[gnunet-scheme] 04/324: Define CHK URIs and parsing

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maxime-devos pushed a commit to branch master
in repository gnunet-scheme.

commit ffc07ba6442692d09124a5eaa765e78647cbfea0
Author: Maxime Devos <maximedevos@telenet.be>
AuthorDate: Mon Nov 2 23:04:27 2020 +0100

    Define CHK URIs and parsing
---
 gnu/gnunet/fs-uri.scm | 161 ++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 161 insertions(+)

diff --git a/gnu/gnunet/fs-uri.scm b/gnu/gnunet/fs-uri.scm
new file mode 100644
index 0000000..3105614
--- /dev/null
+++ b/gnu/gnunet/fs-uri.scm
@@ -0,0 +1,161 @@
+;;   This file is part of scheme-GNUnet, a partial Scheme port of GNUnet.
+;;   Copyright (C) 2003--2014 GNUnet e.V.
+;;   Copyright (C) 2020 Maxime Devos <maxime.devos@student.kuleuven.be>
+;;
+;;   GNUnet is free software: you can redistribute it and/or modify it
+;;   under the terms of the GNU Affero General Public License as published
+;;   by the Free Software Foundation, either version 3 of the License,
+;;   or (at your option) any later version.
+;;
+;;   GNUnet 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
+;;   Affero General Public License for more details.
+;;
+;;   You should have received a copy of the GNU Affero General Public License
+;;   along with this program.  If not, see <http://www.gnu.org/licenses/>.
+;;
+;;   SPDX-License-Identifier: AGPL-3.0-or-later
+;;
+;;   As a special exception to the GNU Affero General Public License,
+;;   the file may be relicensed under any license used for
+;;   most source code of GNUnet 0.13.1, or later versions, as published by
+;;   GNUnet e.V.
+
+;; Upstream file header:
+;; @file fs/fs_uri.c
+;; @brief Parses and produces uri strings.
+;; @author Igor Wronsky, Christian Grothoff
+;;
+;; GNUnet URIs are of the general form "gnunet://MODULE/IDENTIFIER".
+;; The specific structure of "IDENTIFIER" depends on the module and
+;; maybe differenciated into additional subcategories if applicable.
+;; This module only deals with fs identifiers (MODULE = "fs").
+;; <p>
+;;
+;; This module only parses URIs for the AFS module.  The FS URIs fall
+;; into four categories, "chk", "sks", "ksk" and "loc".  The first three
+;; categories were named in analogy (!) to Freenet, but they do NOT
+;; work in exactly the same way.  They are very similar from the user's
+;; point of view (unique file identifier, subspace, keyword), but the
+;; implementation is rather different in pretty much every detail.
+;; The concrete URI formats are:
+;;
+;; </p>
+;;
+;; <ul><li>
+;;
+;; First, there are URIs that identify a file.  They have the format
+;; "gnunet://fs/chk/HEX1.HEX2.SIZE".  These URIs can be used to
+;; download the file.  The description, filename, mime-type and other
+;; meta-data is NOT part of the file-URI since a URI uniquely
+;; identifies a resource (and the contents of the file would be the
+;; same even if it had a different description).
+;;
+;; </li><li>
+;;
+;; The second category identifies entries in a namespace.  The format
+;; is "gnunet://fs/sks/NAMESPACE/IDENTIFIER" where the namespace
+;; should be given in HEX.  Applications may allow using a nickname
+;; for the namespace if the nickname is not ambiguous.  The identifier
+;; can be either an ASCII sequence or a HEX-encoding.  If the
+;; identifier is in ASCII but the format is ambiguous and could denote
+;; a HEX-string a "/" is appended to indicate ASCII encoding.
+;;
+;; </li> <li>
+;;
+;; The third category identifies ordinary searches.  The format is
+;; "gnunet://fs/ksk/KEYWORD[+KEYWORD]*".  Using the "+" syntax
+;; it is possible to encode searches with the boolean "AND" operator.
