llxfermanager.cpp

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#include "linden_common.h"

#include "llxfermanager.h"

#include "llxfer.h"
#include "llxfer_file.h"
#include "llxfer_mem.h"
#include "llxfer_vfile.h"

#include "llerror.h"
#include "lluuid.h"
#include "u64.h"

const F32 LL_XFER_REGISTRATION_TIMEOUT = 60.0f;  // timeout if a registered transfer hasn't been requested in 60 seconds
const F32 LL_PACKET_TIMEOUT = 3.0f;             // packet timeout at 3 s
const S32 LL_PACKET_RETRY_LIMIT = 10;            // packet retransmission limit

const S32 LL_DEFAULT_MAX_SIMULTANEOUS_XFERS = 10;
const S32 LL_DEFAULT_MAX_REQUEST_FIFO_XFERS = 1000;

#define LL_XFER_PROGRESS_MESSAGES 0
#define LL_XFER_TEST_REXMIT       0



LLXferManager::LLXferManager (LLVFS *vfs)
{
        init(vfs);
}


LLXferManager::~LLXferManager ()
{
        free();
}


void LLXferManager::init (LLVFS *vfs)
{
        mSendList = NULL;
        mReceiveList = NULL;

        setMaxOutgoingXfersPerCircuit(LL_DEFAULT_MAX_SIMULTANEOUS_XFERS);
        setMaxIncomingXfers(LL_DEFAULT_MAX_REQUEST_FIFO_XFERS);

        mVFS = vfs;

        // Turn on or off ack throttling
        mUseAckThrottling = FALSE;
        setAckThrottleBPS(100000);
}
        

void LLXferManager::free ()
{
        LLXfer *xferp;
        LLXfer *delp;
        
        mOutgoingHosts.deleteAllData();

        delp = mSendList;
        while (delp)
        {
                xferp = delp->mNext;
                delete delp;
                delp = xferp;
        }
        mSendList = NULL;

        delp = mReceiveList;
        while (delp)
        {
                xferp = delp->mNext;
                delete delp;
                delp = xferp;
        }
        mReceiveList = NULL;
}


void LLXferManager::setMaxIncomingXfers(S32 max_num)
{
        mMaxIncomingXfers = max_num;
}


void LLXferManager::setMaxOutgoingXfersPerCircuit(S32 max_num)
{
        mMaxOutgoingXfersPerCircuit = max_num;
}

void LLXferManager::setUseAckThrottling(const BOOL use)
{
        mUseAckThrottling = use;
}

void LLXferManager::setAckThrottleBPS(const F32 bps)
{
        // Let's figure out the min we can set based on the ack retry rate
        // and number of simultaneous.

        // Assuming we're running as slow as possible, this is the lowest ack
        // rate we can use.
        F32 min_bps = (1000.f * 8.f* mMaxIncomingXfers) / LL_PACKET_TIMEOUT;

        // Set
        F32 actual_rate = llmax(min_bps*1.1f, bps);
        llinfos << "LLXferManager ack throttle min rate: " << min_bps << llendl;
        llinfos << "LLXferManager ack throttle actual rate: " << actual_rate << llendl;
        mAckThrottle.setRate(actual_rate);
}



void LLXferManager::updateHostStatus()
{
    LLXfer *xferp;
        LLHostStatus *host_statusp = NULL;

        mOutgoingHosts.deleteAllData();

        for (xferp = mSendList; xferp; xferp = xferp->mNext)
        {
                for (host_statusp = mOutgoingHosts.getFirstData(); host_statusp; host_statusp = mOutgoingHosts.getNextData())
                {
                        if (host_statusp->mHost == xferp->mRemoteHost)
                        {
                                break;
                        }
                }
                if (!host_statusp)
                {
                        host_statusp = new LLHostStatus();
                        if (host_statusp)
                        {
                                host_statusp->mHost = xferp->mRemoteHost;
                                mOutgoingHosts.addData(host_statusp);
                        }
                }
                if (host_statusp)
                {
                        if (xferp->mStatus == e_LL_XFER_PENDING)
                        {
                                host_statusp->mNumPending++;
                        }
                        else if (xferp->mStatus == e_LL_XFER_IN_PROGRESS)
                        {
                                host_statusp->mNumActive++;
                        }
                }
                
