exists.
60    ///
61    /// # Examples
62    ///
63    /// ```no_run
64    /// # use mount_fstab::Fstab;
65    /// let fstab = Fstab::new();
66    /// fstab.write_to("/tmp/fstab").unwrap();
67    /// ```
68    ///
69    /// # Errors
70    ///
71    /// Returns [`std::io::Error`] if the file cannot be written.
72    pub fn write_to(&self, path: impl AsRef<Path>) -> Result<(), io::Error> {
73        let content = self.to_string();
74        std::fs::write(path, content)
75    }
76
77    /// Atomically write the fstab to a file using a temp file, fsync, and rename.
78    ///
79    /// This ensures the file is never in a partially-written state:
80    /// 1. Write to a temporary file in the same directory
81    /// 2. Call `sync_all()` to flush data to disk
82    /// 3. Rename the temporary file over the target path (atomic on POSIX)
83    ///
84    /// # Examples
85    ///
86    /// ```no_run
87    /// # use mount_fstab::Fstab;
88    /// let fstab = Fstab::parse_str("UUID=root / ext4 defaults 0 1\n").unwrap();
89    /// fstab.write_atomic("/etc/fstab").unwrap();
90    /// ```
91    ///
92    /// # Errors
93    ///
94    /// Returns [`std::io::Error`] if the temp file cannot be created, written,
95    /// synced, or renamed.
96    pub fn write_atomic(&self, path: impl AsRef<Path>) -> Result<(), io::Error> {
97        let path = path.as_ref();
98        let parent = path.parent().unwrap_or(Path::new("."));
99        let mut tmp = tempfile::NamedTempFile::new_in(parent)?;
100        let content = self.to_string();
101        io::Write::write_all(&mut tmp, content.as_bytes())?;
102        tmp.as_file_mut().sync_all()?;
103        tmp.persist(path).map_err(|e| e.error)?;
104        Ok(())
105    }
106}
mount_fstab/write.rs

mount_fstab/
write.rs
