1 files changed, 258 insertions, 0 deletions
diff --git a/xpcom/io/SnappyFrameUtils.cpp b/xpcom/io/SnappyFrameUtils.cpp
new file mode 100644
index 000000000..97883a362
--- /dev/null
+++ b/xpcom/io/SnappyFrameUtils.cpp
@@ -0,0 +1,258 @@
+/* -*- 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::detail::SnappyFrameUtils;
+using mozilla::NativeEndian;
+
+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