DataServiceStreamProviderWrapper.cs source code in C# .NET

Source code for the .NET framework in C#

                        

Code:

/ 4.0 / 4.0 / DEVDIV_TFS / Dev10 / Releases / RTMRel / ndp / fx / src / DataWeb / Server / System / Data / Services / Providers / DataServiceStreamProviderWrapper.cs / 1305376 / DataServiceStreamProviderWrapper.cs

                            //---------------------------------------------------------------------- 
// 
//      Copyright (c) Microsoft Corporation.  All rights reserved.
// 
//  
//      This wrapper class forwards calls to the underlying IDataServiceStreamProvider
//      instance and validates responses from it. 
//  
//
// @owner  [....] 
//---------------------------------------------------------------------

namespace System.Data.Services.Providers
{ 
    using System;
    using System.IO; 
    using System.Diagnostics; 
    using System.Collections;
    using System.Collections.Generic; 
    using System.Linq;
    using System.Data.Services;

    ///  
    /// Wrapper class to forward calls to the underlying IDataServiceStreamProvider instance and validates responses from it.
    ///  
    internal class DataServiceStreamProviderWrapper 
    {
        #region Private Fields 

        /// 
        /// Default buffer size used for stream copy.
        ///  
        private const int DefaultBufferSize = 64 * 1024;
 
        ///  
        /// Stream provider instance
        ///  
        private IDataServiceStreamProvider streamProvider;

        /// 
        /// Data service instance 
        /// 
        private IDataService dataService; 
 
        #endregion Private Fields
 
        #region Constructor

        /// 
        /// Constructs the wrapper class for IDataServiceStreamProvider 
        /// 
        /// Data service instance 
        public DataServiceStreamProviderWrapper(IDataService dataService) 
        {
            Debug.Assert(dataService != null, "dataService != null"); 
            this.dataService = dataService;
        }

        #endregion Constructor 

        #region Public Properties 
 
        /// 
        /// Gets buffer size the data service will use when reading from read stream or writing to the write stream. 
        /// If the size is less than or equals to 0, the default of 64k will be used.
        /// 
        public int StreamBufferSize
        { 
            get
            { 
                int size = this.StreamProvider.StreamBufferSize; 
                return size > 0 ? size : DataServiceStreamProviderWrapper.DefaultBufferSize;
            } 
        }

        #endregion Public Properties
 
        #region Private Properties
 
        ///  
        /// Asks the service for an IDataServiceStreamProvider implementation
        ///  
        private IDataServiceStreamProvider StreamProvider
        {
            get
            { 
                if (this.streamProvider == null)
                { 
                    this.streamProvider = LoadStreamProvider(this.dataService); 
                    Debug.Assert(this.streamProvider != null, "this.streamProvider != null");
                } 

                return this.streamProvider;
            }
        } 

        #endregion Private Properties 
 
        #region Internal Methods
 
        /// 
        /// Take the given Media Link Entry uri, and construct the default Edit Media Uri.
        /// 
        /// Uri to the Media Link Entry. 
        /// Uri to the Media Resource.
        internal static string GetStreamEditMediaUri(string mediaLinkEntryUri) 
        { 
            Debug.Assert(!string.IsNullOrEmpty(mediaLinkEntryUri), "!string.IsNullOrEmpty(mediaLinkEntryUri)");
            string result = mediaLinkEntryUri; 

            if (!result.EndsWith(XmlConstants.UriValueSegment, StringComparison.Ordinal))
            {
                if (!result.EndsWith("/", StringComparison.Ordinal)) 
                {
                    result += "/"; 
                } 

                result += XmlConstants.UriValueSegment; 
            }

            return result;
        } 

        ///  
        /// Asks the data service for a stream provider instance.  Throw if none is implemented. 
        /// 
        /// data service instance 
        /// stream provider instance
        internal static IDataServiceStreamProvider LoadStreamProvider(IDataService dataService)
        {
            IDataServiceStreamProvider streamProvider = dataService.Provider.GetService(dataService); 
            if (streamProvider == null)
            { 
                throw new DataServiceException(500, Strings.DataServiceStreamProviderWrapper_MustImplementIDataServiceStreamProviderToSupportStreaming); 
            }
 
            return streamProvider;
        }

        ///  
        /// This method is invoked by the data services framework to retrieve the default stream associated
        /// with the Entity Type specified by the  parameter. 
        /// Note that we set the response ETag in the host object before we return. 
        /// 
        /// The stream returned should be the default stream associated with this entity. 
        /// A reference to the context for the current operation.
        /// A valid stream the data service use to query / read a streamed BLOB which is associated with the .
        internal Stream GetReadStream(object entity, DataServiceOperationContext operationContext)
        { 
            Debug.Assert(entity != null, "entity != null");
            Debug.Assert(operationContext != null, "operationContext != null"); 
 
