diff --git a/proto/backend.proto b/proto/backend.proto
index 00763dede..f9fcbd689 100644
--- a/proto/backend.proto
+++ b/proto/backend.proto
@@ -157,10 +157,13 @@ service BackendService {
     // sync
 
     rpc SyncMedia (SyncMediaIn) returns (Empty);
-    rpc AbortMediaSync (Empty) returns (Empty);
+    rpc AbortSync (Empty) returns (Empty);
     rpc BeforeUpload (Empty) returns (Empty);
-    rpc SyncLogin (SyncLoginIn) returns (SyncLoginOut);
-    rpc SyncCollection (SyncCollectionIn) returns (SyncCollectionOut);
+    rpc SyncLogin (SyncLoginIn) returns (SyncAuth);
+    rpc SyncStatus (SyncAuth) returns (SyncCollectionOut);
+    rpc SyncCollection (SyncAuth) returns (SyncCollectionOut);
+    rpc FullUpload (SyncAuth) returns (Empty);
+    rpc FullDownload (SyncAuth) returns (Empty);
 
     // translation/messages
 
@@ -449,6 +452,7 @@ message Progress {
     oneof value {
         MediaSyncProgress media_sync = 1;
         string media_check = 2;
+        FullSyncProgress full_sync = 3;
     }
 }
 
@@ -484,6 +488,11 @@ message MediaSyncProgress {
     string removed = 3;
 }
 
+message FullSyncProgress {
+    uint32 transferred = 1;
+    uint32 total = 2;
+}
+
 message MediaSyncUploadProgress {
     uint32 files = 1;
     uint32 deletions = 2;
@@ -884,31 +893,23 @@ message SyncLoginIn {
     string password = 2;
 }
 
-message SyncLoginOut {
-    string hkey = 1;
-}
-
-message SyncCollectionIn {
-    enum SyncAction {
-        CHECK_ONLY = 0;
-        NORMAL_SYNC = 1;
-        UPLOAD = 2;
-        DOWNLOAD = 3;
-    }
-
-    string hkey = 1;
-    uint32 host_number = 2;
-    SyncAction action = 3;
-}
-
 message SyncCollectionOut {
     enum ChangesRequired {
         NO_CHANGES = 0;
         NORMAL_SYNC = 1;
         FULL_SYNC = 2;
+        // local collection has no cards; upload not an option
+        FULL_DOWNLOAD = 3;
+        // remote collection has no cards; download not an option
+        FULL_UPLOAD = 4;
     }
 
-    string host_number = 1;
+    uint32 host_number = 1;
     string server_message = 2;
     ChangesRequired required = 3;
 }
+
+message SyncAuth {
+    string hkey = 1;
+    uint32 host_number = 2;
+}
diff --git a/qt/aqt/mediasync.py b/qt/aqt/mediasync.py
index 7a81b6923..d551fb45d 100644
--- a/qt/aqt/mediasync.py
+++ b/qt/aqt/mediasync.py
@@ -123,7 +123,7 @@ class MediaSyncer:
             return
         self._log_and_notify(tr(TR.SYNC_MEDIA_ABORTING))
         self._want_stop = True
-        self.mw.col.backend.abort_media_sync()
+        self.mw.col.backend.abort_sync()
 
     def is_syncing(self) -> bool:
         return self._syncing
diff --git a/rslib/src/backend/mod.rs b/rslib/src/backend/mod.rs
index 3e67c20ea..02f606f82 100644
--- a/rslib/src/backend/mod.rs
+++ b/rslib/src/backend/mod.rs
@@ -33,6 +33,7 @@ use crate::{
     sched::cutoff::local_minutes_west_for_stamp,
     sched::timespan::{answer_button_time, learning_congrats, studied_today, time_span},
     search::SortMode,
+    sync::{sync_login, FullSyncProgress, SyncActionRequired, SyncAuth, SyncOutput},
     template::RenderedNode,
     text::{extract_av_tags, strip_av_tags, AVTag},
     timestamp::TimestampSecs,
@@ -62,12 +63,13 @@ pub struct Backend {
     progress_callback: Option<ProtoProgressCallback>,
     i18n: I18n,
     server: bool,
-    media_sync_abort: Option<AbortHandle>,
+    sync_abort: Option<AbortHandle>,
 }
 
 enum Progress<'a> {
     MediaSync(&'a MediaSyncProgress),
     MediaCheck(u32),
+    FullSync(&'a FullSyncProgress),
 }
 
 /// Convert an Anki error to a protobuf error.
@@ -924,15 +926,26 @@ impl BackendService for Backend {
     // sync
     //-------------------------------------------------------------------
 
-    fn sync_login(&mut self, input: pb::SyncLoginIn) -> BackendResult<pb::SyncLoginOut> {
-        todo!()
+    fn sync_login(&mut self, input: pb::SyncLoginIn) -> BackendResult<pb::SyncAuth> {
+        self.sync_login_inner(input)
     }
 
