Manual parser for umask values.

[ayosec]

This patch changes the implementation of get_umask_procfs to avoid the dependency on the regex crate.

The original expression ^Umask:\s*(0[0-7]+)$ is implemented as:

if let Some(umask) = line.strip_prefix("Umask:") {
    return Ok(mode_t::from_str_radix(umask.trim(), 8).ok());
}

The previous code was using expect to get the result from from_str_radix. Now it just converts the Result from from_str_radix to an Option. The logic is different, but the behaviour is the same:

• If the value is correct (like Umask: 0022), both Ok(Some(from_str_radix().expect())) and Ok(from_str_radix().ok()) returns the same value.
• If the value is unexpected (like Umask: 0999),
  • The previous code will ignore the line (it does not match the regular expression), and will return Ok(None) after reading the /proc/self/status file.
  • The new code will try to parse 0999 as an octal. It will return an error, which is then converted to None by ok().

Build Improvements

After removing the regex crate, the size of the library and the compilation time improve significantly.

	Before	Now
libpathrs.so size	2.2 M	608 K
Build time	36 s	16 s

• Before the patch:

  $ hyperfine -w 1 -r 4 -p 'cargo clean || :' 'make release'
  Benchmark 1: make release
    Time (mean ± σ):     36.602 s ±  0.050 s    [User: 61.361 s, System: 4.345 s]
    Range (min … max):   36.552 s … 36.669 s    4 runs
  
  $ ls -sh target/release/libpathrs.so
  2.2M target/release/libpathrs.so

• After the patch:

  $ hyperfine -w 1 -r 4 -p 'cargo clean || :' 'make release'
  Benchmark 1: make release
    Time (mean ± σ):     16.919 s ±  0.129 s    [User: 26.672 s, System: 2.974 s]
    Range (min … max):   16.744 s … 17.035 s    4 runs
  
  $ ls -sh target/release/libpathrs.so
  608K target/release/libpathrs.so

[cyphar]

This is nicer, though it seems we might remove this code entirely because it turns out checking the mode this strictly is kind of buggy.

See cyphar/filepath-securejoin#29 and opencontainers/runc#4408.

[ayosec]

This is nicer, though it seems we might remove this code entirely because it turns out checking the mode this strictly is kind of buggy.

No problem!

Feel free to close the pull-request if you plan to remove the umask parser before the next release.

[cyphar]

Actually, let's just merge this as-is since it improves things. We can remove the code later.