G
Guest
Hi,
I have a problem that I have been working with for a while.
I need to be able from server side (asp.net) to detect that the file i'm
streaming down to the client is saved completely/succsessfully on the
client's computer before updating some metadata on the server (file
downloaded date for instance)
However,
All examples i have tried, and all examples I have found that other people
says works - doesn't work for me :-(
Below is the code I'm using at the moment (an http handler for handling all
zip files)
However, the code seems to output the whole file to the response stream
before the user decides to press the saveas or cancel button in the forced
save as dialog in internet explorer.
By then when the user press the save or cancel button (or the x in the upper
right corner of the save as dialog) the server side has already finished the
output and the client is still connected wich results in an update of the
download date- wich is wrong since the user hasn't saved the complete file to
disc - the whole file has only been outstreamed from server.)
It doesn't help to set the bufferoutput=false.
arrgh :-(
Do I need to write an activex on client side to handle the download and to
be able to verify that the download is completed? I don't want to mess the
app up with activex and/or java applets - but maybe I can't solve it without
some more logic on the client side?
Please give me a hint on how to solve this.
Regards,
Roy
*********CODE********
Public Class ZIPHandler
Implements IHttpHandler
#Region "Constants used for HTTP communication"
' The boundary is used in multipart/byteranges responses
' to separate each ranges content. It should be as unique
' as possible to avoid confusion with binary content.
Private Const MULTIPART_BOUNDARY As String = "<q1w2e3r4t5y6u7i8o9p0>"
Private Const MULTIPART_CONTENTTYPE As String = "multipart/byteranges;
boundary=" & MULTIPART_BOUNDARY
Private Const HTTP_HEADER_ACCEPT_RANGES As String = "Accept-Ranges"
Private Const HTTP_HEADER_ACCEPT_RANGES_BYTES As String = "bytes"
Private Const HTTP_HEADER_CONTENT_TYPE As String = "Content-Type"
Private Const HTTP_HEADER_CONTENT_RANGE As String = "Content-Range"
Private Const HTTP_HEADER_CONTENT_LENGTH As String = "Content-Length"
Private Const HTTP_HEADER_ENTITY_TAG As String = "ETag"
Private Const HTTP_HEADER_LAST_MODIFIED As String = "Last-Modified"
Private Const HTTP_HEADER_RANGE As String = "Range"
Private Const HTTP_HEADER_IF_RANGE As String = "If-Range"
Private Const HTTP_HEADER_IF_MATCH As String = "If-Match"
Private Const HTTP_HEADER_IF_NONE_MATCH As String = "If-None-Match"
Private Const HTTP_HEADER_IF_MODIFIED_SINCE As String = "If-Modified-Since"
Private Const HTTP_HEADER_IF_UNMODIFIED_SINCE As String =
"If-Unmodified-Since"
Private Const HTTP_HEADER_UNLESS_MODIFIED_SINCE As String =
"Unless-Modified-Since"
Private Const HTTP_METHOD_GET As String = "GET"
Private Const HTTP_METHOD_HEAD As String = "HEAD"
#End Region
#Region "IHTTPHandler"
Public ReadOnly Property IsReusable() As Boolean Implements
System.Web.IHttpHandler.IsReusable
Get
' Allow ASP.NET to reuse instances of this class...
Return True
End Get
End Property
Public Sub ProcessRequest(ByVal objContext As System.Web.HttpContext)
Implements System.Web.IHttpHandler.ProcessRequest
' The Response object from the Context
Dim objResponse As HttpResponse = objContext.Response
' The Request object from the Context
Dim objRequest As HttpRequest = objContext.Request
' File information object...
Dim objFile As Download.FileInformation
' Long Arrays for Range values:
' ...Begin() contains start positions for each requested Range
Dim alRequestedRangesBegin() As Long
' ...End() contains end positions for each requested Range
Dim alRequestedRangesend() As Long
' Response Header value: Content Length...
Dim iResponseContentLength As Int32
' The Stream we're using to download the file in chunks...
Dim objStream As System.IO.FileStream
' Total Bytes to read (per requested range)
Dim iBytesToRead As Int32
' Size of the Buffer for chunk-wise reading
Dim iBufferSize As Int32 = 25000
' The Buffer itself
Dim bBuffer(iBufferSize) As Byte
' Amount of Bytes read
Dim iLengthOfReadChunk As Int32
' Indicates if the download was interrupted
Dim bDownloadBroken As Boolean
' Indicates if this is a range request
Dim bIsRangeRequest As Boolean
' Indicates if this is a multipart range request
Dim bMultipart As Boolean
' Loop counter used to iterate through the ranges
Dim iLoop As Int32
' ToDo - your code here (Determine which file is requested)
' Using objRequest, determine which file is requested to
' be downloaded, and open objFile with that file:
' Example:
' objFile = New Download.FileInformation(<Full path to the requested
file>)
objFile = New
Download.FileInformation(objContext.Server.MapPath("~/download.zip"))
' Clear the current output content from the buffer
objResponse.Clear()
If Not objRequest.HttpMethod.Equals(HTTP_METHOD_GET) Or _
Not objRequest.HttpMethod.Equals(HTTP_METHOD_HEAD) Then
' Currently, only the GET and HEAD methods
' are supported...
objResponse.StatusCode = 501 ' Not implemented
ElseIf Not objFile.Exists Then
' The requested file could not be retrieved...
objResponse.StatusCode = 404 ' Not found
ElseIf objFile.Length > Int32.MaxValue Then
' The file size is too large...
objResponse.StatusCode = 413 ' Request Entity Too Large
ElseIf Not ParseRequestHeaderRange(objRequest, alRequestedRangesBegin,
alRequestedRangesend, _
objFile.Length, bIsRangeRequest) Then
' The Range request contained bad entries
objResponse.StatusCode = 400 ' Bad Request
ElseIf Not CheckIfModifiedSince(objRequest, objFile) Then
' The entity is still unmodified...
objResponse.StatusCode = 304 ' Not Modified
ElseIf Not CheckIfUnmodifiedSince(objRequest, objFile) Then
' The entity was modified since the requested date...
objResponse.StatusCode = 412 ' Precondition failed
ElseIf Not CheckIfMatch(objRequest, objFile) Then
' The entity does not match the request...
objResponse.StatusCode = 412 ' Precondition failed
ElseIf Not CheckIfNoneMatch(objRequest, objResponse, objFile) Then
' The entity does match the none-match request, the response
' code was set inside the CheckIfNoneMatch function
Else
' Preliminary checks where successful...
