Reading file input from a multipart form-data POST

Question

I m POSTing a file to a WCF REST service through a HTML form  with enctype set to multipart form-data and a single component   lt input type  file  name  data  gt   The resulting stream being read by the server contains the following   ------WebKitFormBoundary Content-Disposition  form-data  name  data   filename  DSCF0001 JPG  Content-Type  image jpeg   lt file bytes gt  ------WebKitFormBoundary--   The problem is that I m not sure how do extract the file bytes from the stream  I need to do this in order to write the file to the disk

User · Answer

I open-sourced a C  Http form parser here   This is slightly more flexible than the other one mentioned which is on CodePlex  since you can use it for both Multipart and non-Multipart form-data  and also it gives you other form parameters formatted in a Dictionary object   This can be used as follows   non-multipart  public void Login Stream stream        string username   null      string password   null       HttpContentParser parser   new HttpContentParser stream       if  parser Success                username   HttpUtility UrlDecode parser Parameters  username             password   HttpUtility UrlDecode parser Parameters  password               multipart  public void Upload Stream stream        HttpMultipartParser parser   new HttpMultipartParser stream   image         if  parser Success                string user   HttpUtility UrlDecode parser Parameters  user             string title   HttpUtility UrlDecode parser Parameters  title                 Save the file somewhere         File WriteAllBytes FILE PATH   title   FILE EXT  parser FileContents

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I have dealt WCF with large file  serveral GB  upload where store data in memory is not an option  My solution is to store message stream to a temp file and use seek to find out begin and end of binary data

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I have implemented MultipartReader NuGet package for ASP NET 4 for reading multipart form data  It is based on Multipart Form Data Parser  but it supports more than one file

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You may take a look at the following blog post which illustrates a technique that could be used to parse multipart form-data on the server using the Multipart Parser   public void Upload Stream stream        MultipartParser parser   new MultipartParser stream       if  parser Success                   Save the file         SaveFile parser Filename  parser ContentType  parser FileContents             Another possibility is to enable aspnet compatibility and use HttpContext Current Request but that s not a very WCFish way

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How about some Regex   I wrote this for a text a file  but I believe this could work for you   In case your text file contains line starting exactly with the  matched  ones below - simply adapt your Regex       private static List lt string gt  fileUploadRequestParser Stream stream                  -----------------------------111111111111111           Content-Disposition  form-data  name  file   filename  data txt            Content-Type  text plain                                       -----------------------------111111111111111           Content-Disposition  form-data  name  submit            Submit           -----------------------------111111111111111--          List lt String gt  lstLines   new List lt string gt             TextReader textReader   new StreamReader stream           string sLine   textReader ReadLine            Regex regex   new Regex    -     content-         submit    RegexOptions IgnoreCase   RegexOptions Compiled   RegexOptions Singleline            while  sLine    null                        if   regex Match sLine  Success                                lstLines Add sLine                             sLine   textReader ReadLine                       return lstLines

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Another way would be to use  Net parser for HttpRequest  To do that you need to use a bit of reflection and simple class for WorkerRequest    First create class that derives from HttpWorkerRequest  for simplicity you can use SimpleWorkerRequest    public class MyWorkerRequest   SimpleWorkerRequest       private readonly string  size      private readonly Stream  data      private string  contentType       public MyWorkerRequest Stream data  string size  string contentType            base   app     c      aa       null                 size   size    data Length ToString CultureInfo InvariantCulture            data   data           contentType   contentType             public override string GetKnownRequestHeader int index                switch  index                        case  int HttpRequestHeader ContentLength                  return  size              case  int HttpRequestHeader ContentType                  return  contentType                    return base GetKnownRequestHeader index              public override int ReadEntityBody byte   buffer  int offset  int size                return  data Read buffer  offset  size              public override int ReadEntityBody byte   buffer  int size                return ReadEntityBody buffer  0  size             Then wherever you have you message stream create and instance of this class  I m doing it like that in WCF Service    WebInvoke Method    POST                  ResponseFormat   WebMessageFormat Json                 BodyStyle   WebMessageBodyStyle Bare       public string Upload Stream data                HttpWorkerRequest workerRequest               new MyWorkerRequest data                                  WebOperationContext Current IncomingRequest ContentLength                                      ToString CultureInfo InvariantCulture                                   WebOperationContext Current IncomingRequest ContentType                      And then create HttpRequest using activator and non public constructor  var r    HttpRequest Activator CreateInstance              typeof HttpRequest               BindingFlags Instance   BindingFlags NonPublic              null              new object                                         workerRequest                      new HttpContext workerRequest                                 null    var runtimeField   typeof  HttpRuntime  GetField   theRuntime   BindingFlags Static   BindingFlags NonPublic   if  runtimeField    null        return     var runtime    HttpRuntime  runtimeField GetValue null   if  runtime    null        return     var codeGenDirField   typeof HttpRuntime  GetField   codegenDir   BindingFlags Instance   BindingFlags NonPublic   if  codeGenDirField    null        return     codeGenDirField SetValue runtime    C  MultipartTemp      After that in r Files you will have files from your stream

