Projet_JAVA_P2P_STRI2A/doc/protocol.md

P2P-JAVA-PROJECT version 1.2 (Binary protocol for step 2+)

All strings in the datagram are utf-8 encoded. All numerical values are big endian.

1 byte:  [(byte  0  ): VERSION(0x11, first quartet is major version, second is minor)]
1 byte:  [(byte  1  ): REQUEST/RESPONSE CODE]
2 bytes: [(bytes 2-3): CHECKSUM (UDP only)]
4 bytes: [(bytes 4-7): PAYLOAD SIZE IN BYTES]
x bytes: [(bytes 8-?): PAYLOAD]

Requests and responses codes

• REQUESTS (msb is 0):

  • LIST (0x00)
  • LOAD (0x01)
  • HASH (0x02)
  • DISCOVER (0x03)
  • REGISTER (0x04)
  • UNREGISTER (0x05)
  • RATIO (0x06)
  • UPDATE RATIO (0x07)
  • SIZE (0x08)

• RESPONSES (msb is 1):

  • LIST (0x80)
  • LOAD (0x81)
  • HASH (0x82)
  • DISCOVER (0x83)
  • RATIO (0x86)
  • DENIED (0x87)
  • SIZE (0x88)
  • VERSION ERROR (0xC0)
  • PROTOCOL ERROR (0xC1)
  • INTERNAL ERROR (0xC2)
  • EMPTY DIRECTORY (0xC3)
  • NOT FOUND (0xC4)
  • EMPTY FILE (0xC5)
  • NOT A TRACKER (0xC6)
  • UNKNOWN HOST (0xC7)

List

Payload size for list request is always zero. Payload for list response is filenames separated by \n. Payload size for list response is never zero.

Empty directory

When directory is empty. Payload size for empty directory is always zero.

Load

Not found

Response when the file requested is not found on the server. Payload size for Not found is zero.

Load response

Payload contains

8 bytes: [(bytes  8-15): OFFSET OF FILE CONTENT IN BYTES]
4 bytes: [(bytes 24-27): FILENAME SIZE] (cannot be > to PAYLOAD_SIZE - 20 or be zero)
y bytes: [<FILENAME>]
z bytes: [PARTIAL CONTENT]

Load request

Payload contains

8 bytes: [(bytes  8-15): OFFSET OF FILE CONTENT IN BYTES]
8 bytes: [(bytes 16-23): MAX SIZE OF PARTIAL CONTENT (partial content in response should not excess this size, but this can be less (by example if endoffile is reached or server doesn't have the full block requested)
4 bytes: [(bytes 24-27): FILENAME SIZE] (cannot be > to PAYLOAD_SIZE - 20 or be zero)
y bytes: [<FILENAME>]
2 bytes: port used to register on tracker
? bytes: hostname used to register on tracker

Possible responses: Load response, or Denied

Size

Size request

Payload contains

? bytes: filename

Possible responses: Size response, Empty file or Not found

Size response

Payload contains

8 bytes: file size
? bytes: filename

Hash

Hash request

Get hash of a file. Payload contains

4 bytes: [(bytes  8-11): FILENAME SIZE]
y bytes: [<FILENAME>]
z bytes: [ALGO_NAMES requested separated by \n] (ex.: SHA-256, MD5)

If file does not exists, a Not found can be responded.

Hash response

Payload contains:

4 bytes: [(bytes  8-11): FILENAME SIZE]
y bytes: [<FILENAME>]
[[ multiple algo hashes bloc]]

A algo hash bloc contains:

4 bytes [ALGO_NAME size]
? [ALGO_NAME]
4 bytes: [HASH SIZE (bytes)] / or 0 if this hash algorithm is unsupported.
?? [HASH]

Tracker specific messages

Register

Used by a server to register itself on a tracker. Server may want to do a free DISCOVER to check if they have been registered. Payload contains:

2 bytes: [<PORT NUMBER>]

Unregister

Used by a server to unregister itself from a tracker. No error is raised if the server was not registered. Server may want to do a free DISCOVER to check if they have been unregistered. Payload contains:

2 bytes: [<PORT NUMBER>]
? bytes: [<HOSTNAME>]

Discover request

If payload size is null, lists all servers registered. If payload contains a filename, list all servers having this file in their list.

? bytes: [<FILENAME>]
? bytes: [<HOSTNAME>]

Discover response

Contains:

4 bytes: [(bytes  8-11): FILENAME SIZE]
y bytes: [<FILENAME>]
? bytes [multiple server blocks] 

Server block is composed with:

2 bytes: [port]
? bytes: hostname
\n

Not a Tracker

This error is raised when receiving a Discover, a Register, or an Unregister request, but this application is not a tracker.

Ratio Request

Contains:

2 bytes: port
? bytes: hostname

Possible responses: Ratio response, or Unknown host

Ratio Response

Contains:

8 bytes: total sent bytes
8 bytes: total received bytes
2 bytes: port
? bytes: hostname

Update Ratio

Contains:

8 bytes: bytes sent by the server
2 bytes: server port
2 bytes: client* port
? bytes: server hostname followed by \n
? bytes: client* hostname
* note: used by client to register on tracker

Possible responses: No response, or Unknown host (if client is not registered or server is not registered)

Note: client must have verified hash before sending Update Ratio to tracker for each server which participated.

Unknown Host

Payload size is zero.

Denied

Contains

8 bytes: offset of content asked
? bytes: filename

Other response code (errors)

Version error

Response when datagram received use wrong version code.

Protocol error

Response when the request cannot be interpreted (but version is correct). Payload size for Protocol error is zero

Internal error

Response in internal failure case. Payload size for Internal error is zero.