-    fn sync_collection(
-        &mut self,
-        input: pb::SyncCollectionIn,
-    ) -> BackendResult<pb::SyncCollectionOut> {
-        todo!()
+    fn sync_status(&mut self, input: pb::SyncAuth) -> BackendResult<pb::SyncCollectionOut> {
+        self.sync_collection_inner(input, true)
+    }
+
+    fn sync_collection(&mut self, input: pb::SyncAuth) -> BackendResult<pb::SyncCollectionOut> {
+        self.sync_collection_inner(input, false)
+    }
+
+    fn full_upload(&mut self, input: pb::SyncAuth) -> BackendResult<Empty> {
+        self.full_sync_inner(input, true)?;
+        Ok(().into())
+    }
+
+    fn full_download(&mut self, input: pb::SyncAuth) -> BackendResult<Empty> {
+        self.full_sync_inner(input, false)?;
+        Ok(().into())
     }
 
     fn sync_media(&mut self, input: SyncMediaIn) -> BackendResult<Empty> {
@@ -954,8 +967,8 @@ impl BackendService for Backend {
         res.map(Into::into)
     }
 
-    fn abort_media_sync(&mut self, _input: Empty) -> BackendResult<Empty> {
-        if let Some(handle) = self.media_sync_abort.take() {
+    fn abort_sync(&mut self, _input: Empty) -> BackendResult<Empty> {
+        if let Some(handle) = self.sync_abort.take() {
             handle.abort();
         }
         Ok(().into())
@@ -1090,7 +1103,7 @@ impl Backend {
             progress_callback: None,
             i18n,
             server,
-            media_sync_abort: None,
+            sync_abort: None,
         }
     }
 
@@ -1148,7 +1161,7 @@ impl Backend {
         log: Logger,
     ) -> Result<()> {
         let (abort_handle, abort_reg) = AbortHandle::new_pair();
-        self.media_sync_abort = Some(abort_handle);
+        self.sync_abort = Some(abort_handle);
 
         let callback = |progress: &MediaSyncProgress| {
             self.fire_progress_callback(Progress::MediaSync(progress))
@@ -1165,10 +1178,112 @@ impl Backend {
                 Err(AnkiError::Interrupted)
             }
         };
-        self.media_sync_abort = None;
+        self.sync_abort = None;
         ret
     }
 
+    fn sync_login_inner(&mut self, input: pb::SyncLoginIn) -> BackendResult<pb::SyncAuth> {
+        let (abort_handle, abort_reg) = AbortHandle::new_pair();
+        self.sync_abort = Some(abort_handle);
+
+        let mut rt = Runtime::new().unwrap();
+        let sync_fut = sync_login(&input.username, &input.password);
+        let abortable_sync = Abortable::new(sync_fut, abort_reg);
+        let ret = match rt.block_on(abortable_sync) {
+            Ok(sync_result) => sync_result,
+            Err(_) => Err(AnkiError::Interrupted),
+        };
+        self.sync_abort = None;
+        ret.map(|a| pb::SyncAuth {
+            hkey: a.hkey,
+            host_number: a.host_number,
+        })
+    }
+
+    fn sync_collection_inner(
+        &mut self,
+        input: pb::SyncAuth,
+        check_only: bool,
+    ) -> BackendResult<pb::SyncCollectionOut> {
+        let (abort_handle, abort_reg) = AbortHandle::new_pair();
+        self.sync_abort = Some(abort_handle);
+
+        let mut rt = Runtime::new().unwrap();
+
+        let ret = self.with_col(|col| {
+            let result = if check_only {
+                let sync_fut = col.get_sync_status(input.into());
+                let abortable_sync = Abortable::new(sync_fut, abort_reg);
+                rt.block_on(abortable_sync)
+            } else {
+                let sync_fut = col.normal_sync(input.into());
+                let abortable_sync = Abortable::new(sync_fut, abort_reg);
+                rt.block_on(abortable_sync)
+            };
+            match result {
+                Ok(sync_result) => sync_result,
+                Err(_) => Err(AnkiError::Interrupted),
+            }
+        });
+        self.sync_abort = None;
+        let output: SyncOutput = ret?;
+        Ok(output.into())
+    }
+
+    fn full_sync_inner(&mut self, input: pb::SyncAuth, upload: bool) -> Result<()> {
+        let mut col = self.col.lock().unwrap();
+        if col.is_none() {
+            return Err(AnkiError::CollectionNotOpen);
+        }
+        if !col.as_ref().unwrap().can_close() {
+            return Err(AnkiError::invalid_input("can't close yet"));
+        }
+
+        let col_inner = col.take().unwrap();
+
+        let (abort_handle, abort_reg) = AbortHandle::new_pair();
+        self.sync_abort = Some(abort_handle);
+
+        let col_path = col_inner.col_path.clone();
+        let media_folder_path = col_inner.media_folder.clone();
+        let media_db_path = col_inner.media_db.clone();
+        let logger = col_inner.log.clone();
+
+        // FIXME: throttle
+        let progress_fn = |progress: &FullSyncProgress| {
+            self.fire_progress_callback(Progress::FullSync(progress));
+        };
+
+        let mut rt = Runtime::new().unwrap();
+
+        let result = if upload {
+            todo!()
+        // let sync_fut = col_inner.full_upload(input.into(), progress_fn);
+        // let abortable_sync = Abortable::new(sync_fut, abort_reg);
+        // rt.block_on(abortable_sync)
+        } else {
+            let sync_fut = col_inner.full_download(input.into(), progress_fn);
+            let abortable_sync = Abortable::new(sync_fut, abort_reg);
+            rt.block_on(abortable_sync)
+        };
+        self.sync_abort = None;
+
+        // ensure re-opened regardless of outcome
+        col.replace(open_collection(
+            col_path,
+            media_folder_path,
+            media_db_path,
+            self.server,
+            self.i18n.clone(),
+            logger,
+        )?);
+
+        match result {
+            Ok(sync_result) => sync_result,
+            Err(_) => Err(AnkiError::Interrupted),
+        }
+    }
+
     pub fn db_command(&self, input: &[u8]) -> Result<String> {
         self.with_col(|col| db_command_bytes(&col.storage, input))
     }
@@ -1230,6 +1345,10 @@ fn progress_to_proto_bytes(progress: Progress, i18n: &I18n) -> Vec<u8> {
                 let s = i18n.trn(TR::MediaCheckChecked, tr_args!["count"=>n]);
                 pb::progress::Value::MediaCheck(s)
             }
+            Progress::FullSync(p) => pb::progress::Value::FullSync(pb::FullSyncProgress {
+                transferred: p.transferred_bytes as u32,
+                total: p.total_bytes as u32,
+            }),
         }),
     };
 
