2 files changed, 74 insertions, 7 deletions

diff --git a/src/writer.c b/src/writer.c
index a2ba0482..b132dc83 100644
--- a/src/writer.c
+++ b/src/writer.c
@@ -501,11 +501,11 @@ reset_context(SerdWriter* writer, bool graph)
 }
 
 static SerdStatus
-free_context(SerdWriter* writer)
+free_context(const WriteContext* const ctx)
 {
-  serd_node_free(writer->context.graph);
-  serd_node_free(writer->context.subject);
-  serd_node_free(writer->context.predicate);
+  serd_node_free(ctx->graph);
+  serd_node_free(ctx->subject);
+  serd_node_free(ctx->predicate);
   return SERD_SUCCESS;
 }
 
@@ -888,6 +888,10 @@ serd_writer_write_statement(SerdWriter* const        writer,
   if (flags & (SERD_ANON_S_BEGIN | SERD_ANON_O_BEGIN)) {
     WriteContext* ctx =
       (WriteContext*)serd_stack_push(&writer->anon_stack, sizeof(WriteContext));
+    if (!ctx) {
+      return SERD_ERR_OVERFLOW;
+    }
+
     *ctx                     = writer->context;
     WriteContext new_context = {
       serd_node_copy(graph), serd_node_copy(subject), NULL};
@@ -916,7 +920,7 @@ serd_writer_end_anon(SerdWriter* writer, const SerdNode* node)
   }
   --writer->indent;
   write_sep(writer, SEP_ANON_END);
-  free_context(writer);
+  free_context(&writer->context);
   writer->context = *anon_stack_top(writer);
   serd_stack_pop(&writer->anon_stack, sizeof(WriteContext));
   const bool is_subject = serd_node_equals(node, writer->context.subject);
@@ -937,7 +941,7 @@ serd_writer_finish(SerdWriter* writer)
     write_sep(writer, SEP_GRAPH_END);
   }
   serd_byte_sink_flush(&writer->byte_sink);
-  free_context(writer);
+  free_context(&writer->context);
   writer->indent  = 0;
   writer->context = WRITE_CONTEXT_NULL;
   return SERD_SUCCESS;
@@ -958,7 +962,7 @@ serd_writer_new(SerdSyntax      syntax,
   writer->env        = env;
   writer->root_node  = NULL;
   writer->root_uri   = SERD_URI_NULL;
-  writer->anon_stack = serd_stack_new(4 * sizeof(WriteContext));
+  writer->anon_stack = serd_stack_new(SERD_PAGE_SIZE);
   writer->context    = context;
   writer->list_subj  = NULL;
   writer->empty      = true;
@@ -1077,6 +1081,13 @@ serd_writer_free(SerdWriter* writer)
   }
 
   serd_writer_finish(writer);
+
+  // Free any leaked entries in the anonymous context stack
+  while (!serd_stack_is_empty(&writer->anon_stack)) {
+    free_context(anon_stack_top(writer));
+    serd_stack_pop(&writer->anon_stack, sizeof(WriteContext));
+  }
+
   serd_stack_free(&writer->anon_stack);
   free(writer->bprefix);
   serd_byte_sink_free(&writer->byte_sink);
diff --git a/test/test_writer.c b/test/test_writer.c
index 190995b6..19aaf4b3 100644
--- a/test/test_writer.c
+++ b/test/test_writer.c
@@ -19,6 +19,7 @@
 #include "serd/serd.h"
 
 #include <assert.h>
+#include <stdio.h>
 #include <string.h>
 
 static void
@@ -82,11 +83,66 @@ test_write_long_literal(void)
   serd_free(out);
 }
 
+static size_t
+null_sink(const void* const buf,
+          const size_t      size,
+          const size_t      nmemb,
+          void* const       stream)
+{
+  (void)buf;
+  (void)stream;
+
+  return size * nmemb;
+}
+
+static void
+test_writer_stack_overflow(void)
+{
+  SerdEnv*    env    = serd_env_new(SERD_EMPTY_STRING());
+  SerdWriter* writer = serd_writer_new(SERD_TURTLE, 0u, env, null_sink, NULL);
+
+  const SerdSink* sink = serd_writer_sink(writer);
+
+  SerdNode* const s = serd_new_uri(SERD_STRING("http://example.org/s"));
+  SerdNode* const p = serd_new_uri(SERD_STRING("http://example.org/p"));
+
+  SerdNode*  o  = serd_new_blank(SERD_STRING("http://example.org/o"));
+  SerdStatus st = serd_sink_write(sink, SERD_ANON_O_BEGIN, s, p, o, NULL);
+  assert(!st);
+
+  // Repeatedly write nested anonymous objects until the writer stack overflows
+  for (unsigned i = 0u; i < 512u; ++i) {
+    char buf[1024];
+    snprintf(buf, sizeof(buf), "b%u", i);
+
+    SerdNode* next_o = serd_new_blank(SERD_STRING(buf));
+
+    st = serd_sink_write(sink, SERD_ANON_O_BEGIN, o, p, next_o, NULL);
+
+    serd_node_free(o);
+    o = next_o;
+
+    if (st) {
+      assert(st == SERD_ERR_OVERFLOW);
+      break;
+    }
+  }
+
+  assert(st == SERD_ERR_OVERFLOW);
+
+  serd_node_free(o);
+  serd_node_free(p);
+  serd_node_free(s);
+  serd_writer_free(writer);
+  serd_env_free(env);
+}
+
 int
 main(void)
 {
   test_write_bad_prefix();
   test_write_long_literal();
+  test_writer_stack_overflow();
 
   return 0;
 }