[idd] clipboard: pipeline helper channel

Publish ordered four-record prefixes through the Helper mapping and ring
once per accepted burst. Wake blocked producers when the peer returns
credits while retaining the bounded polling fallback.

Move received payload ownership into manager work items and place remote
file-read data directly into the waiting caller’s bounded output buffer.
This removes avoidable 256 KiB copies without changing record ordering,
timeouts, cancellation, or reset semantics.

idd/LGCommon/CClipboardChannel.cpp

@@ -24,13 +24,13 @@
 #include "CDebug.h"
 
 #include <new>
+#include <ntstatus.h>
 #include <string.h>
+#include <utility>
 #include <vector>
 
 namespace
 {
-  static constexpr DWORD WAIT_FIRST_OBJECT_VALUE = 0;
-
   struct ClipboardCallbackScope
   {
     CClipboardChannel      * channel;
@@ -171,15 +171,35 @@ bool CClipboardChannel::Attach(HANDLE mapping, uint64_t epoch,
   }
 
   m_stop = CreateEventW(nullptr, TRUE, FALSE, nullptr);
-  m_kick = CreateEventW(nullptr, FALSE, FALSE, nullptr);
-  if (!m_stop || !m_kick)
+  if (!m_stop)
   {
-    DEBUG_ERROR_HR(GetLastError(),
-      "Failed to create clipboard channel events");
-    if (m_kick)
-      CloseHandle(m_kick);
-    if (m_stop)
-      CloseHandle(m_stop);
+    const DWORD error = GetLastError();
+    DEBUG_ERROR_HR(error,
+      "Failed to create clipboard channel stop event");
+    UnmapViewOfFile(view);
+    CloseHandle(mapping);
+    return false;
+  }
+  m_kick = CreateEventW(nullptr, FALSE, FALSE, nullptr);
+  if (!m_kick)
+  {
+    const DWORD error = GetLastError();
+    DEBUG_ERROR_HR(error,
+      "Failed to create clipboard channel kick event");
+    CloseHandle(m_stop);
+    m_stop = nullptr;
+    UnmapViewOfFile(view);
+    CloseHandle(mapping);
+    return false;
+  }
+  m_writeReady = CreateEventW(nullptr, FALSE, FALSE, nullptr);
+  if (!m_writeReady)
+  {
+    const DWORD error = GetLastError();
+    DEBUG_ERROR_HR(error,
+      "Failed to create clipboard channel credit event");
+    CloseHandle(m_kick);
+    CloseHandle(m_stop);
     m_kick = nullptr;
     m_stop = nullptr;
     UnmapViewOfFile(view);
@@ -212,10 +232,12 @@ bool CClipboardChannel::Attach(HANDLE mapping, uint64_t epoch,
     m_threadId = 0;
     m_view = nullptr;
     m_mapping = nullptr;
+    CloseHandle(m_writeReady);
     CloseHandle(m_kick);
     CloseHandle(m_stop);
     UnmapViewOfFile(view);
     CloseHandle(mapping);
+    m_writeReady = nullptr;
     m_kick = nullptr;
     m_stop = nullptr;
     return false;
@@ -259,6 +281,8 @@ void CClipboardChannel::Detach()
   CSRWExclusiveLock lock(m_lifecycleLock);
   if (m_thread)
     CloseHandle(m_thread);
+  if (m_writeReady)
+    CloseHandle(m_writeReady);
   if (m_kick)
     CloseHandle(m_kick);
   if (m_stop)
@@ -270,6 +294,7 @@ void CClipboardChannel::Detach()
 
   m_thread = nullptr;
   m_threadId = 0;
+  m_writeReady = nullptr;
   m_kick = nullptr;
   m_stop = nullptr;
   m_in = nullptr;
@@ -287,8 +312,21 @@ void CClipboardChannel::Detach()
 void CClipboardChannel::Kick(uint64_t epoch)
 {
   CSRWSharedLock lock(m_lifecycleLock);
-  if (Available() && epoch == m_epoch && m_kick)
-    SetEvent(m_kick);
+  if (Available() && epoch == m_epoch && m_kick && m_writeReady)
+  {
+    if (!SetEvent(m_kick))
+    {
+      const DWORD error = GetLastError();
+      DEBUG_ERROR_HR(error,
+        "Failed to signal clipboard channel receive event");
+    }
+    if (!SetEvent(m_writeReady))
+    {
+      const DWORD error = GetLastError();
+      DEBUG_ERROR_HR(error,
+        "Failed to signal clipboard channel credit event");
+    }
+  }
 }
 
 void CClipboardChannel::Reset(uint64_t epoch, uint32_t reason)
@@ -306,34 +344,85 @@ void CClipboardChannel::Reset(uint64_t epoch, uint32_t reason)
   Fail(instance, reason, false);
 }
 
