Repad the Face header in Gnus

* lisp/gnus/gnus-fun.el (gnus-convert-face-to-png): Use it.

* lisp/gnus/gnus-util.el (gnus-base64-repad): New function (bug#43441).

3 files changed, 151 insertions, 5 deletions

diff --git a/lisp/gnus/gnus-fun.el b/lisp/gnus/gnus-fun.el
index c95449762e4..2461fd45fd5 100644
--- a/lisp/gnus/gnus-fun.el
+++ b/lisp/gnus/gnus-fun.el
@@ -205,11 +205,12 @@ different input formats."
 (defun gnus-convert-face-to-png (face)
   "Convert FACE (which is base64-encoded) to a PNG.
 The PNG is returned as a string."
-  (mm-with-unibyte-buffer
-    (insert face)
-    (ignore-errors
-      (base64-decode-region (point-min) (point-max)))
-    (buffer-string)))
+  (let ((face (gnus-base64-repad face)))
+    (mm-with-unibyte-buffer
+      (insert face)
+      (ignore-errors
+        (base64-decode-region (point-min) (point-max)))
+      (buffer-string))))
 
 ;;;###autoload
 (defun gnus-convert-png-to-face (file)
diff --git a/lisp/gnus/gnus-util.el b/lisp/gnus/gnus-util.el
index aa9f137e203..f8126906b87 100644
--- a/lisp/gnus/gnus-util.el
+++ b/lisp/gnus/gnus-util.el
@@ -1343,6 +1343,53 @@ forbidden in URL encoding."
     (setq tmp (concat tmp str))
     tmp))
 
+(defun gnus-base64-repad (str &optional reject-newlines line-length)
+  "Take a base 64-encoded string and return it padded correctly.
+Existing padding is ignored.
+
+If any combination of CR and LF characters are present and
+REJECT-NEWLINES is nil, remove them; otherwise raise an error.
+If LINE-LENGTH is set and the string (or any line in the string
+if REJECT-NEWLINES is nil) is longer than that number, raise an
+error.  Common line length for input characters are 76 plus CRLF
+(RFC 2045 MIME), 64 plus CRLF (RFC 1421 PEM), and 1000 including
+CRLF (RFC 5321 SMTP)."
+  ;; RFC 4648 specifies that:
+  ;; - three 8-bit inputs make up a 24-bit group
+  ;; - the 24-bit group is broken up into four 6-bit values
+  ;; - each 6-bit value is mapped to one character of the base 64 alphabet
+  ;; - if the final 24-bit quantum is filled with only 8 bits the output
+  ;;   will be two base 64 characters followed by two "=" padding characters
+  ;; - if the final 24-bit quantum is filled with only 16 bits the output
+  ;;   will be three base 64 character followed by one "=" padding character
+  ;;
+  ;; RFC 4648 section 3 considerations:
+  ;; - if reject-newlines is nil (default), concatenate multi-line
+  ;;   input (3.1, 3.3)
+  ;; - if line-length is set, error on input exceeding the limit (3.1)
+  ;; - reject characters outside base encoding (3.3, also section 12)
+  (let ((splitstr (split-string str "[\r\n]" t)))
+    (when (and reject-newlines (> (length splitstr) 1))
+      (error "Invalid Base64 string"))
+    (dolist (substr splitstr)
+      (when (and line-length (> (length substr) line-length))
+        (error "Base64 string exceeds line-length"))
+      (when (string-match "[^A-Za-z0-9+/=]" substr)
+        (error "Invalid Base64 string")))
+    (let* ((str (string-join splitstr))
+           (len (length str)))
+      (when (string-match "=" str)
+        (setq len (match-beginning 0)))
+      (concat
+       (substring str 0 len)
+       (make-string (/
+                     (- 24
+                        (pcase (mod (* len 6) 24)
+                          (`0 24)
+                          (n n)))
+                     6)
+                    ?=)))))
+
 (defun gnus-make-predicate (spec)
   "Transform SPEC into a function that can be called.
 SPEC is a predicate specifier that contains stuff like `or', `and',
diff --git a/test/lisp/gnus/gnus-util-tests.el b/test/lisp/gnus/gnus-util-tests.el
index 7eadb0de716..ed33be46a3a 100644
--- a/test/lisp/gnus/gnus-util-tests.el
+++ b/test/lisp/gnus/gnus-util-tests.el
@@ -25,6 +25,65 @@
 (require 'ert)
 (require 'gnus-util)
 
