diff options
| -rw-r--r-- | lisp/image/exif.el | 138 |
1 files changed, 100 insertions, 38 deletions
diff --git a/lisp/image/exif.el b/lisp/image/exif.el index 2ceafd5bfc0..46f4d5c1ee0 100644 --- a/lisp/image/exif.el +++ b/lisp/image/exif.el @@ -51,7 +51,7 @@ ;; in the directory, and then that number of entries follows, and then ;; an offset to the next IFD. -;; Usage: (exif-parse "test.jpg") => +;; Usage: (exif-parse-file "test.jpg") => ;; ((:tag 274 :tag-name orientation :format 3 :format-type short :value 1) ;; (:tag 282 :tag-name x-resolution :format 5 :format-type rational :value ;; (180 . 1)) @@ -75,25 +75,70 @@ (306 date-time)) "Alist of tag values and their names.") -(defun exif-parse (file) +(defconst exif--orientation + '((1 0 nil) + (2 0 t) + (3 180 nil) + (4 180 t) + (5 90 nil) + (6 90 t) + (7 270 nil) + (8 270 t)) + "Alist of Exif orientation codes. +These are mapped onto rotation values and whether the image is +mirrored or not.") + +(define-error 'exif-error "Invalid Exif data") + +(defun exif-parse-file (file) "Parse FILE (a JPEG file) and return the Exif data, if any. -The return value is a list of Exif items." - (when-let ((app1 (cdr (assq #xffe1 (exif--parse-jpeg file))))) - (exif--parse-exif-chunk app1))) +The return value is a list of Exif items. -(defun exif--parse-jpeg (file) +If the data is invalid, an `exif-error' is signalled." (with-temp-buffer (set-buffer-multibyte nil) (insert-file-contents-literally file) - (unless (= (exif--read-number-be 2) #xffd8) ; SOI (start of image) - (error "Not a valid JPEG file")) - (cl-loop for segment = (exif--read-number-be 2) - for size = (exif--read-number-be 2) - ;; Stop parsing when we get to SOS (start of stream); - ;; this is when the image itself starts, and there will - ;; be no more chunks of interest after that. - while (not (= segment #xffda)) - collect (cons segment (exif--read-chunk (- size 2)))))) + (exif-parse-buffer))) + +(defun exif-parse-buffer (&optional buffer) + "Parse BUFFER (which should be a JPEG file) and return the Exif data, if any. +The return value is a list of Exif items. + +If the data is invalid, an `exif-error' is signalled." + (setq buffer (or buffer (current-buffer))) + (with-current-buffer buffer + (if enable-multibyte-characters + (with-temp-buffer + (set-buffer-multibyte nil) + (let ((dest (current-buffer))) + (with-current-buffer buffer + (encode-coding-region (point-min) (point-max) + buffer-file-coding-system + dest)) + (when-let ((app1 (cdr (assq #xffe1 (exif--parse-jpeg))))) + (exif--parse-exif-chunk app1)))) + (when-let ((app1 (cdr (assq #xffe1 (exif--parse-jpeg))))) + (exif--parse-exif-chunk app1))))) + +(defun exif-orientation (exif) + "Return the orientation (in degrees) in EXIF. +If the orientation isn't present in the data, return nil." + (let ((code (plist-get (cl-find 'orientation exif + :key (lambda (e) + (plist-get e :tag-name))) + :value))) + (cadr (assq code exif--orientation)))) + +(defun exif--parse-jpeg () + (unless (= (exif--read-number-be 2) #xffd8) ; SOI (start of image) + (signal 'exif-error "Not a valid JPEG file")) + (cl-loop for segment = (exif--read-number-be 2) + for size = (exif--read-number-be 2) + ;; Stop parsing when we get to SOS (start of stream); + ;; this is when the image itself starts, and there will + ;; be no more chunks of interest after that. + while (not (= segment #xffda)) + collect (cons segment (exif--read-chunk (- size 2))))) (defun exif--parse-exif-chunk (data) (with-temp-buffer @@ -103,7 +148,7 @@ The return value is a list of Exif items." ;; The Exif data is in the APP1 JPEG chunk and starts with ;; "Exif\0\0". (unless (equal (exif--read-chunk 6) (string ?E ?x ?i ?f ?