Re: [pmg-devel] [PATCH log-tracker] drop 'time' dependency

[Stoiko Ivanov <s.ivanov@proxmox.com>]

huge thanks for taking the time ;) to clean-up!


On Tue,  4 Jan 2022 14:57:23 +0100
Wolfgang Bumiller <w.bumiller@proxmox.com> wrote:

> We're using a very old version of it and the functions we
> actually use are available in glibc anyway.
> 
> The only difference I found was that the result of
> glibc's `strptime()`'s `%s` does *not* want an additional
> `.to_local()` call anymore...
> 
> ... which was weird anyway.
since I'm always a bit cautious with "weird" in context of time(zone)
handling (which I do consider a bit brittle) - I tried to find out why
this was needed before and not anymore (took me quite a while)

glibc's strptime - calls localtime_r on the parsed number:
https://code.woboq.org/userspace/glibc/time/strptime_l.c.html#678

OTOH the time crate (in version 0.1.42) skips this step (or rather on the
contrary actively calls `at_utc` on the argument (which calls
sys::time_to_utc_tm with an tm struct with an offset of '0')

in any case since sys::time_to_utc_tm and sys::time_to_local_tm
only differ in the comment:
```
// FIXME: Add timezone logic
```
I am quite confident that your version is more correct (or at least
matches glibc's behaviour better

(might also explain why there's `at_utc` and `at` in the crate but not an
explicit `at_local` ;)

Additionally I did a bit of testing (and am really grateful for the tests
we already have in the repository) - and in addition to the code - the
output also looks correct

With that:

Reviewed-By: Stoiko Ivanov <s.ivanov@proxmox.com>
Tested-By: Stoiko Ivanov <s.ivanov@proxmox.com>

(I'm not directly applying it, in the hope that someone more experienced
with the log-tracker could also throw a quick glance at this)

