MailSlot

trancexx · March 16, 2011

"...Mailslot messages can be of around 400 bytes only.", please check this link: http://www.codeproject.com/KB/threads/Win32IPC.aspx
"...cannot be larger than 424 bytes when sent between computers.", and this: http://msdn.microsoft.com/en-us/library/aa365130%28v=vs.85%29.aspx

Aha, between computers. You are right then.

edit: seems Melba23 knows something about that, I haven't used this between computers since initial testings when writing it. Frankly, I don't remember having problems.

Edited March 16, 2011 by trancexx

JScript · March 16, 2011

jscript,
(...)
Certainly I have never had any trouble sending more than 425 bytes to multiple receiver scripts using the mailslot.
M23

Yes, I saw...

JScript · March 16, 2011

Aha, between computers. You are right then.
edit: seems Melba23 knows something about that, I haven't used this between computers since initial testings when writing it. Frankly, I don't remember having problems.

Yes! (...)To send messages that are larger than 424 bytes between computers, use named pipes instead.

Could you give me an example of using NamedPipes because the AutoIt help file is not in any instance...

Thank you all for attention.

Edit: Using your example, I can not transmit more than 424 bytes (between escrips, not between computers).

Edited March 16, 2011 by jscript

Melba23 · March 16, 2011

jscript & trancexx,

Sorry, I too missed the "between computers" bit - I have only ever used mailslots on the same machine.

M23

JScript · March 16, 2011

jscript & trancexx,
Sorry, I too missed the "between computers" bit - I have only ever used mailslots on the same machine.
M23

OK, but using the example of @trancexx, I can not transmit more than 425 bytes!

Edit: in the same computer...

Edited March 16, 2011 by jscript

Melba23 · March 16, 2011

jscript,

I sent over 1000 bytes between scripts on the same machine without problem earlier today. I did it to test I could before replying to you.

I am using trancexx's UDF with the following script (based on her example). Just compile it and then copy and rename it so you can run several differently named instances:

#AutoIt3Wrapper_Au3Check_Parameters=-d -w 1 -w 2 -w 3 -w 4 -w 5 -w 6

#include "MailSlot.au3"

Global $sMailSlotListFile = @AppDataCommonDir & "\MailSlot\MailSlotList.lst"
Global $sMailSlotTitle = StringRegExpReplace(@ScriptName, "\..*$", "")
Global $sRandomMailSlotname = _RandomStr()

ConsoleWrite( $sMailSlotListFile  & @CRLF)

Global Const $sMailSlotName_Receive = "\\.\mailslot\" & $sRandomMailSlotname

; Add MailSlot to list file
IniWrite($sMailSlotListFile, "MailSlots", $sMailSlotTitle, $sRandomMailSlotname)

Global $hMailSlot = _MailSlotCreate($sMailSlotName_Receive)
If @error Then
    MsgBox(48, "MailSlot", "Failed to create new account!" & @CRLF & "Probably one using that 'address' already exists.")
    Exit
EndIf

Global $iNumberOfMessagesOverall
Global $sMailSlotName_Send = ""

Global $hGUI = GUICreate($sMailSlotTitle, 450, 400, 3 * @DesktopWidth / 4 - 225, -1, -1, 8) ; $WS_EX_TOPMOST

GUICtrlCreateLabel("Message To Send To:", 10, 22, 150, 25)
GUICtrlSetColor(-1, 0x0000CC)
GUICtrlSetFont(-1, 11)

Global $hSend_Combo = GUICtrlCreateCombo("", 180, 22, 100, 25)
_UpdateMail()

Global $hEdit_Send = GUICtrlCreateEdit("", 15, 50, 300, 50, 0x0040) ; $ES_AUTOVSCROLL

GUICtrlCreateLabel("Message Received:", 10, 122, 150, 25)
GUICtrlSetColor(-1, 0x0000CC)
GUICtrlSetFont(-1, 11)

Global $hEdit_Read = GUICtrlCreateEdit("", 15, 150, 300, 200, 0x0800) ; $ES_READONLY