@@ -1332,3 +1451,32 @@ impl From<crate::sched::cutoff::SchedTimingToday> for pb::SchedTimingTodayOut {
         }
     }
 }
+
+impl From<SyncOutput> for pb::SyncCollectionOut {
+    fn from(o: SyncOutput) -> Self {
+        pb::SyncCollectionOut {
+            host_number: o.host_number,
+            server_message: o.server_message,
+            required: match o.required {
+                SyncActionRequired::NoChanges => {
+                    pb::sync_collection_out::ChangesRequired::NoChanges as i32
+                }
+                SyncActionRequired::FullSyncRequired => {
+                    pb::sync_collection_out::ChangesRequired::FullSync as i32
+                }
+                SyncActionRequired::NormalSyncRequired => {
+                    pb::sync_collection_out::ChangesRequired::NormalSync as i32
+                }
+            },
+        }
+    }
+}
+
+impl From<pb::SyncAuth> for SyncAuth {
+    fn from(a: pb::SyncAuth) -> Self {
+        SyncAuth {
+            hkey: a.hkey,
+            host_number: a.host_number,
+        }
+    }
+}
diff --git a/rslib/src/storage/card/mod.rs b/rslib/src/storage/card/mod.rs
index dc5a48158..378f1212a 100644
--- a/rslib/src/storage/card/mod.rs
+++ b/rslib/src/storage/card/mod.rs
@@ -123,7 +123,6 @@ impl super::SqliteStorage {
 
     /// Add or update card, using the provided ID. Used when syncing.
     pub(crate) fn add_or_update_card(&self, card: &Card) -> Result<()> {
-        let now = TimestampMillis::now().0;
         let mut stmt = self.db.prepare_cached(include_str!("add_or_update.sql"))?;
         stmt.execute(params![
             card.id,
@@ -226,11 +225,6 @@ impl super::SqliteStorage {
         new_usn: Usn,
         limit: usize,
     ) -> Result<Vec<CardEntry>> {
-        let mut out = vec![];
-        if limit == 0 {
-            return Ok(out);
-        }
-
         let entries: Vec<CardEntry> = self
             .db
             .prepare_cached(concat!(
@@ -241,11 +235,12 @@ impl super::SqliteStorage {
                 row_to_card(r).map(Into::into).map_err(Into::into)
             })?
             .collect::<Result<_>>()?;
-
-        let ids: Vec<_> = entries.iter().map(|e| e.id).collect();
-        self.db
-            .prepare_cached("update cards set usn=? where usn=-1")?
-            .execute(&[new_usn])?;
+        let mut stmt = self
+            .db
+            .prepare_cached("update cards set usn=? where id=?")?;
+        for entry in &entries {
+            stmt.execute(params![new_usn, entry.id])?;
+        }
 
