inflateInit2_
Create a decoder with a selected wrapper and window.
Full chapter and shared rules ↗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 inflateInit2_(z_streamp strm, int windowBits, const char *version, int stream_size);
Create a decoder with a selected wrapper and window.
Domain Restricted domain: fresh writable stream storage, default allocator, and NULL or readable version pointer; all signed scalar arguments.
Effects Allocates state.
Pre The stream is not live. Allocator fields follow the common convention. Only the first version byte must be readable; a whole string is not inspected.
Post On Z_OK, the stream is live with zero totals, NULL message, zero
data_type, no window, history, buffered bits or header registration. Wrapper
adler starts at 1 for zlib/automatic detection and 0 for gzip-only; raw preserves
it. Buffer pointers and available counts are unchanged.
Accepted windowBits values are:
| Values | Decoder request |
|---|---|
| -15 through -8 | Raw DEFLATE, window bits equal to the magnitude |
| 0; 8 through 15 | Zlib; header-selected size for 0, otherwise that maximum |
| 16; 24 through 31 | Gzip only; default size for 16, otherwise value minus 16 |
| 32; 40 through 47 | Zlib/gzip detection; header/default size for 32, otherwise value minus 32 |
Errors NULL/wrong version first byte or wrong stream_size returns
Z_VERSION_ERROR without changes, before inspecting strm. Otherwise NULL strm
returns Z_STREAM_ERROR. State allocation is attempted before the window argument
is checked. Failure returns Z_MEM_ERROR, retaining the old state field, with
message cleared and default callbacks installed as needed. An invalid window
argument after successful allocation returns Z_STREAM_ERROR, frees that state
and sets state to NULL. No failing init retains a new allocation. Only successful
init needs a later inflateEnd; its window may be allocated by later calls.
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_ERRORwithout 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.inflateInit2_
Proof status: Blocked · Evidence and remaining work
/-- `int inflateInit2_(z_streamp strm, int windowBits, const char *version, int stream_size)`.
All signed window arguments and every allocation oracle are included, in source error order. -/
def Goal.inflateInit2_ : Prop :=
∀ wb, InflateInitContract (fun p v size => Zlib.Inflate.inflateInit2_ p wb v size) wb