* Add profile to json+ld in Accept
It's required by the ActivityPub spec
* Use headers['Content-type'] instead of mime_type
mime_type strips the profile from the content type, but it's still available raw in the headers hash
* Add test for ld+json with profile
* Do not hide boost notifications from followed people with hidden boosts
Not displaying boosts from a followed user in the Home timeline and not
having notifications when they reblog your own content are two very
separate concerns, tying them together seem counter-intuitive and unwanted.
* Update specs accordingly
* Verify link ownership with rel="me"
* Add explanation about verification to UI
* Perform link verifications
* Add click-to-copy widget for verification HTML
* Redesign edit profile page
* Redesign forms
* Improve responsive design of settings pages
* Restore landing page sign-up form
* Fix typo
* Support <link> tags, add spec
* Fix links not being verified on first discovery and passive updates
* Allow accessing local private/DM messages by URL
(Provided the user pasting the URL is authorized to see the toot, obviously)
* Fix SearchServiceSpec tests
* Send rejections to followers when user hides domain they're on
* Use account domain blocks for "authorized followers" action
Replace soft-blocking (block & unblock) behaviour with follow rejection
* Split sync and async work of account domain blocking
Do not create domain block when removing followers by domain, that
is probably unexpected from the user's perspective.
* Adjust confirmation message for domain block
* yarn manage:translations
* No need to re-require sidekiq plugins, they are required via Gemfile
* Add derailed_benchmarks tool, no need to require TTY gems in Gemfile
* Replace ruby-oembed with FetchOEmbedService
Reduce startup by 45382 allocated objects
* Remove preloaded JSON-LD in favour of caching HTTP responses
Reduce boot RAM by about 6 MiB
* Fix tests
* Fix test suite by stubbing out JSON-LD contexts
* Add equals_or_includes_any? helper in JsonLdHelper
* Support arrays in JSON-LD type fields for actors/tags/objects.
* Spec for resolving accounts with extension types
* Style tweaks for codeclimate
* Add bio fields
- Fix#3211
- Fix#232
- Fix#121
* Display bio fields in web UI
* Fix output of links and missing fields
* Federate bio fields over ActivityPub as PropertyValue
* Improve how the fields are stored, add to Edit profile form
* Add rel=me to links in fields
Fix#121
A complemental change for precompute_feed_service_spec.rb also fixes its
random failure which is caused by the Snowlake randomization of the order
of an original status and its reblog.
In cases where a URL has a trailing hyphen the FetchLinkCardService incorrectly removes the hyphen when it is parsed
The hyphen is not a reserved character in the URI spec https://tools.ietf.org/html/rfc3986#section-2.2
* When must_be_following_dm is on, only notify if recipient dm'ed user
Currently, when must_be_following_dm is on, if a user sends a direct
message replying to any status from the recipient, the recipient gets a
notification. This should not be the case, as if the recipient posted
something publicly this can be used to spam their notifications.
* Refactor replied_to_status_is_direct_message?
Following suggestion in PR
* Fix actors accepting invalid URI schemes or different host between URI and URL
* Fix statuses accepting invalid URI scheme or different host to actor
* Adjust tests to new requirements
* Improve readability of mismatching_origin?/invalid_origin? methods
* Add list of lists component to web UI
* Add list adding
* Add list removing
* List editor modal
* Add API account search limited by following=true relation
* Rework list editor modal
* Remove mandatory pagination of GET /api/v1/lists/:id/accounts
* Adjust search input placeholder
* Fix rspec (#5890)
* i18n: (zh-CN) Add missing translations for #5811 (#5891)
* i18n: (zh-CN) yarn manage:translations -- zh-CN
* i18n: (zh-CN) Add missing translations for #5811
* Fix some issues
- Display loading/missing state for list timelines
- Order lists alphabetically in overview
- Fix async list editor reset
- Redirect to /lists after deleting unpinned list
- Redirect to / after pinning a list
* Remove dead list columns when a list is deleted or fetch returns 404
* Add semi-support for Video/Image objects in ActivityPub
Video and Image objects will create corresponding status records
with manually crafted text contents (title + URL)
* Extract html-url-finding logic into JsonLdHelper
* Fallback to id when url missing, extract supported object types
* Allow hiding of reblogs from followed users
This adds a new entry to the account menu to allow users to hide
future reblogs from a user (and then if they've done that, to show
future reblogs instead).
