# Attachments & Drive Shares

## Attachments

Attachment upload and download via `/mail/v4/attachments`.

## Upload

```go
attachment, err := c.UploadAttachment(ctx, addrKR, proton.CreateAttachmentReq{
    MessageID:  "message-id",
    Filename:   "document.pdf",
    MIMEType:   "application/pdf",
    Disposition: proton.AttachmentDisposition,
    Body:       fileBytes,
})
```

Upload is **encrypted with the address keyring** and **signed (detached)** before upload. The server stores the encrypted `KeyPacket`, `DataPacket`, and `Signature` separately.

## Download

```go
// Download as bytes
data, err := c.GetAttachment(ctx, attachmentID)

// Stream into io.ReaderFrom
err := c.GetAttachmentInto(ctx, attachmentID, reader)
```

## Key Types

| Type | Description |
|---|---|
| `Attachment` | ID, name, size, MIME type, disposition (inline/attachment), headers, key packets, signature |
| `CreateAttachmentReq` | MessageID, filename, MIME type, disposition, content ID, body bytes |
| `Disposition` | InlineDisposition, AttachmentDisposition |

---

## Drive Shares

Proton Drive share management via `/drive/shares`.

## Operations

```go
// List shares
shares, err := c.ListShares(ctx, all)

// Get a single share with full key material
share, err := c.GetShare(ctx, shareID)
```

## Key Derivation

Shares use a two-step PGP decryption + passphrase unlock process:

```go
// Decrypt passphrase with address keyring, verify signature, unlock share key
keyRing, err := share.GetKeyRing(addrKR)
// Returns *crypto.KeyRing for Drive access
```

## Key Types

| Type | Description |
|---|---|
| `ShareMetadata` | ShareID, linkID, volumeID, type, state, creation/modify times, creator email |
| `Share` | Extends metadata with addressID, addressKeyID, encrypted key, passphrase, passphrase signature |
| `ShareType` | Main (1), Standard (2), Device (3) |
| `ShareState` | Active (1), Deleted (2) |