Circuit padding ProtoVer plumbing.

This helps us to determine if a middle node can pad to us or not.

Co-authored-by: George Kadianakis <desnacked@riseup.net>

src/core/or/or.h

@@ -836,6 +836,10 @@ typedef struct protover_summary_flags_t {
    * service rendezvous point supporting version 3 as seen in proposal 224.
    * This requires HSRend=2. */
   unsigned int supports_v3_rendezvous_point: 1;
+
+  /** True iff this router has a protocol list that allows clients to
+   * negotiate link-level padding. Requires Padding>=1. */
+  unsigned int supports_padding : 1;
 } protover_summary_flags_t;
 
 typedef struct routerinfo_t routerinfo_t;

src/core/or/protover.c

@@ -39,6 +39,9 @@ static int protocol_list_contains(const smartlist_t *protos,
 static const struct {
   protocol_type_t protover_type;
   const char *name;
+/* If you add a new protocol here, you probably also want to add
+ * parsing for it in routerstatus_parse_entry_from_string() so that
+ * it is set in routerstatus_t */
 } PROTOCOL_NAMES[] = {
   { PRT_LINK, "Link" },
   { PRT_LINKAUTH, "LinkAuth" },
@@ -49,6 +52,7 @@ static const struct {
   { PRT_HSREND, "HSRend" },
   { PRT_DESC, "Desc" },
   { PRT_MICRODESC, "Microdesc"},
+  { PRT_PADDING, "Padding"},
   { PRT_CONS, "Cons" }
 };
 
@@ -396,7 +400,8 @@ protover_get_supported_protocols(void)
     "LinkAuth=3 "
 #endif
     "Microdesc=1-2 "
-    "Relay=1-2";
+    "Relay=1-2 "
+    "Padding=1";
 }
 
 /** The protocols from protover_get_supported_protocols(), as parsed into a

src/core/or/protover.h

@@ -43,6 +43,7 @@ typedef enum protocol_type_t {
   PRT_DESC,
   PRT_MICRODESC,
   PRT_CONS,
+  PRT_PADDING,
 } protocol_type_t;
 
 bool protover_contains_long_protocol_names(const char *s);

src/core/or/versions.c

@@ -448,6 +448,8 @@ memoize_protover_summary(protover_summary_flags_t *out,
   out->supports_v3_rendezvous_point =
     protocol_list_supports_protocol(protocols, PRT_HSREND,
                                     PROTOVER_HS_RENDEZVOUS_POINT_V3);
+    out->supports_padding =
+      protocol_list_supports_protocol(protocols, PRT_PADDING, 1);
 
   protover_summary_flags_t *new_cached = tor_memdup(out, sizeof(*out));
   cached = strmap_set(protover_summary_map, protocols, new_cached);

src/feature/nodelist/nodelist.c

@@ -1106,7 +1106,7 @@ node_ed25519_id_matches(const node_t *node, const ed25519_public_key_t *id)
 /** Dummy object that should be unreturnable.  Used to ensure that
  * node_get_protover_summary_flags() always returns non-NULL. */
 static const protover_summary_flags_t zero_protover_flags = {
-  0,0,0,0,0,0,0
+  0,0,0,0,0,0,0,0
 };
 
 /** Return the protover_summary_flags for a given node. */

src/rust/protover/protover.rs

@@ -46,6 +46,7 @@ pub enum Protocol {
     LinkAuth,
     Microdesc,
     Relay,
+    Padding,
 }
 
 impl fmt::Display for Protocol {
@@ -73,6 +74,7 @@ impl FromStr for Protocol {
             "LinkAuth" => Ok(Protocol::LinkAuth),
             "Microdesc" => Ok(Protocol::Microdesc),
             "Relay" => Ok(Protocol::Relay),
+            "Padding" => Ok(Protocol::Padding),
             _ => Err(ProtoverError::UnknownProtocol),
         }
     }
@@ -163,7 +165,8 @@ pub(crate) fn get_supported_protocols_cstr() -> &'static CStr {
              Link=1-5 \
              LinkAuth=3 \
              Microdesc=1-2 \
-             Relay=1-2"
+             Relay=1-2 \
+             Padding=1"
         )
     } else {
         cstr!(
@@ -176,7 +179,8 @@ pub(crate) fn get_supported_protocols_cstr() -> &'static CStr {
              Link=1-5 \
              LinkAuth=1,3 \
              Microdesc=1-2 \
-             Relay=1-2"
+             Relay=1-2 \
+             Padding=1"
         )
     }
 }