RequestCachePolicy.cs source code in C# .NET

                        Code:
                         / 4.0 / 4.0 / untmp / DEVDIV_TFS / Dev10 / Releases / RTMRel / ndp / fx / src / Net / System / Net / Cache / RequestCachePolicy.cs / 1305376 / RequestCachePolicy.cs
                        
                        
                            /*++ 
Copyright (c) Microsoft Corporation

Module Name:
 
    RequestCachePolicy.cs
 
Abstract: 
    The class implements caching policy paradigms that is used by all webrequest cache-aware clients
 
Author:

    Alexei Vopilov    21-Dec-2002
 
Revision History:
 
    4  Dec 2003  - Reworked as per design review. 

    30 Jul 2004  - Updated to accomodate FTP caching feature 

--*/
namespace System.Net.Cache {
    using System.Globalization; 

 
    // The enum describes cache settings applicable for any webrequest 
    public enum RequestCacheLevel
    { 
        // Default cache behavior determined by the protocol class
        Default             = 0,
        // Bypass the cache completely
        BypassCache         = 1, 
        // Only serve requests from cache, an exception is thrown if not found
        CacheOnly           = 2, 
        // Serve from the cache, but will [....] up with the server if not found 
        CacheIfAvailable    = 3,
        // Attempt to revalidate cache with the server, reload if unable to 
        Revalidate          = 4,
        // Reload the data from the origin server
        Reload              = 5,
        // Bypass the cache and removing existing entries in the cache 
        NoCacheNoStore      = 6
    } 
 

    // 
    // Common request cache policy used for caching of Http, FTP, etc.
    //
    public class RequestCachePolicy
    { 
        private RequestCacheLevel m_Level;
 
        // 
        // Public stuff
        // 
        public RequestCachePolicy(): this (RequestCacheLevel.Default)
        {
        }
 
        public RequestCachePolicy(RequestCacheLevel level)
        { 
            if (level < RequestCacheLevel.Default || level > RequestCacheLevel.NoCacheNoStore) 
                throw new ArgumentOutOfRangeException("level");
 
            m_Level = level;
        }
        //
        public RequestCacheLevel Level 
        {
            get { 
                return m_Level; 
            }
        } 
        //
        public override string ToString()
        {
            return "Level:" + m_Level.ToString(); 
        }
        // 
        // Internal stuff 
        //
        // 
#if TRAVE
        /*
        // Consider removing.
        internal static string ToString(RequestCachePolicy Policy) 
        {
            if (Policy == null) { 
                return "null"; 
            }
            return Policy.ToString(); 
        }
        */
#endif
 
    }
 
    // The enum describes cache settings for http 
    public enum HttpRequestCacheLevel
    { 
        // Default cache behavior, server fresh response fomr cache, otherwise attempt
        // to revalidate with the server or reload
        Default             = 0,
        // Bypass the cache completely 
        BypassCache         = 1,
        // Only serve requests from cache, an exception is thrown if not found 
        CacheOnly           = 2, 
        // Serve from the cache, but will [....] up with the server if not found
        CacheIfAvailable    = 3, 
        // Validate cached data with the server even if it looks fresh
        Revalidate          = 4,
        // Reload the data from the origin server
        Reload              = 5, 
        // Bypass the cache and removing existing entries in the cache
        NoCacheNoStore      = 6, 
        // Serve from cache, or the next cache along the path 
        CacheOrNextCacheOnly= 7,
        // Reload the data either from the origin server or from an uplevel cache 
        //This is equvalent to Cache-Control:MaxAge=0 HTTP semantic
        Refresh             = 8,
    }
    // 
    // CacheAgeControl is used to specify preferences with respect of cached item age and freshness.
    // 
    public enum HttpCacheAgeControl { 
            // Invalid value. Indicates the enum is not initialized
            None               = 0x0, 
            // Cached item must be at least fresh for specified period since now
            MinFresh            = 0x1,
            // Cached item must be fresh and it's age must not exceed specified period
            MaxAge              = 0x2, 
            // Cached item may be not fresh but it's expiration must not exceed specified period
            MaxStale            = 0x4, 
            // Cached item must fresh for some period in future and it's age must be less than specified 
            MaxAgeAndMinFresh   = 0x3, // MaxAge|MinFresh,
            // Cached item may be found as stale for some period but it's age must be less than specified 
            MaxAgeAndMaxStale   = 0x6, // MaxAge|MaxStale,
    }

    // 
    // HTTP cache policy that expresses RFC2616 HTTP caching semantic
    // 
    public class HttpRequestCachePolicy: RequestCachePolicy { 

        internal static readonly HttpRequestCachePolicy BypassCache = new HttpRequestCachePolicy(HttpRequestCacheLevel.BypassCache); 

        //Private members
        private HttpRequestCacheLevel m_Level = HttpRequestCacheLevel.Default;
        private DateTime        m_LastSyncDateUtc   = DateTime.MinValue; 
        private TimeSpan        m_MaxAge     = TimeSpan.MaxValue;
        private TimeSpan        m_MinFresh   = TimeSpan.MinValue; 
        private TimeSpan        m_MaxStale   = TimeSpan.MinValue; 

