sling_gql_link

Run sling_gql's requests through a gql_link Link chain — auth, retries, persisted queries, websockets, whatever links you already have — as the one Transport a SlingClient takes. sling_gql itself stays http-only.

Docs: https://tpucci.github.io/sling_gql/guides/transport/ · Source: https://github.com/tpucci/sling_gql

flutter pub add sling_gql_link gql_link gql_http_link

import 'package:gql_http_link/gql_http_link.dart';
import 'package:gql_link/gql_link.dart';
import 'package:sling_gql_link/sling_gql_link.dart';

final link = Link.from([authLink, retryLink, HttpLink(endpoint)]);

final client = SlingClient<Query>(
  endpoint: Uri.parse(endpoint), // nominal: the terminating link sends
  schema: slingSchema,
  transport: linkTransport(link),
  // Subscriptions too, when the link can run them (a websocket link routed
  // with Link.split):
  subscriptionTransport: linkSubscriptionTransport(link),
);

What goes in

Each batched document is parsed into the Request's DocumentNode, with its variables and operationName (sling_gql's own documents are anonymous). SlingClient.headers are put in the context as HttpLinkHeaders, so an auth link adds to them with request.updateContextEntry<HttpLinkHeaders>(...); content-type and accept are left to the terminating link.

What comes out

The first Response of the link's stream is the result: data, errors (message, locations, path, extensions) and extensions are encoded back into a JSON body the client handles exactly like an HTTP response — partial errors pruned before caching and reported on the scope (or kept, per ErrorPolicy), data: null a SlingGraphQLException.

A LinkException becomes the SlingException it stands for (slingExceptionFromLink), so error handling, RetryPolicy and SlingAuth treat a link exactly like the default transport:

Errors that are not LinkExceptions (a TimeoutException from your own link) are classified by the client like the default transport's (SlingException.from). Prefer the client's own timeout, retry and auth to a link's: they also cover subscriptions and know about scopes.

Subscriptions

linkSubscriptionTransport(link) maps the link's stream one to one: each Response is an event, the stream completing completes the subscription, an error is a transport failure (which reconnects when the subscription has a retryAfter), and cancelling the subscription cancels the link's stream. HttpLink cannot run subscriptions; route them to a websocket link:

final link = Link.split(
  (request) =>
      request.operation.getOperationType() == OperationType.subscription,
  websocketLink,
  Link.from([authLink, HttpLink(endpoint)]),
);

Or keep sling_gql's default GraphQL-over-SSE subscriptions and only pass transport:.

Versioning

From 1.0 sling_gql_link follows semantic versioning and shares its major version with sling_gql. A new major of gql_link / gql_exec (whose types are part of this API) is a major here. Deprecated APIs keep working for at least one minor release and are removed only in the next major. Full policy: Versioning & deprecation; coming from 0.x: Upgrading to 1.0. Security issues: SECURITY.md.