5 See also this page @ref{Новости, on russian}.
12 More intuitive, clear and slightly more flexible behaviour of @command{nncp-rm}.
15 @command{nncp-rm} also removes corresponding @file{hdr/} file for each
21 @section Release 8.7.1
25 @command{nncp-xfer} now correctly checks for @file{seen/} files for
31 @section Release 8.7.0
35 @command{nncp-ack} does not acknowledge ACK-packets, preventing an
39 @command{nncp-ack} previously did not remove corresponding @file{hdr/} files.
42 @command{nncp-rm} now takes list of packet from @code{stdin} when
43 @option{-pkt} option is used.
46 @command{nncp-ack} now generates list of ACK packets it created, that
47 could be used as an input to @command{nncp-rm} to remove outbound ACK
53 @section Release 8.6.0
57 @command{nncp-xfer} checks if locally copied packet's checksum differs
58 from the source's one.
61 @command{nncp-call} has bad return code if its queues contain unfinished jobs.
64 @command{nncp-ack} command appeared, that sends explicit packet receipt
65 acknowledgement (ACK packet). That acknowledgement deletes referenced
66 packet from the outbound spool.
69 Ability to turn @code{fsync} operation off using @env{$NNCPNOSYNC=1}
73 Added various indices in documentation, that should help searching in it.
78 @section Release 8.5.0
82 Fixed @command{nncp-bundle} workability.
85 Mistakenly @option{-mcd-wait} option was enabled by default in
89 Ability to override internal default timeout for online protocol through
90 @env{$NNCPDEADLINE} environment variable. Can be useful for very high
94 NNCP builds on OpenBSD.
99 @section Release 8.4.0
103 Multicast related interface names (@code{mcd-listen} and @code{mcd-send}
104 configuration options) are now regular expressions. By default
105 @command{nncp-cfgnew} uncomments them now with @code{.*} interface name.
108 @command{nncp-call} command has @option{-mcd-wait} option to wait for
109 multicast packet about node's address.
112 @command{nncp-file} command skips everything that is neither regular
113 file nor directory during pax-archive creation.
118 @section Release 8.3.0
122 Fixed building issues on 32-bit systems.
127 @section Release 8.2.0
131 Yggdrasil uses pure-Go IPv6+TCP network stack, instead of naked μTP
132 transport protocol, making it able to work as an ordinary TCP server
133 inside overlay network.
136 Yggdrasil's @code{prv;bind1,bind2;pub@dots{}}-like configuration strings are
137 replaced with URL-like ones (@code{yggdrasils://PRV?bind=BIND1&bind=BIND2&pub=PUB}).
140 Ability to pass multicast-related parameters to Yggdrasil configuration.
143 @command{nncp-daemon} is able to listen on both TCP and Yggdrasil-driven
144 sockets simultaneously.
147 @command{nncp-daemon}'s listening on peering endpoint socket is optional
148 -- you can be reached through the peers.
153 @section Release 8.1.0
157 @command{nncp-cfgdir} does not require @code{self} section existence in
161 Ability to act as Yggdrasil network client, using online protocol on top of it.
166 @section Release 8.0.2
170 Fixed sending ability to areas.
175 @section Release 8.0.1
179 Fixed incorrect @code{freq.chunked} value calculation. If it was missed,
180 then chunked transfer mode was forcefully turned on anyway.
183 Fixed incorrect full file's size calculation in @file{.nncp.meta}.
188 @section Release 8.0.0
192 @strong{Incompatible} encrypted packet format change: payload and pad
193 sizes are sent in-bound in the encrypted stream. That gives ability to
194 streamingly create encrypted packets, without knowing sizes in advance,
195 without creating temporary file or buffer data in memory.
198 Proper encrypted packet padding verification is done now. This is not
199 critical issue, but previously neither padding value, nor its size were
200 authenticated, giving ability to iteratively strip trailing bytes and
201 determine payload's size by observing the reaction of the encrypted
205 @command{nncp-exec} loses its @option{-use-tmp} option, because of
206 streaming-compatible encrypted packets format.
209 @command{nncp-file} and @command{nncp-exec} commands have
210 @option{-maxsize} option, limiting maximal resulting encrypted packet's
211 maximal size (returning error if it is exceeded). Could be useful,
212 because no payload size could be known in advance.