        }       
}


void LLXferManager::printHostStatus()
{
        LLHostStatus *host_statusp = NULL;
        if (mOutgoingHosts.getFirstData())
        {
                llinfos << "Outgoing Xfers:" << llendl;

                for (host_statusp = mOutgoingHosts.getFirstData(); host_statusp; host_statusp = mOutgoingHosts.getNextData())
                {
                        llinfos << "    " << host_statusp->mHost << "  active: " << host_statusp->mNumActive << "  pending: " << host_statusp->mNumPending << llendl;
                }
        }       
}


LLXfer *LLXferManager::findXfer (U64 id, LLXfer *list_head)
{
    LLXfer *xferp;
        for (xferp = list_head; xferp; xferp = xferp->mNext)
        {
                if (xferp->mID == id)
                {
                        return(xferp);
                }
        }
        return(NULL);
}



void LLXferManager::removeXfer (LLXfer *delp, LLXfer **list_head)
{
        // This function assumes that delp will only occur in the list
        // zero or one times.
        if (delp)
        {
                if (*list_head == delp)
                {
                        *list_head = delp->mNext;
                        delete (delp);
                }
                else
                {
                        LLXfer *xferp = *list_head;
                        while (xferp->mNext)
                        {
                                if (xferp->mNext == delp)
                                {
                                        xferp->mNext = delp->mNext;
                                        delete (delp);
                                        break;
                                }
                                xferp = xferp->mNext;
                        }
                }
        }
}


U32 LLXferManager::numActiveListEntries(LLXfer *list_head)
{
        U32 num_entries = 0;

        while (list_head)
        {
                if ((list_head->mStatus == e_LL_XFER_IN_PROGRESS)) 
                {
                        num_entries++;
                }
                list_head = list_head->mNext;
        }
        return(num_entries);
}


S32 LLXferManager::numPendingXfers(const LLHost &host)
{
        LLHostStatus *host_statusp = NULL;

        for (host_statusp = mOutgoingHosts.getFirstData(); host_statusp; host_statusp = mOutgoingHosts.getNextData())
        {
                if (host_statusp->mHost == host)
                {
                        return (host_statusp->mNumPending);
                }
        }
        return 0;
}


S32 LLXferManager::numActiveXfers(const LLHost &host)
{
        LLHostStatus *host_statusp = NULL;

        for (host_statusp = mOutgoingHosts.getFirstData(); host_statusp; host_statusp = mOutgoingHosts.getNextData())
        {
                if (host_statusp->mHost == host)
                {
                        return (host_statusp->mNumActive);
                }
        }
        return 0;
}


void LLXferManager::changeNumActiveXfers(const LLHost &host, S32 delta)
{
        LLHostStatus *host_statusp = NULL;

        for (host_statusp = mOutgoingHosts.getFirstData(); host_statusp; host_statusp = mOutgoingHosts.getNextData())
        {
                if (host_statusp->mHost == host)
                {
                        host_statusp->mNumActive += delta;
                }
        }
}


void LLXferManager::registerCallbacks(LLMessageSystem *msgsystem)
{
        msgsystem->setHandlerFuncFast(_PREHASH_ConfirmXferPacket,  process_confirm_packet, NULL);
        msgsystem->setHandlerFuncFast(_PREHASH_RequestXfer,        process_request_xfer,        NULL);
        msgsystem->setHandlerFuncFast(_PREHASH_SendXferPacket,          continue_file_receive,           NULL);
        msgsystem->setHandlerFuncFast(_PREHASH_AbortXfer,               process_abort_xfer,                  NULL);
}


U64 LLXferManager::getNextID ()
{
        LLUUID a_guid;

        a_guid.generate();

        
        return(*((U64*)(a_guid.mData)));
}


S32 LLXferManager::encodePacketNum(S32 packet_num, BOOL is_EOF)
{
        if (is_EOF)
        {
                packet_num |= 0x80000000;
        }
        return packet_num;
}


S32 LLXferManager::decodePacketNum(S32 packet_num)
{
        return(packet_num & 0x0FFFFFFF);
}


BOOL LLXferManager::isLastPacket(S32 packet_num)
{
        return(packet_num & 0x80000000);
}