If bIsRangeRequest AndAlso CheckIfRange(objRequest, objFile) Then
' This is a Range request...
' If the Range arrays contain more than one entry,
' it even is a multipart range request...
bMultipart = CBool(alRequestedRangesBegin.GetUpperBound(0) > 0)
' Loop through each Range to calculate the entire Response length
For iLoop = alRequestedRangesBegin.GetLowerBound(0) To
alRequestedRangesBegin.GetUpperBound(0)
' The length of the content (for this range)
iResponseContentLength +=
Convert.ToInt32(alRequestedRangesend(iLoop) - alRequestedRangesBegin(iLoop))
+ 1
If bMultipart Then
' If this is a multipart range request, calculate
' the length of the intermediate headers to send
iResponseContentLength += MULTIPART_BOUNDARY.Length
iResponseContentLength += objFile.ContentType.Length
iResponseContentLength +=
alRequestedRangesBegin(iLoop).ToString.Length
iResponseContentLength +=
alRequestedRangesend(iLoop).ToString.Length
iResponseContentLength += objFile.Length.ToString.Length
' 49 is the length of line break and other
' needed characters in one multipart header
iResponseContentLength += 49
End If
Next iLoop
If bMultipart Then
' If this is a multipart range request,
' we must also calculate the length of
' the last intermediate header we must send
iResponseContentLength += MULTIPART_BOUNDARY.Length
' 8 is the length of dash and line break characters
iResponseContentLength += 8
Else
' This is no multipart range request, so
' we must indicate the response Range of
' in the initial HTTP Header
objResponse.AppendHeader(HTTP_HEADER_CONTENT_RANGE, "bytes " & _
alRequestedRangesBegin(0).ToString & "-"
& _
alRequestedRangesend(0).ToString & "/" & _
objFile.Length.ToString)
End If
' Range response
objResponse.StatusCode = 206 ' Partial Response
Else
' This is not a Range request, or the requested Range entity ID
' does not match the current entity ID, so start a new download
' Indicate the file's complete size as content length
iResponseContentLength = Convert.ToInt32(objFile.Length)
' Return a normal OK status...
objResponse.StatusCode = 200
End If
' Write the content length into the Response
objResponse.AppendHeader(HTTP_HEADER_CONTENT_LENGTH,
iResponseContentLength.ToString)
' Write the Last-Modified Date into the Response
objResponse.AppendHeader(HTTP_HEADER_LAST_MODIFIED,
objFile.LastWriteTimeUTC.ToString("r"))
' Tell the client software that we accept Range request
objResponse.AppendHeader(HTTP_HEADER_ACCEPT_RANGES,
HTTP_HEADER_ACCEPT_RANGES_BYTES)
' Write the file's Entity Tag into the Response (in quotes!)
objResponse.AppendHeader(HTTP_HEADER_ENTITY_TAG, """" &
objFile.EntityTag & """")
' Write the Content Type into the Response
If bMultipart Then
' Multipart messages have this special Type.
' In this case, the file's actual mime type is
' written into the Response at a later time...
objResponse.ContentType = MULTIPART_CONTENTTYPE
Else
' Single part messages have the files content type...
objResponse.ContentType = objFile.ContentType
End If
If objRequest.HttpMethod.Equals(HTTP_METHOD_HEAD) Then
' Only the HEAD was requested, so we can quit the Response right
here...
Else
' Flush the HEAD information to the client...
objResponse.Flush()
' Download is in progress...
objFile.State = FileInformation.DownloadState.fsDownloadInProgress
' Open the file as filestream
objStream = New System.IO.FileStream(objFile.FullName,
IO.FileMode.Open, _
IO.FileAccess.Read, _
IO.FileShare.Read)
' Now, for each requested range, stream the chunks to the client:
For iLoop = alRequestedRangesBegin.GetLowerBound(0) To
alRequestedRangesBegin.GetUpperBound(0)
' Move the stream to the desired start position...
objStream.Seek(alRequestedRangesBegin(iLoop), IO.SeekOrigin.Begin)
' Calculate the total amount of bytes for this range
iBytesToRead = Convert.ToInt32(alRequestedRangesend(iLoop) -
alRequestedRangesBegin(iLoop)) + 1
If bMultipart Then
' If this is a multipart response, we must add
' certain headers before streaming the content:
' The multipart boundary
objResponse.Output.WriteLine("--" & MULTIPART_BOUNDARY)
' The mime type of this part of the content
objResponse.Output.WriteLine(HTTP_HEADER_CONTENT_TYPE & ": " &
objFile.ContentType)
' The actual range
objResponse.Output.WriteLine(HTTP_HEADER_CONTENT_RANGE & ":
bytes " & _
alRequestedRangesBegin(iLoop).ToString & "-" & _
alRequestedRangesend(iLoop).ToString & "/" & _
objFile.Length.ToString)
' Indicating the end of the intermediate headers
objResponse.Output.WriteLine()
End If
' Now stream the range to the client...
While iBytesToRead > 0
'THISLOOP
If objResponse.IsClientConnected Then
' Read a chunk of bytes from the stream
iLengthOfReadChunk = objStream.Read(bBuffer, 0,
Math.Min(bBuffer.Length, iBytesToRead))
' Write the data to the current output stream.
objResponse.OutputStream.Write(bBuffer, 0, iLengthOfReadChunk)
' Flush the data to the HTML output.
objResponse.Flush()
' Clear the buffer
ReDim bBuffer(iBufferSize)
' Reduce BytesToRead
iBytesToRead -= iLengthOfReadChunk
Else
' The client was or has disconneceted from the server... stop
downstreaming...
iBytesToRead = -1
bDownloadBroken = True
End If
End While
' In Multipart responses, mark the end of the part
If bMultipart Then objResponse.Output.WriteLine()
' No need to proceed to the next part if the
' client was disconnected
If bDownloadBroken Then Exit For
Next iLoop
' At this point, the response was finished or cancelled...
