Browse zlib specs (24 of 62)
Proofs / zlib / The stream interface
api_deterministic
Two streams with the same parameters, driven by the same calls, produce the same output.
- spec
- 73 lines of C
- with its headers
- 165 lines
- status
- Proved
- 24 of 62
On this page
The spec
The spec is the C program harness/api_deterministic.c, 73 lines, shown whole as it is in the repository at 37189f4. It includes harness/laws_common.h (40 lines) and harness/laws_session.h (52 lines). Its first comment states the property in full, with every bound.
// Law api_deterministic: Two streams made by deflateInit2 with the same level, windowBits, memLevel and strategy in
// zlib.h's ranges (both return Z_OK; Z_MEM_ERROR ends the run) and driven by the same calls on any data (any length the
// allocator provides) -- deflate() with the same next pieces of the data (at most 2^32 - 1 bytes each), the same output
// space (below 2^32) and the same flush Z_NO_FLUSH..Z_BLOCK, Z_FINISH coming with the rest of the data (once one call
// can take it), until Z_STREAM_END, each call after the same deflateParams with any level and strategy (any ints) or
// none -- behave the same: each call returns the same code on both, reads and writes as many bytes, writes the same
// bytes and leaves the same adler (Z_MEM_ERROR ends the run).
#include "laws_common.h"
#include "laws_session.h"
int main(void) {
int level = (int) nondet_u32();
int window_bits = (int) nondet_u32();
int mem_level = (int) nondet_u32();
int strategy = (int) nondet_u32();
gp_assume(deflate_params_ok(level, window_bits, mem_level, strategy));
size_t data_len = upto(PTRDIFF_MAX);
unsigned char *data = alloc_any_bytes(data_len);
if (data == NULL)
return 0;
z_stream first;
z_stream second;
new_stream(&first);
new_stream(&second);
int code_first = deflateInit2(&first, level, Z_DEFLATED, window_bits, mem_level, strategy);
int code_second = deflateInit2(&second, level, Z_DEFLATED, window_bits, mem_level, strategy);
if (code_first == Z_MEM_ERROR || code_second == Z_MEM_ERROR)
return 0;
gp_assert(code_first == Z_OK && code_second == Z_OK);
size_t offered = 0;
size_t read = 0;
int flush = Z_NO_FLUSH;
do {
if (flush != Z_FINISH) {
offered += upto(data_len - offered);
flush = (int) upto(Z_BLOCK);
if (flush == Z_FINISH && data_len - read > UINT_MAX)
flush = Z_NO_FLUSH;
if (flush == Z_FINISH)
offered = data_len;
}
size_t take = clip(offered - read);
size_t room = nondet_u32();
unsigned char *in_first = copy_of(data + read, take);
unsigned char *in_second = copy_of(data + read, take);
unsigned char *out_first = malloc(room);
unsigned char *out_second = malloc(room);
if (in_first == NULL || in_second == NULL || out_first == NULL || out_second == NULL)
return 0;
set_buffer(&first, in_first, take, out_first, room);
set_buffer(&second, in_second, take, out_second, room);
if (nondet_u8() == 0) {
int new_level = (int) nondet_u32();
int new_strategy = (int) nondet_u32();
code_first = deflateParams(&first, new_level, new_strategy);
code_second = deflateParams(&second, new_level, new_strategy);
gp_assert(code_first == code_second);
}
code_first = deflate(&first, flush);
code_second = deflate(&second, flush);
gp_assert(code_first == code_second && first.adler == second.adler);
gp_assert(first.avail_in == second.avail_in && first.avail_out == second.avail_out);
gp_assert(bytes_eq(out_first, out_second, room - first.avail_out));
read += take - first.avail_in;
free(in_first);
free(in_second);
free(out_first);
free(out_second);
} while (code_first != Z_STREAM_END);
return 0;
}harness/laws_common.h, 40 lines
// laws_common.h: trivial helpers shared by the zlib laws (each law includes it once). No models, no algorithms.
#include <limits.h>
#include <stdlib.h>
#include "quickproof.h"
#include "zlib.h"
static size_t upto(size_t max) {
size_t value = nondet_size();
return value < max ? value : max;
}
static uInt clip(size_t n) { return n < UINT_MAX ? (uInt) n : UINT_MAX; }
static unsigned char *alloc_any_bytes(size_t n) {
unsigned char *bytes = malloc(n);
if (bytes != NULL)
nondet_bytes(bytes, n);
return bytes;
}
static unsigned char *copy_of(const unsigned char *source, size_t n) {
unsigned char *copy = malloc(n);
for (size_t i = 0; copy != NULL && i < n; i++)
copy[i] = source[i];
return copy;
}
static int bytes_eq(const unsigned char *a, const unsigned char *b, size_t n) {
for (size_t i = 0; i < n; i++)
if (a[i] != b[i])
return 0;
return 1;
}
static void set_buffer(z_stream *strm, unsigned char *in, size_t in_len, unsigned char *out, size_t out_len) {
strm->next_in = in;
strm->avail_in = (uInt) in_len;
strm->next_out = out;
strm->avail_out = (uInt) out_len;
}
static void new_stream(z_stream *strm) {
strm->zalloc = Z_NULL;
strm->zfree = Z_NULL;
strm->opaque = Z_NULL;
set_buffer(strm, Z_NULL, 0, Z_NULL, 0);
}harness/laws_session.h, 52 lines
// laws_session.h: helpers of the laws that drive a z_stream, included after laws_common.h. No models, no algorithms.