U64 LLXferManager::registerXfer(const void *datap, const S32 length)
{
        LLXfer *xferp;
        U64 xfer_id = getNextID();

        xferp = (LLXfer *) new LLXfer_Mem();
        if (xferp)
        {
                xferp->mNext = mSendList;
                mSendList = xferp;

                xfer_id = ((LLXfer_Mem *)xferp)->registerXfer(xfer_id, datap,length);

                if (!xfer_id)
                {
                        removeXfer(xferp,&mSendList);
                }
        }
        else
        {
                llerrs << "Xfer allocation error" << llendl;
                xfer_id = 0;
        }       

    return(xfer_id);
}


void LLXferManager::requestFile(const char* local_filename,
                                                                const char* remote_filename,
                                                                ELLPath remote_path,
                                                                const LLHost& remote_host,
                                                                BOOL delete_remote_on_completion,
                                                                void (*callback)(void**,S32,LLExtStat),
                                                                void** user_data,
                                                                BOOL is_priority,
                                                                BOOL use_big_packets)
{
        LLXfer *xferp;

        for (xferp = mReceiveList; xferp ; xferp = xferp->mNext)
        {
                if (xferp->getXferTypeTag() == LLXfer::XFER_FILE
                        && (((LLXfer_File*)xferp)->matchesLocalFilename(local_filename))
                        && (((LLXfer_File*)xferp)->matchesRemoteFilename(remote_filename, remote_path))
                        && (remote_host == xferp->mRemoteHost)
                        && (callback == xferp->mCallback)
                        && (user_data == xferp->mCallbackDataHandle))

                {
                        // cout << "requested a xfer already in progress" << endl;
                        return;
                }
        }

        S32 chunk_size = use_big_packets ? LL_XFER_LARGE_PAYLOAD : -1;
        xferp = (LLXfer *) new LLXfer_File(chunk_size);
        if (xferp)
        {
                addToList(xferp, mReceiveList, is_priority);

                // Remove any file by the same name that happens to be lying
                // around.
                // Note: according to AaronB, this is here to deal with locks on files that were
                // in transit during a crash,
                if(delete_remote_on_completion &&
                   (strstr(remote_filename,".tmp") == &remote_filename[strlen(remote_filename)-4]))             /* Flawfinder : ignore */
                {
                        LLFile::remove(local_filename);
                }
                ((LLXfer_File *)xferp)->initializeRequest(
                        getNextID(),
                        local_filename,
                        remote_filename,
                        remote_path,
                        remote_host,
                        delete_remote_on_completion,
                        callback,user_data);
                startPendingDownloads();
        }
        else
        {
                llerrs << "Xfer allocation error" << llendl;
        }
}

void LLXferManager::requestFile(const char* remote_filename,
                                                                ELLPath remote_path,
                                                                const LLHost& remote_host,
                                                                BOOL delete_remote_on_completion,
                                                                void (*callback)(void*,S32,void**,S32,LLExtStat),
                                                                void** user_data,
                                                                BOOL is_priority)
{
        LLXfer *xferp;

        xferp = (LLXfer *) new LLXfer_Mem();
        if (xferp)
        {
                addToList(xferp, mReceiveList, is_priority);
                ((LLXfer_Mem *)xferp)->initializeRequest(getNextID(),
                                                                                                 remote_filename, 
                                                                                                 remote_path,
                                                                                                 remote_host,
                                                                                                 delete_remote_on_completion,
                                                                                                 callback, user_data);
                startPendingDownloads();
        }
        else
        {
                llerrs << "Xfer allocation error" << llendl;
        }
}

void LLXferManager::requestVFile(const LLUUID& local_id,
                                                                 const LLUUID& remote_id,
                                                                 LLAssetType::EType type, LLVFS* vfs,
                                                                 const LLHost& remote_host,
                                                                 void (*callback)(void**,S32,LLExtStat),
                                                                 void** user_data,
                                                                 BOOL is_priority)
{
        LLXfer *xferp;

        for (xferp = mReceiveList; xferp ; xferp = xferp->mNext)
        {
                if (xferp->getXferTypeTag() == LLXfer::XFER_VFILE
                        && (((LLXfer_VFile*)xferp)->matchesLocalFile(local_id, type))
                        && (((LLXfer_VFile*)xferp)->matchesRemoteFile(remote_id, type))
                        && (remote_host == xferp->mRemoteHost)
                        && (callback == xferp->mCallback)
                        && (user_data == xferp->mCallbackDataHandle))