         Ok(entries)
     }
diff --git a/rslib/src/storage/mod.rs b/rslib/src/storage/mod.rs
index 2cd8da66e..8560f777c 100644
--- a/rslib/src/storage/mod.rs
+++ b/rslib/src/storage/mod.rs
@@ -10,6 +10,7 @@ mod note;
 mod notetype;
 mod revlog;
 mod sqlite;
+mod sync_check;
 mod tag;
 mod upgrades;
 
diff --git a/rslib/src/storage/note/mod.rs b/rslib/src/storage/note/mod.rs
index 1ffbccf21..1fe0ee6e6 100644
--- a/rslib/src/storage/note/mod.rs
+++ b/rslib/src/storage/note/mod.rs
@@ -83,7 +83,6 @@ impl super::SqliteStorage {
 
     /// Add or update the provided note, preserving ID. Used by the syncing code.
     pub(crate) fn add_or_update_note(&self, note: &Note) -> Result<()> {
-        let now = TimestampMillis::now().0;
         let mut stmt = self.db.prepare_cached(include_str!("add_or_update.sql"))?;
         stmt.execute(params![
             note.id,
@@ -139,21 +138,17 @@ impl super::SqliteStorage {
         new_usn: Usn,
         limit: usize,
     ) -> Result<Vec<NoteEntry>> {
-        let mut out = vec![];
-        if limit == 0 {
-            return Ok(out);
-        }
-
         let entries: Vec<NoteEntry> = self
             .db
             .prepare_cached(concat!(include_str!("get.sql"), " where usn=-1 limit ?"))?
             .query_and_then(&[limit as u32], |r| row_to_note(r).map(Into::into))?
             .collect::<Result<_>>()?;
-
-        let ids: Vec<_> = entries.iter().map(|e| e.id).collect();
-        self.db
-            .prepare_cached("update notes set usn=? where usn=-1")?
-            .execute(&[new_usn])?;
+        let mut stmt = self
+            .db
+            .prepare_cached("update notes set usn=? where id=?")?;
+        for entry in &entries {
+            stmt.execute(params![new_usn, entry.id])?;
+        }
 
         Ok(entries)
     }
diff --git a/rslib/src/storage/revlog/mod.rs b/rslib/src/storage/revlog/mod.rs
index e1faa00c9..84af63b61 100644
--- a/rslib/src/storage/revlog/mod.rs
+++ b/rslib/src/storage/revlog/mod.rs
@@ -43,11 +43,6 @@ impl SqliteStorage {
         new_usn: Usn,
         limit: usize,
     ) -> Result<Vec<ReviewLogEntry>> {
-        let mut out = vec![];
-        if limit == 0 {
-            return Ok(out);
-        }
-
         let entries: Vec<ReviewLogEntry> = self
             .db
             .prepare_cached(concat!(include_str!("get.sql"), " where usn=-1 limit ?"))?
@@ -66,10 +61,12 @@ impl SqliteStorage {
             })?
             .collect::<Result<_>>()?;
 
-        let ids: Vec<_> = entries.iter().map(|e| e.id).collect();
-        self.db
-            .prepare_cached("update revlog set usn=? where usn=-1")?
-            .execute(&[new_usn])?;
+        let mut stmt = self
+            .db
+            .prepare_cached("update revlog set usn=? where id=?")?;
+        for entry in &entries {
+            stmt.execute(params![new_usn, entry.id])?;
+        }
 
