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* Removed text about source code Source code was removed by hasura/graphql-engine@fb3794c3 * links update for subscriptions/index links updated because 1) facebook.github.io was changed to graphql.github.io/graphql-spec/ 2) path to docs changed by apollographql/apollo-client@41ca8ff1
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93 lines
3.2 KiB
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Subscriptions
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=============
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.. contents:: Table of contents
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:backlinks: none
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:depth: 1
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:local:
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A GraphQL subscription is essentially a query where the client receives an event whenever the value of any field changes
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upstream. The Hasura GraphQL engine supports subscriptions for all kinds of queries. All the concepts of
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:doc:`queries <../queries/index>` hold true for subscriptions as well.
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Convert a query to a subscription
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---------------------------------
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You can turn any query into a subscription by simply replacing ``query`` with ``subscription`` as the operation type.
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.. admonition:: Caveat
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Hasura follows the `GraphQL spec <https://graphql.github.io/graphql-spec/June2018/#sec-Single-root-field>`_ which
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allows for only one root field in a subscription.
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Use cases
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---------
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- :ref:`subscribe_field`
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- :ref:`subscribe_table`
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- :ref:`subscribe_derived`
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Communication protocol
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----------------------
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Hasura GraphQL engine uses the `GraphQL over WebSocket Protocol
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<https://github.com/apollographql/subscriptions-transport-ws/blob/master/PROTOCOL.md>`_ by the
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`apollographql/subscriptions-transport-ws <https://github.com/apollographql/subscriptions-transport-ws>`_ library
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for sending and receiving events.
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.. admonition:: Setting headers for subscriptions with Apollo client
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If you are using Apollo Client, headers can be passed to a subscription by setting ``connectionParams`` while
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`creating the wsLink <https://www.apollographql.com/docs/react/data/subscriptions/#client-setup>`_:
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.. code-block:: js
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:emphasize-lines: 6-8
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// Create a WebSocket link:
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const wsLink = new WebSocketLink({
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uri: `<graphql-endpoint>`,
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options: {
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reconnect: true,
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connectionParams: {
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headers: {headers-object}
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}
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}
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});
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See `this <https://www.apollographql.com/docs/react/data/subscriptions/#authentication-over-websocket>`_ for more info on
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using ``connectionParams``.
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Cookies and WebSockets
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----------------------
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The Hasura GraphQL engine will read cookies sent by the browser when initiating a
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WebSocket connection. The browser will send the cookie only if it is a secure cookie
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(``secure`` flag in the cookie) and if the cookie has a ``HttpOnly`` flag.
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Hasura will read this cookie and use it as headers when resolving authorization
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(i.e. when resolving the auth webhook).
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Cookies, WebSockets and CORS
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^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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As browsers don't enforce Same Origin Policy (SOP) for websockets, the Hasura server
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enforces the CORS rules when accepting the websocket connection.
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It uses the provided CORS configuration (as per :ref:`configure-cors`).
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1. When it is ``*``, the cookie is read and the CORS check is not enforced.
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2. When there are explicit domains, the cookie will only be read if the request originates from one of
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the listed domains.
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3. If CORS is disabled, the default behaviour is that the cookie won't be read
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(because of potential security issues). To override the behaviour, you can
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use the flag ``--ws-read-cookie`` or the environment variable
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``HASURA_GRAPHQL_WS_READ_COOKIE``. See
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:doc:`../deployment/graphql-engine-flags/reference` for the setting.
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.. toctree::
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:maxdepth: 1
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:hidden:
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Sample use cases <use-cases>
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