From 087b4ea280caa05e7213eb2b051782086c96efba Mon Sep 17 00:00:00 2001
From: Piotr Szarmanski
Date: Sat, 22 Oct 2022 13:41:29 +0200
Subject: Add backend.lisp and file-backend.lisp.

---
 src/backend.lisp      | 35 +++++++++++++++++++++++++
 src/file-backend.lisp | 71 +++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 106 insertions(+)
 create mode 100644 src/backend.lisp
 create mode 100644 src/file-backend.lisp

diff --git a/src/backend.lisp b/src/backend.lisp
new file mode 100644
index 0000000..9bb00d0
--- /dev/null
+++ b/src/backend.lisp
@@ -0,0 +1,35 @@
+;; 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 version.
+
+;; 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/>.
+
+;; This file contains the backend protocol.
+(in-package :eris)
+
+(defclass encoding-backend ()
+  ((output-function :type function)))
+
+(defclass decoding-backend ()
+  ((fetch-function :type function)))
+
+(defgeneric fetch-read-capability (read-capability backend &key &allow-other-keys)
+  (:documentation
+   "Using the BACKEND, return a stream that decodes the provided READ-CAPABILITY
+object."))
+
+(defgeneric store-data (input backend &key secret &allow-other-keys)
+  (:documentation
+   "Using the BACKEND, store the INPUT, which is either a stream or an octet
+vector. An additional 32-byte octet-vector SECRET can be provided in order to
+protect the data from attacks against convergent encryption."))
+
diff --git a/src/file-backend.lisp b/src/file-backend.lisp
new file mode 100644
index 0000000..2bb8693
--- /dev/null
+++ b/src/file-backend.lisp
@@ -0,0 +1,71 @@
+;; 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 version.
+
+;; 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)
+
+(defclass file-backend (encoding-backend decoding-backend)
+  ((directory :initarg :directory :type (or string pathname)
+              :documentation
+              "Directory containing ERIS data.")))
+
+
+(define-condition file-backend-error (error)
+  ())
+
+(define-condition directory-error (file-backend-error)
+  ((message :type string :initarg :message))
+  (:report (lambda (condition stream)
+             (format stream "~a" (slot-value condition 'message)))))
+
+(defmethod shared-initialize :after ((file-backend file-backend) slot-names
+                                     &rest initargs
+                                     &key (directory nil directory-p)
+                                     &allow-other-keys)
+  
+  (declare (ignore initargs slot-names))
+  (when (or (null directory-p) (null (pathname-directory directory)))
+    (error 'directory-error :message "Incorrectly specified directory."))
+  (with-slots (directory output-function fetch-function) file-backend
+    (when (or (pathname-name directory)))
+    (setf fetch-function
+          (lambda (reference)
+            (let* ((base32 (bytes-to-base32-unpadded reference))
+                   (file (merge-pathnames directory base32)))
+              (alexandria:read-file-into-byte-vector file)))
+          output-function
+          (lambda (block reference)
+            (let* ((base32 (bytes-to-base32-unpadded reference))
+                   (file (merge-pathnames directory base32)))
+              (unless (probe-file file)
+                (alexandria:write-byte-vector-into-file block file)))))))
+
+(defmethod fetch-read-capability (read-capability (backend file-backend) &key &allow-other-keys)
+  (declare (type read-capability read-capability))
+  (with-slots (fetch-function) backend
+    (eris-decode read-capability fetch-function)))
+
+(defmethod store-data (input (backend file-backend) &key (secret null-secret) &allow-other-keys)
+  (declare (type octet-vector secret))
+  (with-slots (output-function) backend
+    (eris-encode input
+                 (if (> (etypecase input
+                          (stream (file-length input))
+                          (vector (length input)))
+                        16384)
+                     32kib
+                     1kib)
+                 output-function
+                 :hash-output nil
+                 :secret secret)))
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