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52 lines
2.0 KiB
52 lines
2.0 KiB
import {fromFile} from 'file-type';
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import {extension, lookup} from 'mime-types';
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import * as path from 'path';
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/**
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* Get our best guess of the file extension, based on its original extension (as received from the
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* user), mimeType (as reported by the browser upload, or perhaps some API), and the file
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* contents.
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*
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* The resulting extension is used to choose a parser for imports, and to present the file back
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* to the user for attachments.
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*/
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export async function guessExt(filePath: string, fileName: string, mimeType: string|null): Promise<string> {
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const origExt = path.extname(fileName).toLowerCase(); // Has the form ".xls"
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let mimeExt = extension(mimeType); // Has the form "xls"
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mimeExt = mimeExt ? "." + mimeExt : null; // Use the more comparable form ".xls"
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if (mimeExt === ".json") {
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// It's common for JSON APIs to specify MIME type, but origExt might come from a URL with
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// periods that don't indicate a meaningful extension. Trust mime-type here.
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return mimeExt;
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}
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if (origExt === ".csv") {
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// File type detection doesn't work for these, and mime type can't be trusted. E.g. Windows
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// may report "application/vnd.ms-excel" for .csv files. See
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// https://github.com/ManifoldScholar/manifold/issues/2409#issuecomment-545152220
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return origExt;
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}
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// If extension and mime type agree, let's call it a day.
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if (origExt && (origExt === mimeExt || lookup(origExt.slice(1)) === mimeType)) {
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return origExt;
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}
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// If not, let's take a look at the file contents.
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const detected = await fromFile(filePath);
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const detectedExt = detected ? "." + detected.ext : null;
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if (detectedExt) {
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// For the types for which detection works, we think we should prefer it.
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return detectedExt;
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}
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if (mimeExt === '.txt' || mimeExt === '.bin') {
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// text/plain (txt) and application/octet-stream (bin) are too generic, only use them if we
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// don't have anything better.
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return origExt || mimeExt;
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}
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// In other cases, it's a tough call.
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return origExt || mimeExt;
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}
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