Function SnappyBlockDecompress

be/src/util/decompress.cc:443–510

Utility function to decompress snappy block compressed data. If size_only is true, this function does not decompress but only computes the output size and writes the result to *output_len. If size_only is false, output buffer size must be at least *output_len. *output_len is updated with the actual output size if the decompression succeeds, and is set to 0 otherwise. size_only is an O(1) operatio

// otherwise.
// size_only is an O(1) operation (just reads a single varint for each snappy block).
static Status SnappyBlockDecompress(int64_t input_len, const uint8_t* input,
    bool size_only, int64_t* output_len, char* output) {
  int64_t buffer_size = *output_len;
  *output_len = 0;
  int64_t uncompressed_total_len = 0;
  while (input_len > 0) {
    uint32_t uncompressed_block_len = ReadWriteUtil::GetInt<uint32_t>(input);
    input += sizeof(uint32_t);
    input_len -= sizeof(uint32_t);

    if (!size_only) {
      int64_t remaining_output_size = buffer_size - uncompressed_total_len;
      if (remaining_output_size < uncompressed_block_len) {
        return Status(TErrorCode::SNAPPY_DECOMPRESS_DECOMPRESS_SIZE_INCORRECT);
      }
    }

    while (uncompressed_block_len > 0) {
      // Check that input length should not be negative.
      if (input_len < 0) {
        stringstream ss;
        ss << " Corruption snappy decomp input_len " << input_len;
        return Status(ss.str());
      }
      // Read the length of the next snappy compressed block.
      size_t compressed_len = ReadWriteUtil::GetInt<uint32_t>(input);
      input += sizeof(uint32_t);
      input_len -= sizeof(uint32_t);

      if (compressed_len == 0 || compressed_len > input_len) {
        return Status(TErrorCode::SNAPPY_DECOMPRESS_INVALID_COMPRESSED_LENGTH);
      }

      // Read how big the output will be.
      size_t uncompressed_len;
      if (!snappy::GetUncompressedLength(reinterpret_cast<const char*>(input),
              compressed_len, &uncompressed_len)) {
        return Status(TErrorCode::SNAPPY_DECOMPRESS_UNCOMPRESSED_LENGTH_FAILED);
      }
      // Check that uncompressed length should be greater than 0.
      if (uncompressed_len <= 0) {
        return Status(TErrorCode::SNAPPY_DECOMPRESS_UNCOMPRESSED_LENGTH_FAILED);
      }
      DCHECK_GT(uncompressed_len, 0);

      if (!size_only) {
        // Check output bounds
        int64_t remaining_output_size = buffer_size - uncompressed_total_len;
        if (remaining_output_size < uncompressed_len) {
          return Status(TErrorCode::SNAPPY_DECOMPRESS_DECOMPRESS_SIZE_INCORRECT);
        }
        // Decompress this snappy block
        if (!snappy::RawUncompress(reinterpret_cast<const char*>(input),
                compressed_len, output)) {
          return Status(TErrorCode::SNAPPY_DECOMPRESS_RAW_UNCOMPRESS_FAILED);
        }
        output += uncompressed_len;
      }