Initial Save

node_modules/apollo-link/README.md

@@ -0,0 +1,69 @@
+# apollo-link
+
+## Purpose
+
+`apollo-link` is a standard interface for modifying control flow of GraphQL requests and fetching GraphQL results, designed to provide a simple GraphQL client that is capable of extensions.
+The targeted use cases of `apollo-link` are highlighted below:
+
+* fetch queries directly without normalized cache
+* network interface for Apollo Client
+* network interface for Relay Modern
+* fetcher for
+
+Apollo Link is the interface for creating new links in your application.
+
+The client sends a request as a method call to a link and can recieve one or more (in the case of subscriptions) responses from the server. The responses are returned using the Observer pattern.
+
+![Apollo Link Chain](https://cdn-images-1.medium.com/max/1600/1*62VLGUaU-9ULCoBCGvgdkQ.png)
+
+Results from the server can be provided by calling `next(result)` on the observer. In the case of a network/transport error (not a GraphQL Error) the `error(err)` method can be used to indicate a response will not be recieved. If multiple responses are not supported by the link, `complete()` should be called to inform the client no further data will be provided.
+
+In the case of an intermediate link, a second argument to `request(operation, forward)` is the link to `forward(operation)` to. `forward` returns an observable and it can be returned directly or subscribed to.
+
+```js
+forward(operation).subscribe({
+  next: result => {
+    handleTheResult(result)
+  },
+  error: error => {
+    handleTheNetworkError(error)
+  },
+});
+```
+
+## Implementing a basic custom transport
+
+```js
+import { ApolloLink, Observable } from 'apollo-link';
+
+export class CustomApolloLink extends ApolloLink {
+  request(operation /*, forward*/) {
+    //Whether no one is listening anymore
+    let unsubscribed = false;
+
+    return new Observable(observer => {
+      somehowGetOperationToServer(operation, (error, result) => {
+        if (unsubscribed) return;
+        if (error) {
+          //Network error
+          observer.error(error);
+        } else {
+          observer.next(result);
+          observer.complete(); //If subscriptions not supported
+        }
+      });
+
+      function unsubscribe() {
+        unsubscribed = true;
+      }
+
+      return unsubscribe;
+    });
+  }
+}
+```
+
+## Installation
+
+`npm install apollo-link --save`
+