Global $hButtonSend = GUICtrlCreateButton("&Send Mail", 330, 100, 100, 25)

Global $hButton_Update = GUICtrlCreateButton("&Update Accounts", 330, 50, 100, 25)

Global $hButtonRead = GUICtrlCreateButton("Read &Mail", 330, 150, 100, 25)

Global $hButtonCheckCount = GUICtrlCreateButton("&Check Mail Count", 330, 200, 100, 25)

Global $hButtonCloseAccount = GUICtrlCreateButton("Close Mail &Account", 330, 250, 100, 25)

Global $hButtonRestoreAccount = GUICtrlCreateButton("&Restore Account", 330, 300, 100, 25)

Global $hButtonCloseApp = GUICtrlCreateButton("&Exit", 330, 350, 100, 25)

GUISetState()

While 1

    Switch GUIGetMsg()
        Case - 3, $hButtonCloseApp
            IniDelete($sMailSlotListFile, "MailSlots", $sMailSlotTitle)
            Exit
        Case $hButtonSend
            If GUICtrlRead($hSend_Combo) = "" Then
                MsgBox(64, "MailSlot demo", "No account selected!", 0, $hGUI)
            Else
                $sMailSlotName_Send = "\\.\mailslot\" & IniRead($sMailSlotListFile, "MailSlots", GUICtrlRead($hSend_Combo), "")
                If $sMailSlotName_Send <> "\\.\mailslot\" Then
                    _SendMail($sMailSlotName_Send)
                Else
                    MsgBox(48, "MailSlot demo", "Not valid account!", 0, $hGUI)
                EndIf
            EndIf
        Case $hButton_Update
            _UpdateMail()
        Case $hButtonRead
            If $hMailSlot Then
                _ReadMessage($hMailSlot)
            Else
                MsgBox(48, "MailSlot demo", "No account is available!", 0, $hGUI)
            EndIf
        Case $hButtonCheckCount
            If $hMailSlot Then
                _CheckCount($hMailSlot)
            Else
                MsgBox(48, "MailSlot demo", "No account is available!", 0, $hGUI)
            EndIf
        Case $hButtonCloseAccount
            If $hMailSlot Then
                _CloseMailAccount($hMailSlot)
            Else
                MsgBox(64, "MailSlot demo", "No account is available!", 0, $hGUI)
            EndIf
        Case $hButtonRestoreAccount
            If $hMailSlot Then
                MsgBox(64, "MailSlot demo", "This account already exists!", 0, $hGUI)
            Else
                _RestoreAccount($sMailSlotName_Receive)
            EndIf
    EndSwitch

WEnd


; Wrapper functions:

Func _UpdateMail()

    Local $aMailSlots = IniReadSection($sMailSlotListFile, "MailSlots")

    If Not IsArray($aMailSlots) Then MsgBox(64, "MailSlot demo", "No accounts available!", 0, $hGUI)

    Local $sMailSlotList = "|"
    For $i = 1 To $aMailSlots[0][0]
        If $aMailSlots[$i][1] <> $sRandomMailSlotname Then $sMailSlotList &= $aMailSlots[$i][0] & "|"
    Next
    GUICtrlSetData($hSend_Combo, $sMailSlotList)

EndFunc

Func _SendMail($sMailSlotName)

    Local $sDataToSend = GUICtrlRead($hEdit_Send)

    If $sDataToSend Then
        _MailSlotWrite($sMailSlotName, $sDataToSend);, 1)
        Switch @error
            Case 1
                MsgBox(48, "MailSlot demo error", "Account that you try to send to likely doesn't exist!", 0, $hGUI)
            Case 2
                MsgBox(48, "MailSlot demo error", "Message is blocked!", 0, $hGUI)
            Case 3
                MsgBox(48, "MailSlot demo error", "Message is send but there is an open handle left." & @CRLF & "That could lead to possible errors in future", 0, $hGUI)
            Case 4
                MsgBox(48, "MailSlot demo error", "All is fucked up!" & @CRLF & "Try debugging MailSlot.au3 functions. Thanks.", 0, $hGUI)
            Case Else
                MsgBox(64, "MailSlot demo", "Sucessfully sent!", 0, $hGUI)
        EndSwitch
        GUICtrlSetData($hEdit_Send, "")
    Else
        MsgBox(64, "MailSlot demo", "Nothing to send.", 0, $hGUI)
    EndIf

