DotNET6在Linux环境生成验证码

众所周知使用System.Drawing.Imaging是无法在Linux环境生成图片的

因为Linux环境没有相关组件且会报错

The type initializer for 'Gdip' threw an exception

换了一个库SkiaSharp还找来一个帮助类

using SkiaSharp;
using System.Text;

namespace Common.Helper
{
    /// <summary>
    /// 跨平台验证码生成类
    /// https://github.com/mono/SkiaSharp/issues/1341
    /// </summary>
    public class ValidateCodeHelper
    {
        private Random objRandom = new Random();

        #region setting
        /// <summary>
        /// //验证码长度
        /// </summary>
        public int SetLength { get; set; } = 4;

        /// <summary>
        /// 验证码字符串
        /// </summary>
        public string SetVerifyCodeText { get; set; }

        /// <summary>
        /// 是否加入小写字母
        /// </summary>
        public bool SetAddLowerLetter { get; set; } = true;

        /// <summary>
        /// 是否加入大写字母
        /// </summary>
        public bool SetAddUpperLetter { get; set; } = true;

        /// <summary>
        /// 字体大小
        /// </summary>
        public int SetFontSize = 36;

        /// <summary>
        ///  //字体颜色
        /// </summary>
        public SKColor SetFontColor { get; set; } = SKColors.Blue;

        /// <summary>
        /// 字体类型
        /// </summary>
        public string SetFontFamily = "Verdana";

        /// <summary>
        /// 背景色
        /// </summary>
        public SKColor SetBackgroundColor { get; set; } = SKColors.AliceBlue;

        /// <summary>
        /// 是否加入背景线
        /// </summary>
        public bool SetIsBackgroundLine { get; set; }

        /// <summary>
        /// 前景噪点数量
        /// </summary>
        public int SetForeNoisePointCount { get; set; } = 2;

        /// <summary>
        /// 随机码的旋转角度
        /// </summary>
        public int SetRandomAngle { get; set; } = 40;

        /// <summary>
        /// 是否随机字体颜色
        /// </summary>
        public bool SetIsRandomColor { get; set; } = true;

        /// <summary>
        /// 图片宽度
        /// </summary>
        public int SetWith { get; set; } = 200;

        /// <summary>
        /// 图片高度
        /// </summary>
        public int SetHeight { get; set; } = 40;

        /// <summary>
        /// 问题验证码答案，适用于运算符
        /// </summary>
        public string VerifyCodeResult { get; private set; }
        #endregion

        #region Constructor Method
        /// <summary>
        /// ValidateCodeHelper
        /// </summary>
        /// <param name="length"></param>
        /// <param name="isOperation"></param>
        public ValidateCodeHelper(int length = 4, bool isOperation = false)
        {
            if (isOperation)
            {
                var dic = GetQuestion();
                SetVerifyCodeText = dic.Key;
                VerifyCodeResult = dic.Value;
                SetRandomAngle = 0;
            }
            else
            {
                SetLength = length;
                GetVerifyCodeText();
            }
            SetWith = SetVerifyCodeText.Length * SetFontSize;
            SetHeight = Convert.ToInt32((60.0 / 100) * SetFontSize + SetFontSize);

            InitColors();
        }
        #endregion

        #region Private Method

        /// <summary>
        /// 得到验证码字符串
        /// </summary>
        private void GetVerifyCodeText()
        {
            // 没有外部输入验证码时随机生成
            if (string.IsNullOrEmpty(SetVerifyCodeText))
            {
                StringBuilder objStringBuilder = new StringBuilder();

                // 加入数字1-9
                for (int i = 1; i <= 9; i++)
                {
                    objStringBuilder.Append(i.ToString());
                }

                // 加入大写字母A-Z，不包括O
                if (SetAddUpperLetter)
                {
                    char temp = ' ';

                    for (int i = 0; i < 26; i++)
                    {
                        temp = Convert.ToChar(i + 65);

                        // 如果生成的字母不是'O'
                        if (!temp.Equals('O'))
                        {
                            objStringBuilder.Append(temp);
                        }
                    }
                }

                // 加入小写字母a-z，不包括o
                if (SetAddLowerLetter)
                {
                    char temp = ' ';

                    for (int i = 0; i < 26; i++)
                    {
                        temp = Convert.ToChar(i + 97);

