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Diffstat (limited to 'xpcom/io/SnappyFrameUtils.cpp')
| -rw-r--r-- | xpcom/io/SnappyFrameUtils.cpp | 241 |
1 files changed, 241 insertions, 0 deletions
diff --git a/xpcom/io/SnappyFrameUtils.cpp b/xpcom/io/SnappyFrameUtils.cpp new file mode 100644 index 0000000000..c606794fd9 --- /dev/null +++ b/xpcom/io/SnappyFrameUtils.cpp @@ -0,0 +1,241 @@ +/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */ +/* vim: set ts=8 sts=2 et sw=2 tw=80: */ +/* This Source Code Form is subject to the terms of the Mozilla Public + * License, v. 2.0. If a copy of the MPL was not distributed with this + * file, You can obtain one at http://mozilla.org/MPL/2.0/. */ + +#include "mozilla/SnappyFrameUtils.h" + +#include "crc32c.h" +#include "mozilla/EndianUtils.h" +#include "nsDebug.h" +#include "snappy/snappy.h" + +namespace { + +using mozilla::NativeEndian; +using mozilla::detail::SnappyFrameUtils; + +SnappyFrameUtils::ChunkType ReadChunkType(uint8_t aByte) { + if (aByte == 0xff) { + return SnappyFrameUtils::StreamIdentifier; + } else if (aByte == 0x00) { + return SnappyFrameUtils::CompressedData; + } else if (aByte == 0x01) { + return SnappyFrameUtils::UncompressedData; + } else if (aByte == 0xfe) { + return SnappyFrameUtils::Padding; + } + + return SnappyFrameUtils::Reserved; +} + +void WriteChunkType(char* aDest, SnappyFrameUtils::ChunkType aType) { + unsigned char* dest = reinterpret_cast<unsigned char*>(aDest); + if (aType == SnappyFrameUtils::StreamIdentifier) { + *dest = 0xff; + } else if (aType == SnappyFrameUtils::CompressedData) { + *dest = 0x00; + } else if (aType == SnappyFrameUtils::UncompressedData) { + *dest = 0x01; + } else if (aType == SnappyFrameUtils::Padding) { + *dest = 0xfe; + } else { + *dest = 0x02; + } +} + +void WriteUInt24(char* aBuf, uint32_t aVal) { + MOZ_ASSERT(!(aVal & 0xff000000)); + uint32_t tmp = NativeEndian::swapToLittleEndian(aVal); + memcpy(aBuf, &tmp, 3); +} + +uint32_t ReadUInt24(const char* aBuf) { + uint32_t val = 0; + memcpy(&val, aBuf, 3); + return NativeEndian::swapFromLittleEndian(val); +} + +// This mask is explicitly defined in the snappy framing_format.txt file. +uint32_t MaskChecksum(uint32_t aValue) { + return ((aValue >> 15) | (aValue << 17)) + 0xa282ead8; +} + +} // namespace + +namespace mozilla { +namespace detail { + +using mozilla::LittleEndian; + +// static +nsresult SnappyFrameUtils::WriteStreamIdentifier(char* aDest, + size_t aDestLength, + size_t* aBytesWrittenOut) { + if (NS_WARN_IF(aDestLength < (kHeaderLength + kStreamIdentifierDataLength))) { + return NS_ERROR_NOT_AVAILABLE; + } + + WriteChunkType(aDest, StreamIdentifier); + aDest[1] = 0x06; // Data length + aDest[2] = 0x00; + aDest[3] = 0x00; + aDest[4] = 0x73; // "sNaPpY" + aDest[5] = 0x4e; + aDest[6] = 0x61; + aDest[7] = 0x50; + aDest[8] = 0x70; + aDest[9] = 0x59; + + static_assert(kHeaderLength + kStreamIdentifierDataLength == 10, + "StreamIdentifier chunk should be exactly 10 bytes long"); + *aBytesWrittenOut = kHeaderLength + kStreamIdentifierDataLength; + + return NS_OK; +} + +// static +nsresult SnappyFrameUtils::WriteCompressedData(char* aDest, size_t aDestLength, + const char* aData, + size_t aDataLength, + size_t* aBytesWrittenOut) { + *aBytesWrittenOut = 0; + + size_t neededLength = MaxCompressedBufferLength(aDataLength); + if (NS_WARN_IF(aDestLength < neededLength)) { + return NS_ERROR_NOT_AVAILABLE; + } + + size_t offset = 0; + + WriteChunkType(aDest, CompressedData); + offset += kChunkTypeLength; + + // Skip length for now and write