If bDownloadBroken Then
' Download is broken...
objFile.State = FileInformation.DownloadState.fsDownloadBroken
Else
If bMultipart Then
' In multipart responses, close the response once more with
' the boundary and line breaks
objResponse.Output.WriteLine("--" & MULTIPART_BOUNDARY & "--")
objResponse.Output.WriteLine()
End If
' The download was finished
objFile.State = FileInformation.DownloadState.fsDownloadFinished
End If
objStream.Close()
End If
End If
objResponse.End()
End Sub
#End Region
#Region "Private helper functions"
Private Function CheckIfRange(ByVal objRequest As HttpRequest, ByVal
objFile As Download.FileInformation) As Boolean
Dim sRequestHeaderIfRange As String
' Checks the If-Range header if it was sent with the request.
'
' Returns True if the header value matches the file's entity tag,
' or if no header was sent,
' returns False if a header was sent, but does not match the file.
' Retrieve If-Range Header value from Request (objFile.EntityTag if none
is indicated)
sRequestHeaderIfRange = RetrieveHeader(objRequest, HTTP_HEADER_IF_RANGE,
objFile.EntityTag)
' If the requested file entity matches the current
' file entity, return True
Return sRequestHeaderIfRange.Equals(objFile.EntityTag)
End Function
Private Function CheckIfMatch(ByVal objRequest As HttpRequest, ByVal
objFile As Download.FileInformation) As Boolean
Dim sRequestHeaderIfMatch As String
Dim sEntityIDs() As String
Dim bReturn As Boolean
' Checks the If-Match header if it was sent with the request.
'
' Returns True if one of the header values matches the file's entity tag,
' or if no header was sent,
' returns False if a header was sent, but does not match the file.
' Retrieve If-Match Header value from Request (*, meaning any, if none
is indicated)
sRequestHeaderIfMatch = RetrieveHeader(objRequest, HTTP_HEADER_IF_MATCH,
"*")
If sRequestHeaderIfMatch.Equals("*") Then
' The server may perform the request as if the
' If-Match header does not exists...
bReturn = True
Else
' One or more Match IDs where sent by the client software...
sEntityIDs = sRequestHeaderIfMatch.Replace("bytes=",
"").Split(",".ToCharArray)
' Loop through all entity IDs, finding one
' which matches the current file's ID will
' be enough to satisfy the If-Match
For iLoop As Int32 = sEntityIDs.GetLowerBound(0) To
sEntityIDs.GetUpperBound(0)
If sEntityIDs(iLoop).Trim.Equals(objFile.EntityTag) Then
bReturn = True
End If
Next iLoop
End If
' Return the result...
Return bReturn
End Function
Private Function CheckIfNoneMatch(ByVal objRequest As HttpRequest, ByVal
objResponse As HttpResponse, ByVal objFile As Download.FileInformation) As
Boolean
Dim sRequestHeaderIfNoneMatch As String
Dim sEntityIDs() As String
Dim bReturn As Boolean = True
Dim sReturn As String
' Checks the If-None-Match header if it was sent with the request.
'
' Returns True if one of the header values matches the file's entity tag,
' or if "*" was sent,
' returns False if a header was sent, but does not match the file, or
' if no header was sent.
' Retrieve If-None-Match Header value from Request (*, meaning any, if
none is indicated)
sRequestHeaderIfNoneMatch = RetrieveHeader(objRequest,
HTTP_HEADER_IF_NONE_MATCH, String.Empty)
If sRequestHeaderIfNoneMatch.Equals(String.Empty) Then
' Perform the request normally...
bReturn = True
ElseIf sRequestHeaderIfNoneMatch.Equals("*") Then
' The server must not perform the request
objResponse.StatusCode = 412 ' Precondition failed
bReturn = False
Else
' One or more Match IDs where sent by the client software...
sEntityIDs = sRequestHeaderIfNoneMatch.Replace("bytes=",
"").Split(",".ToCharArray)
' Loop through all entity IDs, finding one which
' does not match the current file's ID will be
' enough to satisfy the If-None-Match
For iLoop As Int32 = sEntityIDs.GetLowerBound(0) To
sEntityIDs.GetUpperBound(0)
If sEntityIDs(iLoop).Trim.Equals(objFile.EntityTag) Then
sReturn = sEntityIDs(iLoop)
bReturn = False
End If
Next iLoop
If Not bReturn Then
' One of the requested entities matches the current file's tag,
objResponse.AppendHeader("ETag", sReturn)
objResponse.StatusCode = 304 ' Not Modified
End If
End If
' Return the result...
Return bReturn
End Function
Private Function CheckIfModifiedSince(ByVal objRequest As HttpRequest,
ByVal objFile As Download.FileInformation) As Boolean
Dim sDate As String
Dim dDate As Date
Dim bReturn As Boolean
' Checks the If-Modified header if it was sent with the request.
'
' Returns True, if the file was modified since the
' indicated date (RFC 1123 format), or
' if no header was sent,
' returns False, if the file was not modified since
' the indicated date
' Retrieve If-Modified-Since Header value from Request (Empty if none is
indicated)
sDate = RetrieveHeader(objRequest, HTTP_HEADER_IF_MODIFIED_SINCE,
String.Empty)
If sDate.Equals(String.Empty) Then
' No If-Modified-Since date was indicated,
' so just give this as True
bReturn = True
Else
Try
' ... to parse the indicated sDate to a datetime value
dDate = DateTime.Parse(sDate)
' Return True if the file was modified since or at the indicated
date...
bReturn = objFile.LastWriteTimeUTC >= DateTime.Parse(sDate)
Catch ex As Exception
' Converting the indicated date value failed, return False
bReturn = False
End Try
End If
Return bReturn
End Function
Private Function CheckIfUnmodifiedSince(ByVal objRequest As HttpRequest,
ByVal objFile As Download.FileInformation) As Boolean
Dim sDate As String
Dim dDate As Date
Dim bReturn As Boolean
' Checks the If-Unmodified or Unless-Modified-Since header, if
' one of them was sent with the request.
