Add API for passphrase-protected accounts

To create encrypted account with account manager, call
dc_accounts_add_closed_account(). Open this account with
dc_context_open() using the passphrase you want to use for encryption.

When application is loaded next time and account manager is created,
it will open all accounts that have no passphrase set. For encrypted
accounts dc_context_is_open() will return 0. To open them, call
dc_context_open() with the correct passphrase. After opening, call
dc_context_start_io() on this account or just dc_accounts_start_io()
to start all accounts that are not started yet.

Support for legacy SQLite-based backup format is removed in this
commit.

deltachat-ffi/src/lib.rs

@@ -27,6 +27,7 @@ use async_std::sync::RwLock;
 use async_std::task::{block_on, spawn};
 use deltachat::qr_code_generator::get_securejoin_qr_svg;
 use num_traits::{FromPrimitive, ToPrimitive};
+use rand::Rng;
 
 use deltachat::chat::{ChatId, ChatVisibility, MuteDuration, ProtectionStatus};
 use deltachat::constants::DC_MSG_ID_LAST_SPECIAL;
@@ -75,7 +76,6 @@ pub unsafe extern "C" fn dc_context_new(
     }
 
     let ctx = if blobdir.is_null() || *blobdir == 0 {
-        use rand::Rng;
         // generate random ID as this functionality is not yet available on the C-api.
         let id = rand::thread_rng().gen();
         block_on(Context::new(as_path(dbfile).to_path_buf().into(), id))
@@ -86,12 +86,63 @@ pub unsafe extern "C" fn dc_context_new(
     match ctx {
         Ok(ctx) => Box::into_raw(Box::new(ctx)),
         Err(err) => {
-            eprintln!("failed to create context: {}", err);
+            eprintln!("failed to create context: {:#}", err);
             ptr::null_mut()
         }
     }
 }
 
+#[no_mangle]
+pub unsafe extern "C" fn dc_context_new_closed(dbfile: *const libc::c_char) -> *mut dc_context_t {
+    setup_panic!();
+
+    if dbfile.is_null() {
+        eprintln!("ignoring careless call to dc_context_new_closed()");
+        return ptr::null_mut();
+    }
+
+    let id = rand::thread_rng().gen();
+    match block_on(Context::new_closed(
+        as_path(dbfile).to_path_buf().into(),
+        id,
+    )) {
+        Ok(context) => Box::into_raw(Box::new(context)),
+        Err(err) => {
+            eprintln!("failed to create context: {:#}", err);
+            ptr::null_mut()
+        }
+    }
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn dc_context_open(
+    context: *mut dc_context_t,
+    passphrase: *const libc::c_char,
+) -> libc::c_int {
+    if context.is_null() {
+        eprintln!("ignoring careless call to dc_context_open()");
+        return 0;
+    }
+
+    let ctx = &*context;
+    let passphrase = to_string_lossy(passphrase);
+    block_on(ctx.open(passphrase))
+        .log_err(ctx, "dc_context_open() failed")
+        .map(|b| b as libc::c_int)
+        .unwrap_or(0)
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn dc_context_is_open(context: *mut dc_context_t) -> libc::c_int {
+    if context.is_null() {
+        eprintln!("ignoring careless call to dc_context_is_open()");
+        return 0;
+    }
+
+    let ctx = &*context;
+    block_on(ctx.is_open()) as libc::c_int
+}
+
 /// Release the context structure.
 ///
 /// This function releases the memory of the `dc_context_t` structure.
@@ -3965,6 +4016,30 @@ pub unsafe extern "C" fn dc_accounts_add_account(accounts: *mut dc_accounts_t) -
     })
 }
 
+#[no_mangle]
+pub unsafe extern "C" fn dc_accounts_add_closed_account(accounts: *mut dc_accounts_t) -> u32 {
+    if accounts.is_null() {
+        eprintln!("ignoring careless call to dc_accounts_add_closed_account()");
+        return 0;
+    }
+
+    let accounts = &mut *accounts;
+
+    block_on(async move {
+        let mut accounts = accounts.write().await;
+        match accounts.add_closed_account().await {
+            Ok(id) => id,
+            Err(err) => {
+                accounts.emit_event(EventType::Error(format!(
+                    "Failed to add account: {:#}",
+                    err
+                )));
+                0
+            }
+        }
+    })
+}
+
 #[no_mangle]
 pub unsafe extern "C" fn dc_accounts_remove_account(
     accounts: *mut dc_accounts_t,