joplin/packages/lib/mime-utils.js

const mimeTypes = require('./mime-utils-types');

const mime = {
	fromFileExtension(ext) {
		ext = ext.toLowerCase();
		for (let i = 0; i < mimeTypes.length; i++) {
			const t = mimeTypes[i];
			if (t.e.indexOf(ext) >= 0) {
				return t.t;
			}
		}
		return null;
	},

	fromFilename(name) {
		if (!name) return null;
		const splitted = name.trim().split('.');
		if (splitted.length <= 1) return null;
		return mime.fromFileExtension(splitted[splitted.length - 1]);
	},

	toFileExtension(mimeType) {
		mimeType = mimeType.toLowerCase();
		for (let i = 0; i < mimeTypes.length; i++) {
			const t = mimeTypes[i];
			if (mimeType == t.t) {
				// Return the first file extension that is 3 characters long
				// If none exist return the first one in the list.
				for (let j = 0; j < t.e.length; j++) {
					if (t.e[j].length == 3) return t.e[j];
				}
				return t.e[0];
			}
		}
		return null;
	},

	fromDataUrl(dataUrl) {
		// Example: data:image/jpeg;base64,/9j/4AAQSkZJR.....
		const defaultMime = 'text/plain';
		const p = dataUrl.substr(0, dataUrl.indexOf(',')).split(';');
		let s = p[0];
		s = s.split(':');
		if (s.length <= 1) return defaultMime;
		s = s[1];
		return s.indexOf('/') >= 0 ? s : defaultMime; // https://developer.mozilla.org/en-US/docs/Web/HTTP/Basics_of_HTTP/Data_URIs
	},
};

module.exports = { mime };