Method DecompressData

cpp/src/arrow/io/compressed.cc:302–343

Decompress some data from the compressed_ buffer into decompressor_. Call this function only if the decompressed_ buffer is fully consumed.

  // Decompress some data from the compressed_ buffer into decompressor_.
  // Call this function only if the decompressed_ buffer is fully consumed.
  Status DecompressData() {
    // compressed_buffer_available() could be 0 here because there might
    // still be some decompressed data left to emit even though the compressed
    // data was entirely consumed (especially if the expansion factor is large)
    DCHECK_NE(compressed_->data(), nullptr);
    DCHECK_EQ(0, decompressed_buffer_available());

    int64_t decompress_size = kDecompressSize;

    while (true) {
      if (decompressed_ == nullptr) {
        ARROW_ASSIGN_OR_RAISE(decompressed_,
                              AllocateResizableBuffer(decompress_size, pool_));
      } else {
        // Shrinking the buffer if it's already large enough
        RETURN_NOT_OK(decompressed_->Resize(decompress_size, /*shrink_to_fit=*/true));
      }
      decompressed_pos_ = 0;

      int64_t input_len = compressed_->size() - compressed_pos_;
      const uint8_t* input = compressed_->data() + compressed_pos_;
      int64_t output_len = decompressed_->size();
      uint8_t* output = decompressed_->mutable_data();

      ARROW_ASSIGN_OR_RAISE(
          auto result, decompressor_->Decompress(input_len, input, output_len, output));
      compressed_pos_ += result.bytes_read;
      if (result.bytes_read > 0) {
        fresh_decompressor_ = false;
      }
      if (result.bytes_written > 0 || !result.need_more_output || input_len == 0) {
        // Not calling shrink_to_fit here because we're likely to reusing the buffer.
        RETURN_NOT_OK(
            decompressed_->Resize(result.bytes_written, /*shrink_to_fit=*/false));
        break;
      }
      DCHECK_EQ(result.bytes_written, 0);
      // Need to enlarge output buffer
      decompress_size *= 2;
    }
    return Status::OK();
  }

  // Copying a given number of bytes from the decompressed_ buffer.
  int64_t ReadFromDecompressed(int64_t nbytes, uint8_t* out) {