EndFunc   ;==>_SendMail

Func _ReadMessage($hHandle)

    Local $iSize = _MailSlotCheckForNextMessage($hHandle)

    If $iSize Then
        Local $sData = _MailSlotRead($hMailSlot, $iSize, 1)
        $iNumberOfMessagesOverall += 1
        GUICtrlSetData($hEdit_Read, "Message No" & $iNumberOfMessagesOverall & " , Size = " & $iSize & " :" & @CRLF & @CRLF & $sData)
    Else
        MsgBox(64, "Nothing read", "MailSlot is empty", 0, $hGUI)
    EndIf

EndFunc   ;==>_ReadMessage


Func _CheckCount($hHandle)

    Local $iCount = _MailSlotGetMessageCount($hHandle)
    Switch $iCount
        Case 0
            MsgBox(64, "Messages", "No new messages", 0, $hGUI)
        Case 1
            MsgBox(64, "Messages", "There is 1 message waiting to be read.", 0, $hGUI)
        Case Else
            MsgBox(64, "Messages", "There are " & $iCount & " messages waiting to be read.", 0, $hGUI)
    EndSwitch

EndFunc   ;==>_CheckCount


Func _CloseMailAccount(ByRef $hHandle)

    If _MailSlotClose($hHandle) Then
        $hHandle = 0
        MsgBox(64, "MailSlot demo", "Account succesfully closed.", 0, $hGUI)
        IniDelete($sMailSlotListFile, "MailSlots", $sMailSlotTitle)
    Else
        MsgBox(48, "MailSlot demo error", "Account could not be closed!", 0, $hGUI)
    EndIf

EndFunc   ;==>_CloseMailAccount


Func _RestoreAccount($sMailSlotName_Receive)

    Local $hMailSlotHandle = _MailSlotCreate($sMailSlotName_Receive)

    If @error Then
        MsgBox(48, "MailSlot demo error", "Account could not be created!", 0, $hGUI)
    Else
        MsgBox(64, "MailSlot demo", "New account with the same address successfully created!", 2, $hGUI)
        $hMailSlot = $hMailSlotHandle ; global var
        IniWrite($sMailSlotListFile, "MailSlots", $sMailSlotTitle, $sRandomMailSlotname)
    EndIf

EndFunc   ;==>_RestoreAccount

Func _RandomStr()
    Local $sString
    For $i = 1 To 13
        $sString &= Chr(Random(97, 122, 1))
    Next
    Return $sString
EndFunc   ;==>__RandomStr

You need to press the "Update Accounts" button on the earlier instances when you have all of them running so the earlier ones realise the later ones have come along - otherwise your addess list is not complete. The same is true if you close and restore an account.

M23

JScript · March 16, 2011

jscript,
I sent over 1000 bytes between scripts on the same machine without problem earlier today. I did it to test I could before replying to you.
I am using trancexx's UDF with the following script (based on her example). Just compile it and then copy and rename it so you can run several differently named instances:
(...)
M23

Yes, it works on the same computer. But between computers 425 bytes.

NamedPipes there is no such limit, but do not know how to use it because in the AutoIt help file does not exist examples...

Could you give me an example using NamedPipes?

Because that way I would let the use TCP protocol to a communication program between computers on same network.

Thank you for your attention.

Melba23 · March 16, 2011

jscript,

Could you give me an example using NamedPipes?

Sorry, I have never used them and there is precious little when you search the forum.

M23

trancexx · March 16, 2011

Well, you can send data over more than one message.

JScript · March 16, 2011

@Melba23,

No problem...