                {
                        // cout << "requested a xfer already in progress" << endl;
                        return;
                }
        }

        xferp = (LLXfer *) new LLXfer_VFile();
        if (xferp)
        {
                addToList(xferp, mReceiveList, is_priority);
                ((LLXfer_VFile *)xferp)->initializeRequest(getNextID(),
                        vfs,
                        local_id,
                        remote_id,
                        type,
                        remote_host,
                        callback,
                        user_data);
                startPendingDownloads();
        }
        else
        {
                llerrs << "Xfer allocation error" << llendl;
        }

}

/*
void LLXferManager::requestXfer(
                                                                const char *local_filename, 
                                                                BOOL delete_remote_on_completion,
                                                                U64 xfer_id, 
                                                                const LLHost &remote_host, 
                                                                void (*callback)(void **,S32),
                                                                void **user_data)
{
        LLXfer *xferp;

        for (xferp = mReceiveList; xferp ; xferp = xferp->mNext)
        {
                if (xferp->getXferTypeTag() == LLXfer::XFER_FILE
                        && (((LLXfer_File*)xferp)->matchesLocalFilename(local_filename))
                        && (xfer_id == xferp->mID)
                        && (remote_host == xferp->mRemoteHost)
                        && (callback == xferp->mCallback)
                        && (user_data == xferp->mCallbackDataHandle))

                {
                        // cout << "requested a xfer already in progress" << endl;
                        return;
                }
        }

        xferp = (LLXfer *) new LLXfer_File();
        if (xferp)
        {
                xferp->mNext = mReceiveList;
                mReceiveList = xferp;

                ((LLXfer_File *)xferp)->initializeRequest(xfer_id,local_filename,"",LL_PATH_NONE,remote_host,delete_remote_on_completion,callback,user_data);
                startPendingDownloads();
        }
        else
        {
                llerrs << "Xfer allcoation error" << llendl;
        }
}

void LLXferManager::requestXfer(U64 xfer_id, const LLHost &remote_host, BOOL delete_remote_on_completion, void (*callback)(void *,S32,void **,S32),void **user_data)
{
        LLXfer *xferp;

        xferp = (LLXfer *) new LLXfer_Mem();
        if (xferp)
        {
                xferp->mNext = mReceiveList;
                mReceiveList = xferp;

                ((LLXfer_Mem *)xferp)->initializeRequest(xfer_id,"",LL_PATH_NONE,remote_host,delete_remote_on_completion,callback,user_data);
                startPendingDownloads();
        }
        else
        {
                llerrs << "Xfer allcoation error" << llendl;
        }
}
*/

void LLXferManager::processReceiveData (LLMessageSystem *mesgsys, void ** /*user_data*/)
{
        // there's sometimes an extra 4 bytes added to an xfer payload
        const S32 BUF_SIZE = LL_XFER_LARGE_PAYLOAD + 4;
        char fdata_buf[LL_XFER_LARGE_PAYLOAD + 4];              /* Flawfinder : ignore */
        S32 fdata_size;
        U64 id;
        S32 packetnum;
        LLXfer * xferp;
        
        mesgsys->getU64Fast(_PREHASH_XferID, _PREHASH_ID, id);
        mesgsys->getS32Fast(_PREHASH_XferID, _PREHASH_Packet, packetnum);

        fdata_size = mesgsys->getSizeFast(_PREHASH_DataPacket,_PREHASH_Data);
        mesgsys->getBinaryDataFast(_PREHASH_DataPacket, _PREHASH_Data, fdata_buf, 0, 0, BUF_SIZE);

        xferp = findXfer(id, mReceiveList);

        if (!xferp) 
        {
                char U64_BUF[MAX_STRING];               /* Flawfinder : ignore */
                llwarns << "received xfer data from " << mesgsys->getSender()
                        << " for non-existent xfer id: "
                        << U64_to_str(id, U64_BUF, sizeof(U64_BUF)) << llendl;
                return;
        }