+bool CClipboardChannel::WaitWritable(HANDLE stop, DWORD timeout)
+{
+  if (!stop || stop == INVALID_HANDLE_VALUE)
+    return false;
+
+  CSRWSharedLock lock(m_lifecycleLock);
+  if (!Available() || !m_writeReady)
+    return false;
+  const HANDLE events[] = { stop, m_writeReady };
+  const DWORD result = WaitForMultipleObjects(
+    ARRAYSIZE(events), events, FALSE, timeout);
+  if (result == WAIT_OBJECT_0)
+    return false;
+  if (result == WAIT_OBJECT_0 + 1 || result == WAIT_TIMEOUT)
+    return true;
+  if (result == WAIT_FAILED)
+    DEBUG_ERROR_HR(GetLastError(),
+      "Failed to wait for clipboard channel credit");
+  else
+    DEBUG_ERROR("Invalid clipboard channel credit wait result: %lu",
+      static_cast<unsigned long>(result));
+  return false;
+}
+
 ClipboardChannelResult CClipboardChannel::Send(
   const KVMFRClipboardMessage& record, const void * data)
 {
-  if (!ValidRecord(record, data != nullptr))
+  const ClipboardChannelWrite write = { record, data };
+  size_t accepted = 0;
+  return SendBatch(&write, 1, accepted);
+}
+
+ClipboardChannelResult CClipboardChannel::SendBatch(
+  const ClipboardChannelWrite * records, size_t count, size_t& accepted)
+{
+  accepted = 0;
+  if (!records || !count || count > KVMFR_CLIPBOARD_SLOT_COUNT)
     return ClipboardChannelResult::FAILED;
+  for (size_t i = 0; i < count; ++i)
+    if (!ValidRecord(records[i].record, records[i].data != nullptr))
+      return ClipboardChannelResult::FAILED;
 
   CSRWSharedLock lifecycleLock(m_lifecycleLock);
   if (!Available() || !m_out || !m_doorbell)
     return ClipboardChannelResult::FAILED;
 
+  bool failed = false;
   {
     CSRWExclusiveLock writeLock(m_writeLock);
-    uint32_t ticket;
-    ClipboardRingSlot * slot = CClipboardRing::BeginWrite(*m_out, ticket);
-    if (!slot)
-      return ClipboardChannelResult::BUSY;
+    while (accepted < count)
+    {
+      uint32_t ticket;
+      ClipboardRingSlot * slot = CClipboardRing::BeginWrite(*m_out, ticket);
+      if (!slot)
+        break;
 
-    slot->header = record;
-    if (record.length)
-      memcpy(slot->data, data, record.length);
-    if (!CClipboardRing::EndWrite(*m_out, ticket))
-      return ClipboardChannelResult::FAILED;
+      const ClipboardChannelWrite& write = records[accepted];
+      slot->header = write.record;
+      if (write.record.length)
+        memcpy(slot->data, write.data, write.record.length);
+      if (!CClipboardRing::EndWrite(*m_out, ticket))
+      {
+        failed = true;
+        break;
+      }
+      ++accepted;
+    }
   }
 
-  // Once the producer index advances the record belongs to the channel.
-  // Doorbells are only a latency optimization; the peer also polls.
-  m_doorbell->ClipboardKick(m_epoch);
-  return ClipboardChannelResult::ACCEPTED;
+  if (accepted)
+  {
+    // Once the producer index advances the records belong to the channel.
+    // Doorbells are only a latency optimization; the peer also polls.
+    m_doorbell->ClipboardKick(m_epoch);
+  }
+  if (failed)
+    return ClipboardChannelResult::FAILED;
+  return accepted == count ? ClipboardChannelResult::ACCEPTED :
+    ClipboardChannelResult::BUSY;
 }
 
 void CClipboardChannel::SetHandler(IClipboardChannelHandler * handler)
@@ -381,6 +470,23 @@ void CClipboardChannel::ClearHandler(IClipboardChannelHandler * handler)
 
 CClipboardChannel::DrainResult CClipboardChannel::Drain()
 {
+  struct CreditNotifier
+  {
+    bool pending = false;
+    IClipboardChannelDoorbell * doorbell = nullptr;
+    uint64_t epoch = 0;
+
+    void Notify()
+    {
+      if (pending && doorbell)
+        doorbell->ClipboardKick(epoch);
+      pending = false;
+    }
+
+    ~CreditNotifier() { Notify(); }
+  } credit;
+  size_t consumed = 0;
+
   for (;;)
   {
     KVMFRClipboardMessage record = {};
@@ -417,21 +523,25 @@ CClipboardChannel::DrainResult CClipboardChannel::Drain()
 
