api: cffi api to create account manager with existing events channel to see events emitted during startup. dc_event_channel_new, dc_event_channel_unref, dc_event_channel_get_event_emitter and dc_accounts_new_with_event_channel (#7609)

closes #7606

deltachat-ffi/deltachat.h

@@ -22,6 +22,7 @@ typedef struct _dc_lot       dc_lot_t;
 typedef struct _dc_provider  dc_provider_t;
 typedef struct _dc_event     dc_event_t;
 typedef struct _dc_event_emitter dc_event_emitter_t;
+typedef struct _dc_event_channel dc_event_channel_t;
 typedef struct _dc_jsonrpc_instance dc_jsonrpc_instance_t;
 typedef struct _dc_backup_provider dc_backup_provider_t;
 
@@ -3093,7 +3094,7 @@ int dc_receive_backup (dc_context_t* context, const char* qr);
 
 /**
  * Create a new account manager.
- * The account manager takes an directory
+ * The account manager takes a directory
  * where all context-databases are placed in.
  * To add a context to the account manager,
  * use dc_accounts_add_account() or dc_accounts_migrate_account().
@@ -3115,6 +3116,35 @@ int dc_receive_backup (dc_context_t* context, const char* qr);
  */
 dc_accounts_t* dc_accounts_new                  (const char* dir, int writable);
 
+/**
+ * Create a new account manager with an existing events channel,
+ * which allows you to see events emitted during startup.
+ * 
+ * The account manager takes a directory
+ * where all context-databases are placed in.
+ * To add a context to the account manager,
+ * use dc_accounts_add_account() or dc_accounts_migrate_account().
+ * All account information are persisted.
+ * To remove a context from the account manager,
+ * use dc_accounts_remove_account().
+ *
+ * @memberof dc_accounts_t
+ * @param dir The directory to create the context-databases in.
+ *     If the directory does not exist,
+ *     dc_accounts_new_with_event_channel() will try to create it.
+ * @param writable Whether the returned account manager is writable, i.e. calling these functions on
+ *     it is possible: dc_accounts_add_account(), dc_accounts_add_closed_account(),
+ *     dc_accounts_migrate_account(), dc_accounts_remove_account(), dc_accounts_select_account().
+ * @param dc_event_channel_t Events Channel to be used for this accounts manager, 
+ *      create one with dc_event_channel_new().
+ *      This channel is consumed by this method and can not be used again afterwards,
+ *      so be sure to call `dc_event_channel_get_event_emitter` before.
+ * @return An account manager object.
+ *     The object must be passed to the other account manager functions
+ *     and must be freed using dc_accounts_unref() after usage.
+ *     On errors, NULL is returned.
+ */
+dc_accounts_t* dc_accounts_new_with_event_channel(const char* dir, int writable, dc_event_channel_t* events_channel);
 
 /**
  * Free an account manager object.
@@ -3355,8 +3385,12 @@ void           dc_accounts_set_push_device_token (dc_accounts_t* accounts, const
  *     Must be freed using dc_event_emitter_unref() after usage.
  *
  * Note: Use only one event emitter per account manager.
- * Having more than one event emitter running at the same time on the same account manager
- * will result in events randomly delivered to the one or to the other.
+ * The result of having multiple event emitters is unspecified.
+ * Currently events are broadcasted to all existing event emitters,
+ * but previous versions delivered events to only one event emitter
+ * and this behavior may change again in the future.
+ * Events emitted before creation of event emitter
+ * are not available to event emitter.
  */
 dc_event_emitter_t* dc_accounts_get_event_emitter (dc_accounts_t* accounts);
 
@@ -6000,6 +6034,62 @@ char* dc_jsonrpc_next_response(dc_jsonrpc_instance_t* jsonrpc_instance);
  */
 char* dc_jsonrpc_blocking_call(dc_jsonrpc_instance_t* jsonrpc_instance, const char *input);
 
+/**
+ * @class dc_event_channel_t
+ *
+ * Opaque object that is used to create an event emitter which can be used log events during startup of an accounts manger.
+ * Only used for dc_accounts_new_with_event_channel().
+ * To use it:
+ *   1. create an events channel with `dc_event_channel_new()`.
+ *   2. get an event emitter for it with `dc_event_channel_get_event_emitter()`.
+ *   3. use it to create your account manager with `dc_accounts_new_with_event_channel()`, which consumes the channel.
+ *   4. free the empty channel wrapper object with `dc_event_channel_unref()`.
+ */
+
+ /**
+  * Create a new event channel.
+  *
+  * @memberof dc_event_channel_t
+  * @return An event channel wrapper object (dc_event_channel_t).
+  */
+ dc_event_channel_t* dc_event_channel_new();
+ 
+ /**
+  * Release/free the events channel structure.
+  * This function releases the memory of the `dc_event_channel_t` structure.
+  *
+  * you can call it after calling dc_accounts_new_with_event_channel,
+  * which took the events channel out of it already, so this just frees the underlying option.
+  * 
+  * @memberof dc_event_channel_t
+  */
+void dc_event_channel_unref(dc_event_channel_t* event_channel);
+
+/**
+ * Create the event emitter that is used to receive events.
+ * 
+ * The library will emit various @ref DC_EVENT events, such as "new message", "message read" etc.
+ * To get these events, you have to create an event emitter using this function
+ * and call dc_get_next_event() on the emitter.
+ *
+ * This is similar to dc_get_event_emitter(), which, however,
+ * must not be called for accounts handled by the account manager.
+ * 
+ * @memberof dc_event_channel_t
+ * @param The event channel.
+ * @return Returns the event emitter, NULL on errors.
+ *     Must be freed using dc_event_emitter_unref() after usage.
+ * 
+ * Note: Use only one event emitter per account manager / event channel.
+ * The result of having multiple event emitters is unspecified.
+ * Currently events are broadcasted to all existing event emitters,
+ * but previous versions delivered events to only one event emitter
+ * and this behavior may change again in the future.
+ * Events emitted before creation of event emitter
+ * are not available to event emitter.
+ */
+dc_event_emitter_t* dc_event_channel_get_event_emitter(dc_event_channel_t* event_channel);
+
 /**
  * @class dc_event_emitter_t
  *

