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Design choices

Because the project is relying on DNS request/reply, we have limited amount of bit we can send.

I'll try to explain here the different limits and how I'm trying to stay in bound.

IPv4 datagram

+----------------+-------------+------------------------------------+
|  IPv4 headers  | UDP headers |              UDP data              |
|    20 bytes    |   8 bytes   |        max size 65'507 bytes       |
+----------------+-------------+------------------------------------+
                 \__________________________________________________/
                                 max size 65'515 bytes

DNS packet

DNS packets are stored in the UDP data.

+-------------------+---------+---------+-----------+-----------------+
| DNS fixed headers | Queries | Answers | Authority | Additional info |
|      12 bytes     | section | section |  section  |     section     |
+-------------------+---------+---------+-----------+-----------------+
                    \_________________________________________________/
                                        variable size

According to this blog post by Cloudfare, our DNS answers should fit in a 512 bytes UDP packet, thus we can calculate the variable size:

512B = UDP headers + DNS fixed headers + variable size
512B =      8B     +        12B        + x
x    = 512 - 8 - 12 B
     = 492B

Thus we have only 492 bytes for our data.

[WIP] Compression

To achieve this, we will need to perform some compression. Here I chose to use Huffman coding.