我确实编写了一个 firebase 函数，它可以根据请求操作 PDF 文件，对其进行一些操作，将其保存回存储并将哈希值存档到数据库。
我确实设法让它工作，但它一团糟，因为我从未真正学习过如何使用 ES6 之前的 js 回调。我对这一切都很陌生，并且学会了使用箭头函数和承诺。但在这里，我需要使用纯 JavaScript 的包及其以某种方式工作，但我确实需要清理这个同步/异步混乱，以进行干净的错误处理，并在处理函数后向 firebase 返回一个承诺。
我的函数还包括一些奇怪的文件处理，以便为 pdf 库准备不同的文件： 例如，我创建一个 QR 码，将其保存到 tmp 文件，使用另一个库从 png 创建 jpg 并将其再次保存到 tmp。如果我能做更聪明的事情，我愿意接受任何建议或提示。
链出现问题，因为该函数仍在运行时在几毫秒内完成。
我确实在我的代码中添加了一些注释，但我不知道如何将其更改为 ES6，如果你能帮我清理这个大烂摊子，我将非常感激。
const hummus = require('hummus');
const request = require('request');
const fs = require('fs');
const sha1 = require('sha1');
const images = require("images");
exports.handleDocSignRequests = functions.database.ref('/user_writeable/docrequests/{uid}').onWrite(event => {
var userReq = event.data.val();
var userRef = event.data.ref;
if (!userReq) return Promise.resolve();
if (!userReq.docpath) return Promise.resolve();
let uid = event.params.uid;
let filename = userReq.docpath; // File to sign and hash
return bucket.file(filename).getSignedUrl({ // getting downloadurl from Firebase Storage
action: 'read'
}).then(
(downloadpath) => {
downloadpath = downloadpath[0];
//download pdf - how to turn this into a promise?
download = function (uri, filename, callback) {
request.head(uri, function (err, res, body) {
request(uri).pipe(fs.createWriteStream(filename)).on('close', callback);
});
};
let pdfsourse = LOCAL_TMP_FOLDER + 'downloadedfile.pdf';
return download(downloadpath, pdfsourse, function () { // download callback turn this into ES6
console.log('download finished');
let qrjpg = LOCAL_TMP_FOLDER + 'qrcode.jpg';
var qrpng = LOCAL_TMP_FOLDER + 'qrcode.png';
let qrurl = 'https://some.url/' + userReq.docid;
let pdfdest = LOCAL_TMP_FOLDER + 'newpdf.pdf';
let logfile = './hummus.log';
QRCode.toFile(qrpng, qrurl, { // how to make this a part of the "chain" and go on when finished
version: 4, type: "png", scale: 2, margin: 0
}, function (err) {
if (err) throw err;
console.log('qr png ready');
images(qrpng).save(qrjpg, {operation: 100}); // save png as jpg
console.log('qr jpg ready');
});
// Doing stuff to PDF with HummusJs
let pdfWriter = hummus.createWriterToModify(pdfsourse, {
modifiedFilePath: pdfdest,
log: logfile,
userPassword: 'user',
ownerPassword: 'owner',
userProtectionFlag: 4
});
let pdfReader = pdfWriter.getModifiedFileParser();
let arialFont = pdfWriter.getFontForFile(ariallocal);
let textOptions = {font: arialFont, size: 5, colorspace: 'gray', color: 0x00};
for (let i = 0; i < pdfReader.getPagesCount(); ++i) {
let pageBox = pdfReader.parsePage(i).getMediaBox();
let pageModifier = new hummus.PDFPageModifier(pdfWriter, i, true);
let ctx = pageModifier.startContext().getContext();
ctx.writeText('Document saved', 5, 110, textOptions);
ctx.drawImage(5, 52, qrfile,
{
transformation: {
width: 40,
height: 40,
fit: 'always'
}
});
pageModifier.endContext().writePage();
}
pdfWriter.end();
// How can I be sure PDF is done and written to tmp file? Or is this given by sync function?
// Reading finished PDF from file again, to get base64 for hashing - is there a better way?
