Feature: Added -d/--rm to vorbiscomment to allow removal of tags

This commit adds -d/--rm to vorbiscomment. The new option allows
removal of tags from the processed files. It allows both removal
of specific tags or all tags with a given namen. It also implies
--append (which should maybe be renamed to --update).

Manpage has been updated.
Signed-off-by: Ralph Giles <giles@thaumas.net>

vorbiscomment/vcomment.c

@@ -3,6 +3,7 @@
  *
  * (c) 2000-2002 Michael Smith <msmith@xiph.org>
  * (c) 2001 Ralph Giles <giles@xiph.org>
+ * (c) 2017 Philipp Schafft <phschafft@de.loewenfelsen.net>
  *
  * Front end to show how to use vcedit;
  * Of limited usability on its own, but could be useful.
@@ -35,6 +36,7 @@ struct option long_options[] = {
 	{"list",0,0,'l'},
 	{"append",0,0,'a'},
 	{"tag",required_argument,0,'t'},
+	{"rm",required_argument,0,'d'},
 	{"write",0,0,'w'},
 	{"help",0,0,'h'},
 	{"quiet",0,0,'q'}, /* unused */
@@ -61,6 +63,7 @@ typedef struct {
 	/* comments */
 	int	commentcount;
 	char	**comments;
+	int 	*changetypes;
 } param_t;
 
 #define MODE_NONE  0
@@ -68,10 +71,13 @@ typedef struct {
 #define MODE_WRITE 2
 #define MODE_APPEND 3
 
+#define CHANGETYPE_ADD 0
+#define CHANGETYPE_REMOVE 1
+
 /* prototypes */
 void usage(void);
 void print_comments(FILE *out, vorbis_comment *vc, int raw, int escapes);
-int  add_comment(char *line, vorbis_comment *vc, int raw, int escapes);
+int  alter_comment(char *line, vorbis_comment *vc, int raw, int escapes, int changetype);
 
 char *escape(const char *from, int fromsize);
 char *unescape(const char *from, int *tosize);
@@ -82,6 +88,8 @@ void parse_options(int argc, char *argv[], param_t *param);
 void open_files(param_t *p);
 void close_files(param_t *p, int output_written);
 
+static void _vorbis_comment_rm_tag(vorbis_comment *vc, const char *tag, const char *contents);
+
 char *
 read_line (FILE *input)
 {
@@ -153,6 +161,63 @@ read_line (FILE *input)
         return buffer;
 }
 
+/**********
+
+   Delete a comment from the comment list.
+
+   This deletes a comment from the list.
+   We implement this here as libvorbis does not provide it.
+   Also this is very inefficent as we need to copy the compelet structure.
+   But it is only called once for each file and each deleted key so that is
+   not much of a problem.
+
+***********/
+
+static void _vorbis_comment_rm_tag(vorbis_comment *vc, const char *tag, const char *contents)
+{
+	vorbis_comment vc_tmp;
+	size_t taglen;
+	int i;
+	const char *p;
+	int match;
+
+	taglen = strlen(tag);
+
+	vorbis_comment_init(&vc_tmp);
+
+	for (i = 0; i < vc->comments; i++)
+	{
+		p = vc->user_comments[i];
+		match = 0;
+
+		do {
+			if (strncasecmp(p, tag, taglen) != 0) {
+				break;
+			}
+			p += taglen;
+			if (*p != '=') {
+				break;
+			}
+			p++;
+			if (contents) {
+				if (strcmp(p, contents) != 0) {
+					break;
+				}
+			}
+
+			match = 1;
+		} while (0);
+
+		if (!match) {
+			vorbis_comment_add(&vc_tmp, vc->user_comments[i]);
+		}
+	}
+
+	vorbis_comment_clear(vc);
+
+	*vc = vc_tmp;
+}
+
 /**********
    main.c
 
