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Add a private method on SystemPacketBuffer to find where its reserved space starts. #23284

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merged 1 commit into from
Oct 25, 2022
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Add a private method on SystemPacketBuffer to find where its reserved space starts. #23284

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40 changes: 23 additions & 17 deletions src/system/SystemPacketBuffer.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -133,9 +133,9 @@ void PacketBufferHandle::InternalRightSize()
}

// Reallocate only if enough space will be saved.
uint8_t * const start = reinterpret_cast<uint8_t *>(mBuffer) + PacketBuffer::kStructureSize;
uint8_t * const payload = reinterpret_cast<uint8_t *>(mBuffer->payload);
const uint16_t usedSize = static_cast<uint16_t>(payload - start + mBuffer->len);
const uint8_t * const start = mBuffer->ReserveStart();
const uint8_t * const payload = mBuffer->Start();
const uint16_t usedSize = static_cast<uint16_t>(payload - start + mBuffer->len);
if (usedSize + kRightSizingThreshold > mBuffer->alloc_size)
{
return;
Expand All @@ -149,14 +149,14 @@ void PacketBufferHandle::InternalRightSize()
return;
}

uint8_t * const newStart = reinterpret_cast<uint8_t *>(newBuffer) + PacketBuffer::kStructureSize;
uint8_t * const newStart = newBuffer->ReserveStart();
newBuffer->next = nullptr;
newBuffer->payload = newStart + (payload - start);
newBuffer->tot_len = mBuffer->tot_len;
newBuffer->len = mBuffer->len;
newBuffer->ref = 1;
newBuffer->alloc_size = static_cast<uint16_t>(usedSize);
memcpy(reinterpret_cast<uint8_t *>(newBuffer) + PacketBuffer::kStructureSize, start, usedSize);
memcpy(newStart, start, usedSize);

PacketBuffer::Free(mBuffer);
mBuffer = newBuffer;
Expand Down Expand Up @@ -193,7 +193,7 @@ void PacketBufferHandle::InternalRightSize()

void PacketBuffer::SetStart(uint8_t * aNewStart)
{
uint8_t * const kStart = reinterpret_cast<uint8_t *>(this) + kStructureSize;
uint8_t * const kStart = ReserveStart();
uint8_t * const kEnd = kStart + this->AllocSize();

if (aNewStart < kStart)
Expand Down Expand Up @@ -236,9 +236,7 @@ void PacketBuffer::SetDataLength(uint16_t aNewLen, PacketBuffer * aChainHead)

uint16_t PacketBuffer::MaxDataLength() const
{
const uint8_t * const kStart = reinterpret_cast<const uint8_t *>(this) + kStructureSize;
const ptrdiff_t kDelta = static_cast<uint8_t *>(this->payload) - kStart;
return static_cast<uint16_t>(this->AllocSize() - kDelta);
return static_cast<uint16_t>(AllocSize() - ReservedSize());
}

uint16_t PacketBuffer::AvailableDataLength() const
Expand All @@ -248,10 +246,19 @@ uint16_t PacketBuffer::AvailableDataLength() const

uint16_t PacketBuffer::ReservedSize() const
{
// Cast to size_t is safe because this->payload always points to "after"
// this.
const size_t kDelta = static_cast<size_t>(static_cast<uint8_t *>(this->payload) - reinterpret_cast<const uint8_t *>(this));
return static_cast<uint16_t>(kDelta - kStructureSize);
// Cast to uint16_t is safe because Start() always points to "after"
// ReserveStart(). At least when the payload is stored inline.
return static_cast<uint16_t>(Start() - ReserveStart());
}

uint8_t * PacketBuffer::ReserveStart()
{
return reinterpret_cast<uint8_t *>(this) + kStructureSize;
}

const uint8_t * PacketBuffer::ReserveStart() const
{
return reinterpret_cast<const uint8_t *>(this) + kStructureSize;
}

void PacketBuffer::AddToEnd(PacketBufferHandle && aPacketHandle)
Expand Down Expand Up @@ -282,7 +289,7 @@ void PacketBuffer::AddToEnd(PacketBufferHandle && aPacketHandle)

void PacketBuffer::CompactHead()
{
uint8_t * const kStart = reinterpret_cast<uint8_t *>(this) + kStructureSize;
uint8_t * const kStart = ReserveStart();

if (this->payload != kStart)
{
Expand Down Expand Up @@ -505,7 +512,7 @@ PacketBufferHandle PacketBufferHandle::New(size_t aAvailableSize, uint16_t aRese
return PacketBufferHandle();
}

lPacket->payload = reinterpret_cast<uint8_t *>(lPacket) + PacketBuffer::kStructureSize + aReservedSize;
lPacket->payload = lPacket->ReserveStart() + aReservedSize;
lPacket->len = lPacket->tot_len = 0;
lPacket->next = nullptr;
lPacket->ref = 1;
Expand Down Expand Up @@ -669,8 +676,7 @@ PacketBufferHandle PacketBufferHandle::CloneData() const
return PacketBufferHandle();
}
clone.mBuffer->tot_len = clone.mBuffer->len = original->len;
memcpy(reinterpret_cast<uint8_t *>(clone.mBuffer) + PacketBuffer::kStructureSize,
reinterpret_cast<uint8_t *>(original) + PacketBuffer::kStructureSize, originalDataSize + originalReservedSize);
memcpy(clone->ReserveStart(), original->ReserveStart(), originalDataSize + originalReservedSize);

if (cloneHead.IsNull())
{
Expand Down
8 changes: 8 additions & 0 deletions src/system/SystemPacketBuffer.h
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Original file line number Diff line number Diff line change
Expand Up @@ -383,6 +383,14 @@ class DLL_EXPORT PacketBuffer : private pbuf
void Clear();
void SetDataLength(uint16_t aNewLen, PacketBuffer * aChainHead);

/**
* Get a pointer to the start of the reserved space (which comes before the
* payload). The actual reserved space is the ReservedSize() bytes starting
* at this pointer.
*/
uint8_t * ReserveStart();
const uint8_t * ReserveStart() const;

friend class PacketBufferHandle;
friend class ::PacketBufferTest;
};
Expand Down