it out after we know the compressed length. + size_t lengthOffset = offset; + offset += kChunkLengthLength; + + uint32_t crc = ComputeCrc32c( + ~0, reinterpret_cast<const unsigned char*>(aData), aDataLength); + uint32_t maskedCrc = MaskChecksum(crc); + LittleEndian::writeUint32(aDest + offset, maskedCrc); + offset += kCRCLength; + + size_t compressedLength; + snappy::RawCompress(aData, aDataLength, aDest + offset, &compressedLength); + + // Go back and write the data length. + size_t dataLength = compressedLength + kCRCLength; + WriteUInt24(aDest + lengthOffset, dataLength); + + *aBytesWrittenOut = kHeaderLength + dataLength; + + return NS_OK; +} + +// static +nsresult SnappyFrameUtils::ParseHeader(const char* aSource, + size_t aSourceLength, + ChunkType* aTypeOut, + size_t* aDataLengthOut) { + if (NS_WARN_IF(aSourceLength < kHeaderLength)) { + return NS_ERROR_NOT_AVAILABLE; + } + + *aTypeOut = ReadChunkType(aSource[0]); + *aDataLengthOut = ReadUInt24(aSource + kChunkTypeLength); + + return NS_OK; +} + +// static +nsresult SnappyFrameUtils::ParseData(char* aDest, size_t aDestLength, + ChunkType aType, const char* aData, + size_t aDataLength, + size_t* aBytesWrittenOut, + size_t* aBytesReadOut) { + switch (aType) { + case StreamIdentifier: + return ParseStreamIdentifier(aDest, aDestLength, aData, aDataLength, + aBytesWrittenOut, aBytesReadOut); + + case CompressedData: + return ParseCompressedData(aDest, aDestLength, aData, aDataLength, + aBytesWrittenOut, aBytesReadOut); + + // TODO: support other snappy chunk types + default: + MOZ_ASSERT_UNREACHABLE("Unsupported snappy framing chunk type."); + return NS_ERROR_NOT_IMPLEMENTED; + } +} + +// static +nsresult SnappyFrameUtils::ParseStreamIdentifier(char*, size_t, + const char* aData, + size_t aDataLength, + size_t* aBytesWrittenOut, + size_t* aBytesReadOut) { + *aBytesWrittenOut = 0; + *aBytesReadOut = 0; + if (NS_WARN_IF(aDataLength != kStreamIdentifierDataLength || + aData[0] != 0x73 || aData[1] != 0x4e || aData[2] != 0x61 || + aData[3] != 0x50 || aData[4] != 0x70 || aData[5] != 0x59)) { + return NS_ERROR_CORRUPTED_CONTENT; + } + *aBytesReadOut = aDataLength; + return NS_OK; +} + +// static +nsresult SnappyFrameUtils::ParseCompressedData(char* aDest, size_t aDestLength, + const char* aData, + size_t aDataLength, + size_t* aBytesWrittenOut, + size_t* aBytesReadOut) { + *aBytesWrittenOut = 0; + *aBytesReadOut = 0; + size_t offset = 0; + + uint32_t readCrc = LittleEndian::readUint32(aData + offset); + offset += kCRCLength; + + size_t uncompressedLength; + if (NS_WARN_IF(!snappy::GetUncompressedLength( + aData + offset, aDataLength - offset, &uncompressedLength))) { + return NS_ERROR_CORRUPTED_CONTENT; + } + + if (NS_WARN_IF(aDestLength < uncompressedLength)) { + return NS_ERROR_NOT_AVAILABLE; + } + + if (NS_WARN_IF(!snappy::RawUncompress(aData + offset, aDataLength - offset, + aDest))) { + return NS_ERROR_CORRUPTED_CONTENT; + } + + uint32_t crc = ComputeCrc32c( + ~0, reinterpret_cast<const unsigned char*>(aDest), uncompressedLength); + uint32_t maskedCrc = MaskChecksum(crc); + if (NS_WARN_IF(readCrc != maskedCrc)) { + return NS_ERROR_CORRUPTED_CONTENT; + } + + *aBytesWrittenOut = uncompressedLength; + *aBytesReadOut = aDataLength; + + return NS_OK; +} + +// static +size_t SnappyFrameUtils::MaxCompressedBufferLength(size_t aSourceLength) { + size_t neededLength = kHeaderLength; + neededLength += kCRCLength; + neededLength += snappy::MaxCompressedLength(aSourceLength); + return neededLength; +} + +} // namespace detail +} // namespace mozilla |