title: apollo-link-http
description: Get GraphQL results over a network using HTTP fetch.
The http link is the most common Apollo Link, a system of modular components
for GraphQL networking. If you haven't done so already, read the Apollo Link
docs to learn about the Apollo
Link ecosystem and how to use this link with libraries like Apollo Client and
graphql-tools, or as a standalone client.
The http link is a terminating link that fetches GraphQL results from a GraphQL
endpoint over an http connection. The http link supports both POST and GET
requests with the ability change the http options on a per query basis. This
can be used for authentication, persisted queries, dynamic uris, and other
granular updates.
Usage
Import and initialize this link in just two lines:
import { createHttpLink } from "apollo-link-http";
const link = createHttpLink({ uri: "/graphql" });
Options
HTTP Link takes an object with some options on it to customize the behavior of the link. If your server supports it, the HTTP link can also send over metadata about the request in the extensions field. To enable this, pass includeExtensions
as true. The options you can pass are outlined below:
uri
: the URI key is a string endpoint or function resolving to an endpoint -- will default to "/graphql" if not specifiedincludeExtensions
: allow passing the extensions field to your graphql server, defaults to falsefetch
: a fetch
compatible API for making a requestheaders
: an object representing values to be sent as headers on the requestcredentials
: a string representing the credentials policy you want for the fetch call. Possible values are: omit
, include
and same-origin
fetchOptions
: any overrides of the fetch options argument to pass to the fetch calluseGETForQueries
: set to true
to use the HTTP GET
method for queries (but not for mutations)
Fetch polyfill
The HTTP Link relies on having fetch
present in your runtime environment. If you are running on react-native, or modern browsers, this should be no problem. If you are targeting an environment without fetch
such as older browsers or the server, you will need to pass your own fetch
to the link through the options. We recommend unfetch
for older browsers and node-fetch
for running in Node.
Context
The Http Link uses the headers
field on the context to allow passing headers to the HTTP request. It also supports the credentials
field for defining credentials policy, uri
for changing the endpoint dynamically, and fetchOptions
to allow generic fetch overrides (i.e. method: "GET"
). These options will override the same key if passed when creating the the link.
Note that if you set fetchOptions.method
to GET
, the http link will follow the standard GraphQL HTTP GET encoding: the query, variables, operation name, and extensions will be passed as query parameters rather than in the HTTP request body. If you want mutations to continue to be sent as non-idempotent POST
requests, set the top-level useGETForQueries
option to true
instead of setting fetchOptions.method
to GET
.
This link also attaches the response from the fetch
operation on the context as response
so you can access it from within another link.
headers
: an object representing values to be sent as headers on the requestcredentials
: a string representing the credentials policy you want for the fetch call. Possible values are: omit
, include
and same-origin
uri
: a string of the endpoint you want to fetch fromfetchOptions
: any overrides of the fetch options argument to pass to the fetch callresponse
: this is the raw response from the fetch request after it is made.http
: this is an object to control fine grained aspects of the http link itself, such as persisted queries (see below)
Persisted queries
The http link supports an advanced GraphQL feature called persisted queries. This allows you to not send the stringified query over the wire, but instead send some kind of identifier of the query. To support this you need to attach the id somewhere to the extensions field and pass the following options to the context:
operation.setContext({
http: {
includeExtensions: true,
includeQuery: false,
}
})
The http
object on context currently supports two keys:
includeExtensions
: Send the extensions object for this request.includeQuery
: Don't send the query
field for this request.
One way to use persisted queries is with apollo-link-persisted-queries and Apollo Engine.
Passing context per query
Apollo Client supports passing context separately for every query, so you can do things like pass a special header for a single query invocation if you need to.
import HttpLink from "apollo-link-http";
import ApolloClient from "apollo-client";
import { InMemoryCache } from "apollo-cache-inmemory";
const client = new ApolloClient({
link: new HttpLink({ uri: "/graphql" }),
cache: new InMemoryCache()
});
client.query({
query: MY_QUERY,
context: {
headers: {
special: "Special header value"
}
}
});
Errors
The Http Link draws a distinction between client, server and GraphQL errors. Server errors can occur in three different scenarios: parse, network and data errors. apollo-link-error
provides an interface for handling these errors. This list describes the scenarios that cause different errors:
- Client parse error: the request body is not-serializable due to circular references for example
- Server parse error: the response from the server cannot be parsed (response.json())
- Server network error: the response has a status of >= 300
- Server data error: the parse request does not contain
data
or errors
- GraphQL error: an objects in the
errors
array for a 200 level status
Since many server implementations can return a valid GraphQL result on a server network error, the thrown Error
object contains the parsed server result. A server data error also receives the parsed result.
