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60 lines
2.2 KiB
HTML
60 lines
2.2 KiB
HTML
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<!DOCTYPE html>
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<html lang="en">
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<head>
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<title>example</title>
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<meta charset="utf-8" />
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<meta http-equiv="X-UA-Compatible" content="IE=edge" />
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<meta name="viewport" content="width=device-width, initial-scale=1.0" />
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<style>
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#container { margin-right: auto; margin-left: auto; max-width: 480px; }
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#info { background: #e0f0f0; border-radius: .5em; padding: 2em; margin-bottom: 1em; }
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#result { margin-top: 1em; }
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</style>
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</head>
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<body>
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<div id="container">
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<div id="info">
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On devices with limited RAM, it is important to limit the response size
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of API calls. This example demonstrates how to fetch a large
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data in smaller chunks, and guarantee its integrity.
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Data gets returned in a series of request/response transactions,
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where each response is small enough to fit into available device RAM.
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<br/><br/>
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Data integrity is implemented by versioning.
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The idea is that the first response includes the current "version" of the
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data, and that version is passed to all subsequent requests.
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If data version changes in the middle of the request series,
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client fails with 'wrong version' error.
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</div>
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<button id="btn">fetch data</button>
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<div id="result"></div>
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</div>
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</body>
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<script>
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const getchunk = (start, version) =>
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fetch('/api/data', {method: 'POST', body:JSON.stringify({start, version})})
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.then(r => r.json());
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document.getElementById('btn').onclick = function() {
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var data = [], version = 0;
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const load = offset => getchunk(offset, version)
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.then(r => {
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// console.log(r);
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if (r.error) {
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document.getElementById('result').innerText = 'Error: ' + r.error;
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} else {
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version = r.version;
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data = data.concat(r.data);
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if (r.data.length == 0) {
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document.getElementById('result').innerText = 'Version: ' +
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version + ', data: \n' +
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JSON.stringify(data, null, 2);
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} else {
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load(offset + r.data.length, version);
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}
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}
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});
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load(0);
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};
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</script>
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</html>
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