REFERENCE / ZLIB × LEAN

deflateParams

Change level and strategy, finishing the old block when needed.

Source snapshot · 39ab1ace4bbe0b0e · 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 deflateParams(z_streamp strm, int level, int strategy);

Change level and strategy, finishing the old block when needed.

Domain Restricted domain. Effect: update settings; may consume input and emit output.

Pre live stream before finishing, valid stream buffers and any active header; level is -1 or 0..9 and strategy is 0..4. To choose an exact input boundary, complete deflate(Z_BLOCK) until avail_out is nonzero and supply no new input before this call.

Post Z_OK installs the requested settings (level -1 means 6). Changing level restores that level's standard tuning values. A needed block flush uses the old settings and can consume some input and deliver output. I/O pointers, available counts and totals account for exactly those bytes; unconsumed input remains available.

Z_BUF_ERROR means the old block could not yet be completed; level and strategy remain unchanged, but compression progress and emitted output are retained. Provide more output room and retry. The live stream and its allocation set are preserved on either result.

Outside focused scope: invalid level/strategy gives Z_STREAM_ERROR without changes. A needed block flush can also return Z_STREAM_ERROR, including after finishing has begun.

Shared conditions and scope

API manual · Shared stream rules · Stream decompression

Use a z_stream compressor when input arrives in pieces, output space is limited, or you need a chosen wrapper, dictionary or flush boundary. Initialize once, call deflate with successive buffers, and end the stream even if compression is abandoned. For a single buffer, see compress and compress2.

Task	Entries
Start or reuse	Init, configured init, reset, reset retaining history
Supply metadata or history	Dictionary, read history, gzip header
Compress and size output	Deflate, bound, pending output, last flush bits
Adjust or branch	Parameters, tuning, priming, copy
Release storage	End

These focused contracts follow the pinned deflate.c, applied patches and zlib.h in the default LP64 Linux build. Source readings are to confirm by proof. They leave the broader registered public goals unchanged. See contract conventions for domain/effect labels and progress for proof status and remaining work.

Shared conventions

Each stated Pre requires termination without runtime faults and the stated Post. A call that retains a live stream preserves its representation invariant.

Live stream: a writable z_stream with a compressor state established by successful init or copy, preserved by legal calls, and not ended. The caller does not alter its internal state or allocator fields. Calls on one stream are sequential.
Buffers: input covers avail_in readable bytes; output covers avail_out writable bytes. They do not overlap each other, the stream or its owned state. A non-NULL scalar result points to a writable cell separate from other results and stream memory. These separation conditions are explicit focused assumptions; see safety.md.
Allocator: the default allocator/free pair is used, or both fields are NULL before init. Allocation may fail on any attempt. Custom allocator callbacks are outside this page's scope.
Frame and ownership: calls change only their stream, its owned state and stated output regions. Caller input is read-only. Caller buffers and header records remain caller-owned. Only init and copy allocate; only their failure cleanup and deflateEnd free memory. Other calls preserve the stream's allocation set.
Header lifetime: a retained gzip header and its optional fields remain readable and unchanged while used. Non-NULL name and comment have a terminating zero; extra covers its stated length. Focused format contracts use extra_len <= 65535.
Checked refusals: except for init and bounds, a failed stream check returns Z_STREAM_ERROR before normal operation, without writes. deflateCopy additionally clears a non-NULL destination state. Query output cells are untouched on this refusal.
Restricted domain means these explicit memory, lifetime and call-order conditions, plus the entry's Pre. It does not mean every representable pointer or integer is accepted. Error summaries cover readable checked states, not arbitrary invalid addresses.

Formal contract

ZlibF.Spec.Public.Goal.deflateParams

Proof status: Not completed · Evidence and remaining work

/-- `int deflateParams(z_streamp strm, int level, int strategy)`.
May consume input and write output while finishing the old block. A buffer error retains
the old parameters; successful changes select the canonical tuning row for a changed level. -/
def Goal.deflateParams : Prop :=
  ∀ h r i z s level strategy,
    StreamReachable .deflate h r → Zlib.Deflate.Spec.DGood h r i z s →
    StreamBuffers h r → ActiveHeader h r →
    ∃ rc after z' s' used out,
      C.run (Zlib.Deflate.deflateParams (some r) level strategy) h = .ok (rc, after) ∧
      Zlib.Deflate.Spec.DGood after r i z' s' ∧ StreamAccounting z z' used out.length ∧
      Bytes after z.next_out out.length out ∧
      (rc = Z_OK ∨ rc = Z_BUF_ERROR ∨ rc = Z_STREAM_ERROR) ∧
      (rc = Z_OK → s'.level = (if level = -1 then 6 else level) ∧ s'.strategy = strategy) ∧
      (rc ≠ Z_OK → s'.level = s.level ∧ s'.strategy = s.strategy) ∧
      ((level.toInt < -1 ∨ 9 < level.toInt ∨ strategy.toInt < 0 ∨ 4 < strategy.toInt) →
        rc = Z_STREAM_ERROR ∧ after = h) ∧
      BufferFrame h after (fun b => StreamRoot r b ∨ DeflateOwned i s b) [⟨z.next_out, out.length⟩] ∧
      LiveChange h after (fun _ => False) (fun _ => False) ∧ after.nalloc = h.nalloc

Related definitions and source ↗