static int deflate_params_ok(int level, int window_bits, int mem_level, int strategy) {
// zlib.h, deflateInit2: level "Z_DEFAULT_COMPRESSION, or between 0 and 9"; memLevel 1..MAX_MEM_LEVEL (9,
// zconf.h); strategy Z_DEFAULT_STRATEGY (0) .. Z_FIXED (4); windowBits 8..15, "-8..-15 for raw deflate", "Add 16
// to windowBits to write a simple gzip header", but "For raw deflate or gzip encoding, a request for a 256-byte
// window is rejected as invalid"
int zlib_window = window_bits >= 8 && window_bits <= 15;
int raw_window = window_bits >= -15 && window_bits <= -9;
int gzip_window = window_bits >= 16 + 9 && window_bits <= 16 + 15;
int valid = level >= -1 && level <= 9 && mem_level >= 1 && mem_level <= 9 && strategy >= 0 && strategy <= Z_FIXED;
return valid && (zlib_window || raw_window || gzip_window);
}
static int inflate_window_ok(int window_bits) {
// zlib.h, inflateInit2: windowBits "should be in the range 8..15", "can also be zero to request that inflate
// use the window size in the zlib header", "can also be -8..-15 for raw inflate", "Add 32 to windowBits to
// enable zlib and gzip decoding with automatic header detection, or add 16 to decode only the gzip format"
int low = window_bits & 15;
int raw = window_bits >= -15 && window_bits <= -8;
int wrapped = window_bits >= 0 && window_bits < 48 && (low == 0 || low >= 8);
return raw || wrapped;
}
struct position {
unsigned char *next_in;
uInt avail_in;
unsigned char *next_out;
uInt avail_out;
uLong total_in;
uLong total_out;
};
static void position_of(z_stream *strm, struct position *at) {
at->next_in = strm->next_in;
at->avail_in = strm->avail_in;
at->next_out = strm->next_out;
at->avail_out = strm->avail_out;
at->total_in = strm->total_in;
at->total_out = strm->total_out;
}
static int unmoved(z_stream *strm, struct position *at) {
int in = strm->next_in == at->next_in && strm->avail_in == at->avail_in && strm->total_in == at->total_in;
int out = strm->next_out == at->next_out && strm->avail_out == at->avail_out && strm->total_out == at->total_out;
return in && out;
}
static int accounted(z_stream *strm, struct position *at) {
int in = strm->avail_in <= at->avail_in && strm->next_in + strm->avail_in == at->next_in + at->avail_in;
int out = strm->avail_out <= at->avail_out && strm->next_out + strm->avail_out == at->next_out + at->avail_out;
return in && out;
}
static int counted(z_stream *strm, struct position *at) {
int in = strm->total_in == at->total_in + (at->avail_in - strm->avail_in);
int out = strm->total_out == at->total_out + (at->avail_out - strm->avail_out);
return in && out;
}The theorem
QuickProof generated this statement from the spec, in src/contracts/api_deterministic.v:
Theorem api_deterministic : harness_safe whole_prog.src/contracts/laws.v states it on the spec's own program, whole_prog (the spec linked with the code under test), with its proof:
Theorem api_deterministic : harness_safe Zlib.contracts.api_deterministic.whole_prog.
Proof. exact (proj1 (proj2 (proj2 Zlib.contracts.suite.suite))). Qed.Read as a statement about runs, it says that no run of the program has undefined behaviour or a failing check, for every value the spec can draw. That reading rests on VST's adequacy theorem, which is not yet instantiated in Rocq (formerly Coq) for QuickProof's environment.
The C files (units) its program links
adler32.ccrc32.cdeflate.ctrees.czutil.cquickproof/libc/libc.c
What it leaves out
- What the first comment of the spec excludes, and its bounds.
- Like every spec of this proof: termination (a run that never returns is not a counterexample), and binaries built by a compiler (the theorem is about the code as CompCert defines C for x86_64, LP64), one thread.
- Where zlib reports
Z_MEM_ERROR, most specs end the run and claim nothing about it; the first comment of the spec says so. - The edits to zlib's code, listed in the repository, are tested, not proved.
The summary page says what the proof as a whole covers.
How it was proved
AI agents wrote the proof, and Rocq checks it. qp verify passes on this repository: this statement is the one generated from the spec at the contract commit, and its proof uses only Rocq's standard axioms and VST's abstract malloc library.