WpfWebRequestHelper.cs source code in C# .NET

Source code for the .NET framework in C#

                        
Code:

                         / 4.0 / 4.0 / untmp / DEVDIV_TFS / Dev10 / Releases / RTMRel / wpf / src / Core / CSharp / MS / Internal / WpfWebRequestHelper.cs / 1458001 / WpfWebRequestHelper.cs
                        

                        
                            //+------------------------------------------------------------------------ 
//
//  Copyright (c) Microsoft Corporation.  All rights reserved.
//
//  Description: 
//      Helper class for handling all web requests/responses in the framework. Using it ensures consisent
//      handling and support for special features: cookies, NTLM authentication, caching, inferring MIME 
//      type from filename. 
//
//  History: 
//      2007/04/11   [....]     Created
//
//-----------------------------------------------------------------------
 
using System;
using System.Net; 
using System.Net.Cache; 
using System.Security;
using System.Security.Permissions; 
using System.IO;

using System.Windows.Navigation;
using System.IO.Packaging; 
using MS.Internal.AppModel;
using MS.Internal.Utility; 
using MS.Internal.PresentationCore; 

//From Presharp documentation: 
//In order to avoid generating warnings about unknown message numbers and
//unknown pragmas when compiling your C# source code with the actual C# compiler,
//you need to disable warnings 1634 and 1691.
#pragma warning disable 1634, 1691 

namespace MS.Internal 
{ 

///  
/// Helper class for handling all web requests/responses in the framework. Using it ensures consisent handling
/// and support for special features: cookies, NTLM authentication, caching, inferring MIME type from filename.
///
/// Only two methods are mandatory: 
///   - CreateRequest. (PackWebRequestFactory.CreateWebRequest is an allowed alternative. It delegates to
///     this CreateRequest for non-pack URIs.) 
///   - HandleWebResponse. 
/// The remaining methods just automate the entire request process, up to the point of getting the response
/// stream. Using the SecurityTreatAsSafe ones helps avoid making other code SecurityCritical. 
///
/// Related types:
///   - BaseUriHelper
///   - BindUriHelper (built into Framework, subset into Core) 
///   - PackWebRequestFactory
///   - MimeObjectFactory 
///  
static class WpfWebRequestHelper
{ 
    /// 
    /// Critical: Elevates to set WebRequest.UseDefaultCredentials.
    /// Safe: Activates the CustomCredentialPolicy, which makes sure the user's system credentials are not
    ///     sent across the Internet. 
    /// 
    [SecurityCritical, SecurityTreatAsSafe] 
    [FriendAccessAllowed] 
    internal static WebRequest CreateRequest(Uri uri)
    { 
        // Ideally we would want to use RegisterPrefix and WebRequest.Create.
        // However, these two functions regress 700k working set in System.dll and System.xml.dll
        //  which is mostly for logging and config.
        // Call PackWebRequestFactory.CreateWebRequest to bypass the regression if possible 
        //  by calling Create on PackWebRequest if uri is pack scheme
        if (string.Compare(uri.Scheme, PackUriHelper.UriSchemePack, StringComparison.Ordinal) == 0) 
        { 
            return PackWebRequestFactory.CreateWebRequest(uri);
            // The PackWebRequest may end up creating a "real" web request as its inner request. 
            // It will then call this method again.
        }

        // Work around the issue with FileWebRequest not handling #. Details in bug 1096304. 
        // FileWebRequest doesn't support the concept of query and fragment.
        if (uri.IsFile) 
        { 
            uri = new Uri(uri.GetLeftPart(UriPartial.Path));
        } 

        WebRequest request = WebRequest.Create(uri);

        // It is not clear whether WebRequest.Create() can ever return null, but v1 code make this check in 
        // a couple of places, so it is still done here, just in case.
        if(request == null) 
        { 
            // Unfortunately, there is no appropriate exception string in PresentationCore, and for v3.5
            // we have a total resource freeze. So just report WebExceptionStatus.RequestCanceled: 
            // "The request was canceled, the WebRequest.Abort method was called, or an unclassifiable error
            // occurred. This is the default value for Status."
            Uri requestUri = BaseUriHelper.PackAppBaseUri.MakeRelativeUri(uri);
            throw new WebException(requestUri.ToString(), WebExceptionStatus.RequestCanceled); 
            //throw new IOException(SR.Get(SRID.GetResponseFailed, requestUri.ToString()));
        } 
 
        HttpWebRequest httpRequest = request as HttpWebRequest;
        if (httpRequest != null) 
        {
            if (string.IsNullOrEmpty(httpRequest.UserAgent))
            {
                httpRequest.UserAgent = DefaultUserAgent; 
            }
 
