Let save_self_keypair() also remove a previously used key

The imex code was deleting the key if it was already used.  Turns out
none of the callers would not want this behaviour, so let's just
handle this case generally.

src/imex.rs

@@ -315,13 +315,6 @@ fn set_self_key(
     ensure!(self_addr.is_some(), "Missing self addr");
     let addr = EmailAddress::new(&self_addr.unwrap_or_default())?;
 
-    // XXX maybe better make dc_key_save_self_keypair delete things
-    sql::execute(
-        context,
-        &context.sql,
-        "DELETE FROM keypairs WHERE public_key=? OR private_key=?;",
-        params![public_key.to_bytes(), private_key.to_bytes()],
-    )?;
     let (public, secret) = match (public_key, private_key) {
         (Key::Public(p), Key::Secret(s)) => (p, s),
         _ => bail!("wrong keys unpacked"),

src/key.rs

@@ -11,7 +11,7 @@ use pgp::types::{KeyTrait, SecretKeyTrait};
 use crate::constants::*;
 use crate::context::Context;
 use crate::dc_tools::*;
-use crate::sql::{self, Sql};
+use crate::sql::Sql;
 
 // Re-export key types
 pub use crate::pgp::KeyPair;
@@ -350,46 +350,59 @@ impl SaveKeyError {
 /// "self" here refers to the fact that this DC instance owns the
 /// keypair.  Usually `addr` will be [Config::ConfiguredAddr].
 ///
+/// If either the public or private keys are already present in the
+/// database, this entry will be removed first regardless of the
+/// address associated with it.  Practically this means saving the
+/// same key again overwrites it.
+///
 /// [Config::ConfiguredAddr]: crate::config::Config::ConfiguredAddr
 pub fn save_self_keypair(
     context: &Context,
     keypair: &KeyPair,
     default: KeyPairUse,
 ) -> std::result::Result<(), SaveKeyError> {
-    // Should really be one transaction, more refactoring is needed for that.
-    if default == KeyPairUse::Default {
-        sql::execute(
-            context,
-            &context.sql,
-            "UPDATE keypairs SET is_default=0;",
-            params![],
+    // Everything should really be one transaction, more refactoring
+    // is needed for that.
+    let public_key = keypair
+        .public
+        .to_bytes()
+        .map_err(|err| SaveKeyError::new("failed to serialise public key", err))?;
+    let secret_key = keypair
+        .secret
+        .to_bytes()
+        .map_err(|err| SaveKeyError::new("failed to serialise secret key", err))?;
+    context
+        .sql
+        .execute(
+            "DELETE FROM keypairs WHERE public_key=? OR private_key=?;",
+            params![public_key, secret_key],
         )
-        .map_err(|err| SaveKeyError::new("failed to clear default", err))?;
+        .map_err(|err| SaveKeyError::new("failed to remove old use of key", err))?;
+    if default == KeyPairUse::Default {
+        context
+            .sql
+            .execute("UPDATE keypairs SET is_default=0;", params![])
+            .map_err(|err| SaveKeyError::new("failed to clear default", err))?;
     }
     let is_default = match default {
         KeyPairUse::Default => true,
         KeyPairUse::ReadOnly => false,
     };
-    sql::execute(
-        context,
-        &context.sql,
-        "INSERT INTO keypairs (addr, is_default, public_key, private_key, created)
+    context
+        .sql
+        .execute(
+            "INSERT INTO keypairs (addr, is_default, public_key, private_key, created)
                 VALUES (?,?,?,?,?);",
-        params![
-            keypair.addr.to_string(),
-            is_default as i32,
-            keypair
-                .public
-                .to_bytes()
-                .map_err(|err| SaveKeyError::new("failed to serialise public key", err))?,
-            keypair
-                .secret
-                .to_bytes()
-                .map_err(|err| SaveKeyError::new("failed to serialise secret key", err))?,
-            time()
-        ],
-    )
-    .map_err(|err| SaveKeyError::new("failed to insert keypair", err))
+            params![
+                keypair.addr.to_string(),
+                is_default as i32,
+                public_key,
+                secret_key,
+                time()
+            ],
+        )
+        .map(|_| ())
+        .map_err(|err| SaveKeyError::new("failed to insert keypair", err))
 }
 
 /// Make a fingerprint human-readable, in hex format.
@@ -573,4 +586,22 @@ i8pcjGO+IZffvyZJVRWfVooBJmWWbPB1pueo3tx8w3+fcuzpxz+RLFKaPyqXO+dD
         let public = SignedPublicKey::try_from(public_wrapped).unwrap();
         assert_eq!(public.primary_key, KEYPAIR.public.primary_key);
     }
+
+    #[test]
+    fn test_save_self_key_twice() {
+        // Saving the same key twice should result in only one row in
+        // the keypairs table.
+        let t = dummy_context();
+        let nrows = || {
+            t.ctx
+                .sql
+                .query_get_value::<_, u32>(&t.ctx, "SELECT COUNT(*) FROM keypairs;", params![])
+                .unwrap()
+        };
+        assert_eq!(nrows(), 0);
+        save_self_keypair(&t.ctx, &KEYPAIR, KeyPairUse::Default).unwrap();
+        assert_eq!(nrows(), 1);
+        save_self_keypair(&t.ctx, &KEYPAIR, KeyPairUse::Default).unwrap();
+        assert_eq!(nrows(), 1);
+    }
 }