Reading UDP Packets From UDP/IP

I am writing a program that talks back and forth with an external machine through UDP/IP. I have figured out how to talk to the machine, bu now I need to know how to read the machine's response. I am using the following code:

Dim receiveBytes As [Byte]() = udpClient.Receive(RemoteIpEndPoint)
Dim returnData As String = Encoding.ASCII.GetString(receiveBytes)


TextBox1.Text = returnData

When I break the code down and read receiveBytes, it comes through exactly the way I want it. It is falling apart when it gets encoded and put into a textbox. It just comes out as a "?". Does anybody know how I can do this? Thank you.

Post what you see on the wire, and what gets produced

Likely the encoding again. use default encoding if you want the true byte by byte data.

I tried using Encoding.Default.GetBytes and instead of coming through as a "?" it came through as "—".

When I put a break point in the code on:

Dim returnData As String = Encoding.Default.GetString(receiveBytes)

and I hover over

Dim receiveBytes As [Byte]() = udpClient.Receive(RemoteIpEndPoint)

with my mouse it says:

receiveBytes {Length = 8}

Then I click on the plus symbol to get the drop down menu and it shows each byte in a drop down list:

151 0 0 0 1 105 0 205

These numbers in decimal are exactly what I want. Truly I want them displayed in HEX as:

97 0 0 0 1 69 0 cd

but I'll take what I can get. Then when I step to the next part of the code:

Dim returnData as String = Encoding.Default.GetString(receiveBytes)

and hover my mouse over "returnData" it shows up with "—" or when I use ASCII.GetBytes instead it comes up with "?".

The -- may be due to the font you are using?

Have you tried using the little string to hexstring routine that I posted in your other thread to convert the incoming string to a readable set of hex numbers?

These are the lines from one of my projects.

Send

Code:

---

sBytes = Encoding.Default.GetBytes(DataString)
bSent = wSocket.Send(sBytes)

---

Receive

Code:

---

bReceived = wSocket.Receive(rBytes)
rDataString = System.Text.Encoding.Default.GetString(rBytes, 0, bReceived)

---

I ended up using your string to hex converter. I works out pretty good. I wasn't sure exactly how to incorporate it at first, but I ended up figuring it out. This is my code now:

' UdpClient.Receive blocks until a message is received from a remote host.
Dim receiveBytes As [Byte]() = udpClient.Receive(RemoteIpEndPoint)
Dim returnData As String = Encoding.Default.GetString(receiveBytes)

udpClient.Close()

Dim MyString As String = returnData
Dim TmpString As String = ""
Dim HexString As String = ""
Dim OutputString As String = ""
Dim X As Integer
For X = 0 To MyString.Length - 1
HexString = Asc(MyString.Substring(X, 1))

TmpString = Hex(HexString).ToString.PadLeft(2, "0")
OutputString = OutputString & TmpString
Next
TextBox1.Text = OutputString

Once again, I appreciate your help. I'll tell you what. I would be really stuck without this forum.

Now the code is giving me a problem when I try to read multiple codes from the machine.




'First String
If FirstString = True Then
Dim udpClient As New UdpClient("192.168.123.96", 50000)
udpClient.Connect("192.168.123.96", 50000)

Dim sendBytes As [Byte]() = Encoding.Default.GetBytes(Chr(144) & Chr(0) & Chr(0) & Chr(0) & Chr(4) _
& Chr(64) & Chr(0) & Chr(32))
udpClient.Send(sendBytes, sendBytes.Length)
Dim receiveBytes1 As [Byte]() = udpClient.Receive(RemoteIpEndPoint1)
Dim returnData As String = Encoding.Default.GetString(receiveBytes1)
Dim MyString As String = returnData
Dim TmpString As String = ""
Dim HexString As String = ""
Dim OutputString As String = ""
Dim X As Integer
For X = 0 To MyString.Length - 1
HexString = Asc(MyString.Substring(X, 1))
TmpString = Hex(HexString).ToString.PadLeft(2, "0")
OutputString = OutputString & TmpString
OutputLength = OutputString.Length
Next
TextBox1.Text = OutputString
FirstString = False
If OutputString.StartsWith("910000000169004D") And OutputLength > 6 Then
returnData = ""
MyString = ""
TmpString = ""
HexString = ""
OutputString = ""
SecondString = True
MotoTRBOtimer2 = DateTime.Now.Second
End If
udpClient.Close()
End If