            string etagFromHeader;
            bool? checkETagForEquality; 
            DataServiceStreamProviderWrapper.GetETagFromHeaders(operationContext, out etagFromHeader, out checkETagForEquality);
            Debug.Assert(
                string.IsNullOrEmpty(etagFromHeader) && !checkETagForEquality.HasValue || !string.IsNullOrEmpty(etagFromHeader) && checkETagForEquality.HasValue,
                "etag and checkETagForEquality parameters must both be set or not set at the same time."); 

            Stream readStream = null; 
            try 
            {
                readStream = InvokeApiCallAndValidateHeaders("IDataServiceStreamProvider.GetReadStream", () => this.StreamProvider.GetReadStream(entity, etagFromHeader, checkETagForEquality, operationContext), operationContext); 
            }
            catch (DataServiceException e)
            {
                if (e.StatusCode == (int)System.Net.HttpStatusCode.NotModified) 
                {
                    // For status code 304, we MUST set the etag value.  Our Error handler will translate 
                    // DataServiceException(304) to a normal response with status code 304 and an empty message-body. 
#if DEBUG
                    WebUtil.WriteETagValueInResponseHeader(null, this.GetStreamETag(entity, operationContext), operationContext.Host); 
#else
                    WebUtil.WriteETagValueInResponseHeader(this.GetStreamETag(entity, operationContext), operationContext.Host);
#endif
                } 

                throw; 
            } 

            try 
            {
                if (readStream == null || !readStream.CanRead)
                {
                    throw new InvalidOperationException(Strings.DataService_InvalidStreamFromGetReadStream); 
                }
 
                // GetStreamETag can throw and we need to catch and dispose the stream. 
#if DEBUG
                WebUtil.WriteETagValueInResponseHeader(null, this.GetStreamETag(entity, operationContext), operationContext.Host); 
#else
                WebUtil.WriteETagValueInResponseHeader(this.GetStreamETag(entity, operationContext), operationContext.Host);
#endif
            } 
            catch
            { 
                WebUtil.Dispose(readStream); 
                throw;
            } 

            return readStream;
        }
 
        /// 
        /// This method is invoked by the data services framework whenever an insert or update operation is 
        /// being processed for the stream associated with the Entity Type specified via the entity parameter. 
        /// 
        /// The stream returned should be the default stream associated with this entity. 
        /// A reference to the context for the current operation.
        /// A valid stream the data service use to write the contents of a BLOB which is associated with .
        internal Stream GetWriteStream(object entity, DataServiceOperationContext operationContext)
        { 
            Debug.Assert(entity != null, "entity != null");
            Debug.Assert(operationContext != null, "operationContext != null"); 
 
            string etag;
            bool? checkETagForEquality; 
            DataServiceStreamProviderWrapper.GetETagFromHeaders(operationContext, out etag, out checkETagForEquality);
            Debug.Assert(
                string.IsNullOrEmpty(etag) && !checkETagForEquality.HasValue || !string.IsNullOrEmpty(etag) && checkETagForEquality.HasValue,
                "etag and checkETagForEquality parameters must both be set or not set at the same time."); 

            Stream writeStream = InvokeApiCallAndValidateHeaders("IDataServiceStreamProvider.GetWriteStream", () => this.StreamProvider.GetWriteStream(entity, etag, checkETagForEquality, operationContext), operationContext); 
            if (writeStream == null || !writeStream.CanWrite) 
            {
                WebUtil.Dispose(writeStream); 
                throw new InvalidOperationException(Strings.DataService_InvalidStreamFromGetWriteStream);
            }

            return writeStream; 
        }
 
        ///  
        /// This method is invoked by the data services framework whenever an delete operation is being processed for the stream associated with
        /// the Entity Type specified via the entity parameter. 
        /// 
        /// The stream deleted should be the default stream associated with this entity.
        /// A reference to the context for the current operation.
        internal void DeleteStream(object entity, DataServiceOperationContext operationContext) 
        {
            Debug.Assert(entity != null, "entity != null"); 
            Debug.Assert(operationContext != null, "operationContext != null"); 
            InvokeApiCallAndValidateHeaders("IDataServiceStreamProvider.DeleteStream", () => { this.StreamProvider.DeleteStream(entity, operationContext); return true; }, operationContext);
        } 

