Refuse to write incoherent statements

4 files changed, 87 insertions, 20 deletions

diff --git a/NEWS b/NEWS
index 3b923a9e..12d5b583 100644
--- a/NEWS
+++ b/NEWS
@@ -2,9 +2,10 @@ serd (0.32.5) unstable; urgency=medium
 
   * Fix handling of some invalid EOF cases in lax mode
   * Fix invalid characters in error messages
+  * Refuse to write incoherent statements
   * Remove project and version number from man page OS field
 
- -- David Robillard <d@drobilla.net>  Thu, 30 Jan 2025 20:28:00 +0000
+ -- David Robillard <d@drobilla.net>  Tue, 25 Feb 2025 14:22:43 +0000
 
 serd (0.32.4) stable; urgency=medium
 
diff --git a/src/writer.c b/src/writer.c
index f0a9ad16..ab237099 100644
--- a/src/writer.c
+++ b/src/writer.c
@@ -1,4 +1,4 @@
-// Copyright 2011-2023 David Robillard <d@drobilla.net>
+// Copyright 2011-2025 David Robillard <d@drobilla.net>
 // SPDX-License-Identifier: ISC
 
 #include "attributes.h"
@@ -926,10 +926,6 @@ serd_writer_write_statement(SerdWriter* const     writer,
 
   SerdStatus st = SERD_SUCCESS;
 
-  if (!is_resource(subject) || !is_resource(predicate) || !object->buf) {
-    return SERD_ERR_BAD_ARG;
-  }
-
   if ((flags & SERD_LIST_O_BEGIN) &&
       !strcmp((const char*)object->buf, NS_RDF "nil")) {
     /* Tolerate LIST_O_BEGIN for "()" objects, even though it doesn't make
@@ -938,6 +934,17 @@ serd_writer_write_statement(SerdWriter* const     writer,
     flags &= (SerdStatementFlags)~SERD_LIST_O_BEGIN;
   }
 
+  // Refuse to write incoherent statements
+  if (!is_resource(subject) || !is_resource(predicate) ||
+      object->type == SERD_NOTHING || !object->buf ||
+      (datatype && datatype->buf && lang && lang->buf) ||
+      ((flags & SERD_ANON_S_BEGIN) && (flags & SERD_LIST_S_BEGIN)) ||
+      ((flags & SERD_EMPTY_S) && (flags & SERD_LIST_S_BEGIN)) ||
+      ((flags & SERD_ANON_O_BEGIN) && (flags & SERD_LIST_O_BEGIN)) ||
+      ((flags & SERD_EMPTY_O) && (flags & SERD_LIST_O_BEGIN))) {
+    return SERD_ERR_BAD_ARG;
+  }
+
   // Simple case: write a line of NTriples or NQuads
   if (writer->syntax == SERD_NTRIPLES || writer->syntax == SERD_NQUADS) {
     TRY(st, write_node(writer, subject, NULL, NULL, FIELD_SUBJECT, flags));
diff --git a/test/test_reader_writer.c b/test/test_reader_writer.c
index 61874bc7..829caff5 100644
--- a/test/test_reader_writer.c
+++ b/test/test_reader_writer.c
@@ -168,15 +168,19 @@ test_writer(const char* const path)
 
   const uint8_t buf[] = {0x80, 0, 0, 0, 0};
 
-  SerdNode s = serd_node_from_string(SERD_URI, USTR(""));
-  SerdNode p = serd_node_from_string(SERD_URI, USTR("http://example.org/pred"));
-  SerdNode o = serd_node_from_string(SERD_LITERAL, buf);
+  const SerdNode s = serd_node_from_string(SERD_URI, USTR(""));
+  const SerdNode p =
+    serd_node_from_string(SERD_URI, USTR("http://example.org/pred"));
+  const SerdNode o = serd_node_from_string(SERD_LITERAL, buf);
+  const SerdNode t = serd_node_from_string(SERD_URI, USTR("urn:Type"));
+  const SerdNode l = serd_node_from_string(SERD_LITERAL, USTR("en"));
 
   // Attempt to write invalid statements (should write nothing)
   const SerdNode* junk[][5] = {{&s, &p, &SERD_NODE_NULL, NULL, NULL},
                                {&s, &SERD_NODE_NULL, &o, NULL, NULL},
                                {&SERD_NODE_NULL, &p, &o, NULL, NULL},
                                {&s, &o, &o, NULL, NULL},
+                               {&s, &o, &o, &t, &l},
                                {&o, &p, &o, NULL, NULL},
                                {&s, &p, &SERD_NODE_NULL, NULL, NULL}};
   for (size_t i = 0; i < sizeof(junk) / (sizeof(SerdNode*) * 5); ++i) {
@@ -191,14 +195,11 @@ test_writer(const char* const path)
   }
 
