How to return XML in ASP NET

Question

I have encountered many half-solutions to the task of returning XML in ASP NET  I don t want to blindly copy  amp  paste some code that happens to work most of the time  though  I want the right code  and I want to know why it s right  I want criticism  I want information  I want knowledge  I want understanding   Below are code fragments  in order of increasing complexity  representing some of the partial solutions I ve seen  including some of the further questions each one causes  and which I d like to have answered here   A thorough answer must address why we must have or must not have any of the following things  or else explain why it s irrelevant    Response Clear    Response ContentType    text xml   Response ContentEncoding   Encoding UTF8  Response ContentEncoding   Encoding UTF16  Response ContentType    text xml  charset utf-8   Response ContentType    text xml  charset utf-16   Response End   Using an aspx with the front-file guts ripped out Using an ashx file   In the end  imagine you need to write the contents of a helper function like this       lt summary gt Use this call inside your  Page Xxx  method to write the    xml to the web client   lt  summary gt      lt remarks gt See for https   stackoverflow com questions 543319 how-to-return-xml-in-asp-net    for proper usage  lt  remarks gt  public static void ReturnXmlDocumentToWebClient      XmlDocument document      Page page                 Every solution I see starts with taking an empty aspx page  and trimming all the HTML out of the front file  which causes warnings in Visual Studio     lt    Page Language  C         AutoEventWireup  true        CodeFile  GetTheXml aspx cs        Inherits  GetTheXml    gt    Next we use the Page Load event to write to the output   protected void Page Load object sender  EventArgs e       String xml     lt foo gt Hello  world  lt  foo gt        Response Write xml         Do we need to change the ContentType to  text xml   I e    protected void Page Load object sender  EventArgs e       String xml     lt foo gt Hello  world  lt  foo gt        Response ContentType    text xml      Response Write xml         Do we need to call Response Clear first   protected void Page Load object sender  EventArgs e       String xml     lt foo gt Hello  world  lt  foo gt        Response Clear       Response ContentType    text xml      Response Write xml       Do we really need to call that  Doesn t Response Clear make the prior step of making sure that the code in the front file was empty  not even a space or a carriage return  outside of the  lt         gt  unnecessary   Does Response Clear make it more robust  in case someone left a blank line or space in the code-front file   Is using ashx the same as a blank aspx main file  because it s understood that it s not going to output HTML     Do we need to call Response End  I e    protected void Page Load object sender  EventArgs e       String xml     lt foo gt Hello  world  lt  foo gt        Response Clear       Response ContentType    text xml      Response Write xml      Response End        What else could possibly happen after Response Write that needs us to end the response right now     Is the content-type of text xml sufficient  or should it instead be text xml  charset utf-8   protected void Page Load object sender  EventArgs e       String xml     lt foo gt Hello  world  lt  foo gt        Response Clear       Response ContentType    text xml  charset utf-8      Response Write xml      Response End        Or should it specifically not be that  Does having a charset in the content type  but not setting the property  screw up the server   Why not some other content type  e g     UTF-8 utf-16 UTF-16     Should the charset be specified in Response ContentEncoding   protected void Page Load object sender  EventArgs e       String xml     lt foo gt Hello  world  lt  foo gt        Response Clear       Response ContentType    text xml      Response ContentEncoding   Encoding UTF8     Response Write xml      Response End        Is using Response ContentEncoding better than jamming it into Response ContentType  Is it worse  Is the former supported  Is the latter     I don t actually want to write a String out  I want to write out an XmlDocument  Someone suggests I can use the XmlWriter   protected void Page Load object sender  EventArgs e       XmlDocument xml   GetXmlDocumentToShowTheUser        Response Clear       Response ContentType    text xml      Response ContentEncoding   Encoding UTF8      using  TextWriter textWriter   new StreamWriter           Response OutputStream           Encoding UTF8               XmlTextWriter xmlWriter   new XmlTextWriter textWriter             Write XML using xmlWriter          TODO  How to do this           Note the use of Response OutputStream  rather than Response Write  Is this good  Bad  Better  Worse  Faster  Slower  More memory intensive  Less memory intensive     I read that you should render     the XML in the page   s Render   method   to avoid problems with chunking   encountered when using Page Load      What is chunking  What are the problems with chunking  and how does using using Page Render eliminate them     I don t want to write the contents of my XmlDocument object into a string and then write that because that wastes memory  That is  any of these would be bad   Response Write doc ToString     Response Write doc InnerXml   xmlWrite WriteString doc ToString     xmlWrite WriteString doc InnerXml       Similar Questions  How to return XML in ASP NET  References  How Return XML From ASPX in ASP NET 1 1  Writing XML output to an ASP NET webpage  How do you output XML from ASP NET   Creating an ASHX handler in ASP NET