            CookieHandler.HandleWebRequest(httpRequest); 

            if (String.IsNullOrEmpty(httpRequest.Referer)) 
            {
                httpRequest.Referer = BindUriHelper.GetReferer(uri);
            }
 
            CustomCredentialPolicy.EnsureCustomCredentialPolicy();
 
            // Enable NTLM authentication. 
            // This is safe to do thanks to the CustomCredentialPolicy.
            (new EnvironmentPermission(EnvironmentPermissionAccess.Read, "USERNAME")).Assert(); // BlessedAssert 
            try { httpRequest.UseDefaultCredentials = true; }
            finally { EnvironmentPermission.RevertAssert(); }
        }
 
        return request;
    } 
 
    ///  ******
    /// This method was factored out of the defunct BindUriHelper.ConfigHttpWebRequest(). 
    /// Ideally, all framework-created web requests should use the same caching settings, but in order not to
    /// change behavior in SP1/v3.5, ConfigCachePolicy() is called separately by the code that previously
    /// relied on ConfigHttpWebRequest().
    ///  
    [FriendAccessAllowed]
    static internal void ConfigCachePolicy(WebRequest request, bool isRefresh) 
    { 
        HttpWebRequest httpRequest = request as HttpWebRequest;
        if (httpRequest != null) 
        {
            // Setting CachePolicy to the default level if it is null.
            if (request.CachePolicy == null || request.CachePolicy.Level != RequestCacheLevel.Default)
            { 
                if (isRefresh)
                { 
                    if (_httpRequestCachePolicyRefresh == null) 
                    {
                        _httpRequestCachePolicyRefresh = new HttpRequestCachePolicy(HttpRequestCacheLevel.Refresh); 
                    }
                    request.CachePolicy = _httpRequestCachePolicyRefresh;
                }
                else 
                {
                    if (_httpRequestCachePolicy == null) 
                    { 
                        _httpRequestCachePolicy = new HttpRequestCachePolicy();
                    } 
                    request.CachePolicy = _httpRequestCachePolicy;
                }
            }
        } 
    }
    private static HttpRequestCachePolicy _httpRequestCachePolicy; 
    private static HttpRequestCachePolicy _httpRequestCachePolicyRefresh; 

    ///  
    /// Critical (getter): Calls the native ObtainUserAgentString().
    /// Safe: User-agent string is safe to expose. An XBAP could get it by asking the server what the browser
    ///     sent it initially.
    ///  
    internal static string DefaultUserAgent
    { 
        [SecurityCritical, SecurityTreatAsSafe] 
        get
        { 
            if (_defaultUserAgent == null)
            {
                _defaultUserAgent = MS.Win32.UnsafeNativeMethods.ObtainUserAgentString();
            } 
            return _defaultUserAgent;
        } 
        set // set by ApplicationProxyInternal for browser hosting 
        {
            _defaultUserAgent = value; 
        }
    }
    private static string _defaultUserAgent;
 
    /// 
    /// Critical: Calls the critical CookieHandler.HandleWebResponse(). 
    ///     We need a secure path for passing authentic, unaltered HttpWebRespones. 
    /// CAUTION: Presently, callers of this method are not required to make any security guarantee about
    ///     non-HTTP web responses. They will all need to be revised if secure handling of other types of 
    ///     requests/responses becomes necessary.
    /// 
    [SecurityCritical]
    [FriendAccessAllowed] 
    internal static void HandleWebResponse(WebResponse response)
    { 
        CookieHandler.HandleWebResponse(response); 
    }
 
    [FriendAccessAllowed]
    internal static Stream CreateRequestAndGetResponseStream(Uri uri)
    {
        WebRequest request = CreateRequest(uri); 
        return GetResponseStream(request);
    } 
    [FriendAccessAllowed] 
    internal static Stream CreateRequestAndGetResponseStream(Uri uri, out ContentType contentType)
    { 
        WebRequest request = CreateRequest(uri);
        return GetResponseStream(request, out contentType);
    }
 
    [FriendAccessAllowed]
    internal static WebResponse CreateRequestAndGetResponse(Uri uri) 
    { 
        WebRequest request = CreateRequest(uri);
        return GetResponse(request); 
    }

    /// 
    /// Critical: Calls the critical HandleWebResponse(), which expects unaltered, authentic HttpWebResponses. 
    /// Safe: The response is obtained right here and is passed directly to HandleWebResponse().
    ///     Even if the given request object is bogus, it cannot produce an HttpWebResponse, because the class 
    ///     has no public or protected constructor. However, a bogus request could attach to itself an 
    ///     HttpWebResponse from a real request and alter it. This possibility is prevented by a type check.
    ///     A critical assumption is that HttpWebRequest cannot be derived from and therefore its behavior 
    ///     cannot be altered (beyond what its public APIs allow, but the security-sensitive ones demand
    ///     appropriate permission).
    /// 
    [SecurityCritical, SecurityTreatAsSafe] 
    [FriendAccessAllowed]
    internal static WebResponse GetResponse(WebRequest request) 
    { 
        WebResponse response = request.GetResponse();
 
