Articles
Contact us |
|
VB.NET Imports System Imports System.Data.OleDb
Namespace p2pfirewall Public Class tunnel Inherits System.MarshalByRefObject Dim DSN as string = "Provider=Microsoft.Jet.OLEDB.4.0;" + _ "Data Source=C:\filetransfers.mdb";
Public Sub postRequest(ByVal requestingPeer As String, ByVal _ filename As String, ByVal respondingPeer As String) Dim SQL As String SQL = "insert into requests " SQL = SQL + "(requester,filename,respondent) values (" SQL = SQL + "'" + requestingPeer + "'," SQL = SQL + "'" + filename + "'," SQL = SQL + "'" + respondingPeer + "')" nonQuery(SQL,DSN) End Sub
Public Sub postResponse(ByVal respondingPeer As String, _ ByVal filename As String, ByVal fileContents As String, _ ByVal requestingPeer As String) Dim SQL As String SQL = "insert into responses " SQL = SQL + "((requester,fileContents,filename,respondent) values (" SQL = SQL + "'" + requestingPeer + "'," SQL = SQL + "'" + fileContents + "'," SQL = SQL + "'" + filename + "'," SQL = SQL + "'" + respondingPeer + "')" nonQuery(SQL,DSN) End Sub
Public Function checkRequests(ByVal peer As String) As String Dim SQL As String Dim filename As String SQL = "select top 1 * from requests where " SQL = SQL + " respondent='" + peer + "'" filename = Query("filename",SQL,DSN) ' don't return the same request twice.
SQL = "delete from requests where " SQL = SQL + " respondent='" + peer + "' and " SQL = SQL + " filename='" + filename + "'" nonQuery(SQL,DSN) Return filename End Function
Public Function checkResponse(ByVal respondingPeer As String, _ ByVal filename As String) As String Dim SQL As String SQL = "select top 1 * from responses where " SQL = SQL + " respondent='" + respondingPeer + "' and " SQL = SQL + " filename='" + filename + "'" Return Query("fileContents",SQL,DSN) End Function
End Class End Namespace This class will be used in remoting, so therefore it must inherit from System.MarshalByRefObject. More information on this can be seen in the web services chapter. The public methods will be exposed to the client, but not the private methods and properties. The private string variable DSN is used to determine the location and type of the local database. This information is not relevant to the remote client. Going through the functions one by one, let’s look at postRequest first. What the function does is it adds a new row into the request table, populating the requester, filename and respondent fields. It calls the nonQuery function, which as we shall see later is used to run statements against the database that do not return result sets. PostResponse is quite similar to PostRequest in that it adds a new row into the response table, populating the requester, fileContents, filename, and respondent fields. Once again, it calls the nonQuery function to process the statement. CheckRequests performs two functions. Firstly it retrieves the last row in the requests table that pertains to a particular specified peer. It does this by executing a select statement against the requests table in the database, filtering by respondent. The second task performed by this function is to remove rows in the requests table pertaining to a particular peer. This prevents requests been handled more than once. This action is performed by the nonQuery function processing a SQL delete statement. To complete the class, we need to implement the Query and nonQuery methods. These are taken from chapter 2, with some modification to the Query method, such that it returns a string that corresponds to the specified field as returned in the first row of data. The fourth function, checkResponse reads the topmost row from the responses table that pertains to the specified peer. It returns the filecCntents field to the calling function. Page 2 Page 4Copyright 2012 Open Merchant Account Ltd. 
|
