短信发送是软件开发中的一个常见功能，在国内常用于基于短信验证码的用户注册、找回密码和操作授权等场景。阿里云的短信服务在调用时需要实现一个不是那么容易的签名算法，但如果只是为了发送短信这一个功能就去引用其提供的 SDK 显得非常不经济。同时该 SDK 并未对 .NET 5 进行适配，编译时会提示警告信息：

warning NU1701: 已使用“.NETFramework,Version=v4.6.1, .NETFramework,Version=v4.6.2, .NETFramework,Version=v4.7, .NETFramework,Version=v4.7.1, .NETFramework,Version=v4.7.2, .NETFramework,Version=v4.8”而不是项目目标框架“.NETStandard,Version=v2.0”还原包“BouncyCastle 1.8.6.1”。此包可能与项目不完全兼容。

为了解决上述问题，笔者参照其 SDK 实现了一个简洁版的 AliSmsSender ：仅包含短信发送功能，无需依赖阿里云的 SDK ，仅需要一个文件。

    public class AliSmsSender
    {
        private static readonly HashSet<char> TextTable =
            new HashSet<char>("abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789-_.~");

        private static readonly HttpClient HttpClient = new HttpClient();

        public AliSmsSender(string accessKeyId, string accessKeySecret, string signName)
        {
            if (string.IsNullOrWhiteSpace(accessKeyId))
            {
                throw new ArgumentNullException(nameof(accessKeyId));
            }

            if (string.IsNullOrWhiteSpace(accessKeySecret))
            {
                throw new ArgumentNullException(nameof(accessKeySecret));
            }

            if (string.IsNullOrWhiteSpace(signName))
            {
                throw new ArgumentNullException(nameof(signName));
            }

            AccessKeyId = accessKeyId;
            AccessKeySecret = accessKeySecret;
            SignName = signName;
        }

        public string AccessKeyId { get; }
        public string AccessKeySecret { get; }
        public string SignName { get; }

        public async Task<SendSmsResponse> SendAsync(string phone, string templateCode, object param)
        {
            var dictionary = new SortedDictionary<string, string>(StringComparer.Ordinal)
            {
                {"AccessKeyId", AccessKeyId},
                {"Action", "SendSms"},
                {"Format", "JSON"},
                {"PhoneNumbers", phone},
                {"SignatureMethod", "HMAC-SHA1"},
                {"SignatureNonce", Guid.NewGuid().ToString()},
                {"SignatureVersion", "1.0"},
                {"SignName", SignName},
                {"TemplateCode", templateCode},
                {"TemplateParam", JsonConvert.SerializeObject(param)},
                {"Timestamp", GetTimeStamp()},
                {"Version", "2017-05-25"}
            };
            var source = ComposeStringToSign("POST", dictionary);
            var value = SignString(source, AccessKeySecret + "&");
            dictionary.Add("Signature", value);
            using (var request = new HttpRequestMessage(
                    HttpMethod.Post,
                    "http://dysmsapi.aliyuncs.com"
                )
                {
                    Content = new FormUrlEncodedContent(dictionary)
                }
            )
            {
                using (var response = await HttpClient.SendAsync(request))
                {
                    var json = await response.Content.ReadAsStringAsync();
                    return JsonConvert.DeserializeObject<SendSmsResponse>(json);
                }
            }
        }

        private string SignString(string source, string accessSecret)
        {
            string result;
            using (var keyedHashAlgorithm = KeyedHashAlgorithm.Create("HMACSHA1"))
            {
                keyedHashAlgorithm.Key = Encoding.UTF8.GetBytes(accessSecret.ToCharArray());
                result = Convert.ToBase64String(
                    keyedHashAlgorithm.ComputeHash(
                        Encoding.UTF8.GetBytes(
                            source.ToCharArray()
                        )
                    )
                );
            }

            return result;
        }

        private string ComposeStringToSign(string method, IEnumerable<KeyValuePair<string, string>> items)
        {
            var data = ComposeStringToSign(items);
            return $"{method}&{PercentEncode("/")}&{PercentEncode(data)}";
        }

        private string ComposeStringToSign(IEnumerable<KeyValuePair<string, string>> items)
        {
            var builder = new StringBuilder();
            foreach (var item in items)
            {
                builder.Append(PercentEncode(item.Key))
                    .Append('=')
                    .Append(PercentEncode(item.Value))
                    .Append('&');
            }

            if (builder.Length > 0)
            {
                builder.Length--;
            }

            return builder.ToString();
        }

        private string GetTimeStamp()
        {
            return DateTime.UtcNow.ToString("yyyy-MM-ddTHH:mm:ssZ", DateTimeFormatInfo.InvariantInfo);
        }

        private string PercentEncode(string value)
        {
            var stringBuilder = new StringBuilder();
            var bytes = Encoding.UTF8.GetBytes(value);
            foreach (var b in bytes)
            {
                var c = (char) b;
                if (TextTable.Contains(c))
                {
                    stringBuilder.Append(c);
                }
                else
                {
                    stringBuilder.Append('%')
                        .Append(string.Format(CultureInfo.InvariantCulture, "{0:X2}", (int) c));
                }
            }

            return stringBuilder.ToString();
        }

        public class SendSmsResponse
        {
            [JsonProperty("RequestId")] public string RequestId { get; set; }

            [JsonProperty("Message")] public string Message { get; set; }

            [JsonProperty("BizId")] public string BizId { get; set; }

            [JsonProperty("Code")] public string Code { get; set; }
        }
    }

该实现依赖 Newtonsoft.Json 做 Json 反序列化，同时需要引入以下命名空间：

    using System;
    using System.Collections.Generic;
    using System.Globalization;
    using System.Net.Http;
    using System.Security.Cryptography;
    using System.Text;
    using System.Threading.Tasks;
    using Newtonsoft.Json;

使用时，先用阿里云提供的访问密钥及签名信息构造 AliSmsSender 的实例，并调用其 SendAsync 方法即可：

    var sender = new AliSmsSender("accessKeyId", "accessKeySecret", "签名");
    var result = await sender.SendAsync("13888888888", "模板Code", new { arg = "模板参数值" });
    if (result.Code == "OK")
    {
        Console.WriteLine("发送成功");
    }
    else
    {
        Console.WriteLine("发送失败：{0}", result.Code);
    }

以上代码也可以在 GitHub 上获得，查看地址：

https://gist.github.com/Soar360/18b9fea0ad08e5068e1e072ee4a21aa9