C# WEB API 無法回傳HttpStatusCode NotModified(304)

C# WEB API 無法回傳HttpStatusCode NotModified(304)

實務上在實作WEB API時, 通常會根據結果去回傳合適的HTTP Status Code(狀態碼), 當請求失敗時我們可以從狀態碼清楚地得知原因是什麼

有些狀態碼有其特殊的規範, 如 304 NotModified

如下所示, 這個API 若檢查到POST過來的資料(Activity)早已存在資料庫中時, 會回傳304還有碩誤訊息"item exist already"

        public async Task<IHttpActionResult> Post([FromBody]Activity activity)

        {

            if(Context.Activities.Any(a=>a.Id == activity.Id))

            {

                return ResponseMessage(Request.CreateResponse(HttpStatusCode.NotModified, "item exist already"));

            }

而這是一個錯誤的示範

當使用POSTMAN測試時會報錯

Could not get any response There was an error connecting to http://localhost:58671/api/history. Why this might have happened: The server couldn't send a response: Ensure that the backend is working properly Self-signed SSL certificates are being blocked: Fix this by turning off 'SSL certificate verification' in Settings > General Client certificates are required for this server: Fix this by adding client certificates in Settings > Certificates Request timeout: Change request timeout in Settings > General

根據HTTP Status Code Definitions,

回傳狀態碼304時不能含有body

所以應該改成

                return  ResponseMessage(Request.CreateResponse(HttpStatusCode.NotModified));

REF:

https://www.w3.org/Protocols/rfc2616/rfc2616-sec10.html#sec10.3.5