# `RawPing.Packet`
[🔗](https://github.com/awksedgreep/raw_ping/blob/v0.2.0/lib/raw_ping/packet.ex#L1)

ICMP packet construction and parsing.

Handles building ICMP echo request packets and parsing echo reply packets.

## ICMP Echo Request/Reply Format

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |     Type      |     Code      |          Checksum             |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |           Identifier          |        Sequence Number        |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |     Data ...
    +-+-+-+-+-+-+-+-

- Type 8, Code 0: Echo Request
- Type 0, Code 0: Echo Reply

# `build_echo_request`

```elixir
@spec build_echo_request(non_neg_integer(), non_neg_integer(), non_neg_integer()) ::
  binary()
```

Build an ICMP echo request packet.

## Parameters

  * `id` - Identifier (16-bit)
  * `seq` - Sequence number (16-bit)
  * `payload_size` - Size of payload data in bytes

Returns a binary packet ready to send.

# `calculate_checksum`

```elixir
@spec calculate_checksum(binary()) :: non_neg_integer()
```

Calculate the ICMP checksum (one's complement of one's complement sum).

# `parse_echo_reply`

```elixir
@spec parse_echo_reply(binary()) ::
  {:ok, non_neg_integer(), non_neg_integer(), non_neg_integer()}
  | {:error, term()}
```

Parse an ICMP echo reply packet.

The input includes the IP header (20 bytes typically) followed by the ICMP packet.

Returns `{:ok, id, seq, ttl}` or `{:error, reason}`.

---

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