     ClipboardChannelResult result =
       ValidRecord(record, record.length != 0) ?
-        PublishRecord(record, data.empty() ? nullptr : data.data()) :
+        PublishRecord(record, std::move(data)) :
         ClipboardChannelResult::FAILED;
     if (result == ClipboardChannelResult::BUSY)
       return DrainResult::BUSY;
 
-    IClipboardChannelDoorbell * doorbell;
-    uint64_t epoch;
     {
       CSRWSharedLock lifecycleLock(m_lifecycleLock);
       if (!Available() || !m_in || !m_doorbell)
         return DrainResult::STOPPED;
       if (!CClipboardRing::EndRead(*m_in, ticket))
         return DrainResult::CORRUPT;
-      doorbell = m_doorbell;
-      epoch = m_epoch;
+      credit.pending  = true;
+      credit.doorbell = m_doorbell;
+      credit.epoch    = m_epoch;
+    }
+    if (++consumed == KVMFR_CLIPBOARD_SLOT_COUNT)
+    {
+      credit.Notify();
+      consumed = 0;
     }
 
     if (result == ClipboardChannelResult::FAILED)
@@ -441,8 +551,6 @@ CClipboardChannel::DrainResult CClipboardChannel::Drain()
       // local callback and peer reset outside the ring/lifecycle locks.
       return DrainResult::CORRUPT;
     }
-    else
-      doorbell->ClipboardKick(epoch);
   }
 }
 
@@ -508,6 +616,8 @@ void CClipboardChannel::CleanupDeferredDetach()
 
   if (m_kick)
     CloseHandle(m_kick);
+  if (m_writeReady)
+    CloseHandle(m_writeReady);
   if (m_stop)
     CloseHandle(m_stop);
   if (m_view)
@@ -517,6 +627,7 @@ void CClipboardChannel::CleanupDeferredDetach()
 
   // A later external Detach closes the now-signaled thread handle.
   m_threadId = 0;
+  m_writeReady = nullptr;
   m_kick = nullptr;
   m_stop = nullptr;
   m_in = nullptr;
@@ -546,10 +657,11 @@ void CClipboardChannel::PublishState(bool available, uint64_t epoch)
 }
 
 ClipboardChannelResult CClipboardChannel::PublishRecord(
-  const KVMFRClipboardMessage& record, const uint8_t * data)
+  const KVMFRClipboardMessage& record, std::vector<uint8_t>&& data)
 {
   if (InClipboardCallback(this))
-    return m_handler ? m_handler->ClipboardRecord(record, data) :
+    return m_handler ?
+      m_handler->ClipboardRecord(record, std::move(data)) :
       ClipboardChannelResult::BUSY;
 
   CSRWExclusiveLock lock(m_handlerLock);
@@ -557,7 +669,7 @@ ClipboardChannelResult CClipboardChannel::PublishRecord(
     return ClipboardChannelResult::BUSY;
 
   CClipboardCallbackScope scope(this);
-  return m_handler->ClipboardRecord(record, data);
+  return m_handler->ClipboardRecord(record, std::move(data));
 }
 
 void CClipboardChannel::PublishReset(uint64_t epoch, uint32_t reason)

idd/LGCommon/CClipboardChannel.h

@@ -27,7 +27,9 @@
 #include <Windows.h>
 
 #include <atomic>
+#include <stddef.h>
 #include <stdint.h>
+#include <vector>
 
 enum class ClipboardChannelResult
 {
@@ -36,16 +38,24 @@ enum class ClipboardChannelResult
   FAILED,
 };
 
+struct ClipboardChannelWrite
+{
+  KVMFRClipboardMessage record = {};
+  const void *          data   = nullptr;
+};
+
 class IClipboardChannelHandler
 {
 public:
   virtual ~IClipboardChannelHandler() = default;
 
   virtual void ClipboardState(bool available, uint64_t epoch) = 0;
-  // data is borrowed and remains valid only for the duration of this call.
-  // BUSY leaves the shared ring slot occupied so it can be retried later.
+  // data owns record.length bytes and may be moved by the handler. BUSY
+  // leaves the shared ring slot occupied so it can be reconstructed and
+  // retried later.
   virtual ClipboardChannelResult ClipboardRecord(
-    const KVMFRClipboardMessage& record, const uint8_t * data) = 0;
+    const KVMFRClipboardMessage& record,
+    std::vector<uint8_t>&& data) = 0;
   virtual void ClipboardReset(uint64_t epoch, uint32_t reason) = 0;
 };
 