This does not remove or add historical reblogs from/to the user's
timeline; it only affects new statuses.
The API for this operates by sending a "reblogs" key to the follow
endpoint. If this is sent when starting a new follow, it will be
respected from the beginning of the follow relationship (even if
the follow request must be approved by the followee). If this is
sent when a follow relationship already exists, it will simply
update the existing follow relationship. As with the notification
muting, this will now return an object ({reblogs: [true|false]}) or
false for each follow relationship when requesting relationship
information for an account. This should cause few issues due to an
object being truthy in many languages, but some modifications may
need to be made in pickier languages.
Database changes: adds a show_reblogs column (default true,
non-nullable) to the follows and follow_requests tables. Because
these are non-nullable, we use the existing MigrationHelpers to
perform this change without locking those tables, although the
tables are likely to be small anyway.
Tests included.
See also <https://github.com/glitch-soc/mastodon/pull/212>.
* Rubocop fixes
* Code review changes
* Test fixes
This patchset closes#648 and resolves#3271.
* Rubocop fix
* Revert reblogs defaulting in argument, fix tests
It turns out we needed this for the same reason we needed it in muting:
if nil gets passed in somehow (most usually by an API client not passing
any value), we need to detect and handle it.
We could specify a default in the parameter and then also catch nil, but
there's no great reason to duplicate the default value.
* Add test for temporary account resolving failures in ProcessMentionsService
* Fix processing of mentions to already-known remote accounts on temporary failures
* Add structure for lists
* Add list timeline streaming API
* Add list APIs, bind list-account relation to follow relation
* Add API for adding/removing accounts from lists
* Add pagination to lists API
* Add pagination to list accounts API
* Adjust scopes for new APIs
- Creating and modifying lists merely requires "write" scope
- Fetching information about lists merely requires "read" scope
* Add test for wrong user context on list timeline
* Clean up tests
* Add a hide_notifications column to mutes
* Add muting_notifications? and a notifications argument to mute!
* block notifications in notify_service from hard muted accounts
* Add specs for how mute! interacts with muting_notifications?
* specs testing that hide_notifications in mutes actually hides notifications
* Add support for muting notifications in MuteService
* API support for muting notifications (and specs)
* Less gross passing of notifications flag
* Break out a separate mute modal with a hide-notifications checkbox.
* Convert profile header mute to use mute modal
* Satisfy eslint.
* specs for MuteService notifications params
* add trailing newlines to files for Pork :)
* Put the label for the hide notifications checkbox in a label element.
* Add a /api/v1/mutes/details route that just returns the array of mutes.
* Define a serializer for /api/v1/mutes/details
* Add more specs for the /api/v1/mutes/details endpoint
* Expose whether a mute hides notifications in the api/v1/relationships endpoint
* Show whether muted users' notifications are muted in account lists
* Allow modifying the hide_notifications of a mute with the /api/v1/accounts/:id/mute endpoint
* make the hide/unhide notifications buttons work
* satisfy eslint
* In probably dead code, replace a dispatch of muteAccount that was skipping the modal with launching the mute modal.
* fix a missing import
* add an explanatory comment to AccountInteractions
* Refactor handling of default params for muting to make code cleaner
* minor code style fixes oops
* Fixed a typo that was breaking the account mute API endpoint
* Apply white-space: nowrap to account relationships icons
* Fix code style issues
* Remove superfluous blank line
* Rename /api/v1/mutes/details -> /api/v2/mutes
* Don't serialize "account" in MuteSerializer
Doing so is somewhat unnecessary since it's always the current user's account.
* Fix wrong variable name in api/v2/mutes
* Use Toggle in place of checkbox in the mute modal.
* Make the Toggle in the mute modal look better
* Code style changes in specs and removed an extra space
* Code review suggestions from akihikodaki
Also fixed a syntax error in tests for AccountInteractions.
* Make AddHideNotificationsToMute Concurrent
It's not clear how much this will benefit instances in practice, as the
number of mutes tends to be pretty small, but this should prevent any
blocking migrations nonetheless.
* Fix up migration things
* Remove /api/v2/mutes
* Add option to block direct messages from people you don't follow
Fix#5326
* If the DM responds to a toot by recipient, allow it through
* i18n: Update Polish translation (for #5669) (#5673)
* Retoot count increases without reason
-The store_uri method for Statuses was being called on after_create and causing reblogs to be incremented twice.
