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/*++

Copyright (c) 1993-2000 Microsoft Corporation.  All rights reserved.

Module Name:

    pppframe.c

Abstract:

Environment:

--*/

#include "windows.h"
#include "tapi.h"
#include "ndis.h"
#include "ndiswan.h"
#include "ndistapi.h"
#include "asyncmac.h"
#include "frame.h"


VOID
AssembleSLIPFrame(
    IN        PASYNCMAC_OPEN_LINE pOpenLine,
    IN    OUT    PNDIS_WAN_PACKET    WanPacket)
//
//    Encode an IP packet into a SLIP frame. 
//
//             +---------------------+
//             | IP packet           |
//             +---------------------+
//            /                       \
//           /                         \
//       +--+---------------------------+--+
//       |C0| Escaped IP packet         |C0|
//       +--+---------------------------+--+
//
//    The transformation is done within the WanPacket buffer.
//    Recall that in the function MpInit we set the HeaderPadding in the WAN_INFO structure
//    to a sufficient size to allow for the addition of the leading flag and the expansion
//  of the PPP frame data.  Also, the TailPadding was set to allow for the addition of
//  the escaped CRC and trailing flag.
//
{
    PUCHAR        pOldFrame;
    PUCHAR        pNewFrame;
    int            dataSize;
    UCHAR        c;

    ASSERT(WanPacket->StartBuffer   <= WanPacket->EndBuffer);
    ASSERT(WanPacket->StartBuffer   <= WanPacket->CurrentBuffer);
    ASSERT(WanPacket->CurrentBuffer + WanPacket->CurrentLength <= WanPacket->EndBuffer);

    //
    // Initialize locals
    //

    pOldFrame = WanPacket->CurrentBuffer;

    pNewFrame = WanPacket->StartBuffer;

    //
    // for quicker access, get a copy of data length field
    //
    dataSize = WanPacket->CurrentLength;

    *pNewFrame++ = SLIP_END; //  mark beginning of frame

    //
    // Copy oldFrame to newFrame, escaping all ESC and END chars
    //
    while (dataSize--)
    {
        c = *pOldFrame++;


        //
        // Make sure we aren't overwriting the next byte of the old frame to be processed
        //
        ASSERT(dataSize == 0 || pNewFrame != pOldFrame);

        //
        // Check if we have to escape out this byte or not
        //
        if (c == SLIP_ESC)
        {
            *pNewFrame++ = SLIP_ESC;
            c = SLIP_ESC_ESC;
        }
        else if (c == SLIP_END)
        {
            *pNewFrame++ = SLIP_ESC;
            c = SLIP_ESC_END;
        }

        ASSERT(dataSize == 0 || pNewFrame != pOldFrame);

        *pNewFrame++ = c;
    }

    //
    // Mark end of frame
    //
    *pNewFrame++ = SLIP_END;

    //
    // Calc how many bytes we expanded to including start and end bytes
    //
    WanPacket->CurrentLength = (ULONG)(pNewFrame - WanPacket->StartBuffer);

    //
    // Put in the adjusted length -- actual num of bytes to send
    //

    WanPacket->CurrentBuffer = WanPacket->StartBuffer;

    DEBUGMSG(ZONE_SEND | ZONE_FUNCTION, 
        (TEXT("PPP: -AssembleSLIPFrame: Frame: start=%x end=%x length=%x\n"), WanPacket->CurrentBuffer, pNewFrame, WanPacket->CurrentLength));

    ASSERT(WanPacket->CurrentBuffer + WanPacket->CurrentLength <= WanPacket->EndBuffer);
}