        /// 
        /// This method is invoked by the data services framework to obtain the IANA content type (aka media type) of the stream associated
        /// with the specified entity.  This metadata is needed when constructing the payload for the Media Link Entry associated with the 
        /// stream (aka Media Resource) or setting the Content-Type HTTP response header.
        ///  
        /// The entity associated with the stream for which the content type is to be obtained 
        /// A reference to the context for the current operation.
        /// Valid Content-Type string for the stream associated with the entity 
        internal string GetStreamContentType(object entity, DataServiceOperationContext operationContext)
        {
            Debug.Assert(entity != null, "entity != null");
            Debug.Assert(operationContext != null, "operationContext != null"); 

            string contentType = InvokeApiCallAndValidateHeaders("IDataServiceStreamProvider.GetStreamContentType", () => this.StreamProvider.GetStreamContentType(entity, operationContext), operationContext); 
            if (string.IsNullOrEmpty(contentType)) 
            {
                throw new InvalidOperationException(Strings.DataServiceStreamProviderWrapper_GetStreamContentTypeReturnsEmptyOrNull); 
            }

            return contentType;
        } 

        ///  
        /// This method is invoked by the data services framework to obtain the URI clients should use when making retrieve (ie. GET) 
        /// requests to the stream(ie. Media Resource).   This metadata is needed when constructing the payload for the Media Link Entry
        /// associated with the stream (aka Media Resource). 
        ///
        /// If IDataServiceStreamProvider.GetReadStreamUri returns a valid Uri, we return that as the Uri to the Media Resource.
        /// Otherwise we take the given Media Link Entry uri, and construct the default Media Resource Uri.
        ///  
        /// The entity associated with the stream for which a “read stream” is to be obtained
        /// A reference to the context for the current operation. 
        /// Uri to the Media Link Entry. 
        /// The URI clients should use when making retrieve (ie. GET) requests to the stream(ie. Media Resource).
        internal Uri GetReadStreamUri(object entity, DataServiceOperationContext operationContext, string mediaLinkEntryUri) 
        {
            Debug.Assert(entity != null, "entity != null");
            Debug.Assert(operationContext != null, "operationContext != null");
 
            Uri readStreamUri = InvokeApiCallAndValidateHeaders("IDataServiceStreamProvider.GetReadStreamUri", () => this.StreamProvider.GetReadStreamUri(entity, operationContext), operationContext);
            if (readStreamUri != null) 
            { 
                if (!readStreamUri.IsAbsoluteUri)
                { 
                    throw new InvalidOperationException(Strings.DataServiceStreamProviderWrapper_GetReadStreamUriMustReturnAbsoluteUriOrNull);
                }
                else
                { 
                    return readStreamUri;
                } 
            } 
            else
            { 
                return new Uri(DataServiceStreamProviderWrapper.GetStreamEditMediaUri(mediaLinkEntryUri), UriKind.RelativeOrAbsolute);
            }
        }
 
        /// 
        /// This method is invoked by the data services framework to obtain the ETag of the stream associated with the entity specified. 
        /// This metadata is needed when constructing the payload for the Media Link Entry associated with the stream (aka Media Resource) 
        /// as well as to be used as the value of the ETag HTTP response header.
        ///  
        /// The entity associated with the stream for which an etag is to be obtained
        /// A reference to the context for the current operation.
        /// ETag of the stream associated with the entity specified
        internal string GetStreamETag(object entity, DataServiceOperationContext operationContext) 
        {
            Debug.Assert(entity != null, "entity != null"); 
            Debug.Assert(operationContext != null, "operationContext != null"); 

            string etag = InvokeApiCallAndValidateHeaders("IDataServiceStreamProvider.GetStreamETag", () => this.StreamProvider.GetStreamETag(entity, operationContext), operationContext); 
            if (!WebUtil.IsETagValueValid(etag, true))
            {
                throw new InvalidOperationException(Strings.DataServiceStreamProviderWrapper_GetStreamETagReturnedInvalidETagFormat);
            } 

            return etag; 
        } 

        ///  
        /// This method is invoked by the data services framework when a request is received to insert into an Entity Set with an associated
        /// Entity Type hierarchy that has > 1 Entity Type and >= 1 Entity Type which is tagged as an MLE (ie. includes a stream).
        /// 
        /// Fully qualified name entity set name. 
        /// Data service instance.
        ///  
        /// Namespace qualified type name which represents the type the Astoria framework should instantiate to create the MLE associated 
        /// with the BLOB/MR being inserted.
        ///  
        internal ResourceType ResolveType(string entitySetName, IDataService service)
        {
            DataServiceOperationContext operationContext = service.OperationContext;
            Debug.Assert(operationContext != null, "operationContext != null"); 
            string resourceTypeName = InvokeApiCallAndValidateHeaders("IDataServiceStreamProvider.ResolveType", () => this.StreamProvider.ResolveType(entitySetName, operationContext), operationContext);
            if (string.IsNullOrEmpty(resourceTypeName)) 
            { 
                throw new InvalidOperationException(Strings.DataServiceStreamProviderWrapper_ResolveTypeMustReturnValidResourceTypeName);
            } 

