fix: Correct message viewtype before recoding image blob (#5496)

Otherwise, e.g. if a message is a large GIF, but its viewtype is set to `Image` by the app, this GIF
will be recoded to JPEG to reduce its size. GIFs and other special viewtypes must be always detected
and sent as is.

src/blob.rs

@@ -1330,6 +1330,42 @@ mod tests {
         Ok(img)
     }
 
+    #[tokio::test(flavor = "multi_thread", worker_threads = 2)]
+    async fn test_send_big_gif_as_image() -> Result<()> {
+        let bytes = include_bytes!("../test-data/image/screenshot.gif");
+        let (width, height) = (1920u32, 1080u32);
+        let alice = TestContext::new_alice().await;
+        let bob = TestContext::new_bob().await;
+        alice
+            .set_config(
+                Config::MediaQuality,
+                Some(&(MediaQuality::Worse as i32).to_string()),
+            )
+            .await?;
+        let file = alice.get_blobdir().join("file").with_extension("gif");
+        fs::write(&file, &bytes)
+            .await
+            .context("failed to write file")?;
+        let mut msg = Message::new(Viewtype::Image);
+        msg.set_file(file.to_str().unwrap(), None);
+        let chat = alice.create_chat(&bob).await;
+        let sent = alice.send_msg(chat.id, &mut msg).await;
+        let bob_msg = bob.recv_msg(&sent).await;
+        // DC must detect the image as GIF and send it w/o reencoding.
+        assert_eq!(bob_msg.get_viewtype(), Viewtype::Gif);
+        assert_eq!(bob_msg.get_width() as u32, width);
+        assert_eq!(bob_msg.get_height() as u32, height);
+        let file_saved = bob
+            .get_blobdir()
+            .join("saved-".to_string() + &bob_msg.get_filename().unwrap());
+        bob_msg.save_file(&bob, &file_saved).await?;
+        let blob = BlobObject::new_from_path(&bob, &file_saved).await?;
+        let (file_size, _) = blob.metadata()?;
+        assert_eq!(file_size, bytes.len() as u64);
+        check_image_size(file_saved, width, height);
+        Ok(())
+    }
+
     #[tokio::test(flavor = "multi_thread", worker_threads = 2)]
     async fn test_increation_in_blobdir() -> Result<()> {
         let t = TestContext::new_alice().await;

src/chat.rs

@@ -2505,6 +2505,30 @@ async fn prepare_msg_blob(context: &Context, msg: &mut Message) -> Result<()> {
             .await?
             .with_context(|| format!("attachment missing for message of type #{}", msg.viewtype))?;
 
+        if msg.viewtype == Viewtype::File || msg.viewtype == Viewtype::Image {
+            // Correct the type, take care not to correct already very special
+            // formats as GIF or VOICE.
+            //
+            // Typical conversions:
+            // - from FILE to AUDIO/VIDEO/IMAGE
+            // - from FILE/IMAGE to GIF */
+            if let Some((better_type, _)) = message::guess_msgtype_from_suffix(&blob.to_abs_path())
+            {
+                if better_type != Viewtype::Webxdc
+                    || context
+                        .ensure_sendable_webxdc_file(&blob.to_abs_path())
+                        .await
+                        .is_ok()
+                {
+                    msg.viewtype = better_type;
+                }
+            }
+        } else if msg.viewtype == Viewtype::Webxdc {
+            context
+                .ensure_sendable_webxdc_file(&blob.to_abs_path())
+                .await?;
+        }
+
         let mut maybe_sticker = msg.viewtype == Viewtype::Sticker;
         if msg.viewtype == Viewtype::Image
             || maybe_sticker && !msg.param.exists(Param::ForceSticker)
@@ -2526,34 +2550,6 @@ async fn prepare_msg_blob(context: &Context, msg: &mut Message) -> Result<()> {
                 .set(Param::Filename, stem.to_string() + "." + blob_ext);
         }
 
-        if msg.viewtype == Viewtype::File || msg.viewtype == Viewtype::Image {
-            // Correct the type, take care not to correct already very special
-            // formats as GIF or VOICE.
-            //
-            // Typical conversions:
-            // - from FILE to AUDIO/VIDEO/IMAGE
-            // - from FILE/IMAGE to GIF */
-            if let Some((better_type, better_mime)) =
-                message::guess_msgtype_from_suffix(&blob.to_abs_path())
-            {
-                if better_type != Viewtype::Webxdc
-                    || context
-                        .ensure_sendable_webxdc_file(&blob.to_abs_path())
-                        .await
-                        .is_ok()
-                {
-                    msg.viewtype = better_type;
-                    if !msg.param.exists(Param::MimeType) {
-                        msg.param.set(Param::MimeType, better_mime);
-                    }
-                }
-            }
-        } else if msg.viewtype == Viewtype::Webxdc {
-            context
-                .ensure_sendable_webxdc_file(&blob.to_abs_path())
-                .await?;
-        }
-
         if !msg.param.exists(Param::MimeType) {
             if let Some((_, mime)) = message::guess_msgtype_from_suffix(&blob.to_abs_path()) {
                 msg.param.set(Param::MimeType, mime);