database: Introduce function to delete specific userids.

- Fixes #88.

database/src/lib.rs

@@ -529,6 +529,24 @@ pub trait Database: Sync + Send {
         self.filter_userids(fpr, |_| false)
     }
 
+    /// Deletes all UserID packets matching `addr` (see [RFC2822
+    /// name-addr] and unlinks the email addresses.
+    ///
+    /// [RFC2822 name-addr]: https://tools.ietf.org/html/rfc2822#section-3.4
+    fn delete_userids_matching(&self, fpr: &Fingerprint, addr: &Email)
+                               -> Result <()> {
+        self.filter_userids(fpr, |uid| {
+            match Email::try_from(uid) {
+                // Keep those not matching `addr`.
+                Ok(a) => a != *addr,
+                // This should not happen, because all TPKs in the
+                // database should only have UserIDs with well-formed
+                // values.  Be conservative and keep the component.
+                Err(_) => true,
+            }
+        })
+    }
+
     /// Deletes all user ids NOT matching fulfilling `filter`.
     ///
     /// I.e. we retain fulfilling `filter`.

database/src/test.rs

@@ -323,9 +323,7 @@ pub fn test_uid_deletion<D: Database>(db: &mut D) {
     let fpr = Fingerprint::try_from(tpk.fingerprint()).unwrap();
 
     // Delete second UID.
-    db.filter_userids(
-        &fpr, |u| Email::try_from(u).map(|e| e != email2).unwrap_or(true))
-        .unwrap();
+    db.delete_userids_matching(&fpr, &email2).unwrap();
 
     // Check that the second is still there, and that the TPK is
     // otherwise intact.
@@ -334,9 +332,7 @@ pub fn test_uid_deletion<D: Database>(db: &mut D) {
     assert_eq!(tpk.subkeys().count(), n_subkeys);
 
     // Delete first UID.
-    db.filter_userids(
-        &fpr, |u| Email::try_from(u).map(|e| e != email1).unwrap_or(true))
-        .unwrap();
+    db.delete_userids_matching(&fpr, &email1).unwrap();
 
     // Check that the second is still there, and that the TPK is
     // otherwise intact.