REFERENCE / ZLIB × LEAN

inflateReset2

Reset and select a new wrapper and maximum window size.

Source snapshot · ecafc184cdf44b7f · 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 inflateReset2(z_streamp strm, int windowBits);

Reset and select a new wrapper and maximum window size.

Domain Restricted domain: live streams and every signed windowBits value.

Effects Mutates state and may free the window, never allocates.

Pre The common live-stream conditions hold. Old decoding is being abandoned.

Post For an accepted value, returns Z_OK and has the effect of inflateReset with the new request. Accepted values and meanings are listed under inflateInit2_. Validation is enabled for the new wrapper request.

Edges Invalid values return Z_STREAM_ERROR before changing anything. Changing the requested size frees an incompatible window. Pending header registration and history are discarded, even if the size stays the same.

Shared conditions and scope

API manual · Shared stream rules · Stream compression

Use an inflate stream to decode input in pieces while controlling output space. Select zlib, gzip or raw DEFLATE at initialization, then continue with more input or room until completion, a dictionary request or an error. End releases the decoder after any of those outcomes. For whole-buffer zlib decoding, see uncompress.

Task	Entries
Start or reuse	Init, configured init, reset, new configuration, keep history
Decode or provide metadata	Inflate, set dictionary, read history, gzip header
Recover or inspect	Sync search, sync point, mark, table use
Adjust or branch	Prime bits, validation, distance option, copy
Release storage	End

The focused contracts follow the pinned inflate.c and zlib.h in the default LP64 Linux build, with gzip enabled and without optional invalid-distance or strict-distance modes. Source readings are to confirm by proof. The broader registered public goals retain their domains. See contract conventions for terminology and progress for proof status and remaining work.

Common conditions

All contracts below have a Restricted domain. A C pointer type alone does not supply the storage, lifetime or call history required here.

A live stream was successfully initialised or copied, has not been ended, retains its library-owned state, and is used without concurrent calls. Use the default allocator and free function. Init takes a writable, non-live stream with allocator fields set to NULL or the default functions.
A readable or writable range has the stated capacity for the whole call. Caller ranges are separate from the stream and its owned storage. Input and output ranges do not overlap. Dictionary destinations, the registered header record and its destination buffers are separate from each other and from the stream. Registered header storage is also separate from input/output ranges on calls using it. These are explicit focused-domain restrictions.
The caller owns its stream object and buffers. The library owns the state and optional window. A call changes only its stream, owned storage, stated output ranges and any registered header destination. It never frees caller buffers.
A rejected stream check returns Z_STREAM_ERROR without changes, unless a query or copy contract says otherwise. This covers NULL and safely readable records rejected by the check; it does not cover dangling or arbitrary pointers. The check requires allocators, state, the state's back-pointer and a valid mode.
Counters use the C unsigned widths and wrap. No contract assumes allocation succeeds. End remains available after decoding, dictionary or allocation errors.

flowchart LR
    I["Init"] --> F["inflate"]
    F -->|"Z_NEED_DICT"| D["SetDictionary"] --> F
    F -->|"more room or input"| F
    F -->|"end or abandon"| E["End"]
    F -->|"data error"| R["Reset or Sync"] --> F

Formal contract

ZlibF.Spec.Public.Goal.inflateReset2

Proof status: Registered proof · Evidence and remaining work

/-- `int inflateReset2(z_streamp strm, int windowBits)`.
Invalid parameters leave the heap unchanged. A changed window size releases the old window.
The new request restores validation even if `inflateValidate` previously disabled it. -/
def Goal.inflateReset2 : Prop :=
  ∀ h r i z s wb, InflateView h r i z s → z.zfree = .fn "zcfree" →
    WindowAllocation h s.window →
    C.run (Zlib.Inflate.inflateReset2 (some r) wb) h =
      match Api.inflWbits wb.toInt with
      | none => .ok (Z_STREAM_ERROR, h)
      | some (wrap, bits) =>
        let w : Int32 := match wrap with | .raw => 0 | .zlib => 5 | .gzip => 6 | .auto => 7
        let base := if s.wbits.toNat = bits then h else dropWindow h s.window
        let reset := { s with
          window := if s.wbits.toNat = bits then s.window else .null
          reqbits := UInt32.ofNat bits, wbits := UInt32.ofNat bits
          wrap := w, reqwrap := w, wsize := 0, whave := 0, wnext := 0 }
        .ok (Z_OK, putInflate (r.put base (inflateResetStream z reset)) i (inflateResetState i reset))

Related definitions and source ↗