        // 
        // Public stuff
        //
        public HttpRequestCachePolicy():this(HttpRequestCacheLevel.Default)
        { 
        }
        // 
        public HttpRequestCachePolicy(HttpRequestCacheLevel level): base(MapLevel(level)) 
        {
            m_Level = level; 
        }
        //
        // Creates an automatic cache policy that is bound to a simples age control
        // 
        public HttpRequestCachePolicy(HttpCacheAgeControl cacheAgeControl, TimeSpan ageOrFreshOrStale):this(HttpRequestCacheLevel.Default)
        { 
 
            switch(cacheAgeControl) {
            case HttpCacheAgeControl.MinFresh: 
                m_MinFresh = ageOrFreshOrStale;
                break;
            case HttpCacheAgeControl.MaxAge:
                m_MaxAge = ageOrFreshOrStale; 
                break;
            case HttpCacheAgeControl.MaxStale: 
                m_MaxStale = ageOrFreshOrStale; 
                break;
            default: 
                throw new ArgumentException(SR.GetString(SR.net_invalid_enum, "HttpCacheAgeControl"), "cacheAgeControl");
            }
        }
        // 
        // Creates an automatic cache policy that is bound to a complex age control
        // 
        public HttpRequestCachePolicy(HttpCacheAgeControl cacheAgeControl, TimeSpan maxAge, TimeSpan freshOrStale):this(HttpRequestCacheLevel.Default) 
        {
 
             switch(cacheAgeControl) {
             case HttpCacheAgeControl.MinFresh:
                 m_MinFresh = freshOrStale;
                 break; 
             case HttpCacheAgeControl.MaxAge:
                 m_MaxAge = maxAge; 
                 break; 
             case HttpCacheAgeControl.MaxStale:
                 m_MaxStale = freshOrStale; 
                 break;
             case HttpCacheAgeControl.MaxAgeAndMinFresh:
                 m_MaxAge = maxAge;
                 m_MinFresh = freshOrStale; 
                 break;
             case HttpCacheAgeControl.MaxAgeAndMaxStale: 
                 m_MaxAge = maxAge; 
                 m_MaxStale = freshOrStale;
                 break; 
             default:
                 throw new ArgumentException(SR.GetString(SR.net_invalid_enum, "HttpCacheAgeControl"), "cacheAgeControl");
             }
        } 
        //
        // Creates an automatic cache policy with the Date Synchronization requirement 
        // 
        public HttpRequestCachePolicy(DateTime cacheSyncDate):this(HttpRequestCacheLevel.Default)
        { 
            m_LastSyncDateUtc = cacheSyncDate.ToUniversalTime();
        }
        //
        // 
        //
        public HttpRequestCachePolicy(HttpCacheAgeControl cacheAgeControl, TimeSpan maxAge, TimeSpan freshOrStale, DateTime cacheSyncDate) 
            :this(cacheAgeControl, maxAge, freshOrStale) 
        {
            m_LastSyncDateUtc = cacheSyncDate.ToUniversalTime(); 
        }
        //
        // Properties
        // 
        public new HttpRequestCacheLevel Level
        { 
            get { 
                return m_Level;
            } 
        }
        //
        // Requires revalidation of items stored before lastSyncDate
        // 
        public DateTime  CacheSyncDate {
            get { 
                if (m_LastSyncDateUtc == DateTime.MinValue || m_LastSyncDateUtc == DateTime.MaxValue) { 
                    return m_LastSyncDateUtc;
                } 
                return m_LastSyncDateUtc.ToLocalTime();}
        }
        //
        internal DateTime  InternalCacheSyncDateUtc { 
            get {return m_LastSyncDateUtc;}
        } 
        // 
        // Specifies age policy according to HTTP 1.1 RFC caching semantic
        // 
        public TimeSpan MaxAge {
            get {return m_MaxAge;}
        }
        // 
        // Specifies age policy according to HTTP 1.1 RFC caching semantic
        // 
        public TimeSpan MinFresh { 
            get {return m_MinFresh;}
        } 
        //
        // Specifies age policy according to HTTP 1.1 RFC caching semantic
        //
        public TimeSpan MaxStale { 
            get {return m_MaxStale;}
        } 
        // 
        //
        // 
        public override string ToString()
        {
            return "Level:" + m_Level.ToString() +
                (m_MaxAge == TimeSpan.MaxValue? string.Empty: " MaxAge:" + m_MaxAge.ToString()) + 
                (m_MinFresh == TimeSpan.MinValue? string.Empty: " MinFresh:" + m_MinFresh.ToString()) +
                (m_MaxStale == TimeSpan.MinValue? string.Empty: " MaxStale:" + m_MaxStale.ToString()) + 
                (CacheSyncDate==DateTime.MinValue? string.Empty: " CacheSyncDate:" +  CacheSyncDate.ToString(CultureInfo.CurrentCulture)); 
        }
        // 
        //
        //
        private static RequestCacheLevel MapLevel(HttpRequestCacheLevel level)
        { 

            if (level <= HttpRequestCacheLevel.NoCacheNoStore) 
                return (RequestCacheLevel) level; 

            if (level == HttpRequestCacheLevel.CacheOrNextCacheOnly) 
                return RequestCacheLevel.CacheOnly;

            if (level == HttpRequestCacheLevel.Refresh)
                return RequestCacheLevel.Reload; 

            throw new ArgumentOutOfRangeException("level"); 
        } 
    }
} 

// File provided for Reference Use Only by Microsoft Corporation (c) 2007.
// Copyright (c) Microsoft Corporation. All rights reserved.
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