'
' Returns True, if the file was not modified since the
' indicated date (RFC 1123 format), or
' if no header was sent,
' returns False, if the file was modified since the indicated date
' Retrieve If-Unmodified-Since Header value from Request (Empty if none
is indicated)
sDate = RetrieveHeader(objRequest, HTTP_HEADER_IF_UNMODIFIED_SINCE,
String.Empty)
If sDate.Equals(String.Empty) Then
' If-Unmodified-Since was not sent, check Unless-Modified-Since...
sDate = RetrieveHeader(objRequest, HTTP_HEADER_UNLESS_MODIFIED_SINCE,
String.Empty)
End If
If sDate.Equals(String.Empty) Then
' No date was indicated,
' so just give this as True
bReturn = True
Else
Try
' ... to parse the indicated sDate to a datetime value
dDate = DateTime.Parse(sDate)
' Return True if the file was not modified since the indicated date...
bReturn = objFile.LastWriteTimeUTC < DateTime.Parse(sDate)
Catch ex As Exception
' Converting the indicated date value failed, return False
bReturn = False
End Try
End If
Return bReturn
End Function
Private Function ParseRequestHeaderRange(ByVal objRequest As HttpRequest,
ByRef lBegin() As Long, ByRef lEnd() As Long, ByVal lMax As Long, ByRef
bRangeRequest As Boolean) As Boolean
Dim bValidRanges As Boolean
Dim sSource As String
Dim iLoop As Int32
Dim sRanges() As String
' Parses the Range header from the Request (if there is one)
' Returns True, if the Range header was valid, or if there was no
' Range header at all (meaning that the whole
' file was requested)
' Returns False, if the Range header asked for unsatisfieable
' ranges
' Retrieve Range Header value from Request (Empty if none is indicated)
sSource = RetrieveHeader(objRequest, HTTP_HEADER_RANGE, String.Empty)
If sSource.Equals(String.Empty) Then
' No Range was requested, return the entire file range...
ReDim lBegin(0)
ReDim lEnd(0)
lBegin(0) = 0
lEnd(0) = lMax - 1
' A valid range is returned
bValidRanges = True
' no Range request
bRangeRequest = False
Else
' A Range was requested...
' Preset value...
bValidRanges = True
' Return True for the bRange parameter, telling the caller
' that the Request is indeed a Range request...
bRangeRequest = True
' Remove "bytes=" from the beginning, and split the remaining
' string by comma characters
sRanges = sSource.Replace("bytes=", "").Split(",".ToCharArray)
ReDim lBegin(sRanges.GetUpperBound(0))
ReDim lEnd(sRanges.GetUpperBound(0))
' Check each found Range request for consistency
For iLoop = sRanges.GetLowerBound(0) To sRanges.GetUpperBound(0)
' Split this range request by the dash character,
' sRange(0) contains the requested begin-value,
' sRange(1) contains the requested end-value...
Dim sRange() As String = sRanges(iLoop).Split("-".ToCharArray)
' Determine the end of the requested range
If sRange(1).Equals(String.Empty) Then
' No end was specified, take the entire range
lEnd(iLoop) = lMax - 1
Else
' An end was specified...
lEnd(iLoop) = Long.Parse(sRange(1))
End If
' Determine the begin of the requested range
If sRange(0).Equals(String.Empty) Then
' No begin was specified, which means that
' the end value indicated to return the last n
' bytes of the file:
' Calculate the begin
lBegin(iLoop) = lMax - 1 - lEnd(iLoop)
' ... to the end of the file...
lEnd(iLoop) = lMax - 1
Else
' A normal begin value was indicated...
lBegin(iLoop) = Long.Parse(sRange(0))
End If
' Check if the requested range values are valid,
' return False if they are not.
'
' Note:
' Do not clean invalid values up by fitting them into
' valid parameters using Math.Min and Math.Max, because
' some download clients (like Go!Zilla) might send invalid
' (e.g. too large) range requests to determine the file limits!
' Begin and end must not exceed the file size
If (lBegin(iLoop) > (lMax - 1)) Or (lEnd(iLoop) > (lMax - 1)) Then
bValidRanges = False
End If
' Begin and end cannot be < 0
If (lBegin(iLoop) < 0) Or (lEnd(iLoop) < 0) Then
bValidRanges = False
End If
' End must be larger or equal to begin value
If lEnd(iLoop) < lBegin(iLoop) Then
' The requested Range is invalid...
bValidRanges = False
End If
Next iLoop
End If
Return bValidRanges
End Function
Private Function RetrieveHeader(ByVal objRequest As HttpRequest, ByVal
sHeader As String, ByVal sDefault As String) As String
Dim sReturn As String
' Retrieves the indicated Header's value from the Request,
' if the header was not sent, sDefault is returned.
'
' If the value contains quote characters, they are removed.
sReturn = objRequest.Headers.Item(sHeader)
If (sReturn Is Nothing) OrElse sReturn.Equals(String.Empty) Then
' The Header wos not found in the Request,
' return the indicated default value...
Return sDefault
Else
' Return the found header value, stripped of any quote characters...
Return sReturn.Replace("""", "")
End If
End Function
Private Function GenerateHash(ByVal objStream As System.IO.Stream, ByVal
lBegin As Long, ByVal lEnd As Long) As String
Dim bByte(Convert.ToInt32(lEnd)) As Byte
objStream.Read(bByte, Convert.ToInt32(lBegin), Convert.ToInt32(lEnd -
lBegin) + 1)
'Instantiate an MD5 Provider object
Dim Md5 As New System.Security.Cryptography.MD5CryptoServiceProvider
'Compute the hash value from the source
Dim ByteHash() As Byte = Md5.ComputeHash(bByte)
'And convert it to String format for return
Return Convert.ToBase64String(ByteHash)
End Function
#End Region
End Class
*********END CODE****
I have a problem that I have been working with for a while.