The table below provides a summary of error, Observable
method called by the HTTP link, and type of error thrown for each failure:
Error | Callback | Error Type |
---|
Client Parse | error | ClientParseError |
Server Parse | error | ServerParseError |
Server Network | error | ServerError |
Server Data | error | ServerError |
GraphQL Error | next | Object |
All error types inherit the name
, message
, and nullable stack
properties from the generic javascript Error.
{
parseError: Error;
};
{
response: Response;
statusCode: number;
bodyText: string
};
{
result: Record<string, any>;
response: Response;
statusCode: number;
};
Custom fetching
You can use the fetch
option when creating an http-link to do a lot of custom networking. This is useful if you want to modify the request based on the calculated headers or calculate the uri based on the operation:
Custom auth
const customFetch = (uri, options) => {
const { header } = Hawk.client.header(
"http://example.com:8000/resource/1?b=1&a=2",
"POST",
{ credentials: credentials, ext: "some-app-data" }
);
options.headers.Authorization = header;
return fetch(uri, options);
};
const link = createHttpLink({ fetch: customFetch });
Dynamic URI
const customFetch = (uri, options) => {
const { operationName } = JSON.parse(options.body);
return fetch(`${uri}/graph/graphql?opname=${operationName}`, options);
};
const link = createHttpLink({ fetch: customFetch });
Upgrade: Apollo Client 1.0
If you previously used either apollo-fetch
or apollo-client
's createNetworkInterface
, you will need to change the way use
and useAfter
are implemented in your app. Both can be implemented by writing a custom link. It's important to note that regardless of whether you're adding middleware or afterware, your Http link will always be last in the chain since it's a terminating link.
Middleware
Before
import ApolloClient, { createNetworkInterface } from "apollo-client";
const networkInterface = createNetworkInterface({ uri: "/graphql" });
networkInterface.use([
{
applyMiddleware(req, next) {
if (!req.options.headers) {
req.options.headers = {};
}
req.options.headers["authorization"] = localStorage.getItem("token")
? localStorage.getItem("token")
: null;
next();
}
}
]);
After
import { ApolloLink } from "apollo-link";
import { createHttpLink } from "apollo-link-http";
const httpLink = createHttpLink({ uri: "/graphql" });
const middlewareLink = new ApolloLink((operation, forward) => {
operation.setContext({
headers: {
authorization: localStorage.getItem("token") || null
}
});
return forward(operation);
});
const link = middlewareLink.concat(httpLink);
Afterware (error)
Before
import ApolloClient, { createNetworkInterface } from "apollo-client";
import { logout } from "./logout";
const networkInterface = createNetworkInterface({ uri: "/graphql" });
networkInterface.useAfter([
{
applyAfterware({ response }, next) {
if (response.statusCode === 401) {
logout();
}
next();
}
}
]);
After
import { ApolloLink } from "apollo-link";
import { createHttpLink } from "apollo-link-http";
import { onError } from "apollo-link-error";
import { logout } from "./logout";
const httpLink = createHttpLink({ uri: "/graphql" });
const errorLink = onError(({ networkError }) => {
if (networkError.statusCode === 401) {
logout();
}
});
const link = errorLink.concat(httpLink);
Afterware (data manipulation)
Before
import ApolloClient, { createNetworkInterface } from "apollo-client";
const networkInterface = createNetworkInterface({ uri: "/graphql" });
networkInterface.useAfter([
{
applyAfterware({ response }, next) {
if (response.data.user.lastLoginDate) {
response.data.user.lastLoginDate = new Date(
response.data.user.lastLoginDate
);
}
next();
}
}
]);
After
import { ApolloLink } from "apollo-link";
import { createHttpLink } from "apollo-link-http";
const httpLink = createHttpLink({ uri: "/graphql" });
const addDatesLink = new ApolloLink((operation, forward) => {
return forward(operation).map(response => {
if (response.data.user.lastLoginDate) {
response.data.user.lastLoginDate = new Date(
response.data.user.lastLoginDate
);
}
return response;
});
});
const link = addDatesLink.concat(httpLink);