            ResourceType resourceType = service.Provider.TryResolveResourceType(resourceTypeName);
            if (resourceType == null)
            { 
                throw new InvalidOperationException(Strings.DataServiceStreamProviderWrapper_ResolveTypeMustReturnValidResourceTypeName);
            } 
 
            return resourceType;
        } 

        /// 
        /// Gets the ETag, ReadStreamUri and ContentType of the stream
        ///  
        /// MLE instance
        /// context of the current operation 
        /// Uri to the MLE 
        /// returns the etag for the stream
        /// returns the read stream uri 
        /// returns the content type of the stream
        internal void GetStreamDescription(object entity, DataServiceOperationContext operationContext, string mediaLinkEntryUri, out string etag, out Uri readStreamUri, out string contentType)
        {
            Debug.Assert(entity != null, "entity != null"); 
            Debug.Assert(operationContext != null, "operationContext != null");
 
            // Call order is part of our contract, do not change it. 
            etag = this.GetStreamETag(entity, operationContext);
            readStreamUri = this.GetReadStreamUri(entity, operationContext, mediaLinkEntryUri); 
            contentType = this.GetStreamContentType(entity, operationContext);
        }

        ///  
        /// Dispose the stream provider instance
        ///  
        internal void DisposeProvider() 
        {
            if (this.streamProvider != null) 
            {
                WebUtil.Dispose(this.streamProvider);
                this.streamProvider = null;
            } 
        }
 
        #endregion Public Methods 

        #region Private Methods 

        /// 
        /// Get the ETag header value from the request headers.
        ///  
        /// A reference to the context for the current operation.
        ///  
        /// The etag value sent by the client (as the value of an If[-None-]Match header) as part of the HTTP request sent to the data service 
        /// This parameter will be null if no If[-None-]Match header was present
        ///  
        /// 
        /// True if an value of the etag parameter was sent to the server as the value of an If-Match HTTP request header
        /// False if an value of the etag parameter was sent to the server as the value of an If-None-Match HTTP request header
        /// null if the HTTP request for the stream was not a conditional request 
        /// 
        private static void GetETagFromHeaders(DataServiceOperationContext operationContext, out string etag, out bool? checkETagForEquality) 
        { 
            Debug.Assert(operationContext != null, "operationContext != null");
            Debug.Assert(operationContext.Host != null, "operationContext.Host != null"); 
            DataServiceHostWrapper host = operationContext.Host;
            Debug.Assert(string.IsNullOrEmpty(host.RequestIfMatch) || string.IsNullOrEmpty(host.RequestIfNoneMatch), "IfMatch and IfNoneMatch should not be both set.");

            if (string.IsNullOrEmpty(host.RequestIfMatch) && string.IsNullOrEmpty(host.RequestIfNoneMatch)) 
            {
                etag = null; 
                checkETagForEquality = null; 
            }
            else if (!string.IsNullOrEmpty(host.RequestIfMatch)) 
            {
                etag = host.RequestIfMatch;
                checkETagForEquality = true;
            } 
            else
            { 
                etag = host.RequestIfNoneMatch; 
                checkETagForEquality = false;
            } 
        }

        /// 
        /// Invokes an API call and verifies the response Content-Type and ETag headers are not being modified by the API call. 
        /// 
        /// Return type from the API call 
        /// API name 
        /// Delegate to be called
        /// A reference to the context for the current operation. 
        /// Returns the result from the api call
        private static T InvokeApiCallAndValidateHeaders(string methodName, Func apiCall, DataServiceOperationContext operationContext)
        {
            Debug.Assert(!string.IsNullOrEmpty(methodName), "!string.IsNullOrEmpty(methodName)"); 
            Debug.Assert(operationContext != null, "operationContext != null");
            Debug.Assert(apiCall != null, "apiCall != null"); 
 
            string responseContentType = operationContext.Host.ResponseContentType;
            string responseETag = operationContext.Host.ResponseETag; 
            T result = apiCall();
            if (operationContext.Host.ResponseContentType != responseContentType || operationContext.Host.ResponseETag != responseETag)
            {
                throw new InvalidOperationException(Strings.DataServiceStreamProviderWrapper_MustNotSetContentTypeAndEtag(methodName)); 
            }
 
