文件大小错误节点js

Question

从大文件下载 25mb 小块时，这些块实际上比 25mb 大得多。有人可以帮忙吗？

const fs = require('fs')
const files = fs.readdirSync('../in/')
files.map(fileName => {
  const readable = fs.createReadStream('../in/'+fileName)
  let size = 0

  let temp_chunk;
  let count = 0 

  readable.on("data", (chunk) => {
    temp_chunk += chunk
    const byteSize = new Blob([chunk]).size;

    size += byteSize
    let amount = size / 1000000
    amount = amount.toString()
    amount = amount.substring(0, 5) + 'mb'

    console.log(amount)
    if (amount > 24.5) {
      console.log(fileName+' '+count+' downloaded')
      fs.writeFileSync('../out/'+fileName+count, temp_chunk)
      temp_chunk = ''
      size = 0
      count++
    }
  })
})
  

我尝试从 temp_chunk 读取文件的大小，这有效，但使下载速度明显变慢。

Answer 1

使用 Buffer 来连接块。在字符串上直接使用 += 连接二进制数据（如 temp_chunk += chunk）不适合二进制数据，并且可能会导致意外结果。

解决方案

const fs = require('fs');
const files = fs.readdirSync('../in/');
files.forEach(fileName => {
  const readable = fs.createReadStream('../in/' + fileName);
  let size = 0;
  let temp_chunk = Buffer.alloc(0); // Initialize as an empty buffer
  let count = 0;

  readable.on("data", (chunk) => {
    temp_chunk = Buffer.concat([temp_chunk, chunk]);
    size += chunk.length; // Use chunk.length to get the size in bytes

    let amount = size / 1000000; // Convert to megabytes

    console.log(amount + 'mb');
    if (amount > 24.5) {
      console.log(fileName + ' ' + count + ' downloaded');
      fs.writeFileSync('../out/' + fileName + count, temp_chunk);
      temp_chunk = Buffer.alloc(0); // Reset to an empty buffer
      size = 0;
      count++;
    }
  });

  readable.on("end", () => {
    if (temp_chunk.length > 0) {
      // Write the remaining chunk if there is any
      console.log(fileName + ' ' + count + ' downloaded (last chunk)');
      fs.writeFileSync('../out/' + fileName + count, temp_chunk);
    }
  });
});