Backslashes in path in VB.Net - asp.net

Question

It seems I'm not lucky with backslashes in ASP.Net VB.Net.
I'm trying to output some infos about files with ffprobe and my paths are cut randomly at some backslash in every string containing backslash.
I debugged this function to return the path generated by fileToProcess:
Function ffprobe_show_format(ByVal arg As String) As String
Dim myProcess As New System.Diagnostics.Process()
Dim fileToProcess As String = MapPath(".") & "\temps\" & arg
myProcess.StartInfo.FileName = MapPath(".") & "\ffprobe.exe"
myProcess.StartInfo.Arguments = "-show_format " & fileToProcess & " >C:\inetpub\vhosts\mysite.com\httpdocs\absolutefs\ffmpegtemp.txt"
myProcess.StartInfo.UseShellExecute = False
myProcess.StartInfo.RedirectStandardInput = True
myProcess.StartInfo.RedirectStandardOutput = True
myProcess.Start()
Dim myStreamWriter As StreamWriter = myProcess.StandardInput
Dim mystreamreader As StreamReader = myProcess.StandardOutput
Dim str As String = mystreamreader.ReadToEnd
Return str & ";" & "FileToProcess=" & fileToProcess & "MapPath(.) AND ffprobe.exe" & MapPath(".") & "\\ffprobe.exe"
End Function
And it returns ;FileToProcess=C:
It means that
My file is not processed because of some errors
My Path is cut at backslashes
The rest of the string is then broken
Does I need to tell asp.net to represent backslashes in another way?
[EDIT]
I can't choose an answer but will upvote since I made two mistakes:
- To debug, I was reading my value once it was put in SQL variables with limites size then
- ... fetched with Newtonsoft.Json parser that probably was refusing some chars.
I'm new on ASP.Net so I have difficulties finding a good way to debug. So I finally made as usual when I'm not able to debug on a platform: I've written my debug vars in a text file, and everything was there using this way:
Function ffprobe_show_format(ByVal file As String, ByVal app As String) As String
Dim myProcess As New System.Diagnostics.Process()
myProcess.StartInfo.FileName = app
Dim argz As String = FormatCommandLine("-show_format", file)
myProcess.StartInfo.Arguments = argz
myProcess.StartInfo.UseShellExecute = False
myProcess.StartInfo.RedirectStandardOutput = True
myProcess.Start()
Dim mystreamreader As StreamReader = myProcess.StandardOutput str As String = mystreamreader.ReadToEnd
MapPath(".") & "/ffprobe.exe"
Dim objWriter As New System.IO.StreamWriter(MapPath(".") & "\debug.txt")
objWriter.Write(str)
objWriter.Close()
Return str
End Function
I'll add an ffmpeg tag since it's also another example on how to call it and process a file.

Answer 1

You don't need to worry about the backslashes. The backslash is not a special character in VB like it is in C#. In fact if you do double them up you might hit errors.
It's hard to tell where the problem is occurring. Some ideas to try to narrow it down:
Try not redirecting StandardInput since you aren't passing it anything.
Read from StandardError to make sure it is empty. It may contain an error message.
I would make use of Debug.WriteLine to trace the function and try to spot where things begin to go wrong.
This may not matter, but I would place myProcess.WaitForExit after mystreamreader.ReadToEnd.
Larry's suggestion to use System.IO.Path is a good one.
Some hastily modified code based on all this:
Function ffprobe_show_format(ByVal arg As String) As String
Debug.WriteLine("arg: " & arg)
Dim fileToProcess As String = IO.Path.Combine(MapPath("."), "temps\" & arg)
Debug.WriteLine("fileToProcess = " & fileToProcess)
Debug.WriteLine("MapPath AND ffprobe.exe: " & IO.Path.Combine(MapPath(".") & "\\ffprobe.exe"))
Dim myProcess As New System.Diagnostics.Process()
myProcess.StartInfo.FileName = IO.Path.Combine(MapPath("."), "\ffprobe.exe")
myProcess.StartInfo.Arguments = "-show_format " & fileToProcess & " >C:\inetpub\vhosts\mysite.com\httpdocs\absolutefs\ffmpegtemp.txt"
myProcess.StartInfo.UseShellExecute = False
'myProcess.StartInfo.RedirectStandardOutput = True
myProcess.StartInfo.RedirectStandardError = True
myProcess.Start()
'Dim str As String = myProcess.StandardOutput.ReadToEnd
Dim errStr as string = myProcess.StandardError.ReadToEnd
myProcess.WaitForExit()
Debug.WriteLine("myProcess exit code = " & myProcess.ExitCode.ToString())
'Debug.WriteLine("stdOutput: " & str)
Debug.WriteLine("stdError: " & errStr)
Return str & ";" & "FileToProcess=" & fileToProcess
End Function

Answer 2

There are a few things to consider here.
First, the back-slash character is the escape character (i.e. \t \n \r ...) and should be double-escaped \\ IF you MUST embed it into strings.
However, the .NET framework contains a very good class: System.IO.Path that has several Combine method overloads that can help you to construct paths without embedding back-slash characters into strings. This also makes your code more portable in the (somewhat unlikely) event that you would ever run it on a non-Windows platform.
http://msdn.microsoft.com/en-us/library/system.io.path

Answer 3

Try closing the StreamReader before accessing its contents:
Dim myStreamReader As StreamReader = myProcess.StandardOutput
Dim str As String = myStreamReader.ReadToEnd
myStreamReader.Close()
Return str & ";" & "FileToProcess=" & fileToProcess & "MapPath(.) AND ffprobe.exe" & MapPath(".") & "\\ffprobe.exe"
When I run your function in my local devbox:
Function ffprobe_show_format(ByVal arg As String) As String
Dim myProcess As New System.Diagnostics.Process()
Dim fileToProcess As String = HttpContext.Current.Server.MapPath(".") & "\temps\" & arg
myProcess.StartInfo.FileName = HttpContext.Current.Server.MapPath(".") & "\ffprobe.exe"
myProcess.StartInfo.Arguments = "-show_format " & fileToProcess & " >C:\inetpub\vhosts\mysite.com\httpdocs\absolutefs\ffmpegtemp.txt"
'myProcess.StartInfo.UseShellExecute = False
'myProcess.StartInfo.RedirectStandardInput = True
'myProcess.StartInfo.RedirectStandardOutput = True
'myProcess.Start()
'Dim myStreamWriter As StreamWriter = myProcess.StandardInput
'Dim myStreamReader As StreamReader = myProcess.StandardOutput
Dim str As String = String.Empty 'myStreamReader.ReadToEnd
Return str & ";" & "FileToProcess=" & fileToProcess & "MapPath(.) AND ffprobe.exe" & HttpContext.Current.Server.MapPath(".") & "\\ffprobe.exe"
End Function
I get what I consider to be a somewhat normal string returned for ffprobe_show_format:
";FileToProcess=C:\Documents and Settings\Me\My Documents\Proj1\SubApp1\temps\testMapPath(.) AND ffprobe.exeC:\Documents and Settings\Me\My Documents\Proj1\SubApp1\\"
I commented out the System.Diagnostics.Process() as I don't have an executable called ffprobe.exe.
Given that the rest of it works, Try closing the StreamReader before accessing its contents.

Answer 4

You should just need to escape each backslash with another backslash.
Or, you might be able to prefix your string with the # symbol (works in C#, not sure about VB.NET).
I.E.
instead of "C:\this\that.exe"
use "C:\this\that.exe"
or #"C:\this\that.exe"