Android Code Snippet VB6 VBA uses prefix mode and data structure of prefix mode.

boy8199 · Jun 5, 2019

因为使用VBA，使用了 b4a 的前缀模式传输数据。但是我查了论坛没有找到VBA VB6的代码，但是有VB.net的代码。但是 VB.net有很多VBA VB6 没有的新功能和函数。我用了很多时间去尝试。最终我成功的使用前缀模式发送文件成功。我希望分享我的代码，帮助新的朋友。

同时希望论坛能提供一下更详细的指导。

1、文件名的长度，VB6， 4个字符，32位（倒序）
2、文件名，vb6 string --> utf-8，长度为文件名长度
3、STREAM_PREFIX标志，vb6 4个字符，long（倒序）
4、文件数据长度，vb6（不支持）8个字符，64位，我只用了最后4位 Long（倒序）
6、文件数据
7、Adler-32校验码，vb6（不支持）8个字符，64位，我只用了最后4位 Long（正序）

上面的正序，是指VB6 中的数字存储模式：Long 类型，从左边位，开始存储数据，而V4A的socket是从右开始读取数据的。
代码，我将完善好后在上传给大家。
=================
Because of the use of VBA, the prefix mode of b4a is used to transmit data. But I checked the forum did not find VBA VB6 code, but there is VB. net code. But VB.net has many new functions and functions that VBA VB6 does not have. I spent a lot of time trying. Eventually, I succeeded in sending files in prefix mode. I want to share my code and help new friends.
At the same time, I hope the forum can provide more detailed guidance.
1. File name length, VB6, 4 characters, 32 bits (reverse order)
2. File name, VB6 string - > utf-8, length is file name length
3. STREAM_PREFIX flag, vb64 characters, long (reverse order)
4. File data length, VB6 (not supported) 8 characters, 64 bits, I only used the last 4 bits Long (reverse order)
6. Document data
7. Adler-32 check code, VB6 (unsupported) 8 characters, 64 bits, I only used the last 4 bits Long (positive order)
The positive order above refers to the digital storage mode in VB6: Long type, which stores data from the left bit, while V4A socket reads data from the right.

Code, I will improve it and upload it to you.

boy8199 · Jun 5, 2019

这是Adler-32，的VB6代码。

B4X:

Public Function Adler32Byte(bString() As Byte, Optional ReturnByteCount As Long = 4, _
                             Optional A As Long = 1) As Byte()

    Dim B As Long, x As Long
    Dim bA(3) As Byte
    Dim bB(3) As Byte
    Dim bBA(3) As Byte
    Dim bBa8(7) As Byte
  
    A = (A + (bString(x) And 255)) Mod 65521
  
    For x = 1 To UBound(bString)
        B = (B + A) Mod 65521
        A = (A + (bString(x) And 255)) Mod 65521
    Next x

    CopyMemory bA(0), A, 4
    CopyMemory bB(0), B, 4
  
    CopyMemory bBA(0), bB(1), 1
    CopyMemory bBA(1), bB(0), 1
    CopyMemory bBA(2), bA(1), 1
    CopyMemory bBA(3), bA(0), 1

    If ReturnByteCount = 8 Then
      
        Call CopyMemory(ByVal VarPtr(bBa8(4)), ByVal VarPtr(bBA(0)), 4)
        '8个字节,则前面4个为空白,暂未处理.
        Adler32Byte = bBa8
    Else
        Adler32Byte = bBA
    End If
 
End Function

===================

我发现一个问题: 双方的缓冲区应该一致才能正常工作.
如果服务器一次性验证,那么客户端也应该该一次性验证,否则会出现CRC不匹配的情况.

一次性验证中的 B值,会比多次验证的情况少一次.
=========
A = (A + (bString(x) And 255)) Mod 65521

For x = 1 To UBound(bString)
B = (B + A) Mod 65521
A = (A + (bString(x) And 255)) Mod 65521
Next x

这段代码是用于一次性验证文件的情况.
=============

For x = 0 To UBound(bString)
A = (A + (bString(x) And 255)) Mod 65521
B = (B + A) Mod 65521

Next x
这一段是正常的算法.用于分段验证.

==================

I found a problem: the buffers on both sides should be consistent in order to work properly.
If the server is authenticated once, then the client should also verify it once, otherwise there will be a CRC mismatch.

The B value in one-time verification will be less than the case of multiple verifications.
=========
A = (A + (bString(x) And 255)) Mod 65521

For x = 1 To UBound(bString)
B = (B + A) Mod 65521
A = (A + (bString(x) And 255)) Mod 65521
Next x

This code is used to verify the file once.
=============

For x = 0 To UBound(bString)
A = (A + (bString(x) And 255)) Mod 65521
B = (B + A) Mod 65521

Next x
This section is a normal algorithm. It is used for segmentation verification.

=================

Android Code Snippet VB6 VBA uses prefix mode and data structure of prefix mode.

boy8199

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Android Code Snippet VB6 VBA uses prefix mode and data structure of prefix mode.

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