[RFC] Vortex: A P2P File Transfer Protocol Based on TLV

[gaius-qi]

Overview

Vortex is a peer-to-peer (P2P) file transfer protocol that utilizes the TLV (Tag-Length-Value) format for efficient and flexible data transmission. This protocol is designed to provide reliable and scalable file sharing capabilities.

Protocol Fields

• Packet Identifier (8 bits): Uniquely identifies each packet.
• Tag (T, 8 bits): Specifies the type of data in the value field.
• Length (L, 32 bits): Indicates the length (in bytes) of the Value field, supporting up to 4GiB of data.
• Value (V, variable length): The actual data, up to 1GiB.

Tag Definitions

Tag	Name	Description
0	Download Piece	Download the content of a piece from a peer. It is composed of {Task ID}-{Piece ID}, where the Task ID is a 32-byte SHA-256 value and the Piece ID is a number.
1	Piece Content	The content of a piece, with a maximum size of 1 GiB per piece.
2-254	Reserved	Reserved for future use.
255	Error	Error message.

Packet Format

Packet ID (8 bits)	Tag (8 bits)	Length (32 bits)	Value (up to 4GiB)
8-bit	8-bit	32-bit	variable

• Packet ID: 8-bit unsigned integer.
• Tag: 8-bit field describing the content type.
• Length: 32-bit field specifying the size of the Value.
• Value: Actual data, size determined by Length.

Behavior

• Download Piece (Tag=0x00): Download the content of a piece from a peer.
• Piece Content (Tag=0x01): Raw piece data or piece fragments.
• Error (Tag=0xFF): Conveys error.
• Reserved Tags: May be allocated for metadata, compression, encryption, or future protocol extensions.

Example

• Packet ID: 0x12
• Tag: 0x00 (download piece)
• Length: 10 (indicating "HelloWorld" is 10 bytes)
• Value: "HelloWorld"

Conclusion

This TLV-based protocol, with an 8-bit Packet Identifier and support for up to 1GiB in the Value field, offers flexibility, simplicity, and room for future enhancements. By reserving Tags, it is scalable for evolving P2P file transfer requirements.

References

• https://en.wikipedia.org/wiki/Type%E2%80%93length%E2%80%93value
• https://en.wikipedia.org/wiki/Link_Layer_Discovery_Protocol
• https://en.wikipedia.org/wiki/Dynamic_Host_Configuration_Protocol
• https://en.wikipedia.org/wiki/RADIUS