        S32 xfer_size;

        if (decodePacketNum(packetnum) != xferp->mPacketNum) // is the packet different from what we were expecting?
        {
                // confirm it if it was a resend of the last one, since the confirmation might have gotten dropped
                if (decodePacketNum(packetnum) == (xferp->mPacketNum - 1))
                {
                        llinfos << "Reconfirming xfer " << xferp->mRemoteHost << ":" << xferp->getName() << " packet " << packetnum << llendl;                  sendConfirmPacket(mesgsys, id, decodePacketNum(packetnum), mesgsys->getSender());
                }
                else
                {
                        llinfos << "Ignoring xfer " << xferp->mRemoteHost << ":" << xferp->getName() << " recv'd packet " << packetnum << "; expecting " << xferp->mPacketNum << llendl;
                }
                return;         
        }

        S32 result = 0;

        if (xferp->mPacketNum == 0) // first packet has size encoded as additional S32 at beginning of data
        {
                ntohmemcpy(&xfer_size,fdata_buf,MVT_S32,sizeof(S32));
                
// do any necessary things on first packet ie. allocate memory
                xferp->setXferSize(xfer_size);

                // adjust buffer start and size
                result = xferp->receiveData(&(fdata_buf[sizeof(S32)]),fdata_size-(sizeof(S32)));
        }
        else
        {
                result = xferp->receiveData(fdata_buf,fdata_size);
        }
        
        if (result == LL_ERR_CANNOT_OPEN_FILE)
        {
                        xferp->abort(LL_ERR_CANNOT_OPEN_FILE);
                        removeXfer(xferp,&mReceiveList);
                        startPendingDownloads();
                        return;         
        }

        xferp->mPacketNum++;  // expect next packet

        if (!mUseAckThrottling)
        {
                // No throttling, confirm right away
                sendConfirmPacket(mesgsys, id, decodePacketNum(packetnum), mesgsys->getSender());
        }
        else
        {
                // Throttling, put on queue to be confirmed later.
                LLXferAckInfo ack_info;
                ack_info.mID = id;
                ack_info.mPacketNum = decodePacketNum(packetnum);
                ack_info.mRemoteHost = mesgsys->getSender();
                mXferAckQueue.push(ack_info);
        }

        if (isLastPacket(packetnum))
        {
                xferp->processEOF();
                removeXfer(xferp,&mReceiveList);
                startPendingDownloads();
        }
}


void LLXferManager::sendConfirmPacket (LLMessageSystem *mesgsys, U64 id, S32 packetnum, const LLHost &remote_host)
{
#if LL_XFER_PROGRESS_MESSAGES
        if (!(packetnum % 50))
        {
                cout << "confirming xfer packet #" << packetnum << endl;
        }
#endif
        mesgsys->newMessageFast(_PREHASH_ConfirmXferPacket);
        mesgsys->nextBlockFast(_PREHASH_XferID);
        mesgsys->addU64Fast(_PREHASH_ID, id);
        mesgsys->addU32Fast(_PREHASH_Packet, packetnum);

        mesgsys->sendMessage(remote_host);
}


void LLXferManager::processFileRequest (LLMessageSystem *mesgsys, void ** /*user_data*/)
{
                
        U64 id;
        char local_filename[MAX_STRING];                /* Flawfinder : ignore */
        ELLPath local_path = LL_PATH_NONE;
        S32 result = LL_ERR_NOERR;
        LLUUID  uuid;
        LLAssetType::EType type;
        S16 type_s16;
        BOOL b_use_big_packets;

        mesgsys->getBOOL("XferID", "UseBigPackets", b_use_big_packets);
        
        mesgsys->getU64Fast(_PREHASH_XferID, _PREHASH_ID, id);
        char U64_BUF[MAX_STRING];               /* Flawfinder : ignore */
        llinfos << "xfer request id: " << U64_to_str(id, U64_BUF, sizeof(U64_BUF))
                   << " to " << mesgsys->getSender() << llendl;

        mesgsys->getStringFast(_PREHASH_XferID, _PREHASH_Filename, MAX_STRING, local_filename);
        
        U8 local_path_u8;
        mesgsys->getU8("XferID", "FilePath", local_path_u8);
        if( local_path_u8 < (U8)LL_PATH_COUNT )
        {
                local_path = (ELLPath)local_path_u8;
        }
        else
        {
                llwarns << "Invalid file path in LLXferManager::processFileRequest() " << (U32)local_path_u8 << llendl;
        }

        mesgsys->getUUIDFast(_PREHASH_XferID, _PREHASH_VFileID, uuid);
        mesgsys->getS16Fast(_PREHASH_XferID, _PREHASH_VFileType, type_s16);
        type = (LLAssetType::EType)type_s16;