I need to be able from server side (asp.net) to detect that the file i'm
streaming down to the client is saved completely/succsessfully on the
client's computer before updating some metadata on the server (file
downloaded date for instance)
However,
All examples i have tried, and all examples I have found that other people
says works - doesn't work for me :-(
Below is the code I'm using at the moment (an http handler for handling all
zip files)
However, the code seems to output the whole file to the response stream
before the user decides to press the saveas or cancel button in the forced
save as dialog in internet explorer.
By then when the user press the save or cancel button (or the x in the upper
right corner of the save as dialog) the server side has already finished the
output and the client is still connected wich results in an update of the
download date- wich is wrong since the user hasn't saved the complete file to
disc - the whole file has only been outstreamed from server.)
It doesn't help to set the bufferoutput=false.
arrgh :-(
Do I need to write an activex on client side to handle the download and to
be able to verify that the download is completed? I don't want to mess the
app up with activex and/or java applets - but maybe I can't solve it without
some more logic on the client side?
Please give me a hint on how to solve this.
Regards,
Roy
*********CODE********
Public Class ZIPHandler
Implements IHttpHandler
#Region "Constants used for HTTP communication"
' The boundary is used in multipart/byteranges responses
' to separate each ranges content. It should be as unique
' as possible to avoid confusion with binary content.
Private Const MULTIPART_BOUNDARY As String = "<q1w2e3r4t5y6u7i8o9p0>"
Private Const MULTIPART_CONTENTTYPE As String = "multipart/byteranges;
boundary=" & MULTIPART_BOUNDARY
Private Const HTTP_HEADER_ACCEPT_RANGES As String = "Accept-Ranges"
Private Const HTTP_HEADER_ACCEPT_RANGES_BYTES As String = "bytes"
Private Const HTTP_HEADER_CONTENT_TYPE As String = "Content-Type"
Private Const HTTP_HEADER_CONTENT_RANGE As String = "Content-Range"
Private Const HTTP_HEADER_CONTENT_LENGTH As String = "Content-Length"
Private Const HTTP_HEADER_ENTITY_TAG As String = "ETag"
Private Const HTTP_HEADER_LAST_MODIFIED As String = "Last-Modified"
Private Const HTTP_HEADER_RANGE As String = "Range"
Private Const HTTP_HEADER_IF_RANGE As String = "If-Range"
Private Const HTTP_HEADER_IF_MATCH As String = "If-Match"
Private Const HTTP_HEADER_IF_NONE_MATCH As String = "If-None-Match"
Private Const HTTP_HEADER_IF_MODIFIED_SINCE As String = "If-Modified-Since"
Private Const HTTP_HEADER_IF_UNMODIFIED_SINCE As String =
"If-Unmodified-Since"
Private Const HTTP_HEADER_UNLESS_MODIFIED_SINCE As String =
"Unless-Modified-Since"
Private Const HTTP_METHOD_GET As String = "GET"
Private Const HTTP_METHOD_HEAD As String = "HEAD"
#End Region
#Region "IHTTPHandler"
Public ReadOnly Property IsReusable() As Boolean Implements
System.Web.IHttpHandler.IsReusable
Get
' Allow ASP.NET to reuse instances of this class...
Return True
End Get
End Property
Public Sub ProcessRequest(ByVal objContext As System.Web.HttpContext)
Implements System.Web.IHttpHandler.ProcessRequest
' The Response object from the Context
Dim objResponse As HttpResponse = objContext.Response
' The Request object from the Context
Dim objRequest As HttpRequest = objContext.Request
' File information object...
Dim objFile As Download.FileInformation
' Long Arrays for Range values:
' ...Begin() contains start positions for each requested Range
Dim alRequestedRangesBegin() As Long
' ...End() contains end positions for each requested Range
Dim alRequestedRangesend() As Long
' Response Header value: Content Length...
Dim iResponseContentLength As Int32
' The Stream we're using to download the file in chunks...
Dim objStream As System.IO.FileStream
' Total Bytes to read (per requested range)
Dim iBytesToRead As Int32
' Size of the Buffer for chunk-wise reading
Dim iBufferSize As Int32 = 25000
' The Buffer itself
Dim bBuffer(iBufferSize) As Byte
' Amount of Bytes read
Dim iLengthOfReadChunk As Int32
' Indicates if the download was interrupted
Dim bDownloadBroken As Boolean
' Indicates if this is a range request
Dim bIsRangeRequest As Boolean
' Indicates if this is a multipart range request
Dim bMultipart As Boolean
' Loop counter used to iterate through the ranges
Dim iLoop As Int32
' ToDo - your code here (Determine which file is requested)
' Using objRequest, determine which file is requested to
' be downloaded, and open objFile with that file:
' Example:
' objFile = New Download.FileInformation(<Full path to the requested
file>)
objFile = New
Download.FileInformation(objContext.Server.MapPath("~/download.zip"))
' Clear the current output content from the buffer
objResponse.Clear()
If Not objRequest.HttpMethod.Equals(HTTP_METHOD_GET) Or _
Not objRequest.HttpMethod.Equals(HTTP_METHOD_HEAD) Then
' Currently, only the GET and HEAD methods
' are supported...
objResponse.StatusCode = 501 ' Not implemented
ElseIf Not objFile.Exists Then
' The requested file could not be retrieved...
objResponse.StatusCode = 404 ' Not found
ElseIf objFile.Length > Int32.MaxValue Then
' The file size is too large...
objResponse.StatusCode = 413 ' Request Entity Too Large
ElseIf Not ParseRequestHeaderRange(objRequest, alRequestedRangesBegin,
alRequestedRangesend, _
objFile.Length, bIsRangeRequest) Then
' The Range request contained bad entries
objResponse.StatusCode = 400 ' Bad Request
ElseIf Not CheckIfModifiedSince(objRequest, objFile) Then
' The entity is still unmodified...
objResponse.StatusCode = 304 ' Not Modified
ElseIf Not CheckIfUnmodifiedSince(objRequest, objFile) Then
' The entity was modified since the requested date...
objResponse.StatusCode = 412 ' Precondition failed
ElseIf Not CheckIfMatch(objRequest, objFile) Then
' The entity does not match the request...
objResponse.StatusCode = 412 ' Precondition failed
ElseIf Not CheckIfNoneMatch(objRequest, objResponse, objFile) Then
' The entity does match the none-match request, the response
' code was set inside the CheckIfNoneMatch function
Else
' Preliminary checks where successful...
