hs: Add single-onion-service line to v3 descriptor

This field indicates if the service is a Single Onion Service if present in
the descriptor.

Closes #19642

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

src/or/hs_descriptor.c

@@ -26,6 +26,7 @@
 /* Constant string value for the encrypted part of the descriptor. */
 #define str_create2_formats "create2-formats"
 #define str_auth_required "authentication-required"
+#define str_single_onion "single-onion-service"
 #define str_intro_point "introduction-point"
 #define str_ip_auth_key "auth-key"
 #define str_ip_enc_key "enc-key"
@@ -63,6 +64,7 @@ static token_rule_t hs_desc_v3_token_table[] = {
 static token_rule_t hs_desc_encrypted_v3_token_table[] = {
   T1_START(str_create2_formats, R3_CREATE2_FORMATS, CONCAT_ARGS, NO_OBJ),
   T01(str_auth_required, R3_AUTHENTICATION_REQUIRED, ARGS, NO_OBJ),
+  T01(str_single_onion, R3_SINGLE_ONION_SERVICE, ARGS, NO_OBJ),
   END_OF_TABLE
 };
 
@@ -692,6 +694,10 @@ encode_encrypted_data(const hs_descriptor_t *desc,
       smartlist_add_asprintf(lines, "%s %s\n", str_auth_required, buf);
       tor_free(buf);
     }
+
+    if (desc->encrypted_data.single_onion_service) {
+      smartlist_add_asprintf(lines, "%s\n", str_single_onion);
+    }
   }
 
   /* Build the introduction point(s) section. */
@@ -1613,6 +1619,13 @@ desc_decode_encrypted_v3(const hs_descriptor_t *desc,
       goto err;
     }
   }
+
+  /* Is this service a single onion service? */
+  tok = find_opt_by_keyword(tokens, R3_SINGLE_ONION_SERVICE);
+  if (tok) {
+    desc_encrypted_out->single_onion_service = 1;
+  }
+
   /* Initialize the descriptor's introduction point list before we start
    * decoding. Having 0 intro point is valid. Then decode them all. */
   desc_encrypted_out->intro_points = smartlist_new();

src/or/hs_descriptor.h

@@ -128,6 +128,9 @@ typedef struct hs_desc_encrypted_data_t {
    * in order to contact the service. Contains NULL terminated strings. */
   smartlist_t *auth_types;
 
+  /* Is this descriptor a single onion service? */
+  unsigned int single_onion_service : 1;
+
   /* A list of intro points. Contains hs_desc_intro_point_t objects. */
   smartlist_t *intro_points;
 } hs_desc_encrypted_data_t;

src/or/parsecommon.h

@@ -158,6 +158,7 @@ typedef enum {
   R3_SIGNATURE,
   R3_CREATE2_FORMATS,
   R3_AUTHENTICATION_REQUIRED,
+  R3_SINGLE_ONION_SERVICE,
   R3_INTRODUCTION_POINT,
   R3_INTRO_AUTH_KEY,
   R3_INTRO_ENC_KEY,

src/test/test_hs_descriptor.c

@@ -102,6 +102,7 @@ helper_build_hs_desc(unsigned int no_ip)
   /* Setup encrypted data section. */
   desc->encrypted_data.create2_ntor = 1;
   desc->encrypted_data.auth_types = smartlist_new();
+  desc->encrypted_data.single_onion_service = 1;
   smartlist_add(desc->encrypted_data.auth_types, tor_strdup("ed25519"));
   desc->encrypted_data.intro_points = smartlist_new();
   if (!no_ip) {