@@ -75,16 +85,17 @@ private:
   CSRWLock m_handlerLock;
   CSRWLock m_writeLock;
 
-  HANDLE             m_mapping = nullptr;
-  ClipboardMapping * m_view    = nullptr;
-  ClipboardRing    * m_in      = nullptr;
-  ClipboardRing    * m_out     = nullptr;
-  HANDLE             m_stop    = nullptr;
-  HANDLE             m_kick    = nullptr;
-  HANDLE             m_thread  = nullptr;
-  DWORD              m_threadId = 0;
-  uint64_t           m_epoch   = 0;
-  uint64_t           m_instance = 0;
+  HANDLE             m_mapping        = nullptr;
+  ClipboardMapping * m_view           = nullptr;
+  ClipboardRing    * m_in             = nullptr;
+  ClipboardRing    * m_out            = nullptr;
+  HANDLE             m_stop           = nullptr;
+  HANDLE             m_kick           = nullptr;
+  HANDLE             m_writeReady     = nullptr;
+  HANDLE             m_thread         = nullptr;
+  DWORD              m_threadId       = 0;
+  uint64_t           m_epoch          = 0;
+  uint64_t           m_instance       = 0;
   bool               m_deferredDetach = false;
 
   IClipboardChannelHandler  * m_handler  = nullptr;
@@ -97,7 +108,8 @@ private:
   void CleanupDeferredDetach();
   void PublishState(bool available, uint64_t epoch);
   ClipboardChannelResult PublishRecord(
-    const KVMFRClipboardMessage& record, const uint8_t * data);
+    const KVMFRClipboardMessage& record,
+    std::vector<uint8_t>&& data);
   void PublishReset(uint64_t epoch, uint32_t reason);
 
   static DWORD WINAPI ThreadProc(void * context);
@@ -114,10 +126,17 @@ public:
   void Detach();
   void Kick(uint64_t epoch);
   void Reset(uint64_t epoch, uint32_t reason);
+  bool WaitWritable(HANDLE stop, DWORD timeout);
 
   ClipboardChannelResult Send(
     const KVMFRClipboardMessage& record, const void * data = nullptr);
 
+  // Publish an ordered prefix of records, bounded by the physical ring
+  // window. BUSY may return a non-zero accepted count; the caller must resume
+  // at that prefix boundary. A single doorbell covers the entire prefix.
+  ClipboardChannelResult SendBatch(const ClipboardChannelWrite * records,
+    size_t count, size_t& accepted);
+
   void SetHandler(IClipboardChannelHandler * handler);
   void ClearHandler(IClipboardChannelHandler * handler);
 

idd/LGIdd/transport/CClipboardHub.cpp

@@ -326,7 +326,7 @@ void CClipboardHub::ClipboardState(bool available, uint64_t epoch)
 }
 
 ClipboardChannelResult CClipboardHub::ClipboardRecord(
-  const KVMFRClipboardMessage& record, const uint8_t * data)
+  const KVMFRClipboardMessage& record, std::vector<uint8_t>&& data)
 {
   if (!ValidHelperDirection(record))
     return ClipboardChannelResult::FAILED;
@@ -347,7 +347,8 @@ ClipboardChannelResult CClipboardHub::ClipboardRecord(
   KVMFRClipboardMessage stamped = record;
   stamped.generation = generation;
   const ClipboardChannelResult result =
-    source->SendClipboard(stamped, data);
+    source->SendClipboard(stamped,
+      data.empty() ? nullptr : data.data());
   if (result != ClipboardChannelResult::FAILED)
     return result;
 

idd/LGIdd/transport/CClipboardHub.h

@@ -55,7 +55,7 @@ private:
   void ClipboardState(bool available, uint64_t epoch) override;
   ClipboardChannelResult ClipboardRecord(
     const KVMFRClipboardMessage& record,
-    const uint8_t * data) override;
+    std::vector<uint8_t>&& data) override;
   void ClipboardReset(uint64_t epoch, uint32_t reason) override;
 
 public:

idd/LGIddHelper/CClipboardManager.cpp

@@ -1737,7 +1737,7 @@ void CClipboardManager::ProcessSend(Work&& work)
 