If bIsRangeRequest AndAlso CheckIfRange(objRequest, objFile) Then
' This is a Range request...
' If the Range arrays contain more than one entry,
' it even is a multipart range request...
bMultipart = CBool(alRequestedRangesBegin.GetUpperBound(0) > 0)
' Loop through each Range to calculate the entire Response length
For iLoop = alRequestedRangesBegin.GetLowerBound(0) To
alRequestedRangesBegin.GetUpperBound(0)
' The length of the content (for this range)
iResponseContentLength +=
Convert.ToInt32(alRequestedRangesend(iLoop) - alRequestedRangesBegin(iLoop))
+ 1
If bMultipart Then
' If this is a multipart range request, calculate
' the length of the intermediate headers to send
iResponseContentLength += MULTIPART_BOUNDARY.Length
iResponseContentLength += objFile.ContentType.Length
iResponseContentLength +=
alRequestedRangesBegin(iLoop).ToString.Length
iResponseContentLength +=
alRequestedRangesend(iLoop).ToString.Length
iResponseContentLength += objFile.Length.ToString.Length
' 49 is the length of line break and other
' needed characters in one multipart header
iResponseContentLength += 49
End If
Next iLoop
If bMultipart Then
' If this is a multipart range request,
' we must also calculate the length of
' the last intermediate header we must send
iResponseContentLength += MULTIPART_BOUNDARY.Length
' 8 is the length of dash and line break characters
iResponseContentLength += 8
Else
' This is no multipart range request, so
' we must indicate the response Range of
' in the initial HTTP Header
objResponse.AppendHeader(HTTP_HEADER_CONTENT_RANGE, "bytes " & _
alRequestedRangesBegin(0).ToString & "-"
& _
alRequestedRangesend(0).ToString & "/" & _
objFile.Length.ToString)
End If
' Range response
objResponse.StatusCode = 206 ' Partial Response
Else
' This is not a Range request, or the requested Range entity ID
' does not match the current entity ID, so start a new download
' Indicate the file's complete size as content length
iResponseContentLength = Convert.ToInt32(objFile.Length)
' Return a normal OK status...
objResponse.StatusCode = 200
End If
' Write the content length into the Response
objResponse.AppendHeader(HTTP_HEADER_CONTENT_LENGTH,
iResponseContentLength.ToString)
' Write the Last-Modified Date into the Response
objResponse.AppendHeader(HTTP_HEADER_LAST_MODIFIED,
objFile.LastWriteTimeUTC.ToString("r"))
' Tell the client software that we accept Range request
objResponse.AppendHeader(HTTP_HEADER_ACCEPT_RANGES,
HTTP_HEADER_ACCEPT_RANGES_BYTES)
' Write the file's Entity Tag into the Response (in quotes!)
objResponse.AppendHeader(HTTP_HEADER_ENTITY_TAG, """" &
objFile.EntityTag & """")
' Write the Content Type into the Response
If bMultipart Then
' Multipart messages have this special Type.
' In this case, the file's actual mime type is
' written into the Response at a later time...
objResponse.ContentType = MULTIPART_CONTENTTYPE
Else
' Single part messages have the files content type...
objResponse.ContentType = objFile.ContentType
End If
If objRequest.HttpMethod.Equals(HTTP_METHOD_HEAD) Then
' Only the HEAD was requested, so we can quit the Response right
here...
Else
' Flush the HEAD information to the client...
objResponse.Flush()
' Download is in progress...
objFile.State = FileInformation.DownloadState.fsDownloadInProgress
' Open the file as filestream
objStream = New System.IO.FileStream(objFile.FullName,
IO.FileMode.Open, _
IO.FileAccess.Read, _
IO.FileShare.Read)
' Now, for each requested range, stream the chunks to the client:
For iLoop = alRequestedRangesBegin.GetLowerBound(0) To
alRequestedRangesBegin.GetUpperBound(0)
' Move the stream to the desired start position...
objStream.Seek(alRequestedRangesBegin(iLoop), IO.SeekOrigin.Begin)
' Calculate the total amount of bytes for this range
iBytesToRead = Convert.ToInt32(alRequestedRangesend(iLoop) -
alRequestedRangesBegin(iLoop)) + 1
If bMultipart Then
' If this is a multipart response, we must add
' certain headers before streaming the content:
' The multipart boundary
objResponse.Output.WriteLine("--" & MULTIPART_BOUNDARY)
' The mime type of this part of the content
objResponse.Output.WriteLine(HTTP_HEADER_CONTENT_TYPE & ": " &
objFile.ContentType)
' The actual range
objResponse.Output.WriteLine(HTTP_HEADER_CONTENT_RANGE & ":
bytes " & _
alRequestedRangesBegin(iLoop).ToString & "-" & _
alRequestedRangesend(iLoop).ToString & "/" & _
objFile.Length.ToString)
' Indicating the end of the intermediate headers
objResponse.Output.WriteLine()
End If
' Now stream the range to the client...
While iBytesToRead > 0
'THISLOOP
If objResponse.IsClientConnected Then
' Read a chunk of bytes from the stream
iLengthOfReadChunk = objStream.Read(bBuffer, 0,
Math.Min(bBuffer.Length, iBytesToRead))
' Write the data to the current output stream.
objResponse.OutputStream.Write(bBuffer, 0, iLengthOfReadChunk)
' Flush the data to the HTML output.
objResponse.Flush()
' Clear the buffer
ReDim bBuffer(iBufferSize)
' Reduce BytesToRead
iBytesToRead -= iLengthOfReadChunk
Else
' The client was or has disconneceted from the server... stop
downstreaming...
iBytesToRead = -1
bDownloadBroken = True
End If
End While
' In Multipart responses, mark the end of the part
If bMultipart Then objResponse.Output.WriteLine()
' No need to proceed to the next part if the
' client was disconnected
If bDownloadBroken Then Exit For
Next iLoop
' At this point, the response was finished or cancelled...