            return result; 
        }
 
        #endregion Private Methods
    }
}

// File provided for Reference Use Only by Microsoft Corporation (c) 2007.
//---------------------------------------------------------------------- 
// 
//      Copyright (c) Microsoft Corporation.  All rights reserved.
// 
//  
//      This wrapper class forwards calls to the underlying IDataServiceStreamProvider
//      instance and validates responses from it. 
//  
//
// @owner  [....] 
//---------------------------------------------------------------------

namespace System.Data.Services.Providers
{ 
    using System;
    using System.IO; 
    using System.Diagnostics; 
    using System.Collections;
    using System.Collections.Generic; 
    using System.Linq;
    using System.Data.Services;

    ///  
    /// Wrapper class to forward calls to the underlying IDataServiceStreamProvider instance and validates responses from it.
    ///  
    internal class DataServiceStreamProviderWrapper 
    {
        #region Private Fields 

        /// 
        /// Default buffer size used for stream copy.
        ///  
        private const int DefaultBufferSize = 64 * 1024;
 
        ///  
        /// Stream provider instance
        ///  
        private IDataServiceStreamProvider streamProvider;

        /// 
        /// Data service instance 
        /// 
        private IDataService dataService; 
 
        #endregion Private Fields
 
        #region Constructor

        /// 
        /// Constructs the wrapper class for IDataServiceStreamProvider 
        /// 
        /// Data service instance 
        public DataServiceStreamProviderWrapper(IDataService dataService) 
        {
            Debug.Assert(dataService != null, "dataService != null"); 
            this.dataService = dataService;
        }

        #endregion Constructor 

        #region Public Properties 
 
        /// 
        /// Gets buffer size the data service will use when reading from read stream or writing to the write stream. 
        /// If the size is less than or equals to 0, the default of 64k will be used.
        /// 
        public int StreamBufferSize
        { 
            get
            { 
                int size = this.StreamProvider.StreamBufferSize; 
                return size > 0 ? size : DataServiceStreamProviderWrapper.DefaultBufferSize;
            } 
        }

        #endregion Public Properties
 
        #region Private Properties
 
        ///  
        /// Asks the service for an IDataServiceStreamProvider implementation
        ///  
        private IDataServiceStreamProvider StreamProvider
        {
            get
            { 
                if (this.streamProvider == null)
                { 
                    this.streamProvider = LoadStreamProvider(this.dataService); 
                    Debug.Assert(this.streamProvider != null, "this.streamProvider != null");
                } 

                return this.streamProvider;
            }
        } 

        #endregion Private Properties 
 
        #region Internal Methods
 
        /// 
        /// Take the given Media Link Entry uri, and construct the default Edit Media Uri.
        /// 
        /// Uri to the Media Link Entry. 
        /// Uri to the Media Resource.
        internal static string GetStreamEditMediaUri(string mediaLinkEntryUri) 
        { 
            Debug.Assert(!string.IsNullOrEmpty(mediaLinkEntryUri), "!string.IsNullOrEmpty(mediaLinkEntryUri)");
            string result = mediaLinkEntryUri; 

            if (!result.EndsWith(XmlConstants.UriValueSegment, StringComparison.Ordinal))
            {
                if (!result.EndsWith("/", StringComparison.Ordinal)) 
                {
                    result += "/"; 
                } 

                result += XmlConstants.UriValueSegment; 
            }

            return result;
        } 

        ///  
        /// Asks the data service for a stream provider instance.  Throw if none is implemented. 
        /// 
        /// data service instance 
        /// stream provider instance
        internal static IDataServiceStreamProvider LoadStreamProvider(IDataService dataService)
        {
            IDataServiceStreamProvider streamProvider = dataService.Provider.GetService(dataService); 
            if (streamProvider == null)
            { 
                throw new DataServiceException(500, Strings.DataServiceStreamProviderWrapper_MustImplementIDataServiceStreamProviderToSupportStreaming); 
            }
 
            return streamProvider;
        }

        ///  
        /// This method is invoked by the data services framework to retrieve the default stream associated
        /// with the Entity Type specified by the  parameter. 
        /// Note that we set the response ETag in the host object before we return. 
        /// 
        /// The stream returned should be the default stream associated with this entity. 
        /// A reference to the context for the current operation.
        /// A valid stream the data service use to query / read a streamed BLOB which is associated with the .
        internal Stream GetReadStream(object entity, DataServiceOperationContext operationContext)
        { 
            Debug.Assert(entity != null, "entity != null");
            Debug.Assert(operationContext != null, "operationContext != null"); 
 
            string etagFromHeader;
            bool? checkETagForEquality; 
            DataServiceStreamProviderWrapper.GetETagFromHeaders(operationContext, out etagFromHeader, out checkETagForEquality);
            Debug.Assert(
                string.IsNullOrEmpty(etagFromHeader) && !checkETagForEquality.HasValue || !string.IsNullOrEmpty(etagFromHeader) && checkETagForEquality.HasValue,
                "etag and checkETagForEquality parameters must both be set or not set at the same time."); 