   if (result == ClipboardChannelResult::BUSY &&
       GetTickCount64() < work.deadline &&
-      WaitForSingleObject(m_stop, CHANNEL_RETRY_MS) != WAIT_OBJECT_0)
+      m_channel.WaitWritable(m_stop, CHANNEL_RETRY_MS))
   {
     if (work.record.type == KVMFR_CLIPBOARD_MESSAGE_CANCEL)
       QueueCancel(work.record, work.record.token, work.deadline);
@@ -1824,15 +1824,17 @@ void CClipboardManager::ProcessSendData(Work&& work)
     QueueCancel(work.record, ERROR_INVALID_DATA);
     return;
   }
-  const size_t length = static_cast<size_t>((std::min<uint64_t>)(
-    KVMFR_CLIPBOARD_REPRESENTATION_BYTES,
-    total - work.record.offset));
+
+  const uint64_t batchBytes = (std::min<uint64_t>)(
+    static_cast<uint64_t>(KVMFR_CLIPBOARD_REPRESENTATION_BYTES) *
+      KVMFR_CLIPBOARD_SLOT_COUNT,
+    total - work.record.offset);
   std::vector<uint8_t> data;
-  if (length)
+  if (batchBytes)
   {
     try
     {
-      data.resize(length);
+      data.resize(static_cast<size_t>(batchBytes));
     }
     catch (const std::bad_alloc&)
     {
@@ -1840,7 +1842,7 @@ void CClipboardManager::ProcessSendData(Work&& work)
       QueueCancel(work.record, ERROR_OUTOFMEMORY);
       return;
     }
-    if (!work.spool->Read(work.record.offset, data.data(), length))
+    if (!work.spool->Read(work.record.offset, data.data(), data.size()))
     {
       const DWORD error = GetLastError();
       ReleaseOutgoing(work.record.transfer);
@@ -1849,49 +1851,82 @@ void CClipboardManager::ProcessSendData(Work&& work)
     }
   }
 
-  KVMFRClipboardMessage message = work.record;
-  message.type = KVMFR_CLIPBOARD_MESSAGE_DATA;
-  message.token = 0;
-  message.length = static_cast<uint32_t>(length);
-  message.flags = 0;
-  if (!message.offset)
-    message.flags |= KVMFR_CLIPBOARD_FLAG_BEGIN;
-  if (message.offset + length == total)
-    message.flags |= KVMFR_CLIPBOARD_FLAG_END;
-  message.size = message.flags & KVMFR_CLIPBOARD_FLAG_END ? total :
-    (message.flags & KVMFR_CLIPBOARD_FLAG_BEGIN ? total :
-      KVMFR_CLIPBOARD_SIZE_UNKNOWN);
+  std::array<ClipboardChannelWrite, KVMFR_CLIPBOARD_SLOT_COUNT> batch;
+  size_t batchCount = 0;
+  uint64_t offset = work.record.offset;
+  uint32_t sequence = work.record.sequence;
+  do
+  {
+    ClipboardChannelWrite& write = batch[batchCount++];
+    const size_t length = static_cast<size_t>((std::min<uint64_t>)(
+      KVMFR_CLIPBOARD_REPRESENTATION_BYTES, total - offset));
+    write.record = work.record;
+    write.record.type = KVMFR_CLIPBOARD_MESSAGE_DATA;
+    write.record.token = 0;
+    write.record.offset = offset;
+    write.record.sequence = sequence;
+    write.record.length = static_cast<uint32_t>(length);
+    write.record.flags = 0;
+    if (!offset)
+      write.record.flags |= KVMFR_CLIPBOARD_FLAG_BEGIN;
+    if (offset + length == total)
+      write.record.flags |= KVMFR_CLIPBOARD_FLAG_END;
+    write.record.size =
+      write.record.flags & KVMFR_CLIPBOARD_FLAG_END ? total :
+      (write.record.flags & KVMFR_CLIPBOARD_FLAG_BEGIN ? total :
+        KVMFR_CLIPBOARD_SIZE_UNKNOWN);
+    write.data = length ? data.data() +
+      static_cast<size_t>(offset - work.record.offset) : nullptr;
+    offset += length;
+    ++sequence;
+  }
+  while (batchCount < batch.size() && offset < total);
 