If bDownloadBroken Then
' Download is broken...
objFile.State = FileInformation.DownloadState.fsDownloadBroken
Else
If bMultipart Then
' In multipart responses, close the response once more with
' the boundary and line breaks
objResponse.Output.WriteLine("--" & MULTIPART_BOUNDARY & "--")
objResponse.Output.WriteLine()
End If
' The download was finished
objFile.State = FileInformation.DownloadState.fsDownloadFinished
End If
objStream.Close()
End If
End If
objResponse.End()
End Sub
#End Region
#Region "Private helper functions"
Private Function CheckIfRange(ByVal objRequest As HttpRequest, ByVal
objFile As Download.FileInformation) As Boolean
Dim sRequestHeaderIfRange As String
' Checks the If-Range header if it was sent with the request.
'
' Returns True if the header value matches the file's entity tag,
' or if no header was sent,
' returns False if a header was sent, but does not match the file.
' Retrieve If-Range Header value from Request (objFile.EntityTag if none
is indicated)
sRequestHeaderIfRange = RetrieveHeader(objRequest, HTTP_HEADER_IF_RANGE,
objFile.EntityTag)
' If the requested file entity matches the current
' file entity, return True
Return sRequestHeaderIfRange.Equals(objFile.EntityTag)
End Function
Private Function CheckIfMatch(ByVal objRequest As HttpRequest, ByVal
objFile As Download.FileInformation) As Boolean
Dim sRequestHeaderIfMatch As String
Dim sEntityIDs() As String
Dim bReturn As Boolean
' Checks the If-Match header if it was sent with the request.
'
' Returns True if one of the header values matches the file's entity tag,
' or if no header was sent,
' returns False if a header was sent, but does not match the file.
' Retrieve If-Match Header value from Request (*, meaning any, if none
is indicated)
sRequestHeaderIfMatch = RetrieveHeader(objRequest, HTTP_HEADER_IF_MATCH,
"*")
If sRequestHeaderIfMatch.Equals("*") Then
' The server may perform the request as if the
' If-Match header does not exists...
bReturn = True
Else
' One or more Match IDs where sent by the client software...
sEntityIDs = sRequestHeaderIfMatch.Replace("bytes=",
"").Split(",".ToCharArray)
' Loop through all entity IDs, finding one
' which matches the current file's ID will
' be enough to satisfy the If-Match
For iLoop As Int32 = sEntityIDs.GetLowerBound(0) To
sEntityIDs.GetUpperBound(0)
If sEntityIDs(iLoop).Trim.Equals(objFile.EntityTag) Then
bReturn = True
End If
Next iLoop
End If
' Return the result...
Return bReturn
End Function
Private Function CheckIfNoneMatch(ByVal objRequest As HttpRequest, ByVal
objResponse As HttpResponse, ByVal objFile As Download.FileInformation) As
Boolean
Dim sRequestHeaderIfNoneMatch As String
Dim sEntityIDs() As String
Dim bReturn As Boolean = True
Dim sReturn As String
' Checks the If-None-Match header if it was sent with the request.
'
' Returns True if one of the header values matches the file's entity tag,
' or if "*" was sent,
' returns False if a header was sent, but does not match the file, or
' if no header was sent.
' Retrieve If-None-Match Header value from Request (*, meaning any, if
none is indicated)
sRequestHeaderIfNoneMatch = RetrieveHeader(objRequest,
HTTP_HEADER_IF_NONE_MATCH, String.Empty)
If sRequestHeaderIfNoneMatch.Equals(String.Empty) Then
' Perform the request normally...
bReturn = True
ElseIf sRequestHeaderIfNoneMatch.Equals("*") Then
' The server must not perform the request
objResponse.StatusCode = 412 ' Precondition failed
bReturn = False
Else
' One or more Match IDs where sent by the client software...
sEntityIDs = sRequestHeaderIfNoneMatch.Replace("bytes=",
"").Split(",".ToCharArray)
' Loop through all entity IDs, finding one which
' does not match the current file's ID will be
' enough to satisfy the If-None-Match
For iLoop As Int32 = sEntityIDs.GetLowerBound(0) To
sEntityIDs.GetUpperBound(0)
If sEntityIDs(iLoop).Trim.Equals(objFile.EntityTag) Then
sReturn = sEntityIDs(iLoop)
bReturn = False
End If
Next iLoop
If Not bReturn Then
' One of the requested entities matches the current file's tag,
objResponse.AppendHeader("ETag", sReturn)
objResponse.StatusCode = 304 ' Not Modified
End If
End If
' Return the result...
Return bReturn
End Function
Private Function CheckIfModifiedSince(ByVal objRequest As HttpRequest,
ByVal objFile As Download.FileInformation) As Boolean
Dim sDate As String
Dim dDate As Date
Dim bReturn As Boolean
' Checks the If-Modified header if it was sent with the request.
'
' Returns True, if the file was modified since the
' indicated date (RFC 1123 format), or
' if no header was sent,
' returns False, if the file was not modified since
' the indicated date
' Retrieve If-Modified-Since Header value from Request (Empty if none is
indicated)
sDate = RetrieveHeader(objRequest, HTTP_HEADER_IF_MODIFIED_SINCE,
String.Empty)
If sDate.Equals(String.Empty) Then
' No If-Modified-Since date was indicated,
' so just give this as True
bReturn = True
Else
Try
' ... to parse the indicated sDate to a datetime value
dDate = DateTime.Parse(sDate)
' Return True if the file was modified since or at the indicated
date...
bReturn = objFile.LastWriteTimeUTC >= DateTime.Parse(sDate)
Catch ex As Exception
' Converting the indicated date value failed, return False
bReturn = False
End Try
End If
Return bReturn
End Function
Private Function CheckIfUnmodifiedSince(ByVal objRequest As HttpRequest,
ByVal objFile As Download.FileInformation) As Boolean
Dim sDate As String
Dim dDate As Date
Dim bReturn As Boolean
' Checks the If-Unmodified or Unless-Modified-Since header, if
' one of them was sent with the request.
