Add Sig.issuer_key_id, Sig.signers_user_id, and Sig.expiration

Signed-off-by: Daniel Alley <dalley@redhat.com>

Author: dralley

src/signature.rs

@@ -87,6 +87,26 @@ impl Sig {
             .map(|issuer| format!("{issuer:x}"))
     }
 
+    /// The short key ID of the key that made this signature, as a lowercase hex string.
+    ///
+    /// Returns ``None`` if the signature does not carry an issuer key ID subpacket.
+    /// Prefer ``issuer_fingerprint`` over this where possible, as key IDs are not collision-resistant.
+    #[getter]
+    pub fn issuer_key_id(&self) -> Option<String> {
+        self.sig.issuers().next().map(|id| format!("{id:x}"))
+    }
+
+    /// The User ID of the signer, as declared in the signature's Signer's User ID subpacket.
+    ///
+    /// Returns ``None`` if the signature does not carry a Signer's User ID subpacket.
+    /// Note that this value is self-reported by the signer and is not verified against any cert.
+    #[getter]
+    pub fn signers_user_id(&self) -> Option<String> {
+        self.sig
+            .signers_user_id()
+            .map(|uid| String::from_utf8_lossy(uid).into_owned())
+    }
+
     /// The time at which this signature was created.
     ///
     /// Returns ``None`` if the signature does not carry a creation time subpacket.
@@ -95,6 +115,17 @@ impl Sig {
         self.sig.signature_creation_time().map(Into::into)
     }
 
+    /// The time at which this signature expires, or ``None`` if it does not expire.
+    ///
+    /// Computed as the signature creation time plus the signature validity period.
+    /// Returns ``None`` if either subpacket is absent.
+    #[getter]
+    pub fn expiration(&self) -> Option<chrono::DateTime<chrono::Utc>> {
+        let created = self.sig.signature_creation_time()?;
+        let validity = self.sig.signature_validity_period()?;
+        Some(created.checked_add(validity)?.into())
+    }
+
     /// Return the ASCII-armored representation of the signature.
     pub fn __str__(&self) -> PyResult<String> {
         let bytes = crate::serialize(self.sig.clone().into(), armor::Kind::Signature)?;