Two-Phase Init, Provable

Implement a two-phase connection object. The boilerplate declares: ``c typedef enum { C_NEW, C_READY, C_CONNECTED, C_FAILED } CState; typedef struct { CState state; char target[32]; int attempts; } Conn; int conn_init(Conn *c); /* -> C_READY; 0 ok, -1 NULL */ int conn_connect(Conn *c, const char *target);/* 0 ok, -1 bad; -> C_CONNECTED or C_FAILED (attempts counted) */ void conn_close(Conn *c); /* -> C_READY from CONNECTED/FAILED; no-op from NEW/READY */ int conn_destroy(Conn *c); /* safe from EVERY state; 0 ok, -1 NULL */ `` connect fails (state C_FAILED) iff target is NULL/empty or longer than 31 chars. destroy must succeed from every reachable state.

Difficulty: intermediate