'Second String
MotoTRBOdelay2 = DateTime.Now.Second - MotoTRBOtimer2
If MotoTRBOdelay2 > 2 Or (MotoTRBOdelay2 < 0 And MotoTRBOdelay2 > -57) Then
If SecondString = True Then

Dim udpClient As New UdpClient("192.168.123.96", 50000)
udpClient.Connect("192.168.123.96", 50000)

Dim sendBytes As [Byte]() = Encoding.Default.GetBytes(Chr(150) & Chr(0) & Chr(0) & Chr(0) & Chr(4) _
& Chr(64) & Chr(0) & Chr(32))
udpClient.Send(sendBytes, sendBytes.Length)
Dim receiveBytes2 As [Byte]() = udpClient.Receive(RemoteIpEndPoint2)
Dim returnData As String = Encoding.Default.GetString(receiveBytes2)
Dim MyString As String = returnData
Dim TmpString As String = ""
Dim HexString As String = ""
Dim OutputString As String = ""
Dim X As Integer
For X = 0 To MyString.Length - 1
HexString = Asc(MyString.Substring(X, 1))
TmpString = Hex(HexString).ToString.PadLeft(2, "0")
OutputString = OutputString & TmpString
OutputLength = OutputString.Length
Next
TextBox1.Text = OutputString
SecondString = False
If OutputString = "970000000169004D" And OutputLength > 6 Then
returnData = ""
MyString = ""
TmpString = ""
HexString = ""
OutputString = ""
ThirdString = True
MotoTRBOtimer3 = DateTime.Now.Second
End If
udpClient.Close()
End If
End If

'Third String
MotoTRBOdelay3 = DateTime.Now.Second - MotoTRBOtimer3
If MotoTRBOdelay3 > 2 Or (MotoTRBOdelay3 < 0 And MotoTRBOdelay3 > -57) Then
If ThirdString = True Then

Dim udpClient As New UdpClient("192.168.123.96", 50000)
udpClient.Connect("192.168.123.96", 50000)

Dim sendBytes As [Byte]() = Encoding.Default.GetBytes(Chr(112) & Chr(0) & Chr(0) & Chr(0) _
& Chr(4) & Chr(0) & Chr(12) & Chr(0) & Chr(3) & Chr(0) & Chr(0) & Chr(0) & Chr(0) & Chr(0) _
& Chr(0) & Chr(0) & Chr(0) & Chr(0) & Chr(0))
udpClient.Send(sendBytes, sendBytes.Length)
Dim receiveBytes3 As [Byte]() = udpClient.Receive(RemoteIpEndPoint3)
Dim returnData As String = Encoding.Default.GetString(receiveBytes3)
Dim MyString As String = returnData
Dim TmpString As String = ""
Dim HexString As String = ""
Dim OutputString As String = ""
Dim X As Integer
For X = 0 To MyString.Length - 1
HexString = Asc(MyString.Substring(X, 1))
TmpString = Hex(HexString).ToString.PadLeft(2, "0")
OutputString = OutputString & TmpString
OutputLength = OutputString.Length
Next
TextBox1.Text = OutputString
ThirdString = False
If OutputString = "7000000001001300020000000000060000000700000001010101" And OutputLength > 6 Then
returnData = ""
MyString = ""
TmpString = ""
HexString = ""
OutputString = ""
FourthString = True
MotoTRBOtimer4 = DateTime.Now.Second
End If
udpClient.Close()
End If
End If




The First String and the Second String work fine, but for some reason when it gets to the Third String it locks up when I try to declare the value "receiveBytes3". It will all of a sudden just stop and freeze up. If I put a break point on this part of the code and step through it, it will work though. I tried using timers to slow it down. I also tried using "System.Threading.Thread.Sleep" to slow it down thinking maybe something in the code just needed a second to clear itself out. Neither worked. Does anybody have any ideas? Thank you.

