From 4d82ef18a8bb18317be3e089f432f95b6e5dbd4a Mon Sep 17 00:00:00 2001
From: Piotr Szarmanski
Date: Thu, 22 Sep 2022 11:16:44 +0200
Subject: Implement stream-read-byte

---
 src/eris-decode.lisp | 31 ++++++++++++++++++++++++-------
 1 file changed, 24 insertions(+), 7 deletions(-)

(limited to 'src/eris-decode.lisp')

diff --git a/src/eris-decode.lisp b/src/eris-decode.lisp
index b7575ab..43f8db0 100644
--- a/src/eris-decode.lisp
+++ b/src/eris-decode.lisp
@@ -186,7 +186,7 @@ fetched from a trusted party.")
                     (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)
+                    (if (< (- eof (mod eof block-size)) new-pos)
                         (unpad-buffer buffer)
                         (setf (eof buffer) block-size))))))
 
@@ -199,23 +199,25 @@ fetched from a trusted party.")
 
 
 (defun eris-decode (read-capability fetch-function &key (cache-capacity 2048))
-  "With a given fetch-function, return a stream that decodes the read-capability.
+  "Using the 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. "
+gethash. 
+
+The keyword argument CACHE-CAPACITY indicates the amount of blocks stored in the
+cache."
   (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)))
+                          (unless block (error 'missing-block :reference reference))
                           (hash-check block reference)
-                          (if block
-                              (decrypt-block block key nonce)
-                              (error 'missing-block :reference reference)))))
+                          (decrypt-block block key nonce))))
            (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."
@@ -282,10 +284,25 @@ the new position is beyond the end of file.."
     (read-to-seq seq buffer :start start :end (if end end (length seq)) :stream stream)))
 
 (defmethod stream-read-byte ((stream eris-decode-stream))
-  nil)
+  (when (minusp (pos (buffer stream)))
+    ;; initializes the buffer
+    (reupdate-block stream (pos stream)))
+  (with-slots (position buffer block-size) stream
+    (with-slots (pos eof data) buffer
+      (cond
+        ((eql pos block-size)
+         (setf pos 0)
+         (advance-next-block stream)
+         (stream-read-byte stream))
+        ((eql pos eof)
+         :eof)
+        (t (prog1 (aref data pos)
+             (incf pos)
+             (incf position)))))))
 
 (defmethod stream-element-type ((stream eris-decode-stream))
   '(unsigned-byte 8))
 
 (defun eris-file-length (stream)
+  "This is the equivalent of \"file-length\" for eris-decode-stream."
   (eof stream))
-- 
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