User · Answer

Below is the server side code that would call the handler and recieve the stream data and loads into xml doc          Stream stream   null           Create a web request with the specified URL           WebRequest myWebRequest   WebRequest Create   http   localhost XMLProvider XMLProcessorHandler ashx              Senda a web request and wait for response            WebResponse webResponse   myWebRequest GetResponse              Get the stream object from response object           stream   webResponse GetResponseStream            XmlDocument xmlDoc   new XmlDocument            Load stream data into xml          xmlDoc Load stream

User · Answer

XmlDocument xd   new XmlDocument    xd LoadXml xmlContent    context Response Clear    context Response ContentType    text xml   context Response ContentEncoding   System Text Encoding UTF8  xd Save context Response Output   context Response Flush    context Response SuppressContent   true  context ApplicationInstance CompleteRequest

User · Answer

Ideally you would use an ashx to send XML although I do allow code in an ASPX to intercept normal execution   Response Clear     I don t use this if you not sure you ve dumped anything in the response already the go find it and get rid of it   Response ContentType    text xml    Definitely  a common client will not accept the content as XML without this content type present    Response Charset    UTF-8     Let the response class handle building the content type header properly   Use UTF-8 unless you have a really  really good reason not to   Response Cache SetCacheability HttpCacheability NoCache   Response Cache SetAllowResponseInBrowserHistory true     If you don t send cache headers some browsers  namely IE  will cache the response  subsequent requests will not necessarily come to the server   You also need to AllowResponseInBrowser if you want this to work over HTTPS  due to yet another bug in IE    To send content of an XmlDocument simply use     dom Save Response OutputStream       dom Save Response Output     Just be sure the encodings match   another good reason to use UTF-8    The XmlDocument object will automatically adjust its embedded encoding       encoding to that of the Response  e g  UTF-8   Response End     If you really have to in an ASPX but its a bit drastic  in an ASHX don t do it

User · Answer

Below is the way a handler will returns stream data that would contain xml data in the server side    Here is the handler code that would returns the data       public void ProcessRequest HttpContext context                 StringBuilder xmlBuilder   new StringBuilder             xmlBuilder Append   lt Names gt             xmlBuilder Append   lt Name gt             xmlBuilder Append  Sheo            xmlBuilder Append   lt  Name gt             xmlBuilder Append   lt  Names gt             context Response ContentType    application octet-stream           context Response BinaryWrite Encoding UTF8 GetBytes xmlBuilder ToString              context Response End

User · Answer

Seems like at least 10 questions rolled into one here  a couple points      Response Clear - it really depends on what else is going on in the app - if you have httpmodules early in the pipeline that might be writing stuff you don t want - then clear it  Test it and find out  Fiddler or Wireshark useful for this   Content Type to text xml - yup - good idea - read up on HTTP spec as to why this is important   IMO anyone doing web work should have read the 1 0 and 1 1 spec at least once     Encoding - how is your xml encoded - if it is utf-8  then say so  if not  say something else appropriate  just make sure they all match     Page - personally  would use ashx or httpmodule  if you are using page  and want it a bit faster  get rid of autoeventwireup and bind the event handlers manually    Would probably be a bit of a waste of memory to dump the xml into a string first  but it depends a lot on the size of the xml as to whether you would ever notice     As others have suggested  saving the xml to the output stream probably the fastest  I would normally do that  but if you aren t sure  test it  don t rely on what you read on the interweb  Don t just believe anything I say   For another approach  if the xml doesn t change that much  you could just write it to the disk and serve the file directly  which would likely be quite performant  but like everything in programming  it depends

User · Answer

You ve basically answered anything and everything already  so I m no sure what the point is here   FWIW I would use an httphandler - there seems no point in invoking a page lifecycle and having to deal with clipping off the bits of viewstate and session and what have you which don t make sense for an XML doc  It s like buying a car and stripping it for parts to make your motorbike   And content-type is all important  it s how the requester knows what to do with the response

