View Source zlib (erts v14.3)
zlib compression interface.
This module provides an API for the zlib library (www.zlib.net). It is used to compress and decompress data. The data format is described by RFC 1950, RFC 1951, and RFC 1952.
A typical (compress) usage is as follows:
Z = zlib:open(),
ok = zlib:deflateInit(Z,default),
Compress = fun(end_of_data, _Cont) -> [];
(Data, Cont) ->
[zlib:deflate(Z, Data)|Cont(Read(),Cont)]
end,
Compressed = Compress(Read(),Compress),
Last = zlib:deflate(Z, [], finish),
ok = zlib:deflateEnd(Z),
zlib:close(Z),
list_to_binary([Compressed|Last])
In all functions errors, {'EXIT',{Reason,Backtrace}}
, can be thrown, where
Reason
describes the error.
Typical Reason
s:
badarg
- Bad argument.not_initialized
- The stream hasn't been initialized, eg. ifinflateInit/1
wasn't called prior to a call toinflate/2
.not_on_controlling_process
- The stream was used by a process that doesn't control it. Useset_controlling_process/2
if you need to transfer a stream to a different process.data_error
- The data contains errors.stream_error
- Inconsistent stream state.{need_dictionary,Adler32}
- Seeinflate/2
.
Summary
Types
Normally in the range -15..-8 | 8..15
.
Functions
Closes the stream referenced by Z
.
Compresses data with zlib headers and checksum.
Same as deflate(Z, Data, none)
.
Compresses as much data as possible, and stops when the input buffer becomes empty.
Ends the deflate session and cleans all data used.
Same as zlib:deflateInit(Z, default)
.
Initializes a zlib stream for compression.
Initiates a zlib stream for compression.
Dynamically updates the compression level and compression strategy.
Equivalent to deflateEnd/1
followed by deflateInit/1,2,6
,
but does not free and reallocate all the internal compression state.
Initializes the compression dictionary from the specified byte sequence without producing any compressed output.
Uncompresses data with gz headers and checksum.
Compresses data with gz headers and checksum.
Equivalent to inflate(Z, Data, [])
Decompresses as much data as possible. It can introduce some output latency (reading input without producing any output).
Ends the inflate session and cleans all data used.
Returns the decompression dictionary currently in use by the stream.
Initializes a zlib stream for decompression.
Initializes a decompression session on zlib stream.
Equivalent to inflateEnd/1
followed by inflateInit/1
, but does not free and
reallocate all the internal decompression state. The stream will keep attributes
that could have been set by inflateInit/1,2
.
Initializes the decompression dictionary from the specified uncompressed byte sequence.
Opens a zlib stream.
Like inflate/2
, but returns once it has expanded beyond a small
implementation-defined threshold. It's useful when decompressing untrusted input
which could have been maliciously crafted to expand until the system runs out of
memory.
Changes the controlling process of Z
to Pid
, which must be a local process.
Uncompresses data with zlib headers and checksum.
Uncompresses data without zlib headers and checksum.
Compresses data without zlib headers and checksum.
Types
-type zflush() :: none | sync | full | finish.
-type zlevel() :: none | default | best_compression | best_speed | 0..9.
-type zmemlevel() :: 1..9.
-type zmethod() :: deflated.
-type zstrategy() :: default | filtered | huffman_only | rle.
-type zstream() :: reference().
A zlib stream, see open/0
.
-type zwindowbits() :: -15..-8 | 8..47.
Normally in the range -15..-8 | 8..15
.
Functions
-spec close(Z) -> ok when Z :: zstream().
Closes the stream referenced by Z
.
Compresses data with zlib headers and checksum.
Same as deflate(Z, Data, none)
.
-spec deflate(Z, Data, Flush) -> Compressed when Z :: zstream(), Data :: iodata(), Flush :: zflush(), Compressed :: iolist().
Compresses as much data as possible, and stops when the input buffer becomes empty.
It can introduce some output latency (reading input without producing any output) except when forced to flush.
If Flush
is set to sync
, all pending output is flushed to the output buffer
and the output is aligned on a byte boundary, so that the decompressor can get
all input data available so far. Flushing can degrade compression for some
compression algorithms; thus, use it only when necessary.
If Flush
is set to full
, all output is flushed as with sync
, and the
compression state is reset so that decompression can restart from this point if
previous compressed data has been damaged or if random access is desired. Using
full
too often can seriously degrade the compression.
If Flush
is set to finish
, pending input is processed, pending output is
flushed, and deflate/3
returns. Afterwards the only possible
operations on the stream are deflateReset/1
or deflateEnd/1
.
Flush
can be set to finish
immediately after
deflateInit
if all compression is to be done in one step.
