.NET Core 中生成验证码

在开发中，有时候生成验证码的场景目前还是存在的，本篇演示不依赖第三方组件，生成随机验证码图片。

先添加验证码接口

public interface ICaptcha

{

///

///

///

Task GenerateRandomCaptchaAsync(int codeLength = 4);

///

/// 验证码

/// 宽为0将根据验证码长度自动匹配合适宽度

/// 高

///

Task GenerateCaptchaImageAsync(string captchaCode, int width = 0, int height = 30);

}

验证码返回模型

public class CaptchaResult

{

///

public string CaptchaCode { get; set; }

///

public MemoryStream CaptchaMemoryStream { get; set; }

///

public DateTime Timestamp { get; set; }

}

接下来实现接口，主要是依赖微软的System.Drawing.Common组件，注意命名空间的引用

using System;

using System.Drawing;

using System.Drawing.Imaging;

using System.IO;

using System.Threading.Tasks;

...

public class Captcha : ICaptcha

{

private const string Letters = "1,2,3,4,5,6,7,8,9,A,B,C,D,E,F,G,H,J,K,L,M,N,P,Q,R,S,T,U,V,W,X,Y,Z";

public Task GenerateCaptchaImageAsync(string captchaCode, int width = 0, int height = 30)

{

//验证码颜色集合

Color[] c = { Color.Black, Color.Red, Color.DarkBlue, Color.Green, Color.Orange, Color.Brown, Color.DarkCyan, Color.Purple };

//验证码字体集合

string[] fonts = { "Verdana", "Microsoft Sans Serif", "Comic Sans MS", "Arial" };

//定义图像的大小，生成图像的实例

var image = new Bitmap(width == 0 ? captchaCode.Length * 25 : width, height);

var g = Graphics.FromImage(image);

//背景设为白色

g.Clear(Color.White);

var random = new Random();

for (var i = 0; i < 100; i++)

{

var x = random.Next(image.Width);

var y = random.Next(image.Height);

g.DrawRectangle(new Pen(Color.LightGray, 0), x, y, 1, 1);

}

//验证码绘制在g中

for (var i = 0; i < captchaCode.Length; i++)

{

//随机颜色索引值

var cindex = random.Next(c.Length);

//随机字体索引值

var findex = random.Next(fonts.Length);

//字体

var f = new Font(fonts[findex], 15, FontStyle.Bold);

//颜色

Brush b = new SolidBrush(c[cindex]);

var ii = 4;

if ((i + 1) % 2 == 0)

ii = 2;

//绘制一个验证字符

g.DrawString(captchaCode.Substring(i, 1), f, b, 17 + (i * 17), ii);

}

var ms = new MemoryStream();

image.Save(ms, ImageFormat.Png);

g.Dispose();

image.Dispose();

return Task.FromResult(new CaptchaResult

{

CaptchaCode = captchaCode,

CaptchaMemoryStream = ms,

Timestamp = DateTime.Now

});

}

public Task GenerateRandomCaptchaAsync(int codeLength = 4)

{

var array = Letters.Split(new[] { ',' });

var random = new Random();

var temp = -1;

var captcheCode = string.Empty;

for (int i = 0; i < codeLength; i++)

{

if (temp != -1)

random = new Random(i * temp * unchecked((int)DateTime.Now.Ticks));

var index = random.Next(array.Length);

if (temp != -1 && temp == index)

return GenerateRandomCaptchaAsync(codeLength);

temp = index;

captcheCode += array[index];

}

return Task.FromResult(captcheCode);

}

}

在控制器中注入调用

using Microsoft.AspNetCore.Mvc;

using System.Threading.Tasks;

[Route("api/[controller]")]

[ApiController]

public class CaptchaController : ControllerBase

{

[HttpGet]

public async Task CaptchaAsync([FromServices] ICaptcha _captcha)

{

var code = await _captcha.GenerateRandomCaptchaAsync();

var result = await _captcha.GenerateCaptchaImageAsync(code);

return File(result.CaptchaMemoryStream.ToArray(), "image/png");

}

}

实际使用的时候，code就是本次生成的验证码，可以将其保存在session中，进行验证，或者其它方式。

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