在项目中,我有一个循环遍历URL列表。它从每个网址下载文件,并通过下载的文件进行一些后期处理。完成forEach后运行回调函数
完成所有过程(包括下载过程和后期过程)之后,我想要执行回调函数。由于后期处理包含一些流式处理任务,因此它具有关闭事件如果可以识别最后一项,我可以将回调函数传递给关闭事件。但是,由于循环是异步的,因此我无法跟踪哪个项目最后完成。
现在,我使用5秒的超时时间来确保在整个过程之后执行回调。显然,这是不可持续的。处理这个问题的好方法是什么?
循环代码:
exports.processArray = (items, process, callback) => {
var todo = items.concat();
setTimeout(function() {
process(todo.shift());
if(todo.length > 0) {
// execute download and post process each second
// however it doesn't guarantee one start after previous one done
setTimeout(arguments.callee, 1000);
} else {
setTimeout(() => {callback();}, 5000);
}
}, 1000);
};
processArray(
// First param, the array
urlList,
// Second param, download and post process
(url) => {
if(url.startsWith('http')) {
getDataReg(url, uid);
}
else if(url.startsWith('ftp')) {
getDataFtp(url, uid);
}
else {
console.log('not a valid resource');
}
},
// Third param, callback to be executed after all done
() => {
Request.get(`${config.demouri}bound=${request.query.boundary};uid=${uid}`, {
method: 'GET',
auth: auth
})
.on('response', (response) => {
console.log('response event emmits');
zipFiles(uid)
.then((path) => {
reply.file(path, { confine: false, filename: uid + '.zip', mode: 'inline'}).header('Content-Disposition');
});
});
}
);
下载和后处理:
exports.getDataFtp = (url, uid) => {
console.log('get into ftp');
var usefulUrl = url.split('//')[1];
var spliter = usefulUrl.indexOf('/');
var host = usefulUrl.substring(0, spliter);
var dir = usefulUrl.substring(spliter+1, usefulUrl.length);
var client = new ftp();
var connection = {
host: host
};
var fileNameStart = dir.lastIndexOf('/') + 1;
var fileNameEnd = dir.length;
var fileName = dir.substring(fileNameStart, fileNameEnd);
console.log('filename: ', fileName);
client.on('ready',() => {
console.log('get into ftp ready');
client.get(dir, (err, stream) => {
if (err) {
console.log('get file err:', err);
return;
} else{
console.log('get into ftp get');
stream.pipe(fs.createWriteStream(datadir + `download/${uid}/${fileName}`));
stream.on('end',() => {
console.log('get into ftp close');
unzipData(datadir + `download/${uid}/`, fileName, uid);
client.end();
});
}
});
});
client.connect(connection);
};
exports.getDataReg = (url, uid) => {
console.log('get into http');
var fileNameStart = url.lastIndexOf('/') + 1;
var fileNameEnd = url.length;
var fileName = url.substring(fileNameStart, fileNameEnd);
var file = fs.createWriteStream(datadir + `download/${uid}/${fileName}`);
if (url.startsWith('https')) {
https.get(url, (response) => {
console.log('start piping file');
response.pipe(file);
file.on('finish',() => {
console.log('get into http finish');
unzipData(datadir + `download/${uid}/`, fileName, uid);
});
}).on('error', (err) => { // Handle errors
fs.unlink(datadir + `download/${uid}/${fileName}`);
console.log('download file err: ', err);
});
} else {
http.get(url, (response) => {
console.log('start piping file');
response.pipe(file);
file.on('finish',() => {
unzipData(datadir + `download/${uid}/`, fileName, uid);
});
}).on('error', (err) => {
fs.unlink(datadir + `download/${uid}/${fileName}`);
console.log('download file err: ', err);
});
}
};
function unzipData(path, fileName, uid) {
console.log('get into unzip');
console.log('creating: ', path + fileName);
fs.createReadStream(path + fileName)
.pipe(unzip.Extract({path: path}))
.on('close',() => {
console.log('get into unzip close');
var filelist = listFile(path);
filelist.forEach((filePath) => {
if (!filePath.endsWith('.zip')) {
var components = filePath.split('/');
var component = components[components.length-1];
mv(filePath, datadir + `processing/${uid}/${component}`, (err) => {
if(err) {
console.log('move file err: ');
} else {
console.log('move file done');
}
});
}
});
fs.unlink(path + fileName, (err) => {});
});
}
处理它通过处理异步代码“正确” - 使用回调或承诺 –
可以'processArray()'调用中使用'Promise'构造。不知道为什么'nodejs'没有实现流标准来使用'Promise'而不是回调。这个问题在过去一周左右出现了好几次。 – guest271314
你能用代码示例回答这个问题吗? – zhangjinzhou