.netCore 图形验证码，非System.Drawing.Common

netcore需要跨平台，说白点就是放在windows服务器要能用，放在linux服务器上也能用，甚至macos上。

很多时候需要使用到图形验证码，这就有问题了。

旧方案
1.引入包
<PackageReference Include="System.Drawing.Common" Version="5.0.3" />
2.添加引用
using System.Drawing;
using System.Drawing.Drawing2D;
using System.Drawing.Imaging;
3.在linux上安装libgdiplus
问题在于这个libgdiplus东西非常大，这个东西是moon兼容而来的，而且！！！.net6.0开始不支持这个东西了。

新方案
1.安装包

<PackageReference Include="SixLabors.ImageSharp.Drawing" Version="1.0.0-beta15" />

要勾选预览版，不然找不到这个包

2.添加引用

using SixLabors.Fonts;
using SixLabors.ImageSharp;
using SixLabors.ImageSharp.Drawing.Processing;
using SixLabors.ImageSharp.Formats.Jpeg;
using SixLabors.ImageSharp.PixelFormats;
using SixLabors.ImageSharp.Processing;

3.生成一个验证码图片

public byte[] CreateByteByImgVerifyCode(string verifyCode, int width, int height)
{

using Image image = new Image<Rgba32>(width, height);
//漆底色白色
image.Mutate(x => x.DrawLines(Pens.DashDot(Color.White, width), new PointF[] { new PointF() { X = 0, Y = 0 }, new PointF() { X = width, Y = height } }));

FontCollection collection = new();
FontFamily family = collection.Add("font/font.ttf");
Font font = family.CreateFont(20, FontStyle.Bold);

PointF startPointF = new PointF(5, 5);
Random random = new Random(); //随机数产生器

Color[] colors = new Color[] { Color.Red, Color.Blue, Color.Green, Color.Purple, Color.Peru, Color.LightSeaGreen, Color.Lime, Color.Magenta, Color.Maroon, Color.MediumBlue, Color.MidnightBlue, Color.Navy };
//绘制大小
for (int i = 0; i < verifyCode.Length; i++)
{
image.Mutate(x => x.DrawText(verifyCode[i].ToString(), font, colors[random.Next(colors.Length)], startPointF));
//Console.WriteLine($"draw code:{verifyCode[i]} point:{startPointF.X}-{startPointF.Y}");
startPointF.X += (int)(width - 10) / verifyCode.Length;
startPointF.Y = random.Next(5, 10);
}

IPen pen = Pens.DashDot(Color.Silver, 1);

//绘制干扰线
for (var k = 0; k < 40; k++)
{
PointF[] points = new PointF[2];
points[0] = new PointF(random.Next(width), random.Next(height));
points[1] = new PointF(random.Next(width), random.Next(height));
image.Mutate(x => x.DrawLines(pen, points));
}


using MemoryStream stream = new MemoryStream();
image.Save(stream, JpegFormat.Instance);
//输出图片流
return stream.ToArray();

}

4.在controller中调用它

[HttpGet]
public FileContentResult Code(string guid)
{
try
{
if (String.IsNullOrEmpty(guid))
{
throw new Exception("验证码代码错误，guid不能为空!");
}

//进行特殊符号的替换工作
if (!new System.Text.RegularExpressions.Regex("[0-9,a-z,A-Z]{16}").Match(guid).Success)
{
throw new Exception("guid的位数不足，应为16位随机数，不能包含特殊符号，需要为字母和数字的组合");
}

if (_cache.KeyExits(string.Format(PublicString.CacheImageHead, guid))) { throw new Exception("guid不能重复使用！"); }

//判断guid是否存在

string code = _imgHelper.CreateVerifyCode(ImageHelper.VerifyCodeType.NumberVerifyCode);

_cache.SetString(string.Format(PublicString.CacheImageHead, guid), code, 300);

byte[] codeImage = _imgHelper.CreateByteByImgVerifyCode(code, 80, 36);

return File(codeImage, @"image/jpeg");
}
catch (Exception exl)
{
_logger.LogException(exl);
throw new Exception(exl.Message);
}
}

5.随机数计算，缓存帮助类自己实现。
6.新方案不需要安装libgdiplus
7.旧方案占用内存很大，新方案内存消耗很划算
附上一个Dockerfile的文件内容

FROM mcr.microsoft.com/dotnet/aspnet:6.0-alpine AS base
# 安装tzdata
RUN sed -i 's/dl-cdn.alpinelinux.org/mirrors.aliyun.com/g' /etc/apk/repositories
RUN apk add --no-cache tzdata
#RUN apk add libgdiplus --update-cache --repository http://dl-3.alpinelinux.org/alpine/edge/testing/ --allow-untrusted
#RUN apk add terminus-font
# 设置时区
ENV TZ="Asia/Shanghai"
ENV LANG C.UTF-8

FROM base AS final
WORKDIR /app
EXPOSE 80
COPY . .

ENTRYPOINT ["dotnet", "xxx.HttpApi.Host.dll"]

当前为草稿，暂未完善