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(in-package 3bz)
(defstruct (gzip-state (:conc-name gs-)
(:include deflate-state))
;; A compliant decompressor must check ID1, ID2, and CM, and provide
;; an error indication if any of these have incorrect values. It
;; must examine FEXTRA/XLEN, FNAME, FCOMMENT and FHCRC at least so
;; it can skip over the optional fields if they are present. It
;; need not examine any other part of the header or trailer; in
;; particular, a decompressor may ignore FTEXT and OS and always
;; produce binary output, and still be compliant. A compliant
;; decompressor must give an error indication if any reserved bit is
;; non-zero, since such a bit could indicate the presence of a new
;; field that would cause subsequent data to be interpreted
;; incorrectly.
(gzip-state :header)
(compression-method nil)
(flags nil)
(extra nil)
(name nil)
(comment nil)
(operating-system nil)
(mtime/unix nil)
(mtime/universal nil)
(compression-level :default)
(header-bytes (make-array 16 :adjustable t :fill-pointer 0))
(crc32 0 :type (unsigned-byte 32)))
(defun decompress-gzip (read-context state)
(check-type state gzip-state)
;; fixme: avoid duplication with these from deflate/zlib
(with-reader-contexts (read-context)
(with-accessors ((input-underrun gs-input-underrun)
(gzip-state gs-gzip-state)
(partial-bits gs-partial-bits)
(bits-remaining gs-bits-remaining)
(finished gs-finished)
(flags gs-flags)
(compression-level gs-compression-level)
(compression-method gs-compression-method)
(output-buffer gs-output-buffer)
(output-offset gs-output-offset)
(output-overflow gs-output-overflow)
(header-bytes gs-header-bytes)
(mtime/unix gs-mtime/unix)
(mtime/universal gs-mtime/universal)
(extra gs-extra)
(name gs-name)
(comment gs-comment)
(operating-system gs-operating-system)
(crc32 gs-crc32))
state
(labels ((%fill-bits32 (n)
(multiple-value-bind (input octets)
(word32)
(declare (type (mod 5) octets))
(setf partial-bits
(logior
(ash (ldb (byte 32 0) input)
(min 32 bits-remaining))
partial-bits))
(incf bits-remaining (* 8 octets))
(>= bits-remaining n)))
(%bits (n)
(prog1 (ldb (byte n 0) partial-bits)
(setf partial-bits (ash partial-bits (- n)))
(decf bits-remaining n)))
(header-byte ()
(let ((b (%bits 8)))
;; might need to crc header, so store a copy
(when header-bytes
(vector-push-extend b header-bytes))
b))
(byte-align ()
(let ((r (mod bits-remaining 8)))
(unless (zerop r)
(setf partial-bits (ash partial-bits (- r)))
(decf bits-remaining r))))
(update-checksum ()
(setf crc32 (crc32/table output-buffer output-offset crc32)))
(crc ()
(when (and (< bits-remaining 32)
(not (%fill-bits32 32)))
(setf input-underrun t)
(return-from decompress-gzip 0))
(let ((crc (logior (ash (header-byte) 0)
(ash (header-byte) 8)
(ash (header-byte) 16)
(ash (header-byte) 24))))
#++(format t "crc = ~8,'0x ?= ~8,'0x~%"
crc crc32)
(assert (= crc crc32))
(setf gzip-state :final-len)))
(len ()
(when (and (< bits-remaining 32)
(not (%fill-bits32 32)))
(setf input-underrun t)
(return-from decompress-gzip 0))
(let ((len (logior (ash (header-byte) 0)
(ash (header-byte) 8)
(ash (header-byte) 16)
(ash (header-byte) 24))))
#++(format t "len = ~8,'0x ?= ~8,'0x~%"
len output-offset)
len)))
(declare (inline %fill-bits32 %bits byte-align)
(optimize (speed 1)))
(setf input-underrun nil)
(loop
until (or finished output-overflow input-underrun)
do (ecase gzip-state
(:header ;; magic #
(when (and (< bits-remaining 16)
(not (%fill-bits32 16)))
(setf input-underrun t)
(return-from decompress-gzip 0))
(let ((id1 (header-byte))
(id2 (header-byte)))
(assert (= id1 #x1f))
(assert (= id2 #x8b))
(setf gzip-state :header2)))
(:header2 ;; compression method, flags
(when (and (< bits-remaining 16)
(not (%fill-bits32 16)))
(setf input-underrun t)
(return-from decompress-gzip 0))
(let ((cm (header-byte))
(flg (header-byte)))
(if (= cm 8)
(setf compression-method :deflate)
(error "unknown compression method ~s~%" cm))
(when (plusp (ldb (byte 3 5) flg))
(error "reserved flag bits set in ~8,'0b" flg))
(when (logbitp 0 flg) (push :text flags))
(if (logbitp 1 flg)
(push :header-crc flags)
;; no crc, stop remembering header contents