+(ert-deftest gnus-string> ()
+  ;; Failure paths
+  (should-error (gnus-string> "" 1)
+                :type 'wrong-type-argument)
+  (should-error (gnus-string> "")
+                :type 'wrong-number-of-arguments)
+
+  ;; String tests
+  (should (gnus-string> "def" "abc"))
+  (should (gnus-string> 'def 'abc))
+  (should (gnus-string> "abc" "DEF"))
+  (should (gnus-string> "abc" 'DEF))
+  (should (gnus-string> "αβγ" "abc"))
+  (should (gnus-string> "אבג" "αβγ"))
+  (should (gnus-string> nil ""))
+  (should (gnus-string> "abc" ""))
+  (should (gnus-string> "abc" "ab"))
+  (should-not (gnus-string> "abc" "abc"))
+  (should-not (gnus-string> "abc" "def"))
+  (should-not (gnus-string> "DEF" "abc"))
+  (should-not (gnus-string> 'DEF "abc"))
+  (should-not (gnus-string> "123" "abc"))
+  (should-not (gnus-string> "" "")))
+
+(ert-deftest gnus-string< ()
+  ;; Failure paths
+  (should-error (gnus-string< "" 1)
+                :type 'wrong-type-argument)
+  (should-error (gnus-string< "")
+                :type 'wrong-number-of-arguments)
+
+  ;; String tests
+  (setq case-fold-search nil)
+  (should (gnus-string< "abc" "def"))
+  (should (gnus-string< 'abc 'def))
+  (should (gnus-string< "DEF" "abc"))
+  (should (gnus-string< "DEF" 'abc))
+  (should (gnus-string< "abc" "αβγ"))
+  (should (gnus-string< "αβγ" "אבג"))
+  (should (gnus-string< "" nil))
+  (should (gnus-string< "" "abc"))
+  (should (gnus-string< "ab" "abc"))
+  (should-not (gnus-string< "abc" "abc"))
+  (should-not (gnus-string< "def" "abc"))
+  (should-not (gnus-string< "abc" "DEF"))
+  (should-not (gnus-string< "abc" 'DEF))
+  (should-not (gnus-string< "abc" "123"))
+  (should-not (gnus-string< "" ""))
+
+  ;; gnus-string< checks case-fold-search
+  (setq case-fold-search t)
+  (should (gnus-string< "abc" "DEF"))
+  (should (gnus-string< "abc" 'GHI))
+  (should (gnus-string< 'abc "DEF"))
+  (should (gnus-string< 'GHI 'JKL))
+  (should (gnus-string< "abc" "ΑΒΓ"))
+  (should-not (gnus-string< "ABC" "abc"))
+  (should-not (gnus-string< "def" "ABC")))
+
 (ert-deftest gnus-subsetp ()
   ;; False for non-lists.
   (should-not (gnus-subsetp "1" "1"))
@@ -73,4 +132,43 @@
   (should (equal '("1") (gnus-setdiff '(2 "1" 2) '(2))))
   (should (equal '("1" "1") (gnus-setdiff '(2 "1" 2 "1") '(2)))))
 
+(ert-deftest gnus-base64-repad ()
+  (should-error (gnus-base64-repad "" nil nil nil)
+                :type 'wrong-number-of-arguments)
+  (should-error (gnus-base64-repad 1)
+                :type 'wrong-type-argument)
+
+  ;; RFC4648 test vectors
+  (should (equal "" (gnus-base64-repad "")))
+  (should (equal "Zg==" (gnus-base64-repad "Zg==")))
+  (should (equal "Zm8=" (gnus-base64-repad "Zm8=")))
+  (should (equal "Zm9v" (gnus-base64-repad "Zm9v")))
+  (should (equal "Zm9vYg==" (gnus-base64-repad "Zm9vYg==")))
+  (should (equal "Zm9vYmE=" (gnus-base64-repad "Zm9vYmE=")))
+  (should (equal "Zm9vYmFy" (gnus-base64-repad "Zm9vYmFy")))
+
+  (should (equal "Zm8=" (gnus-base64-repad "Zm8")))
+  (should (equal "Zg==" (gnus-base64-repad "Zg")))
+  (should (equal "Zg==" (gnus-base64-repad "Zg====")))
+
+  (should-error (gnus-base64-repad " ")
+                :type 'error)
+  (should-error (gnus-base64-repad "Zg== ")
+                :type 'error)
+  (should-error (gnus-base64-repad "Z?\x00g==")
+                :type 'error)
+  ;; line-length
+  (should-error (gnus-base64-repad "Zg====" nil 4)
+                :type 'error)
+  ;; reject-newlines
+  (should-error (gnus-base64-repad "Zm9v\r\nYmFy" t)
+                :type 'error)
+  (should (equal "Zm9vYmFy" (gnus-base64-repad "Zm9vYmFy" t)))
+  (should (equal "Zm9vYmFy" (gnus-base64-repad "Zm9v\r\nYmFy" nil)))
+  (should (equal "Zm9vYmFy" (gnus-base64-repad "Zm9v\r\nYmFy\n" nil)))
+  (should-error (gnus-base64-repad "Zm9v\r\n YmFy\r\n" nil)
+                :type 'error)
+  (should-error (gnus-base64-repad "Zm9v\r\nYmFy" nil 3)
+                :type 'error))
+
 ;;; gnustest-gnus-util.el ends here