From eec5ae96e89d3349440a46d34880470c429a0f6f Mon Sep 17 00:00:00 2001
From: Floris Bruynooghe <flub@devork.be>
Date: Tue, 7 Mar 2023 15:36:33 +0100
Subject: [PATCH] Update docs and fix string allocation

The docs say you should always unref the string and NULL is never
returned.  The implementation should follow that.
---
 deltachat-ffi/deltachat.h | 13 ++++++++++---
 deltachat-ffi/src/lib.rs  |  4 ++--
 2 files changed, 12 insertions(+), 5 deletions(-)

diff --git a/deltachat-ffi/deltachat.h b/deltachat-ffi/deltachat.h
index d00d9c0d7..bdf9bd025 100644
--- a/deltachat-ffi/deltachat.h
+++ b/deltachat-ffi/deltachat.h
@@ -2645,12 +2645,17 @@ void dc_str_unref (char* str);
 /**
  * Creates an object for sending a backup to another device.
  *
+ * Before calling this function IO must be stopped using dc_accounts_stop_io()
+ * or dc_stop_io().  IO should only be restarted once
+ * dc_backup_provider_wait() has returned.
+ *
  * The backup is sent to through a peer-to-peer channel which is bootstrapped
  * by a QR-code.  The backup contains the entire state of the account
  * including credentials.  This can be used to setup a new device.
  *
- * Once this function returns, the backup is being offered to remote devices.
- * To wait until one device received the backup, use
+ * This is a blocking call as some preparations are made like e.g. exporting
+ * the database.  Once this function returns, the backup is being offered to
+ * remote devices.  To wait until one device received the backup, use
  * dc_backup_provider_wait().  Alternatively abort the operation using
  * dc_stop_ongoing_process().
  *
@@ -2706,7 +2711,9 @@ char* dc_backup_provider_get_qr_svg (const dc_backup_provider_t* backup_provider
 /**
  * Waits for the sending to finish and frees the backup provider object.
  *
- * This should only be called once.
+ * This is a blocking call and should only be called once.  Once this function
+ * returns IO can be started again using dc_accounts_start_io() or
+ * dc_start_io().
  *
  * @memberof dc_backup_provider_t
  * @param context The context.
diff --git a/deltachat-ffi/src/lib.rs b/deltachat-ffi/src/lib.rs
index 87bc517e2..9e6edb7c4 100644
--- a/deltachat-ffi/src/lib.rs
+++ b/deltachat-ffi/src/lib.rs
@@ -4171,7 +4171,7 @@ pub unsafe extern "C" fn dc_backup_provider_get_qr(
 ) -> *mut libc::c_char {
     if provider.is_null() {
         eprintln!("ignoring careless call to dc_backup_provider_qr");
-        return ptr::null_mut();
+        return "".strdup();
     }
     let ffi_provider = &*provider;
     deltachat::qr::format_backup(&ffi_provider.provider.qr())
@@ -4185,7 +4185,7 @@ pub unsafe extern "C" fn dc_backup_provider_get_qr_svg(
 ) -> *mut libc::c_char {
     if provider.is_null() {
         eprintln!("ignoring careless call to dc_backup_provider_qr_svg()");
-        return ptr::null_mut();
+        return "".strdup();
     }
     let ffi_provider = &*provider;
     let ctx = &*ffi_provider.context;