Use code tags and indent your code. To hard to read as is.

like this but with an e

[cod][/cod]

I haven't worked with UDP in dot net at all and have not used UDP in years so I am not sure how much it works like TCP but I would think many of the methods are the same.

A couple of things I noticed are there seems to be a lot more code there than is needed but that is not a big deal at this point. More importantly you are sending then reading data. You really should be checking the port status for errors and then looking to see if there is anything to read before you issue a read statement. The method you are using could very well cause the program to hang under certian conditions. I also do not understand why you are opening and closing the connection for every string you send other than it looks like you just copied the code and repeated the entire piece 3 times.

Here is an edited section of code from one of my projects which uses TCP.

Code:

---

bTimeOut = TimeOfDay
                Do While wSocket.Poll(1, SelectMode.SelectRead) = False
                    bTimeTaken = DateDiff(DateInterval.Second, bTimeOut, TimeOfDay)
                    If bTimeTaken > wTimeout Then
                        Disconnect()
                        ErrFlag = True
                        Return "ERR:6:Receive Timeout"
                    End If
                    Application.DoEvents()
                Loop
                Try
                    If wSocket.Available < 1 Then
                        ErrFlag = True
                        Disconnect()
                        Return "ERR:7:No Data available. Connection may be broken."
                    End If
                    bReceived = wSocket.Receive(rBytes)
                    rDataString = System.Text.Encoding.Default.GetString(rBytes, 0, bReceived)
                    mByte = Right(rDataString, 1)
                    Do While mByte <> Chr(4)
                        Do While wSocket.Available > 0
                            bReceived = wSocket.Receive(rBytes)
                            rDataString = rDataString & System.Text.Encoding.ASCII.GetString(rBytes, 0, bReceived)
                            Application.DoEvents()
                        Loop
                        mByte = Right(rDataString, 1)
                    Loop
                    Return Mid(rDataString, 1, Len(rDataString) - 1)
                Catch ex As Exception
                    ErrFlag = True
                  Disconnect()
                    Return "ERR:8:" & ex.Message
                End Try

---

In my case the data will always be terminated by the character 4 so the code will loop until it sees that as the last character to make sure it received the entire string from the host. My receive buffer in this case is defined as 1k but sometimes the data received is larger.

I just found out that it's not actually giving me the problem when it reads it. I'm still not able to read from the UDP/IP, but something different is going on when I try to send to the machine a third time. I am using Wireshark to monitor the UDP/IP activity. When I send the first two parts of the code:

Code:

---

'First String
        If FirstString = True Then

            Dim sendBytes As [Byte]() = Encoding.Default.GetBytes(Chr(144) & Chr(0) & Chr(0) & Chr(0) & Chr(4) _
                & Chr(64) & Chr(0) & Chr(32))
            UdpClient.Send(sendBytes, sendBytes.Length)
            Dim receiveBytes1 As [Byte]() = UdpClient.Receive(RemoteIpEndPoint1)
            Dim returnData As String = Encoding.Default.GetString(receiveBytes1)
            Dim MyString As String = returnData
            Dim TmpString As String = ""
            Dim HexString As String = ""
            Dim OutputString As String = ""
            Dim X As Integer
            For X = 0 To MyString.Length - 1
                HexString = Asc(MyString.Substring(X, 1))
                TmpString = Hex(HexString).ToString.PadLeft(2, "0")
                OutputString = OutputString & TmpString
                OutputLength = OutputString.Length
            Next

            TextBox1.Text = OutputString
            FirstString = False
            'If OutputString.StartsWith("910000000169004D") And OutputLength >= 20 Then
            If OutputLength >= 20 Then
                returnData = ""
                MyString = ""
                TmpString = ""
                HexString = ""
                OutputString = ""
                SecondString = True
                MotoTRBOtimer2 = DateTime.Now.Second
            End If
        End If