(setf header-bytes nil))
(when (logbitp 2 flg) (push :extra flags))
(when (logbitp 3 flg) (push :name flags))
(when (logbitp 4 flg) (push :comment flags))
(setf gzip-state :header-mtime)))
(:header-mtime
(when (and (< bits-remaining 32)
(not (%fill-bits32 32)))
(setf input-underrun t)
(return-from decompress-gzip 0))
(let ((mtime (logior (ash (header-byte) 0)
(ash (header-byte) 8)
(ash (header-byte) 16)
(ash (header-byte) 24))))
(unless (zerop mtime)
(setf mtime/unix mtime)
(setf mtime/universal
(+ mtime (encode-universal-time 0 0 0 1 1 1970 0))))
(setf gzip-state :header3)))
(:header3 ;; extra flags, os
(when (and (< bits-remaining 16)
(not (%fill-bits32 16)))
(setf input-underrun t)
(return-from decompress-gzip 0))
(let ((xfl (header-byte))
(os (header-byte)))
(setf compression-level
(or (case xfl (2 :maximum) (4 :fastest))
xfl))
(setf operating-system
(if (<= 0 os 13)
(aref #(:fat :amiga :vms :unix :vm/cms
:atari-tos :hpfs :macintosh
:z-system :cp/m :tops-20
:ntfs :qdos :acorn-riscos)
os)
(list :unknown os)))
(setf gzip-state :header-extra)))
(:header-extra
(when (member :extra flags)
(unless extra
(when (and (< bits-remaining 16)
(not (%fill-bits32 16)))
(setf input-underrun t)
(return-from decompress-gzip 0))
(let ((xlen (logior (ash (header-byte) 0)
(ash (header-byte) 8))))
(setf extra (make-array xlen :element-type 'octet
:fill-pointer 0))))
(loop while (< (fill-pointer extra)
(length extra))
do (when (and (< bits-remaining 8)
(not (%fill-bits32 8)))
(setf input-underrun t)
(return-from decompress-gzip 0))
(vector-push (header-byte) extra))
(setf extra (coerce extra '(simple-array octet 1))))
(setf gzip-state :header-name))
(:header-name
(when (member :name flags)
(unless name
(setf name (make-array 16 :adjustable t :fill-pointer 0
:element-type 'octet)))
(loop do (when (and (< bits-remaining 8)
(not (%fill-bits32 8)))
(setf input-underrun t)
(return-from decompress-gzip 0))
(let ((b (header-byte)))
(cond
((not (zerop b))
(vector-push-extend b name))
(t
(setf name
;; rfc says 8859-1, but try utf8 anyway
(or (babel:octets-to-string
name :encoding :utf-8 :errorp nil)
(babel:octets-to-string
name :encoding :iso8859-1)))
(loop-finish))))))
(setf gzip-state :header-comment))
(:header-comment
(when (member :comment flags)
(unless comment
(setf comment (make-array 16 :adjustable t :fill-pointer 0
:element-type 'octet)))
(loop do (when (and (< bits-remaining 8)
(not (%fill-bits32 8)))
(setf input-underrun t)
(return-from decompress-gzip 0))
(let ((b (header-byte)))
(cond
((not (zerop b))
(vector-push-extend b comment))
(t
(setf comment
;; rfc says 8859-1, but try utf8 anyway
(or (babel:octets-to-string
comment :encoding :utf-8 :errorp nil)
(babel:octets-to-string
comment :encoding :iso8859-1)))
(loop-finish))))))
(setf gzip-state :header-crc))
(:header-crc
;; check hcrc if present
(when (member :header-crc flags)
(when (and (< bits-remaining 16)
(not (%fill-bits32 16)))
(setf input-underrun t)
(return-from decompress-gzip 0))
(let* ((hb (coerce header-bytes 'octet-vector))
(crc (logior (ash (%bits 8) 0)
(ash (%bits 8) 8)))
(crc32 (crc32/table hb (length hb) 0)))
(format t "got header crc ~4,'0x, expected ~8,'0x~%"
crc crc32)
(assert (= crc (ldb (byte 16 0) crc32)))))
#++(format t "gzip header: method ~s, level ~s, os ~s, flags ~s~%"
compression-method compression-level
operating-system flags)
#++(when mtime/universal
(format t " mtime: ~s~%"
(reverse (multiple-value-list
(decode-universal-time mtime/universal)))))
#++(format t " name: ~s~%" name)
#++(format t " comment: ~s~%" comment)
#++(format t " extra: ~s~%" extra)
(setf gzip-state :deflate))
(:deflate
(decompress-deflate read-context state)
(when (or finished output-overflow)
(update-checksum))
(when finished
(byte-align)
(setf gzip-state :final-crc)
(setf finished nil)))
(:final-crc
(crc))
(:final-len
(len)
(setf finished t)
;; not a valid state, so calling this again after it
;; finishes is an error. If it were valid and just
;; ignored, caller would probably need to be checking
;; state before calling anyway to avoid an infinite
;; loop, so an error seems like the safer choice here.
(setf gzip-state :done)
(loop-finish))))
output-offset))))
|
