Using serialization to emulate an assembly

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Introduction

When working in a team environment, factors such as limited license keys, security, or network access may hinder the creation of a test environment. In a recent project, one of my requirements was to interface with an existing .NET component. The existing component could not be duplicated in my off-site office environment, and existing security policies would not allow network access. Coding and testing the interface was looking very difficult.

In this article, I will present a method I have used to overcome this problem. In a nutshell, the approach I have used captured the output from an interface query (function call), then serialized the result, wrote it to a file, and emailed it to my office. Later, when I needed to emulate the original component offsite, I called a substitute function with the same parameters and interface as the original, and deserialized my stored result.

This method allows me to mimic exactly the interface for specific tests. The actual concept is quite simple, and the results have been very effective in providing a temporary test environment.

First, a quick look at the class I wish to emulate...

For the purpose of explanation, I have created a class with a complex result set. The actual internal processing is not important, in fact, for this example, it should not matter if I cannot view the internal workings.

Public Class clsMyResult
    'clsMyResult is complex (output) class, 
    'the result am interested in emulating.
    Public myDS As DataSet
    Public strDesc As String
    Public myCounter As Int16 = 0
End Class

Public Class clsOriginalClassIWishToEmulate
    'this is the original class I wish to emulate - 
    'but I want to pretend I don't know 
    '(or have access to) the internal workings
    Public Function MakeResult(ByVal newTables As Int16) As clsMyResult
        Dim myResult As New clsMyResult
        Dim localDS As New DataSet
        For y As Int16 = 1 To newTables
            Dim thisTable As New DataTable("table" & y)
            thisTable.Columns.Add("tab:" & y & "-col")
            Dim myDataRow As DataRow
            For x As Int16 = 1 To 10
                myDataRow = thisTable.NewRow
                myDataRow(0) = "table:" & y & " row:" & x
                thisTable.Rows.Add(myDataRow)
            Next
            localDS.Tables.Add(thisTable)
            myResult.myCounter += 1
        Next
        myResult.myDS = localDS
        myResult.strDesc = "There are " & myResult.myCounter & _
                                        " tables in the dataset"
        Return myResult

    End Function
End Class

Calling clsOriginalClassIWishToEmulate.MakeResult will produce an output class containing a populated DataSet, a text string, and counter for the number of tables in the DataSet.

Capture the output from the original class

The first step in this emulation is to get access to the original class - say on a local developer computer, and run a query against it.

In my case, I will create an instance of the original class and call the function I wish to emulate. I will pass the function the int16 value 10: myOriginalClass.MakeResult(10).

Private Sub Serialize_Click(ByVal sender As System.Object, _
        ByVal e As System.EventArgs) Handles Button1.Click
    ' I want to use clsOriginalClassIWishToEmulate but
    ' I cannot because of access restrictions
    ' First thing to do is to instantiate the class
    ' and the results I want to copy
    Dim myOrginalClass As New clsOriginalClassIWishToEmulate
    Dim myResult As clsMyResult 
    'myResult is the output of clsOriginalClassIWishToEmulate.
    'Let's decide we want to emulate as close as possible 
    'the class which is fed a value of "10"
    'Next, let's get the result value
    myResult = myOrginalClass.MakeResult(10)
    'define an file to write the result to...
    Dim myStreamWriter As StreamWriter
    myStreamWriter = New StreamWriter("myresult.xml")
    'and serialize the class
    Dim mySerializer As New XmlSerializer(GetType(clsMyResult))
    mySerializer.Serialize(myStreamWriter, myResult)
    myStreamWriter.Close()
End Sub

After the function returns a value, I serialize the result into an XML file. Note that I need to know the structure of the response for this segment of code to work.

Emulate the original class interface

The next step requires creating a substitute class with the same parameters as the original. This class opens the stored XML file, and returns an actual value (in this case, for '10').

Public Class clsEmulatedClass
    Public Function MakeResult(ByVal newTables As Int16) As clsMyResult
        'the point of this class is to mimic the original - but in this case 
        'will only mimic correct functions for input value "10"
        Dim myResult As New clsMyResult
        'setup the stream reader and xml serializetion object
        Dim myStreamReader As StreamReader
        Dim mySerializer As New XmlSerializer(GetType(clsMyResult))
        'load the saved XML file
        myStreamReader = New StreamReader("myresult.xml")
        myResult = mySerializer.Deserialize(myStreamReader)
        myStreamReader.Close()
        Return myResult
    End Function
End Class

Using the new function

The newly created function will operate identical to the original for the function we have emulated. Of course, the returned class is only correct for a particular set of input values.

Enhancements

Further additions to this example could include:

• Store the results for multiple inputs (the emulated class could return the result from the example with the matching input value);
• Emulate properties and;
• Duplicate relevant aspects of the namespace of the original class.

Conclusions

The method displayed here allows the creation of an emulated class. This is particularly useful when the original class is not available due to security, network, or licensing restrictions. Although the method is extremely simple, it can allow a development and testing environment not otherwise possible.

Good luck and happy coding!!