+;; "+" is used since it indicates a commutative 'and' operation and
+;; is unlikely to be used in a keyword by itself.
+;;
+;; </li><li>
+;;
+;; The last category identifies a datum on a specific machine.  The
+;; format is "gnunet://fs/loc/HEX1.HEX2.SIZE.PEER.SIG.EXPTIME".  PEER is
+;; the BinName of the public key of the peer storing the datum.  The
+;; signature (SIG) certifies that this peer has this content.
+;; HEX1, HEX2 and SIZE correspond to a 'chk' URI.
+;;
+;; </li></ul>
+;;
+;; The encoding for hexadecimal values is defined in the hashing.c
+;; module in the gnunetutil library and discussed there.
+
+(library (gnu gnunet fs-uri (1 1))
+  (export chk? make-chk chk-key chk-query
+          chk-uri? make-chk-uri chk-uri-file-length chk-uri-chk
+         chk-uri-parse)
+  (import (rnrs base)
+          (rnrs records syntactic)
+         (gnu gnunet hashcode)
+         (gnu gnunet hashcode-ascii)
+         ;; TODO portability
+         (only (guile) make-regexp regexp-exec)
+         (only (ice-9 regex) match:substring)
+         (only (srfi srfi-2) and-let*))
+
+  ;; Size of the individual blocks used for file-sharing.
+  ;; TODO: what is the proper place to define this constant
+  #;(define DBLOCK_SIZE (* 32 1024))
+
+  ;; Content hash key
+  (define-record-type (<content-hash-key> %make-content-hash-key chk?)
+    (fields ;; Hash of the original content, used for encryption.
+            ;; Of type <hash-code>.
+            (immutable key chk-key)
+            ;; Hash of the encrypted content, used for querying.
+            ;; Of type <hash-code>
+            (immutable query chk-query)))
+
+  (define (make-chk key query)
+    "Construct a <content-hash-key>"
+    (assert (hashcode? key))
+    (assert (hashcode? query))
+    (%make-content-hash-key key query))
+
+  ;; Information needed to retrieve a file (content-hash-key
+  ;; plus file size)
+  (define-record-type (<chk-uri> %make-chk-uri chk-uri?)
+    (fields ;; Total size of the file referred to in bytes.
+            (immutable file-length chk-uri-file-length)
+            ;; Query and key of the top GNUNET_EC_IBlock.
+            ;; Of type <content-hash-key>.
+            (immutable chk chk-uri-chk)))
+
+  ;; TODO: is this limitation on file size
+  ;; merely a limit of the implementation?
+  (define file-length-limit (expt 2 64))
+
+  (define (make-chk-uri file-length chk)
+    "Make a chk-URI"
+    (assert (and (exact? file-length)
+                (integer? file-length)))
+    (assert (and (<= 0 file-length)
+                (< file-length file-length-limit)))
+    (assert (chk? chk))
+    (%make-chk-uri file-length chk))
+
+  ;; TODO: location URIs, ksk URIs?
+  ;; Why does GNUnet have location URIs?
+
+  (define chk-uri-parse
+    (let ((rx
+          (make-regexp
+           "^gnunet://fs/chk/([0-9A-Z]+).([0-9A-Z]+).(0|[1-9][0-9]+)$")))
+      (lambda (str)
+       "Parse a ‘Content Hash Key’ URI, return @lisp{#f} in case of a syntax
+error."
+       (and-let* ((match (regexp-exec rx str))
+                  (key-match (match:substring match 1))
+                  (query-match (match:substring match 2))
+                  (size-match (match:substring match 3))
+                  (key-hashcode (ascii->hashcode key-match))
+                  (query-hashcode (ascii->hashcode query-match))
+                  (size (string->number size-match 10))
+                  (size-ok (< size file-length-limit)))
+         (%make-chk-uri size
+                        (%make-content-hash-key key-hashcode
+                                                query-hashcode)))))))
+

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