harvey/sys/src/cmd/auth/secstore/SConn.h

// delimited, authenticated, encrypted connection
enum{ Maxmsg=4096 };	// messages > Maxmsg bytes are truncated
typedef struct SConn SConn;

extern SConn* newSConn(int);	// arg is open file descriptor
struct SConn{
	void *chan;
	int secretlen;
	int (*secret)(SConn*, uchar*, int);// 
	int (*read)(SConn*, uchar*, int); // <0 if error;  errmess in buffer
	int (*write)(SConn*, uchar*, int);
	void (*free)(SConn*);		// also closes file descriptor
};
// secret(s,b,dir) sets secret for digest, encrypt, using the secretlen
//		bytes in b to form keys 	for the two directions;
//	  set dir=0 in client, dir=1 in server

// error convention: write !message in-band
extern void writerr(SConn*, char*);
extern int readstr(SConn*, char*);  // call with buf of size Maxmsg+1
	// returns -1 upon error, with error message in buf

extern void *emalloc(ulong); /* dies on failure; clears memory */
extern void *erealloc(void *, ulong);
extern char *estrdup(char *);