        LLXfer *xferp;

        if (uuid != LLUUID::null)
        {
                if(NULL == LLAssetType::lookup(type))
                {
                        llwarns << "Invalid type for xfer request: " << uuid << ":"
                                        << type_s16 << " to " << mesgsys->getSender() << llendl;
                        return;
                }
                        
                llinfos << "starting vfile transfer: " << uuid << "," << LLAssetType::lookup(type) << " to " << mesgsys->getSender() << llendl;

                if (! mVFS)
                {
                        llwarns << "Attempt to send VFile w/o available VFS" << llendl;
                        return;
                }

                xferp = (LLXfer *)new LLXfer_VFile(mVFS, uuid, type);
                if (xferp)
                {
                        xferp->mNext = mSendList;
                        mSendList = xferp;      
                        result = xferp->startSend(id,mesgsys->getSender());
                }
                else
                {
                        llerrs << "Xfer allcoation error" << llendl;
                }
        }
        else if (strlen(local_filename))                /* Flawfinder : ignore */
        {
                std::string expanded_filename = gDirUtilp->getExpandedFilename( local_path, local_filename );
                llinfos << "starting file transfer: " <<  expanded_filename << " to " << mesgsys->getSender() << llendl;

                BOOL delete_local_on_completion = FALSE;
                mesgsys->getBOOL("XferID", "DeleteOnCompletion", delete_local_on_completion);

                // -1 chunk_size causes it to use the default
                xferp = (LLXfer *)new LLXfer_File(expanded_filename, delete_local_on_completion, b_use_big_packets ? LL_XFER_LARGE_PAYLOAD : -1);
                
                if (xferp)
                {
                        xferp->mNext = mSendList;
                        mSendList = xferp;      
                        result = xferp->startSend(id,mesgsys->getSender());
                }
                else
                {
                        llerrs << "Xfer allcoation error" << llendl;
                }
        }
        else
        {
                char U64_BUF[MAX_STRING];               /* Flawfinder : ignore */
                llinfos << "starting memory transfer: "
                        << U64_to_str(id, U64_BUF, sizeof(U64_BUF)) << " to "
                        << mesgsys->getSender() << llendl;

                xferp = findXfer(id, mSendList);
                
                if (xferp)
                {
                        result = xferp->startSend(id,mesgsys->getSender());
                }
                else
                {
                        llinfos << "Warning: " << U64_BUF << " not found." << llendl;
                        result = LL_ERR_FILE_NOT_FOUND;
                }
        }

        if (result)
        {
                if (xferp)
                {
                        xferp->abort(result);
                        removeXfer(xferp,&mSendList);
                }
                else // can happen with a memory transfer not found
                {
                        llinfos << "Aborting xfer to " << mesgsys->getSender() << " with error: " << result << llendl;

                        mesgsys->newMessageFast(_PREHASH_AbortXfer);
                        mesgsys->nextBlockFast(_PREHASH_XferID);
                        mesgsys->addU64Fast(_PREHASH_ID, id);
                        mesgsys->addS32Fast(_PREHASH_Result, result);
        
                        mesgsys->sendMessage(mesgsys->getSender());             
                }
        }
        else if(xferp && (numActiveXfers(xferp->mRemoteHost) < mMaxOutgoingXfersPerCircuit))
        {
                xferp->sendNextPacket();
                changeNumActiveXfers(xferp->mRemoteHost,1);
//              llinfos << "***STARTING XFER IMMEDIATELY***" << llendl;
        }
        else
        {
                if(xferp)
                {
                        llinfos << "  queueing xfer request, " << numPendingXfers(xferp->mRemoteHost) << " ahead of this one" << llendl;
                }
                else
                {
                        llwarns << "LLXferManager::processFileRequest() - no xfer found!"
                                        << llendl;
                }
        }
}


void LLXferManager::processConfirmation (LLMessageSystem *mesgsys, void ** /*user_data*/)
{
        U64 id = 0;
        S32 packetNum = 0;

        mesgsys->getU64Fast(_PREHASH_XferID, _PREHASH_ID, id);
        mesgsys->getS32Fast(_PREHASH_XferID, _PREHASH_Packet, packetNum);