@trancexx,

Yes, to circumvent this limitation, I'm using the following code below:

Local $iSize = Int(StringLen($sDataToSend) / 420)
For $i = 0 To $iSize
    _MailSlotWrite($sMailSlotName, StringMid($sDataToSend, $i * 420 + 1, 420))
Next
;_MailSlotWrite($sMailSlotName, $sDataToSend);, 1)

But I will try to use NamedPipes because I do not need this modification to transmit more than 425 bytes...

Thank you for your attention.

Digisoul · May 16, 2011

Hi trancexx,

I want to know that how can I use the mailslots in multiple sessions ?

I mean, I created a Slot in "System Account" and when my user mode app in "Administrator/Limited Account" try to open the handle of Service Slot, it will give "Access is Denied" (by GetLastErrorMessage ).

Edited May 16, 2011 by Digisoul

JScript · May 16, 2011

Hi trancexx,
I want to know that how can I use the mailslots in multiple sessions ?
I mean, I created a Slot in "System Account" and when my user mode app in "Administrator/Limited Account" try to open the handle of Service Slot, it will give "Access is Denied" (by GetLastErrorMessage ).

Why you run a program in "System Account"? Your intentions are good?

Digisoul · May 16, 2011

Why you run a program in "System Account"? Your intentions are good?

Yes! as a service process. I am using service for Service Control notifications and my application is a multi user and a security app (for USB Devices).

I found the problem, why its not working; I need to set the lpSecurityDescriptor but i am unable to understand it.

Edited May 16, 2011 by Digisoul

Digisoul · May 16, 2011

Hi trancexx,

I want to know that how can I use the mailslots in multiple sessions ?
I mean, I created a Slot in "System Account" and when my user mode app in "Administrator/Limited Account" try to open the handle of Service Slot, it will give "Access is Denied" (by GetLastErrorMessage ).

I found the solution Posted Image

Here is a function; If any body have a same problem (Its already exists in Misc.au3 as _Singleton Posted Image )

; Author ........: Valik
Func GetSecurity(ByRef $structSecurityDescriptor)
    Local Const $ERROR_ALREADY_EXISTS = 183
    Local Const $SECURITY_DESCRIPTOR_REVISION = 1
    Local $handle, $lastError, $pSecurityAttributes = 0

    ; The size of SECURITY_DESCRIPTOR is 20 bytes.  We just
    ; need a block of memory the right size, we aren't going to
    ; access any members directly so it's not important what
    ; the members are, just that the total size is correct.
    $structSecurityDescriptor = DllStructCreate("dword[5]")
    Local $pSecurityDescriptor = DllStructGetPtr($structSecurityDescriptor)
    ; Initialize the security descriptor.
    Local $aRet = DllCall("advapi32.dll", "int", "InitializeSecurityDescriptor", _
            "ptr", $pSecurityDescriptor, "dword", $SECURITY_DESCRIPTOR_REVISION)
    If Not @error And $aRet[0] Then
        ; Add the NULL DACL specifying access to everybody.
        $aRet = DllCall("advapi32.dll", "int", "SetSecurityDescriptorDacl", _
                "ptr", $pSecurityDescriptor, "int", 1, "ptr", 0, "int", 0)
        If Not @error And $aRet[0] Then
            ; Create a SECURITY_ATTRIBUTES structure.
            Local $structSecurityAttributes = DllStructCreate("dword;ptr;int")
            ; Assign the members.
            DllStructSetData($structSecurityAttributes, 1, DllStructGetSize($structSecurityAttributes))
            DllStructSetData($structSecurityAttributes, 2, $pSecurityDescriptor)
            DllStructSetData($structSecurityAttributes, 3, 0)
            ; Everything went okay so update our pointer to point to our structure.
            $pSecurityAttributes = DllStructGetPtr($structSecurityAttributes)
            Return SetError(0, 0, $pSecurityAttributes)
        Else
            Return SetError(2)
        EndIf
    Else
        Return SetError(1)
    EndIf
EndFunc   ;==>GetSecurity

Reaper HGN · September 13, 2011

I know this is old, but I wanted to say how awesome this UDF is. Thank you. I wrote a script that does a lot of processing of the same rules against data. I am able to 10x the speed simply by spinning off 10 processes, each with their own mailslot. I think scan the slots and simply send a chunk of data when a slot is available. If I want to improve performance further, I simply scale up the processes (takes more memory, sure). Great work on this. If anyone is interested in IPC in AutoIt, this is a great way.