User · Answer

I m surprised that nobody seems to have ever mentioned that you can use XDocument   XElement which are available in  NET 4 0 and make it much easier to output XML

User · Answer

Below is an example of the correct way I think   At least it is what I use  You need to do Response Clear to get rid of any headers that are already populated  You need to pass the correct ContentType of text xml   That is the way you serve xml  In general you want to serve it as charset UTF-8 as that is what most parsers are expecting   But I don t think it has to be that   But if you change it make sure to change your xml document declaration and indicate the charset in there  You need to use the XmlWriter so you can actually write in UTF-8 and not whatever charset is the default   And to have it properly encode your xml data in UTF-8        -----------------------------------------------------------------------------      OutputDataSetAsXML           Description  outputs the given dataset as xml to the response object           Arguments          dsSource           - source data set           Dependencies            History      2006-05-02 - WSR   created         Private Sub OutputDataSetAsXML ByRef dsSource As System Data DataSet         Dim xmlDoc As System Xml XmlDataDocument       Dim xmlDec As System Xml XmlDeclaration       Dim xmlWriter As System Xml XmlWriter          setup response       Me Response Clear         Me Response ContentType    text xml        Me Response Charset    utf-8        xmlWriter   New System Xml XmlTextWriter Me Response OutputStream  System Text Encoding UTF8           create xml data document with xml declaration       xmlDoc   New System Xml XmlDataDocument dsSource        xmlDoc DataSet EnforceConstraints   False       xmlDec   xmlDoc CreateXmlDeclaration  1 0    UTF-8   Nothing        xmlDoc PrependChild xmlDec           write xml document to response       xmlDoc WriteTo xmlWriter        xmlWriter Flush         xmlWriter Close         Response End       End Sub      -----------------------------------------------------------------------------

