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#include <cobs.h>
/*@ requires \valid(dst + (0..dstlen-1));
@ requires \valid_read(src + (0..srclen-1));
@ requires \separated(dst + (0..dstlen-1), src + (0..srclen-1));
@
@ behavior valid:
@ assumes 0 <= srclen <= 254;
@ assumes 0 <= dstlen <= 65535;
@ assumes dstlen >= srclen+2;
@ assigns dst[0..srclen+1];
@ ensures \forall integer i; (0 <= i < srclen && \old(src[i]) != 0) ==> dst[i+1] == src[i];
@ ensures \result == srclen+2;
@ ensures \forall integer i; 0 <= i <= srclen ==> dst[i] != 0;
@ ensures dst[srclen+1] == 0;
@
@ behavior invalid:
@ assumes srclen < 0 || srclen > 254
@ || dstlen < 0 || dstlen > 65535
@ || dstlen < srclen+2;
@ assigns \nothing;
@ ensures \result == -1;
@
@ complete behaviors;
@ disjoint behaviors;
@*/
ssize_t cobs_encode(char *dst, size_t dstlen, char *src, size_t srclen) {
if (dstlen > 65535 || srclen > 254)
return -1;
//@ assert 0 <= dstlen <= 65535 && 0 <= srclen <= 254;
if (dstlen < srclen+2)
return -1;
//@ assert 0 <= srclen < srclen+2 <= dstlen;
size_t p = 0;
/*@ loop invariant 0 <= p <= srclen+1;
@ loop invariant \forall integer i; 0 <= i < p ==> dst[i] != 0;
@ loop invariant \forall integer i; 0 < i < p ==> (src[i-1] != 0 ==> dst[i] == src[i-1]);
@ loop assigns p, dst[0..srclen+1];
@ loop variant srclen-p+1;
@*/
while (p <= srclen) {
char val;
if (p != 0 && src[p-1] != 0) {
val = src[p-1];
} else {
size_t q = p;
/*@ loop invariant 0 <= p <= q <= srclen;
@ loop invariant \forall integer i; p <= i < q ==> src[i] != 0;
@ loop assigns q;
@ loop variant srclen-q;
@*/
while (q < srclen && src[q] != 0)
q++;
//@ assert q == srclen || src[q] == 0;
//@ assert q <= srclen <= 254;
val = (char)q-p+1;
//@ assert val != 0;
}
dst[p] = val;
p++;
}
dst[p] = 0;
//@ assert p == srclen+1;
return srclen+2;
}
int cobs_encode_incremental(void *f, int (*output)(void *f, char c), char *src, size_t srclen) {
if (srclen > 254)
return -1;
//@ assert 0 <= srclen <= 254;
size_t p = 0;
/*@ loop invariant 0 <= p <= srclen+1;
@ loop assigns p;
@ loop variant srclen-p+1;
@*/
while (p <= srclen) {
char val;
if (p != 0 && src[p-1] != 0) {
val = src[p-1];
} else {
size_t q = p;
/*@ loop invariant 0 <= p <= q <= srclen;
@ loop invariant \forall integer i; p <= i < q ==> src[i] != 0;
@ loop assigns q;
@ loop variant srclen-q;
@*/
while (q < srclen && src[q] != 0)
q++;
//@ assert q == srclen || src[q] == 0;
//@ assert q <= srclen <= 254;
val = (char)q-p+1;
//@ assert val != 0;
}
int rv = output(f, val);
if (rv)
return rv;
p++;
}
int rv = output(f, 0);
if (rv)
return rv;
//@ assert p == srclen+1;
return 0;
}
/*@ requires \valid(dst + (0..dstlen-1));
@ requires \valid_read(src + (0..srclen-1));
@ requires \separated(dst + (0..dstlen-1), src + (0..srclen-1));
@
@ behavior maybe_valid_frame:
@ assumes 1 <= srclen <= dstlen <= 65535;
@ assumes \exists integer j; j > 0 && \forall integer i; 0 <= i < j ==> src[i] != 0;
@ assumes \exists integer i; 0 <= i < srclen && src[i] == 0;
@ assigns dst[0..dstlen-1];
@ ensures \result >= 0 || \result == -3;