                        // 如果生成的字母不是'o'
                        if (!temp.Equals('o'))
                        {
                            objStringBuilder.Append(temp);
                        }
                    }
                }

                // 生成验证码字符串
                {
                    int index = 0;

                    for (int i = 0; i < SetLength; i++)
                    {
                        index = objRandom.Next(0, objStringBuilder.Length);

                        SetVerifyCodeText += objStringBuilder[index];

                        objStringBuilder.Remove(index, 1);
                    }
                }
            }
        }

        /// <summary>
        /// 获取随机颜色
        /// </summary>
        /// <returns></returns>
        private SKColor GetRandomColor()
        {
            Random RandomNum_First = new Random((int)DateTime.Now.Ticks);

            // 对于C#的随机数，没什么好说的
            System.Threading.Thread.Sleep(RandomNum_First.Next(50));
            Random RandomNum_Sencond = new Random((int)DateTime.Now.Ticks)

            // 为了在白色背景上显示，尽量生成深色
            int int_Red = RandomNum_First.Next(256);
            int int_Green = RandomNum_Sencond.Next(256);
            int int_Blue = (int_Red + int_Green > 400) ? 0 : 400 - int_Red - int_Green;
            int_Blue = (int_Blue > 255) ? 255 : int_Blue;
            return SKColor.FromHsv(int_Red, int_Green, int_Blue);
        }
        #endregion

        #region Public Method
        /// <summary>
        /// 获取问题
        /// </summary>
        /// <param name="questionList">默认数字加减验证</param>
        /// <returns></returns>
        public KeyValuePair<string, string> GetQuestion(Dictionary<string, string> questionList = null)
        {
            if (questionList == null)
            {
                questionList = new Dictionary<string, string>();
                var operArray = new string[] { "+", "*", "-", "/" };
                var left = objRandom.Next(0, 10);
                var right = objRandom.Next(0, 10);
                var oper = operArray[objRandom.Next(0, operArray.Length)];
                string key = string.Empty, val = string.Empty;
                switch (oper)
                {
                    case "+":
                        key = string.Format("{0}+{1}=?", left, right);
                        val = (left + right).ToString();
                        questionList.Add(key, val);
                        break;
                    case "*":
                        key = string.Format("{0}×{1}=?", left, right);
                        val = (left * right).ToString();
                        questionList.Add(key, val);
                        break;
                    case "-":
                        if (left < right)
                        {
                            var intTemp = left;
                            left = right;
                            right = intTemp;
                        }
                        questionList.Add(left + "-" + right + "= ?", (left - right).ToString());
                        break;
                    case "/":
                        right = objRandom.Next(1, 10);
                        left = right * objRandom.Next(1, 10);
                        questionList.Add(left + "÷" + right + "= ?", (left / right).ToString());
                        break;
                }
            }
            return questionList.ToList()[objRandom.Next(0, questionList.Count)];
        }
        #endregion

        #region newCode
        /// <summary>
        /// 干扰线的颜色集合
        /// </summary>
        private List<SKColor> colors { get; set; }

