1 files changed, 68 insertions, 0 deletions
diff --git a/crates/dinggerd/src/platform.rs b/crates/dinggerd/src/platform.rs
new file mode 100644
index 0000000..8504a83
--- /dev/null
+++ b/crates/dinggerd/src/platform.rs
@@ -0,0 +1,68 @@
+//! macOS process inspection.
+
+/// A process's exact argument vector, from the kernel (`KERN_PROCARGS2`):
+/// unlike `ps`, it keeps arguments that contain spaces intact.
+#[cfg(target_os = "macos")]
+pub fn process_argv(pid: u32) -> Option<Vec<String>> {
+    use std::os::raw::{c_int, c_uint, c_void};
+    extern "C" {
+        fn sysctl(
+            name: *mut c_int,
+            namelen: c_uint,
+            oldp: *mut c_void,
+            oldlenp: *mut usize,
+            newp: *mut c_void,
+            newlen: usize,
+        ) -> c_int;
+    }
+    const CTL_KERN: c_int = 1;
+    const KERN_PROCARGS2: c_int = 49;
+    let mut mib = [CTL_KERN, KERN_PROCARGS2, pid as c_int];
+    let mut buffer = vec![0u8; 256 * 1024];
+    let mut size = buffer.len();
+    // SAFETY: mib has 3 entries; buffer is writable for `size` bytes, and the
+    // kernel writes at most that many, updating `size`.
+    let status = unsafe {
+        sysctl(mib.as_mut_ptr(), 3, buffer.as_mut_ptr().cast(), &mut size, std::ptr::null_mut(), 0)
+    };
+    if status != 0 || size < 4 {
+        return None;
+    }
+    let data = &buffer[..size];
+    let argc = i32::from_ne_bytes(data[..4].try_into().ok()?).max(0) as usize;
+    // Layout: argc, the executable path, NUL padding, then argv strings.
+    let rest = &data[4..];
+    let after_path = rest.iter().position(|&b| b == 0)?;
+    let args_start = after_path + rest[after_path..].iter().position(|&b| b != 0)?;
+    let argv: Vec<String> = rest[args_start..]
+        .split(|&b| b == 0)
+        .take(argc)
+        .map(|arg| String::from_utf8_lossy(arg).into_owned())
+        .collect();
+    (argv.len() == argc).then_some(argv)
+}
+
+#[cfg(not(target_os = "macos"))]
+pub fn process_argv(_pid: u32) -> Option<Vec<String>> {
+    None
+}
+
+#[cfg(test)]
+mod tests {
+    #[test]
+    fn reads_a_processs_exact_arguments() {
+        // A compound command keeps sh alive (it would exec a lone command).
+        let mut child = std::process::Command::new("/bin/sh")
+            .args(["-c", "sleep 30; :", "two words"])
+            .spawn()
+            .unwrap_or_else(|err| panic!("spawn: {err}"));
+        std::thread::sleep(std::time::Duration::from_millis(100));
+        let argv = super::process_argv(child.id());
+        let _ = child.kill();
+        let _ = child.wait();
+        assert_eq!(
+            argv,
+            Some(vec!["/bin/sh".into(), "-c".into(), "sleep 30; :".into(), "two words".into()])
+        );
+    }
+}