def prepare_read(manifest: LocalFileManifest, size: int, offset: int) -> Chunks:
# Prepare
chunks: List[Chunk] = []
offset = min(offset, manifest.size)
size = min(size, manifest.size - offset)
# Loop over blocks
for block, length, start in split_read(size, offset, manifest.blocksize):
# Loop over chunks
block_chunks = manifest.get_chunks(block)
chunks += block_read(block_chunks, length, start)
# Return read result
return tuple(chunks)
def prepare_write(
manifest: LocalFileManifest, size: int, offset: int, timestamp: DateTime
) -> Tuple[LocalFileManifest, WriteOperationList, ChunkIDSet]:
# Prepare
padding = 0
removed_ids: ChunkIDSet = set()
write_operations: WriteOperationList = []
# Padding
if offset > manifest.size:
padding = offset - manifest.size
size += padding
offset = manifest.size
# Copy buffers
blocks = list(manifest.blocks)
# Loop over blocks
for block, subsize, start, content_offset in split_write(
size, offset, manifest.blocksize):
# Prepare new chunk
new_chunk = Chunk.new(start, start + subsize)
write_operations.append((new_chunk, content_offset - padding))
# Lazy block write
chunks = manifest.get_chunks(block)
new_chunks, more_removed_ids = block_write(chunks, subsize, start,
new_chunk)
# Update data structures
removed_ids |= more_removed_ids
if len(blocks) == block:
blocks.append(new_chunks)
else:
blocks[block] = new_chunks
# Evolve manifest
new_size = max(manifest.size, offset + size)
new_manifest = manifest.evolve_and_mark_updated(size=new_size,
blocks=tuple(blocks),
timestamp=timestamp)
# Return write result
return new_manifest, write_operations, removed_ids