small nit (maybe as hint to the person applying):
> 
> As a minor optimization I pass the format string as `&CStr`
> to avoid the memcpy.
> 
> (The CString::new() call in `strptime()` only happens during
> parameter parsing)
> 
> Signed-off-by: Wolfgang Bumiller <w.bumiller@proxmox.com>
> ---
>  Cargo.toml  |   1 -
>  src/main.rs |  75 ++++++++---------------
>  src/time.rs | 169 ++++++++++++++++++++++++++++++++++++++++++++++++++++
>  3 files changed, 194 insertions(+), 51 deletions(-)
>  create mode 100644 src/time.rs
> 
> diff --git a/Cargo.toml b/Cargo.toml
> index a975d39..7c31157 100644
> --- a/Cargo.toml
> +++ b/Cargo.toml
> @@ -14,4 +14,3 @@ anyhow = "1"
>  clap = "2.32"
>  flate2 = "1.0"
>  libc = "0.2.48"
> -time = "0.1.42"
> diff --git a/src/main.rs b/src/main.rs
> index fb06463..bf9783b 100644
> --- a/src/main.rs
> +++ b/src/main.rs
> @@ -15,6 +15,9 @@ use libc::time_t;
>  
>  use clap::{App, Arg};
>  
> +mod time;
> +use time::{Tm, CAL_MTOD};
> +
>  fn main() -> Result<(), Error> {
>      let matches = App::new(clap::crate_name!())
>          .version(clap::crate_version!())
> @@ -114,7 +117,7 @@ fn main() -> Result<(), Error> {
>          )
>          .get_matches();
>  
> -    let mut parser = Parser::new();
> +    let mut parser = Parser::new()?;
>      parser.handle_args(matches)?;
>  
>      println!("# LogReader: {}", std::process::id());
> @@ -144,12 +147,12 @@ fn main() -> Result<(), Error> {
>  
>      println!(
>          "# Start: {} ({})",
> -        time::strftime("%F %T", &parser.start_tm)?,
> +        time::strftime(c_str!("%F %T"), &parser.start_tm)?,
>          parser.options.start
>      );
>      println!(
>          "# End: {} ({})",
> -        time::strftime("%F %T", &parser.end_tm)?,
> +        time::strftime(c_str!("%F %T"), &parser.end_tm)?,
>          parser.options.end
>      );
>  
> @@ -1743,10 +1746,10 @@ struct Parser {
>  }
>  
>  impl Parser {
> -    fn new() -> Self {
> -        let ltime = time::now();
> +    fn new() -> Result<Self, Error> {
> +        let ltime = Tm::now_local()?;
>  
> -        Self {
> +        Ok(Self {
>              sentries: HashMap::new(),
>              fentries: HashMap::new(),
>              qentries: HashMap::new(),
> @@ -1760,12 +1763,12 @@ impl Parser {
>              count: 0,
>              buffered_stdout: BufWriter::with_capacity(4 * 1024 * 1024, std::io::stdout()),
>              options: Options::default(),
> -            start_tm: time::empty_tm(),
> -            end_tm: time::empty_tm(),
> +            start_tm: Tm::zero(),
> +            end_tm: Tm::zero(),
>              ctime: 0,
>              string_match: false,
>              lines: 0,
> -        }
> +        })
>      }
>  
>      fn free_sentry(&mut self, sentry_pid: u64) {
> @@ -1976,40 +1979,38 @@ impl Parser {
>          }
>  
>          if let Some(start) = args.value_of("start") {
> -            if let Ok(res) = time::strptime(start, "%F %T") {
> -                self.options.start = mkgmtime(&res);
> +            if let Ok(res) = time::strptime(start, c_str!("%F %T")) {
> +                self.options.start = res.as_utc_to_epoch();
>                  self.start_tm = res;
> -            } else if let Ok(res) = time::strptime(start, "%s") {
> -                let res = res.to_local();
> -                self.options.start = mkgmtime(&res);
> +            } else if let Ok(res) = time::strptime(start, c_str!("%s")) {
> +                self.options.start = res.as_utc_to_epoch();
>                  self.start_tm = res;
>              } else {
>                  bail!("failed to parse start time");
>              }
>          } else {
> -            let mut ltime = time::now();
> +            let mut ltime = Tm::now_local()?;
>              ltime.tm_sec = 0;
>              ltime.tm_min = 0;
>              ltime.tm_hour = 0;
> -            self.options.start = mkgmtime(&ltime);
> +            self.options.start = ltime.as_utc_to_epoch();
>              self.start_tm = ltime;
>          }
>  
>          if let Some(end) = args.value_of("end") {
> -            if let Ok(res) = time::strptime(end, "%F %T") {
> -                self.options.end = mkgmtime(&res);
> +            if let Ok(res) = time::strptime(end, c_str!("%F %T")) {
> +                self.options.end = res.as_utc_to_epoch();
>                  self.end_tm = res;
> -            } else if let Ok(res) = time::strptime(end, "%s") {
> -                let res = res.to_local();
> -                self.options.end = mkgmtime(&res);
> +            } else if let Ok(res) = time::strptime(end, c_str!("%s")) {
> +                self.options.end = res.as_utc_to_epoch();
>                  self.end_tm = res;
>              } else {
>                  bail!("failed to parse end time");
>              }
>          } else {
> -            let ltime = time::now();
> -            self.options.end = mkgmtime(&ltime);
> -            self.end_tm = ltime;
> +            // FIXME: just use libc::time(NULL) here
this comment is addressed and can be removed

