Core format

This is a description of the transit-independent, extensible PearDrop protocol.

Packet types

All offsets are in big endian, and offsets and lengths are in bytes. Multi-byte payloads are to be coded in big endian.

In bitfields, offsets are in little endian, and offsets and lengths are in bits.

Advertisement packet

Maximum length: 128 bytes

From: sender

To: advertise

Offset	Length	Type	Name	Description
0x0	0x1	u8	exts_len	Number of extensions this packet contains.
0x1	max 0x7d	[Extension; ext_len]	exts	The extensions in this packet. Maximum 125 bytes total.
0x7d	0x1	u8	name_len	Length of the name of the advertised file. Maximum 125 bytes.
0x7d	name_len	&str	name	Name of the advertised file. Maximum length of 125 bytes.
0x7e	0x1	u8	mt_len	Length of the mimetype of the advertised file. Maximum 125 bytes.
0x7e	mt_len	&str	mimetype	MIME type of the advertised file. Maximum length of 125 bytes.
end: 0x7f (= 0x80-1)

AdFlags bitfield

Reserved for extensions.

Sender packet

Maximum length: 4096 bytes

From: sender

To: single receiver

Offset	Length	Type	Name	Description
0x0	0x1	u8	ext_len	Number of extensions this packet contains.
0x1	max 0xff7	[Extension; ext_len]	exts	The extensions in this packet. Maximum 4087 bytes total.
0xff7	0x8	u64	len	Length of the data.
end: 0xfff (= 0x1000-1)

Receiver acknowledge packet

Maximum length: 128 bytes

From: receiver

To: sender

Offset	Length	Type	Name	Description
0x0	4 bits	ReceiverAcknowledgeType	type	Type of the packet being acknowledged.
4 bits	4 bits	u4	exts_len	Number of extensions in this packet.
0x1	max 0x7f	[Extension; ext_len]	exts	The extensions in this packet. Maximum 31 bytes total.
end: 0x80

Data packet

No maximum length. This should be the length specified in the sender packet.

This should be sent over a reliable stream protocol (like TCP), or properly chunked otherwise.

This packet simply consists of the data and nothing else.

Common types

Extension trait

Reserved for extensions. All sub-structs must have these fields at the start:

Offset	Length	Type	Name	Description
0x0	0x1	ExtType	type	Type of this extension.
0x1	0x1	u8	len	Length of this entire structure.

ExtType enum

Must fit in a u8. Reserved for extensions.

Handshake

Sender     Receiver(s)     Receiver
   ------------->
   advertisement

   <----------------------------
   acknowledge: advertisement

   <--------------------------->
   (optional) extension pre-handshakes

   ---------------------------->
   sender packet

   <----------------------------
   acknowledge: sender

   <--------------------------->
   (optional) extension post-handshakes

   ---------------------------->
   data packet

   <----------------------------
   acknowledge: data

   transfer complete :)