        // 'is' is used here instead of exact type checks to allow for the (remote) possibility that an internal
        // implementation type derived from HttpWebRequest/Response may be used by System.Net.
        if (response is HttpWebResponse && !(request is HttpWebRequest))
            throw new ArgumentException(); 

        // It is not clear whether WebRequest.GetRespone() can ever return null, but some of the v1 code had 
        // this check, so it is added here just in case. 
        if (response == null)
        { 
            Uri requestUri = BaseUriHelper.PackAppBaseUri.MakeRelativeUri(request.RequestUri);
            throw new IOException(SR.Get(SRID.GetResponseFailed, requestUri.ToString()));
        }
 
        HandleWebResponse(response);
        return response; 
    } 
    /// 
    /// [See GetResponse()] 
    /// 
    [SecurityCritical, SecurityTreatAsSafe]
    [FriendAccessAllowed]
    internal static WebResponse EndGetResponse(WebRequest request, IAsyncResult ar) 
    {
        WebResponse response = request.EndGetResponse(ar); 
        if (response is HttpWebResponse && !(request is HttpWebRequest)) 
            throw new ArgumentException();
        // It is not clear whether WebRequest.GetRespone() can ever return null, but some of the v1 code had 
        // this check, so it is added here just in case.
        if (response == null)
        {
            Uri requestUri = BaseUriHelper.PackAppBaseUri.MakeRelativeUri(request.RequestUri); 
            throw new IOException(SR.Get(SRID.GetResponseFailed, requestUri.ToString()));
        } 
        HandleWebResponse(response); 
        return response;
    } 

    [FriendAccessAllowed]
    internal static Stream GetResponseStream(WebRequest request)
    { 
        WebResponse response = GetResponse(request);
        return response.GetResponseStream(); 
    } 
    /// 
    /// Gets the response from the given request and determines the content type using the special rules 
    /// implemented in GetContentType().
    /// 
    [FriendAccessAllowed]
    internal static Stream GetResponseStream(WebRequest request, out ContentType contentType) 
    {
        WebResponse response = GetResponse(request); 
        contentType = GetContentType(response); 
        return response.GetResponseStream();
    } 


    // [Apr'07. Code moved here from BaseUriHelper.GetContentType().]
    ///  
    /// Tries hard to obtain the content type of the given WebResponse. Special cases:
    /// - The ContentType property may throw if not implemented. 
    /// - Unconfigured web servers don't return the right type for WPF content. This method does lookup based on 
    ///   file extension.
    ///  
    [FriendAccessAllowed]
    internal static ContentType GetContentType(WebResponse response)
    {
        ContentType contentType = ContentType.Empty; 

        // FileWebResponse returns a generic mime type for all files regardless of extension. 
        // We have requested fix but it's postponed to orcas. This is a work around for that. 
        //
 
        if (!(response is FileWebResponse))
        {
            // For all other cases use the WebResponse's ContentType if it is available
            try 
            {
                contentType = new ContentType(response.ContentType); 
 
                // If our content type is octet-stream or text/plain, we might be dealing with an unconfigured server.
                // If the extension is .xaml or .xbap we ignore the server's content type and determine 
                // the content type based on the URI's extension.
                if (MimeTypeMapper.OctetMime.AreTypeAndSubTypeEqual(contentType, true) ||
                    MimeTypeMapper.TextPlainMime.AreTypeAndSubTypeEqual(contentType, true))
                { 
                    string extension = MimeTypeMapper.GetFileExtension(response.ResponseUri);
                    if ((String.Compare(extension, MimeTypeMapper.XamlExtension, StringComparison.OrdinalIgnoreCase) == 0) || 
                            (String.Compare(extension, MimeTypeMapper.XbapExtension, StringComparison.OrdinalIgnoreCase) == 0)) 
                    {
                        contentType = ContentType.Empty;  // Will cause GetMimeTypeFromUri to be called below 
                    }
                }
            }
#pragma warning disable 6502 
            catch (NotImplementedException)
            { 
                // this is a valid result and indicates that the subclass chose not to implement this property 
            }
            catch (NotSupportedException) 
            {
                // this is a valid result and indicates that the subclass chose not to implement this property
            }
#pragma warning restore 6502 
        }
 
        if (contentType == ContentType.Empty) 
        {
            contentType = MimeTypeMapper.GetMimeTypeFromUri(response.ResponseUri); 
        }

        return contentType;
    } 

}; 
 
}

// File provided for Reference Use Only by Microsoft Corporation (c) 2007.

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