Xml Resource Resolver

By jayharlow

XmlResourceResolver is a class derived from System.Xml.XmlResolver used to find resources stored as manifest resource streams in an assembly.


Problem


I wanted to:



  • Store a number XSLT files as embedded resources, so that I could deploy the assembly without deploying each of the individual XSLT files

  • Optionally allow an XSLT file to be overloaded by the user

  • Allow an XSLT file to be localized in a language satellite assembly

  • Allow xsl:include & xsl:import statements to find the file as an embedded resource

The new System.Xml.XmlResolver class in .NET 1.1 looked promising!


I knew about the Assembly.GetManifestResourceStream call to load the embedded XSLT files as a Stream into my program. I also found that by including the culture identifier in the file name (between the name & the extension) that VS.NET will create the respective satellite assemblies for you, with the XSLT file embedded. Unfortunately looking at ResourceManager was not giving me what I needed…


What I was missing was how to find the satellite assemblies.


A quick search on Google lead me to Shawn A. Van Ness’ article I Hate ResX Files giving me to the piece I was missing Assembly.GetSatelliteAssembly.


I must have been looking too hard at ResourceManager to have noticed Assembly.GetSatelliteAssembly! 🙂


Solution


The XmlResourceResolver class is my solution; I hope you find it useful. Like Shawn’s ResourceLoader class, it can be used for any type of embedded resource, not just XSLT files!


Discussion


m_assembly — Defines the primary Assembly where the embedded resources are found


m_type — Defines the Type that is used to indentify the namespace where the embedded resources are. NOTE: Only the namespace of this Type is used.


New(type) — Initializes the m_assembly & m_type fields.


Credentials — Not supported


ResolveUri(baseUri, relativeUri) — Overridden to set the baseUri to the Assembly.Location if the baseUri is not given.


GetEntity(absoluteUri, role, ofObjectToReturn) — Returns a Stream representing the resource from the first of the following places: File in same location as assembly, Specific Culture Assembly (de-DE), Specific Culture’s Parent Assembly (de), or finally the primary assembly itself. If the resource is not found in any of the four places a FileNotFoundException is thrown.


GetManifestResourceStream(culture, name) — Helper function used by GetEntity to find the resource in a satellite assembly.


GetManifestResourceStream(name) — Helper function used by GetEntity to find the resource in the primary assembly.


Example


The following is a sample using the class:

Dim name As String
Dim resolver As New XmlResourceResolver(GetType(TestModule))
Dim absoluteUri As Uri = resolver.ResolveUri(Nothing, name)
Dim Input As Stream = DirectCast(resolver.GetEntity(absoluteUri, Nothing, Nothing), Stream)
Dim xslt As New XslTransform
xslt.Load(New XmlTextReader(Input), resolver, Nothing)

Source

‘
‘ Copyright © 2005, Jay B. Harlow, All Rights Reserved.
‘
Option Strict On
Option Explicit On 



Imports System.IO
Imports System.Net
Imports System.Xml
Imports System.Globalization
Imports System.Reflection
Imports System.Resources



Public Class XmlResourceResolver
    Inherits XmlResolver



    Private ReadOnly m_assembly As [Assembly]
    Private ReadOnly m_type As Type



    Public Sub New(ByVal type As Type)
        m_assembly = type.Assembly
        m_type = type
    End Sub



    Public Overrides WriteOnly Property Credentials() As ICredentials
        Set(ByVal value As ICredentials)
            Throw New NotSupportedException
        End Set
    End Property



    Public Overrides Function ResolveUri(ByVal baseUri As System.Uri, ByVal relativeUri As String) As System.Uri
        If baseUri Is Nothing Then
            baseUri = New Uri(m_assembly.Location, True)
        End If
        Return MyBase.ResolveUri(baseUri, relativeUri)
    End Function



    Public Overrides Function GetEntity(ByVal absoluteUri As Uri, ByVal role As String, ByVal ofObjectToReturn As Type) As Object
        Dim fullPath As String = absoluteUri.AbsolutePath
        If File.Exists(fullPath) Then
            Return New FileStream(fullPath, FileMode.Open, FileAccess.Read, FileShare.Read)
        Else
            Dim name As String = Path.GetFileName(fullPath)
            Dim culture As CultureInfo = CultureInfo.CurrentUICulture
            Dim stream As stream
 
            ‘ Try the specific culture
            stream = GetManifestResourceStream(culture, name)



            ‘ Try the neutral culture
            If stream Is Nothing AndAlso Not culture.IsNeutralCulture Then
                stream = GetManifestResourceStream(culture.Parent, name)
            End If



            ‘ Try the default culture
            If stream Is Nothing Then
                stream = GetManifestResourceStream(name)
            End If
 
            If stream Is Nothing Then
                Throw New FileNotFoundException(Nothing, name)
            End If



            Return stream
        End If
    End Function



    Private Function GetManifestResourceStream(ByVal culture As CultureInfo, ByVal name As String) As Stream
        Try
            Dim satellite As [Assembly] = m_assembly.GetSatelliteAssembly(culture)
            Return satellite.GetManifestResourceStream(m_type, name)
        Catch ex As FileNotFoundException
            Return Nothing
        End Try
    End Function



    Private Function GetManifestResourceStream(ByVal name As String) As Stream
        Return m_assembly.GetManifestResourceStream(m_type, name)
    End Function



End Class