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Diffstat (limited to 'src/eris-decode.lisp')
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1 files changed, 291 insertions, 0 deletions
diff --git a/src/eris-decode.lisp b/src/eris-decode.lisp new file mode 100644 index 0000000..b7575ab --- /dev/null +++ b/src/eris-decode.lisp @@ -0,0 +1,291 @@ +;; This file is part of eris-cl. +;; Copyright (C) 2022 Piotr Szarmański + +;; eris-cl is free software: you can redistribute it and/or modify it under the +;; terms of the GNU Lesser General Public License as published by the Free +;; Software Foundation, either version 3 of the License, or (at your option) any +;; later versqion. + +;; eris-cl is distributed in the hope that it will be useful, but WITHOUT ANY +;; WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR +;; A PARTICULAR PURPOSE. See the GNU General Public License for more details. + +;; You should have received a copy of the GNU General Public License along with +;; eris-cl. If not, see <https://www.gnu.org/licenses/>. + +(in-package :eris) + +(defvar *decode-safety-checks* t + "If set to nil, disable computationally expensive safety checks that ensure the +fetched blocks are what they claim to be. Only disable this if the blocks are +fetched from a trusted party.") + +(defmacro hash-check (block hash) + `(when *decode-safety-checks* + (let ((hash (ironclad:digest-sequence :blake2/256 ,block))) + (unless (equalp ,hash hash) + (error 'hash-mismatch :reference ,hash :hash hash ))))) + +(defun key-reference-null? (kr) + (and (equalp (reference kr) null-secret) + (equalp (key kr) null-secret))) + +(defclass high-block () + ((data :initarg :data :accessor data :type (simple-array (unsigned-byte 8))) + (position :initarg :position :accessor pos :type integer + :documentation "Position relative to the higher block.") + (level :initarg :level :accessor level :type (unsigned-byte 8)))) + +(defclass buffer () + ((data :initarg :data :accessor data :type (simple-array (unsigned-byte 8))) + (pos :initarg :pos :accessor pos :type fixnum) + (eof :initarg :eof :accessor eof :type fixnum + :documentation "Either the position of the EOF in the buffer, or the length of the buffer."))) + +(defclass eris-decode-stream (fundamental-binary-input-stream) + ((position :initform 0 :accessor pos :initarg :position :type integer) + (get-block :accessor get-block :initarg :get-block :type function) + (block-size :accessor block-size :type block-size :initarg :block-size) + (root :accessor root :type high-block :initarg :root :documentation "A list of blocks, starting from the root to the level 1 block.") + (buffer :accessor buffer :initarg :buffer :type buffer) + (eof :accessor eof :initarg :eof :type integer) + (nonce-array :accessor nonce-array :initarg :nonce-array :type simple-array))) + +(defun initialize-nonce-array (level) + (let ((array (make-array (1+ level)))) + (loop for i from 0 to level + do (setf (aref array i) (make-nonce i))) + array)) + +(defun unpad-block (block) + (let ((padding (position #x80 block :from-end t))) + (unless padding + (error 'padding-error)) + (unless (loop for i across (subseq-shared block (1+ padding)) + always (zerop i)) + (error 'padding-error)) + padding)) + +(defun unpad-buffer (buffer) + (with-slots (eof data) buffer + (setf eof + (unpad-block data)))) + +(defun ls (level block-size) + (declare ;; (type (unsigned-byte 8) level) + (type block-size block-size)) + (ecase block-size + (1024 (expt 2 (+ 10 (* level 4)))) + (32768 (expt 2 (+ 15 (* level 9)))))) + +(defun find-eof (root get-block block-size level) + "Find the end of file in a given tree." + ;; The standard states that: + ;; If 64 bytes of zeroes are encountered the rest of the node MUST be checked to be all zeroes + ;; This procedure processes the block from right to left so it's not really applicable here + + (flet ((find-last-reference (block) + (loop for i from (1- (/ block-size 64)) downto 0 + for key-reference = (octets-to-reference-pair (subseq-shared block (* 64 i))) + unless (key-reference-null? key-reference) + return (values key-reference i)))) + (loop with position = 0 + for local-level = level then (1- local-level) + for block = root then (funcall get-block (reference key-reference) (key key-reference) (make-nonce local-level)) + for (key-reference block-pos) = (multiple-value-list (find-last-reference block)) + if (eql 0 local-level) + do (setf position (+ position (unpad-block block))) + and return position + else + do (setf position (+ position (* block-pos (ls (1- local-level) block-size))))))) + +(defun advance-next-block (stream) + "Advance to the next block. This function is called by update-buffer." + (declare (optimize (speed 3) (debug 0))) + (with-slots (buffer position eof block-size root get-block nonce-array) stream + (declare (type integer position eof) + (type block-size block-size) + #+sbcl (sb-ext:muffle-conditions sb-ext:compiler-note)) + (labels ((process-block (blocks mod level) ;; A recursive function that 1+'s each block until the + (declare (type fixnum mod)) + (let* ((current (car blocks)) + (next-pos (setf (pos current) + (mod (the fixnum (1+ (the fixnum (pos current)))) mod)))) + (declare (type high-block current) + (type fixnum next-pos)) + (when (zerop next-pos) ;; if 1+ mod blocks results in a zero, then update the next block + (process-block (cdr blocks) mod (1+ level))) + (let ((kr (octets-to-reference-pair + (subseq-shared (data (cadr blocks)) + (the fixnum (* next-pos 64)))))) + (setf (data current) + (funcall get-block (reference kr) (key kr) (svref nonce-array level))))))) + (process-block (reverse root) (/ block-size 64) 0) ;; process the blocks from level 0 up + ;; setf the buffer data to the level 0 block + (setf (data buffer) + (data (car (last root)))) + ;; if the EOF block is reached, unpad it. + (when (= (- eof (mod eof block-size)) position) + (unpad-buffer buffer))))) + +(defun read-to-seq (sequence buf &key (start 0) (end (length sequence)) stream) + (declare (optimize (speed 3) (debug 0)) + (type integer end start sum) + #+sbcl (sb-ext:muffle-conditions sb-ext:compiler-note)) + (with-slots (data pos eof) buf + (declare (type (integer 0 32768) pos eof) + (type (simple-array (unsigned-byte 8)) data)) + (let ((buffer-bytes (- eof pos)) + (seq-bytes (- end start))) + (declare (dynamic-extent buffer-bytes seq-bytes) + (type integer seq-bytes) + (type (integer 0 32768) buffer-bytes)) + (cond + ((> buffer-bytes seq-bytes) ;; seq is smaller than buffer case + (replace sequence data :start1 start :end1 end :start2 pos) + (setf pos (+ pos seq-bytes) + (pos stream) (+ (pos stream) seq-bytes)) + (+ start seq-bytes)) + ((eql eof (length data)) ;; seq is larger or equal than buffer case + (replace sequence data :start1 start :end1 end :start2 pos) + (setf pos 0 + (pos stream) (+ (pos stream) buffer-bytes)) + (advance-next-block stream) + (read-to-seq sequence buf :start (+ start buffer-bytes) :end end :stream stream)) + (t ;; if there is an eof in the buffer + (replace sequence data :start1 start :end1 end :start2 pos :end2 eof) + (setf pos (+ pos buffer-bytes) + (pos stream) (+ (pos stream) buffer-bytes)) + (+ start buffer-bytes)))))) + + +(defun reupdate-block (stream new-pos) + "Update the blocks of the stream according to new-pos. Used for random access and initialization." + (unless (root stream) + (error 'eof :eof new-pos :position (pos stream))) + (with-slots (block-size root get-block buffer nonce-array eof) stream + (loop with update-tree = nil + for blocks = root then (cdr blocks) + for level = (level (car blocks)) ;; then (decf level) + for position = new-pos then (mod position (ls (1- level) block-size)) ;; local position + for block-position = (floor (/ position (ls (1- level) block-size))) ;; the position of the block + for lower-block = (second blocks) + when (> block-position (/ block-size 64)) + do (error 'eof :eof new-pos :position (pos stream)) + until (eq nil (cdr blocks)) + when (or update-tree (not (eq block-position (pos lower-block)))) + do (let ((rk (octets-to-reference-pair + (subseq-shared (data (car blocks)) + (* 64 block-position))))) + (when (key-reference-null? rk) + (error 'eof :eof new-pos :position (pos stream))) + (setf (data lower-block) (funcall get-block (reference rk) (key rk) (svref nonce-array (1- level))) + (pos lower-block) block-position + update-tree t)) + finally (when update-tree ;; if anything