         Ok(entries)
     }
diff --git a/rslib/src/storage/sync_check.rs b/rslib/src/storage/sync_check.rs
new file mode 100644
index 000000000..80afc3ec4
--- /dev/null
+++ b/rslib/src/storage/sync_check.rs
@@ -0,0 +1,60 @@
+// Copyright: Ankitects Pty Ltd and contributors
+// License: GNU AGPL, version 3 or later; http://www.gnu.org/licenses/agpl.html
+
+use super::*;
+use crate::{
+    err::SyncErrorKind,
+    prelude::*,
+    sync::{SanityCheckCounts, SanityCheckDueCounts},
+};
+use rusqlite::NO_PARAMS;
+
+impl SqliteStorage {
+    fn table_has_usn(&self, table: &str) -> Result<bool> {
+        Ok(self
+            .db
+            .prepare(&format!("select null from {} where usn=-1", table))?
+            .query(NO_PARAMS)?
+            .next()?
+            .is_some())
+    }
+
+    fn table_count(&self, table: &str) -> Result<u32> {
+        self.db
+            .query_row(&format!("select count() from {}", table), NO_PARAMS, |r| {
+                r.get(0)
+            })
+            .map_err(Into::into)
+    }
+
+    pub(crate) fn sanity_check_info(&self) -> Result<SanityCheckCounts> {
+        for table in &[
+            "cards",
+            "notes",
+            "revlog",
+            "graves",
+            "decks",
+            "deck_config",
+            "tags",
+            "notetypes",
+        ] {
+            if self.table_has_usn(table)? {
+                return Err(AnkiError::SyncError {
+                    info: format!("table had usn=-1: {}", table),
+                    kind: SyncErrorKind::Other,
+                });
+            }
+        }
+
+        Ok(SanityCheckCounts {
+            counts: SanityCheckDueCounts::default(),
+            cards: self.table_count("cards")?,
+            notes: self.table_count("notes")?,
+            revlog: self.table_count("revlog")?,
+            graves: self.table_count("graves")?,
+            notetypes: self.table_count("notetypes")?,
+            decks: self.table_count("decks")?,
+            deck_config: self.table_count("deck_config")?,
+        })
+    }
+}
diff --git a/rslib/src/sync/http_client.rs b/rslib/src/sync/http_client.rs
index 089f61b8f..55ca3d672 100644
--- a/rslib/src/sync/http_client.rs
+++ b/rslib/src/sync/http_client.rs
@@ -69,20 +69,21 @@ struct ApplyChunkIn {
 #[derive(Serialize, Deserialize, Debug)]
 struct SanityCheckIn {
     client: SanityCheckCounts,
+    full: bool,
 }
 
 #[derive(Serialize)]
 struct Empty {}
 
 impl HTTPSyncClient {
-    pub fn new<'a>(hkey: Option<String>, endpoint_suffix: &str) -> HTTPSyncClient {
+    pub fn new<'a>(hkey: Option<String>, host_number: u32) -> HTTPSyncClient {
         let client = Client::builder()
             .connect_timeout(Duration::from_secs(30))
             .timeout(Duration::from_secs(60))
             .build()
             .unwrap();
         let skey = guid();
-        let endpoint = endpoint(&endpoint_suffix);
+        let endpoint = sync_endpoint(host_number);
         HTTPSyncClient {
             hkey,
             skey,
@@ -204,7 +205,7 @@ impl HTTPSyncClient {
     }
 
     pub(crate) async fn sanity_check(&self, client: SanityCheckCounts) -> Result<SanityCheckOut> {
-        let input = SanityCheckIn { client };
+        let input = SanityCheckIn { client, full: true };
         self.json_request_deserialized("sanityCheck2", &input).await
     }
 
@@ -319,10 +320,15 @@ where
     }
 }
 
-fn endpoint(suffix: &str) -> String {
+fn sync_endpoint(host_number: u32) -> String {
     if let Ok(endpoint) = std::env::var("SYNC_ENDPOINT") {
         endpoint
     } else {
+        let suffix = if host_number > 0 {
+            format!("{}", host_number)
+        } else {
+            "".to_string()
+        };
         format!("https://sync{}.ankiweb.net/sync/", suffix)
     }
 }
@@ -334,7 +340,7 @@ mod test {
     use tokio::runtime::Runtime;
 
     async fn http_client_inner(username: String, password: String) -> Result<()> {
-        let mut syncer = HTTPSyncClient::new(None, "");
+        let mut syncer = HTTPSyncClient::new(None, 0);
 
         assert!(matches!(
             syncer.login("nosuchuser", "nosuchpass").await,
@@ -346,7 +352,7 @@ mod test {
 
         assert!(syncer.login(&username, &password).await.is_ok());
 
-        syncer.meta().await?;
+        let _meta = syncer.meta().await?;
 
         // aborting before a start is a conflict
         assert!(matches!(
@@ -393,7 +399,8 @@ mod test {
             })
             .await?;
 
-        syncer.finish().await?;
+        // failed sanity check will have cleaned up; can't finish
+        // syncer.finish().await?;
 
         use tempfile::tempdir;
 
diff --git a/rslib/src/sync/mod.rs b/rslib/src/sync/mod.rs
index e328d30ef..f2006e957 100644
--- a/rslib/src/sync/mod.rs
+++ b/rslib/src/sync/mod.rs
@@ -44,7 +44,9 @@ pub struct SyncMeta {
     #[serde(rename = "cont")]
     should_continue: bool,
     #[serde(rename = "hostNum")]
-    shard_number: u32,
+    host_number: u32,
+    #[serde(default)]
+    empty: bool,
 }
 
 #[derive(Serialize, Deserialize, Debug, Default)]
@@ -159,68 +161,80 @@ enum SanityCheckStatus {
 