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I ve found the proper way to return XML to a client in ASP NET  I think if I point out the wrong ways  it will make the right way more understandable  Incorrect  Response Write doc ToString      Incorrect  Response Write doc InnerXml    Incorrect  Response ContentType    quot text xml quot   Response ContentEncoding   System Text Encoding UTF8  doc Save Response OutputStream    Correct  Response ContentType    quot text xml quot     Must be  text xml  Response ContentEncoding   System Text Encoding UTF8    We d like UTF-8 doc Save Response Output     Save to the text-writer         using the encoding of the text-writer          which comes from response contentEncoding    Use a TextWriter Do not use Response OutputStream Do use Response Output Both are streams  but Output is a TextWriter  When an XmlDocument saves itself to a TextWriter  it will use the encoding specified by that TextWriter  The XmlDocument will automatically change the xml declaration node to match the encoding used by the TextWriter  e g  in this case the XML declaration node   lt  xml version  quot 1 0 quot  encoding  quot ISO-8859-1 quot   gt   would become  lt  xml version  quot 1 0 quot  encoding  quot UTF-8 quot   gt   This is because the TextWriter has been set to UTF-8   More on this in a moment   As the TextWriter is fed character data  it will encode it with the byte sequences appropriate for its set encoding  Incorrect  doc Save Response OutputStream    In this example the document is incorrectly saved to the OutputStream  which performs no encoding change  and may not match the response s content-encoding or the XML declaration node s specified encoding  Correct doc Save Response Output    The XML document is correctly saved to a TextWriter object  ensuring the encoding is properly handled   Set Encoding The encoding given to the client in the header  Response ContentEncoding        must match the XML document s encoding   lt  xml version  quot 1 0 quot  encoding  quot     quot   gt   must match the actual encoding present in the byte sequences sent to the client  To make all three of these things agree  set the single line  Response ContentEncoding   System Text Encoding UTF8   When the encoding is set on the Response object  it sets the same encoding on the TextWriter  The encoding set of the TextWriter causes the XmlDocument to change the xml declaration   lt  xml version  quot 1 0 quot  encoding  quot UTF-8 quot   gt   when the document is Saved  doc Save someTextWriter     Save to the response Output You do not want to save the document to a binary stream  or write a string  Incorrect  doc Save Response OutputStream    Here the XML is incorrectly saved to a binary stream  The final byte encoding sequence won t match the XML declaration  or the web-server response s content-encoding  Incorrect  Response Write doc ToString     Response Write doc InnerXml    Here the XML is incorrectly converted to a string  which does not have an encoding  The XML declaration node is not updated to reflect the encoding of the response  and the response is not properly encoded to match the response s encoding  Also  storing the XML in an intermediate string wastes memory  You don t want to save the XML to a string  or stuff the XML into a string and response Write a string  because that  - doesn t follow the encoding specified - doesn t set the XML declaration node to match - wastes memory  Do use doc Save Response Output   Do not use doc Save Response OutputStream   Do not use Response Write doc ToString     Do not use  Response Write doc InnerXml     Set the content-type The Response s ContentType must be set to  quot text xml quot   If not  the client will not know you are sending it XML  Final Answer Response Clear      Optional  if we ve sent anything before Response ContentType    quot text xml quot     Must be  text xml  Response ContentEncoding   System Text Encoding UTF8    We d like UTF-8 doc Save Response Output     Save to the text-writer       using the encoding of the text-writer        which comes from response contentEncoding  Response End      Optional  will end processing  Complete Example Rob Kennedy had the good point that I failed to include the start-to-finish example  GetPatronInformation ashx   lt    WebHandler Language  quot C  quot  Class  quot Handler quot    gt   using System  using System Web  using System Xml  using System IO  using System Data Common     Why a  quot Handler quot  and not a full ASP NET form    Because many people online critisized my original solution   that involved the aspx  and cutting out all the HTML in the front file     noting the overhead of a full viewstate build-up tear-down and processing    when it s not a web-form at all   It s a pure processing    public class Handler   IHttpHandler      public void ProcessRequest HttpContext context               GetXmlToShow will look for parameters from the context       XmlDocument doc   GetXmlToShow context            Don t forget to set a valid xml type          If you leave the default  quot text html quot   the browser will refuse to display it correctly       context Response ContentType    quot text xml quot            We d like UTF-8        context Response ContentEncoding   System Text Encoding UTF8          context Response ContentEncoding   System Text Encoding UnicodeEncoding    But no reason you couldn t use UTF-16          context Response ContentEncoding   System Text Encoding UTF32    Or UTF-32         context Response ContentEncoding   new System Text Encoding 500     Or EBCDIC  500 is the code page for IBM EBCDIC International          context Response ContentEncoding   System Text Encoding ASCII    Or ASCII         context Response ContentEncoding   new System Text Encoding 28591     Or ISO8859-1         context Response ContentEncoding   new System Text Encoding 1252     Or Windows-1252  a version of ISO8859-1  but with 18 useful characters where they were empty spaces           Tell the client don t cache it  it s too volatile          Commenting out NoCache allows the browser to cache the results  so they can view the XML source          But leaves the possiblity that the browser might not request a fresh copy         context Response Cache SetCacheability HttpCacheability NoCache            And now we tell the browser that it expires immediately  and the cached copy you have should be refreshed       context Response Expires   -1         context Response Cache SetAllowResponseInBrowserHistory true      quot works around an Internet amp nbsp Explorer bug quot         doc Save context Response Output     doc saves itself to the textwriter  using the encoding of the text-writer  which comes from response contentEncoding          region Notes                   1  Use Response Output  and NOT Response OutputStream            Both are streams  but Output is a TextWriter            When an XmlDocument saves itself to a TextWriter  it will use the encoding           specified by the TextWriter  The XmlDocument will automatically change any           XML declaration node  i e                 lt  xml version  quot 1 0 quot  encoding  quot ISO-8859-1 quot   gt            to match the encoding used by the Response Output s encoding setting          2  The Response Output TextWriter s encoding settings comes from the           Response ContentEncoding value           3  Use doc Save  not Response Write doc ToString    or Response Write doc InnerXml           3  You DON T want to save the XML to a string  or stuff the XML into a string           and response Write that  because that            - doesn t follow the encoding specified            - wastes memory                   To sum up  by Saving to a TextWriter  the XML Declaration node  the XML contents           and the HTML Response content-encoding will all match                   endregion Notes          private XmlDocument GetXmlToShow HttpContext context               Use context Request to get the account number they want to return         GET  GetPatronInformation ashx accountNumber 619          Or since this is sample code  pull XML out of your rear        XmlDocument doc   new XmlDocument          doc LoadXml  quot  lt Patron gt  lt Name gt Rob Kennedy lt  Name gt  lt  Patron gt  quot           return doc           public bool IsReusable   get   return false

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