index.js

/* eslint-disable security/detect-non-literal-fs-filename */
const autoParse = require("auto-parse");
const fp = require("fastify-plugin");
const fs = require("fs").promises;
const glob = require("glob");
const path = require("upath");
const { Poppler } = require("node-poppler");
const { v4 } = require("uuid");

/**
 * @author Frazer Smith
 * @description Pre-handler plugin that uses Poppler to convert Buffer containing
 * PDF file in `req.body` to TXT.
 * `req` object is decorated with `conversionResults.body` holding the converted document.
 * @param {Function} server - Fastify instance.
 * @param {object} options - Plugin config values.
 * @param {string} options.binPath - Path to Poppler binary.
 * @param {object=} options.pdfToTxtOptions - Refer to
 * https://github.com/Fdawgs/node-poppler/blob/master/API.md#Poppler+pdfToText
 * for options.
 * @param {string=} options.pdfToTxtOptions.encoding - Sets the encoding to use for text output.
 * @param {string=} options.tempDirectory - Directory for temporarily storing
 * files during conversion. Required for OCR.
 */
async function plugin(server, options) {
	server.addHook("onRequest", async (req) => {
		req.conversionResults = { body: undefined };
	});

	// "onSend" hook used instead of "onResponse" ensures
	// cancelled request temp data is also removed
	server.addHook("onSend", async (req, res) => {
		if (req?.conversionResults?.docLocation) {
			// Remove files from temp directory after response sent
			const files = glob.sync(
				`${path.joinSafe(
					req.conversionResults.docLocation.directory,
					req.conversionResults.docLocation.id
				)}*`
			);

			await Promise.all(files.map((file) => fs.unlink(file)));
		}

		return res;
	});

	server.addHook("preHandler", async (req, res) => {
		/**
		 * `pdfToText` Poppler function still attempts to parse empty bodies/input
		 * and produces results, so catch them here
		 */
		if (req.body === undefined || Object.keys(req.body).length === 0) {
			throw res.badRequest();
		}

		// Define any default settings the plugin should have to get up and running
		const config = {
			binPath: undefined,
			pdfToTxtOptions: { outputEncoding: "UTF-8" },
			tempDirectory: path.joinSafe(__dirname, "..", "temp"),
		};
		Object.assign(config, options);

		const directory = path.normalizeTrim(config.tempDirectory);
		const poppler = new Poppler(config.binPath);

		/**
		 * Create copy of query string params and convert query string params to literal
		 * values to allow Poppler module to use them, as some of the params may be used
		 * in other plugins
		 */
		const query = { ...req.query };
		Object.keys(query).forEach((value) => {
			query[value] = autoParse(query[value]);
		});

		/**
		 * If `ocr` query string param passed then use pdfToCairo and Tesseract OCR engine.
		 * image-to-txt plugin adds the "tesseract" decorator to server instance,
		 * if this is missing then OCR is not supported
		 */
		if (query?.ocr === true && server.tesseract) {
			// Prune params that pdfToCairo cannot accept
			const pdfToCairoAcceptedParams = [
				"cropHeight",
				"cropWidth",
				"cropXAxis",
				"cropYAxis",
				"firstPageToConvert",
				"lastPageToConvert",
			];
			Object.keys(query).forEach((value) => {
				if (!pdfToCairoAcceptedParams.includes(value)) {
					delete query[value];
				}
			});

			// Create temp directory if missing
			await fs.mkdir(directory).catch((err) => {
				// Ignore "EEXIST: An object by the name pathname already exists" error
				/* istanbul ignore if */
				if (err.code !== "EEXIST") {
					throw err;
				}
			});

			// Build temporary file for Poppler to write to, and following plugins to read from
			const id = v4();
			const tempFile = path.joinSafe(directory, id);
			req.conversionResults.docLocation = {
				directory,
				id,
			};

			await poppler
				.pdfToCairo(req.body, tempFile, {
					resolutionXYAxis: 300,
					grayscaleFile: true,
					pngFile: true,
					...query,
				})
				.catch((err) => {
					/**
					 * Poppler will throw if the .pdf file provided
					 * by client is malformed, thus client error code
					 */
					/* istanbul ignore else */
					if (/Syntax Error:/.test(err)) {
						throw res.badRequest();
					} else {
						throw err;
					}
				});

			const files = glob.sync(`${tempFile}*.png`);

			// Pass each image file generate to Tesseract OCR
			const results = await Promise.all(
				files.map(async (file) => {
					try {
						const {
							data: { text },
						} = await server.tesseract.addJob("recognize", file);

						return Promise.resolve(text);
					} catch (err) {
						/* istanbul ignore next */
						return Promise.reject(err);
					}
				})
			);

			req.conversionResults.body = results.join(" ");
		} else {
			// Prune params that pdfToTxt cannot accept
			const pdfToTxtAcceptedParams = [
				"boundingBoxXhtml",
				"boundingBoxXhtmlLayout",
				"cropHeight",
				"cropWidth",
				"cropXAxis",
				"cropYAxis",
				"eolConvention",
				"firstPageToConvert",
				"fixedWidthLayout",
				"generateHtmlMetaFile",
				"lastPageToConvert",
				"listEncodingOptions",
				"maintainLayout",
				"noDiagonalText",
				"noPageBreaks",
				"outputEncoding",
				"ownerPassword",
				"rawLayout",
				"userPassword",
			];
			Object.keys(query).forEach((value) => {
				if (!pdfToTxtAcceptedParams.includes(value)) {
					delete query[value];
				}
			});
			Object.assign(config.pdfToTxtOptions, query);

			try {
				req.conversionResults.body = await poppler.pdfToText(
					req.body,
					undefined,
					config.pdfToTxtOptions
				);
			} catch (err) {
				/**
				 * Poppler will throw if the .pdf file provided
				 * by client is malformed, thus client error code
				 */
				/* istanbul ignore else */
				if (/Syntax Error:/.test(err)) {
					throw res.badRequest();
				} else {
					throw err;
				}
			}
		}

		// Certain querystring options alter output to HTML rather than TXT
		let contentType = "text/plain";
		if (
			query.boundingBoxXhtml ||
			query.boundingBoxXhtmlLayout ||
			query.generateHtmlMetaFile
		) {
			contentType = "text/html";
		}
		res.header(
			"content-type",
			`${contentType}; charset=${config.pdfToTxtOptions.outputEncoding.toLowerCase()}`
		);
	});
}

module.exports = fp(plugin, {
	fastify: "3.x",
	name: "pdf-to-txt",
	dependencies: ["fastify-sensible"],
});