217 @section Release 7.7.0
221 Experimental @code{kqueue} and @code{inotify} based notifications
222 support about spool directory changes, for reducing their often reading
226 @file{.seen} and @file{.hdr} files moved to @file{seen/} and @file{hdr/}
227 subdirectories, for faster scanning of spool directories.
228 Current files migration required:
231 $ find $NNCPSPOOL -type f -name "*.hdr" -exec rm @{@} +
233 $ find $NNCPSPOOL -type d -name rx | while read rx ; do
236 find . -type f -name "*.seen" | while read fn ; do
237 mv $fn seen/$@{fn%.seen@}
241 $ find $NNCPSPOOL -type d -name area | while read area ; do
242 find $area -type f -name "*.seen" | while read fn ; do
251 @section Release 7.6.0
255 Logging may be done to specified opened file descriptor
256 (@env{$NNCPLOG=FD:5} for example).
257 That is friendly to use under @command{daemontools}.
260 Added additional checks of public keys existence in configuration file,
261 preventing some commands from failing.
266 @section Release 7.5.1
270 NNCP builds on NetBSD.
275 @section Release 7.5.0
279 @command{nncp-daemon} is compatible with UCSPI-TCP interface, so log
280 will contain remote side's address (when running under appropriate
281 utility). @option{-ucspi} option should be used instead of @option{-inetd}.
284 @command{nncp-call} can be UCSPI-TCP client, using @option{-ucspi} option.
287 Do not exit if some of MCD network interfaces can not be listened --
288 only warn about that.
293 @section Release 7.4.0
297 Fixed simultaneous @command{nncp-daemon} and @command{nncp-caller} MCD work.
302 @section Release 7.3.2
306 @command{hjson-cli} utility builds in vendor-mode now.
311 @section Release 7.3.1
315 Fixed possibly left opened file descriptor in online commands.
318 Severely decreased memory usage of MTH hashing.
323 @section Release 7.3.0
327 Fixed some workability problems on 32-bit systems with big files.
330 Ability to use directory with a bunch of files as a configuration.
331 @command{nncp-cfgdir} command appeared.
336 @section Release 7.2.1
340 Small optimizations in online commands.
345 @section Release 7.2.0
349 @command{nncp-trns} command appeared for manual transition packets creation.
352 If destination node of transitional packet has non empty @option{via}
353 route, then do not ignore, but use it.
356 Do not relay multicast packet to area message's originator, that
357 obviously has seen its own packet.
360 Much less memory usage during MTH hashing when offset is zero: when
361 packet is not resumed, but for example checked with @command{nncp-check}
367 @section Release 7.1.1
371 Fixed failing directories @code{fsync} after @file{.seen} file creation.
376 @section Release 7.1.0
380 Multicasting areas feature appeared. Implemented merely by an additional
381 plain packet type with @command{nncp-toss}, @command{nncp-file} and
382 @command{nncp-exec} commands modification.
385 Fixed workability of @command{nncp-file} and @command{nncp-exec}
386 commands, that use temporary file (@code{stdin} and @option{-use-tmp}).
389 Fixed disappearing bad return code in @command{nncp-exec} command.
392 Fixed invalid @file{.hdr} generation when transitional packets are used.
395 @option{-all} option appeared in @command{nncp-rm} command, applying to
396 all the nodes at once.
399 @option{-cycle} option appeared in @command{nncp-check} command, looping
400 the check in infinite cycle.
403 @command{nncp-rm} command can take node alias name.
406 @command{nncp-pkt} can parse @file{.hdr} files.
411 @section Release 7.0.0
415 Minimal required Go version 1.13.
418 Merkle Tree-based Hashing with BLAKE3 (MTH) is used instead of BLAKE2b.
419 Because of that, there are backward @strong{incompatible} changes of
420 encrypted files (everything laying in the spool directory) and
421 @file{.meta} files of chunked transfer.
423 Current implementation is far from being optimal: it lacks
424 parallelizable calculations and has higher memory consumption: nearly
425 512 KiB for each 1 GiB of file's data. Future performance and memory
426 size optimizations should not lead to packet's format change. But it is
427 still several times faster than BLAKE2b.
430 Resumed online downloads, because of MTH, require reading only of the
431 preceding part of file, not the whole one as was before.
434 @command{nncp-hash} utility appeared for calculating file's MTH hash.
