Efficient way of downloading a zip file, unzip and delete it safely - zip

Question

I am writing a small program which can download stock market information. Below is the code:
Dim DLink As String = "https://www.nseindia.com/content/historical/EQUITIES/" & strThisYear & "/" & txtMonth & "/cm" & strDate & "bhav.csv.zip"
Dim SaveDir As String = GetLocation()
Dim strFile As String = SaveDir & "\Bhavcopy\" & strDate & "bhav.csv.zip"
Dim webClient As New WebClient()
webClient.Headers(HttpRequestHeader.Accept) = "text/html,application/xhtml+xml,application/xml;q=0.9,/;q=0.8"
webClient.Headers.Add("user-agent", "Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/537.31 (KHTML, Like Gecko) Chrome/26.0.1410.64 Safari/537.31")
webClient.DownloadFileAsync(New Uri(DLink), strFile)
System.Threading.Thread.Sleep(500) ' Using Thread.sleep to give time for writing. Else, the next operation fails with error 'File in Use'
Dim myFile As New FileInfo(SaveDir & "\Bhavcopy\" & strDate & "bhav.csv.zip")
Dim sizeInBytes As Long = myFile.Length
If myFile.Exists = True And myFile.Length > 0 Then ' Checking file size>0 then only unzip
System.IO.Compression.ZipFile.ExtractToDirectory(myFile.ToString, SaveDir & "\Bhavcopy\")
End If
System.Threading.Thread.Sleep(500) ' again thread.sleep used for unzipping operation..else file in use error appears
If myFile.Exists = True Then
Try
myFile.Delete()
Catch ex As Exception
MessageBox.Show(ex.ToString)
End Try
End If
I believe this is not efficient since I am using Thread.Sleep a few times in order to overcome 'File in Use' error. I have adjusted the sleep time from 2000ms to 500 ms but sometimes it still gives an error.
Checking the filesize > 0 is to check the fact that the download can be a holiday or weekend when there exists no data on that day.
Is there a better way to convert this code to efficiently download the zip file, check for file size > 0, then unzip it and then safely delete it?

Answer 1

Dim saveAs as string="C:\Documents and Settings\All Users\Documents\google.zip"
Dim theResponse As HttpWebResponse
Dim theRequest As HttpWebRequest
Try 'Checks if the file exist
theRequest = WebRequest.Create(fileUrl) 'fileUrl is your zip url
theResponse = theRequest.GetResponse
Catch ex As Exception
'could not be found on the server (network delay maybe)
Exit sub 'Exit sub or function, because if not found can't be downloaded
End Try
Dim length As Long = theResponse.ContentLength
Dim writeStream As New IO.FileStream(saveAs, IO.FileMode.Create)
Dim nRead As Integer
Do
Dim readBytes(4095) As Byte
Dim bytesread As Integer = theResponse.GetResponseStream.Read(readBytes, 0, 4096)
nRead += bytesread
If bytesread = 0 Then Exit Do
writeStream.Write(readBytes, 0, bytesread)
Loop
theResponse.GetResponseStream.Close()
writeStream.Close()
'File downloaded 100%
This code snippet too came stackoverflow but I forgot to note down the original post URL. Thanks for that code.
With this, the files are downloaded, I added code to unzip, no file lock occurs