changed + (setf (pos stream) new-pos + (data buffer) (data (car (last root))) + (pos buffer) (mod new-pos block-size)) + (if (= (- eof (mod eof block-size)) new-pos) + (unpad-buffer buffer) + (setf (eof buffer) block-size)))))) + +(defun initialize-high-blocks (level) + (case level + (-1 nil) + (t (cons (make-instance 'high-block :level level :position -1 :data (make-array 0 :element-type '(unsigned-byte 8))) + (initialize-high-blocks (1- level)))))) + + + +(defun eris-decode (read-capability fetch-function &key (cache-capacity 2048)) + "With a given fetch-function, return a stream that decodes the read-capability. + +Fetch-function must be a function with one argument, the reference octet, which +returns a (simple-array (unsigned-byte 8)) containing the block. The block will +be destructively modified, so you MUST provide a fresh array every time. If a +hash-table is used, a (copy-seq) needs to be done on the return value of +gethash. " + (with-slots (level block-size root-reference-pair) read-capability + (let* ((get-block (cached-lambda (:cache-class 'lru-cache + :capacity cache-capacity + :table (make-hash-table :size (1+ cache-capacity) :test #'equalp)) + (reference key &optional nonce) + (let* ((block (funcall fetch-function reference))) + (hash-check block reference) + (if block + (decrypt-block block key nonce) + (error 'missing-block :reference reference))))) + (root (funcall get-block (reference root-reference-pair) (key root-reference-pair) (make-nonce level)))) + ;; "Implementations MUST verify the key appearing in the read capability + ;; if level of encoded content is larger than 0." + ;;(when (> level 0) (hash-check root (key root-reference-pair))) + (case level + ;; Treat level 0 blocks specially, since those are just a single buffer. + (0 (let ((stream + (make-instance 'eris-decode-stream + :buffer (make-instance 'buffer + :data (make-array block-size :element-type '(unsigned-byte 8)) + :pos 0 + :eof -1) + :get-block (lambda (reference key) + (declare (ignore key)) + (error 'missing-block :reference reference)) + :block-size block-size + :root nil + :eof (find-eof root get-block block-size level) + :nonce-array (initialize-nonce-array 0)))) + (replace (data (buffer stream)) root) + (unpad-buffer (buffer stream)) + stream)) + (t (make-instance 'eris-decode-stream + :buffer (make-instance 'buffer + :data (make-array block-size :element-type '(unsigned-byte 8)) + :pos -1 + :eof block-size) + :get-block get-block + :block-size block-size + :root (cons (make-instance 'high-block :level level + :data root + :position 0) + (initialize-high-blocks (1- level))) + :eof (find-eof root get-block block-size level) + :nonce-array (initialize-nonce-array level))))))) + +(defmethod stream-file-position ((stream eris-decode-stream) &optional (set-position nil)) + "Provides the file position of the stream. If the optional second argument is +set, try to move the stream to that position. It may signal an EOF condition if +the new position is beyond the end of file.." + ;; NOTE: this should accept a "file-spec", which I believe is either an int, a + ;; :start or an :end. This only accepts a number. + (with-slots (position block-size buffer eof) stream + (when set-position + (let ((buffer-pos (mod set-position block-size))) + (if (< set-position eof) + (cond + ;; If the pos is within the buffer (and initialized): + ((and (<= 0 (- set-position (- position (pos buffer))) (1- block-size)) + (not (minusp (pos buffer)))) + (setf (pos buffer) buffer-pos + position set-position)) + + (t (reupdate-block stream set-position) + (setf (pos buffer) buffer-pos))) + (error 'eof :eof eof :position position)))) + position)) + +(defmethod stream-read-sequence ((stream eris-decode-stream) seq &optional (start 0) (end (length seq))) + (when (minusp (pos (buffer stream))) + ;; initializes the buffer + (reupdate-block stream (pos stream))) + (with-slots (buffer position) stream + (read-to-seq seq buffer :start start :end (if end end (length seq)) :stream stream))) + +(defmethod stream-read-byte ((stream eris-decode-stream)) + nil) + +(defmethod stream-element-type ((stream eris-decode-stream)) + '(unsigned-byte 8)) + +(defun eris-file-length (stream) + (eof stream)) |