> +            self.options.end = unsafe { libc::time(std::ptr::null_mut()) };
> +            self.end_tm = Tm::at_local(self.options.end)?;
>          }
>  
>          if self.options.end < self.options.start {
> @@ -2171,30 +2172,6 @@ fn get_or_create_fentry(
>      }
>  }
>  
> -fn mkgmtime(tm: &time::Tm) -> time_t {
> -    let mut res: time_t;
> -
> -    let mut year = tm.tm_year as i64 + 1900;
> -    let mon = tm.tm_mon;
> -
> -    res = (year - 1970) * 365 + CAL_MTOD[mon as usize];
> -
> -    if mon <= 1 {
> -        year -= 1;
> -    }
> -
> -    res += (year - 1968) / 4;
> -    res -= (year - 1900) / 100;
> -    res += (year - 1600) / 400;
> -
> -    res += (tm.tm_mday - 1) as i64;
> -    res = res * 24 + tm.tm_hour as i64;
> -    res = res * 60 + tm.tm_min as i64;
> -    res = res * 60 + tm.tm_sec as i64;
> -
> -    res
> -}
> -
>  const LOGFILES: [&str; 32] = [
>      "/var/log/syslog",
>      "/var/log/syslog.1",
> @@ -2397,8 +2374,6 @@ fn parse_time<'a>(
>      Some((ltime, data))
>  }
>  
> -const CAL_MTOD: [i64; 12] = [0, 31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334];
> -
>  type ByteSlice<'a> = &'a [u8];
>  /// Parse Host, Service and PID at the beginning of data. Returns a tuple of (host, service, pid, remaining_text).
>  fn parse_host_service_pid(data: &[u8]) -> Option<(ByteSlice, ByteSlice, u64, ByteSlice)> {
> diff --git a/src/time.rs b/src/time.rs
> new file mode 100644
> index 0000000..5851496
> --- /dev/null
> +++ b/src/time.rs
> @@ -0,0 +1,169 @@
> +//! Time support library.
> +//!
> +//! Contains wrappers for `strftime`, `strptime`, `libc::localtime_r`.
> +
> +use std::ffi::{CStr, CString};
> +use std::fmt;
> +use std::mem::MaybeUninit;
> +
> +use anyhow::{bail, format_err, Error};
> +
> +/// Calender month index to *non-leap-year* day-of-the-year.
> +pub const CAL_MTOD: [i64; 12] = [0, 31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334];
> +
> +/// Shortcut for generating an `&'static CStr`.
> +#[macro_export]
> +macro_rules! c_str {
> +    ($data:expr) => {{
> +        let bytes = concat!($data, "\0");
> +        unsafe { ::std::ffi::CStr::from_bytes_with_nul_unchecked(bytes.as_bytes()) }
> +    }};
> +}
> +
> +// Wrapper around `libc::tm` providing `Debug` and some helper methods.
> +pub struct Tm(libc::tm);
> +
> +impl std::ops::Deref for Tm {
> +    type Target = libc::tm;
> +
> +    fn deref(&self) -> &libc::tm {
> +        &self.0
> +    }
> +}
> +
> +impl std::ops::DerefMut for Tm {
> +    fn deref_mut(&mut self) -> &mut libc::tm {
> +        &mut self.0
> +    }
> +}
> +
> +// (or add libc feature 'extra-traits' but that's the only struct we need it for...)
> +impl fmt::Debug for Tm {
> +    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
> +        f.debug_struct("Tm")
> +            .field("tm_sec", &self.tm_sec)
> +            .field("tm_min", &self.tm_min)
> +            .field("tm_hour", &self.tm_hour)
> +            .field("tm_mday", &self.tm_mday)
> +            .field("tm_mon", &self.tm_mon)
> +            .field("tm_year", &self.tm_year)
> +            .field("tm_wday", &self.tm_wday)
> +            .field("tm_yday", &self.tm_yday)
> +            .field("tm_isdst", &self.tm_isdst)
> +            .field("tm_gmtoff", &self.tm_gmtoff)
> +            .field("tm_zone", &self.tm_zone)
> +            .finish()
> +    }
> +}
> +
> +/// These are now exposed via `libc`, but they're part of glibc.