   ClipboardChannelResult result = ClipboardChannelResult::FAILED;
+  size_t accepted = 0;
   bool stale = false;
   bool timedOut = false;
   {
     std::lock_guard<std::mutex> lock(m_outgoingLock);
     stale = Atomic::Load(m_outgoingTransfer, std::memory_order_acquire) !=
-        message.transfer ||
-      message.clipboardGeneration != Atomic::Load(
+        work.record.transfer ||
+      work.record.clipboardGeneration != Atomic::Load(
         m_liveLocalGeneration, std::memory_order_acquire);
     timedOut = GetTickCount64() >= work.deadline;
     if (!stale && !timedOut)
-      result = m_channel.Send(message,
-        data.empty() ? nullptr : data.data());
+      result = m_channel.SendBatch(batch.data(), batchCount, accepted);
   }
   if (stale)
   {
-    ReleaseOutgoing(message.transfer);
-    QueueCancel(message, ERROR_OPERATION_ABORTED);
+    ReleaseOutgoing(work.record.transfer);
+    QueueCancel(work.record, ERROR_OPERATION_ABORTED);
     return;
   }
   if (timedOut)
   {
-    ReleaseOutgoing(message.transfer);
-    QueueCancel(message, ERROR_TIMEOUT);
+    ReleaseOutgoing(work.record.transfer);
+    QueueCancel(work.record, ERROR_TIMEOUT);
     return;
   }
+
+  KVMFRClipboardMessage progress = work.record;
+  if (accepted)
+  {
+    progress = batch[accepted - 1U].record;
+    work.record.offset = progress.offset + progress.length;
+    work.record.sequence = progress.sequence + 1U;
+    work.deadline = GetTickCount64() + SEND_TIMEOUT_MS;
+    if (progress.flags & KVMFR_CLIPBOARD_FLAG_END)
+    {
+      ReleaseOutgoing(progress.transfer);
+      return;
+    }
+  }
+
   if (result == ClipboardChannelResult::BUSY)
   {
     if (GetTickCount64() < work.deadline &&
-        WaitForSingleObject(m_stop, CHANNEL_RETRY_MS) != WAIT_OBJECT_0)
+        m_channel.WaitWritable(m_stop, CHANNEL_RETRY_MS))
     {
       const KVMFRClipboardMessage record = work.record;
       if (!QueueWork(std::move(work)))
@@ -1909,19 +1944,11 @@ void CClipboardManager::ProcessSendData(Work&& work)
   }
   if (result != ClipboardChannelResult::ACCEPTED)
   {
-    ReleaseOutgoing(work.record.transfer);
-    QueueCancel(work.record, ERROR_DEVICE_NOT_CONNECTED);
-    return;
-  }
-  work.deadline = GetTickCount64() + SEND_TIMEOUT_MS;
-  if (message.flags & KVMFR_CLIPBOARD_FLAG_END)
-  {
-    ReleaseOutgoing(work.record.transfer);
+    ReleaseOutgoing(progress.transfer);
+    QueueCancel(progress, ERROR_DEVICE_NOT_CONNECTED);
     return;
   }
 
-  work.record.offset += length;
-  ++work.record.sequence;
   const KVMFRClipboardMessage record = work.record;
   if (!QueueWork(std::move(work)))
   {
@@ -1985,52 +2012,75 @@ void CClipboardManager::ProcessSendFileData(Work&& work)
     QueueFileCancel(work.record, KVMFR_CLIPBOARD_FILE_ERROR_INVALID);
     return;
   }
-  const size_t length = static_cast<size_t>((std::min<uint64_t>)(
-    KVMFR_CLIPBOARD_DATA_BYTES, total - work.record.offset));
-  KVMFRClipboardMessage message = work.record;
-  message.version = KVMFR_CLIPBOARD_VERSION;
-  message.type = KVMFR_CLIPBOARD_MESSAGE_FILE_DATA;
-  message.length = static_cast<uint32_t>(length);
-  message.flags = 0;
-  if (!message.offset)
-    message.flags |= KVMFR_CLIPBOARD_FLAG_BEGIN;
-  if (message.offset + length == total)
-    message.flags |= KVMFR_CLIPBOARD_FLAG_END;
-  message.size = message.flags & KVMFR_CLIPBOARD_FLAG_END ? total :
-    (message.flags & KVMFR_CLIPBOARD_FLAG_BEGIN ? total :
-      KVMFR_CLIPBOARD_SIZE_UNKNOWN);
 
