前端JS 大于5M的文件分片上传 前端JS代码，服务端VB代码

前端 JavaScript 大于5MB的文件分片上传，通常是通过分块并将每个块作为独立请求发送到服务器，而不是一次性加载整个文件。这里提供一个简单的前端 JavaScript 代码示例和基础的服务器 VB（Visual Basic）代码示例：

**前端 JavaScript (Node.js with axios) 示例**:

const axios = require('axios');
const fs = require('fs');

const FILE_SIZE_LIMIT = 5 * 1024 * 1024; // 5MB

async function uploadLargeFile(filePath) {
  const chunks = [];
  let fileSize = fs.statSync(filePath).size;
  
  for (let i = 0; i <= Math.ceil(fileSize / FILE_SIZE_LIMIT); i++) {
    const start = i * FILE_SIZE_LIMIT;
    const end = Math.min(start + FILE_SIZE_LIMIT, fileSize);
    
    const chunkBuffer = fs.readFileSync(filePath, {start, end});
    chunks.push(chunkBuffer);
    
    // 使用axios发起POST请求
    await axios.post('/upload', {chunk: Buffer.from(chunkBuffer), index: i}, {
      onUploadProgress: ({loaded}) => {
        console.log(`Uploading chunk ${i+1}/${Math.ceil(fileSize / FILE_SIZE_LIMIT)}...`);
      }
    });
  }
}

// 调用函数开始上传
uploadLargeFile('large_file.txt');

**后端 Visual Basic (ASP.NET Core) 示例**:

Imports Microsoft.AspNetCore.Http
Imports Microsoft.AspNetCore.Mvc

Public Class FileUploadController
    <HttpPost>
    Public Async Function Upload([FromBody] UpstreamFiles[] files) As async Task<IActionResult>
        Dim uploadedChunks As New List(Of byte())
        
        For Each file In files
            ' 检查每个分块的有效性，例如检查MD5或文件偏移量
            If ValidateChunk(file.Chunk, file.Index) Then
                uploadedChunks.Add(file.Chunk)
            Else
                Return BadRequest("Invalid chunk")
            End If
        Next
        
        ' 合并所有分块
        Dim mergedFile = MergeChunks(uploadedChunks)
        
        ' 保存合并后的文件到服务器
        SaveToDisk(mergedFile, "received_large_file.txt")

        Return Ok()
    End Function

    Private Function ValidateChunk(chunk As Byte(), index As Integer) As Boolean
        ' 这里只是一个简化的例子，实际应用中应更严谨地验证
        ' 可能包括对比MD5或检查文件偏移
        Return True
    End Function

    Private Function MergeChunks(chunks As List(Of Byte())) As Byte()
        ' 合并分块
        Dim mergedBytes As New ArraySegment(Of Byte)(New Byte(chunks.Sum(Function(c) c.Length))(0))
        Using buffer As New MemoryStream(mergedBytes.Array)
            For Each c In chunks
                buffer.Write(c, 0, c.Length)
            Next
            buffer.Seek(0, SeekOrigin.Begin)
            Return buffer.ToArray()
        End Using
    End Function
    
    Private Sub SaveToDisk(content As Byte(), filePath As String)
        ' 实际上应写入到服务器文件系统
        Using fileStream = New FileStream(filePath, FileMode.Create)
            fileStream.Write(content, 0, content.Length)
        End Using
    End Sub
End Class

注意这仅是个基础示例，实际部署时还需要考虑错误处理、进度反馈以及文件名生成等问题。同时，后端的验证部分应根据实际需求进行调整，如完整性检查等。