[PATCH proxmox 1/6] systemd: add support for machine-id generation

["Fabian Grünbichler" <f.gruenbichler@proxmox.com>]

the plain machine-id should not be leaked to external systems, but libsystemd
provides helpers for deriving application-id based identifiers that are useful
for identifying a machine externally.

Signed-off-by: Fabian Grünbichler <f.gruenbichler@proxmox.com>
---

Notes:
    to be used in the next patch by proxmox-subscription

 proxmox-systemd/src/lib.rs      |  2 +
 proxmox-systemd/src/sd_id128.rs | 70 +++++++++++++++++++++++++++++++++
 proxmox-systemd/src/sys.rs      |  6 +++
 3 files changed, 78 insertions(+)
 create mode 100644 proxmox-systemd/src/sd_id128.rs

diff --git a/proxmox-systemd/src/lib.rs b/proxmox-systemd/src/lib.rs
index 456d88c3..f79c204c 100644
--- a/proxmox-systemd/src/lib.rs
+++ b/proxmox-systemd/src/lib.rs
@@ -7,3 +7,5 @@ pub use escape::{escape_unit, unescape_unit, unescape_unit_path, UnescapeError};
 
 pub mod journal;
 pub mod notify;
+
+pub mod sd_id128;
diff --git a/proxmox-systemd/src/sd_id128.rs b/proxmox-systemd/src/sd_id128.rs
new file mode 100644
index 00000000..a98a6663
--- /dev/null
+++ b/proxmox-systemd/src/sd_id128.rs
@@ -0,0 +1,70 @@
+use std::fmt;
+
+use crate::sys::{self, sd_id128_t};
+
+#[derive(Debug, PartialEq, Eq)]
+pub enum SystemdId128Error {
+    InvalidAppId,
+    GenerationError,
+}
+
+impl std::error::Error for SystemdId128Error {
+    fn source(&self) -> Option<&(dyn std::error::Error + 'static)> {
+        None
+    }
+}
+
+impl fmt::Display for SystemdId128Error {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match self {
+            SystemdId128Error::InvalidAppId => f.write_str("Provided application ID is invalid."),
+            SystemdId128Error::GenerationError => {
+                f.write_str("Failed to generate machine-id based on application ID.")
+            }
+        }
+    }
+}
+
+pub fn get_app_specific_id(app_id: [u8; 16]) -> Result<[u8; 16], SystemdId128Error> {
+    let mut res = sd_id128_t { bytes: [0; 16] };
+
+    if app_id.iter().all(|b| *b == 0) {
+        return Err(SystemdId128Error::InvalidAppId);
+    }
+    unsafe {
+        sys::sd_id128_get_machine_app_specific(sd_id128_t { bytes: app_id }, &mut res);
+    }
+    if res.bytes.iter().all(|b| *b == 0) {
+        return Err(SystemdId128Error::GenerationError);
+    }
+    Ok(res.bytes)
+}
+
+#[test]
+fn test_invalid_app_id() {
+    let invalid = [0; 16];
+    let res = get_app_specific_id(invalid);
+    assert!(res.is_err());
+    assert_eq!(res, Err(SystemdId128Error::InvalidAppId));
+}
+
+#[test]
+fn test_valid_app_id() {
+    // no machine-id, no app-specific ID either..
+    if !std::path::Path::new("/etc/machine-id").exists() {
+        return;
+    }
+
+    // UUID generated with `systemd-id128 new` and converted from hex
+    let valid = 950247666410175165299169499632875718_u128.to_le_bytes();
+
+    let res = get_app_specific_id(valid);
+    assert!(res.is_ok());
+
+    let res2 = get_app_specific_id(valid);
+    assert!(res2.is_ok());
+
+    // cannot verify the expected result, since that depends on the machine the test runs on
+    // we can verify that two generations using the same machine and app-id give identical results
+    assert_eq!(res, res2);
+}
diff --git a/proxmox-systemd/src/sys.rs b/proxmox-systemd/src/sys.rs
index eabd44d1..ea2b6061 100644
--- a/proxmox-systemd/src/sys.rs
+++ b/proxmox-systemd/src/sys.rs
@@ -4,6 +4,11 @@ use std::os::fd::RawFd;
 
 pub const LISTEN_FDS_START: RawFd = 3;
 
+#[repr(C)]
+pub struct sd_id128_t {
+    pub bytes: [u8; 16],
+}
+
 #[link(name = "systemd")]
 unsafe extern "C" {
     pub fn sd_journal_stream_fd(
@@ -24,6 +29,7 @@ unsafe extern "C" {
         unset_environment: c_int,
         names: *mut *mut *mut c_char,
     ) -> c_int;
+    pub fn sd_id128_get_machine_app_specific(app_id: sd_id128_t, ret: *mut sd_id128_t) -> c_int;
 }
 
 pub fn check_call(ret: c_int) -> Result<c_int, io::Error> {
-- 
2.47.3