3 files changed, 73 insertions, 0 deletions
diff --git a/src/common/compat_rust.c b/src/common/compat_rust.c
new file mode 100644
index 0000000000..366fd4037b
--- /dev/null
+++ b/src/common/compat_rust.c
@@ -0,0 +1,39 @@
+/* Copyright (c) 2017, The Tor Project, Inc. */
+/* See LICENSE for licensing information */
+
+/**
+ * \file rust_compat.c
+ * \brief Rust FFI compatibility functions and helpers. This file is only built
+ * if Rust is not used.
+ **/
+
+#include "compat_rust.h"
+#include "util.h"
+
+/**
+ * Free storage pointed to by <b>str</b>, and itself.
+ */
+void
+rust_str_free(rust_str_t str)
+{
+    char *s = (char *)str;
+    tor_free(s);
+}
+
+/**
+ * Return zero-terminated contained string.
+ */
+const char *
+rust_str_get(const rust_str_t str)
+{
+    return (const char *)str;
+}
+
+/* If we were using Rust, we'd say so on startup. */
+rust_str_t
+rust_welcome_string(void)
+{
+    char *s = tor_malloc_zero(1);
+    return (rust_str_t)s;
+}
+
diff --git a/src/common/compat_rust.h b/src/common/compat_rust.h
new file mode 100644
index 0000000000..752a29b56c
--- /dev/null
+++ b/src/common/compat_rust.h
@@ -0,0 +1,28 @@
+/* Copyright (c) 2017, The Tor Project, Inc. */
+/* See LICENSE for licensing information */
+
+/**
+ * \file rust_compat.h
+ * \brief Headers for rust_compat.c
+ **/
+
+#ifndef TOR_RUST_COMPAT_H
+#define TOR_RUST_COMPAT_H
+
+#include "torint.h"
+
+/**
+ * Strings allocated in Rust must be freed from Rust code again. Let's make
+ * it less likely to accidentally mess up and call tor_free() on it, because
+ * currently it'll just work but might break at any time.
+ */
+typedef uintptr_t rust_str_t;
+
+void rust_str_free(rust_str_t);
+
+const char *rust_str_get(const rust_str_t);
+
+rust_str_t rust_welcome_string(void);
+
+#endif
+
diff --git a/src/common/include.am b/src/common/include.am
index e285ef5f86..b37b363b82 100644
--- a/src/common/include.am
+++ b/src/common/include.am
@@ -100,6 +100,11 @@ LIBOR_A_SRC = \
   $(threads_impl_source)				\
   $(readpassphrase_source)
 
+if USE_RUST
+else
+LIBOR_A_SRC += src/common/compat_rust.c
+endif
+
 src/common/src_common_libor_testing_a-log.$(OBJEXT) \
   src/common/log.$(OBJEXT): micro-revision.i
 
@@ -146,6 +151,7 @@ COMMONHEADERS = \
   src/common/compat.h				\
   src/common/compat_libevent.h			\
   src/common/compat_openssl.h			\
+  src/common/compat_rust.h			\
   src/common/compat_threads.h			\
   src/common/compat_time.h			\
   src/common/compress.h			\