-This calls it when the transaction is finished by using after_create_commit.
-Fixes #4916.
* Added test case for after_create_commit callback for checking reblog count.
* Rewrote test to keep original, but added one for only the after_create_commit callback.
- Rename Mastodon::TimestampIds into Mastodon::Snowflake for clarity
- Skip for statuses coming from inbox, aka delivered in real-time
- Skip for statuses that claim to be from the future
* Use non-serial IDs
This change makes a number of nontrivial tweaks to the data model in
Mastodon:
* All IDs are now 8 byte integers (rather than mixed 4- and 8-byte)
* IDs are now assigned as:
* Top 6 bytes: millisecond-resolution time from epoch
* Bottom 2 bytes: serial (within the millisecond) sequence number
* See /lib/tasks/db.rake's `define_timestamp_id` for details, but
note that the purpose of these changes is to make it difficult to
determine the number of objects in a table from the ID of any
object.
* The Redis sorted set used for the feed will have values used to look
up toots, rather than scores. This is almost always the same as the
existing behavior, except in the case of boosted toots. This change
was made because Redis stores scores as double-precision floats,
which cannot store the new ID format exactly. Note that this doesn't
cause problems with sorting/pagination, because ZREVRANGEBYSCORE
sorts lexicographically when scores are tied. (This will still cause
sorting issues when the ID gains a new significant digit, but that's
extraordinarily uncommon.)
Note a couple of tradeoffs have been made in this commit:
* lib/tasks/db.rake is used to enforce many/most column constraints,
because this commit seems likely to take a while to bring upstream.
Enforcing a post-migrate hook is an easier way to maintain the code
in the interim.
* Boosted toots will appear in the timeline as many times as they have
been boosted. This is a tradeoff due to the way the feed is saved in
Redis at the moment, but will be handled by a future commit.
This would effectively close Mastodon's #1059, as it is a
snowflake-like system of generating IDs. However, given how involved
the changes were simply within Mastodon, it may have unexpected
interactions with some clients, if they store IDs as doubles
(or as 4-byte integers). This was a problem that Twitter ran into with
their "snowflake" transition, particularly in JavaScript clients that
treated IDs as JS integers, rather than strings. It therefore would be
useful to test these changes at least in the web interface and popular
clients before pushing them to all users.
* Fix JavaScript interface with long IDs
Somewhat predictably, the JS interface handled IDs as numbers, which in
JS are IEEE double-precision floats. This loses some precision when
working with numbers as large as those generated by the new ID scheme,
so we instead handle them here as strings. This is relatively simple,
and doesn't appear to have caused any problems, but should definitely
be tested more thoroughly than the built-in tests. Several days of use
appear to support this working properly.
BREAKING CHANGE:
The major(!) change here is that IDs are now returned as strings by the
REST endpoints, rather than as integers. In practice, relatively few
changes were required to make the existing JS UI work with this change,
but it will likely hit API clients pretty hard: it's an entirely
different type to consume. (The one API client I tested, Tusky, handles
this with no problems, however.)
Twitter ran into this issue when introducing Snowflake IDs, and decided
to instead introduce an `id_str` field in JSON responses. I have opted
to *not* do that, and instead force all IDs to 64-bit integers
represented by strings in one go. (I believe Twitter exacerbated their
problem by rolling out the changes three times: once for statuses, once
for DMs, and once for user IDs, as well as by leaving an integer ID
value in JSON. As they said, "If you’re using the `id` field with JSON
in a Javascript-related language, there is a very high likelihood that
the integers will be silently munged by Javascript interpreters. In most
cases, this will result in behavior such as being unable to load or
delete a specific direct message, because the ID you're sending to the
API is different than the actual identifier associated with the
message." [1]) However, given that this is a significant change for API
users, alternatives or a transition time may be appropriate.
1: https://blog.twitter.com/developer/en_us/a/2011/direct-messages-going-snowflake-on-sep-30-2011.html
* Restructure feed pushes/unpushes
This was necessary because the previous behavior used Redis zset scores
to identify statuses, but those are IEEE double-precision floats, so we
can't actually use them to identify all 64-bit IDs. However, it leaves
the code in a much better state for refactoring reblog handling /
coalescing.
