tftp-client-coq
Simple TFTP client written in Coq (with IO handling done in OCaml) as an assesment for the Computer-Aided Verification course at MIMUW. The program is written as a state machine that reacts on two kinds of events: new packet income and timeout signal from OCaml.
The implementation follows RFC1350 standard. The compliance with the specification is ensured by tight typing and constructively proven theorems in intuitionistic logic.
Example usage
Downloading a file
ocamlrun main.byte -h 127.0.0.1 -m w file.txt
Uploading a file
ocamlrun main.byte -h 127.0.0.1 -m r file.txt
Proven/constrained stuff
- 16 bits bounds checks for datagram naturals
- 8 bits bounds checks for ascii to nat conversions
- Error code bounds and embedding
- Packet sender control (for instance, there is no such thing as "WRQ sent by server")
- Reading/Writing mode packet control (for instance, it is impossible to send WRQ in downloading mode)
- Packet opcode bounds and embedding
- Additional string appending and splitting lemmas
- Reading/Writing mode event control (for instance, it is impossible to receive ACK in Reading mode)
- Error state will persist regardless of events
- Any event that occured after final state leads to an error state
- Receiving block smaller than 512 bytes causes transition to final state
- The communication port (beside initial) doesn't change
- After receiving nth block that is not final client will wait for (n+1)th
- After receiving data block the correct ACK will be sent
- After reaching the end of file the writing state becomes finalized
- After receiving ACK last sent block and there is any data left, the next block will be sent and the state will move on
- After receiving ACK for previous block the previous block will be retransmitted and the state will persist