# `F3.Metadata`

File metadata from the postscript, the FlatBuffers footer, and the
out-of-band column metadata those tables point at.

Checksums are copied from the postscript. They are not recomputed.
Optional section offsets are recorded and not read. Nothing in this
struct is a Wasm module or a column payload.

`to_map/1` is the JSON shape compared with the upstream reader. It uses
string keys and does not include column names, which exist only on
`row_groups` after the schema is aligned.

# `encoding_version`

```elixir
@type encoding_version() :: %{
  encoding: F3.RowGroup.encoding(),
  version: %{
    major: non_neg_integer(),
    minor: non_neg_integer(),
    patch: non_neg_integer()
  }
}
```

# `logical_id`

```elixir
@type logical_id() ::
  :flat | :list | :struct | :list_of_struct_of_primitive | non_neg_integer()
```

# `logical_tree`

```elixir
@type logical_tree() :: %{id: logical_id(), children: [logical_tree()]}
```

# `section`

```elixir
@type section() :: %{
  name: String.t(),
  offset: non_neg_integer(),
  size: non_neg_integer(),
  compression: F3.RowGroup.compression()
}
```

# `shared_dictionary`

```elixir
@type shared_dictionary() :: %{
  chunks: [F3.RowGroup.chunk()],
  positions: [[non_neg_integer()]],
  schema: F3.Schema.t() | nil,
  schema_bytes: non_neg_integer()
}
```

# `t`

```elixir
@type t() :: %F3.Metadata{
  checksum_type: F3.Postscript.checksum_type(),
  data_checksum: non_neg_integer(),
  encoding_versions: [encoding_version()],
  footer_compression: :uncompressed,
  footer_size: non_neg_integer(),
  logical_tree: logical_tree(),
  major_version: non_neg_integer(),
  metadata_size: non_neg_integer(),
  minor_version: non_neg_integer(),
  optional_sections: [section()],
  row_groups: [F3.RowGroup.t()],
  schema: F3.Schema.t(),
  schema_checksum: non_neg_integer(),
  shared_dictionary: shared_dictionary() | nil
}
```

# `to_map`

```elixir
@spec to_map(t()) :: map()
```

Map compared with the committed upstream golden files.

Keys are strings. Column payloads are not included. A value that is not
metadata raises `FunctionClauseError`.

## Examples

    iex> {:ok, file} = F3.open("test/fixtures/small.f3")
    iex> {:ok, meta} = F3.metadata(file)
    iex> map = F3.Metadata.to_map(meta)
    iex> map["postscript"]["major_version"]
    0

---

*Consult [api-reference.md](api-reference.md) for complete listing*