Example:
zlib:deflateInit(Z),
B1 = zlib:deflate(Z,Data),
B2 = zlib:deflate(Z,<< >>,finish),
zlib:deflateEnd(Z),
list_to_binary([B1,B2])
-spec deflateEnd(Z) -> ok when Z :: zstream().
Ends the deflate session and cleans all data used.
Notice that this function throws a data_error
exception if the last call to
deflate/3
was not called with Flush
set to finish
.
-spec deflateInit(Z) -> ok when Z :: zstream().
Same as zlib:deflateInit(Z, default)
.
Initializes a zlib stream for compression.
Level
decides the compression level to be used:
default
gives default compromise between speed and compressionnone
(0) gives no compressionbest_speed
(1) gives best speedbest_compression
(9) gives best compression
-spec deflateInit(Z, Level, Method, WindowBits, MemLevel, Strategy) -> ok when Z :: zstream(), Level :: zlevel(), Method :: zmethod(), WindowBits :: zwindowbits(), MemLevel :: zmemlevel(), Strategy :: zstrategy().
Initiates a zlib stream for compression.
Level
- Compression level to use:default
gives default compromise between speed and compressionnone
(0) gives no compressionbest_speed
(1) gives best speedbest_compression
(9) gives best compression
Method
- Compression method to use, currently the only supported method isdeflated
.WindowBits
- The base two logarithm of the window size (the size of the history buffer). It is to be in the range 8 through 15. Larger values result in better compression at the expense of memory usage. Defaults to 15 ifdeflateInit/2
is used. A negativeWindowBits
value suppresses the zlib header (and checksum) from the stream. Notice that the zlib source mentions this only as a undocumented feature.Warning
Due to a known bug in the underlying zlib library,
WindowBits
values 8 and -8 do not work as expected. In zlib versions before 1.2.9 values 8 and -8 are automatically changed to 9 and -9. From zlib version 1.2.9 value -8 is rejected causingzlib:deflateInit/6
to fail (8 is still changed to 9). It also seem possible that future versions of zlib may fix this bug and start accepting 8 and -8 as is.Conclusion: Avoid values 8 and -8 unless you know your zlib version supports them.
MemLevel
- Specifies how much memory is to be allocated for the internal compression state:MemLevel
=1 uses minimum memory but is slow and reduces compression ratio;MemLevel
=9 uses maximum memory for optimal speed. Defaults to 8.Strategy
- Tunes the compression algorithm. Use the following values:default
for normal datafiltered
for data produced by a filter (or predictor)huffman_only
to force Huffman encoding only (no string match)rle
to limit match distances to one (run-length encoding)
Filtered data consists mostly of small values with a somewhat random distribution. In this case, the compression algorithm is tuned to compress them better. The effect of
filtered
is to force more Huffman coding and less string matching; it is somewhat intermediate betweendefault
andhuffman_only
.rle
is designed to be almost as fast ashuffman_only
, but gives better compression for PNG image data.Strategy
affects only the compression ratio, but not the correctness of the compressed output even if it is not set appropriately.
-spec deflateParams(Z, Level, Strategy) -> ok when Z :: zstream(), Level :: zlevel(), Strategy :: zstrategy().
Dynamically updates the compression level and compression strategy.
The interpretation of Level
and Strategy
is as in deflateInit/6
. This can be
used to switch between compression and straight copy of the input data, or to
switch to a different kind of input data requiring a different strategy. If the
compression level is changed, the input available so far is compressed with the
old level (and can be flushed); the new level takes effect only at the next call
of deflate/3
.
Before the call of deflateParams
, the stream state must be set as for a call
of deflate/3
, as the currently available input may have to be
compressed and flushed.
-spec deflateReset(Z) -> ok when Z :: zstream().
Equivalent to deflateEnd/1
followed by deflateInit/1,2,6
,
but does not free and reallocate all the internal compression state.
The stream keeps the same compression level and any other attributes.
-spec deflateSetDictionary(Z, Dictionary) -> Adler32 when Z :: zstream(), Dictionary :: iodata(), Adler32 :: non_neg_integer().
Initializes the compression dictionary from the specified byte sequence without producing any compressed output.
This function must be called immediately after
deflateInit/1,2,6
or deflateReset/1
, before any call of
deflate/3
.
The compressor and decompressor must use the same dictionary (see
inflateSetDictionary/2
).
The Adler checksum of the dictionary is returned.
Uncompresses data with gz headers and checksum.
Compresses data with gz headers and checksum.
-spec inflate(Z, Data) -> Decompressed when Z :: zstream(), Data :: iodata(), Decompressed :: iolist().
Equivalent to inflate(Z, Data, [])
-spec inflate(Z, Data, Options) -> Decompressed when Z :: zstream(), Data :: iodata(), Options :: [{exception_on_need_dict, boolean()}], Decompressed :: iolist() | {need_dictionary, Adler32 :: non_neg_integer(), Output :: iolist()}.
