For #152 - Remove chrono dependency

Cargo.toml

@@ -7,7 +7,6 @@ edition = "2021"
 
 [dependencies]
 subprocess = "0.2"
-chrono = "0.4"
 clap = { version = "4.5", features = ["derive"] }
 log = "0.4"
 env_logger = "0.11"

src/main.rs

@@ -14,6 +14,7 @@ mod procfsapi;
 mod ps;
 mod slurm;
 mod sysinfo;
+mod time;
 mod users;
 mod util;
 
@@ -80,7 +81,7 @@ fn main() {
     // obtained, not the time when reporting was allowed to run.  The latter is subject to greater
     // system effects, and using that timestamp increases the risk that the samples' timestamp order
     // improperly reflects the true order in which they were obtained.  See #100.
-    let timestamp = util::time_iso8601();
+    let timestamp = time::now_iso8601();
 
     env_logger::init();
 

src/time.rs

@@ -0,0 +1,70 @@
+use libc;
+use std::ffi::CStr;
+
+// Get current time as an ISO time stamp: yyyy-mm-ddThh:mm:ss+hhmm
+//
+// Use libc to avoid pulling in all of Chrono for this:
+//   t = time()
+//   localtime_r(&t, timebuf)
+//   strftime(strbuf, strbufsize, "%FT%T%z", timebuf)
+//
+// Panic on errors, there should never be any.
+
+pub fn now_iso8601() -> String {
+    let mut timebuf = libc::tm {
+        tm_sec: 0,
+        tm_min: 0,
+        tm_hour: 0,
+        tm_mday: 0,
+        tm_mon: 0,
+        tm_year: 0,
+        tm_wday: 0,
+        tm_yday: 0,
+        tm_isdst: 0,
+        tm_gmtoff: 0,
+        tm_zone: std::ptr::null(),
+    };
+    const SIZE: usize = 32;     // We need 25 unless something is greatly off
+    let mut buffer = vec![0i8; SIZE];
+    unsafe {
+        let t = libc::time(std::ptr::null_mut());
+
+        if libc::localtime_r(&t, &mut timebuf) == std::ptr::null_mut() {
+            panic!("localtime_r");
+        }
+
+        // strftime returns 0 if the buffer is too small for the result + NUL.
+        if libc::strftime(
+            buffer.as_mut_ptr(),
+            SIZE,
+            CStr::from_bytes_with_nul_unchecked(b"%FT%T%z\0").as_ptr(),
+            &timebuf) == 0 {
+            panic!("strftime");
+        }
+
+        return CStr::from_ptr(buffer.as_ptr()).to_str().unwrap().to_string();
+    }
+}
+
+#[test]
+pub fn test_isotime() {
+    let t = now_iso8601();
+    let ts = t.as_str().chars().collect::<Vec<char>>();
+    let expect = "dddd-dd-ddTdd:dd:dd+dddd";
+    let mut i = 0;
+    for c in expect.chars() {
+        match c {
+            'd' => {
+                assert!(ts[i] >= '0' && ts[i] <= '9');
+            }
+            '+' => {
+                assert!(ts[i] == '+' || ts[i] == '-');
+            }
+            _ => {
+                assert!(ts[i] == c);
+            }
+        }
+        i += 1;
+    }
+    assert!(i == ts.len());
+}

src/util.rs

@@ -1,8 +1,6 @@
 #![allow(unused_imports)]
 #![allow(unused_macros)]
 
-use chrono::prelude::Local;
-
 // Populate a HashSet.
 #[cfg(test)]
 macro_rules! set(
@@ -37,12 +35,6 @@ pub(crate) use map;
 #[cfg(test)]
 pub(crate) use set;
 
-// Get current time as an ISO time stamp.
-pub fn time_iso8601() -> String {
-    let local_time = Local::now();
-    format!("{}", local_time.format("%Y-%m-%dT%H:%M:%S%Z"))
-}
-
 // Carve up a line of text into space-separated chunks + the start indices of the chunks.
 pub fn chunks(input: &str) -> (Vec<usize>, Vec<&str>) {
     let mut start_indices: Vec<usize> = Vec::new();