@@ -236,8 +301,8 @@ int main(int argc, char **argv)
 
 		for(i=0; i < param->commentcount; i++)
 		{
-			if (add_comment(param->comments[i], vc,
-					param->raw, param->escapes) < 0)
+			if (alter_comment(param->comments[i], vc,
+					param->raw, param->escapes, param->changetypes[i]) < 0)
 				fprintf(stderr, _("Bad comment: \"%s\"\n"), param->comments[i]);
 		}
 
@@ -248,7 +313,7 @@ int main(int argc, char **argv)
 
 			while ((comment = read_line (param->com)))
                         {
-                                if (add_comment(comment, vc, param->raw, param->escapes) < 0)
+                                if (alter_comment(comment, vc, param->raw, param->escapes, CHANGETYPE_ADD) < 0)
                                 {
                                         fprintf (stderr, _("bad comment: \"%s\"\n"),
                                                  comment);
@@ -319,7 +384,7 @@ void print_comments(FILE *out, vorbis_comment *vc, int raw, int escapes)
 /**********
 
    Take a line of the form "TAG=value string", parse it, convert the
-   value to UTF-8, and add it to the
+   value to UTF-8, and add or remove it from vc comment block.
    Error checking is performed (return 0 if OK, negative on error).
 
    Note that this assumes a null-terminated string, which may cause
@@ -327,10 +392,21 @@ void print_comments(FILE *out, vorbis_comment *vc, int raw, int escapes)
 
 ***********/
 
-int  add_comment(char *line, vorbis_comment *vc, int raw, int escapes)
+int  alter_comment(char *line, vorbis_comment *vc, int raw, int escapes, int changetype)
 {
 	char *mark, *value, *utf8_value, *unescaped_value;
 	int unescaped_len;
+	int allow_empty = 0;
+	int is_empty = 0;
+
+	if (changetype != CHANGETYPE_ADD &&
+	    changetype != CHANGETYPE_REMOVE) {
+		return -1;
+	}
+
+	if (changetype == CHANGETYPE_REMOVE) {
+		allow_empty = 1;
+	}
 
 	/* strip any terminal newline */
 	{
@@ -339,12 +415,19 @@ int  add_comment(char *line, vorbis_comment *vc, int raw, int escapes)
 	}
 
 	/* validation: basically, we assume it's a tag
-	 * if it has an '=' after one or more valid characters,
-	 * as the comment spec requires. For the moment, we
-	 * also restrict ourselves to 0-terminated values */
+	 * if if has an '=' after valid tag characters,
+	 * or if it just contains valid tag characters
+	 * and we're allowing empty values. */
 
 	mark = strchr(line, '=');
-	if (mark == NULL) return -1;
+	if (mark == NULL) {
+		if (allow_empty) {
+			mark = line + strlen(line);
+			is_empty = 1;
+		} else {
+			return -1;
+		}
+	}
 
 	value = line;
 	while (value < mark) {
@@ -352,6 +435,9 @@ int  add_comment(char *line, vorbis_comment *vc, int raw, int escapes)
 		value++;
 	}
 
+	if (is_empty) {
+		unescaped_value = NULL;
+	} else {
 		/* split the line by turning the '=' in to a null */
 		*mark = '\0';
 		value++;
@@ -389,12 +475,21 @@ int  add_comment(char *line, vorbis_comment *vc, int raw, int escapes)
 		} else {
 			unescaped_value = utf8_value;
 		}
+	}
 
-	/* append the comment and return */
+	/* append or delete the comment and return */
+	switch (changetype) {
+	case CHANGETYPE_ADD:
 		vorbis_comment_add_tag(vc, line, unescaped_value);
+		break;
+	case CHANGETYPE_REMOVE:
+		_vorbis_comment_rm_tag(vc, line, unescaped_value);
+		break;
+	}
+
 	if (escapes)
 		free(unescaped_value);
-	if (!raw)
+	if (!raw && !is_empty)
 		free(utf8_value);
 	return 0;
 }
@@ -540,9 +635,13 @@ void usage(void)
   printf ("\n");
 
   printf (_("Editing options\n"));
-  printf (_("  -a, --append            Append comments\n"));
+  printf (_("  -a, --append            Update comments\n"));
   printf (_("  -t \"name=value\", --tag \"name=value\"\n"
             "                          Specify a comment tag on the commandline\n"));
+  printf (_("  -d \"name[=value]\", --rm \"name[=value]\"\n"
+            "                          Specify a comment tag on the commandline to remove\n"
+            "                          If no value is given all tags with that name are removed\n"
+            "                          This implies -a,\n"));
   printf (_("  -w, --write             Write comments, replacing the existing ones\n"));
   printf ("\n");
 
