Add empty syntax type for suppressing output

6 files changed, 39 insertions, 19 deletions

diff --git a/doc/serdi.1 b/doc/serdi.1
index 77f1bb1a..6e99693a 100644
--- a/doc/serdi.1
+++ b/doc/serdi.1
@@ -60,7 +60,8 @@ This will normalize statement order, at the cost of performance and memory consu
 .TP
 .BR \-o " " \fISYNTAX\fR
 Write output as \fISYNTAX\fR.
-Valid values (case-insensitive): \*(lqturtle\*(rq, \*(lqntriples\*(rq, \*(lqtrig\*(rq, \*(lqnquads\*(rq.
+Valid values (case-insensitive): \*(lqturtle\*(rq, \*(lqntriples\*(rq, \*(lqtrig\*(rq, \*(lqnquads\*(rq, \*(lqempty\*(rq.
+When \*(lqempty\*(rq is given, output is suppressed, so only errors will be printed.
 
 .TP
 .BR \-p " " \fIPREFIX\fR
diff --git a/serd/serd.h b/serd/serd.h
index c48ace10..e76aaa44 100644
--- a/serd/serd.h
+++ b/serd/serd.h
@@ -117,10 +117,11 @@ typedef enum {
 
 /// RDF syntax type
 typedef enum {
-	SERD_TURTLE   = 1,  ///< Terse triples http://www.w3.org/TR/turtle
-	SERD_NTRIPLES = 2,  ///< Line-based triples http://www.w3.org/TR/n-triples/
-	SERD_NQUADS   = 3,  ///< Line-based quads http://www.w3.org/TR/n-quads/
-	SERD_TRIG     = 4   ///< Terse quads http://www.w3.org/TR/trig/
+	SERD_SYNTAX_EMPTY = 0,  ///< Empty syntax (suppress input or output)
+	SERD_TURTLE       = 1,  ///< Terse triples http://www.w3.org/TR/turtle
+	SERD_NTRIPLES     = 2,  ///< Flat triples http://www.w3.org/TR/n-triples/
+	SERD_NQUADS       = 3,  ///< Flat quads http://www.w3.org/TR/n-quads/
+	SERD_TRIG         = 4   ///< Terse quads http://www.w3.org/TR/trig/
 } SerdSyntax;
 
 /// Flags indicating inline abbreviation information for a statement
@@ -473,8 +474,8 @@ serd_byte_sink_free(SerdByteSink* sink);
 /**
    Get a syntax by name
 
-   Case-insensitive, supports "Turtle", "NTriples", "NQuads", and "TriG".  Zero
-   is returned if the name is not recognized.
+   Case-insensitive, supports "Turtle", "NTriples", "NQuads", and "TriG".
+   `SERD_SYNTAX_EMPTY` is returned if the name is not recognized.
 */
 SERD_API
 SerdSyntax
@@ -483,8 +484,8 @@ serd_syntax_by_name(const char* name);
 /**
    Guess a syntax from a filename
 
-   This uses the file extension to guess the syntax of a file.  Zero is
-   returned if the extension is not recognized.
+   This uses the file extension to guess the syntax of a file.
+   `SERD_SYNTAX_EMPTY` is returned if the extension is not recognized.
 */
 SERD_API
 SerdSyntax
diff --git a/src/serdi.c b/src/serdi.c
index 9eaf5eb4..c707f42d 100644
--- a/src/serdi.c
+++ b/src/serdi.c
@@ -27,6 +27,7 @@
 #include <stdbool.h>
 #include <stdio.h>
 #include <stdlib.h>
+#include <string.h>
 
 #define SERDI_ERROR(msg)       fprintf(stderr, "serdi: " msg)
 #define SERDI_ERRORF(fmt, ...) fprintf(stderr, "serdi: " fmt, __VA_ARGS__)
@@ -87,14 +88,15 @@ main(int argc, char** argv)
 	}
 
 	SerdNode*       base          = NULL;
-	SerdSyntax      input_syntax  = (SerdSyntax)0;
-	SerdSyntax      output_syntax = (SerdSyntax)0;
+	SerdSyntax      input_syntax  = SERD_SYNTAX_EMPTY;
+	SerdSyntax      output_syntax = SERD_SYNTAX_EMPTY;
 	SerdReaderFlags reader_flags  = 0;
 	SerdWriterFlags writer_flags  = 0;
 	bool            from_stdin    = false;
 	bool            bulk_read     = true;
 	bool            bulk_write    = false;
 	bool            no_inline     = false;
+	bool            osyntax_set   = false;
 	bool            use_model     = false;
 	bool            quiet         = false;
 	size_t          stack_size    = 4194304;
@@ -158,8 +160,11 @@ main(int argc, char** argv)
 			}
 			stack_size = (size_t)size;
 		} else if (argv[a][1] == 'o') {
+			osyntax_set = true;
 			if (++a == argc) {
 				return missing_arg(argv[0], 'o');
+			} else if (!strcmp(argv[a], "empty")) {
+				output_syntax = SERD_SYNTAX_EMPTY;
 			} else if (!(output_syntax = serd_syntax_by_name(argv[a]))) {
 				return print_usage(argv[0], true);
 			}
@@ -202,7 +207,7 @@ main(int argc, char** argv)
 	}
 
 	const bool input_has_graphs = serd_syntax_has_graphs(input_syntax);
-	if (!output_syntax) {
+	if (!output_syntax && !osyntax_set) {
 		output_syntax = input_has_graphs ? SERD_NQUADS : SERD_NTRIPLES;
 	}
 
diff --git a/src/syntax.c b/src/syntax.c
index 8f091a1d..98fcefbc 100644
--- a/src/syntax.c
+++ b/src/syntax.c
@@ -32,7 +32,7 @@ static const Syntax syntaxes[] = {
 	{"ntriples", ".nt",   SERD_NTRIPLES},
 	{"nquads",   ".nq",   SERD_NQUADS},
 	{"trig",     ".trig", SERD_TRIG},
-	{NULL,       NULL,	  (SerdSyntax)0},
+	{NULL,       NULL,	  SERD_SYNTAX_EMPTY},
 };
 
 SerdSyntax
@@ -43,7 +43,7 @@ serd_syntax_by_name(const char* const name)
 			return s->syntax;
 		}
 	}
-	return (SerdSyntax)0;
+	return SERD_SYNTAX_EMPTY;
 }
 
 SerdSyntax
@@ -52,12 +52,13 @@ serd_guess_syntax(const char* const filename)
 	const char* ext = strrchr(filename, '.');
 	if (ext) {
 		for (const Syntax* s = syntaxes; s->name; ++s) {
-			if (!serd_strncasecmp(s->extension, ext, strlen(ext))) {
+			if (s->extension &&
+			    !serd_strncasecmp(s->extension, ext, strlen(ext))) {
 				return s->syntax;
 			}
 		}
 	}
-	return (SerdSyntax)0;
+	return SERD_SYNTAX_EMPTY;
 }
 
 bool
diff --git a/src/writer.c b/src/writer.c
index cd6b8437..4f41b303 100644
--- a/src/writer.c
+++ b/src/writer.c
@@ -733,6 +733,8 @@ write_curie(SerdWriter* const        writer,
 		if (is_inline_start(writer, field, flags)) {
 			TRY(st, esink(" ;", 2, writer));
 		}
+	case SERD_SYNTAX_EMPTY:
+		break;
 	}
 	return st;
 }
@@ -831,6 +833,10 @@ serd_writer_write_statement(SerdWriter*          writer,
 	assert(!((flags & SERD_ANON_S) && (flags & SERD_LIST_S)));
 	assert(!((flags & SERD_ANON_O) && (flags & SERD_LIST_O)));
 
+	if (writer->syntax == SERD_SYNTAX_EMPTY) {
+		return SERD_SUCCESS;
+	}
+
 	const SerdNode* const subject   = serd_statement_subject(statement);
 	const SerdNode* const predicate = serd_statement_predicate(statement);
 	const SerdNode* const object    = serd_statement_object(statement);
@@ -969,10 +975,9 @@ serd_writer_write_statement(SerdWriter*          writer,
 }
 
 SERD_WARN_UNUSED_RESULT static SerdStatus
-serd_writer_end_anon(SerdWriter*     writer,
-                     const SerdNode* node)
+serd_writer_end_anon(SerdWriter* writer, const SerdNode* node)
 {
-	if (writer->syntax == SERD_NTRIPLES || writer->syntax == SERD_NQUADS) {
+	if (writer->syntax != SERD_TURTLE && writer->syntax != SERD_TRIG) {
 		return SERD_SUCCESS;
 	} else if (serd_stack_is_empty(&writer->anon_stack)) {
 		return SERD_LOG_ERROR(writer->world, SERD_ERR_UNKNOWN,
diff --git a/wscript b/wscript
index cb930677..8b30fea5 100644
--- a/wscript
+++ b/wscript
@@ -672,9 +672,16 @@ def test(tst):
         check([serdi, '-h'])
         check([serdi, '-k', '512', '-s', '<foo> a <#Thingie> .'])
         check([serdi, os.devnull])
+
         with tempfile.TemporaryFile(mode='r') as stdin:
             check([serdi, '-'], stdin=stdin)
 
+        with tempfile.TemporaryFile(mode='w') as stdout:
+            cmd = [serdi, '-o', 'empty', '%s/serd.ttl' % srcdir]
+            check(cmd, stdout=stdout)
+            stdout.seek(0, 2)  # Seek to end
+            check(lambda: stdout.tell() == 0, name='empty output')
+
     with tst.group('BadCommands',
                    expected=1,
                    stderr=autowaf.NONEMPTY) as check: