2018-12-21 22:39:01 +05:30
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<html>
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2019-01-09 15:36:09 +05:30
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<head><meta charset="utf-8"></head>
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2018-12-21 22:39:01 +05:30
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<body>
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<ul id="messages"></ul>
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<script type="text/javascript">
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class Key {
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constructor() {
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this._keys = new Int32Array(2);
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}
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get gapKey() {
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return this._keys[0];
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}
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set gapKey(value) {
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this._keys[0] = value;
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}
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get eventKey() {
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return this._keys[1];
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}
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set eventKey(value) {
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this._keys[1] = value;
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}
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buffer() {
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return this._keys.buffer;
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}
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nextKeyWithGap() {
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const k = new Key();
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k.gapKey = this.gapKey + 1;
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k.eventKey = 0;
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return k;
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}
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nextKey() {
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const k = new Key();
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k.gapKey = this.gapKey;
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k.eventKey = this.eventKey + 1;
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return k;
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}
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previousKey() {
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const k = new Key();
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k.gapKey = this.gapKey;
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k.eventKey = this.eventKey - 1;
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return k;
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}
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clone() {
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const k = new Key();
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k.gapKey = this.gapKey;
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k.eventKey = this.eventKey;
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return k;
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}
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}
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function reqAsPromise(req) {
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return new Promise((resolve, reject) => {
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req.onsuccess = () => resolve(req);
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req.onerror = (err) => reject(err);
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});
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}
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function fetchResults(cursor, isDone, resultMapper) {
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return new Promise((resolve, reject) => {
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const results = [];
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cursor.onerror = (event) => {
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reject(new Error("Query failed: " + event.target.errorCode));
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};
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// collect results
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cursor.onsuccess = (event) => {
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console.log("got a result");
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const cursor = event.target.result;
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if (!cursor) {
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resolve(results);
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return; // end of results
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}
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results.push(resultMapper(cursor));
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if (!isDone(results)) {
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cursor.continue();
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} else {
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resolve(results);
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}
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};
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});
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}
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class Storage {
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constructor(databaseName) {
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this._databaseName = databaseName;
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this._database = null;
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}
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async open() {
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const req = window.indexedDB.open(this._databaseName);
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2019-01-09 15:36:09 +05:30
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req.onupgradeneeded = (ev) => {
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2018-12-21 22:39:01 +05:30
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const db = ev.target.result;
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const oldVersion = ev.oldVersion;
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this._createStores(db, oldVersion);
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};
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await reqAsPromise(req);
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this._database = req.result;
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}
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_createStores(db) {
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db.createObjectStore("timeline", {keyPath: ["roomId", "sortKey"]});
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}
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async insert(value) {
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const tx = this._database.transaction(["timeline"], "readwrite");
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const store = tx.objectStore("timeline");
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await reqAsPromise(store.add(value));
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}
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async selectAt(roomId, sortKey, amount) {
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const tx = this._database.transaction(["timeline"], "readonly");
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const store = tx.objectStore("timeline");
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const range = IDBKeyRange.lowerBound([roomId, sortKey.buffer()]);
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const cursor = store.openCursor(range);
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return await fetchResults(cursor,
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(results) => results.length === amount,
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(cursor) => cursor.value);
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}
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}
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(async () => {
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const initialSortKey = new Key();
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initialSortKey.gapKey = 1000;
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const roomId = "!abc:hs.tld";
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const storage = new Storage("mysession");
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await storage.open();
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let records = await storage.selectAt(roomId, initialSortKey, 15);
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if (!records.length) {
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// insert first batch backwards,
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// to see we're not assuming insertion order to sort
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let sortKey = initialSortKey.clone();
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sortKey.eventKey = 10;
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for (var i = 10; i > 0; i--) {
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await storage.insert({
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roomId,
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sortKey: sortKey.buffer(),
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message: `message ${i} before gap`
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});
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sortKey = sortKey.previousKey();
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}
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sortKey = sortKey.nextKeyWithGap();
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await storage.insert({
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roomId,
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sortKey: sortKey.buffer(),
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message: `event to represent gap!`
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});
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for (var i = 1; i <= 10; i++) {
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sortKey = sortKey.nextKey();
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await storage.insert({
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roomId,
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sortKey: sortKey.buffer(),
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message: `message ${i} after gap`
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});
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}
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records = await storage.selectAt(roomId, initialSortKey, 15);
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}
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console.log(records, "records");
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const nodes = records.map(r => {
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const li = document.createElement("li");
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li.appendChild(document.createTextNode(r.message));
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return li;
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});
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const parentNode = document.getElementById("messages");
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nodes.forEach(n => parentNode.appendChild(n));
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})();
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</script>
|
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</body>
|
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</html>
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