        /// <summary>
        /// InitColors
        /// </summary>
        public void InitColors()
        {
            colors = new List<SKColor>();
            colors.Add(SKColors.AliceBlue);
            colors.Add(SKColors.PaleGreen);
            colors.Add(SKColors.PaleGoldenrod);
            colors.Add(SKColors.Orchid);
            colors.Add(SKColors.OrangeRed);
            colors.Add(SKColors.Orange);
            colors.Add(SKColors.OliveDrab);
            colors.Add(SKColors.Olive);
            colors.Add(SKColors.OldLace);
            colors.Add(SKColors.Navy);
            colors.Add(SKColors.NavajoWhite);
            colors.Add(SKColors.Moccasin);
            colors.Add(SKColors.MistyRose);
            colors.Add(SKColors.MintCream);
            colors.Add(SKColors.MidnightBlue);
            colors.Add(SKColors.MediumVioletRed);
            colors.Add(SKColors.MediumTurquoise);
            colors.Add(SKColors.MediumSpringGreen);
            colors.Add(SKColors.LightSlateGray);
            colors.Add(SKColors.LightSteelBlue);
            colors.Add(SKColors.LightYellow);
            colors.Add(SKColors.Lime);
            colors.Add(SKColors.LimeGreen);
            colors.Add(SKColors.Linen);
            colors.Add(SKColors.PaleTurquoise);
            colors.Add(SKColors.Magenta);
            colors.Add(SKColors.MediumAquamarine);
            colors.Add(SKColors.MediumBlue);
            colors.Add(SKColors.MediumOrchid);
            colors.Add(SKColors.MediumPurple);
            colors.Add(SKColors.MediumSeaGreen);
            colors.Add(SKColors.MediumSlateBlue);
            colors.Add(SKColors.Maroon);
            colors.Add(SKColors.PaleVioletRed);
            colors.Add(SKColors.PapayaWhip);
            colors.Add(SKColors.PeachPuff);
            colors.Add(SKColors.Snow);
            colors.Add(SKColors.SpringGreen);
            colors.Add(SKColors.SteelBlue);
            colors.Add(SKColors.Tan);
            colors.Add(SKColors.Teal);
            colors.Add(SKColors.Thistle);
            colors.Add(SKColors.SlateGray);
            colors.Add(SKColors.Tomato);
            colors.Add(SKColors.Violet);
            colors.Add(SKColors.Wheat);
            colors.Add(SKColors.White);
            colors.Add(SKColors.WhiteSmoke);
            colors.Add(SKColors.Yellow);
            colors.Add(SKColors.YellowGreen);
            colors.Add(SKColors.Turquoise);
            colors.Add(SKColors.LightSkyBlue);
            colors.Add(SKColors.SlateBlue);
            colors.Add(SKColors.Silver);
            colors.Add(SKColors.Peru);
            colors.Add(SKColors.Pink);
            colors.Add(SKColors.Plum);
            colors.Add(SKColors.PowderBlue);
            colors.Add(SKColors.Purple);
            colors.Add(SKColors.Red);
            colors.Add(SKColors.SkyBlue);
            colors.Add(SKColors.RosyBrown);
            colors.Add(SKColors.SaddleBrown);
            colors.Add(SKColors.Salmon);
            colors.Add(SKColors.SandyBrown);
            colors.Add(SKColors.SeaGreen);
            colors.Add(SKColors.SeaShell);
            colors.Add(SKColors.Sienna);
            colors.Add(SKColors.RoyalBlue);
            colors.Add(SKColors.LightSeaGreen);
            colors.Add(SKColors.LightSalmon);
            colors.Add(SKColors.LightPink);
            colors.Add(SKColors.Crimson);
            colors.Add(SKColors.Cyan);
            colors.Add(SKColors.DarkBlue);
            colors.Add(SKColors.DarkCyan);
            colors.Add(SKColors.DarkGoldenrod);
            colors.Add(SKColors.DarkGray);
            colors.Add(SKColors.Cornsilk);
            colors.Add(SKColors.DarkGreen);
            colors.Add(SKColors.DarkMagenta);
            colors.Add(SKColors.DarkOliveGreen);
            colors.Add(SKColors.DarkOrange);
            colors.Add(SKColors.DarkOrchid);
            colors.Add(SKColors.DarkRed);
            colors.Add(SKColors.DarkSalmon);
            colors.Add(SKColors.DarkKhaki);
            colors.Add(SKColors.DarkSeaGreen);
            colors.Add(SKColors.CornflowerBlue);
            colors.Add(SKColors.Chocolate);
            colors.Add(SKColors.AntiqueWhite);
            colors.Add(SKColors.Aqua);
            colors.Add(SKColors.Aquamarine);
            colors.Add(SKColors.Azure);
            colors.Add(SKColors.Beige);
            colors.Add(SKColors.Bisque);
            colors.Add(SKColors.Coral);
            colors.Add(SKColors.Black);
            colors.Add(SKColors.Blue);
            colors.Add(SKColors.BlueViolet);
            colors.Add(SKColors.Brown);
            colors.Add(SKColors.BurlyWood);
            colors.Add(SKColors.CadetBlue);
            colors.Add(SKColors.Chartreuse);
            colors.Add(SKColors.BlanchedAlmond);
            colors.Add(SKColors.Transparent);
            colors.Add(SKColors.DarkSlateBlue);
            colors.Add(SKColors.DarkTurquoise);
            colors.Add(SKColors.IndianRed);
            colors.Add(SKColors.Indigo);
            colors.Add(SKColors.Ivory);
            colors.Add(SKColors.Khaki);
            colors.Add(SKColors.Lavender);
            colors.Add(SKColors.LavenderBlush);
            colors.Add(SKColors.HotPink);
            colors.Add(SKColors.LawnGreen);
            colors.Add(SKColors.LightBlue);
            colors.Add(SKColors.LightCoral);
            colors.Add(SKColors.LightCyan);
            colors.Add(SKColors.LightGoldenrodYellow);
            colors.Add(SKColors.LightGray);
            colors.Add(SKColors.LightGreen);
            colors.Add(SKColors.LemonChiffon);
            colors.Add(SKColors.DarkSlateGray);
            colors.Add(SKColors.Honeydew);
            colors.Add(SKColors.Green);
            colors.Add(SKColors.DarkViolet);
            colors.Add(SKColors.DeepPink);
            colors.Add(SKColors.DeepSkyBlue);
            colors.Add(SKColors.DimGray);
            colors.Add(SKColors.DodgerBlue);
            colors.Add(SKColors.Firebrick);
            colors.Add(SKColors.GreenYellow);
            colors.Add(SKColors.FloralWhite);
            colors.Add(SKColors.Fuchsia);
            colors.Add(SKColors.Gainsboro);
            colors.Add(SKColors.GhostWhite);
            colors.Add(SKColors.Gold);
            colors.Add(SKColors.Goldenrod);
            colors.Add(SKColors.Gray);
            colors.Add(SKColors.ForestGreen);
        }

