xml字符串拼接的时候如果不考虑用户输入信息包含大于小于的情况, 会导致系统崩溃.
所以如果是纯xml拼接,一定要将 xml的敏感字符给转义掉或者 用 包括起来.

xml敏感的字符包含下面几个. <, > , ", ', &

微软底层已经为我们做了一些工作, 我们只需要调用既可以了.
方法如下.

var safexml = System.Security.SecurityElement.Escape(xml);

用法如下

var safetxt = System.Security.SecurityElement.Escape(txt);
var xml = "<data>"+ safetxt+"</data>"

System.Security.SecurityElement.Escape 我们反编译其源代码可以看到是
如果不想引用这个dll, 可以把下面的源代码复制过来处理一下.


//主要的代码就是这些. 
static SecurityElement()
{
    s_tagIllegalCharacters = new char[] { ' ', '<', '>' };
    s_textIllegalCharacters = new char[] { '<', '>' };
    s_valueIllegalCharacters = new char[] { '<', '>', '"' };
    s_escapeStringPairs = new string[] { "<", "&lt;", ">", "&gt;", "\"", "&quot;", "'", "&apos;", "&", "&amp;" };
    s_escapeChars = new char[] { '<', '>', '"', '\'', '&' };
}

public static string Escape(string str)
{
    if (str == null)
    {
        return null;
    }
    StringBuilder builder = null;
    int length = str.Length;
    int startIndex = 0;
    while (true)
    {
        int num2 = str.IndexOfAny(s_escapeChars, startIndex);
        if (num2 == -1)
        {
            if (builder == null)
            {
                return str;
            }
            builder.Append(str, startIndex, length - startIndex);
            return builder.ToString();
        }
        if (builder == null)
        {
            builder = new StringBuilder();
        }
        builder.Append(str, startIndex, num2 - startIndex);
        builder.Append(GetEscapeSequence(str[num2]));
        startIndex = num2 + 1;
    }
}

private static string GetEscapeSequence(char c)
{
    int length = s_escapeStringPairs.Length;
    for (int i = 0; i < length; i += 2)
    {
        string str = s_escapeStringPairs[i];
        string str2 = s_escapeStringPairs[i + 1];
        if (str[0] == c)
        {
            return str2;
        }
    }
    return c.ToString();
}