diff --git a/src/common/util.c b/src/common/util.c
index 597ff2c420..fc996f16c1 100644
--- a/src/common/util.c
+++ b/src/common/util.c
@@ -2595,30 +2595,6 @@ expand_filename(const char *filename)
 #endif /* defined(_WIN32) */
 }
 
-/** Append the string produced by tor_asprintf(<b>pattern</b>, <b>...</b>)
- * to <b>sl</b>. */
-void
-smartlist_add_asprintf(struct smartlist_t *sl, const char *pattern, ...)
-{
-  va_list ap;
-  va_start(ap, pattern);
-  smartlist_add_vasprintf(sl, pattern, ap);
-  va_end(ap);
-}
-
-/** va_list-based backend of smartlist_add_asprintf. */
-void
-smartlist_add_vasprintf(struct smartlist_t *sl, const char *pattern,
-                        va_list args)
-{
-  char *str = NULL;
-
-  tor_vasprintf(&str, pattern, args);
-  tor_assert(str != NULL);
-
-  smartlist_add(sl, str);
-}
-
 /** Return a new list containing the filenames in the directory <b>dirname</b>.
  * Return NULL on error or if <b>dirname</b> is not a directory.
  */
diff --git a/src/common/util.h b/src/common/util.h
index 5833fe567f..de6ba8ece0 100644
--- a/src/common/util.h
+++ b/src/common/util.h
@@ -126,13 +126,6 @@ const char *escaped(const char *string);
 char *tor_escape_str_for_pt_args(const char *string,
                                  const char *chars_to_escape);
 
-struct smartlist_t;
-void smartlist_add_asprintf(struct smartlist_t *sl, const char *pattern, ...)
-  CHECK_PRINTF(2, 3);
-void smartlist_add_vasprintf(struct smartlist_t *sl, const char *pattern,
-                             va_list args)
-  CHECK_PRINTF(2, 0);
-
 /* Time helpers */
 long tv_udiff(const struct timeval *start, const struct timeval *end);
 long tv_mdiff(const struct timeval *start, const struct timeval *end);
@@ -250,6 +243,7 @@ typedef struct sized_chunk_t {
   const char *bytes;
   size_t len;
 } sized_chunk_t;
+struct smartlist_t;
 int write_chunks_to_file(const char *fname, const struct smartlist_t *chunks,
                          int bin, int no_tempfile);
 int append_bytes_to_file(const char *fname, const char *str, size_t len,
diff --git a/src/lib/container/smartlist.c b/src/lib/container/smartlist.c
index 3a0a2d1068..57b88415a3 100644
--- a/src/lib/container/smartlist.c
+++ b/src/lib/container/smartlist.c
@@ -18,6 +18,7 @@
 #include "lib/defs/digest_sizes.h"
 #include "lib/ctime/di_ops.h"
 #include "lib/string/util_string.h"
+#include "lib/string/printf.h"
 
 #include <stdlib.h>
 #include <string.h>
@@ -124,6 +125,30 @@ smartlist_add_strdup(struct smartlist_t *sl, const char *string)
   smartlist_add(sl, copy);
 }
 
+/** Append the string produced by tor_asprintf(<b>pattern</b>, <b>...</b>)
+ * to <b>sl</b>. */
+void
+smartlist_add_asprintf(struct smartlist_t *sl, const char *pattern, ...)
+{
+  va_list ap;
+  va_start(ap, pattern);
+  smartlist_add_vasprintf(sl, pattern, ap);
+  va_end(ap);
+}
+
+/** va_list-based backend of smartlist_add_asprintf. */
+void
+smartlist_add_vasprintf(struct smartlist_t *sl, const char *pattern,
+                        va_list args)
+{
+  char *str = NULL;
+
+  tor_vasprintf(&str, pattern, args);
+  tor_assert(str != NULL);
+
+  smartlist_add(sl, str);
+}
+
 /** Remove all elements E from sl such that E==element.  Preserve
  * the order of any elements before E, but elements after E can be
  * rearranged.
diff --git a/src/lib/container/smartlist.h b/src/lib/container/smartlist.h
index 7b80a9fed3..53a4948cf6 100644
--- a/src/lib/container/smartlist.h
+++ b/src/lib/container/smartlist.h
@@ -37,6 +37,11 @@ void smartlist_clear(smartlist_t *sl);
 void smartlist_add(smartlist_t *sl, void *element);
 void smartlist_add_all(smartlist_t *sl, const smartlist_t *s2);
 void smartlist_add_strdup(struct smartlist_t *sl, const char *string);
+void smartlist_add_asprintf(struct smartlist_t *sl, const char *pattern, ...)
+  CHECK_PRINTF(2, 3);
+void smartlist_add_vasprintf(struct smartlist_t *sl, const char *pattern,
+                             va_list args)
+  CHECK_PRINTF(2, 0);
 void smartlist_remove(smartlist_t *sl, const void *element);
 void smartlist_remove_keeporder(smartlist_t *sl, const void *element);
 void *smartlist_pop_last(smartlist_t *sl);
diff --git a/src/rust/build.rs b/src/rust/build.rs
index a4f38d3b46..5c80265e55 100644
--- a/src/rust/build.rs
+++ b/src/rust/build.rs
@@ -152,6 +152,7 @@ pub fn main() {
             cfg.component("tor-crypt-ops-testing");
             cfg.component("or-testing");
             cfg.component("tor-container-testing");
+            cfg.component("tor-string-testing");
             cfg.component("tor-malloc");
             cfg.component("tor-err-testing");
             cfg.component("or-event-testing");