437 BLAKE2 KDF and XOF functions are replaced with BLAKE3 in encrypted
438 packets. Lowering number of used primitives. Also, its encrypted
439 packet's header is used as an associated data during encryption.
442 MultiCast Discovery uses
443 @verb{|ff02::4e4e:4350|} address instead of @verb{|ff02::1|}.
446 @command{nncp-cfgenc} mistakenly asked passphrase three times during encryption.
449 @command{nncp-stat} reports about partly downloaded packets.
452 Updated dependencies.
457 @section Release 6.6.0
461 @command{nncp-daemon}, @command{nncp-call} and @command{nncp-caller}
462 commands wait for all background checksummers completion after
463 connection is finished.
466 Added possibility of address determining through multicast announcement
467 in local area network, so called MCD (MultiCast Discovery).
472 @section Release 6.5.0
476 Fixed segfault in @command{nncp-daemon} when SP handshake did not succeed.
479 Fixed possible bad return code ignoring in automatic tosser.
482 Fixed race during file descriptors closing when online protocol call is
483 finished, that could lead to write error of received packet fragment.
486 Kill all packet transmission progress bars in @command{nncp-daemon},
487 @command{nncp-call} and @command{nncp-caller} when call is finished.
492 @section Release 6.4.0
496 Fixed possible race in online protocol, that lead to panic.
501 @section Release 6.3.0
505 Fixed possible panic while showing progress during online protocol.
510 @section Release 6.2.1
514 Three places in logs contained excess @code{%s}.
519 @section Release 6.2.0
523 Returned @command{nncp-caller}'s @option{-autotoss*} options workability.
526 Yet another logging refactoring and simplification.
527 Should be no visible differences to the end user.
532 @section Release 6.1.0
536 Optimization: most commands do not keep opened file descriptors now.
537 Previously you can exceed maximal number of opened files if you have got
538 many packets in the spool directory.
541 Optimization: do not close file descriptor of the file we download
542 online. Previously each chunk lead to expensive open/close calls.
545 Online downloaded files are saved with @file{.nock} (non-checksummed)
546 suffix, waiting either for @command{nncp-check}, or online daemons to
547 perform integrity check.
550 Optimization: files, that are not resumed, are checksummed immediately
551 during the online download, skipping @file{.nock}-intermediate step.
554 Ability to store encrypted packet's header in @file{.hdr} file, close to
555 the packet itself. That can greatly increase performance of packets
556 listing on filesystems with big block's size.
561 @section Release 6.0.0
565 Log uses human readable and easy machine parseable
566 @url{https://www.gnu.org/software/recutils/, recfile} format for the
567 records, instead of structured RFC 3339 lines. Old logs are not readable
568 by @command{nncp-log} anymore.
571 @option{-autotoss*} option workability with @command{nncp-daemon}'s
572 @option{-inetd} mode.
575 Call's @option{when-tx-exists} allows to make a call only when outbound
576 packets exists. Combined with seconds-aware cron expression that can be
577 used as some kind of auto dialler.
580 @command{nncp-cronexpr} command allows you to check validity and
581 expectations of specified cron expression.
586 @section Release 5.6.0
590 @option{-autotoss*} option runs tosser not after the call, but every
591 second while it is active.
594 @option{autotoss}, @option{autotoss-doseen},
595 @option{autotoss-nofile}, @option{autotoss-nofreq},
596 @option{autotoss-noexec}, @option{autotoss-notrns} options available in
597 @option{calls} configuration section. You can configure per-call
598 automatic tosser options.
601 Use vendoring, instead of @env{$GOPATH} overriding during tarball
602 installation, because current minimal Go's version is 1.12 and it
608 @section Release 5.5.1
612 Respect for @env{$BINDIR}, @env{$INFODIR} and @env{$DOCDIR} environment
613 variables in @file{config} during installation.
618 @section Release 5.5.0
622 Bugfixes in @command{nncp-call(er)}/@command{nncp-daemon},
623 @command{nncp-bundle} and @command{nncp-stat}.
626 @command{nncp-rm} has @option{-dryrun} and @option{-older} options now.
629 @command{nncp-exec} has @option{-use-tmp} and @option{-nocompress}
630 options now. Uncompressed packets are not compatible with previous NNCP
634 @command{nncp-call}, @command{nncp-caller} and @command{nncp-daemon} commands
635 have @option{-autotoss*} options for running tosser after call is ended.