 #[derive(Serialize_tuple, Deserialize, Debug)]
 pub struct SanityCheckCounts {
-    counts: SanityCheckDueCounts,
-    cards: u32,
-    notes: u32,
-    revlog: u32,
-    graves: u32,
+    pub counts: SanityCheckDueCounts,
+    pub cards: u32,
+    pub notes: u32,
+    pub revlog: u32,
+    pub graves: u32,
     #[serde(rename = "models")]
-    notetypes: u32,
-    decks: u32,
-    deck_config: u32,
+    pub notetypes: u32,
+    pub decks: u32,
+    pub deck_config: u32,
 }
 
-#[derive(Serialize_tuple, Deserialize, Debug)]
+#[derive(Serialize_tuple, Deserialize, Debug, Default)]
 pub struct SanityCheckDueCounts {
-    new: u32,
-    learn: u32,
-    review: u32,
+    pub new: u32,
+    pub learn: u32,
+    pub review: u32,
 }
 
 #[derive(Debug, Default)]
 pub struct FullSyncProgress {
-    transferred_bytes: usize,
-    total_bytes: usize,
+    pub transferred_bytes: usize,
+    pub total_bytes: usize,
 }
 
-pub enum SyncState {
+#[derive(PartialEq)]
+pub enum SyncActionRequired {
     NoChanges,
     FullSyncRequired,
-    NormalSyncRequired(NormalSyncMeta),
+    NormalSyncRequired,
 }
 
-pub struct NormalSyncMeta {
+struct SyncState {
+    required: SyncActionRequired,
     local_is_newer: bool,
     local_usn: Usn,
     remote_usn: Usn,
     server_message: String,
-    shard_number: u32,
+    host_number: u32,
 }
 
-struct SyncDriver<'a> {
+pub struct SyncOutput {
+    pub required: SyncActionRequired,
+    pub server_message: String,
+    pub host_number: u32,
+}
+
+pub struct SyncAuth {
+    pub hkey: String,
+    pub host_number: u32,
+}
+
+struct NormalSyncer<'a> {
     col: &'a mut Collection,
     remote: HTTPSyncClient,
 }
 
-impl SyncDriver<'_> {
-    async fn from_login<'a>(
-        col: &'a mut Collection,
-        username: &str,
-        password: &str,
-    ) -> Result<SyncDriver<'a>> {
-        let mut remote = HTTPSyncClient::new(None, "");
-        remote.login(username, password).await?;
-        Ok(SyncDriver { col, remote })
+impl NormalSyncer<'_> {
+    /// Create a new syncing instance. If host_number is unavailable, use 0.
+    pub fn new<'a>(col: &'a mut Collection, auth: SyncAuth) -> NormalSyncer<'a> {
+        NormalSyncer {
+            col,
+            remote: HTTPSyncClient::new(Some(auth.hkey), auth.host_number),
+        }
     }
 
-    fn from_hkey<'a>(
-        col: &'a mut Collection,
-        hkey: String,
-        endpoint_suffix: &str,
-    ) -> SyncDriver<'a> {
-        SyncDriver {
-            col,
-            remote: HTTPSyncClient::new(Some(hkey), endpoint_suffix),
+    pub async fn sync(&mut self) -> Result<SyncOutput> {
+        let state: SyncState = self.get_sync_state().await?;
+        match state.required {
+            SyncActionRequired::NoChanges => Ok(state.into()),
+            SyncActionRequired::FullSyncRequired => Ok(state.into()),
+            SyncActionRequired::NormalSyncRequired => {
+                // fixme: transaction
+                self.normal_sync_inner(state).await
+            }
         }
     }
 
@@ -242,61 +256,57 @@ impl SyncDriver<'_> {
             });
         }
 
-        if remote.modified == local.modified {
-            return Ok(SyncState::NoChanges);
-        }
+        let required = if remote.modified == local.modified {
+            SyncActionRequired::NoChanges
+        } else if remote.schema != local.schema {
+            SyncActionRequired::FullSyncRequired
+        } else {
+            SyncActionRequired::NormalSyncRequired
+        };
 
-        if remote.schema != local.schema {
-            return Ok(SyncState::FullSyncRequired);
-        }
-
-        Ok(SyncState::NormalSyncRequired(NormalSyncMeta {
+        Ok(SyncState {
+            required,
             local_is_newer: local.modified > remote.modified,
             local_usn: local.usn,
             remote_usn: remote.usn,
             server_message: remote.server_message,
-            shard_number: remote.shard_number,
-        }))
+            host_number: remote.host_number,
+        })
     }
 
     /// Sync. Caller must have created a transaction, and should call
-    /// abort on
-    pub(crate) async fn sync(&mut self, meta: NormalSyncMeta) -> Result<()> {
-        self.col.basic_check_for_sync()?;
-        self.start_and_process_deletions(&meta).await?;
-        self.process_unchunked_changes(meta.remote_usn, meta.local_is_newer)
+    /// abort on failure.
+    async fn normal_sync_inner(&mut self, mut state: SyncState) -> Result<SyncOutput> {
+        self.start_and_process_deletions(&state).await?;
+        self.process_unchunked_changes(state.remote_usn, state.local_is_newer)
             .await?;
         self.process_chunks_from_server().await?;
-        self.send_chunks_to_server(meta.remote_usn).await?;
+        self.send_chunks_to_server(state.remote_usn).await?;
         self.sanity_check().await?;
-        self.finalize(meta).await?;
-        Ok(())
-    }
-
-    /// Return the remote client for use in a full sync.
-    fn into_remote(self) -> HTTPSyncClient {
-        self.remote
+        self.finalize(&state).await?;
+        state.required = SyncActionRequired::NoChanges;
+        Ok(state.into())
     }
 
     // The following operations assume a transaction has been set up.
 
