電商系統架構總結4（webapi 版本控制)

    為了 順利迭代升級，web api 在維護過程是不斷升級的，但使用者是不能強迫他們每次都跟隨你去升級，這樣會讓使用者不勝其煩。為了保證不同版本的客戶端能同時相容，在web api介面上加入版本控制就很有必要了。

當然，對於我們開發的程式碼進行版本控制也有利，不至於陷入混亂。版本引數可以放置在請求的url 作為路由引數的一部分，也可以放在header裡。實現的辦法是 實現 IHttpControllerSelector 並在WebApiConfig的註冊方法裡進行替換。

    public class VersionHttpControllerSelector : IHttpControllerSelector
    {
        private const string VersionKey = "version";
        private const string ControllerKey = "controller";

        private readonly HttpConfiguration _configuration;
        private readonly Lazy<Dictionary<string, HttpControllerDescriptor>> _controllers;
        private readonly HashSet<string> _duplicates;

        public VersionHttpControllerSelector(HttpConfiguration config)
        {
            _configuration = config;
            _duplicates = new HashSet<string>(StringComparer.OrdinalIgnoreCase);
            _controllers = new Lazy<Dictionary<string, HttpControllerDescriptor>>(InitializeControllerDictionary);
        }

        private Dictionary<string, HttpControllerDescriptor> InitializeControllerDictionary()
        {
            var dictionary = new Dictionary<string, HttpControllerDescriptor>(StringComparer.OrdinalIgnoreCase);
            IAssembliesResolver assembliesResolver = _configuration.Services.GetAssembliesResolver();
            IHttpControllerTypeResolver controllersResolver = _configuration.Services.GetHttpControllerTypeResolver();
            ICollection<Type> controllerTypes = controllersResolver.GetControllerTypes(assembliesResolver);

            foreach (Type t in controllerTypes)
            {
                var segments = t.Namespace.Split(Type.Delimiter);

                var controllerName = t.Name.Remove(t.Name.Length - DefaultHttpControllerSelector.ControllerSuffix.Length);
                string version = segments[segments.Length - 1];
                var key = String.Format(CultureInfo.InvariantCulture, "{0}.{1}", version, controllerName);
                if (version == "Controllers")
                {
                    key = String.Format(CultureInfo.InvariantCulture, "{0}", controllerName);
                }
                // Check for duplicate keys.
                if (dictionary.Keys.Contains(key))
                {
                    _duplicates.Add(key);
                }
                else
                {
                    dictionary[key] = new HttpControllerDescriptor(_configuration, t.Name, t);
                }
            }
            foreach (string s in _duplicates)
            {
                dictionary.Remove(s);
            }
            return dictionary;
        }

        // Get a value from the route data, if present.
        private static T GetRouteVariable<T>(IHttpRouteData routeData, string name)
        {
            object result = null;
            if (routeData.Values.TryGetValue(name, out result))
            {
                return (T)result;
            }
            return default(T);
        }

        public HttpControllerDescriptor SelectController(HttpRequestMessage request)
        {
            IHttpRouteData routeData = request.GetRouteData();
            if (routeData == null)
            {
                throw new HttpResponseException(HttpStatusCode.NotFound);
            }

            // Get the version and controller variables from the route data.
            string version = GetRouteVariable<string>(routeData, VersionKey);
            if (string.IsNullOrEmpty(version))
            {
                version = GetVersionFromHTTPHeaderAndAcceptHeader(request);
            }
            string controllerName = GetRouteVariable<string>(routeData, ControllerKey);
            if (controllerName == null)
            {
                throw new HttpResponseException(HttpStatusCode.NotFound);
            }

            // Find a matching controller.
            string key = String.Format(CultureInfo.InvariantCulture, "{0}", controllerName);
            if (!string.IsNullOrEmpty(version))
            {
                key = String.Format(CultureInfo.InvariantCulture, "{0}.{1}", version, controllerName);
            }

            HttpControllerDescriptor controllerDescriptor;
            if (_controllers.Value.TryGetValue(key, out controllerDescriptor))
            {
                return controllerDescriptor;
            }
            else if (_duplicates.Contains(key))
            {
                throw new HttpResponseException(
                    request.CreateErrorResponse(HttpStatusCode.InternalServerError,
                    "Multiple controllers were found that match this request."));
            }
            else
            {
                throw new HttpResponseException(HttpStatusCode.NotFound);
            }
        }

        public IDictionary<string, HttpControllerDescriptor> GetControllerMapping()
        {
            return _controllers.Value;
        }
        private string GetVersionFromHTTPHeaderAndAcceptHeader(HttpRequestMessage request)
        {
            if (request.Headers.Contains(VersionKey))
            {
                var versionHeader = request.Headers.GetValues(VersionKey).FirstOrDefault();
                if (versionHeader != null)
                {
                    return versionHeader;
                }
            }
            var acceptHeader = request.Headers.Accept;
            foreach (var mime in acceptHeader)
            {
                if (mime.MediaType == "application/json" || mime.MediaType == "text/html")
                {
                    var version = mime.Parameters
                                     .Where(v => v.Name.Equals(VersionKey, StringComparison.OrdinalIgnoreCase))
                                      .FirstOrDefault();

                    if (version != null)
                    {
                        return version.Value;
                    }
                    return string.Empty;
                }
            }
            return string.Empty;
        }
    }

重點是SelectController方法，從http請求裡找出合適版本的controller。我這裡相容了從路由和header裡獲取版本，先從路由裡獲取，沒有再從header裡獲取。

           IHttpRouteData routeData = request.GetRouteData();
            if (routeData == null)
            {
                throw new HttpResponseException(HttpStatusCode.NotFound);
            }

            // Get the version and controller variables from the route data.
            string version = GetRouteVariable<string>(routeData, VersionKey);
            if (string.IsNullOrEmpty(version))
            {
                version = GetVersionFromHTTPHeaderAndAcceptHeader(request);
            }

      private string GetVersionFromHTTPHeaderAndAcceptHeader(HttpRequestMessage request)
        {
            if (request.Headers.Contains(VersionKey))
            {
                var versionHeader = request.Headers.GetValues(VersionKey).FirstOrDefault();
                if (versionHeader != null)
                {
                    return versionHeader;
                }
            }
            var acceptHeader = request.Headers.Accept;
            foreach (var mime in acceptHeader)
            {
                if (mime.MediaType == "application/json" || mime.MediaType == "text/html")
                {
                    var version = mime.Parameters
                                     .Where(v => v.Name.Equals(VersionKey, StringComparison.OrdinalIgnoreCase))
                                      .FirstOrDefault();

                    if (version != null)
                    {
                        return version.Value;
                    }
                    return string.Empty;
                }
            }
            return string.Empty;
        }

WebApiConfig檔案呼叫程式碼如下：

   public static void Register(HttpConfiguration config)
        {
。。。
config.Services.Replace(typeof(IHttpControllerSelector), new VersionHttpControllerSelector((config)));

}

web api的定義呢，則從名稱空間上區分就可以了。 比如版本號為V1的  LoginApiController 的名稱空間 為定義為    xxx.WebAPI.Controllers.V1，版本號為V2的  LoginApiController 的名稱空間 為定義為    xxx.WebAPI.Controllers.V2，如此類推,

客戶端在header里加上引數 versoin=v1/v2... 就可以指定使用不同版本的api了。