.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{ /// <summary> /// 生成随机验证码 /// </summary> /// <param name="codeLength"></param> /// <returns></returns> Task<string> GenerateRandomCaptchaAsync(int codeLength = 4); /// <summary> /// 生成验证码图片 /// </summary> /// <param name="captchaCode">验证码</param> /// <param name="width">宽为0将根据验证码长度自动匹配合适宽度</param> /// <param name="height">高</param> /// <returns></returns> Task<CaptchaResult> GenerateCaptchaImageAsync(string captchaCode, int width = 0, int height = 30);}

验证码返回模型

public class CaptchaResult{ /// <summary> /// CaptchaCode /// </summary> public string CaptchaCode { get; set; } /// <summary> /// CaptchaMemoryStream /// </summary> public MemoryStream CaptchaMemoryStream { get; set; } /// <summary> /// Timestamp /// </summary> 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<CaptchaResult> 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<string> 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<FileContentResult> 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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