            Stream readStream = null; 
            try 
            {
                readStream = InvokeApiCallAndValidateHeaders("IDataServiceStreamProvider.GetReadStream", () => this.StreamProvider.GetReadStream(entity, etagFromHeader, checkETagForEquality, operationContext), operationContext); 
            }
            catch (DataServiceException e)
            {
                if (e.StatusCode == (int)System.Net.HttpStatusCode.NotModified) 
                {
                    // For status code 304, we MUST set the etag value.  Our Error handler will translate 
                    // DataServiceException(304) to a normal response with status code 304 and an empty message-body. 
#if DEBUG
                    WebUtil.WriteETagValueInResponseHeader(null, this.GetStreamETag(entity, operationContext), operationContext.Host); 
#else
                    WebUtil.WriteETagValueInResponseHeader(this.GetStreamETag(entity, operationContext), operationContext.Host);
#endif
                } 

                throw; 
            } 

            try 
            {
                if (readStream == null || !readStream.CanRead)
                {
                    throw new InvalidOperationException(Strings.DataService_InvalidStreamFromGetReadStream); 
                }
 
                // GetStreamETag can throw and we need to catch and dispose the stream. 
#if DEBUG
                WebUtil.WriteETagValueInResponseHeader(null, this.GetStreamETag(entity, operationContext), operationContext.Host); 
#else
                WebUtil.WriteETagValueInResponseHeader(this.GetStreamETag(entity, operationContext), operationContext.Host);
#endif
            } 
            catch
            { 
                WebUtil.Dispose(readStream); 
                throw;
            } 

            return readStream;
        }
 
        /// 
        /// This method is invoked by the data services framework whenever an insert or update operation is 
        /// being processed for the stream associated with the Entity Type specified via the entity parameter. 
        /// 
        /// The stream returned should be the default stream associated with this entity. 
        /// A reference to the context for the current operation.
        /// A valid stream the data service use to write the contents of a BLOB which is associated with .
        internal Stream GetWriteStream(object entity, DataServiceOperationContext operationContext)
        { 
            Debug.Assert(entity != null, "entity != null");
            Debug.Assert(operationContext != null, "operationContext != null"); 
 
            string etag;
            bool? checkETagForEquality; 
            DataServiceStreamProviderWrapper.GetETagFromHeaders(operationContext, out etag, out checkETagForEquality);
            Debug.Assert(
                string.IsNullOrEmpty(etag) && !checkETagForEquality.HasValue || !string.IsNullOrEmpty(etag) && checkETagForEquality.HasValue,
                "etag and checkETagForEquality parameters must both be set or not set at the same time."); 

            Stream writeStream = InvokeApiCallAndValidateHeaders("IDataServiceStreamProvider.GetWriteStream", () => this.StreamProvider.GetWriteStream(entity, etag, checkETagForEquality, operationContext), operationContext); 
            if (writeStream == null || !writeStream.CanWrite) 
            {
                WebUtil.Dispose(writeStream); 
                throw new InvalidOperationException(Strings.DataService_InvalidStreamFromGetWriteStream);
            }

            return writeStream; 
        }
 
        ///  
        /// This method is invoked by the data services framework whenever an delete operation is being processed for the stream associated with
        /// the Entity Type specified via the entity parameter. 
        /// 
        /// The stream deleted should be the default stream associated with this entity.
        /// A reference to the context for the current operation.
        internal void DeleteStream(object entity, DataServiceOperationContext operationContext) 
        {
            Debug.Assert(entity != null, "entity != null"); 
            Debug.Assert(operationContext != null, "operationContext != null"); 
            InvokeApiCallAndValidateHeaders("IDataServiceStreamProvider.DeleteStream", () => { this.StreamProvider.DeleteStream(entity, operationContext); return true; }, operationContext);
        } 