638 Updated dependencies. Minimal required Go version is 1.12.
643 @section Release 5.4.1
647 Fixed @code{SENDMAIL} variable usage during the build.
652 @section Release 5.4.0
656 Updated dependencies.
659 Build system is moved from Makefiles to @url{http://cr.yp.to/redo.html, redo}.
660 This should not influence package maintainers, because minimal @command{redo}
661 implementation is included in tarball.
666 @section Release 5.3.3
670 More various error checks.
673 Updated dependencies.
678 @section Release 5.3.2
682 Fixed incorrect logic of @option{onlinedeadline} timeout, where
683 connection won't take into account incoming packets events and will
684 forcefully disconnect.
689 @section Release 5.3.1
693 Fixed @option{onlinedeadline} workability with call addresses that use
694 external commands (@verb{#"|somecmd"#}).
697 @command{nncp-stat} has @option{-pkt} option displaying information
698 about each packet in the spool.
703 @section Release 5.3.0
707 Progress messages contain prefix, describing the running action.
710 Fixed not occurring handshake messages padding.
713 Finish all SP protocol related goroutines, less memory leak.
716 SP protocol generates less socket write calls, thus generating less TCP
720 Check @option{onlinedeadline} and @option{maxonlinetime} options every
721 second, independently from socket reads (up to 10 seconds).
724 Once per minute, if no other traffic exists, PING packets are sent in
725 SP-connection. That allows faster determining of connection unworkability.
728 @command{nncp-toss} uses lock-file to prevent simultaneous tossing.
733 @section Release 5.2.1
737 Fixed SP protocol error handling, sometimes causing program panic.
742 @section Release 5.2.0
746 Most commands by default show oneline operations progress.
747 @option{-progress}, @option{-noprogress} command line options,
748 @option{noprogress} configuration file option appeared.
751 Fixed incorrect @command{nncp-check} command return code, that returned
752 bad code when everything is good.
755 Free disk space check during @command{nncp-bundle -rx} call.
760 @section Release 5.1.2
764 @strong{Critical} vulnerability: remote peers authentication could lead
765 to incorrect identification of remote side, allowing foreign encrypted
769 Bugfix: private and public Noise keys were swapped in newly created
770 configuration files, that lead to inability to authenticate online peers.
773 Explicit directories @code{fsync}-ing for guaranteed files renaming.
778 @section Release 5.1.1
782 Fixed workability of @command{nncp-file} with @option{-chunked 0} option.
787 @section Release 5.1.0
791 @command{nncp-file} can send directories, automatically creating pax
795 Free disk space is checked during outbound packets creation.
798 @option{freq}, @option{freqminsize}, @option{freqchunked} configuration
799 file options replaced with the structure:
800 @option{freq: @{path: @dots{}, minsize: @dots{}, chunked: @dots{}@}}.
803 Added @option{freq.maxsize} configuration file option, forbidding of
804 freq sending larger than specified size.
807 Ability to notify about successfully executed commands (exec) with
808 @option{notify.exec} configuration file option.
813 @section Release 5.0.0
817 @strong{Incompatible} configuration file format change: YAML is
818 replaced with Hjson, due to its simplicity, without noticeable lack
819 of either functionality or convenience.
822 @strong{Incompatible} plain packet format changes. Older versions are
823 not supported. @code{zlib} compression is replaced with
824 @code{Zstandard}, due to its speed and efficiency, despite library
825 version is not mature enough.
828 Ability to call remote nodes via pipe call of external command, not only
832 @command{nncp-cfgnew} generates configuration file with many
833 comments. @option{-nocomments} option can be used for an old
837 Duplicate filenames have @file{.CTR} suffix, instead of @file{CTR}, to
838 avoid possible collisions with @file{.nncp.chunkCTR}.
841 Ability to override process umask through configuration file option.
844 Files and directories are created with 666/777 permissions by default,
845 allowing control with @command{umask}.
848 Updated dependencies.
851 Full usage of go modules for dependencies management
852 (@code{go.cypherpunks.ru/nncp/v5} namespace is used).
855 Forbid any later GNU GPL version autousage
856 (project's licence now is GNU GPLv3-only).
