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api: item/sync: handle sync_token behind cursor_token 

this can happen e.g. the client synchronizes new items but have nothing
new to send back to the server.
This commit is contained in:
Peter Cai 2020-02-22 09:03:27 +08:00
parent 908c62b0a1
commit 915f9893a5
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1 changed files with 33 additions and 4 deletions
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37
src/api.rs
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@ -194,6 +194,8 @@ fn items_sync(db: DbConn, u: user::User, params: Json<SyncParams>) -> Custom<Jso
let mut from_id: Option<i64> = None;
let mut max_id: Option<i64> = None;
let mut had_cursor = false;
// mark if we have a larger sync_token than cursor_token
let mut sync_token_ahead = false;
if let Some(cursor_token) = inner_params.cursor_token {
// If the client provides cursor_token,
@ -211,7 +213,25 @@ fn items_sync(db: DbConn, u: user::User, params: Json<SyncParams>) -> Custom<Jso
} else {
// When we have both a cursor_token and a sync_token,
// we need to always make sure we don't go *beyond* sync_token
max_id = sync_token.parse().ok();
max_id = sync_token.parse().ok()
.and_then(|x| {
if x < from_id.unwrap() {
// If sync_token is smaller than cursor_token
// we don't set a max_id
// we will synchronize the two later after
// items are retrieved.
// We don't need to worry about the case
// where sync_token = cursor_token, because
// in that case we will get empty result,
// and sync_token will get updated anyway
None
} else {
// Tell our program logic later to not update
// sync_token (because it's already ahead)
sync_token_ahead = true;
Some(x)
}
});
}
}
@ -238,9 +258,18 @@ fn items_sync(db: DbConn, u: user::User, params: Json<SyncParams>) -> Custom<Jso
}
}
// Always keep sync_token unchanged in this case
// (this may change later when we save items)
resp.sync_token = inner_params.sync_token;
if sync_token_ahead {
// Always keep sync_token unchanged in this case
// (this may change later when we save items)
resp.sync_token = inner_params.sync_token;
} else {
// If sync_token is not ahead of cursor_token
// (or cursor_token is simply null)
// update it to latest
// Since it's sync_token, we don't need to worry
// about whether we *actually* have anything to fetch
resp.sync_token = Some(next_from.to_string());
}
} else {
if had_cursor {
// If we already have no item to give, but the client still holds a cursor