resolve the ETag issue when restarting BrowserLink.

Author: Yang Lyu

src/Microsoft.VisualStudio.Web.BrowserLink/BrowserLinkMiddleWare.cs

@@ -4,6 +4,7 @@
 using System;
 using System.Threading.Tasks;
 using Microsoft.AspNetCore.Http;
+using Microsoft.AspNetCore.Http.Headers;
 
 namespace Microsoft.VisualStudio.Web.BrowserLink
 {
@@ -23,8 +24,6 @@ internal class BrowserLinkMiddleware
         private RequestDelegate _next;
         private string _applicationPath;
 
-        private const string headerIfNoneMatch = "If-None-Match";
-
         internal BrowserLinkMiddleware(string applicationPath, RequestDelegate next)
         {
             _applicationPath = applicationPath;
@@ -46,7 +45,9 @@ internal Task Invoke(HttpContext context)
             }
             else
             {
-                if (context.Request.Headers.ContainsKey(headerIfNoneMatch) && BrowserLinkMiddleWareUtil.GetRequestPort(context.Request.Headers) != -1)
+                RequestHeaders requestHeader = new RequestHeaders(context.Request.Headers); 
+
+                if (requestHeader.IfNoneMatch != null && BrowserLinkMiddleWareUtil.GetRequestPort(context.Request.Headers) != -1)
                 {
                     BrowserLinkMiddleWareUtil.RemoveETagAndTimeStamp(context.Request.Headers);
                 }
@@ -226,7 +227,9 @@ private static bool EnsureHostServerStarted(string applicationPath, ref HostConn
 
         private void PreprocessRequestHeader(HttpContext httpContext, ref int currentPort)
         {
-            if (httpContext.Request.Headers.ContainsKey(headerIfNoneMatch))
+            RequestHeaders requestHeader = new RequestHeaders(httpContext.Request.Headers);
+
+            if (requestHeader.IfNoneMatch != null)
             {
                 HostConnectionData connectionData;
 

src/Microsoft.VisualStudio.Web.BrowserLink/BrowserLinkMiddleWareUtil.cs

@@ -2,14 +2,12 @@
 using System;
 using Microsoft.AspNetCore.Http.Headers;
 using Microsoft.Net.Http.Headers;
-using Microsoft.Extensions.Primitives;
+using System.Collections.Generic;
 
 namespace Microsoft.VisualStudio.Web.BrowserLink
 {
     internal static class BrowserLinkMiddleWareUtil
     {
-        private const string headerIfNoneMatch = "If-None-Match";
-
         internal static int GetRequestPort(IHeaderDictionary headers)
         {
             RequestHeaders requestHeader = new RequestHeaders(headers);
@@ -52,23 +50,24 @@ internal static void RemoveETagAndTimeStamp(IHeaderDictionary headers)
         internal static void DeletePortFromETag(IHeaderDictionary headers)
         {
             RequestHeaders requestHeader = new RequestHeaders(headers);
-            string newEtag = "";
+            string newETag = "";
+            IList<EntityTagHeaderValue> list = requestHeader.IfNoneMatch;
 
-            foreach(EntityTagHeaderValue value in requestHeader.IfNoneMatch)
+            foreach(EntityTagHeaderValue value in list)
             {
                 String[] strings = value.ToString().Split(':');
 
                 if (strings.Length >= 2)
                 {
-                    newEtag = strings[0] + "\"";
+                    newETag = strings[0] + "\"";
                     break;
                 }
             }
 
-            if (newEtag.Length > 0)
+            if (newETag.Length > 0)
             {
-                headers.Remove(headerIfNoneMatch);
-                headers.Add(headerIfNoneMatch, new StringValues(newEtag));
+                list[0] = new EntityTagHeaderValue(newETag);
+                requestHeader.IfNoneMatch = list;
             }
         }