-    async fn start_and_process_deletions(&self, meta: &NormalSyncMeta) -> Result<()> {
+    async fn start_and_process_deletions(&self, state: &SyncState) -> Result<()> {
         let removed_on_remote = self
             .remote
             .start(
-                meta.local_usn,
+                state.local_usn,
                 self.col.get_local_mins_west(),
-                meta.local_is_newer,
+                state.local_is_newer,
             )
             .await?;
 
-        let mut locally_removed = self.col.storage.take_pending_graves(meta.remote_usn)?;
+        let mut locally_removed = self.col.storage.take_pending_graves(state.remote_usn)?;
 
         while let Some(chunk) = locally_removed.take_chunk() {
             self.remote.apply_graves(chunk).await?;
         }
 
-        self.col.apply_graves(removed_on_remote, meta.local_usn)?;
+        self.col.apply_graves(removed_on_remote, state.local_usn)?;
 
         Ok(())
     }
@@ -343,7 +353,7 @@ impl SyncDriver<'_> {
 
     /// Caller should force full sync after rolling back.
     async fn sanity_check(&self) -> Result<()> {
-        let local_counts = self.col.sanity_check_info()?;
+        let local_counts = self.col.storage.sanity_check_info()?;
         let out: SanityCheckOut = self.remote.sanity_check(local_counts).await?;
         if out.status != SanityCheckStatus::Ok {
             Err(AnkiError::SyncError {
@@ -355,9 +365,9 @@ impl SyncDriver<'_> {
         }
     }
 
-    async fn finalize(&self, meta: NormalSyncMeta) -> Result<()> {
+    async fn finalize(&self, state: &SyncState) -> Result<()> {
         let new_server_mtime = self.remote.finish().await?;
-        self.col.finalize_sync(meta, new_server_mtime)
+        self.col.finalize_sync(state, new_server_mtime)
     }
 }
 
@@ -387,7 +397,70 @@ impl Graves {
     }
 }
 
+pub async fn sync_login(username: &str, password: &str) -> Result<SyncAuth> {
+    let mut remote = HTTPSyncClient::new(None, 0);
+    remote.login(username, password).await?;
+    Ok(SyncAuth {
+        hkey: remote.hkey().to_string(),
+        host_number: 0,
+    })
+}
+
 impl Collection {
+    // fixme: upload only, download only case
+    pub async fn get_sync_status(&mut self, auth: SyncAuth) -> Result<SyncOutput> {
+        NormalSyncer::new(self, auth)
+            .get_sync_state()
+            .await
+            .map(Into::into)
+    }
+
+    pub async fn normal_sync(&mut self, auth: SyncAuth) -> Result<SyncOutput> {
+        // fixme: server abort on failure
+        NormalSyncer::new(self, auth).sync().await
+    }
+
+    /// Upload collection to AnkiWeb. Caller must re-open afterwards.
+    pub async fn full_upload<F>(mut self, auth: SyncAuth, progress_fn: F) -> Result<()>
+    where
+        F: Fn(&FullSyncProgress) + Send + Sync + 'static,
+    {
+        self.before_upload()?;
+        let col_path = self.col_path.clone();
+        self.close(true)?;
+        let mut remote = HTTPSyncClient::new(Some(auth.hkey), auth.host_number);
+        remote.upload(&col_path, progress_fn).await?;
+        Ok(())
+    }
+
+    /// Download collection from AnkiWeb. Caller must re-open afterwards.
+    pub async fn full_download<F>(self, auth: SyncAuth, progress_fn: F) -> Result<()>
+    where
+        F: Fn(&FullSyncProgress),
+    {
+        let col_path = self.col_path.clone();
+        let folder = col_path.parent().unwrap();
+        self.close(false)?;
+        let remote = HTTPSyncClient::new(Some(auth.hkey), auth.host_number);
+        let out_file = remote.download(folder, progress_fn).await?;
+        // check file ok
+        let db = rusqlite::Connection::open(out_file.path())?;
+        let check_result: String = db.pragma_query_value(None, "integrity_check", |r| r.get(0))?;
+        if check_result != "ok" {
+            return Err(AnkiError::SyncError {
+                info: "download corrupt".into(),
+                kind: SyncErrorKind::Other,
+            });
+        }
+        // overwrite existing collection atomically
+        out_file
+            .persist(&col_path)
+            .map_err(|e| AnkiError::IOError {
+                info: format!("download save failed: {}", e),
+            })?;
+        Ok(())
+    }
+
     fn sync_meta(&self) -> Result<SyncMeta> {
         Ok(SyncMeta {
             modified: self.storage.get_modified_time()?,
@@ -396,14 +469,11 @@ impl Collection {
             current_time: TimestampSecs::now(),
             server_message: "".into(),
             should_continue: true,
-            shard_number: 0,
+            host_number: 0,
+            empty: false,
         })
     }
 
