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.NET Forum / .NET Framework / New Users / March 2008XMLDocument and NetworkStream (VB.NET 2005)
Hello, I have an application that needs to receive XML documents over a TCP/IP connection. I have tried several approaches and so far have failed to find one that I can get to work. The server is sending the XML correctly since I can replace my XML receiver with a byte buffer and string builder and I see the document. Here is the code that I am trying to make work: Dim netStream As NetworkStream = tcpClient.GetStream() If netStream.CanRead = True Then Dim oData As XmlDocument = New XmlDocument oData.Load(netStream) ' read the xml doc from the server ... blocking call The "Load" never returns. As I said if I replace the oData.Load call with code to read the stream into a byte buffer the data is received. Any help or pointers would be much appreciated, Sid. There's a good chance the XML you are attempting to load is not well-formed and thus, the object is not being created. -Scott > Hello, > I have an application that needs to receive XML documents over a TCP/IP [quoted text clipped - 17 lines] > > Sid. Hi Scott, The server is my code too and I wrote the XML to a file as part of my testing, it appears well formed and is opened by several XML apps I have including XMLNotepad without complaint. Sid. > There's a good chance the XML you are attempting to load is not > well-formed and thus, the object is not being created. [quoted text clipped - 22 lines] >> >> Sid. Well, then only other possibility I see is that something is happening to the XML to cause it to not be well-formed when you read it in. Have you tried reading the stream into an XMLReader first? Check out: http://msdn2.microsoft.com/en-us/library/e48zttz7.aspx for details. -Scott > Hi Scott, > The server is my code too and I wrote the XML to a file as part of my [quoted text clipped - 29 lines] >>> >>> Sid. Hello again Scott, I have done a little more research on my problem and although I don't really understand what is wrong with the transmitted document when I look at the XMLDocument object's properties I do see something odd. The Property "InnerXML" has the following: "<?xml version="1.0" encoding="UTF-8"?><RouteStatus><Devices><Device><Name>RMX_24</Name><Number>1</Number></Device></Devices><Routes /></RouteStatus>" I think this is well formed XML, any comments? The Property "InnerText" has: "RMX_241" This is odd and if I select the XMLVisualizer I see the following: The XML page cannot be displayed Cannot view XML input using style sheet. Please correct the error and then click the Refresh button, or try again later. Invalid at the top level of the document. Error processing resource 'file:///C:/Documents and Settings/Sid Price/Local Sett... RMX_241 ^ Any comments would be appreciated. Also, at the client end I have changed the code to read the stream into a byte buffer, convert it to string and then use XMLDocument.LoadXML to load my document. I do get an exception reported that the root of the document is not correctly formed. If I look at the string I see some odd characters before the XML. "???<?xml version="1.0" encoding="UTF-8"?><RouteStatus> <Devices> <Device> <Name>RMX_24</Name> <Number>1</Number> </Device> </Devices> <Routes /></RouteStatus> I don't know where these extra bytes are coming from, again any pointers would be much appreciated. Sid > Well, then only other possibility I see is that something is happening to > the XML to cause it to not be well-formed when you read it in. Have you [quoted text clipped - 38 lines] >>>> >>>> Sid. The XML is well-formed (easy way to test is to just copy it to a text file, save with an .xml extension and open in IE). So, my next question is, what error are you getting when you use this code? -Scott > Hello again Scott, > I have done a little more research on my problem and although I don't [quoted text clipped - 76 lines] >>>>> >>>>> Sid. Here is the code I am using to receive the document: Dim bytes(tcpClient.ReceiveBufferSize) As Byte netStream.Read(bytes, 0, CInt(tcpClient.ReceiveBufferSize)) Dim returnData As String = System.Text.Encoding.ASCII.GetString(bytes) Debug.WriteLine(returnData) oData.LoadXml(returnData) The exception from the LoadXML says "Data at the root level is invalid. Line 1, position 1." As you will see in my previous post there are a few strange bytes at the head of the document. Sid. > The XML is well-formed (easy way to test is to just copy it to a text > file, save with an .xml extension and open in IE). [quoted text clipped - 84 lines] >>>>>> >>>>>> Sid. Here is the code I am using to receive the document: Dim bytes(tcpClient.ReceiveBufferSize) As Byte netStream.Read(bytes, 0, CInt(tcpClient.ReceiveBufferSize)) Dim returnData As String = System.Text.Encoding.ASCII.GetString(bytes) Debug.WriteLine(returnData) oData.LoadXml(returnData) The exception from the LoadXML says "Data at the root level is invalid. Line 1, position 1." As you will see in my previous post there are a few strange bytes at the head of the document. Sid. > The XML is well-formed (easy way to test is to just copy it to a text > file, save with an .xml extension and open in IE). [quoted text clipped - 84 lines] >>>>>> >>>>>> Sid. > Here is the code I am using to receive the document: > Dim bytes(tcpClient.ReceiveBufferSize) As Byte [quoted text clipped - 12 lines] > As you will see in my previous post there are a few strange bytes at the > head of the document. That's not good code to receive an XML document: 1) It's using UTF-8, not ASCII. Don't do decoding yourself - let the document loader do it. 2) There's no guarantee that Read will return the whole of the document in a single call. If you're going to load it all first, you should loop round, reading into a buffer until there's no more data. (An alternative is to read from the NetworkStream and write to a MemoryStream until you're done - then rewind the MemoryStream.)  