Http使用请求首部Range标头分段传输时遇到的问题

ly5222518000 2019-01-27 03:48:28

新人分不多请大佬帮帮忙
最近在学习Http原理，了解到请求首部的Range标头可以通知服务器返回的响应正文字节范围
于是有个想法，断点续传的功能是不是就可以这么实现
在本地IIS上放了一个图片，开始测试分段传输这张图片
由于WebClient的DownloadFile方法不能实现断点续传（也有可能是我不会用它实现断点续传）
所以我就使用HttpWebRequest来编写代码
下面是代码

Public Class Form1



    Public url As String = "http://localhost/image/1.jpg"        '原图

    Public save As String = "C:\Users\李阳\Desktop\1.jpg"      '下载文件保存的位置

    Public file As String = "C:\Users\李阳\Desktop\12.jpg"      '这也是原图，我放到桌面上了一个



    Private Sub Form1_Load(sender As Object, e As EventArgs) Handles Me.Load

        DownloadFirst5000()             '下载前5000字节

        DownloadNext5000()            '下载接下来的5000字节

    End Sub



    Private Sub BtnStart_Click(sender As Object, e As EventArgs) Handles btnStart.Click

        Dim stream1 As FileStream = New FileStream(save, FileMode.Open)     '流1是下载的图片

        Dim stream2 As FileStream = New FileStream(file, FileMode.Open)      '流2是原图

        Dim builder As New Text.StringBuilder

        For i As Integer = 1 To New FileInfo(save).Length                    '一个字节一个字节的比较

            Dim byte1 As Integer = stream1.ReadByte

            Dim byte2 As Integer = stream2.ReadByte

            If byte1 <> byte2 Then                                         '找到不同的

                builder.AppendFormat(String.Format("第{0,7} 位，流1:{1,4} ，流2:{2,4}", i, byte1, byte2)).AppendLine()

            End If

        Next

        Log(builder.ToString)

    End Sub



    Sub DownloadFirst5000()

        Dim request As HttpWebRequest = WebRequest.Create(url)

        request.AddRange("bytes", 0, 4999)

        Dim response As HttpWebResponse = request.GetResponse

        Dim buffer(response.ContentLength - 1) As Byte

        Dim stream As Stream = response.GetResponseStream

        stream.Read(buffer, 0, buffer.Count)

        With New FileStream(save, FileMode.CreateNew)

            .Write(buffer, 0, buffer.Count)

            .Close()

        End With

        Log(response.Headers(HttpResponseHeader.ContentRange))

    End Sub



    Sub DownloadNext5000()

        Dim request As HttpWebRequest = WebRequest.Create(url)

        request.AddRange("bytes", 5000， 9999)

        Dim response As HttpWebResponse = request.GetResponse

        Dim buffer(response.ContentLength - 1) As Byte

        Dim stream As Stream = response.GetResponseStream

        stream.Read(buffer, 0, buffer.Count)

        With New FileStream(save, FileMode.Append)

            .Write(buffer, 0, buffer.Count)

            .Close()

        End With

        Log(response.Headers(HttpResponseHeader.ContentRange))

    End Sub



    Sub 直接下载整个图片()

        Dim request As HttpWebRequest = WebRequest.Create(url)

        Dim response As HttpWebResponse = request.GetResponse

        Dim buffer(response.ContentLength - 1) As Byte

        Dim stream As Stream = response.GetResponseStream

        stream.Read(buffer, 0, buffer.Count)

        With New FileStream(save, FileMode.CreateNew)

            .Write(buffer, 0, buffer.Count)

            .Close()

        End With

        Log(response.Headers(HttpResponseHeader.ContentLength))

    End Sub



    Sub Log(text As String)                              '写日志

        With New StreamWriter("C:\Users\李阳\Desktop\log.txt", True, System.Text.Encoding.Unicode)

            .WriteLine(text)

            .Close()

        End With

    End Sub

End Class

DownloadFirst5000()是下载前5000字节
DownloadNext5000()是下载接下来的5000字节
按钮是对比两个文件前10000个字节的不同处，然后写到日志里
下面是日志的截图

日志中可以看到，IIS返回的信息没有任何问题分别是从 0-4999 字节和 5000-9999 字节
前4000多字节没有任何问题，但是从4614字节开始，下载的文件中所有字节都是0，后面截图就不放了，全是0
这个图片是40多万字节，哪怕不用Range标头，直接全都接收了再比较也是同样的结果，依旧是4614位开始全是0
我把url换成本地iis首页，重新测试500字节一组，没有任何问题，下面是截图