@ ensures \result >= 0 ==> src[\result+1] == 0;
@ ensures \result >= 0 ==> (\forall integer i; 0 <= i < \result ==> src[i] != 0);
@
@ behavior invalid_frame:
@ assumes 1 <= srclen <= dstlen <= 65535;
@ assumes src[0] == 0 || \forall integer i; 0 <= i < srclen ==> src[i] != 0;
@ assigns dst[0..dstlen-1];
@ ensures \result == -2;
@
@ behavior invalid_buffers:
@ assumes dstlen < 0 || dstlen > 65535
@ || srclen < 1 || srclen > 65535
@ || dstlen < srclen;
@ assigns \nothing;
@ ensures \result == -1;
@
@ complete behaviors;
@ disjoint behaviors;
@*/
ssize_t cobs_decode(char *dst, size_t dstlen, char *src, size_t srclen) {
if (dstlen > 65535 || srclen > 65535)
return -1;
if (srclen < 1)
return -1;
if (dstlen < srclen)
return -1;
size_t p = 1;
size_t c = (unsigned char)src[0];
//@ assert 0 <= c < 256;
//@ assert 0 <= c;
//@ assert c < 256;
if (c == 0)
return -2; /* invalid framing. An empty frame would be [...] 00 01 00, not [...] 00 00 */
//@ assert c >= 0;
//@ assert c != 0;
//@ assert c <= 257;
//@ assert c > 0;
//@ assert c >= 0 && c != 0 ==> c > 0;
/*@ //loop invariant \forall integer i; 0 <= i <= p ==> (i == srclen || src[i] != 0);
@ loop invariant \forall integer i; 1 <= i < p ==> src[i] != 0;
@ loop invariant c > 0;
@ loop invariant 1 <= p <= srclen <= dstlen <= 65535;
@ loop invariant \separated(dst + (0..dstlen-1), src + (0..srclen-1));
@ loop invariant \valid_read(src + (0..srclen-1));
@ loop invariant \forall integer i; 1 <= i <= srclen ==> \valid(dst + i - 1);
@ loop assigns dst[0..dstlen-1], p, c;
@ loop variant srclen-p;
@*/
while (p < srclen && src[p]) {
char val;
c--;
//@ assert src[p] != 0;
if (c == 0) {
c = (unsigned char)src[p];
val = 0;
} else {
val = src[p];
}
//@ assert 0 <= p-1 <= dstlen-1;
dst[p-1] = val;
p++;
}
if (p == srclen)
return -2; /* Invalid framing. The terminating null byte should always be present in the input buffer. */
if (c != 1)
return -3; /* Invalid framing. The skip counter does not hit the end of the frame. */
//@ assert 0 < p <= srclen <= 65535;
//@ assert src[p] == 0;
//@ assert \forall integer i; 1 <= i < p ==> src[i] != 0;
return p-1;
}
void cobs_decode_incremental_initialize(struct cobs_decode_state *state) {
state->p = 0;
state->c = 0;
}
/*@ requires \separated(state, dst + (0..dstlen-1));
requires \valid(state);
requires \valid(dst + (0..dstlen-1));
requires 0 < dstlen <= 65535;
requires 0 <= state->p <= dstlen+1;
requires state->p != 0 ==> 1 <= state->c <= 255;
ensures state->p != 0 ==> 1 <= state->c <= 255;
ensures 0 <= state->p <= dstlen+1;
ensures 0 <= \result <= dstlen || \result \in {-1, -2, -3, -4};
ensures \result < -1 ==> state->p == 0 && state->c == 0;
assigns *state, dst[0..dstlen-1];
behavior eof_bad_empty_frame:
assumes state->p == 0 && src == 0;
ensures \result == -3;
assigns *state;
behavior eof_good_frame:
assumes state->p != 0 && src == 0;
ensures \result >= 0 || \result == -2;
assigns *state;
behavior decoding_no_overflow:
assumes src != 0 && state->p <= dstlen;
ensures \result == -1;
assigns *state, dst[0..dstlen-1];
behavior decoding_overflow:
assumes src != 0 && state->p > dstlen;
ensures \result == -4;
assigns *state;
complete behaviors;
disjoint behaviors;
@*/
int cobs_decode_incremental(struct cobs_decode_state *state, unsigned char *dst, size_t dstlen, unsigned char src) {
if (state->p == 0) {
if (src == 0) {
/* invalid framing. An empty frame would be [...] 00 01 00, not [...] 00 00 */
cobs_decode_incremental_initialize(state);
//@ assert 0 <= state->p <= dstlen;
return -3;
}
state->c = src;
state->p++;
//@ assert 0 <= state->p <= dstlen;
return -1;
}
if (!src) {
if (state->c != 1) {
/* Invalid framing. The skip counter does not hit the end of the frame. */
cobs_decode_incremental_initialize(state);
//@ assert 0 <= state->p <= dstlen;
return -2;
}
size_t rv = state->p-1;
cobs_decode_incremental_initialize(state);
//@ assert 0 <= state->p <= dstlen;
return rv;
}
char val;
state->c--;
if (state->c == 0) {
state->c = src;
val = 0;
} else {
val = src;
}
size_t pos = state->p-1;
if (pos >= dstlen) {
cobs_decode_incremental_initialize(state);
//@ assert 0 <= state->p <= dstlen+1;
return -4; /* output buffer too small */
}
dst[pos] = val;
//@ assert 0 <= state->p <= dstlen;
state->p++;
//@ assert 0 <= state->p <= dstlen+1;
return -1;
}
/*@ requires \valid_read(buf + (0..len-1));
assigns \nothing;
@*/
void handle_packet(unsigned char *buf, size_t len);
/*@ requires \valid(dst + (0..dstlen-1));
requires \valid_read(src + (0..srclen-1));
requires 0 < dstlen <= 65535;
assigns dst[0..dstlen-1];
@*/
void cobs_decode_test(unsigned char *src, size_t srclen, unsigned char *dst, size_t dstlen) {
struct cobs_decode_state state;
cobs_decode_incremental_initialize(&state);
//@ assert state.p == 0;
//@ assert state.c == 0;
//@ assert state.p != 0 ==> 1 <= state.c <= 255;
/*@ loop invariant \separated(&state, dst + (0..dstlen-1), &i);
loop invariant \valid(&state);
loop invariant \valid(dst + (0..dstlen-1));
loop invariant 0 < dstlen <= 65535;
loop invariant 0 <= state.p <= dstlen+1;
loop invariant state.p != 0 ==> 1 <= state.c <= 255;
loop assigns dst[0..dstlen-1], state, i;
loop variant srclen-i;
@*/
for (size_t i=0; i<srclen; i++) {
int rv = cobs_decode_incremental(&state, dst, dstlen, src[i]);
if (rv >= 0)
handle_packet(dst, rv);
if (rv == -1)
continue;
if (rv < -1)
continue;
}
}
#ifdef VALIDATION
/*@
@ requires 0 <= d < 256;
@ assigns \nothing;
@*/
size_t test(char foo, unsigned int d) {
unsigned int c = (unsigned char)foo;
if (c != 0) {
//@ assert c < 256;
//@ assert c >= 0;
//@ assert c != 0;
//@ assert c > 0;
}
if (d != 0) {
//@ assert d >= 0;
//@ assert d != 0;
//@ assert d > 0;
}
return c + d;
}
#include <__fc_builtin.h>
void main(void) {
char inbuf[254];
char cobsbuf[256];
char outbuf[256];
size_t range = Frama_C_interval(0, sizeof(inbuf));
Frama_C_make_unknown((char *)inbuf, range);
cobs_encode(cobsbuf, sizeof(cobsbuf), inbuf, sizeof(inbuf));
cobs_decode(outbuf, sizeof(outbuf), cobsbuf, sizeof(cobsbuf));
//@ assert \forall integer i; 0 <= i < sizeof(inbuf) ==> outbuf[i] == inbuf[i];
}
#endif//VALIDATION
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