电商系统架构总结4（webapi 版本控制)

为了顺利迭代升级，web api 在维护过程是不断升级的，但用户是不能强迫他们每次都跟随你去升级，这样会让用户不胜其烦。为了保证不同版本的客户端能同时兼容，在web api接口上加入版本控制就很有必要了。

当然，对于我们开发的代码进行版本控制也有利，不至于陷入混乱。版本参数可以放置在请求的url 作为路由参数的一部分，也可以放在header里。实现的办法是实现 IHttpControllerSelector 并在WebApiConfig的注册方法里进行替换。

    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 - ];

                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;

        }

    }

重点是SelectController方法，从http请求里找出合适版本的controller。我这里兼容了从路由和header里获取版本，先从路由里获取，没有再从header里获取。

           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文件调用代码如下：

   public static void Register(HttpConfiguration config)

        {

。。。

config.Services.Replace(typeof(IHttpControllerSelector), new VersionHttpControllerSelector((config)));

}

web api的定义呢，则从命名空间上区分就可以了。比如版本号为V1的 LoginApiController 的命名空间为定义为 xxx.WebAPI.Controllers.V1，版本号为V2的 LoginApiController 的命名空间为定义为 xxx.WebAPI.Controllers.V2，如此类推,

客户端在header里加上参数 versoin=v1/v2... 就可以指定使用不同版本的api了。

巴特西

电商系统架构总结4（webapi 版本控制)

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