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The guy who solved this posted it as LGPL and you re not allowed to modify it   I didn t even click on it when I saw that  Here s my version   This needs to be tested   There are probably bugs   Please post any updates   No warranty   You can modify this all you want  call it your own  print it out on a piece of paper and use it for kennel scrap      don t care   using System Collections Generic  using System Collections Specialized  using System IO  using System Net  using System Text  using System Web   namespace DigitalBoundaryGroup       class HttpNameValueCollection               public class File                       private string  fileName              public string FileName   get   return  fileName      fileName          set    fileName   value                   private string  fileData              public string FileData   get   return  fileData      fileName          set    fileData   value                   private string  contentType              public string ContentType   get   return  contentType      contentType          set    contentType   value                         private NameValueCollection  post          private Dictionary lt string  File gt   files          private readonly HttpListenerContext  ctx           public NameValueCollection Post   get   return  post      post   new NameValueCollection       set    post   value              public NameValueCollection Get   get   return  ctx Request QueryString              public Dictionary lt string  File gt  Files   get   return  files      files   new Dictionary lt string  File gt        set    files   value               private void PopulatePostMultiPart string post string                        var boundary index    ctx Request ContentType IndexOf  boundary      9              var boundary    ctx Request ContentType Substring boundary index   ctx Request ContentType Length - boundary index                var upper bound   post string Length - 4               if  post string Substring 2  boundary Length     boundary                  throw  new InvalidDataException                  var current string   new StringBuilder                 for  var x   4   boundary Length  x  lt  upper bound    x                                if  post string Substring x  boundary Length     boundary                                        x    boundary Length   1                       var post variable string   current string Remove current string Length - 4  4  ToString                         var end of header   post variable string IndexOf   r n r n                         if  end of header    -1  throw  new InvalidDataException                          var filename index   post variable string IndexOf  filename      0  end of header                       var filename starts   filename index   10                      var content type starts   post variable string IndexOf  Content-Type     0  end of header    14                      var name starts   post variable string IndexOf  name        6                      var data starts   end of header   4                       if  filename index    -1                                                var filename   post variable string Substring filename starts  post variable string IndexOf       filename starts  - filename starts                           var content type   post variable string Substring content type starts  post variable string IndexOf   r n   content type starts  - content type starts                           var file data   post variable string Substring data starts  post variable string Length - data starts                           var name   post variable string Substring name starts  post variable string IndexOf       name starts  - name starts                           Files Add name  new File     FileName   filename  ContentType   content type  FileData   file data                                               else                                               var name   post variable string Substring name starts  post variable string IndexOf       name starts  - name starts                           var value   post variable string Substring data starts  post variable string Length - data starts                           Post Add name  value                                              current string Clear                        continue                                     current string Append post string x                                     private void PopulatePost                         if   ctx Request HttpMethod     POST      ctx Request ContentType    null  return               var post string   new StreamReader  ctx Request InputStream   ctx Request ContentEncoding  ReadToEnd                 if   ctx Request ContentType StartsWith  multipart form-data                    PopulatePostMultiPart post string               else                 Post   HttpUtility ParseQueryString post string                       public HttpNameValueCollection ref HttpListenerContext ctx                         ctx   ctx              PopulatePost

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Sorry for joining the party late  but there is a way to do this with Microsoft public API   Here s what you need    System Net Http dll  Included in  NET 4 5 For  NET 4 get it via NuGet  System Net Http Formatting dll  For  NET 4 5 get this NuGet package For  NET 4 get this NuGet package    Note The Nuget packages come with more assemblies  but at the time of writing you only need the above    Once you have the assemblies referenced  the code can look like this  using  NET 4 5 for convenience    public static async Task ParseFiles      Stream data  string contentType  Action lt string  Stream gt  fileProcessor        var streamContent   new StreamContent data       streamContent Headers ContentType   MediaTypeHeaderValue Parse contentType        var provider   await streamContent ReadAsMultipartAsync         foreach  var httpContent in provider Contents                var fileName   httpContent Headers ContentDisposition FileName          if  string IsNullOrWhiteSpace fileName                         continue                     using  Stream fileContents   await httpContent ReadAsStreamAsync                          fileProcessor fileName  fileContents                       As for usage  say you have the following WCF REST method    OperationContract   WebInvoke Method   WebRequestMethods Http Post  UriTemplate     Upload    void Upload Stream data     You could implement it like so  public void Upload Stream data        MultipartParser ParseFiles             data              WebOperationContext Current IncomingRequest ContentType              MyProcessMethod

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I ve had some issues with parser that are based on string parsing particularly with large files I found it would run out of memory and fail to parse binary data    To cope with these issues I ve open sourced my own attempt at a C  multipart form-data parser here  Features    Handles very large files well   Data is streamed in and streamed out while reading  Can handle multiple file uploads and automatically detects if a section is a file or not  Returns files as a stream not as a byte    good for large files   Full documentation for the library including a MSDN-style generated website  Full unit tests    Restrictions    Doesn t handle non-multipart data   Code is more complicated then Lorenzo s   Just use the MultipartFormDataParser class like so   Stream data   GetTheStream        Boundary is auto-detected but can also be specified  var parser   new MultipartFormDataParser data  Encoding UTF8       The stream is parsed  if it failed it will throw an exception  Now we can use    your data      The key of these maps corresponds to the name field in your    form string username   parser Parameters  username   Data  string password   parser Parameters  password   Data     Single file access  var file   parser Files First    string filename   file FileName  Stream data   file Data      Multi-file access foreach var f in parser Files           Do stuff with each file      In the context of a WCF service you could use it like this   public ResponseClass MyMethod Stream multipartData           First we need to get the boundary from the header  this is sent        with the HTTP request  We can do that in WCF using the WebOperationConext      var type   WebOperationContext Current IncomingRequest Headers  Content-Type            Now we want to strip the boundary out of the Content-Type  currently the string        looks like   multipart form-data  boundary ---------------------124123qase124      var boundary   type Substring type IndexOf      1           Now that we ve got the boundary we can parse our multipart and use it as normal     var parser   new MultipartFormDataParser data  boundary  Encoding UTF8                Or like this  slightly slower but more code friendly    public ResponseClass MyMethod Stream multipartData        var parser   new MultipartFormDataParser data  Encoding UTF8       Documentation is also available  when you clone the repository simply navigate to HttpMultipartParserDocumentation Help index html

[c#] Reading file input from a multipart/form-data POST

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