-  const uint8_t * data = length ?
-    work.fileData->data() + static_cast<size_t>(message.offset) : nullptr;
-  const ClipboardChannelResult result = m_channel.Send(message, data);
+  std::array<ClipboardChannelWrite, KVMFR_CLIPBOARD_SLOT_COUNT> batch;
+  size_t batchCount = 0;
+  uint64_t offset = work.record.offset;
+  uint32_t sequence = work.record.sequence;
+  do
+  {
+    ClipboardChannelWrite& write = batch[batchCount++];
+    const size_t length = static_cast<size_t>((std::min<uint64_t>)(
+      KVMFR_CLIPBOARD_DATA_BYTES, total - offset));
+    write.record = work.record;
+    write.record.version = KVMFR_CLIPBOARD_VERSION;
+    write.record.type = KVMFR_CLIPBOARD_MESSAGE_FILE_DATA;
+    write.record.offset = offset;
+    write.record.sequence = sequence;
+    write.record.length = static_cast<uint32_t>(length);
+    write.record.flags = 0;
+    if (!offset)
+      write.record.flags |= KVMFR_CLIPBOARD_FLAG_BEGIN;
+    if (offset + length == total)
+      write.record.flags |= KVMFR_CLIPBOARD_FLAG_END;
+    write.record.size =
+      write.record.flags & KVMFR_CLIPBOARD_FLAG_END ? total :
+      (write.record.flags & KVMFR_CLIPBOARD_FLAG_BEGIN ? total :
+        KVMFR_CLIPBOARD_SIZE_UNKNOWN);
+    write.data = length ? work.fileData->data() +
+      static_cast<size_t>(offset) : nullptr;
+    offset += length;
+    ++sequence;
+  }
+  while (batchCount < batch.size() && offset < total);
+
+  size_t accepted = 0;
+  const ClipboardChannelResult result =
+    m_channel.SendBatch(batch.data(), batchCount, accepted);
+  KVMFRClipboardMessage progress = work.record;
+  if (accepted)
+  {
+    progress = batch[accepted - 1U].record;
+    work.record.offset = progress.offset + progress.length;
+    work.record.sequence = progress.sequence + 1U;
+    work.deadline = GetTickCount64() + SEND_TIMEOUT_MS;
+    if (progress.flags & KVMFR_CLIPBOARD_FLAG_END)
+    {
+      std::lock_guard<std::mutex> lock(m_fileLock);
+      m_outgoingFileRequests.erase(progress.transfer);
+      return;
+    }
+  }
+
   if (result == ClipboardChannelResult::BUSY &&
       GetTickCount64() < work.deadline &&
-      WaitForSingleObject(m_stop, CHANNEL_RETRY_MS) != WAIT_OBJECT_0)
+      m_channel.WaitWritable(m_stop, CHANNEL_RETRY_MS))
   {
     if (!QueueWork(std::move(work)))
-      QueueFileCancel(message, KVMFR_CLIPBOARD_FILE_ERROR_NO_MEMORY);
+      QueueFileCancel(progress, KVMFR_CLIPBOARD_FILE_ERROR_NO_MEMORY);
     return;
   }
   if (result != ClipboardChannelResult::ACCEPTED)
   {
-    QueueFileCancel(message,
+    QueueFileCancel(progress,
       result == ClipboardChannelResult::BUSY ?
         KVMFR_CLIPBOARD_FILE_ERROR_IO :
         KVMFR_CLIPBOARD_FILE_ERROR_DISCONNECTED);
     return;
   }
 
-  if (message.flags & KVMFR_CLIPBOARD_FLAG_END)
-  {
-    std::lock_guard<std::mutex> lock(m_fileLock);
-    m_outgoingFileRequests.erase(message.transfer);
-    return;
-  }
-  work.record.offset += length;
-  ++work.record.sequence;
-  work.deadline = GetTickCount64() + SEND_TIMEOUT_MS;
   if (!QueueWork(std::move(work)))
-    QueueFileCancel(message, KVMFR_CLIPBOARD_FILE_ERROR_NO_MEMORY);
+    QueueFileCancel(progress, KVMFR_CLIPBOARD_FILE_ERROR_NO_MEMORY);
 }
 
 void CClipboardManager::ProcessFileRecord(
@@ -2423,15 +2473,30 @@ void CClipboardManager::ProcessFileData(
 
       if (valid && record.length)
       {
-        try
+        if (request->operation == KVMFR_CLIPBOARD_FILE_OP_READ &&
+            request->output)
         {
-          request->data.insert(request->data.end(), data,
-            data + record.length);
+          if (request->nextOffset > request->outputCapacity ||
+              record.length >
+                request->outputCapacity - request->nextOffset)
+            valid = false;
+          else
+            memcpy(request->output +
+              static_cast<size_t>(request->nextOffset), data,
+              record.length);
         }
-        catch (const std::bad_alloc&)
+        else
         {
-          valid = false;
-          request->error = KVMFR_CLIPBOARD_FILE_ERROR_NO_MEMORY;
+          try
+          {
+            request->data.insert(request->data.end(), data,
+              data + record.length);
+          }
+          catch (const std::bad_alloc&)
+          {
+            valid = false;
+            request->error = KVMFR_CLIPBOARD_FILE_ERROR_NO_MEMORY;
+          }
         }
       }
       if (valid)
@@ -2809,6 +2874,8 @@ HRESULT CClipboardManager::ReadRemoteFile(uint64_t dataset,
   read = 0;
   if (Atomic::Load(m_shutdown))
     return STG_E_READFAULT;
+  if (!output && length)
+    return STG_E_INVALIDPOINTER;
   uint8_t * destination = static_cast<uint8_t *>(output);
   while (length)
   {
@@ -2831,6 +2898,8 @@ HRESULT CClipboardManager::ReadRemoteFile(uint64_t dataset,
     request->node = node;
     request->operation = KVMFR_CLIPBOARD_FILE_OP_READ;
     request->requestedBytes = wanted;
+    request->output = destination;
+    request->outputCapacity = wanted;
     KVMFRClipboardFileError insertError =
       KVMFR_CLIPBOARD_FILE_ERROR_NONE;
     {
@@ -2906,11 +2975,9 @@ HRESULT CClipboardManager::ReadRemoteFile(uint64_t dataset,
     if (request->error != KVMFR_CLIPBOARD_FILE_ERROR_NONE)
       return request->error == KVMFR_CLIPBOARD_FILE_ERROR_ACCESS ?
         STG_E_ACCESSDENIED : STG_E_READFAULT;
-    if (request->data.size() > wanted)
+    if (request->nextOffset > wanted)
       return STG_E_READFAULT;
-    if (!request->data.empty())
-      memcpy(destination, request->data.data(), request->data.size());
-    const ULONG actual = static_cast<ULONG>(request->data.size());
+    const ULONG actual = static_cast<ULONG>(request->nextOffset);
     destination += actual;
     read += actual;
     offset += actual;
@@ -2996,8 +3063,11 @@ void CClipboardManager::ClipboardState(bool available, uint64_t epoch)
 }
 