Decompresses as much data as possible. It can introduce some output latency (reading input without producing any output).
Currently the only available option is {exception_on_need_dict,boolean()}
which controls whether the function should throw an exception when a preset
dictionary is required for decompression. When set to false, a need_dictionary
tuple will be returned instead. See inflateSetDictionary/2
for details.
Warning
This option defaults to
true
for backwards compatibility but we intend to remove the exception behavior in a future release. New code that needs to handle dictionaries manually should always specify{exception_on_need_dict,false}
.
-spec inflateEnd(Z) -> ok when Z :: zstream().
Ends the inflate session and cleans all data used.
Notice that this function throws a data_error
exception if no end of stream
was found (meaning that not all data has been uncompressed).
Returns the decompression dictionary currently in use by the stream.
This function must be called between inflateInit/1,2
and
inflateEnd
.
Only supported if ERTS was compiled with zlib >= 1.2.8.
-spec inflateInit(Z) -> ok when Z :: zstream().
Initializes a zlib stream for decompression.
-spec inflateInit(Z, WindowBits) -> ok when Z :: zstream(), WindowBits :: zwindowbits().
Initializes a decompression session on zlib stream.
WindowBits
is the base two logarithm of the maximum window size (the size of
the history buffer). It is to be in the range 8 through 15. Default to 15 if
inflateInit/1
is used.
If a compressed stream with a larger window size is specified as input,
inflate/2
throws the data_error
exception.
A negative WindowBits
value makes zlib ignore the zlib header (and checksum)
from the stream. Notice that the zlib source mentions this only as a
undocumented feature.
-spec inflateReset(Z) -> ok when Z :: zstream().
Equivalent to inflateEnd/1
followed by inflateInit/1
, but does not free and
reallocate all the internal decompression state. The stream will keep attributes
that could have been set by inflateInit/1,2
.
Initializes the decompression dictionary from the specified uncompressed byte sequence.
This function must be called as a response to an inflate operation
(eg. safeInflate/2
) returning {need_dictionary,Adler,Output}
or in the case
of deprecated functions, throwing an
{'EXIT',{{need_dictionary,Adler},_StackTrace}}
exception.
The dictionary chosen by the compressor can be determined from the Adler value
returned or thrown by the call to the inflate function. The compressor and
decompressor must use the same dictionary (See deflateSetDictionary/2
).
After setting the dictionary the inflate operation should be retried without new input.
Example:
deprecated_unpack(Z, Compressed, Dict) ->
case catch zlib:inflate(Z, Compressed) of
{'EXIT',{{need_dictionary,_DictID},_}} ->
ok = zlib:inflateSetDictionary(Z, Dict),
Uncompressed = zlib:inflate(Z, []);
Uncompressed ->
Uncompressed
end.
new_unpack(Z, Compressed, Dict) ->
case zlib:inflate(Z, Compressed, [{exception_on_need_dict, false}]) of
{need_dictionary, _DictId, Output} ->
ok = zlib:inflateSetDictionary(Z, Dict),
[Output | zlib:inflate(Z, [])];
Uncompressed ->
Uncompressed
end.
-spec open() -> zstream().
Opens a zlib stream.
-spec safeInflate(Z, Data) -> Result when Z :: zstream(), Data :: iodata(), Result :: {continue, Output :: iolist()} | {finished, Output :: iolist()} | {need_dictionary, Adler32 :: non_neg_integer(), Output :: iolist()}.
Like inflate/2
, but returns once it has expanded beyond a small
implementation-defined threshold. It's useful when decompressing untrusted input
which could have been maliciously crafted to expand until the system runs out of
memory.
This function returns {continue | finished, Output}
, where Output is the data
that was decompressed in this call. New input can be queued up on each call if
desired, and the function will return {finished, Output}
once all queued data
has been decompressed.
This function can introduce some output latency (reading input without producing any output).
If a preset dictionary is required for further decompression, this function
returns a need_dictionary
tuple. See inflateSetDictionary/2
) for details.
Example:
walk(Compressed, Handler) ->
Z = zlib:open(),
zlib:inflateInit(Z),
loop(Z, Handler, zlib:safeInflate(Z, Compressed)),
zlib:inflateEnd(Z),
zlib:close(Z).
loop(Z, Handler, {continue, Output}) ->
Handler(Output),
loop(Z, Handler, zlib:safeInflate(Z, []));
loop(Z, Handler, {finished, Output}) ->
Handler(Output).
Changes the controlling process of Z
to Pid
, which must be a local process.
Uncompresses data with zlib headers and checksum.
Uncompresses data without zlib headers and checksum.
Compresses data without zlib headers and checksum.