在尝试将文件上传到Google存储时的承诺优先级
在尝试将文件上传到Google存储时的承诺优先级
提问于 2018-06-08 04:18:17
我正在上传一个文件到Google Cloud。完成后，我希望返回文件URL和一些元数据。我试着这样做：
blobStream.on('finish', () => {
var fileSize;
var fileCreated;
fileUpload.getMetadata()
.then(metadata => {
const mObj = metadata[0];
fileSize = mObj.size;
fileCreated = mObj.timeCreated;
});
fileUpload.getSignedUrl({
action: 'read',
expires: '03-09-2491'
}).then(signedUrl => {
let response = {};
response.name = newFileName;
response.size = fileSize;
response.created = fileCreated;
response.url = signedUrl[0];
resolve(response);
}).catch(error => {
reject(error);
});
});问题是，getSignedUrl方法总是首先触发，"fileSize“+ "fileCreated”永远不会被填充。
我认为我需要链接事件，这样getMetadata才会首先发生，但我对Node (和Promises)相对较新，可以使用一些建议。
根据BERGI的回复编辑的：(以下方法有效)
uploadFileToStorage(file) {
let utils = new Utils();
let newFileName = `${utils._guid()}-${Date.now()}`;
let bucket = admin.storage().bucket();
let filePath = url.format('audioFiles/' + newFileName);
let fileUpload = bucket.file(filePath);
let prom = new Promise(function(resolve, reject) {
if (!file) {
reject('No file provided');
return;
}
const blobStream = fileUpload.createWriteStream({
metadata: {
contentType: file.mimetype
}
});
blobStream.on('error', (error) => {
reject('Something is wrong! Unable to upload at the moment.');
return;
});
blobStream.on('finish', resolve);
blobStream.end(file.buffer);
}).then(() => {
return Promise.all([
fileUpload.getMetadata(),
fileUpload.getSignedUrl({
action: 'read',
expires: '03-09-2491'
}),
]);
}).then(([metadata, signedUrl]) => {
const fileSize = metadata[0].size;
const fileCreated = metadata[0].timeCreated;
const response = {
name: newFileName,
size: fileSize,
created: fileCreated,
url: signedUrl[0],
};
return response;
});
return prom;
}回答 1
Stack Overflow用户
回答已采纳
发布于 2018-06-08 05:39:23
不要创建两个独立的promises，也不要使用你永远不知道什么时候会被赋值的外部作用域变量。相反，使用Promise.all来等待多个承诺：
new Promise(resolve => {
blobStream.on('finish', resolve);
}).then(() => {
return Promise.all([
fileUpload.getMetadata(),
fileUpload.getSignedUrl({
action: 'read',
expires: '03-09-2491'
}),
]);
}).then(([metadata, signedUrl]) => {
const fileSize = metadata[0].size;
const fileCreated = metadata[0].timeCreated;
const response = {
name: newFileName,
size: fileSize,
created: fileCreated,
url: signedUrl[0],
});
return response;
});也要避免使用using further promises inside the Promise constructor！
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原文链接：
https://stackoverflow.com/questions/50749581
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