        /// 
        /// This method is invoked by the data services framework to obtain the IANA content type (aka media type) of the stream associated
        /// with the specified entity.  This metadata is needed when constructing the payload for the Media Link Entry associated with the 
        /// stream (aka Media Resource) or setting the Content-Type HTTP response header.
        ///  
        /// The entity associated with the stream for which the content type is to be obtained 
        /// A reference to the context for the current operation.
        /// Valid Content-Type string for the stream associated with the entity 
        internal string GetStreamContentType(object entity, DataServiceOperationContext operationContext)
        {
            Debug.Assert(entity != null, "entity != null");
            Debug.Assert(operationContext != null, "operationContext != null"); 

            string contentType = InvokeApiCallAndValidateHeaders("IDataServiceStreamProvider.GetStreamContentType", () => this.StreamProvider.GetStreamContentType(entity, operationContext), operationContext); 
            if (string.IsNullOrEmpty(contentType)) 
            {
                throw new InvalidOperationException(Strings.DataServiceStreamProviderWrapper_GetStreamContentTypeReturnsEmptyOrNull); 
            }

            return contentType;
        } 

        ///  
        /// This method is invoked by the data services framework to obtain the URI clients should use when making retrieve (ie. GET) 
        /// requests to the stream(ie. Media Resource).   This metadata is needed when constructing the payload for the Media Link Entry
        /// associated with the stream (aka Media Resource). 
        ///
        /// If IDataServiceStreamProvider.GetReadStreamUri returns a valid Uri, we return that as the Uri to the Media Resource.
        /// Otherwise we take the given Media Link Entry uri, and construct the default Media Resource Uri.
        ///  
        /// The entity associated with the stream for which a “read stream” is to be obtained
        /// A reference to the context for the current operation. 
        /// Uri to the Media Link Entry. 
        /// The URI clients should use when making retrieve (ie. GET) requests to the stream(ie. Media Resource).
        internal Uri GetReadStreamUri(object entity, DataServiceOperationContext operationContext, string mediaLinkEntryUri) 
        {
            Debug.Assert(entity != null, "entity != null");
            Debug.Assert(operationContext != null, "operationContext != null");
 
            Uri readStreamUri = InvokeApiCallAndValidateHeaders("IDataServiceStreamProvider.GetReadStreamUri", () => this.StreamProvider.GetReadStreamUri(entity, operationContext), operationContext);
            if (readStreamUri != null) 
            { 
                if (!readStreamUri.IsAbsoluteUri)
                { 
                    throw new InvalidOperationException(Strings.DataServiceStreamProviderWrapper_GetReadStreamUriMustReturnAbsoluteUriOrNull);
                }
                else
                { 
                    return readStreamUri;
                } 
            } 
            else
            { 
                return new Uri(DataServiceStreamProviderWrapper.GetStreamEditMediaUri(mediaLinkEntryUri), UriKind.RelativeOrAbsolute);
            }
        }
 
        /// 
        /// This method is invoked by the data services framework to obtain the ETag of the stream associated with the entity specified. 
        /// This metadata is needed when constructing the payload for the Media Link Entry associated with the stream (aka Media Resource) 
        /// as well as to be used as the value of the ETag HTTP response header.
        ///  
        /// The entity associated with the stream for which an etag is to be obtained
        /// A reference to the context for the current operation.
        /// ETag of the stream associated with the entity specified
        internal string GetStreamETag(object entity, DataServiceOperationContext operationContext) 
        {
            Debug.Assert(entity != null, "entity != null"); 
            Debug.Assert(operationContext != null, "operationContext != null"); 

            string etag = InvokeApiCallAndValidateHeaders("IDataServiceStreamProvider.GetStreamETag", () => this.StreamProvider.GetStreamETag(entity, operationContext), operationContext); 
            if (!WebUtil.IsETagValueValid(etag, true))
            {
                throw new InvalidOperationException(Strings.DataServiceStreamProviderWrapper_GetStreamETagReturnedInvalidETagFormat);
            } 

            return etag; 
        } 

        ///  
        /// This method is invoked by the data services framework when a request is received to insert into an Entity Set with an associated
        /// Entity Type hierarchy that has > 1 Entity Type and >= 1 Entity Type which is tagged as an MLE (ie. includes a stream).
        /// 
        /// Fully qualified name entity set name. 
        /// Data service instance.
        ///  
        /// Namespace qualified type name which represents the type the Astoria framework should instantiate to create the MLE associated 
        /// with the BLOB/MR being inserted.
        ///  
        internal ResourceType ResolveType(string entitySetName, IDataService service)
        {
            DataServiceOperationContext operationContext = service.OperationContext;
            Debug.Assert(operationContext != null, "operationContext != null"); 
            string resourceTypeName = InvokeApiCallAndValidateHeaders("IDataServiceStreamProvider.ResolveType", () => this.StreamProvider.ResolveType(entitySetName, operationContext), operationContext);
            if (string.IsNullOrEmpty(resourceTypeName)) 
            { 
                throw new InvalidOperationException(Strings.DataServiceStreamProviderWrapper_ResolveTypeMustReturnValidResourceTypeName);
            } 

