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// Copyright (c) Microsoft Corporation. All rights reserved. See License.txt in the project root for license information.
using System.Web.Hosting;
namespace System.Web.WebPages
{
/// <summary>
/// Extension methods used to determine what browser a visitor wants to be seen as using.
/// </summary>
public static class BrowserHelpers
{
/// <summary>
/// Stock IE6 user agent string
/// </summary>
private const string DesktopUserAgent = "Mozilla/4.0 (compatible; MSIE 6.1; Windows XP)";
/// <summary>
/// Stock Windows Mobile 6.0 user agent string
/// </summary>
private const string MobileUserAgent = "Mozilla/4.0 (compatible; MSIE 6.0; Windows CE; IEMobile 8.12; MSIEMobile 6.0)";
private static readonly object _browserOverrideKey = new object();
private static readonly object _userAgentKey = new object();
/// <summary>
/// Clears the set browser for the request. After clearing the browser the overridden browser will be the browser for the request.
/// </summary>
public static void ClearOverriddenBrowser(this HttpContextBase httpContext)
{
SetOverriddenBrowser(httpContext, userAgent: null);
}
// Default implementation to generate an HttpBrowserCapabilities object using the current HttpCapabilitiesProvider
private static HttpBrowserCapabilitiesBase CreateOverriddenBrowser(string userAgent)
{
HttpBrowserCapabilities overriddenBrowser = new HttpContext(new UserAgentWorkerRequest(userAgent)).Request.Browser;
return new HttpBrowserCapabilitiesWrapper(overriddenBrowser);
}
/// <summary>
/// Gets the overridden browser for the request based on the overridden user agent.
/// If no overridden user agent is set, returns the browser for the request.
/// </summary>
public static HttpBrowserCapabilitiesBase GetOverriddenBrowser(this HttpContextBase httpContext)
{
return GetOverriddenBrowser(httpContext, CreateOverriddenBrowser);
}
internal static HttpBrowserCapabilitiesBase GetOverriddenBrowser(this HttpContextBase httpContext, Func<string, HttpBrowserCapabilitiesBase> createBrowser)
{
HttpBrowserCapabilitiesBase overriddenBrowser = (HttpBrowserCapabilitiesBase)httpContext.Items[_browserOverrideKey];
if (overriddenBrowser == null)
{
string overriddenUserAgent = GetOverriddenUserAgent(httpContext);
if (!String.Equals(overriddenUserAgent, httpContext.Request.UserAgent))
{
overriddenBrowser = createBrowser(overriddenUserAgent);
}
else
{
overriddenBrowser = httpContext.Request.Browser;
}
httpContext.Items[_browserOverrideKey] = overriddenBrowser;
}
return overriddenBrowser;
}
/// <summary>
/// Gets the overridden user agent for the request. If no overridden user agent is set, returns the user agent for the request.
/// </summary>
public static string GetOverriddenUserAgent(this HttpContextBase httpContext)
{
return (string)httpContext.Items[_userAgentKey] ??
BrowserOverrideStores.Current.GetOverriddenUserAgent(httpContext) ??
httpContext.Request.UserAgent;
}
/// <summary>
/// Gets a string that varies based upon the type of the browser. Can be used to override
/// System.Web.HttpApplication.GetVaryByCustomString to differentiate cache keys based on
/// the overridden browser.
/// </summary>
public static string GetVaryByCustomStringForOverriddenBrowser(this HttpContext httpContext)
{
return GetVaryByCustomStringForOverriddenBrowser(new HttpContextWrapper(httpContext));
}
/// <summary>
/// Gets a string that varies based upon the type of the browser. Can be used to override
/// System.Web.HttpApplication.GetVaryByCustomString to differentiate cache keys based on
/// the overridden browser.
/// </summary>
public static string GetVaryByCustomStringForOverriddenBrowser(this HttpContextBase httpContext)
{
return GetVaryByCustomStringForOverriddenBrowser(httpContext, userAgent => CreateOverriddenBrowser(userAgent));
}
internal static string GetVaryByCustomStringForOverriddenBrowser(this HttpContextBase httpContext, Func<string, HttpBrowserCapabilitiesBase> generateBrowser)
{
return GetOverriddenBrowser(httpContext, generateBrowser).Type;
}
/// <summary>
/// Sets the overridden user agent for the request using a BrowserOverride.
/// </summary>
public static void SetOverriddenBrowser(this HttpContextBase httpContext, BrowserOverride browserOverride)
{
string userAgent = null;
switch (browserOverride)
{
case BrowserOverride.Desktop:
// bug:262389 override only if the request was not made from a browser or the browser is not of a desktop device
if (httpContext.Request.Browser == null || httpContext.Request.Browser.IsMobileDevice)
{
userAgent = DesktopUserAgent;
}
break;
case BrowserOverride.Mobile:
if (httpContext.Request.Browser == null || !httpContext.Request.Browser.IsMobileDevice)
{
userAgent = MobileUserAgent;
}
break;
}
if (userAgent != null)
{
SetOverriddenBrowser(httpContext, userAgent);
}
else
{
ClearOverriddenBrowser(httpContext);
}
}
/// <summary>
/// Sets the overridden user agent for the request using a string
/// </summary>
public static void SetOverriddenBrowser(this HttpContextBase httpContext, string userAgent)
{
// Set the overridden user agent and clear the overridden browser
// so that it can be generated from the new overridden user agent.
httpContext.Items[_userAgentKey] = userAgent;
httpContext.Items[_browserOverrideKey] = null;
BrowserOverrideStores.Current.SetOverriddenUserAgent(httpContext, userAgent);
}
private sealed class UserAgentWorkerRequest : SimpleWorkerRequest
{
private readonly string _userAgent;
public UserAgentWorkerRequest(string userAgent)
: base(String.Empty, String.Empty, output: null)
{
_userAgent = userAgent;
}
public override string GetKnownRequestHeader(int index)
{
return index == HeaderUserAgent ? _userAgent : null;
}
}
}
}
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