Function write_buffer

arrow-ipc/src/writer.rs:2116–2144

Write a buffer into `arrow_data`, a vector of bytes, and adds its [`crate::Buffer`] to `buffers`. Returns the new offset in `arrow_data` From Each constituent buffer is first compressed with the indicated compressor, and then written with the uncompressed length in the first 8 bytes as a 64-bit

(
    buffer: &[u8],                    // input
    buffers: &mut Vec<crate::Buffer>, // output buffer descriptors
    arrow_data: &mut Vec<u8>,         // output stream
    offset: i64,             

/// follows is not compressed, which can be useful for cases where
/// compression does not yield appreciable savings.
fn write_buffer(
    buffer: &[u8],                    // input
    buffers: &mut Vec<crate::Buffer>, // output buffer descriptors
    arrow_data: &mut Vec<u8>,         // output stream
    offset: i64,                      // current output stream offset
    compression_codec: Option<CompressionCodec>,
    compression_context: &mut CompressionContext,
    alignment: u8,
) -> Result<i64, ArrowError> {
    let len: i64 = match compression_codec {
        Some(compressor) => compressor.compress_to_vec(buffer, arrow_data, compression_context)?,
        None => {
            arrow_data.extend_from_slice(buffer);
            buffer.len()
        }
    }
    .try_into()
    .map_err(|e| {
        ArrowError::InvalidArgumentError(format!("Could not convert compressed size to i64: {e}"))
    })?;

    // make new index entry
    buffers.push(crate::Buffer::new(offset, len));
    // padding and make offset aligned
    let pad_len = pad_to_alignment(alignment, len as usize);
    arrow_data.extend_from_slice(&PADDING[..pad_len]);

    Ok(offset + len + (pad_len as i64))
}

const PADDING: [u8; 64] = [0; 64];