feat: pre-messages / next version of download on demand (#7371)

Closes <https://github.com/chatmail/core/issues/7367>

Co-authored-by: iequidoo <dgreshilov@gmail.com>
Co-authored-by: Hocuri <hocuri@gmx.de>

src/tests/pre_messages/util.rs

@@ -0,0 +1,65 @@
+use anyhow::Result;
+use async_zip::tokio::write::ZipFileWriter;
+use async_zip::{Compression, ZipEntryBuilder};
+use futures::io::Cursor as FuturesCursor;
+use pretty_assertions::assert_eq;
+use tokio_util::compat::FuturesAsyncWriteCompatExt;
+
+use crate::chat::{self, ChatId};
+use crate::download::PRE_MSG_ATTACHMENT_SIZE_THRESHOLD;
+use crate::message::{Message, MsgId, Viewtype};
+use crate::test_utils::{SentMessage, TestContext, create_test_image};
+
+pub async fn send_large_file_message<'a>(
+    sender: &'a TestContext,
+    target_chat: ChatId,
+    view_type: Viewtype,
+    content: &[u8],
+) -> Result<(SentMessage<'a>, SentMessage<'a>, MsgId)> {
+    let mut msg = Message::new(view_type);
+    let file_name = if view_type == Viewtype::Webxdc {
+        "test.xdc"
+    } else {
+        "test.bin"
+    };
+    msg.set_file_from_bytes(sender, file_name, content, None)?;
+    msg.set_text("test".to_owned());
+
+    // assert that test attachment is bigger than limit
+    assert!(msg.get_filebytes(sender).await?.unwrap() > PRE_MSG_ATTACHMENT_SIZE_THRESHOLD);
+
+    let msg_id = chat::send_msg(sender, target_chat, &mut msg).await?;
+    let smtp_rows = sender.get_smtp_rows_for_msg(msg_id).await;
+
+    assert_eq!(smtp_rows.len(), 2);
+    let pre_message = smtp_rows.first().expect("Pre-Message exists");
+    let post_message = smtp_rows.get(1).expect("Post-Message exists");
+    Ok((pre_message.to_owned(), post_message.to_owned(), msg_id))
+}
+
+pub async fn send_large_webxdc_message<'a>(
+    sender: &'a TestContext,
+    target_chat: ChatId,
+) -> Result<(SentMessage<'a>, SentMessage<'a>, MsgId)> {
+    let futures_cursor = FuturesCursor::new(Vec::new());
+    let mut buffer = futures_cursor.compat_write();
+    let mut writer = ZipFileWriter::with_tokio(&mut buffer);
+    writer
+        .write_entry_whole(
+            ZipEntryBuilder::new("index.html".into(), Compression::Stored),
+            &[0u8; 1_000_000],
+        )
+        .await?;
+    writer.close().await?;
+    let big_webxdc_app = buffer.into_inner().into_inner();
+    send_large_file_message(sender, target_chat, Viewtype::Webxdc, &big_webxdc_app).await
+}
+
+pub async fn send_large_image_message<'a>(
+    sender: &'a TestContext,
+    target_chat: ChatId,
+) -> Result<(SentMessage<'a>, SentMessage<'a>, MsgId)> {
+    let (width, height) = (1080, 1920);
+    let test_img = create_test_image(width, height)?;
+    send_large_file_message(sender, target_chat, Viewtype::Image, &test_img).await
+}