let newpdf = fs.readFileSync(pdfdest);
let base64pdf = newpdf.toString('base64');
let hash = sha1(base64pdf);
let signobj = {};
signobj['hash'] = hash;
// Check if document already in database, if not write hash to database,
// upload finished pdf to original place and archive
// and return remove request
let sign_ref = docsign_ref.child(userReq.docid);
return sign_ref.once('value').then(function (snap) {
if (!snap.val()) { //Document is new
let upload1 = bucket.upload(destcry, {destination: filename}).then
(suc => {
console.log('uploaded');
});
//
let upload2 = bucket.upload(destcry, {destination: 'signed/' + userReq.docid + '.pdf'}).then
(suc => {
console.log('uploaded');
});
return Promise.all([upload1, upload2]).then( // When both uploads are finished go on
(suc) => {
return sign_ref.set(signobj).then(
(suc) => {
// Remove Request and return Promise
return userRef.remove();
});
});
}
else {
//Document already in database, this should never happen, only for seq reasons
console.log('doc already in database);
return Promise.resolve();
}
});
});
});
});
正如我在评论中所写，你的问题太宽泛了。我将重点关注您在标题中提出的问题。
ES6 Promise 的主要改进是你应该：
then最后，当您调用外部函数时，请确保将其视为承诺：一旦进行异步操作，您就需要坚持该模式。所以你可以这样调用你的 main 函数：
handleDocSignRequests().then( .... );
这是一些未经测试（！）的代码重写，以解决上述两点。主要变化用
***const hummus = require('hummus');
const request = require('request');
const fs = require('fs');
const sha1 = require('sha1');
const images = require("images");
exports.handleDocSignRequests = functions.database.ref('/user_writeable/docrequests/{uid}').onWrite(event => {
var userReq = event.data.val();
var userRef = event.data.ref;
if (!userReq) return Promise.resolve();
if (!userReq.docpath) return Promise.resolve();
let uid = event.params.uid;
let filename = userReq.docpath; // File to sign and hash
// *** Define these variables at this level, so they are accessible throughout
// the flattened promise-chain:
let signobj = {};
let sign_ref = docsign_ref.child(userReq.docid);
return bucket.file(filename).getSignedUrl({ // getting downloadurl from Firebase Storage
action: 'read'
}).then((downloadpath) => {
downloadpath = downloadpath[0];
let pdfsourse = LOCAL_TMP_FOLDER + 'downloadedfile.pdf';
// *** turned into promise:
// *** return the promise to the main promise chain
return new Promise(resolve => {
request.head(downloadpath, function (err, res, body) {
request(downloadpath)
.pipe(fs.createWriteStream(pdfsourse))
.on('close', resolve);
});
});
}).then(function () {
console.log('download finished');
let qrjpg = LOCAL_TMP_FOLDER + 'qrcode.jpg';
var qrpng = LOCAL_TMP_FOLDER + 'qrcode.png';
let qrurl = 'https://some.url/' + userReq.docid;
// *** Return a promise to make this a part of the "chain" and go on when finished
return new Promise( (resolve, reject) => {
QRCode.toFile(qrpng, qrurl, {
version: 4, type: "png", scale: 2, margin: 0
}, function (err) {
if (err) reject(err); // *** reject
console.log('qr png ready');
images(qrpng).save(qrjpg, {operation: 100}); // save png as jpg
console.log('qr jpg ready');
resolve(); // *** resolve the promise now it's done
});
});
}).then(function () {
// Doing stuff to PDF with HummusJs
let pdfdest = LOCAL_TMP_FOLDER + 'newpdf.pdf';
let logfile = './hummus.log';
let pdfWriter = hummus.createWriterToModify(pdfsourse, {
modifiedFilePath: pdfdest,
log: logfile,
userPassword: 'user',
ownerPassword: 'owner',
userProtectionFlag: 4
});
let pdfReader = pdfWriter.getModifiedFileParser();
let arialFont = pdfWriter.getFontForFile(ariallocal);
let textOptions = {font: arialFont, size: 5, colorspace: 'gray', color: 0x00};
for (let i = 0; i < pdfReader.getPagesCount(); ++i) {
let pageBox = pdfReader.parsePage(i).getMediaBox();
let pageModifier = new hummus.PDFPageModifier(pdfWriter, i, true);
let ctx = pageModifier.startContext().getContext();
ctx.writeText('Document saved', 5, 110, textOptions);
ctx.drawImage(5, 52, qrfile, {
transformation: {
width: 40,
height: 40,
fit: 'always'
}
});
pageModifier.endContext().writePage();
}
pdfWriter.end();
// How can I be sure PDF is done and written to tmp file? Or is this given by sync function?
// Reading finished PDF from file again, to get base64 for hashing - is there a better way?
let newpdf = fs.readFileSync(pdfdest);
let base64pdf = newpdf.toString('base64');
let hash = sha1(base64pdf);
signobj['hash'] = hash;
// Check if document already in database, if not write hash to database,
// upload finished pdf to original place and archive
// and return remove request
// *** Only return the basic promise. Perform the `then` on the outer chain.
return sign_ref.once('value');
}).then(function (snap) {
// *** Do simple case first:
if (snap.val()) {
//Document already in database, this should never happen, only for seq reasons
console.log('doc already in database);
return Promise.resolve();
} // *** No need for `else` here. The above `return` is enough
//Document is new
// *** use array to replace two blocks of very similar code
let promises = [filename, 'signed/' + userReq.docid + '.pdf'].map(destination =>
return bucket.upload(destcry, {destination}).then(suc => {
console.log('uploaded');
});
});
// *** Return the basic promise. Perform the `then` on the outer chain
return Promise.all(promises);// Wait for both uploads to finish
}).then( suc => {
// *** I suppose this also has to run when not a new document....
// *** Again: return the promise and perform the `then` on the outer chain
return sign_ref.set(signobj);
}).then( suc => {
// Remove Request and return Promise
return userRef.remove();
});
});