        LLXfer* xferp = findXfer(id, mSendList);
        if (xferp)
        {
//              cout << "confirmed packet #" << packetNum << " ping: "<< xferp->ACKTimer.getElapsedTimeF32() <<  endl;
                xferp->mWaitingForACK = FALSE;
                if (xferp->mStatus == e_LL_XFER_IN_PROGRESS)
                {
                        xferp->sendNextPacket();
                }
                else
                {
                        removeXfer(xferp, &mSendList);
                }
        }
}


void LLXferManager::retransmitUnackedPackets ()
{
        LLXfer *xferp;
        LLXfer *delp;
        xferp = mReceiveList;
        while(xferp)
        {
                if (xferp->mStatus == e_LL_XFER_IN_PROGRESS)
                {
                        // if the circuit dies, abort
                        if (! gMessageSystem->mCircuitInfo.isCircuitAlive( xferp->mRemoteHost ))
                        {
                                llinfos << "Xfer found in progress on dead circuit, aborting" << llendl;
                                xferp->mCallbackResult = LL_ERR_CIRCUIT_GONE;
                                xferp->processEOF();
                                delp = xferp;
                                xferp = xferp->mNext;
                                removeXfer(delp,&mReceiveList);
                                continue;
                        }
                                
                }
                xferp = xferp->mNext;
        }

        xferp = mSendList; 
        updateHostStatus();
        F32 et;
        while (xferp)
        {
                if (xferp->mWaitingForACK && ( (et = xferp->ACKTimer.getElapsedTimeF32()) > LL_PACKET_TIMEOUT))
                {
                        if (xferp->mRetries > LL_PACKET_RETRY_LIMIT)
                        {
                                llinfos << "dropping xfer " << xferp->mRemoteHost << ":" << xferp->getName() << " packet retransmit limit exceeded, xfer dropped" << llendl;
                                xferp->abort(LL_ERR_TCP_TIMEOUT);
                                delp = xferp;
                                xferp = xferp->mNext;
                                removeXfer(delp,&mSendList);
                        }
                        else
                        {
                                llinfos << "resending xfer " << xferp->mRemoteHost << ":" << xferp->getName() << " packet unconfirmed after: "<< et << " sec, packet " << xferp->mPacketNum << llendl;
                                xferp->resendLastPacket();
                                xferp = xferp->mNext;
                        }
                }
                else if ((xferp->mStatus == e_LL_XFER_REGISTERED) && ( (et = xferp->ACKTimer.getElapsedTimeF32()) > LL_XFER_REGISTRATION_TIMEOUT))
                {
                        llinfos << "registered xfer never requested, xfer dropped" << llendl;
                        xferp->abort(LL_ERR_TCP_TIMEOUT);
                        delp = xferp;
                        xferp = xferp->mNext;
                        removeXfer(delp,&mSendList);
                }
                else if (xferp->mStatus == e_LL_XFER_ABORTED)
                {
                        llwarns << "Removing aborted xfer " << xferp->mRemoteHost << ":" << xferp->getName() << llendl;
                        delp = xferp;
                        xferp = xferp->mNext;
                        removeXfer(delp,&mSendList);
                }
                else if (xferp->mStatus == e_LL_XFER_PENDING)
                {
//                      llinfos << "*** numActiveXfers = " << numActiveXfers(xferp->mRemoteHost) << "        mMaxOutgoingXfersPerCircuit = " << mMaxOutgoingXfersPerCircuit << llendl;   
                        if (numActiveXfers(xferp->mRemoteHost) < mMaxOutgoingXfersPerCircuit)
                        {
//                          llinfos << "bumping pending xfer to active" << llendl;
                                xferp->sendNextPacket();
                                changeNumActiveXfers(xferp->mRemoteHost,1);
                        }                       
                        xferp = xferp->mNext;
                }
                else
                {
                        xferp = xferp->mNext;
                }
        }