SSzretter · April 6, 2014

Will this work between an auto-it script running as a system service, and an auto-it running under the local user?

I am finding that the service is able to create a mail slot, send a message to it, and retrieve messages from it.

However, the auto-it running under the logged in user process is not able to send a message to that mail slot. It throws an @error "1".

Possibly some kind of permissions issue?

Is there something I can do, or some other option to allow communication between these two auto-its (service / user)?

trancexx · April 7, 2014

Security attributes parameter for CreateMailslot function needs adjusted for that.

It's rather simple task, so google a bit, it's been explained many times.

SSzretter · April 7, 2014

Security attributes parameter for CreateMailslot function needs adjusted for that.
It's rather simple task, so google a bit, it's been explained many times.

Um, if you could spare a few moments to point me at something, it would be greatly appreciated - I already did spend some time searching and I cant find anything.

TheDcoder · April 11, 2015

Pretty old UDF but Pretty useful though, 5 stars from me!!!

TD

Lecdev · July 15, 2018

I know this is pretty old now but i was trying to get comms accross local system, admin and limited users for months in windows 10 and was just not having any luck with anything at all.

ended up finding this solution, CreateFileW kernel32 dll call to create the handle to write the message in mailslot.au3 had to be changed because it still worked between admin and another limited user as it was, but not from local system to any other user.

had to change the file attributes to normal instead of the original flag $SECURITY_ANONYMOUS. see below

only after this would the security attributes pointer used to create the mailslot actually take affect on the system account.

Func _MailSlotWrite($sMailSlotName, $vData, $iMode = 0)

    Local $aCall = DllCall("kernel32.dll", "ptr", "CreateFileW", _
            "wstr", $sMailSlotName, _
            "dword", 0x40000000, _ ; GENERIC_WRITE
            "dword", 1, _ ; FILE_SHARE_READ
            "ptr", 0, _  ; lp security attributes (ignored on open existing)
            "dword", 3, _ ; OPEN_EXISTING
            "dword", 128, _ ; 0, _ ; SECURITY_ANONYMOUS  replaced with file attribute normal 128
            "ptr", 0)
            
            
            ; .........

above now works when creating the mailslot with a security pointer which i have used permissions.au3 udf to create, shown below.

#include "MailSlot.au3"

#include <Permissions.au3>

Global Const $sMailSlotName = "\\.\mailslot\SampleCrossSessonMailslot"
Global $ptrSecurityDescriptor = _ConvertStringSecurityDescriptorToSecurityDescriptor("O:BAD:(A;OICI;GRGW;;;AU)(A;OICI;GA;;;BA)(A;OICI;GA;;;SY)")
    If @error Then
        Global $aError = DllCall("kernel32.dll", "dword", "GetLastError")
        if not @Compiled Then ConsoleWrite("err: " & $aError[0] & @CR)
    EndIf
    Global $tSecurityAttributes = DllStructCreate("dword Length;ptr Descriptor;bool InheritHandle")
    DllStructSetData($tSecurityAttributes, 1, DllStructGetSize($tSecurityAttributes))
    DllStructSetData($tSecurityAttributes, 2, DllStructGetPtr($ptrSecurityDescriptor))
    DllStructSetData($tSecurityAttributes, 3, 0) ; InheritHandle = FALSE
Global $hMailSlot = _MailSlotCreate($sMailSlotName,0,0,$tSecurityAttributes)

hopefully this saves someone else from banging their head against the wall.

MailSlot

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