element-web/res/decoder-ring/decoder.js

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class StartupError extends Error {}
/*
* We need to know the bundle path before we can fetch the sourcemap files. In a production environment, we can guess
* it using this.
*/
async function getBundleName(baseUrl) {
const res = await fetch(new URL("index.html", baseUrl).toString());
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if (!res.ok) {
throw new StartupError(`Couldn't fetch index.html to prefill bundle; ${res.status} ${res.statusText}`);
}
const index = await res.text();
return index.split("\n").map((line) =>
line.match(/<script src="bundles\/([^/]+)\/bundle.js"/),
)
.filter((result) => result)
.map((result) => result[1])[0];
}
function validateBundle(value) {
return value.match(/^[0-9a-f]{20}$/) ? Some.of(value) : None;
}
/* A custom fetcher that abandons immediately upon getting a response.
* The purpose of this is just to validate that the user entered a real bundle, and provide feedback.
*/
const bundleCache = new Map();
function bundleSubject(baseUrl, bundle) {
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if (!bundle.match(/^[0-9a-f]{20}$/)) throw new Error("Bad input");
if (bundleCache.has(bundle)) {
return bundleCache.get(bundle);
}
const fetcher = new rxjs.BehaviorSubject(Pending.of());
bundleCache.set(bundle, fetcher);
fetch(new URL(`bundles/${bundle}/bundle.js.map`, baseUrl).toString()).then((res) => {
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res.body.cancel(); /* Bail on the download immediately - it could be big! */
const status = res.ok;
if (status) {
fetcher.next(Success.of());
} else {
fetcher.next(FetchError.of(`Failed to fetch: ${res.status} ${res.statusText}`));
}
});
return fetcher;
}
/*
* Convert a ReadableStream of bytes into an Observable of a string
* The observable will emit a stream of Pending objects and will concatenate
* the number of bytes received with whatever pendingContext has been supplied.
* Finally, it will emit a Success containing the result.
* You'd use this on a Response.body.
*/
function observeReadableStream(readableStream, pendingContext = {}) {
let bytesReceived = 0;
let buffer = "";
const pendingSubject = new rxjs.BehaviorSubject(Pending.of({ ...pendingContext, bytesReceived }));
const throttledPending = pendingSubject.pipe(rxjs.operators.throttleTime(100));
const resultObservable = new rxjs.Subject();
const reader = readableStream.getReader();
const utf8Decoder = new TextDecoder("utf-8");
function readNextChunk() {
reader.read().then(({ done, value }) => {
if (done) {
pendingSubject.complete();
resultObservable.next(Success.of(buffer));
return;
}
bytesReceived += value.length;
pendingSubject.next(Pending.of({...pendingContext, bytesReceived }));
/* string concatenation is apparently the most performant way to do this */
buffer += utf8Decoder.decode(value);
readNextChunk();
});
}
readNextChunk();
return rxjs.concat(throttledPending, resultObservable);
}
/*
* A wrapper which converts the browser's `fetch()` mechanism into an Observable. The Observable then provides us with
* a stream of datatype values: first, a sequence of Pending objects that keep us up to date with the download progress,
* finally followed by either a Success or Failure object. React then just has to render each of these appropriately.
*/
const fetchCache = new Map();
function fetchAsSubject(endpoint) {
if (fetchCache.has(endpoint)) {
// TODO: expiry/retry logic here?
return fetchCache.get(endpoint);
}
const fetcher = new rxjs.BehaviorSubject(Pending.of());
fetchCache.set(endpoint, fetcher);
fetch(endpoint).then((res) => {
if (!res.ok) {
fetcher.next(FetchError.of(`Failed to fetch endpoint ${endpoint}: ${res.status} ${res.statusText}`));
return;
}
const contentLength = res.headers.get("content-length");
const context = contentLength ? { length: parseInt(contentLength) } : {};
const streamer = observeReadableStream(res.body, context);
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streamer.subscribe((value) => {
fetcher.next(value);
});
});
return fetcher;
}
/* ===================== */
/* ==== React stuff ==== */
/* ===================== */
/* Rather than importing an entire build infrastructure, for now we just use React without JSX */
const e = React.createElement;
/*
* Provides user feedback given a FetchStatus object.
*/
function ProgressBar({ fetchStatus }) {
return e('span', { className: "progress "},
fetchStatus.fold({
pending: ({ bytesReceived, length }) => {
if (!bytesReceived) {
return e('span', { className: "spinner" }, "\u29b5");
}
const kB = Math.floor(10 * bytesReceived / 1024) / 10;
if (!length) {
return e('span', null, `Fetching (${kB}kB)`);
}
const percent = Math.floor(100 * bytesReceived / length);
return e('span', null, `Fetching (${kB}kB) ${percent}%`);
},
success: () => e('span', null, "\u2713"),
error: (reason) => {
return e('span', { className: 'error'}, `\u2717 ${reason}`);
},
},
));
}
/*
* The main component.