        /// <summary>
        /// 创建画笔
        /// </summary>
        /// <param name="color"></param>
        /// <param name="fontSize"></param>
        /// <returns></returns>
        private SKPaint CreatePaint(SKColor color, float fontSize)
        {
            SkiaSharp.SKTypeface font = SKTypeface.FromFamilyName(null, SKFontStyleWeight.SemiBold, SKFontStyleWidth.ExtraCondensed, SKFontStyleSlant.Upright);
            SKPaint paint = new SKPaint();
            paint.IsAntialias = true;
            paint.Color = color;
            paint.Typeface = font;
            paint.TextSize = fontSize;
            return paint;
        }

        /// <summary>
        /// 获取验证码图片
        /// </summary>
        /// <param name="lineNum">干扰线数量</param>
        /// <param name="lineStrookeWidth">干扰线宽度</param>
        /// <returns></returns>
        public byte[] GetVerifyCodeImage(int lineNum = 1, int lineStrookeWidth = 1)
        {
            // 创建bitmap位图
            using (SKBitmap image2d = new SKBitmap(SetWith, SetHeight, SKColorType.Bgra8888, SKAlphaType.Premul))
            {
                // 创建画笔
                using (SKCanvas canvas = new SKCanvas(image2d))
                {
                    // 填充背景颜色为白色
                    if (SetIsRandomColor)
                    {
                        SetFontColor = GetRandomColor();
                    }

                    // 填充白色背景
                    canvas.Clear(SetBackgroundColor);

                    AddForeNoisePoint(image2d);
                    AddBackgroundNoisePoint(image2d, canvas);

                    // 将文字写到画布上
                    var drawStyle = new SKPaint();
                    drawStyle.IsAntialias = true;
                    drawStyle.TextSize = SetFontSize;
                    char[] chars = SetVerifyCodeText.ToCharArray();
                    for (int i = 0; i < chars.Length; i++)
                    {
                        var font = SKTypeface.FromFamilyName(SetFontFamily, SKFontStyleWeight.SemiBold, SKFontStyleWidth.ExtraCondensed, SKFontStyleSlant.Upright);

                        // 转动的度数
                        float angle = objRandom.Next(-30, 30);

                        canvas.Translate(12, 12);

                        float px = ((i) * SetFontSize);
                        float py = (SetHeight) / 2;

                        canvas.RotateDegrees(angle, px, py);