\0 ?\0)) - (error "Not a valid Exif chunk")) + (signal 'exif-error "Not a valid Exif chunk")) (delete-region (point-min) (point)) (let* ((endian-marker (exif--read-chunk 2)) (le (cond @@ -114,12 +159,15 @@ The return value is a list of Exif items." ((equal endian-marker "II") t) (t - (error "Invalid endian-ness %s" endian-marker))))) + (signal 'exif-error + (format "Invalid endian-ness %s" endian-marker)))))) ;; Another magical number. (unless (= (exif--read-number 2 le) #x002a) - (error "Invalid TIFF header length")) + (signal 'exif-error "Invalid TIFF header length")) (let ((offset (exif--read-number 2 le))) ;; Jump to where the IFD (directory) starts and parse it. + (when (> (1+ offset) (point-max)) + (signal 'exif-error "Invalid IFD (directory) offset")) (goto-char (1+ offset)) (exif--parse-directory le))))) @@ -145,31 +193,39 @@ The return value is a list of Exif items." for length = (* (exif--read-number 4 le) (cdr field-format)) for value = (exif--read-number 4 le) - collect (list :tag tag - :tag-name (cadr (assq tag exif-tag-alist)) - :format format - :format-type (car field-format) - :value (exif--process-value - (if (> length 4) - ;; If the length of the data - ;; is more than 4 bytes, then - ;; it's actually stored after - ;; this directory, and the - ;; value here is just the - ;; offset to use to find the - ;; data. - (buffer-substring - (1+ value) (+ (1+ value) length)) - ;; The value is stored - ;; directly in the directory. - value) - (car field-format) - le))))) + collect (list + :tag tag + :tag-name (cadr (assq tag exif-tag-alist)) + :format format + :format-type (car field-format) + :value (exif--process-value + (if (> length 4) + ;; If the length of the data is + ;; more than 4 bytes, then it's + ;; actually stored after this + ;; directory, and the value + ;; here is just the offset to + ;; use to find the data. + (progn + (when (> (+ (1+ value) length) + (point-max)) + (signal 'exif-error + "Premature end of file")) + (buffer-substring + (1+ value) + (+ (1+ value) length))) + ;; The value is stored directly + ;; in the directory. + value) + (car field-format) + le))))) (let ((next (exif--read-number 4 le))) (if (> next 0) ;; There's more than one directory; if so, jump to it and ;; keep parsing. (progn + (when (> (1+ next) (point-max)) + (signal 'exif-error "Invalid IFD (directory) next-offset")) (goto-char (1+ next)) (nconc dir (exif--parse-directory le))) ;; We've reached the end of the directories. @@ -190,6 +246,8 @@ The return value is a list of Exif items." (defun exif--read-chunk (bytes) "Return BYTES octets from the buffer and advance point that much." + (when (> (+ (point) bytes) (point-max)) + (signal 'exif-error "Premature end of file")) (prog1 (buffer-substring (point) (+ (point) bytes)) (forward-char bytes))) @@ -197,6 +255,8 @@ The return value is a list of Exif items." (defun exif--read-number-be (bytes) "Read BYTES octets from the buffer as a chunk of big-endian bytes. Advance point to after the read bytes." + (when (> (+ (point) bytes) (point-max)) + (signal 'exif-error "Premature end of file")) (let ((sum 0)) (dotimes (_ bytes) (setq sum (+ (* sum 256) (following-char))) @@ -206,6 +266,8 @@ Advance point to after the read bytes." (defun exif--read-number-le (bytes) "Read BYTES octets from the buffer as a chunk of low-endian bytes. Advance point to after the read bytes." + (when (> (+ (point) bytes) (point-max)) + (signal 'exif-error "Premature end of file")) (let ((sum 0)) (dotimes (i bytes) (setq sum (+ (* (following-char) (expt 256 i)) sum)) |