Parse GuardFraction info from consensuses and votes.

Also introduce the UseGuardFraction torrc option which decides whether
clients should use guardfraction information found in the consensus.

src/or/routerparse.c

@@ -9,6 +9,8 @@
  * \brief Code to parse and validate router descriptors and directories.
  **/
 
+#define ROUTERPARSE_PRIVATE
+
 #include "or.h"
 #include "config.h"
 #include "circuitstats.h"
@@ -23,6 +25,7 @@
 #include "networkstatus.h"
 #include "rephist.h"
 #include "routerparse.h"
+#include "entrynodes.h"
 #undef log
 #include <math.h>
 
@@ -1792,6 +1795,63 @@ find_start_of_next_routerstatus(const char *s)
     return eos;
 }
 
+/** Parse the GuardFraction string from a consensus or vote.
+ *
+ *  If <b>vote</b> or <b>vote_rs</b> are set the document getting
+ *  parsed is a vote routerstatus. Otherwise it's a consensus. This is
+ *  the same semantic as in routerstatus_parse_entry_from_string(). */
+STATIC int
+routerstatus_parse_guardfraction(const char *guardfraction_str,
+                                 networkstatus_t *vote,
+                                 vote_routerstatus_t *vote_rs,
+                                 routerstatus_t *rs)
+{
+  int ok;
+  const char *end_of_header = NULL;
+  int is_consensus = !vote_rs;
+  uint32_t guardfraction;
+
+  tor_assert(bool_eq(vote, vote_rs));
+
+  /* If this info comes from a consensus, but we should't apply
+     guardfraction, just exit. */
+  if (is_consensus && !should_apply_guardfraction(NULL)) {
+    return 0;
+  }
+
+  end_of_header = strchr(guardfraction_str, '=');
+  if (!end_of_header) {
+    return -1;
+  }
+
+  guardfraction = (uint32_t)tor_parse_ulong(end_of_header+1,
+                                         10, 0, 100, &ok, NULL);
+  if (!ok) {
+    log_warn(LD_DIR, "Invalid GuardFraction %s", escaped(guardfraction_str));
+    return -1;
+  }
+
+  log_warn(LD_GENERAL, "[*] Parsed %s guardfraction '%s' for '%s'.",
+           is_consensus ? "consensus" : "vote",
+           guardfraction_str, rs->nickname);
+
+  if (!is_consensus) { /* We are parsing a vote */
+    vote_rs->status.guardfraction_percentage = guardfraction;
+    vote_rs->status.has_guardfraction = 1;
+  } else {
+    /* We are parsing a consensus. Only apply guardfraction to guards. */
+    if (rs->is_possible_guard) {
+      rs->guardfraction_percentage = guardfraction;
+      rs->has_guardfraction = 1;
+    } else {
+      log_warn(LD_BUG, "Got GuardFraction for non-guard %s. "
+               "This is not supposed to happen. Not applying. ", rs->nickname);
+    }
+  }
+
+  return 0;
+}
+
 /** Given a string at *<b>s</b>, containing a routerstatus object, and an
  * empty smartlist at <b>tokens</b>, parse and return the first router status
  * object in the string, and advance *<b>s</b> to just after the end of the
@@ -1994,6 +2054,11 @@ routerstatus_parse_entry_from_string(memarea_t *area,
         vote->has_measured_bws = 1;
       } else if (!strcmpstart(tok->args[i], "Unmeasured=1")) {
         rs->bw_is_unmeasured = 1;
+      } else if (!strcmpstart(tok->args[i], "GuardFraction=")) {
+        if (routerstatus_parse_guardfraction(tok->args[i],
+                                             vote, vote_rs, rs) < 0) {
+          goto err;
+        }
       }
     }
   }