api: add dc_context_change_passphrase()

deltachat-ffi/deltachat.h

@@ -301,6 +301,19 @@ dc_context_t*   dc_context_new_closed        (const char* dbfile);
 int             dc_context_open              (dc_context_t *context, const char* passphrase);
 
 
+/**
+ * Changes the passphrase on the open database.
+ * Existing database must already be encrypted and the passphrase cannot be NULL or empty.
+ * It is impossible to encrypt unencrypted database with this method and vice versa.
+ *
+ * @memberof dc_context_t
+ * @param context The context object.
+ * @param passphrase The new passphrase.
+ * @return 1 on success, 0 on error.
+ */
+int             dc_context_change_passphrase (dc_context_t* context, const char* passphrase);
+
+
 /**
  * Returns 1 if database is open.
  *

deltachat-ffi/src/lib.rs

@@ -167,6 +167,24 @@ pub unsafe extern "C" fn dc_context_open(
         .unwrap_or(0)
 }
 
+#[no_mangle]
+pub unsafe extern "C" fn dc_context_change_passphrase(
+    context: *mut dc_context_t,
+    passphrase: *const libc::c_char,
+) -> libc::c_int {
+    if context.is_null() {
+        eprintln!("ignoring careless call to dc_context_change_passphrase()");
+        return 0;
+    }
+
+    let ctx = &*context;
+    let passphrase = to_string_lossy(passphrase);
+    block_on(ctx.change_passphrase(passphrase))
+        .context("dc_context_change_passphrase() failed")
+        .log_err(ctx)
+        .is_ok() as libc::c_int
+}
+
 #[no_mangle]
 pub unsafe extern "C" fn dc_context_is_open(context: *mut dc_context_t) -> libc::c_int {
     if context.is_null() {

src/context.rs

@@ -332,6 +332,12 @@ impl Context {
         }
     }
 
+    /// Changes encrypted database passphrase.
+    pub async fn change_passphrase(&self, passphrase: String) -> Result<()> {
+        self.sql.change_passphrase(passphrase).await?;
+        Ok(())
+    }
+
     /// Returns true if database is open.
     pub async fn is_open(&self) -> bool {
         self.sql.is_open().await

src/sql.rs

@@ -304,6 +304,20 @@ impl Sql {
         }
     }
 
+    /// Changes the passphrase of encrypted database.
+    ///
+    /// The database must already be encrypted and the passphrase cannot be empty.
+    /// It is impossible to turn encrypted database into unencrypted
+    /// and vice versa this way, use import/export for this.
+    pub async fn change_passphrase(&self, passphrase: String) -> Result<()> {
+        self.call_write(move |conn| {
+            conn.pragma_update(None, "rekey", passphrase)
+                .context("failed to set PRAGMA rekey")?;
+            Ok(())
+        })
+        .await
+    }
+
     /// Locks the write transactions mutex in order to make sure that there never are
     /// multiple write transactions at once.
     ///
@@ -1246,6 +1260,49 @@ mod tests {
         sql.open(&t, "foo".to_string())
             .await
             .context("failed to open the database second time")?;
+
+        Ok(())
+    }
+
+    #[tokio::test(flavor = "multi_thread", worker_threads = 2)]
+    async fn test_change_passphrase() -> Result<()> {
+        use tempfile::tempdir;
+
+        // The context is used only for logging.
+        let t = TestContext::new().await;
+
+        // Create a separate empty database for testing.
+        let dir = tempdir()?;
+        let dbfile = dir.path().join("testdb.sqlite");
+        let sql = Sql::new(dbfile.clone());
+
+        sql.open(&t, "foo".to_string())
+            .await
+            .context("failed to open the database first time")?;
+        sql.close().await;
+
+        // Change the passphrase from "foo" to "bar".
+        let sql = Sql::new(dbfile.clone());
+        sql.open(&t, "foo".to_string())
+            .await
+            .context("failed to open the database second time")?;
+        sql.change_passphrase("bar".to_string())
+            .await
+            .context("failed to change passphrase")?;
+        sql.close().await;
+
+        let sql = Sql::new(dbfile);
+
+        // Test that old passphrase is not working.
+        assert!(sql.open(&t, "foo".to_string()).await.is_err());
+
+        // Open the database with the new passphrase.
+        sql.check_passphrase("bar".to_string()).await?;
+        sql.open(&t, "bar".to_string())
+            .await
+            .context("failed to open the database third time")?;
+        sql.close().await;
+
         Ok(())
     }
 }