   // Write some valid statements
-  const SerdNode  t         = serd_node_from_string(SERD_URI, USTR("urn:Type"));
-  const SerdNode  l         = serd_node_from_string(SERD_LITERAL, USTR("en"));
   const SerdNode* good[][5] = {{&s, &p, &o, NULL, NULL},
                                {&s, &p, &lit, NULL, NULL},
                                {&s, &p, &o, &SERD_NODE_NULL, &SERD_NODE_NULL},
                                {&s, &p, &o, &t, NULL},
                                {&s, &p, &o, NULL, &l},
-                               {&s, &p, &o, &t, &l},
                                {&s, &p, &o, &t, &SERD_NODE_NULL},
                                {&s, &p, &o, &SERD_NODE_NULL, &l},
                                {&s, &p, &o, NULL, &SERD_NODE_NULL},
@@ -260,7 +261,7 @@ test_reader(const char* const path)
 
   const SerdStatus st = serd_reader_read_file(reader, USTR(path));
   assert(!st);
-  assert(rt->n_statement == 13);
+  assert(rt->n_statement == 12);
   assert(rt->graph && rt->graph->buf &&
          !strcmp((const char*)rt->graph->buf, "http://example.org/"));
 
diff --git a/test/test_writer.c b/test/test_writer.c
index 27ce6138..7f8d2f94 100644
--- a/test/test_writer.c
+++ b/test/test_writer.c
@@ -309,17 +309,74 @@ test_write_nothing_node(void)
   SerdNode s = serd_node_from_string(SERD_URI, USTR(""));
   SerdNode p = serd_node_from_string(SERD_URI, USTR("http://example.org/pred"));
   SerdNode o = serd_node_from_string(SERD_NOTHING, USTR(""));
-  assert(!serd_writer_write_statement(writer, 0, NULL, &s, &p, &o, NULL, NULL));
-
-  assert(
-    !strncmp((const char*)chunk.buf, "<>\n\t<http://example.org/pred> ", 30));
+  assert(serd_writer_write_statement(writer, 0, NULL, &s, &p, &o, NULL, NULL) ==
+         SERD_ERR_BAD_ARG);
 
+  assert(!chunk.buf);
   serd_writer_free(writer);
+  serd_env_free(env);
+}
 
-  uint8_t* const out = serd_chunk_sink_finish(&chunk);
-  assert(!strcmp((const char*)out, "<>\n\t<http://example.org/pred>  .\n"));
-  serd_free(out);
+static void
+test_write_bad_statement(void)
+{
+  SerdEnv* const env = serd_env_new(NULL);
+  assert(env);
 
+  SerdChunk         chunk  = {NULL, 0};
+  SerdWriter* const writer = serd_writer_new(
+    SERD_TURTLE, (SerdStyle)0, env, NULL, serd_chunk_sink, &chunk);
+  assert(writer);
+
+  SerdNode s = serd_node_from_string(SERD_URI, USTR("http://example.org/s"));
+  SerdNode p = serd_node_from_string(SERD_URI, USTR("http://example.org/p"));
+  SerdNode o = serd_node_from_string(SERD_URI, USTR("http://example.org/o"));
+  SerdNode l = serd_node_from_string(SERD_LITERAL, USTR("lang"));
+
+  assert(serd_writer_write_statement(
+           writer,
+           (SerdStatementFlags)(SERD_ANON_S_BEGIN | SERD_LIST_S_BEGIN),
+           NULL,
+           &s,
+           &p,
+           &o,
+           NULL,
+           NULL) == SERD_ERR_BAD_ARG);
+
+  assert(serd_writer_write_statement(
+           writer,
+           (SerdStatementFlags)(SERD_EMPTY_S | SERD_LIST_S_BEGIN),
+           NULL,
+           &s,
+           &p,
+           &o,
+           NULL,
+           NULL) == SERD_ERR_BAD_ARG);
+
+  assert(serd_writer_write_statement(
+           writer,
+           (SerdStatementFlags)(SERD_ANON_O_BEGIN | SERD_LIST_O_BEGIN),
+           NULL,
+           &s,
+           &p,
+           &o,
+           NULL,
+           NULL) == SERD_ERR_BAD_ARG);
+
+  assert(serd_writer_write_statement(
+           writer,
+           (SerdStatementFlags)(SERD_EMPTY_O | SERD_LIST_O_BEGIN),
+           NULL,
+           &s,
+           &p,
+           &o,
+           NULL,
+           NULL) == SERD_ERR_BAD_ARG);
+
+  assert(serd_writer_write_statement(writer, 0U, NULL, &s, &p, &o, &o, &l) ==
+         SERD_ERR_BAD_ARG);
+
+  serd_writer_free(writer);
   serd_env_free(env);
 }
 
@@ -334,6 +391,7 @@ main(void)
   test_write_error();
   test_chunk_sink();
   test_write_nothing_node();
+  test_write_bad_statement();
 
   return 0;
 }