SignatureJon Skeet - <skeet@pobox.com> http://www.pobox.com/~skeet Blog: http://www.msmvps.com/jon.skeet World class .NET training in the UK: http://iterativetraining.co.uk Jon wrote: > That's not good code to receive an XML document: > [quoted text clipped - 6 lines] > alternative is to read from the NetworkStream and write to a > MemoryStream until you're done - then rewind the MemoryStream.) The code I posted is not the code I wrote originally and posted in my first message. I wrote this code to try and figure out why my original code was not working. Here is what I started with: Dim netStream As NetworkStream = tcpClient.GetStream() If netStream.CanRead = True Then Dim oData As XmlDocument = New XmlDocument oData.Load(netStream) With this code the "Load" never returns. Sid. <snip> > The code I posted is not the code I wrote originally and posted in my first > message. I wrote this code to try and figure out why my original code was [quoted text clipped - 8 lines] > > With this code the "Load" never returns. Okay - so what's the protocol involved? Are you expecting the connection to be closed after the whole document has been written? If not, I suspect Load won't work - I'd at least *expect* it to read to the end of the stream. If the stream never ends, that's quite possibly the problem... SignatureJon Skeet - <skeet@pobox.com> http://www.pobox.com/~skeet Blog: http://www.msmvps.com/jon.skeet World class .NET training in the UK: http://iterativetraining.co.uk >> With this code the "Load" never returns. > [quoted text clipped - 3 lines] > the end of the stream. If the stream never ends, that's quite possibly > the problem... Hi Jon, That then is probably the issue, the stream indeed stays open. Can you suggest a scheme that would enable me to send an XMLDocument to a stream and receive it into new document? If possible can one send an EOF and have the "Load" terminate? You mentioned in another thread that you may have seen the strange bytes that are at the head of the stream before, did you discover any information about that? Thanks so much for your help, Sid. > That then is probably the issue, the stream indeed stays open. Can you > suggest a scheme that would enable me to send an XMLDocument to a stream and > receive it into new document? If possible can one send an EOF and have the > "Load" terminate? I'm not really sure what you mean. The reader would have to notice that it's read a complete document, and stop at that point. What exactly is the protocol you're using here? > You mentioned in another thread that you may have seen the strange bytes > that are at the head of the stream before, did you discover any information > about that? The bytes are almost certainly a UTF-8 byte-order mark - nothing particularly odd about that. However, I *think* I've seen an issue where if only part of a byte- order mark is read in the first read, things can get screwy. I haven't tried to reproduce that though, and it sounds like it isn't your issue. SignatureJon Skeet - <skeet@pobox.com> http://www.pobox.com/~skeet Blog: http://www.msmvps.com/jon.skeet World class .NET training in the UK: http://iterativetraining.co.uk >> That then is probably the issue, the stream indeed stays open. Can you >> suggest a scheme that would enable me to send an XMLDocument to a stream [quoted text clipped - 6 lines] > it's read a complete document, and stop at that point. What exactly is > the protocol you're using here? I am not using any wrapper protocol around the XML document. The sender writes the document to the stream and the reader reads it from the stream, expecting only the XML document. So, if I understand correctly you are saying that I need to add a protocol layer between the sender and the stream that delimits the XML document, is that correct? Thanks, Sid. > > I'm not really sure what you mean. The reader would have to notice that > > it's read a complete document, and stop at that point. What exactly is > > the protocol you're using here? > > > I am not using any wrapper protocol around the XML document. No, in terms of the network connection. Are you talking to a web server, an IRC server, a telnet server, an ssh server, etc? What's the protocol of the network? > The sender > writes the document to the stream and the reader reads it from the stream, > expecting only the XML document. So, if I understand correctly you are > saying that I need to add a protocol layer between the sender and the stream > that delimits the XML document, is that correct? Pretty much. I find the best way is to get the sender to prefix the actual data with how many bytes of data they're going to send. The receiver then knows when they're "done" just from the amount of data received, without having to parse it until it's all ready. SignatureJon Skeet - <skeet@pobox.com> http://www.pobox.com/~skeet Blog: http://www.msmvps.com/jon.skeet World