F3.Footer (F3 v0.1.0)

Decodes an F3 footer into F3.Metadata.

The footer FlatBuffers buffer is the last footer_size bytes of the metadata span. Column metadata is a separate FlatBuffers root in the bytes before that footer. Both reads stay inside the span already accepted by F3.Postscript. Wasm section payloads are not read.

Summary

Functions

decode(span, postscript)

Decodes a metadata span that was already bounds-checked.

load(file, max)

Reads the metadata span and returns the decoded file metadata.

Functions

decode(span, postscript)

@spec decode(binary(), F3.Postscript.t()) ::
  {:ok, F3.Metadata.t()} | {:error, F3.Error.t()}

Decodes a metadata span that was already bounds-checked.

span is the metadata bytes. postscript.footer_size selects the footer at the end of that span. A span shorter than footer_size raises ArgumentError. A span that is not a FlatBuffers table returns :corrupt_metadata.

Examples

iex> post = %F3.Postscript{
...>   metadata_size: 1,
...>   footer_size: 1,
...>   footer_compression: :uncompressed,
...>   checksum_type: :xxhash,
...>   data_checksum: 0,
...>   schema_checksum: 0,
...>   major_version: 0,
...>   minor_version: 1,
...>   metadata_offset: 0,
...>   footer_offset: 0,
...>   file_size: 1
...> }
iex> {:error, error} = F3.Footer.decode(<<0>>, post)
iex> error.category
:corrupt_metadata

load(file, max)

@spec load(F3.File.t(), non_neg_integer()) ::
  {:ok, F3.Metadata.t()} | {:error, F3.Error.t()}

Reads the metadata span and returns the decoded file metadata.

max is the metadata cap in bytes. A short file is :truncated. A file that is not an F3.File, or a negative max, raises FunctionClauseError.

Examples

iex> {:ok, file} = F3.open("test/fixtures/small.f3")
iex> {:ok, meta} = F3.Footer.load(file, F3.Postscript.max_metadata_bytes())
iex> Enum.map(meta.schema.fields, & &1.name)
["trade_id", "symbol", "price"]

iex> {:ok, short} = F3.open({:memory, "no"})
iex> {:error, error} = F3.Footer.load(short, 32)
iex> error.category
:truncated