# `Portals.Codec`
[🔗](https://github.com/Ziinc/portals/blob/v0.1.0/lib/portals/codec.ex#L1)

Behaviour implemented by every wire codec (`Portals.Codec.MessagePack` in
production, `Portals.Codec.ETFBench` for internal benchmarking only).

A codec encodes/decodes a single frame envelope (a list whose head is the
integer frame tag) to/from a binary. Codecs never see connection or
transport state; they are pure functions over bytes and terms.

# `decode_error`

```elixir
@type decode_error() ::
  {:truncated, non_neg_integer()}
  | {:trailing_bytes, non_neg_integer()}
  | {:max_depth_exceeded, non_neg_integer()}
  | {:max_length_exceeded, non_neg_integer()}
  | {:max_size_exceeded, non_neg_integer()}
  | {:unsafe_atom, binary()}
  | {:invalid_extension, term()}
  | {:invalid_encoding, term()}
```

# `envelope`

```elixir
@type envelope() :: list()
```

# `decode`

```elixir
@callback decode(binary(), Portals.Protocol.limits()) ::
  {:ok, envelope(), rest :: binary()} | {:error, decode_error()}
```

# `encode`

```elixir
@callback encode(envelope(), Portals.Protocol.limits()) ::
  {:ok, binary()} | {:error, decode_error()}
```

---

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