        //
        // HACK - if we're using xfer confirm throttling, throttle our xfer confirms here
        // so we don't blow through bandwidth.
        //

        while (mXferAckQueue.getLength())
        {
                if (mAckThrottle.checkOverflow(1000.0f*8.0f))
                {
                        break;
                }
                //llinfos << "Confirm packet queue length:" << mXferAckQueue.getLength() << llendl;
                LLXferAckInfo ack_info;
                mXferAckQueue.pop(ack_info);
                //llinfos << "Sending confirm packet" << llendl;
                sendConfirmPacket(gMessageSystem, ack_info.mID, ack_info.mPacketNum, ack_info.mRemoteHost);
                mAckThrottle.throttleOverflow(1000.f*8.f); // Assume 1000 bytes/packet
        }
}



void LLXferManager::processAbort (LLMessageSystem *mesgsys, void ** /*user_data*/)
{
        U64 id = 0;
        S32 result_code = 0;
        LLXfer * xferp;

        mesgsys->getU64Fast(_PREHASH_XferID, _PREHASH_ID, id);
        mesgsys->getS32Fast(_PREHASH_XferID, _PREHASH_Result, result_code);

        xferp = findXfer(id, mReceiveList);
        if (xferp)
        {
                xferp->mCallbackResult = result_code;
                xferp->processEOF();
                removeXfer(xferp, &mReceiveList);
                startPendingDownloads();
        }
}


void LLXferManager::startPendingDownloads()
{
        // This method goes through the list, and starts pending
        // operations until active downloads == mMaxIncomingXfers. I copy
        // the pending xfers into a temporary data structure because the
        // xfers are stored as an intrusive linked list where older
        // requests get pushed toward the back. Thus, if we didn't do a
        // stateful iteration, it would be possible for old requests to
        // never start.
        LLXfer* xferp = mReceiveList;
        LLLinkedList<LLXfer> pending_downloads;
        S32 download_count = 0;
        S32 pending_count = 0;
        while(xferp)
        {
                if(xferp->mStatus == e_LL_XFER_PENDING)
                {
                        ++pending_count; // getLength() is O(N), so track it here.
                        pending_downloads.addData(xferp);
                }
                else if(xferp->mStatus == e_LL_XFER_IN_PROGRESS)
                {
                        ++download_count;
                }
                xferp = xferp->mNext;
        }

        S32 start_count = mMaxIncomingXfers - download_count;

        lldebugs << "LLXferManager::startPendingDownloads() - XFER_IN_PROGRESS: "
                         << download_count << " XFER_PENDING: " << pending_count
                         << " startring " << llmin(start_count, pending_count) << llendl;

        if((start_count > 0) && (pending_count > 0))
        {
                S32 result;
                xferp = pending_downloads.getFirstData();
                while(start_count-- && xferp)
                {
                        result = xferp->startDownload();
                        if(result)
                        {
                                xferp->abort(result);
                                ++start_count;
                        }
                        xferp = pending_downloads.getNextData();
                }
        }
}


void LLXferManager::addToList(LLXfer* xferp, LLXfer*& head, BOOL is_priority)
{
        if(is_priority)
        {
                xferp->mNext = NULL;
                LLXfer* next = head;
                if(next)
                {
                        while(next->mNext)
                        {
                                next = next->mNext;
                        }
                        next->mNext = xferp;
                }
                else
                {
                        head = xferp;
                }
        }
        else
        {
                xferp->mNext = head;
                head = xferp;
        }
}

//  Globals and C routines

LLXferManager *gXferManager = NULL;


void start_xfer_manager(LLVFS *vfs)
{
        gXferManager = new LLXferManager(vfs);
}

void cleanup_xfer_manager()
{
        if (gXferManager)
        {
                delete(gXferManager);
                gXferManager = NULL;
        }
}

void process_confirm_packet (LLMessageSystem *mesgsys, void **user_data)
{
        gXferManager->processConfirmation(mesgsys,user_data);
}

void process_request_xfer(LLMessageSystem *mesgsys, void **user_data)
{
        gXferManager->processFileRequest(mesgsys,user_data);
}

void continue_file_receive(LLMessageSystem *mesgsys, void **user_data)
{
#if LL_TEST_XFER_REXMIT
        if (ll_frand() > 0.05f)
        {
#endif
                gXferManager->processReceiveData(mesgsys,user_data);
#if LL_TEST_XFER_REXMIT
        }
        else
        {
                cout << "oops! dropped a xfer packet" << endl;
        }
#endif
}

void process_abort_xfer(LLMessageSystem *mesgsys, void **user_data)
{
        gXferManager->processAbort(mesgsys,user_data);
}

---