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Prettify formalization of cobs_decode_incremental

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Among others, add synchronization guarantees
This commit is contained in:
jaseg 2018-12-17 19:36:01 +09:00
parent 447d084d79
commit b457eb1a91
1 changed files with 24 additions and 20 deletions
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44
src/cobs.c
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@ -213,17 +213,28 @@ void cobs_decode_incremental_initialize(struct cobs_decode_state *state) {
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;
/*@ requires separation: \separated(state, dst + (0..dstlen-1));
requires state_valid: \valid(state);
requires dst_valid: \valid(dst + (0..dstlen-1));
requires dstlen_bounds: 0 < dstlen <= INT_MAX;
requires p_valid: 0 <= state->p <= dstlen+1;
requires c_valid: 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;
// Sanity properties
ensures c_valid: state->p != 0 ==> 1 <= state->c <= 255;
ensures buffer_bounds: 0 <= state->p <= dstlen+1;
ensures return_value: 0 <= \result <= dstlen || \result \in {-1, -2, -3, -4};
ensures reset_on_error: \result < -1 ==> state->p == 0 && state->c == 0;
// Synchronization properties
ensures self_synchronization: src == 0 ==> \result >= 0 || \result \in {-2, -3};
ensures synchronization_robustness: src != 0 ==> \result \in {-1, -4};
// Basic functional sanity
ensures legal_advance: \result != -1 <==> state->p \in {0, \old(state->p)};
ensures incremental_advance: \result == -1 <==> state->p == \old(state->p) + 1;
ensures nonzero_unmodified: \result == -1 && state->p > 1 ==> dst[state->p-2] \in {0, src};
assigns *state, dst[0..dstlen-1];
behavior eof_bad_empty_frame:
@ -231,7 +242,7 @@ void cobs_decode_incremental_initialize(struct cobs_decode_state *state) {
ensures \result == -3;
assigns *state;
behavior eof_good_frame:
behavior eof_maybe_good_frame:
assumes state->p != 0 && src == 0;
ensures \result >= 0 || \result == -2;
assigns *state;
@ -254,29 +265,25 @@ int cobs_decode_incremental(struct cobs_decode_state *state, unsigned char *dst,
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. */
/* 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;
unsigned char val;
state->c--;
if (state->c == 0) {
@ -289,13 +296,10 @@ int cobs_decode_incremental(struct cobs_decode_state *state, unsigned char *dst,
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;
}