deltachat-ffi/src/lib.rs

@@ -17,7 +17,7 @@ use std::fmt::Write;
 use std::future::Future;
 use std::ptr;
 use std::str::FromStr;
-use std::sync::{Arc, LazyLock};
+use std::sync::{Arc, LazyLock, Mutex};
 use std::time::{Duration, SystemTime};
 
 use anyhow::Context as _;
@@ -4764,6 +4764,98 @@ pub unsafe extern "C" fn dc_accounts_new(
     }
 }
 
+pub type dc_event_channel_t = Mutex<Option<Events>>;
+
+#[no_mangle]
+pub unsafe extern "C" fn dc_event_channel_new() -> *mut dc_event_channel_t {
+    Box::into_raw(Box::new(Mutex::new(Some(Events::new()))))
+}
+
+/// Release the events channel structure.
+///
+/// This function releases the memory of the `dc_event_channel_t` structure.
+///
+/// you can call it after calling dc_accounts_new_with_event_channel,
+/// which took the events channel out of it already, so this just frees the underlying option.
+#[no_mangle]
+pub unsafe extern "C" fn dc_event_channel_unref(event_channel: *mut dc_event_channel_t) {
+    if event_channel.is_null() {
+        eprintln!("ignoring careless call to dc_event_channel_unref()");
+        return;
+    }
+    drop(Box::from_raw(event_channel))
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn dc_event_channel_get_event_emitter(
+    event_channel: *mut dc_event_channel_t,
+) -> *mut dc_event_emitter_t {
+    if event_channel.is_null() {
+        eprintln!("ignoring careless call to dc_event_channel_get_event_emitter()");
+        return ptr::null_mut();
+    }
+
+    let Some(event_channel) = &*(*event_channel)
+        .lock()
+        .expect("call to dc_event_channel_get_event_emitter() failed: mutex is poisoned")
+    else {
+        eprintln!(
+            "ignoring careless call to dc_event_channel_get_event_emitter() 
+            -> channel was already consumed, make sure you call this before dc_accounts_new_with_event_channel"
+        );
+        return ptr::null_mut();
+    };
+
+    let emitter = event_channel.get_emitter();
+
+    Box::into_raw(Box::new(emitter))
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn dc_accounts_new_with_event_channel(
+    dir: *const libc::c_char,
+    writable: libc::c_int,
+    event_channel: *mut dc_event_channel_t,
+) -> *const dc_accounts_t {
+    setup_panic!();
+
+    if dir.is_null() || event_channel.is_null() {
+        eprintln!("ignoring careless call to dc_accounts_new_with_event_channel()");
+        return ptr::null_mut();
+    }
+
+    // consuming channel enforce that you need to get the event emitter
+    // before initializing the account manager,
+    // so that you don't miss events/errors during initialisation.
+    // It also prevents you from using the same channel on multiple account managers.
+    let Some(event_channel) = (*event_channel)
+        .lock()
+        .expect("call to dc_event_channel_get_event_emitter() failed: mutex is poisoned")
+        .take()
+    else {
+        eprintln!(
+            "ignoring careless call to dc_accounts_new_with_event_channel()
+            -> channel was already consumed"
+        );
+        return ptr::null_mut();
+    };
+
+    let accs = block_on(Accounts::new_with_events(
+        as_path(dir).into(),
+        writable != 0,
+        event_channel,
+    ));
+
+    match accs {
+        Ok(accs) => Arc::into_raw(Arc::new(RwLock::new(accs))),
+        Err(err) => {
+            // We are using Anyhow's .context() and to show the inner error, too, we need the {:#}:
+            eprintln!("failed to create accounts: {err:#}");
+            ptr::null_mut()
+        }
+    }
+}
+
 /// Release the accounts structure.
 ///
 /// This function releases the memory of the `dc_accounts_t` structure.

src/accounts.rs

@@ -60,8 +60,18 @@ impl Accounts {
         if writable && !dir.exists() {
             Accounts::create(&dir).await?;
         }
+        let events = Events::new();
+        Accounts::open(events, dir, writable).await
+    }
 
-        Accounts::open(dir, writable).await
+    /// Loads or creates an accounts folder at the given `dir`.
+    /// Uses an existing events channel.
+    pub async fn new_with_events(dir: PathBuf, writable: bool, events: Events) -> Result<Self> {
+        if writable && !dir.exists() {
+            Accounts::create(&dir).await?;
+        }
+
+        Accounts::open(events, dir, writable).await
     }
 
     /// Get the ID used to log events.
@@ -85,14 +95,14 @@ impl Accounts {
 
     /// Opens an existing accounts structure. Will error if the folder doesn't exist,
     /// no account exists and no config exists.
-    async fn open(dir: PathBuf, writable: bool) -> Result<Self> {
+    async fn open(events: Events, dir: PathBuf, writable: bool) -> Result<Self> {
         ensure!(dir.exists(), "directory does not exist");
 
         let config_file = dir.join(CONFIG_NAME);
         ensure!(config_file.exists(), "{config_file:?} does not exist");
 
         let config = Config::from_file(config_file, writable).await?;
-        let events = Events::new();
+
         let stockstrings = StockStrings::new();
         let push_subscriber = PushSubscriber::new();
         let accounts = config