Feed-management code has been consolidated in FeedManager, including:
* BatchedRemoveStatusService no longer directly manipulates feed zsets
* RemoveStatusService no longer directly manipulates feed zsets
* PrecomputeFeedService has moved its logic to FeedManager#populate_feed
(PrecomputeFeedService largely made lots of calls to FeedManager, but
didn't follow the normal adding-to-feed process.)
This has the effect of unifying all of the feed push/unpush logic in
FeedManager, making it much more tractable to update it in the future.
Due to some additional checks that must be made during, for example,
batch status removals, some Redis pipelining has been removed. It does
not appear that this should cause significantly increased load, but if
necessary, some optimizations are possible in batch cases. These were
omitted in the pursuit of simplicity, but a batch_push and batch_unpush
would be possible in the future.
Tests were added to verify that pushes happen under expected conditions,
and to verify reblog behavior (both on pushing and unpushing). In the
case of unpushing, this includes testing behavior that currently leads
to confusion such as Mastodon's #2817, but this codifies that the
behavior is currently expected.
* Rubocop fixes
I could swear I made these changes already, but I must have lost them
somewhere along the line.
* Address review comments
This addresses the first two comments from review of this feature:
https://github.com/tootsuite/mastodon/pull/4801#discussion_r139336735https://github.com/tootsuite/mastodon/pull/4801#discussion_r139336931
This adds an optional argument to FeedManager#key, the subtype of feed
key to generate. It also tests to ensure that FeedManager's settings are
such that reblogs won't be tracked forever.
* Hardcode IdToBigints migration columns
This addresses a comment during review:
https://github.com/tootsuite/mastodon/pull/4801#discussion_r139337452
This means we'll need to make sure that all _id columns going forward
are bigints, but that should happen automatically in most cases.
* Additional fixes for stringified IDs in JSON
These should be the last two. These were identified using eslint to try
to identify any plain casts to JavaScript numbers. (Some such casts are
legitimate, but these were not.)
Adding the following to .eslintrc.yml will identify casts to numbers:
~~~
no-restricted-syntax:
- warn
- selector: UnaryExpression[operator='+'] > :not(Literal)
message: Avoid the use of unary +
- selector: CallExpression[callee.name='Number']
message: Casting with Number() may coerce string IDs to numbers
~~~
The remaining three casts appear legitimate: two casts to array indices,
one in a server to turn an environment variable into a number.
* Only implement timestamp IDs for Status IDs
Per discussion in #4801, this is only being merged in for Status IDs at
this point. We do this in a migration, as there is no longer use for
a post-migration hook. We keep the initialization of the timestamp_id
function as a Rake task, as it is also needed after db:schema:load (as
db/schema.rb doesn't store Postgres functions).
* Change internal streaming payloads to stringified IDs as well
This is equivalent to 591a9af356faf2d5c7e66e3ec715502796c875cd from
#5019, with an extra change for the addition to FeedManager#unpush.
* Ensure we have a status_id_seq sequence
Apparently this is not a given when specifying a custom ID function,
so now we ensure it gets created. This uses the generic version of this
function to more easily support adding additional tables with timestamp
IDs in the future, although it would be possible to cut this down to a
less generic version if necessary. It is only run during db:schema:load
or the relevant migration, so the overhead is extraordinarily minimal.
* Transition reblogs to new Redis format
This provides a one-way migration to transition old Redis reblog entries
into the new format, with a separate tracking entry for reblogs.
It is not invertible because doing so could (if timestamp IDs are used)
require a database query for each status in each users' feed, which is
likely to be a significant toll on major instances.
* Address review comments from @akihikodaki
No functional changes.
* Additional review changes
* Heredoc cleanup
* Run db:schema:load hooks for test in development
This matches the behavior in Rails'
ActiveRecord::Tasks::DatabaseTasks.each_current_configuration, which
would otherwise break `rake db:setup` in development.
It also moves some functionality out to a library, which will be a good
place to put additional related functionality in the near future.
Additionally, ActivityPub::FetchRemoteStatusService no longer parses
activities.
OStatus::Activity::Creation no longer delegates to ActivityPub because
the provided ActivityPub representations are not signed while OStatus
representations are.
