c# - 如何从 C# 的 BinaryWriter 创建的二进制文件中读取 php 中的字符串

Question

我的 C# 代码正在使用 BinaryWriter 编写这样的二进制文件:

writer.Write(Encoding.ASCII.GetBytes("MAGIC")); //5 ascii characters
writer.Write(version.ToString()); // could be any System.Version.ToString(): "1.2.3.4" or "1.2" or "1.1.1.11", etc
writer.Write(hash); // byte[20]
writer.Write(signature); // byte[256]
// etc.

在 PHP 中，我正在尝试阅读它。现在我正在这样做:

$myfile = fopen("private/test.txt", "r+") or die("Unable to open file!");
echo fread($myfile,5); // read/print the magic file identifier

// problem start
$versionLength = ?????;
//problem end

$versionString = fread($myfile,$versionLength);
.....

据我了解，BinaryWriter 将在 LEB128 format 中为字符串加上可变大小的值作为前缀.我怎样才能从这个长度的二进制文件中读取，以便我可以读取字符串的正确长度？我想我会用 Google 和搜索 Stack Overflow 找到一些东西，但我没有运气。我尝试了 unpack 变量但没有成功。

Answer 1

好吧，我的同事为我写了一个方法来做这件事，就在这里:

function ReadVarInt($file) {
$val = 0;
$bits = 0;
while ($bits != 35) {
    $n = ord(fread($file, 1));
    if ($n === FALSE) return FALSE;
    $val |= ($n & 0x7F) << $bits;
    $bits += 7;
    if (!($n & 0x80))
        return $val;
}
//error "Too many bytes in what should have been a 7 bit encoded Int32.";
return FALSE;
}

function ReadString($file) {
    $len = ReadVarInt($file);
    if ($len === FALSE) return FALSE;
    if ($len < 0) {
        //error "Negative String Length";
        return FALSE;
    }
    return fread($file, $len);
}

像这样简单地调用:

$myfile = fopen($filename, "r+") or die("Unable to open file!");
$string = ReadString($myfile);