-    fn basic_check_for_sync(&self) -> Result<()> {
-        todo!();
-    }
-
     fn apply_graves(&self, graves: Graves, local_usn: Usn) -> Result<()> {
         for nid in graves.notes {
             self.storage.remove_note(nid)?;
@@ -438,7 +508,7 @@ impl Collection {
             ..Default::default()
         };
         if local_is_newer {
-            changes.config = Some(todo!());
+            changes.config = Some(self.changed_config()?);
             changes.creation_stamp = Some(self.storage.creation_stamp()?);
         }
 
@@ -476,7 +546,7 @@ impl Collection {
 
     /// Currently this is all config, as legacy clients overwrite the local items
     /// with the provided value.
-    fn changed_config(&self, new_usn: Usn) -> Result<HashMap<String, Value>> {
+    fn changed_config(&self) -> Result<HashMap<String, Value>> {
         let conf = self.storage.get_all_config()?;
         self.storage.clear_config_usns()?;
         Ok(conf)
@@ -502,7 +572,7 @@ impl Collection {
     }
 
     fn merge_notetypes(&mut self, notetypes: Vec<NoteTypeSchema11>) -> Result<()> {
-        for mut nt in notetypes {
+        for nt in notetypes {
             let nt: NoteType = nt.into();
             let proceed = if let Some(existing_nt) = self.storage.get_notetype(nt.id)? {
                 if existing_nt.mtime_secs < nt.mtime_secs {
@@ -530,7 +600,7 @@ impl Collection {
     }
 
     fn merge_decks(&mut self, decks: Vec<DeckSchema11>) -> Result<()> {
-        for mut deck in decks {
+        for deck in decks {
             let proceed = if let Some(existing_deck) = self.storage.get_deck(deck.id())? {
                 existing_deck.mtime_secs < deck.common().mtime
             } else {
@@ -546,7 +616,7 @@ impl Collection {
     }
 
     fn merge_deck_config(&self, dconf: Vec<DeckConfSchema11>) -> Result<()> {
-        for mut conf in dconf {
+        for conf in dconf {
             let proceed = if let Some(existing_conf) = self.storage.get_deck_config(conf.id)? {
                 existing_conf.mtime_secs < conf.mtime
             } else {
@@ -655,14 +725,9 @@ impl Collection {
     // Final steps
     //----------------------------------------------------------------
 
-    fn sanity_check_info(&self) -> Result<SanityCheckCounts> {
-        self.basic_check_for_sync()?;
-        todo!();
-    }
-
-    fn finalize_sync(&self, meta: NormalSyncMeta, new_server_mtime: TimestampMillis) -> Result<()> {
+    fn finalize_sync(&self, state: &SyncState, new_server_mtime: TimestampMillis) -> Result<()> {
         self.storage.set_last_sync(new_server_mtime)?;
-        let mut usn = meta.remote_usn;
+        let mut usn = state.remote_usn;
         usn.0 += 1;
         self.storage.set_usn(usn)?;
         self.storage.set_modified_time(new_server_mtime)
@@ -752,3 +817,13 @@ impl From<Note> for NoteEntry {
         }
     }
 }
+
+impl From<SyncState> for SyncOutput {
+    fn from(s: SyncState) -> Self {
+        SyncOutput {
+            required: s.required,
+            server_message: s.server_message,
+            host_number: s.host_number,
+        }
+    }
+}
diff --git a/rspy/src/lib.rs b/rspy/src/lib.rs
index 970db7bef..c423b27b0 100644
--- a/rspy/src/lib.rs
+++ b/rspy/src/lib.rs
@@ -91,7 +91,7 @@ fn want_release_gil(method: u32) -> bool {
             BackendMethod::RestoreTrash => true,
             BackendMethod::OpenCollection => true,
             BackendMethod::CloseCollection => true,
-            BackendMethod::AbortMediaSync => true,
+            BackendMethod::AbortSync => true,
             BackendMethod::BeforeUpload => true,
             BackendMethod::TranslateString => false,
             BackendMethod::FormatTimespan => false,