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.

```Datagram format

1 byte:  [0-7   (byte  0  ): VERSION(0x11, first quartet is major version, second is minor)]
1 byte:  [8-15  (byte  1  ): REQUEST/RESPONSE CODE]
2 bytes: [16-31 (bytes 2-3): RESERVED FOR FUTURE USE]
4 bytes: [32-63 (bytes 4-7): PAYLOAD SIZE IN BYTES]
x bytes: [64-xx (bytes 8-?): PAYLOAD]

```

## Requests and responses codes
- REQUESTS (msb is 0):
	- `LIST` (0x00)
	- `LOAD` (0x01)

- RESPONSES (msb is 1):
	- `LIST` (0x80)
	- `LOAD` (0x81)
	- `VERSION ERROR` (0xC0)
	- `PROTOCOL ERROR` (0xC1)
	- `INTERNAL ERROR` (0xC2)
	- `EMPTY DIRECTORY` (0xC3)
	- `NOT FOUND` (0xC4)
	- `EMPTY FILE` (0xC5)

### 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: [64-127  (bytes  8-16): OFFSET OF FILE CONTENT IN BYTES]
8 bytes: [128-191 (bytes 17-24): TOTAL FILESIZE]
4 bytes: [192-223 (bytes 25-28): FILENAME SIZE] (cannot be > to PAYLOAD_SIZE - 20 or be zero)
y bytes: [<FILENAME>]
z bytes: [PARTIAL CONTENT]
```

#### Load request
Payload contains

```
8 bytes: [64-127  (bytes  8-16): OFFSET OF FILE CONTENT IN BYTES]
8 bytes: [128-191 (bytes 17-24): 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: [192-223 (bytes 25-28): FILENAME SIZE] (cannot be > to PAYLOAD_SIZE - 20 or be zero)
y 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.