        'Second String
        MotoTRBOdelay2 = DateTime.Now.Second - MotoTRBOtimer2
        If MotoTRBOdelay2 > 2 Or (MotoTRBOdelay2 < 0 And MotoTRBOdelay2 >= -57) Then
            If SecondString = True Then

                Dim sendBytes As [Byte]() = Encoding.Default.GetBytes(Chr(150) & Chr(0) & Chr(0) & Chr(0) & Chr(4) _
                    & Chr(64) & Chr(0) & Chr(32))
                udpClient.Send(sendBytes, sendBytes.Length)
                Dim receiveBytes2 As [Byte]() = udpClient.Receive(RemoteIpEndPoint2)
                Dim returnData As String = Encoding.Default.GetString(receiveBytes2)
                Dim MyString As String = returnData
                Dim TmpString As String = ""
                Dim HexString As String = ""
                Dim OutputString As String = ""
                Dim X As Integer
                For X = 0 To MyString.Length - 1
                    HexString = Asc(MyString.Substring(X, 1))
                    TmpString = Hex(HexString).ToString.PadLeft(2, "0")
                    OutputString = OutputString & TmpString
                    OutputLength = OutputString.Length
                Next

                TextBox1.Text = OutputString
                SecondString = False
                'If OutputString = "970000000169004D" And OutputLength > 6 Then
                If OutputLength >= 16 Then
                    returnData = ""
                    MyString = ""
                    TmpString = ""
                    HexString = ""
                    OutputString = ""
                    ThirdString = True
                    MotoTRBOtimer3 = DateTime.Now.Second
                End If
            End If
        End If

---

it says "Source port: cppdp Destination port: 50000" when it sends and
"Source port 50000 Destination port: cppdp" when it receives.

On the third section, where I am having the problem:

Code:

---

'Third String
        MotoTRBOdelay3 = DateTime.Now.Second - MotoTRBOtimer3
        If MotoTRBOdelay3 > 1 Or (MotoTRBOdelay3 < 0 And MotoTRBOdelay3 >= -59) Then
            If ThirdString = True Then

                'Send
                Dim sendBytes As [Byte]() = Encoding.Default.GetBytes(Chr(112) & Chr(0) & Chr(0) & Chr(0) _
            & Chr(4) & Chr(0) & Chr(12) & Chr(0) & Chr(3) & Chr(0) & Chr(0) & Chr(0) & Chr(0) & Chr(0) _
            & Chr(0) & Chr(0) & Chr(0) & Chr(0) & Chr(0))
                udpClient.Send(sendBytes, sendBytes.Length)

                'Recieve
                Dim receiveBytes3 As [Byte]() = udpClient.Receive(RemoteIpEndPoint3)
                Dim returnData As String = Encoding.Default.GetString(receiveBytes3)
                Dim MyString As String = returnData
                Dim TmpString As String = ""
                Dim HexString As String = ""
                Dim OutputString As String = ""
                Dim X As Integer
                For X = 0 To MyString.Length - 1
                    HexString = Asc(MyString.Substring(X, 1))
                    TmpString = Hex(HexString).ToString.PadLeft(2, "0")
                    OutputString = OutputString & TmpString
                    OutputLength = OutputString.Length
                Next

                TextBox1.Text = OutputString
                ThirdString = False
                'If OutputString = "7000000001001300020000000000060000000700000001010101" And OutputLength > 6 Then
                If OutputLength >= 52 Then
                    returnData = ""
                    MyString = ""
                    TmpString = ""
                    HexString = ""
                    OutputString = ""
                    FourthString = True
                    MotoTRBOtimer4 = DateTime.Now.Second
                End If
            End If
        End If

---

it says "Destination unreachable (Port unreachable)"

So now I'm wondering if there is maybe a way, or even a need, to discard any outgoing information after sending each time.

You really should have some tests in there to insure that the port is ready to send or receive data and check the port error status as well before you attempt to send or receive anything. Failure to do so can cause many odd problems.