                        drawStyle.Typeface = font;
                        drawStyle.Color = SetFontColor;
                        // 写字 (i + 1) * 16, 28
                        canvas.DrawText(chars[i].ToString(), px, py, drawStyle);
                        canvas.RotateDegrees(-angle, px, py);
                        canvas.Translate(-12, -12);
                    }
                    // 画随机干扰线
                    using (SKPaint disturbStyle = new SKPaint())
                    {
                        Random random = new Random();
                        for (int i = 0; i < lineNum; i++)
                        {
                            disturbStyle.Color = colors[random.Next(colors.Count)];
                            disturbStyle.StrokeWidth = lineStrookeWidth;
                            canvas.DrawLine(random.Next(0, SetWith), random.Next(0, SetHeight), random.Next(0, SetWith), random.Next(0, SetHeight), disturbStyle);
                        }
                    }
                    // 返回图片byte
                    using (SKImage img = SKImage.FromBitmap(image2d))
                    {
                        using (SKData p = img.Encode(SKEncodedImageFormat.Png, 100))
                        {
                            return p.ToArray();
                        }
                    }
                }
            }
        }

        /// <summary>
        /// AddForeNoisePoint
        /// </summary>
        /// <param name="objBitmap"></param>
        private void AddForeNoisePoint(SKBitmap objBitmap)
        {
            for (int i = 0; i < objBitmap.Width * SetForeNoisePointCount; i++)
            {
                objBitmap.SetPixel(objRandom.Next(objBitmap.Width), objRandom.Next(objBitmap.Height), SetFontColor);
            }
        }

        /// <summary>
        /// AddBackgroundNoisePoint
        /// </summary>
        /// <param name="objBitmap"></param>
        /// <param name="objGraphics"></param>
        private void AddBackgroundNoisePoint(SKBitmap objBitmap, SKCanvas objGraphics)
        {
            using (SKPaint objPen = CreatePaint(SKColors.Azure, 0))
            {
                for (int i = 0; i < objBitmap.Width * 2; i++)
                {
                    objGraphics.DrawRect(objRandom.Next(objBitmap.Width), objRandom.Next(objBitmap.Height), 1, 1, objPen);
                }
            }
            if (SetIsBackgroundLine)
            {
                //画图片的背景噪音线
                for (var i = 0; i < 12; i++)
                {
                    var x1 = objRandom.Next(objBitmap.Width);
                    var x2 = objRandom.Next(objBitmap.Width);
                    var y1 = objRandom.Next(objBitmap.Height);
                    var y2 = objRandom.Next(objBitmap.Height);

                    objGraphics.DrawLine(x1, y1, x2, y2, CreatePaint(SKColors.Silver, 0));
                }
            }
        }
        #endregion
    }
}

根据GitHub文档装了这三个包但也还是在报错

<PackageReference Include="SkiaSharp" Version="2.88.6" />
<PackageReference Include="SkiaSharp.NativeAssets.Linux" Version="2.88.6" />
<PackageReference Include="SkiaSharp.NativeAssets.Linux.NoDependencies" Version="2.88.6" />

报错信息如下

The type initializer for 'SkiaSharp.SKFontManager' threw an exception.

最后在GitHub上找到了一个解决方案

再添加以下两个包

<PackageReference Include="Microsoft.Maui.Graphics" Version="8.0.3" />
<PackageReference Include="Microsoft.Maui.Graphics.Skia" Version="8.0.3" />

另外Linux还是需要安装libgdiplus组件

apt-get update
apt-get install vim
apt-get install -y libgdiplus && apt-get clean && ln -s /usr/lib/libgdiplus.so /usr/lib/gdiplus.dll

如果是Dockerfile的话则加最后

FROM base AS final
WORKDIR /app
RUN apt-get update -y && apt-get install -y libgdiplus && apt-get clean && ln -s /usr/lib/libgdiplus.so /usr/lib/gdiplus.dll
COPY --from=publish /app/publish .
ENTRYPOINT ["dotnet", "project.dll"]

最后大功告成并附上调用代码

/// <summary>
/// 获取验证码图片
/// </summary>
/// <param name="fileName">默认为空或者传值例如1.png</param>
/// <returns></returns>
[HttpGet]
public IActionResult GetVerifyCodeImage(string? fileName)
{
    ValidateCodeHelper helper = new ValidateCodeHelper();
    var verifyCodeImage = helper.GetVerifyCodeImage(1, 1);
    return File(new MemoryStream(verifyCodeImage), "image/png", fileName);
}