            ResourceType resourceType = service.Provider.TryResolveResourceType(resourceTypeName);
            if (resourceType == null)
            { 
                throw new InvalidOperationException(Strings.DataServiceStreamProviderWrapper_ResolveTypeMustReturnValidResourceTypeName);
            } 
 
            return resourceType;
        } 

        /// 
        /// Gets the ETag, ReadStreamUri and ContentType of the stream
        ///  
        /// MLE instance
        /// context of the current operation 
        /// Uri to the MLE 
        /// returns the etag for the stream
        /// returns the read stream uri 
        /// returns the content type of the stream
        internal void GetStreamDescription(object entity, DataServiceOperationContext operationContext, string mediaLinkEntryUri, out string etag, out Uri readStreamUri, out string contentType)
        {
            Debug.Assert(entity != null, "entity != null"); 
            Debug.Assert(operationContext != null, "operationContext != null");
 
            // Call order is part of our contract, do not change it. 
            etag = this.GetStreamETag(entity, operationContext);
            readStreamUri = this.GetReadStreamUri(entity, operationContext, mediaLinkEntryUri); 
            contentType = this.GetStreamContentType(entity, operationContext);
        }

        ///  
        /// Dispose the stream provider instance
        ///  
        internal void DisposeProvider() 
        {
            if (this.streamProvider != null) 
            {
                WebUtil.Dispose(this.streamProvider);
                this.streamProvider = null;
            } 
        }
 
        #endregion Public Methods 

        #region Private Methods 

        /// 
        /// Get the ETag header value from the request headers.
        ///  
        /// A reference to the context for the current operation.
        ///  
        /// The etag value sent by the client (as the value of an If[-None-]Match header) as part of the HTTP request sent to the data service 
        /// This parameter will be null if no If[-None-]Match header was present
        ///  
        /// 
        /// True if an value of the etag parameter was sent to the server as the value of an If-Match HTTP request header
        /// False if an value of the etag parameter was sent to the server as the value of an If-None-Match HTTP request header
        /// null if the HTTP request for the stream was not a conditional request 
        /// 
        private static void GetETagFromHeaders(DataServiceOperationContext operationContext, out string etag, out bool? checkETagForEquality) 
        { 
            Debug.Assert(operationContext != null, "operationContext != null");
            Debug.Assert(operationContext.Host != null, "operationContext.Host != null"); 
            DataServiceHostWrapper host = operationContext.Host;
            Debug.Assert(string.IsNullOrEmpty(host.RequestIfMatch) || string.IsNullOrEmpty(host.RequestIfNoneMatch), "IfMatch and IfNoneMatch should not be both set.");

            if (string.IsNullOrEmpty(host.RequestIfMatch) && string.IsNullOrEmpty(host.RequestIfNoneMatch)) 
            {
                etag = null; 
                checkETagForEquality = null; 
            }
            else if (!string.IsNullOrEmpty(host.RequestIfMatch)) 
            {
                etag = host.RequestIfMatch;
                checkETagForEquality = true;
            } 
            else
            { 
                etag = host.RequestIfNoneMatch; 
                checkETagForEquality = false;
            } 
        }

        /// 
        /// Invokes an API call and verifies the response Content-Type and ETag headers are not being modified by the API call. 
        /// 
        /// Return type from the API call 
        /// API name 
        /// Delegate to be called
        /// A reference to the context for the current operation. 
        /// Returns the result from the api call
        private static T InvokeApiCallAndValidateHeaders(string methodName, Func apiCall, DataServiceOperationContext operationContext)
        {
            Debug.Assert(!string.IsNullOrEmpty(methodName), "!string.IsNullOrEmpty(methodName)"); 
            Debug.Assert(operationContext != null, "operationContext != null");
            Debug.Assert(apiCall != null, "apiCall != null"); 
 
            string responseContentType = operationContext.Host.ResponseContentType;
            string responseETag = operationContext.Host.ResponseETag; 
            T result = apiCall();
            if (operationContext.Host.ResponseContentType != responseContentType || operationContext.Host.ResponseETag != responseETag)
            {
                throw new InvalidOperationException(Strings.DataServiceStreamProviderWrapper_MustNotSetContentTypeAndEtag(methodName)); 
            }
 
            return result; 
        }
 
        #endregion Private Methods
    }
}

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

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