class .NET training in the UK: http://iterativetraining.co.uk > No, in terms of the network connection. Are you talking to a web > server, an IRC server, a telnet server, an ssh server, etc? What's the > protocol of the network? The protocol being used is TCP/IP, the server needs to send the XML to each client that is logged in. >> The sender >> writes the document to the stream and the reader reads it from the [quoted text clipped - 8 lines] > receiver then knows when they're "done" just from the amount of data > received, without having to parse it until it's all ready. That's kind of where I was thinking I needed to go. Since I am generating the class libray for both the client and server I can prepend the byte count, read the stream into memory and when I have a full document load it into into an XMLDocument object for the user. Many thanks for helping think this through, Sid. > "Jon Skeet [C# MVP]" <skeet@pobox.com> wrote in message >> Pretty much. I find the best way is to get the sender to prefix the [quoted text clipped - 7 lines] > into into an XMLDocument object for the user. Many thanks for helping > think this through, Okay, so I have a new wrapper class that handles the sending of the document to the stream by prepending the length of the document to the document and a reader that uses the length to read the document into a memory stream and then this is loaded into an XMLDocument object. I still have the same issue of the three "rogue" bytes on the front of the document, these bytes cause the XMLDocument object to throw an exception that the document does not contain a root element. Here is the sender: ' ' Send the passed doc to the passed stream ' theDoc.Save(theData) messageLength = theData.Length ' ' write the number of bytes in the message ' to the stream theBuffer = Array.CreateInstance(GetType(Byte), 4) ' theBuffer(0) = messageLength And &HFF theBuffer(1) = (messageLength >> 8) And &HFF theBuffer(2) = (messageLength >> 16) And &HFF theBuffer(3) = (messageLength >> 24) And &HFF theStream.Write(theBuffer, 0, 4) ' ' Now the data ' theBuffer = Array.CreateInstance(GetType(Byte), theData.Length) theBuffer = theData.ToArray() theStream.Write(theBuffer, 0, theBuffer.Length) And the reader theBuffer = Array.CreateInstance(GetType(Byte), 4) theStream.Read(theBuffer, 0, 4) messageLength = theBuffer(0) messageLength += (theBuffer(1) << 8) messageLength += (theBuffer(2) << 16) messageLength += (theBuffer(3) << 24) Dim rxBytes As Int32 = 0 theBuffer = Array.CreateInstance(GetType(Byte), messageLength) While (rxBytes <> messageLength) rxBytes += theStream.Read(theBuffer, rxBytes, messageLength - rxBytes) End While theData.Write(theBuffer, 0, messageLength) theDoc.Load(theData) Seems that altough I now have better stream i/o code I still have the same issue, any ideas? Thanks, Sid. > > That's kind of where I was thinking I needed to go. Since I am generating > > the class libray for both the client and server I can prepend the byte [quoted text clipped - 9 lines] > contain a root element. > Here is the sender: <snip> 1) BinaryWriter/BinaryReader and/or BitConverter are your friends :) 2) You're not not rewinding your MemoryStream on the reading side. Use theData.Position = 0 before passing it to theDoc.Load SignatureJon Skeet - <skeet@pobox.com> http://www.pobox.com/~skeet Blog: http://www.msmvps.com/jon.skeet World class .NET training in the UK: http://iterativetraining.co.uk > 2) You're not not rewinding your MemoryStream on the reading side. Use > theData.Position = 0 > before passing it to theDoc.Load Thank you for spotting that, when I correct that error the code works as required. BTW: the three strange bytes (EF BB EF) are indeed the BOM for UTF-8 encoding and they appear not be a problem. Again Jon thank you for all your help, Sid. > > No, in terms of the network connection. Are you talking to a web > > server, an IRC server, a telnet server, an ssh server, etc? What's the > > protocol of the network? > > The protocol being used is TCP/IP, the server needs to send the XML to each > client that is logged in. Well, I'm sure there's some protocol involved above that level, even if it's one you've created yourself (which it sounds like you are). > >> The sender > >> writes the document to the stream and the reader reads it from the [quoted text clipped - 14 lines] > into into an XMLDocument object for the user. Many thanks for helping think > this through, Sounds like the way to go. Best of luck. SignatureJon Skeet - <skeet@pobox.com> http://www.pobox.com/~skeet Blog: http://www.msmvps.com/jon.skeet World class .NET training in the UK: http://iterativetraining.co.uk <snip> > If I look at the string I see some odd characters before the XML. > "???<?xml version="1.0" encoding="UTF-8"?><RouteStatus> <Devices> > <Device> <Name>RMX_24</Name> <Number>1</Number> </Device> > </Devices> <Routes /></RouteStatus> > I don't know where these extra bytes are coming from, again any pointers > would be much appreciated. They're almost certainly Byte-Order Marks. I *think* I've seen an issue like this before, where the first packet of data only contains a few bytes. I'll see if I can reproduce it without network streams... SignatureJon Skeet - <skeet@pobox.com> http://www.pobox.com/~skeet Blog: http://www.msmvps.com/jon.skeet World class .NET training in the UK: http://iterativetraining.co.uk
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