 ClipboardChannelResult CClipboardManager::ClipboardRecord(
-  const KVMFRClipboardMessage& record, const uint8_t * data)
+  const KVMFRClipboardMessage& record, std::vector<uint8_t>&& data)
 {
+  if (data.size() != record.length)
+    return ClipboardChannelResult::FAILED;
+
   switch (record.type)
   {
     case KVMFR_CLIPBOARD_MESSAGE_OFFER:
@@ -3028,8 +3098,7 @@ ClipboardChannelResult CClipboardManager::ClipboardRecord(
     case KVMFR_CLIPBOARD_MESSAGE_DATA:
       if (!record.clipboardGeneration || !record.transfer ||
           !kvmfrClipboardTransferFromHelper(record.transfer) ||
-          !kvmfrClipboardRepresentationFormatValid(record.format) ||
-          (record.length && !data))
+          !kvmfrClipboardRepresentationFormatValid(record.format))
         return ClipboardChannelResult::FAILED;
       break;
 
@@ -3056,8 +3125,7 @@ ClipboardChannelResult CClipboardManager::ClipboardRecord(
           (record.type == KVMFR_CLIPBOARD_MESSAGE_FILE_REQUEST &&
             !kvmfrClipboardTransferFromClient(record.transfer)) ||
           (record.type == KVMFR_CLIPBOARD_MESSAGE_FILE_DATA &&
-            !kvmfrClipboardTransferFromHelper(record.transfer)) ||
-          (record.length && !data))
+            !kvmfrClipboardTransferFromHelper(record.transfer)))
         return ClipboardChannelResult::FAILED;
       break;
     default:
@@ -3068,16 +3136,7 @@ ClipboardChannelResult CClipboardManager::ClipboardRecord(
   work.type = WorkType::RECORD;
   work.record = record;
   if (record.length)
-  {
-    try
-    {
-      work.data.assign(data, data + record.length);
-    }
-    catch (const std::bad_alloc&)
-    {
-      return ClipboardChannelResult::BUSY;
-    }
-  }
+    work.data = std::move(data);
   if (QueueWork(std::move(work)))
     return ClipboardChannelResult::ACCEPTED;
   return Atomic::Load(m_shutdown) ? ClipboardChannelResult::FAILED :

idd/LGIddHelper/CClipboardManager.h

@@ -138,6 +138,10 @@ private:
     bool manifest = false;
     KVMFRClipboardFileError error = KVMFR_CLIPBOARD_FILE_ERROR_NONE;
     HANDLE event = nullptr;
+    // Borrowed by a synchronous READ until this request is removed while
+    // holding m_fileLock. Manifest LIST responses retain owned vector data.
+    uint8_t * output = nullptr;
+    uint32_t outputCapacity = 0;
     std::vector<uint8_t> data;
 
     ~IncomingFileRequest();
@@ -322,8 +326,9 @@ private:
     CClipboardSpool& spool);
 
   void ClipboardState(bool available, uint64_t epoch) override;
-  ClipboardChannelResult ClipboardRecord(const KVMFRClipboardMessage& record,
-    const uint8_t * data) override;
+  ClipboardChannelResult ClipboardRecord(
+    const KVMFRClipboardMessage& record,
+    std::vector<uint8_t>&& data) override;
   void ClipboardReset(uint64_t epoch, uint32_t reason) override;
 
 public: