Add option --output-cover

opustags.1

@@ -106,6 +106,16 @@ Edit tags interactively by spawning the program specified by the EDITOR
 environment variable. The allowed format is the same as \fB--set-all\fP.
 If TERM and VISUAL are set, VISUAL takes precedence over EDITOR.
 .TP
+.B \-\-output-cover \fIFILE\fP
+Save the cover art of the input file at the specified location.
+If the input file does not contain any cover art, this option has no effect.
+To allow overwriting the target location, specify \fB--overwrite\fP.
+In the case of multiple pictures embedded in the Opus tags, only the first one is saved.
+Note that the since the image format is not fixed, you should consider an extension-less file name
+and rely on the magic number to deduce the type. opustags does not add or check the target file’s
+extension.
+You can specify \fB-\fP for standard output, in which case the regular output will be suppressed.
+.TP
 .B \-\-raw
 OpusTags metadata should always be encoded in UTF-8, as per RFC 7845. However, some files may be
 corrupted or possibly even contain intentional binary data. In that case, --raw lets you edit that

src/cli.cc

@@ -36,6 +36,7 @@ Usage: opustags --help
   -s, --set FIELD=VALUE         replace a comment
   -S, --set-all                 import comments from standard input
   -e, --edit                    edit tags interactively in VISUAL/EDITOR
+  --output-cover FILE           extract and save the cover art, if any
   --raw                         disable encoding conversion
 
 See the man page for extensive documentation.
@@ -52,6 +53,7 @@ static struct option getopt_options[] = {
 	{"delete-all", no_argument, 0, 'D'},
 	{"set-all", no_argument, 0, 'S'},
 	{"edit", no_argument, 0, 'e'},
+	{"output-cover", required_argument, 0, 'c'},
 	{"raw", no_argument, 0, 'r'},
 	{NULL, 0, 0, 0}
 };
@@ -107,6 +109,11 @@ ot::options ot::parse_options(int argc, char** argv, FILE* comments_input)
 		case 'e':
 			opt.edit_interactively = true;
 			break;
+		case 'c':
+			if (opt.cover_out)
+				throw status {st::bad_arguments, "Cannot specify --output-cover more than once."};
+			opt.cover_out = optarg;
+			break;
 		case 'r':
 			opt.raw = true;
 			break;
@@ -160,6 +167,12 @@ ot::options ot::parse_options(int argc, char** argv, FILE* comments_input)
 	if (opt.edit_interactively && (opt.delete_all || !opt.to_add.empty() || !opt.to_delete.empty()))
 		throw status {st::bad_arguments, "Cannot mix --edit with -adDsS."};
 
+	if (opt.cover_out == "-" && opt.path_out == "-")
+		throw status {st::bad_arguments, "Cannot specify standard output for both --output and --output-cover."};
+
+	if (opt.cover_out && opt.paths_in.size() > 1)
+		throw status {st::bad_arguments, "Cannot use --output-cover with multiple input files."};
+
 	if (set_all) {
 		// Read comments from stdin and prepend them to opt.to_add.
 		std::list<std::string> comments = read_comments(comments_input, opt.raw);
@@ -385,6 +398,35 @@ static void edit_tags_interactively(ot::opus_tags& tags, const std::optional<std
 	remove(tags_path.c_str());
 }
 
+static void output_cover(const ot::opus_tags& tags, const ot::options &opt)
+{
+	std::optional<ot::picture> cover = extract_cover(tags);
+	if (!cover) {
+		fputs("warning: no cover found.\n", stderr);
+		return;
+	}
+
+	ot::file output;
+	if (opt.cover_out == "-") {
+		output = stdout;
+	} else {
+		struct stat output_info;
+		if (stat(opt.cover_out->c_str(), &output_info) == 0) {
+			if (S_ISREG(output_info.st_mode) && !opt.overwrite)
+				throw ot::status {ot::st::error, "'" + opt.cover_out.value() + "' already exists. Use -y to overwrite."};
+		} else if (errno != ENOENT) {
+			throw ot::status {ot::st::error, "Could not identify '" + opt.cover_out.value() + "': " + strerror(errno)};
+		}
+
+		output = fopen(opt.cover_out->c_str(), "w");
+		if (output == nullptr)
+			throw ot::status {ot::st::standard_error, "Could not open '" + opt.cover_out.value() + "' for writing: " + strerror(errno)};
+	}
+
+	if (fwrite(cover->picture_data.data(), 1, cover->picture_data.size(), output.get()) < cover->picture_data.size())
+		throw ot::status {ot::st::standard_error, "fwrite error: "s + strerror(errno)};
+}
+
 /**
  * Main loop of opustags. Read the packets from the reader, and forwards them to the writer.
  * Transform the OpusTags packet on the fly.
@@ -420,6 +462,8 @@ static void process(ot::ogg_reader& reader, ot::ogg_writer* writer, const ot::op
 		} else if (reader.absolute_page_no == 1) { // Comment header
 			ot::opus_tags tags;
 			reader.process_header_packet([&tags](ogg_packet& p) { tags = ot::parse_tags(p); });
+			if (opt.cover_out)
+				output_cover(tags, opt);
 			edit_tags(tags, opt);
 			if (writer) {
 				if (opt.edit_interactively) {
@@ -430,7 +474,8 @@ static void process(ot::ogg_reader& reader, ot::ogg_writer* writer, const ot::op
 				writer->write_header_packet(serialno, pageno, packet);
 				pageno_offset = writer->next_page_no - 1 - reader.absolute_page_no;
 			} else {
-				ot::print_comments(tags.comments, stdout, opt.raw);
+				if (opt.cover_out != "-")
+					ot::print_comments(tags.comments, stdout, opt.raw);
 				break;
 			}
 		} else if (writer) {

src/opustags.h

@@ -504,6 +504,14 @@ struct options {
 	 * Options: --add, --set, --set-all
 	 */
 	std::list<std::string> to_add;
+	/**
+	 * If set, the input file’s cover art is exported to the specified file. - for stdout. Does
+	 * not overwrite the file if it already exists unless -y is specified. Does nothing if the
+	 * input file does not contain a cover art.
+	 *
+	 * Option: --output-cover
+	 */
+	std::optional<std::string> cover_out;
 	/**
 	 * Disable encoding conversions. OpusTags are specified to always be encoded as UTF-8, but
 	 * if for some reason a specific file contains binary tags that someone would like to

t/cli.cc

@@ -180,6 +180,12 @@ void check_bad_arguments()
 	error_case({"opustags", "--edit", "x", "-i", "-d", "X"}, "Cannot mix --edit with -adDsS.", "mixing -e and -d");
 	error_case({"opustags", "--edit", "x", "-i", "-D"}, "Cannot mix --edit with -adDsS.", "mixing -e and -D");
 	error_case({"opustags", "--edit", "x", "-i", "-S"}, "Cannot mix --edit with -adDsS.", "mixing -e and -S");
+	error_case({"opustags", "--output-cover", "x", "--output-cover", "y"},
+	           "Cannot specify --output-cover more than once.", "multiple --output-cover");
+	error_case({"opustags", "x", "-o", "-", "--output-cover", "-"},
+	            "Cannot specify standard output for both --output and --output-cover.", "-o and --output-cover conflict");
+	error_case({"opustags", "-i", "x", "y", "--output-cover", "z"},
+	            "Cannot use --output-cover with multiple input files.", "--output-cover with multiple input");
 	error_case({"opustags", "-d", "\xFF", "x"},
 	           "Could not encode argument into UTF-8:",
 	           "-d with binary data");

t/opustags.t

@@ -72,6 +72,7 @@ Options:
   -s, --set FIELD=VALUE         replace a comment
   -S, --set-all                 import comments from standard input
   -e, --edit                    edit tags interactively in VISUAL/EDITOR
+  --output-cover FILE           extract and save the cover art, if any
   --raw                         disable encoding conversion
 
 See the man page for extensive documentation.