Report with different error codes if library will block until buffer is free or if the supplied block is too big to fit into the buffer

fastwriter.c

@@ -241,9 +241,13 @@ static void *fastwriter_writer_thread(void *user) {
 int fastwriter_push(fastwriter_t *ctx, size_t size, const void *data) {
     size_t part1, end;
     size_t free = fastwriter_compute_free_space(ctx);
-
+    
     if (free < size) {
 	ctx->max_usage = ctx->size;
+
+        if (size > ctx->size) {
+            return EOVERFLOW;
+        }
 	
 	if ((ctx->flags&FASTWRITER_FLAGS_BLOCK)==0)
 	    return EWOULDBLOCK;