# `Layr8.Attachment`
[🔗](https://github.com/layr8/elixir_sdk/blob/main/lib/layr8/attachment.ex#L1)

A DIDComm v2 attachment.

Attachments carry payloads that travel alongside a message but are not part
of the message body — signed credentials, large binaries, file references, etc.

## Fields

- `id` — unique attachment identifier (within the containing message)
- `description` — human-readable description
- `filename` — suggested filename for downloaded content
- `media_type` — IANA media type of the content (e.g. `application/jwt`)
- `format` — protocol-specific format identifier (e.g. `application/vc+jwt`)
- `lastmod_time` — last modification time as a Unix timestamp (integer)
- `byte_count` — size of the attached content in bytes
- `data` — map carrying the payload; see DIDComm v2 spec §5

## `data` map

The `data` map may contain one or more of:

- `"base64"` — base64url-encoded bytes (no padding)
- `"json"` — inline JSON value
- `"jws"` — a JSON-serialized JWS (object, not a compact string)
- `"hash"` — base64url-encoded SHA-256 of the referenced content
- `"links"` — list of URLs pointing to the content

For signed credentials sent as compact JWT strings, use `data.base64`:

    Base.url_encode64(compact_jwt, padding: false)

placed under the `"base64"` key.

## Wire format

    %{
      "id" => "...",
      "format" => "...",
      "media_type" => "...",
      "data" => %{"base64" => "..."}
    }

Optional fields are omitted when empty/nil.

# `data_map`

```elixir
@type data_map() :: %{optional(String.t()) => term()}
```

# `t`

```elixir
@type t() :: %Layr8.Attachment{
  byte_count: non_neg_integer() | nil,
  data: data_map(),
  description: String.t(),
  filename: String.t(),
  format: String.t(),
  id: String.t(),
  lastmod_time: non_neg_integer() | nil,
  media_type: String.t()
}
```

# `marshal`

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

Serializes an `Attachment` into a DIDComm v2 JSON envelope map.

Optional string fields are omitted when empty; optional numeric fields are
omitted when `nil`. `data` is always included (defaults to `%{}`).

# `parse`

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

Parses a DIDComm v2 attachment map into an `Attachment` struct.

Missing fields default to empty strings / `nil` / `%{}`.

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