NodeJS无法从busboy finish事件返回数据

Question

我目前正在尝试开发一个google云功能来解析多部分文件(excel格式或csv)，以填充防火墙数据库。

我在帮助函数中使用busboy解析文件，将其转换为json并将其返回到主函数。

在我试图返回解析的数据之前，一切都进行得很顺利。我认为最符合逻辑的方法是从busboy 'finish‘事件返回数据，但它似乎不返回数据，因为一旦返回主函数，它就没有定义。我第一次想到了一些与异步代码执行有关的问题，但当我试图只在busboy finish事件中打印数据时，它正常工作。

我试图在网上找到一些相关的内容，但不幸的是没有成功。下面是我的助手函数：

// 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);
}

我一定有一些误解，但到目前为止，我还不能指出什么。

提前谢谢您的时间:)

Answer 1

您并不是在等待CSV解析真正完成。

最好将异步代码重构为使用async/await。

由于您使用的库可能只支持回调样式的异步，所以您需要自己执行一些new Promise包装。

可以理解，我还没有测试下面的代码，但是像这样的东西.

/**
 * 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;
}