@@ -616,6 +715,7 @@ param_t *new_param(void)
 	/* comments */
 	param->commentcount=0;
 	param->comments=NULL;
+	param->changetypes=NULL;
 
 	return param;
 }
@@ -636,7 +736,7 @@ void parse_options(int argc, char *argv[], param_t *param)
 
 	setlocale(LC_ALL, "");
 
-	while ((ret = getopt_long(argc, argv, "alwhqVc:t:Re",
+	while ((ret = getopt_long(argc, argv, "alwhqVc:t:d:Re",
 			long_options, &option_index)) != -1) {
 		switch (ret) {
 			case 0:
@@ -675,7 +775,21 @@ void parse_options(int argc, char *argv[], param_t *param)
 			case 't':
 				param->comments = realloc(param->comments, 
 						(param->commentcount+1)*sizeof(char *));
-				param->comments[param->commentcount++] = strdup(optarg);
+				param->changetypes = realloc(param->changetypes,
+						(param->commentcount+1)*sizeof(int));
+				param->comments[param->commentcount] = strdup(optarg);
+				param->changetypes[param->commentcount] = CHANGETYPE_ADD;
+				param->commentcount++;
+				break;
+			case 'd':
+				param->comments = realloc(param->comments, 
+						(param->commentcount+1)*sizeof(char *));
+				param->changetypes = realloc(param->changetypes,
+						(param->commentcount+1)*sizeof(int));
+				param->comments[param->commentcount] = strdup(optarg);
+				param->changetypes[param->commentcount] = CHANGETYPE_REMOVE;
+				param->commentcount++;
+				param->mode = MODE_APPEND;
 				break;
 			default:
 				usage();

vorbiscomment/vorbiscomment.1

@@ -15,7 +15,7 @@ vorbiscomment \- List or edit comments in Ogg Vorbis files
 .br
 .B vorbiscomment
 .B -a
-.B [ -c commentfile | -t \*(lqname=value\*(rq ]
+.B [ -c commentfile | -t \*(lqname=value\*(rq | -d \*(lqname=value\*(rq ]
 .RB [ -q ]
 .RB [ -R ]
 .RB [ -e ]
@@ -37,7 +37,7 @@ Reads, modifies, and appends Ogg Vorbis audio file metadata tags.
 
 .SH OPTIONS
 .IP "-a, --append"
-Append comments.
+Updates comments.
 .IP "-c file, --commentfile file"
 Take comments from a file. The file is the same format as is output by the the -l option or given to the -t option: one element per line in 'tag=value' format. If the file is /dev/null and -w was passed, the existing comments will be removed.
 .IP "-h, --help"
@@ -48,6 +48,8 @@ List the comments in the Ogg Vorbis file.
 Quiet mode.  No messages are displayed.
 .IP "-t 'name=value', --tag 'name=value'"
 Specify a new tag on the command line. Each tag is given as a single string. The part before the '=' is treated as the tag name and the part after as the value.
+.IP "-d 'name[=value]', --rm 'name[=value]'"
+Specify a tag on the command line for removal. Each tag is given as a single string. The part before the '=' is treated as the tag name and the part after as the value. If no value is given all tags are deleted with the given name. Otherwise only those with matching values are deleted.
 .IP "-w, --write"
 Replace comments with the new set given either on the command line with -t or from a file with -c. If neither -c nor -t is given, the new set will be read from the standard input.
 .IP "-R, --raw"