1 files changed, 95 insertions, 0 deletions
diff --git a/src/mail/unique_ident.rs b/src/mail/unique_ident.rs
new file mode 100644
index 0000000..6046281
--- /dev/null
+++ b/src/mail/unique_ident.rs
@@ -0,0 +1,95 @@
+use std::str::FromStr;
+use std::sync::atomic::{AtomicU64, Ordering};
+
+use lazy_static::lazy_static;
+use rand::prelude::*;
+use serde::{de::Error, Deserialize, Deserializer, Serialize, Serializer};
+
+use crate::time::now_msec;
+
+/// An internal Mail Identifier is composed of two components:
+/// - a process identifier, 128 bits, itself composed of:
+///   - the timestamp of when the process started, 64 bits
+///   - a 64-bit random number
+/// - a sequence number, 64 bits
+/// They are not part of the protocol but an internal representation
+/// required by Mailrage/Aerogramme.
+/// Their main property is to be unique without having to rely
+/// on synchronization between IMAP processes.
+#[derive(Clone, Copy, PartialOrd, Ord, PartialEq, Eq, Hash, Debug)]
+pub struct UniqueIdent(pub [u8; 24]);
+
+struct IdentGenerator {
+    pid: u128,
+    sn: AtomicU64,
+}
+
+impl IdentGenerator {
+    fn new() -> Self {
+        let time = now_msec() as u128;
+        let rand = thread_rng().gen::<u64>() as u128;
+        Self {
+            pid: (time << 64) | rand,
+            sn: AtomicU64::new(0),
+        }
+    }
+
+    fn gen(&self) -> UniqueIdent {
+        let sn = self.sn.fetch_add(1, Ordering::Relaxed);
+        let mut res = [0u8; 24];
+        res[0..16].copy_from_slice(&u128::to_be_bytes(self.pid));
+        res[16..24].copy_from_slice(&u64::to_be_bytes(sn));
+        UniqueIdent(res)
+    }
+}
+
+lazy_static! {
+    static ref GENERATOR: IdentGenerator = IdentGenerator::new();
+}
+
+pub fn gen_ident() -> UniqueIdent {
+    GENERATOR.gen()
+}
+
+// -- serde --
+
+impl<'de> Deserialize<'de> for UniqueIdent {
+    fn deserialize<D>(d: D) -> Result<Self, D::Error>
+    where
+        D: Deserializer<'de>,
+    {
+        let v = String::deserialize(d)?;
+        UniqueIdent::from_str(&v).map_err(D::Error::custom)
+    }
+}
+
+impl Serialize for UniqueIdent {
+    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+    where
+        S: Serializer,
+    {
+        serializer.serialize_str(&self.to_string())
+    }
+}
+
+impl std::fmt::Display for UniqueIdent {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        write!(f, "{}", hex::encode(self.0))
+    }
+}
+
+impl FromStr for UniqueIdent {
+    type Err = &'static str;
+
+    fn from_str(s: &str) -> Result<UniqueIdent, &'static str> {
+        let bytes = hex::decode(s).map_err(|_| "invalid hex")?;
+
+        if bytes.len() != 24 {
+            return Err("bad length");
+        }
+
+        let mut tmp = [0u8; 24];
+        tmp[..].copy_from_slice(&bytes);
+        Ok(UniqueIdent(tmp))
+    }
+}