'
' Returns True, if the file was not modified since the
' indicated date (RFC 1123 format), or
' if no header was sent,
' returns False, if the file was modified since the indicated date
' Retrieve If-Unmodified-Since Header value from Request (Empty if none
is indicated)
sDate = RetrieveHeader(objRequest, HTTP_HEADER_IF_UNMODIFIED_SINCE,
String.Empty)
If sDate.Equals(String.Empty) Then
' If-Unmodified-Since was not sent, check Unless-Modified-Since...
sDate = RetrieveHeader(objRequest, HTTP_HEADER_UNLESS_MODIFIED_SINCE,
String.Empty)
End If
If sDate.Equals(String.Empty) Then
' No date was indicated,
' so just give this as True
bReturn = True
Else
Try
' ... to parse the indicated sDate to a datetime value
dDate = DateTime.Parse(sDate)
' Return True if the file was not modified since the indicated date...
bReturn = objFile.LastWriteTimeUTC < DateTime.Parse(sDate)
Catch ex As Exception
' Converting the indicated date value failed, return False
bReturn = False
End Try
End If
Return bReturn
End Function
Private Function ParseRequestHeaderRange(ByVal objRequest As HttpRequest,
ByRef lBegin() As Long, ByRef lEnd() As Long, ByVal lMax As Long, ByRef
bRangeRequest As Boolean) As Boolean
Dim bValidRanges As Boolean
Dim sSource As String
Dim iLoop As Int32
Dim sRanges() As String
' Parses the Range header from the Request (if there is one)
' Returns True, if the Range header was valid, or if there was no
' Range header at all (meaning that the whole
' file was requested)
' Returns False, if the Range header asked for unsatisfieable
' ranges
' Retrieve Range Header value from Request (Empty if none is indicated)
sSource = RetrieveHeader(objRequest, HTTP_HEADER_RANGE, String.Empty)
If sSource.Equals(String.Empty) Then
' No Range was requested, return the entire file range...
ReDim lBegin(0)
ReDim lEnd(0)
lBegin(0) = 0
lEnd(0) = lMax - 1
' A valid range is returned
bValidRanges = True
' no Range request
bRangeRequest = False
Else
' A Range was requested...
' Preset value...
bValidRanges = True
' Return True for the bRange parameter, telling the caller
' that the Request is indeed a Range request...
bRangeRequest = True
' Remove "bytes=" from the beginning, and split the remaining
' string by comma characters
sRanges = sSource.Replace("bytes=", "").Split(",".ToCharArray)
ReDim lBegin(sRanges.GetUpperBound(0))
ReDim lEnd(sRanges.GetUpperBound(0))
' Check each found Range request for consistency
For iLoop = sRanges.GetLowerBound(0) To sRanges.GetUpperBound(0)
' Split this range request by the dash character,
' sRange(0) contains the requested begin-value,
' sRange(1) contains the requested end-value...
Dim sRange() As String = sRanges(iLoop).Split("-".ToCharArray)
' Determine the end of the requested range
If sRange(1).Equals(String.Empty) Then
' No end was specified, take the entire range
lEnd(iLoop) = lMax - 1
Else
' An end was specified...
lEnd(iLoop) = Long.Parse(sRange(1))
End If
' Determine the begin of the requested range
If sRange(0).Equals(String.Empty) Then
' No begin was specified, which means that
' the end value indicated to return the last n
' bytes of the file:
' Calculate the begin
lBegin(iLoop) = lMax - 1 - lEnd(iLoop)
' ... to the end of the file...
lEnd(iLoop) = lMax - 1
Else
' A normal begin value was indicated...
lBegin(iLoop) = Long.Parse(sRange(0))
End If
' Check if the requested range values are valid,
' return False if they are not.
'
' Note:
' Do not clean invalid values up by fitting them into
' valid parameters using Math.Min and Math.Max, because
' some download clients (like Go!Zilla) might send invalid
' (e.g. too large) range requests to determine the file limits!
' Begin and end must not exceed the file size
If (lBegin(iLoop) > (lMax - 1)) Or (lEnd(iLoop) > (lMax - 1)) Then
bValidRanges = False
End If
' Begin and end cannot be < 0
If (lBegin(iLoop) < 0) Or (lEnd(iLoop) < 0) Then
bValidRanges = False
End If
' End must be larger or equal to begin value
If lEnd(iLoop) < lBegin(iLoop) Then
' The requested Range is invalid...
bValidRanges = False
End If
Next iLoop
End If
Return bValidRanges
End Function
Private Function RetrieveHeader(ByVal objRequest As HttpRequest, ByVal
sHeader As String, ByVal sDefault As String) As String
Dim sReturn As String
' Retrieves the indicated Header's value from the Request,
' if the header was not sent, sDefault is returned.
'
' If the value contains quote characters, they are removed.
sReturn = objRequest.Headers.Item(sHeader)
If (sReturn Is Nothing) OrElse sReturn.Equals(String.Empty) Then
' The Header wos not found in the Request,
' return the indicated default value...
Return sDefault
Else
' Return the found header value, stripped of any quote characters...
Return sReturn.Replace("""", "")
End If
End Function
Private Function GenerateHash(ByVal objStream As System.IO.Stream, ByVal
lBegin As Long, ByVal lEnd As Long) As String
Dim bByte(Convert.ToInt32(lEnd)) As Byte
objStream.Read(bByte, Convert.ToInt32(lBegin), Convert.ToInt32(lEnd -
lBegin) + 1)
'Instantiate an MD5 Provider object
Dim Md5 As New System.Security.Cryptography.MD5CryptoServiceProvider
'Compute the hash value from the source
Dim ByteHash() As Byte = Md5.ComputeHash(bByte)
'And convert it to String format for return
Return Convert.ToBase64String(ByteHash)
End Function
#End Region
End Class
*********END CODE****