.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。