Add empty syntax type for suppressing output

3 files changed, 20 insertions, 9 deletions

diff --git a/src/serdi.c b/src/serdi.c
index 72b7afe1..e546f463 100644
--- a/src/serdi.c
+++ b/src/serdi.c
@@ -31,6 +31,7 @@
 #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__)
@@ -95,14 +96,15 @@ main(int argc, char** argv)
     return print_usage(argv[0], true);
   }
 
-  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_string   = false;
   bool            from_stdin    = false;
   bool            bulk_read     = true;
   bool            bulk_write    = false;
+  bool            osyntax_set   = false;
   bool            quiet         = false;
   size_t          stack_size    = 4194304;
   const char*     add_prefix    = NULL;
@@ -158,11 +160,14 @@ 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');
       }
 
-      if (!(output_syntax = serd_syntax_by_name(argv[a]))) {
+      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);
       }
     } else if (argv[a][1] == 'p') {
@@ -206,7 +211,7 @@ 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 61814709..59453bca 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 +52,12 @@ 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 71766d9d..afeee33d 100644
--- a/src/writer.c
+++ b/src/writer.c
@@ -843,6 +843,8 @@ write_curie(SerdWriter* const        writer,
     if (is_inline_start(writer, field, flags)) {
       TRY(st, esink(" ;", 2, writer));
     }
+  case SERD_SYNTAX_EMPTY:
+    break;
   }
   return st;
 }
@@ -946,6 +948,10 @@ 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;
+  }
+
   SerdStatus            st        = SERD_SUCCESS;
   const SerdNode* const subject   = serd_statement_subject(statement);
   const SerdNode* const predicate = serd_statement_predicate(statement);
@@ -1093,7 +1099,7 @@ serd_writer_write_statement(SerdWriter*          writer,
 SERD_WARN_UNUSED_RESULT static SerdStatus
 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;
   }