Add test "prod_jumps_to_buffer_start_and_pushes_too_long_message"

.gitignore

@@ -39,5 +39,6 @@
 /tests/test_main
 /tests/test_cons_pops_buffer_start
 /tests/test_cons_reaches_queue_end
+/tests/test_prod_jumps_to_buffer_start_and_pushes_too_long_message
 /tests/test_prod_jumps_to_buffer_start_and_reaches_cons
 /tests/test_prod_reaches_buffer_end

Makefile.am

@@ -12,6 +12,7 @@ TESTS = \
 	tests/test_main \
 	tests/test_cons_pops_buffer_start \
 	tests/test_cons_reaches_queue_end \
+	tests/test_prod_jumps_to_buffer_start_and_pushes_too_long_message \
 	tests/test_prod_jumps_to_buffer_start_and_reaches_cons \
 	tests/test_prod_reaches_buffer_end
 
@@ -42,6 +43,10 @@ tests_test_cons_reaches_queue_end_SOURCES = \
 	$(libshmemq_a_SOURCES) \
 	tests/test_cons_reaches_queue_end.c
 
+tests_test_prod_jumps_to_buffer_start_and_pushes_too_long_message_SOURCES = \
+	$(libshmemq_a_SOURCES) \
+	tests/test_prod_jumps_to_buffer_start_and_pushes_too_long_message.c
+
 tests_test_prod_jumps_to_buffer_start_and_reaches_cons_SOURCES = \
 	$(libshmemq_a_SOURCES) \
 	tests/test_prod_jumps_to_buffer_start_and_reaches_cons.c

include/shmemq.h

@@ -29,6 +29,7 @@ typedef enum ShmemqError {
     // Bugs in user code.
     SHMEMQ_ERROR_BUG_POP_END_ON_EMPTY_QUEUE = 50,
     SHMEMQ_ERROR_BUG_PUSH_END_ON_FULL_QUEUE = 51,
+    SHMEMQ_ERROR_BUG_PUSH_END_OVERFLOW      = 52,
 
     // Failed system calls.
     SHMEMQ_ERROR_FAILED_MALLOC     = 100,

src/main.c

@@ -217,9 +217,21 @@ void shmemq_push_end(
             header_and_data_size / SHMEMQ_FRAME_SIZE + 1;
     }
 
-    shmemq->buffer->header.write_frame_index =
+    const size_t new_write_frame_index =
         shmemq->buffer->header.write_frame_index +
         frame->header.message_frames_count;
+
+    if (
+        shmemq->buffer->header.write_frame_index <
+        shmemq->buffer->header.read_frame_index &&
+        new_write_frame_index >=
+        shmemq->buffer->header.read_frame_index
+    ) {
+        if (error_ptr) *error_ptr = SHMEMQ_ERROR_BUG_PUSH_END_OVERFLOW;
+        return;
+    }
+
+    shmemq->buffer->header.write_frame_index = new_write_frame_index;
 }
 
 ShmemqFrame shmemq_pop_start(const Shmemq shmemq)

tests/test_prod_jumps_to_buffer_start_and_pushes_too_long_message.c

@@ -0,0 +1,60 @@
+#include <shmemq.h>
+
+#include <assert.h>
+
+static const char name[] = "/foobar";
+
+int main()
+{
+    ShmemqError error;
+
+    const Shmemq consumer = shmemq_new(name, true, &error);
+    assert(error == SHMEMQ_ERROR_NONE);
+
+    const Shmemq producer = shmemq_new(name, false, &error);
+    assert(error == SHMEMQ_ERROR_NONE);
+
+    for (unsigned i = 0; i < 100; ++i) {
+        const ShmemqFrame frame = shmemq_push_start(producer);
+        assert(frame != NULL);
+
+        *(unsigned*)frame->data = i;
+
+        shmemq_push_end(producer, sizeof(unsigned), &error);
+        assert(error == SHMEMQ_ERROR_NONE);
+    }
+
+    for (unsigned i = 0; i < 10; ++i) {
+        const ShmemqFrame frame = shmemq_pop_start(consumer);
+        assert(frame != NULL);
+
+        assert(*(unsigned*)frame->data == i);
+
+        shmemq_pop_end(consumer, &error);
+        assert(error == SHMEMQ_ERROR_NONE);
+    }
+
+    for (unsigned i = 0; i < 8; ++i) {
+        const ShmemqFrame frame = shmemq_push_start(producer);
+        assert(frame != NULL);
+
+        *(unsigned*)frame->data = i;
+
+        shmemq_push_end(producer, sizeof(unsigned), &error);
+        assert(error == SHMEMQ_ERROR_NONE);
+    }
+
+    const ShmemqFrame frame = shmemq_push_start(producer);
+    assert(frame != NULL);
+
+    shmemq_push_end(producer, 9, &error);
+    assert(error == SHMEMQ_ERROR_BUG_PUSH_END_OVERFLOW);
+
+    shmemq_delete(consumer, &error);
+    assert(error == SHMEMQ_ERROR_NONE);
+
+    shmemq_delete(producer, &error);
+    assert(error == SHMEMQ_ERROR_NONE);
+
+    return 0;
+}