compress2
The uLong form of compress2_z.
Full chapter and shared rules ↗767fa1407a7fe3d1 · Source at the matching commit ↗Read the function’s preconditions and results first. Expand the shared rules below for buffer and ownership requirements used throughout this API group.
int ZEXPORT compress2(Bytef *dest, uLongf *destLen, const Bytef *source,
uLong sourceLen, int level);
The uLong form of compress2_z.
Domain Restricted domain.
Pre Restricted domain of compress2_z, with a non-NULL destLen cell.
The wrapper reads that cell before calling the checked _z entry.
Post Same encoding and return-code contract as compress2_z.
Effects Stateful; same buffer and cleanup effects. The wrapper copies the length back on every return, including errors. Early argument rejection preserves its original value; invalid level or allocation failure leaves it zero.
Shared conditions and scope
API manual · Shared stream rules · Checksums
Use the buffer utilities when the complete input and output capacity are known at the call. They manage a temporary stream internally. Use the stream pages when you need incremental I/O, a different wrapper, a dictionary or explicit flush boundaries.
| Task | Entries |
|---|---|
| Compress a buffer | Choose a level, default level, size the destination |
| Decompress a buffer | Report input consumed, output only |
| Inspect the library | Version, compile flags, error text |
The focused contracts follow compress.c, uncompr.c, zutil.c and zlib.h in the default
LP64 Linux build. _z forms use z_size_t; plain forms use uLong. Both are 64-bit here.
Source readings are to confirm by proof. They do not narrow the registered targets in
Utilities.lean and
Queries.lean.
Calls.lean fixes translated arguments and results.
See contract conventions for domain/effect labels and
progress for proof status and remaining work.
The buffer utilities create and release a local stream with the zlib wrapper and default settings.
flowchart LR
B["compressBound"] --> C["compress / compress2"]
C --> Z["zlib stream"] --> U["uncompress / uncompress2"]
U --> D["decoded bytes"]
Common conventions
For buffer calls, the domain is restricted to valid memory: non-NULL sources cover the stated readable input; non-NULL destinations cover the stated writable capacity. Non-NULL length pointers name readable, writable scalar cells. Input, output and length cells are separate, including the two length cells when both occur. The caller keeps those objects live and does not modify them during the call. Each entry states its allowed NULL cases. Other invalid pointers are outside this scope. Decompression error handling needs no valid compressed-data assumption.
Common effects. Every in-scope call terminates without a fault. Buffer calls preserve input and memory outside the output and length cells. They write at most the original capacity. All internal allocations are released before return, including on allocation failure; no local stream or owned allocation is returned. Pointer-valued queries return borrowed immutable storage. These are contract requirements, not claims that the implementation proofs are complete.
Formal contract
ZlibF.Spec.Public.Goal.compress2
Proof status: Not completed · Evidence and remaining work
/-- `int compress2(Bytef *dest, uLongf *destLen, const Bytef *source, uLong sourceLen, int level)`.
The wrapper reads the length cell before `_z` checks; its length cell must be nonnull. -/
def Goal.compress2 : Prop :=
∀ level, CompressorContract (fun d c s n => do
let (rc, size) ← Zlib.Compress.compress2 d c s n level
pure (rc, some size)) level false