863 @item Workability on GNU/Linux systems and Go 1.10 is fixed.
871 @strong{Incompatible} encrypted and eblob packet format change: AEAD
872 encryption mode with 128 KiB blocks is used now, because previously
873 @command{nncp-toss} did not verify encrypted packet's MAC before feeding
874 decrypted data to external command. Older versions are not supported.
877 Available free space checking before copying in @command{nncp-xfer},
878 @command{nncp-daemon}, @command{nncp-call(er)}.
881 @command{nncp-call} has ability only to list packets on remote node,
882 without their transmission.
885 @command{nncp-call} has ability to transfer only specified packets.
888 Workability of @option{xxrate} preference in @option{calls}
889 configuration file section.
892 Dependant libraries are updated.
898 Begin using of @code{go.mod} subsystem.
905 @item @command{nncp-daemon} can be run as @command{inetd}-service.
913 @command{nncp-daemon}, @command{nncp-call}, @command{nncp-caller} check
914 if @file{.seen} exists and treat it like file was already downloaded.
915 Possibly it was transferred out-of-bound and remote side needs to be
919 If higher priority packet is spooled, then @command{nncp-daemon} will
920 queue its sending first, interrupting lower priority transmissions.
923 Simple packet rate limiter added to online-related tools
924 (@command{nncp-daemon}, @command{nncp-call}, @command{nncp-caller}).
927 Ability to specify niceness with symbolic notation:
928 @verb{|NORMAL|}, @verb{|BULK+10|}, @verb{|PRIORITY-5|}, etc.
931 Changed default niceness levels:
932 for @command{nncp-exec} from 64 to 96,
933 for @command{nncp-freq} from 64 to 160,
934 for @command{nncp-file} from 196 to 224.
942 @strong{Incompatible} @emph{bundle} archive format changes and
943 @command{nncp-bundle} workability with Go 1.10+. Bundles must be
944 valid tar archives, but Go 1.9 made them invalid because of long paths
945 inside. NNCP accidentally was dependant on that bug. Explicit adding of
946 @file{NNCP/} directory in archive restores workability with valid tar
954 Ability to disable relaying at all using @verb{|-via -|} command line option.
962 @strong{Incompatible} plain packet format changes. Older versions are
966 Ability to queue remote command execution, by configuring @option{exec}
967 option in configuration file and using @command{nncp-exec} command:
970 @command{nncp-mail} command is replaced with more flexible
971 @command{nncp-exec}. Instead of @verb{|nncp-mail NODE RECIPIENT|}
972 you must use @verb{|nncp-exec NODE sendmail RECIPIENT|}.
974 @option{sendmail} configuration file option is replaced with
975 @option{exec}. @code{sendmail: [@dots{}]} must be replaced with
976 @code{exec: sendmail: [@dots{}]}.
980 Ability to override @option{via} configuration option for destination
981 node via @option{-via} command line option for following commands:
982 @command{nncp-file}, @command{nncp-freq}, @command{nncp-exec}.
985 Chunked files, having size less than specified chunk size, will be sent
986 as an ordinary single file.
989 Exec commands are invoked with additional @env{$NNCP_NICE} and
990 @env{$NNCP_SELF} environment variables.
993 Files, that are sent as a reply to freq, have niceness level taken from
994 the freq packet. You can set desired niceness during @command{nncp-freq}
995 invocation using @option{-replynice} option.
998 @command{nncp-toss} command can ignore specified packet types during
999 processing: @option{-nofile}, @option{-nofreq}, @option{-noexec},
1003 @command{nncp-file} command uses
1004 @option{FreqMinSize}/@option{FreqChunked} configuration file options
1005 for @option{-minsize}/@option{-chunked} by default. You can turn this
1006 off by specifying zero value.
1011 @section Release 2.0
1015 @strong{Incompatible} encrypted/eblob packet format changes. Older
1016 versions are not supported.
1019 Twofish encryption algorithm is replaced with ChaCha20. It is much more
1020 faster. One cryptographic primitive less.
1023 HKDF-BLAKE2b-256 KDF algorithm is replaced with BLAKE2Xb XOF. Yet
1024 another cryptographic primitive less (assuming that BLAKE2X is nearly
1025 identical to BLAKE2).