*/
function BundlePicker() {
const [baseUrl, setBaseUrl] = React.useState(new URL("..", window.location).toString());
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const [bundle, setBundle] = React.useState("");
const [file, setFile] = React.useState("");
const [line, setLine] = React.useState("1");
const [column, setColumn] = React.useState("");
const [result, setResult] = React.useState(None);
const [bundleFetchStatus, setBundleFetchStatus] = React.useState(None);
const [fileFetchStatus, setFileFetchStatus] = React.useState(None);
/* On baseUrl change, try to fill in the bundle name for the user */
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React.useEffect(() => {
console.log("DEBUG", baseUrl);
getBundleName(baseUrl).then((name) => {
console.log("DEBUG", name);
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if (bundle === "" && validateBundle(name) !== None) {
setBundle(name);
}
}, console.log.bind(console));
}, [baseUrl]);
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/* ------------------------- */
/* Follow user state changes */
/* ------------------------- */
const onBaseUrlChange = React.useCallback((event) => {
const value = event.target.value;
setBaseUrl(value);
}, []);
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const onBundleChange = React.useCallback((event) => {
const value = event.target.value;
setBundle(value);
}, []);
const onFileChange = React.useCallback((event) => {
const value = event.target.value;
setFile(value);
}, []);
const onLineChange = React.useCallback((event) => {
const value = event.target.value;
setLine(value);
}, []);
const onColumnChange = React.useCallback((event) => {
const value = event.target.value;
setColumn(value);
}, []);
/* ------------------------------------------------ */
/* Plumb data-fetching observables through to React */
/* ------------------------------------------------ */
/* Whenever a valid bundle name is input, go see if it's a real bundle on the server */
React.useEffect(() =>
validateBundle(bundle).fold({
some: (value) => {
const subscription = bundleSubject(baseUrl, value)
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.pipe(rxjs.operators.map(Some.of))
.subscribe(setBundleFetchStatus);
return () => subscription.unsubscribe();
},
none: () => setBundleFetchStatus(None),
}),
[baseUrl, bundle]);
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/* Whenever a valid javascript file is input, see if it corresponds to a sourcemap file and initiate a fetch
* if so. */
React.useEffect(() => {
if (!file.match(/.\.js$/) || validateBundle(bundle) === None) {
setFileFetchStatus(None);
return;
}
const observable = fetchAsSubject(new URL(`bundles/${bundle}/${file}.map`, baseUrl).toString())
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.pipe(
rxjs.operators.map((fetchStatus) => fetchStatus.flatMap(value => {
try {
return Success.of(JSON.parse(value));
} catch (e) {
return FetchError.of(e);
}
})),
rxjs.operators.map(Some.of),
);
const subscription = observable.subscribe(setFileFetchStatus);
return () => subscription.unsubscribe();
}, [baseUrl, bundle, file]);
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/*
* Whenever we have a valid fetched sourcemap, and a valid line, attempt to find the original position from the
* sourcemap.
*/
React.useEffect(() => {
// `fold` dispatches on the datatype, like a switch statement
fileFetchStatus.fold({
some: (fetchStatus) =>
// `fold` just returns null for all of the cases that aren't `Success` objects here
fetchStatus.fold({
success: (value) => {
if (!line) return setResult(None);
const pLine = parseInt(line);
const pCol = parseInt(column);
sourceMap.SourceMapConsumer.with(value, undefined, (consumer) =>
consumer.originalPositionFor({ line: pLine, column: pCol }),
).then((result) => setResult(Some.of(JSON.stringify(result))));
},
}),
none: () => setResult(None),
});
}, [fileFetchStatus, line, column]);
/* ------ */
/* Render */
/* ------ */
return e('div', {},
e('div', { className: 'inputs' },
e('div', { className: 'baseUrl' },
e('label', { htmlFor: 'baseUrl'}, 'Base URL'),
e('input', {
name: 'baseUrl',
required: true,
pattern: ".+",
onChange: onBaseUrlChange,
value: baseUrl,
}),
),
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e('div', { className: 'bundle' },
e('label', { htmlFor: 'bundle'}, 'Bundle'),
e('input', {
name: 'bundle',
required: true,
pattern: "[0-9a-f]{20}",
onChange: onBundleChange,
value: bundle,
}),
bundleFetchStatus.fold({
some: (fetchStatus) => e(ProgressBar, { fetchStatus }),
none: () => null,
}),
),
e('div', { className: 'file' },
e('label', { htmlFor: 'file' }, 'File'),
e('input', {
name: 'file',
required: true,
pattern: ".+\\.js",
onChange: onFileChange,
value: file,
}),
fileFetchStatus.fold({
some: (fetchStatus) => e(ProgressBar, { fetchStatus }),
none: () => null,
}),
),
e('div', { className: 'line' },
e('label', { htmlFor: 'line' }, 'Line'),
e('input', {
name: 'line',
required: true,
pattern: "[0-9]+",
onChange: onLineChange,
value: line,
}),
),
e('div', { className: 'column' },
e('label', { htmlFor: 'column' }, 'Column'),
e('input', {
name: 'column',
required: true,
pattern: "[0-9]+",
onChange: onColumnChange,
value: column,
}),
),
),
e('div', null,
result.fold({
none: () => "Select a bundle, file and line",
some: (value) => e('pre', null, value),
}),
),
);
}
/* Global stuff */
window.Decoder = {
BundlePicker,
};