hs: Learn service version by trying to load the keys

In order to switch the default HS version from 2 to 3, we need tor to be smart
and be able to decide on the version by trying to load the service keys during
configuration validation.

Part of #27215

Signed-off-by: David Goulet <dgoulet@torproject.org>

2 files changed, 24 insertions, 0 deletions

diff --git a/src/feature/rend/rendservice.c b/src/feature/rend/rendservice.c
index 1a99bd56ed..1af9117aaf 100644
--- a/src/feature/rend/rendservice.c
+++ b/src/feature/rend/rendservice.c
@@ -1341,6 +1341,29 @@ rend_service_poison_new_single_onion_dir(const rend_service_t *s,
   return 0;
 }
 
+/* Return true iff the given service identity key is present on disk. This is
+ * used to try to learn the service version during configuration time. */
+int
+rend_service_key_on_disk(const char *directory_path)
+{
+  int ret = 0;
+  char *fname;
+  crypto_pk_t *pk = NULL;
+
+  tor_assert(directory_path);
+
+  /* Load key */
+  fname = hs_path_from_filename(directory_path, private_key_fname);
+  pk = init_key_from_file(fname, 0, LOG_DEBUG, 0);
+  if (pk) {
+    ret = 1;
+  }
+
+  crypto_pk_free(pk);
+  tor_free(fname);
+  return ret;
+}
+
 /** Load and/or generate private keys for all hidden services, possibly
  * including keys for client authorization.
  * If a <b>service_list</b> is provided, treat it as the list of hidden
diff --git a/src/feature/rend/rendservice.h b/src/feature/rend/rendservice.h
index 7096789629..7186289fc7 100644
--- a/src/feature/rend/rendservice.h
+++ b/src/feature/rend/rendservice.h
@@ -145,6 +145,7 @@ int rend_config_service(const struct config_line_t *line_,
 void rend_service_prune_list(void);
 void rend_service_free_staging_list(void);
 int rend_service_load_all_keys(const smartlist_t *service_list);
+int rend_service_key_on_disk(const char *directory_path);
 void rend_services_add_filenames_to_lists(smartlist_t *open_lst,
                                           smartlist_t *stat_lst);
 void rend_consider_services_intro_points(time_t now);