1 files changed, 50 insertions, 0 deletions
diff --git a/crates/tor-proto/src/circuit/unique_id.rs b/crates/tor-proto/src/circuit/unique_id.rs
new file mode 100644
index 000000000..c8778f36e
--- /dev/null
+++ b/crates/tor-proto/src/circuit/unique_id.rs
@@ -0,0 +1,50 @@
+//! Unique identifiers for circuits.
+
+use std::fmt::{Display, Formatter};
+
+use derive_deftly::Deftly;
+use tor_memquota::derive_deftly_template_HasMemoryCost;
+
+/// Process-unique identifier for a circuit.
+///
+/// We could use channel_id.circid here, but the circid can be reused
+/// over time.  This won't ever repeat on a 64-bit architecture, and
+/// is super-unlikely to repeat on a 32-bit architecture.  (If
+/// we're about to return a repeat value, we assert instead.)
+#[derive(Copy, Clone, Debug, Eq, PartialEq, Hash, Deftly)]
+#[derive_deftly(HasMemoryCost)]
+pub struct UniqId {
+    /// Channel that this circuit is on.
+    chan: usize,
+    /// ID for the circuit on the channel
+    circ: usize,
+}
+
+impl UniqId {
+    /// Construct a new circuit UniqId from its parts
+    pub(crate) fn new(chan: usize, circ: usize) -> Self {
+        UniqId { chan, circ }
+    }
+
+    /// A helper for displaying the process-unique identifiers of this circuit.
+    ///
+    /// Unlike the [`Display`] implementation, this does not display a `Circ` prefix.
+    pub fn display_chan_circ(&self) -> impl Display + '_ {
+        DisplayChanCirc(self)
+    }
+}
+
+impl Display for UniqId {
+    fn fmt(&self, f: &mut Formatter<'_>) -> std::fmt::Result {
+        write!(f, "Circ {}", self.display_chan_circ())
+    }
+}
+
+/// A helper for displaying the process-unique identifiers of this circuit.
+struct DisplayChanCirc<'a>(&'a UniqId);
+
+impl<'a> Display for DisplayChanCirc<'a> {
+    fn fmt(&self, f: &mut Formatter<'_>) -> std::fmt::Result {
+        write!(f, "{}.{}", self.0.chan, self.0.circ)
+    }
+}