1030 @section Release 1.0
1034 @strong{Incompatible} encrypted packet format changes. Older versions
1038 @command{nncp-bundle} command can either create stream of encrypted
1039 packets, or digest it. It is useful when dealing with
1040 @code{stdin}/@code{stdout} based transmission methods (like writing to
1041 CD-ROM without intermediate prepared ISO image and working with tape
1045 @command{nncp-toss} is able to create @file{.seen} files preventing
1046 duplicate packets receiving.
1049 Single background checksum verifier worker is allowed in
1050 @command{nncp-call}. This is helpful when thousands of small inbound
1051 packets could create many goroutines.
1054 Ability to override path to spool directory and logfile through either
1055 command line argument, or environment variable.
1058 @command{nncp-rm} is able to delete outbound/inbound, @file{.seen},
1059 @file{.part}, @file{.lock} and temporary files.
1064 @section Release 0.12
1066 @item Sendmail command is called with @env{$NNCP_SENDER} environment variable.
1070 @section Release 0.11
1072 @item @command{nncp-stat}'s command output is sorted by node name.
1076 @section Release 0.10
1079 @command{nncp-freq}'s @file{DST} argument is optional now. Last
1080 @file{SRC} path's element will be used by default.
1084 @section Release 0.9
1087 Fix @option{-rx}/@option{-tx} arguments processing in
1088 @command{nncp-call} command. They were ignored.
1092 @section Release 0.8
1095 Little bugfix in @command{nncp-file} command, where @option{-minsize}
1096 option for unchunked transfer was not in KiBs, but in bytes.
1100 @section Release 0.7
1104 Ability to feed @command{nncp-file} from @code{stdin}, that uses an
1105 encrypted temporary file for that.
1108 Chunked files transmission appeared with corresponding
1109 @command{nncp-reass} command and @option{freqchunked} configuration file
1110 entry. Useful for transferring big files over small storage devices.
1113 @option{freqminsize} configuration file option, analogue to
1114 @option{-minsize} one.
1117 @command{nncp-xfer}'s @option{-force} option is renamed to
1118 @option{-mkdir} for clarity.
1121 @option{-minsize} option is specified in KiBs, not bytes, for
1125 @command{nncp-newcfg} command is renamed to @command{nncp-cfgnew},
1126 and @command{nncp-mincfg} to @command{nncp-cfgmin} -- now they have
1127 common prefix and are grouped together for convenience.
1130 @command{nncp-cfgenc} command appeared, allowing configuration file
1131 encryption/decryption, for keeping it safe without any either OpenPGP or
1132 similar tools usage.
1135 Cryptographic libraries (dependencies) are updated.
1140 @section Release 0.6
1142 @item Small @command{nncp-rm} command appeared.
1143 @item Cryptographic libraries (dependencies) are updated.
1147 @section Release 0.5
1150 Trivial small fix in default niceness level of @command{nncp-file}
1151 and @command{nncp-freq} commands.
1155 @section Release 0.4
1159 Small fix in @command{nncp-call}, @command{nncp-caller},
1160 @command{nncp-daemon}: they can segmentation fail sometimes (no data is
1164 @command{nncp-newnode} renamed to @command{nncp-newcfg} -- it is shorter
1165 and more convenient to use.
1168 @command{nncp-mincfg} command appeared: helper allowing to create
1169 minimalistic stripped down configuration file without private keys, that
1170 is useful during @command{nncp-xfer} usage.
1175 @section Release 0.3
1177 @item Fixed compatibility with Go 1.6.
1181 @section Release 0.2
1185 @strong{Incompatible} packet's format change (magic number is changed
1186 too): size field is encrypted and is not send in plaintext anymore.
1189 @option{-minsize} option gives ability to automatically pad outgoing
1190 packets to specified minimal size.
1193 @command{nncp-daemon} and @command{nncp-call}/@command{nncp-caller}
1194 always check new @emph{tx} packets appearance in the background while
1195 connected. Remote side is immediately notified.
1198 @option{-onlinedeadline} option gives ability to configure timeout of
1199 inactivity of online connection, when it could be disconnected. It could
1200 be used to keep connection alive for a long time.
1203 @option{-maxonlinetime} option gives ability to set maximal allowable
1204 online connection aliveness time.
1207 @command{nncp-caller} command appeared: cron-ed TCP daemon caller.
1210 @command{nncp-pkt} command can decompress the data.