requestFileData (11)

The requestFileData message is sent by the file recipient to the sender to request a specific portion (a "chunk" or "packet") of the file. This pull-based mechanism allows the receiver to manage the download rate and re-request missing chunks.

Core Data Types

• string: A standard UTF-8 encoded string.
• uint64: A 64-bit unsigned integer, serialized in Little-Endian format.

Payload Structure

Field	Data Type	Min	Max	Description
uid	string	*	*	The unique identifier of the file transfer session.
packetNumber	uint64	0	*	The sequential index of the file chunk being requested (starting from 0).

Behavioral Notes

• Receiver-Driven: The file download is driven by the receiver. After sending acceptFile, the receiver's client begins sending a series of requestFileData messages, typically in sequential order, until all chunks have been requested.
• Sender Response: When the sender's client receives a requestFileData message, it must read the corresponding chunk of data from the source file and send it back to the recipient in a fileData message.
• Retries: If a fileData message for a specific chunk is not received within a timeout period, the recipient can resend the requestFileData message for that same packetNumber.