prop224 prepwork: Introduce HS circuitmap subsystem.

The HS circuitmap is a hash table that maps introduction and rendezvous
tokens to specific circuits such that given a token it's easy to find
the corresponding circuit. It supports rend circuits and v2/v3 intro
circuits.

It will be used by the prop224 ESTABLISH_INTRO code to register and
lookup v3 introduction circuits.

The next commit after this removes the old code and fixes the unittests.
Please consult both commits while reviewing functionality differences
between the old and new code. Let me know if you want this rebased
differently :)

WRT architectural differences, this commit removes the rendinfo pointer
from or_circuit_t. It then adds an hs_token_t pointer and a hashtable
node for the HS circuitmap. IIUC, this adds another pointer to the
weight of or_circuit_t. Let me know if you don't like this, or if you
have suggestions on improving it.

1 files changed, 7 insertions, 1 deletions

diff --git a/src/or/or.h b/src/or/or.h
index eb94f63d5e..9581c6da7a 100644
--- a/src/or/or.h
+++ b/src/or/or.h
@@ -80,6 +80,7 @@
 #include "crypto_ed25519.h"
 #include "tor_queue.h"
 #include "util_format.h"
+#include "hs_circuitmap.h"
 
 /* These signals are defined to help handle_control_signal work.
  */
@@ -3352,7 +3353,12 @@ typedef struct or_circuit_t {
    * is not marked for close. */
   struct or_circuit_t *rend_splice;
 
-  struct or_circuit_rendinfo_s *rendinfo;
+  /** If set, points to an HS token that this circuit might be carrying.
+   *  Used by the HS circuitmap.  */
+  hs_token_t *hs_token;
+  /** Hashtable node: used to look up the circuit by its HS token using the HS
+      circuitmap. */
+  HT_ENTRY(or_circuit_t) hs_circuitmap_node;
 
   /** Stores KH for the handshake. */
   char rend_circ_nonce[DIGEST_LEN];/* KH in tor-spec.txt */