When a new user confirms their e-mail, bootstrap their home timeline
by automatically following a set of accounts. By default, all local
admin accounts (that are unlocked). Can be customized by new admin
setting (comma-separated usernames, local and unlocked only)
* Decouple Status#local? from uri being nil
* Replace on-the-fly URI generation with stored URIs
- Generate URI in after_save hook for local statuses
- Use static value in TagManager when available, fallback to tag format
- Make TagManager use ActivityPub::TagManager to understand new format
- Adjust tests
* Use other heuristic for locality of old statuses, do not perform long query
* Exclude tombstone stream entries from Atom feed
* Prevent nil statuses from landing in Pubsubhubbub::DistributionWorker
* Fix URI not being saved (#4818)
* Add more specs for Status
* Save generated uri immediately
and also fix method order to minimize diff.
* Fix alternate HTML URL in Atom
* Fix tests
* Remove not-null constraint from statuses migration to speed it up
* Make PreviewCard records reuseable between statuses
**Warning!** Migration truncates preview_cards tablec
* Allow a wider thumbnail for link preview, display it in horizontal layout (#4648)
* Delete preview cards files before truncating
* Rename old table instead of truncating it
* Add mastodon:maintenance:remove_deprecated_preview_cards
* Ignore deprecated_preview_cards in schema definition
* Fix null behaviour
Requires moving Atom rendering from DistributionWorker (where
`stream_entry.status` is already nil) to inline (where
`stream_entry.status.destroyed?` is true) and distributing that.
Unfortunately, such XML renderings can no longer be easily chained
together into one payload of n items.
* Add handling of Linked Data Signatures in payloads
* Add a way to sign JSON, fix canonicalization of signature options
* Fix signatureValue encoding, send out signed JSON when distributing
* Add missing security context
* Process Create / Announce activity in FetchRemoteStatusService
* Use activity URL in ActivityPub for reblogs
* Redirect to the original status on StatusesController#show
* Fallback to OStatus in FetchAtomService
* Skip activity+json link if that activity is Person without inbox
* If unsupported activity was detected and all other URLs failed, retry with ActivityPub-less Accept header
* Allow mention to OStatus account in ActivityPub
* Don't update profile with inbox-less Person object
* Add ActivityPub inbox
* Handle ActivityPub deletes
* Handle ActivityPub creates
* Handle ActivityPub announces
* Stubs for handling all activities that need to be handled
* Add ActivityPub actor resolving
* Handle conversation URI passing in ActivityPub
* Handle content language in ActivityPub
* Send accept header when fetching actor, handle JSON parse errors
* Test for ActivityPub::FetchRemoteAccountService
* Handle public key and icon/image when embedded/as array/as resolvable URI
* Implement ActivityPub::FetchRemoteStatusService
* Add stubs for more interactions
* Undo activities implemented
* Handle out of order activities
* Hook up ActivityPub to ResolveRemoteAccountService, handle
Update Account activities
* Add fragment IDs to all transient activity serializers
* Add tests and fixes
* Add stubs for missing tests
* Add more tests
* Add more tests
* Do not raise unretryable exceptions in ResolveRemoteAccountService
* Removed fatal exceptions from ResolveRemoteAccountService
Exceptions that cannot be retried should not be raised. New exception
class for those that can be retried (Mastodon::UnexpectedResponseError)
* Refactor ResolveRemoteAccountService
* Remove trailing whitespace
* Use redis locks around critical ResolveRemoteAccountService code
* Add test for race condition of lock
* Wrap methods of ProcessFeedService::ProcessEntry in classes
This is a change same with 425acecfdb, except
that it has the following changes:
* Revert irrelevant change in find_or_create_conversation
* Fix error handling for RemoteActivity
* Introduce Ostatus name space
* Specs for language detection
* Use CharlockHolmes instead of NKF
* Correct mistakes
* Correct style
* Set hint_enc instead of falling back and strip_tags
* Improve specs
* Add dependencies
* Make Pubsubhubbub::DistributionWorker handle both single stream entry
arguments, as well as arrays of stream entries
* Add BatchedRemoveStatusService, make SuspendAccountService use it
* Improve method names
* Add test
* Add more tests
* Use PuSH payloads of 100 to have a clear mapping of
1000 input statuses -> 10 PuSH payloads
It was nice while it lasted
* Add buttons to block and unblock domain
* Relationship API now returns "domain_blocking" status for accounts,
rename "block entire domain" to "hide entire domain", fix unblocking domain,
do not block notifications from domain-blocked-but-followed people, do
not send Salmons to domain blocked users
* Add test
* Personal domain blocks shouldn't affect Salmon after all, since in this
direction of communication the control is very thin when it comes to
public stuff. Best stay consistent and not affect federation in this way
* Ignore followers and follow request from domain blocked folks,
ensure account domain blocks are not created for empty domain,
and avoid duplicates in validation
* Purge followers when blocking domain (without soft-blocks, since they
are useless here)
* Add tests, fix local timeline being empty when having any domain blocks
* Add <ostatus:conversation /> tag to Atom input/output
Only uses ref attribute (not href) because href would be
the alternate link that's always included also.