> +mod imports {
> +    extern "C" {
> +        pub fn strftime(
> +            s: *mut libc::c_char,
> +            max: libc::size_t,
> +            format: *const libc::c_char,
> +            tm: *const libc::tm,
> +        ) -> libc::size_t;
> +
> +        pub fn strptime(
> +            s: *const libc::c_char,
> +            format: *const libc::c_char,
> +            tm: *mut libc::tm,
> +        ) -> *const libc::c_char;
> +    }
> +}
> +
> +impl Tm {
> +    /// A zero-initialized time struct.
> +    #[inline(always)]
> +    pub fn zero() -> Self {
> +        unsafe { std::mem::zeroed() }
> +    }
> +
> +    /// Get the current time in the local timezone.
> +    pub fn now_local() -> Result<Self, Error> {
> +        Self::at_local(unsafe { libc::time(std::ptr::null_mut()) })
> +    }
> +
> +    /// Get a local time from a unix time stamp.
> +    pub fn at_local(time: libc::time_t) -> Result<Self, Error> {
> +        let mut out = MaybeUninit::<libc::tm>::uninit();
> +        Ok(Self(unsafe {
> +            if libc::localtime_r(&time, out.as_mut_ptr()).is_null() {
> +                bail!("failed to convert timestamp to local time");
> +            }
> +            out.assume_init()
> +        }))
> +    }
> +
> +    /// Assume this is an UTC time and convert it to a unix time stamp.
> +    ///
> +    /// Equivalent to `timegm(3)`, the gmt equivalent of `mktime(3)`.
> +    pub fn as_utc_to_epoch(&self) -> libc::time_t {
> +        let mut year = self.0.tm_year as i64 + 1900;
> +        let mon = self.0.tm_mon;
> +
> +        let mut res: libc::time_t = (year - 1970) * 365 + CAL_MTOD[mon as usize];
> +
> +        if mon <= 1 {
> +            year -= 1;
> +        }
> +
> +        res += (year - 1968) / 4;
> +        res -= (year - 1900) / 100;
> +        res += (year - 1600) / 400;
> +
> +        res += (self.0.tm_mday - 1) as i64;
> +        res = res * 24 + self.0.tm_hour as i64;
> +        res = res * 60 + self.0.tm_min as i64;
> +        res = res * 60 + self.0.tm_sec as i64;
> +
> +        res
> +    }
> +}
> +
> +/// Wrapper around `strftime(3)` to format time strings.
> +pub fn strftime(format: &CStr, tm: &Tm) -> Result<String, Error> {
> +    let mut buf = MaybeUninit::<[u8; 64]>::uninit();
> +
> +    let size = unsafe {
> +        imports::strftime(
> +            buf.as_mut_ptr() as *mut libc::c_char,
> +            64,
> +            format.as_ptr(),
> +            &tm.0,
> +        )
> +    };
> +    if size == 0 {
> +        bail!("failed to format time");
> +    }
> +    let size = size as usize;
> +
> +    let buf = unsafe { buf.assume_init() };
> +
> +    std::str::from_utf8(&buf[..size])
> +        .map_err(|_| format_err!("formatted time was not valid utf-8"))
> +        .map(str::to_string)
> +}
> +
> +/// Wrapper around `strptime(3)` to parse time strings.
> +pub fn strptime(time: &str, format: &CStr) -> Result<Tm, Error> {
> +    let mut out = MaybeUninit::<libc::tm>::uninit();
> +
> +    let time = CString::new(time).map_err(|_| format_err!("time string contains nul bytes"))?;
> +
> +    let end = unsafe {
> +        imports::strptime(
> +            time.as_ptr() as *const libc::c_char,
> +            format.as_ptr(),
> +            out.as_mut_ptr(),
> +        )
> +    };
> +
> +    if end.is_null() {
> +        bail!("failed to parse time string {:?}", time);
> +    }
> +
> +    Ok(Tm(unsafe { out.assume_init() }))
> +}