Programmatically Executing HTTP POST

_{Code submitted by Jason Penny.}

Upload Multiple Files

File uploads are most commonly carried out as HTTP POST. If you need to programmatically upload multiple files to an HTML form using the HTTP Post method - use the "UploadFilesHttpPost" procedure.

The "UploadFilesHttpPost" procedure takes six parameters: the TWebBrowser ("wb") instance, the target url ("URLstring") and the four file name arrays.

 procedure UploadFilesHttpPost(const wb:TWebBrowser; const URLstring: string; names, values, nFiles, vFiles: array of string) ;
 var
   strData, n, v, boundary: string;
   URL: OleVariant;
   Flags: OleVariant;
   PostData: OleVariant;
   Headers: OleVariant;
   idx: Integer;
 
   ms: TMemoryStream;
   ss: TStringStream;
 begin
   if Length(names) <> Length(values) then
     raise Exception.Create('UploadFilesHttpPost: Names and Values must have the same length.') ;
   if Length(nFiles) <> Length(vFiles) then
     raise Exception.Create('UploadFilesHttpPost: FileNames and FileValues must have the same length.') ;
 
   URL := 'about:blank';
   Flags := NavNoHistory or NavNoReadFromCache or NavNoWriteToCache or NavAllowAutosearch;
   wb.Navigate2(URL, Flags) ;
   while wb.ReadyState < READYSTATE_INTERACTIVE do Application.ProcessMessages;
 
   // anything random that WILL NOT occur in the data.
   boundary := '---------------------------123456789';
 
   strData := '';
   for idx := Low(names) to High(names) do
   begin
     n := names[idx];
     v := values[idx];
 
     strData := strData + '--' + boundary + #13#10 + 'Content-Disposition: form-data; name="' + n + '"' + #13#10#13#10 + v + #13#10;
   end;
 
   for idx := Low(nFiles) to High(nFiles) do
   begin
     n := nFiles[idx];
     v := vFiles[idx];
 
     strData := strData + '--' + boundary + #13#10 + 'Content-Disposition: form-data; name="' + n + '"; filename="' + v + '"' + #13#10;
 
     if v = '' then
     begin
        strData := strData + 'Content-Transfer-Encoding: binary''#13#10#13#10;
     end
     else
     begin
       if (CompareText(ExtractFileExt(v), '.JPG') = 0) or (CompareText(ExtractFileExt(v), '.JPEG') = 0) then
       begin
         strData := strData + 'Content-Type: image/pjpeg'#13#10#13#10;
       end
       else if (CompareText(ExtractFileExt(v), '.PNG') = 0) then
       begin
         strData := strData + 'Content-Type: image/x-png'#13#10#13#10;
       end
       else if (CompareText(ExtractFileExt(v), '.PDF') = 0) then
       begin
         strData := strData + 'Content-Type: application/pdf'#13#10#13#10;
       end
       else if (CompareText(ExtractFileExt(v), '.HTML') = 0) then
       begin
       end;
 
       strData := strData + 'Content-Type: text/html'#13#10#13#10;
 
       ms := TMemoryStream.Create;
       try
         ms.LoadFromFile(v) ;
         ss := TStringStream.Create('') ;
         try
           ss.CopyFrom(ms, ms.Size) ;
 
           strData := strData + ss.DataString + #13#10;
         finally
           ss.Free;
         end;
       finally
         ms.Free;
       end;
     end;
 
     strData := strData + '--' + boundary + '--'#13#10; // FOOTER
   end;
 
   strData := strData + #0;
 
   {2. you must convert a string into variant array of bytes and every character from string is a value in array}
   PostData := VarArrayCreate([0, Length(strData) - 1], varByte) ;
 
   { copy the ordinal value of the character into the PostData array}
   for idx := 1 to Length(strData) do PostData[idx-1] := Ord(strData[idx]) ;
 
   {3. prepare headers which will be sent to remote web-server}
   Headers := 'Content-Type: multipart/form-data; boundary=' + boundary + #13#10;
 
   {4. you must navigate to the URL with your script and send as parameters your array with POST-data and headers}
   URL := URLstring;
   wb.Navigate2(URL, Flags, EmptyParam, PostData, Headers) ;
   while wb.ReadyState < READYSTATE_INTERACTIVE do Application.ProcessMessages;
 end;
 

Here's an example of usage - the "blank.htm" file is uploaded to the "http://validator.w3.org/check" W3 validator:

UploadFilesHttpPost(
  WebBrowser1,
  'http://validator.w3.org/check',
  [],
  [],
  ['uploaded_file'],
  ['C:\blank.htm'] );

Note: you'll need a TWebBrowser (named "WebBrowser1") control on a form for the above to compile.

Delphi tips navigator:
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