Creates new conversation for every non-reply status. Carries
over conversation for every reply. Keeps remote URIs verbatim,
generates local URIs on the fly like the rest of them.
* Conversation muting - prevents notifications that reference a conversation
(including replies, favourites, reblogs) from being created. API endpoints
/api/v1/statuses/:id/mute and /api/v1/statuses/:id/unmute
Currently no way to tell when a status/conversation is muted, so the web UI
only has a "disable notifications" button, doesn't work as a toggle
* Display "Dismiss notifications" on all statuses in notifications column, not just own
* Add "muted" as a boolean attribute on statuses JSON
For now always false on contained reblogs, since it's only relevant for
statuses returned from the notifications endpoint, which are not nested
Remove "Disable notifications" from detailed status view, since it's
only relevant in the notifications column
* Up max class length
* Remove pending test for conversation mute
* Add tests, clean up
* Rename to "mute conversation" and "unmute conversation"
* Raise validation error when trying to mute/unmute status without conversation
* Adding account domain blocks that filter notifications and public timelines
* Add tests for domain blocks in notifications, public timelines
Filter reblogs of blocked domains from home
* Add API for listing and creating account domain blocks
* API for creating/deleting domain blocks, tests for Status#ancestors
and Status#descendants, filter domain blocks from them
* Filter domains in streaming API
* Update account_domain_block_spec.rb
* Add <ostatus:conversation /> tag to Atom input/output
Only uses ref attribute (not href) because href would be
the alternate link that's always included also.
Creates new conversation for every non-reply status. Carries
over conversation for every reply. Keeps remote URIs verbatim,
generates local URIs on the fly like the rest of them.
* Conversation muting - prevents notifications that reference a conversation
(including replies, favourites, reblogs) from being created. API endpoints
/api/v1/statuses/:id/mute and /api/v1/statuses/:id/unmute
Currently no way to tell when a status/conversation is muted, so the web UI
only has a "disable notifications" button, doesn't work as a toggle
* Display "Dismiss notifications" on all statuses in notifications column, not just own
* Add "muted" as a boolean attribute on statuses JSON
For now always false on contained reblogs, since it's only relevant for
statuses returned from the notifications endpoint, which are not nested
Remove "Disable notifications" from detailed status view, since it's
only relevant in the notifications column
* Up max class length
* Remove pending test for conversation mute
* Add tests, clean up
* Rename to "mute conversation" and "unmute conversation"
* Raise validation error when trying to mute/unmute status without conversation
* Dont use raise_error by itself (avoids warning)
* Add coverage for AccountFilter
* Improve coverage and refactor for Subscription#lease_seconds
* Improve coverage and refactor for NotificationMailer
* Simplify assignment of min/max threshold on subscription
* Fix#2473 - Use sidekiq scheduler to refresh PuSH subscriptions instead of cron
Fix an issue where / in domain would raise exception in TagManager#normalize_domain
PuSH subscriptions refresh done in a round-robin way to avoid hammering a single
server's hub in sequence. Correct handling of failures/retries through Sidekiq (see
also #2613). Optimize Account#with_followers scope. Also, since subscriptions
are now delegated to Sidekiq jobs, an uncaught exception will not stop the entire
refreshing operation halfway through
Fix#2702 - Correct user agent header on outgoing http requests
* Add test for SubscribeService
* Extract #expiring_accounts into method
* Make mastodon:push:refresh no-op
* Queues are now defined in sidekiq.yml
* Queues are now in sidekiq.yml
Eugen Rochko