我目前正在嘗試開發一個谷歌云功能來決議多部分檔案（excel 格式或 csv）以填充 firestore 資料庫。
我在輔助函式中使用 busboy 來決議檔案，將其轉換為 json 并將其回傳給主函式。
一切順利，直到我試圖回傳決議的資料。我認為最合乎邏輯的做法是從 busboy 'finish' 事件回傳資料，但它似乎沒有回傳資料，因為它一旦回傳到未定義的主函式中。我首先想到了一些與異步代碼執行相關的問題，但是當我嘗試只列印 busboy 完成事件中的資料時，它作業正常。
我試圖在網上找到一些相關的內容，但不幸的是沒有成功。這是我的輔助功能：
// Takes a multipart request and sends back redable data
const processRequest = (req) => {
const busboy = Busboy({headers: req.headers});
formats = ['application/vnd.ms-excel', 'text/csv', 'application/vnd.openxmlformats-officedocument.spreadsheetml.sheet'];
var finalData;
// fieldname is the request key name of the file
// file is the stream
// fname is the name of the fileq
busboy.on('file', (fieldname, file, fname) => {
// Checks if file is right format
if(!formats.includes(fname.mimeType)) throw new FileFormatError('File must be excel or csv');
bytes = [];
// Checks that the request key is the right one
if(fieldname == 'file') {
// Data is the actual bytes, adds it to the buffer each time received
file.on('data', (data) => {
bytes.push(data);
});
// Concatenates the bytes into a buffer and reads data given mimetype
file.on('end', async () => {
buffer = Buffer.concat(bytes);
if(fname.mimeType === 'application/vnd.ms-excel' ||
fname.mimeType === 'application/vnd.openxmlformats-officedocument.spreadsheetml.sheet') {
workbook = XLSX.read(buffer, {type: 'buffer'});
json = excelToJson(workbook);
console.log(json);
finalData = json;
}
if (fname.mimeType === 'text/csv') {
var csv = [];
const stream = Readable.from(buffer.toString());
stream.pipe(CSV.parse({delimiter: ','}))
.on('error', (err) => {
console.log('csv parsing error');
console.log(err.message);
}).on('data', (row) => {
csv.push(row);
}).on('end', () => {
console.log('csv file properly processed');
console.log(csv);
// CSV PARSING LOGIC TO COME, JUST TESTING RIGHT NOW
finalData = csv;
});
}
});
}
});
busboy.on('finish', () => {
console.log('busboy finished');
return finalData;
// WHEN ONLY PRINTED THE DATA IS PRESENT AND DISPLAYS PROPERLY HERE
})
// Processes request body bytes
busboy.end(req.rawBody);
}
我一定有什么誤解，但到目前為止我還不能指出是什么。
在此先感謝您的時間 ：）
uj5u.com熱心網友回復：
您無需等待 CSV 決議真正完成。
最好將您的異步代碼重構為使用async/ await。
由于您使用的庫可能僅支持回呼樣式異步，因此您需要new Promise自己進行一些包裝。
可以理解的是，我沒有測驗過下面的代碼，但是像這樣......
/**
* Parse the given buffer as a CSV, return a promise of rows
*/
function parseCSV(buffer) {
return new Promise((resolve, reject) => {
const csv = [];
const stream = Readable.from(buffer.toString());
stream
.pipe("text/csv".parse({ delimiter: "," }))
.on("error", reject)
.on("data", (row) => csv.push(row))
.on("end", () => resolve(csv));
});
}
/**
* Parse the given buffer as a spreadsheet, return a promise
*/
async function parseSpreadsheet(mimeType, buffer) {
if (
mimeType === "application/vnd.ms-excel" ||
mimeType === "application/vnd.openxmlformats-officedocument.spreadsheetml.sheet"
) {
const workbook = XLSX.read(buffer, { type: "buffer" });
return excelToJson(workbook);
}
if (mimeType === "text/csv") {
return parseCSV(buffer);
}
throw new Error(`Unknown mime type ${mimeType}`);
}
/**
* Get the bytes of the field `fieldName` in the request.
*/
function getFileFromRequest(req, fieldName) {
return new Promise((resolve, reject) => {
const busboy = Busboy({ headers: req.headers });
busboy.on("file", (name, file, info) => {
// Only process the field we care about
if (name != fieldName) {
return;
}
const bytes = [];
file.on("data", (data) => bytes.push(data));
file.on("end", () =>
resolve({
info,
buffer: Buffer.concat(bytes),
}),
);
file.on("error", reject);
});
busboy.end(req.rawBody);
});
}
async function parseRequest(req) {
// (1) Get the file as a buffer
const { info, buffer } = await getFileFromRequest(req, "file");
// (2) Try parsing it as a spreadsheet
const data = await parseSpreadsheet(info.mimeType, buffer);
// (3) Do something with the data?
return data;
}
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