1+ import { openDB } from 'idb' ;
2+
3+ const dbPromise = openDB ( 'restful-queue' , 1 , {
4+ upgrade ( db ) {
5+ db . createObjectStore ( 'requests' , {
6+ keyPath : 'id' ,
7+ autoIncrement : true ,
8+ } ) ;
9+ } ,
10+ } ) ;
11+
12+ /**
13+ * Stores a request in the queue and then attempts to send it to the server
14+ *
15+ * @param {Request } request A Request object from the Fetch API, which isn't unusable
16+ *
17+ * @returns {Promise }
18+ */
19+ export async function queueAndAttemptRequest ( request ) {
20+ const requestid = await queueRequest ( request ) ;
21+ syncRequests ( ) ;
22+ return new Response ( new Blob ( ) , { status : 202 , statusText : "Added to Queue" } ) ;
23+ }
24+
25+ /**
26+ * Stores a request object in indexDB
27+ *
28+ * @param {Request } request A Request object from the Fetch API
29+ *
30+ * @returns {Promise.<number> } A promise which resolves with a unique requestid when succesfully stored (or rejects on failure)
31+ */
32+ async function queueRequest ( request ) {
33+
34+ // Store a cloned version of the request, so the orginal can still be fetched later
35+ request = request . clone ( ) ;
36+ const { url, method } = request ;
37+ const headers = [ ...request . headers ] ;
38+ const body = await request . blob ( ) ;
39+ const rawData = { url, method, headers, body } ;
40+
41+ const db = await dbPromise ;
42+ const requestid = await db . add ( 'requests' , rawData ) ;
43+ return requestid ;
44+ }
45+
46+ /**
47+ * Attempts to fetch a request from the queue. If successful, the request is removed from the queue.
48+ *
49+ * @param {number } requestid The unique ID for this request stored in indexDB
50+ * @param {Request } request A Request object from the Fetch API
51+ *
52+ * @returns {Promise.<Response> } A promise which resolves with the requests response following removal from the queue (or rejects on failure)
53+ */
54+ async function attemptRequest ( requestid , request ) {
55+ const response = await fetch ( request ) ;
56+ await removeFromQueue ( requestid ) ;
57+ return response ;
58+ }
59+
60+ /**
61+ * Removes a request from the queue
62+ *
63+ * @param {number } requestid The unique ID for the request to remove from indexDB+
64+ *
65+ * @returns {Promise } A promise which resolves when succesfully removed (or rejects on failure)
66+ */
67+ async function removeFromQueue ( requestid ) {
68+ const db = await dbPromise ;
69+ await db . delete ( 'requests' , requestid ) ;
70+ }
71+
72+ /**
73+ * Fetches all the outstanding requests, along with their IDs from indexDB
74+ * NB: getOutstandRequests is a simplified public wrapper for this function, which doesn't expose the internal requestids
75+ *
76+ * @returns {Array.<{id: number, request: Request}> } An array containing requests and their associated requestids
77+ */
78+ async function getOutstandingRequestsAndIds ( ) {
79+ const db = await dbPromise ;
80+ return ( await db . getAll ( 'requests' ) ) . map ( raw => {
81+ const { url, method, headers, body, id } = raw ;
82+ const request = new Request ( url , { method, headers, body} ) ;
83+ return { id, request} ;
84+ } ) ;
85+ }
86+
87+ /**
88+ * Fetches all the outstanding requests from indexDB
89+ *
90+ * @returns {Array.<Request> } An array containing Fetch API Request objects
91+ */
92+ export async function getOutstandingRequests ( ) {
93+ return ( await getOutstandingRequestsAndIds ( ) )
94+ . map ( ( { request} ) => request ) ;
95+ }
96+
97+ let currentSync = null ;
98+
99+ /**
100+ * Starts off an asynchronous function to sync up any outstanding requests with the server
101+ * Ensures there's only one running at a time to avoid race conditions
102+ */
103+ export function syncRequests ( ) {
104+
105+ // If there's no existing sync, then start one
106+ if ( ! currentSync ) {
107+ currentSync = attemptOutstandingRequests ( ) ;
108+ return ;
109+ }
110+
111+ // Otherwise, queue another sync after the current one.
112+ currentSync = currentSync . then ( attemptOutstandingRequests ) ;
113+
114+ }
115+
116+ /**
117+ * Attempts to fetch an outstanding requests, and if successful remove them from the queue.
118+ * Stops after the first failure and doesn't attempt any subsequent requests in the queue.
119+ * NB: Calling this function whilst a previous invocation hasn't completed yet, may cause a race condition. Use the `syncRequests` function to avoid this.
120+ *
121+ * @returns {Promise } A promise which resolves when all requests have been succesfully removed from the queue, or rejects after encountering the first failure
122+ */
123+ async function attemptOutstandingRequests ( ) {
124+ const requests = await getOutstandingRequestsAndIds ( ) ;
125+ for ( const { id, request} of requests ) {
126+ await attemptRequest ( id , request ) ;
127+ }
128+ }
0 commit comments