Whoops. Protover.[ch] belong in src/core/or

1 files changed, 923 insertions, 0 deletions

diff --git a/src/core/or/protover.c b/src/core/or/protover.c
new file mode 100644
index 0000000000..362a5becac
--- /dev/null
+++ b/src/core/or/protover.c
@@ -0,0 +1,923 @@
+/* Copyright (c) 2016-2018, The Tor Project, Inc. */
+/* See LICENSE for licensing information */
+
+/**
+ * \file protover.c
+ * \brief Versioning information for different pieces of the Tor protocol.
+ *
+ * Starting in version 0.2.9.3-alpha, Tor places separate version numbers on
+ * each of the different components of its protocol. Relays use these numbers
+ * to advertise what versions of the protocols they can support, and clients
+ * use them to find what they can ask a given relay to do.  Authorities vote
+ * on the supported protocol versions for each relay, and also vote on the
+ * which protocols you should have to support in order to be on the Tor
+ * network. All Tor instances use these required/recommended protocol versions
+ * to tell what level of support for recent protocols each relay has, and
+ * to decide whether they should be running given their current protocols.
+ *
+ * The main advantage of these protocol versions numbers over using Tor
+ * version numbers is that they allow different implementations of the Tor
+ * protocols to develop independently, without having to claim compatibility
+ * with specific versions of Tor.
+ **/
+
+#define PROTOVER_PRIVATE
+
+#include "core/or/or.h"
+#include "core/or/protover.h"
+#include "feature/nodelist/routerparse.h"
+
+#ifndef HAVE_RUST
+
+static const smartlist_t *get_supported_protocol_list(void);
+static int protocol_list_contains(const smartlist_t *protos,
+                                  protocol_type_t pr, uint32_t ver);
+
+/** Mapping between protocol type string and protocol type. */
+/// C_RUST_COUPLED: src/rust/protover/protover.rs `PROTOCOL_NAMES`
+static const struct {
+  protocol_type_t protover_type;
+  const char *name;
+} PROTOCOL_NAMES[] = {
+  { PRT_LINK, "Link" },
+  { PRT_LINKAUTH, "LinkAuth" },
+  { PRT_RELAY, "Relay" },
+  { PRT_DIRCACHE, "DirCache" },
+  { PRT_HSDIR, "HSDir" },
+  { PRT_HSINTRO, "HSIntro" },
+  { PRT_HSREND, "HSRend" },
+  { PRT_DESC, "Desc" },
+  { PRT_MICRODESC, "Microdesc"},
+  { PRT_CONS, "Cons" }
+};
+
+#define N_PROTOCOL_NAMES ARRAY_LENGTH(PROTOCOL_NAMES)
+
+/* Maximum allowed length of any single subprotocol name. */
+// C_RUST_COUPLED: src/rust/protover/protover.rs
+//                 `MAX_PROTOCOL_NAME_LENGTH`
+static const unsigned MAX_PROTOCOL_NAME_LENGTH = 100;
+
+/**
+ * Given a protocol_type_t, return the corresponding string used in
+ * descriptors.
+ */
+STATIC const char *
+protocol_type_to_str(protocol_type_t pr)
+{
+  unsigned i;
+  for (i=0; i < N_PROTOCOL_NAMES; ++i) {
+    if (PROTOCOL_NAMES[i].protover_type == pr)
+      return PROTOCOL_NAMES[i].name;
+  }
+  /* LCOV_EXCL_START */
+  tor_assert_nonfatal_unreached_once();
+  return "UNKNOWN";
+  /* LCOV_EXCL_STOP */
+}
+
+/**
+ * Given a string, find the corresponding protocol type and store it in
+ * <b>pr_out</b>. Return 0 on success, -1 on failure.
+ */
+STATIC int
+str_to_protocol_type(const char *s, protocol_type_t *pr_out)
+{
+  if (BUG(!pr_out))
+    return -1;
+
+  unsigned i;
+  for (i=0; i < N_PROTOCOL_NAMES; ++i) {
+    if (0 == strcmp(s, PROTOCOL_NAMES[i].name)) {
+      *pr_out = PROTOCOL_NAMES[i].protover_type;
+      return 0;
+    }
+  }
+
+  return -1;
+}
+
+/**
+ * Release all space held by a single proto_entry_t structure
+ */
+STATIC void
+proto_entry_free_(proto_entry_t *entry)
+{
+  if (!entry)
+    return;
+  tor_free(entry->name);
+  SMARTLIST_FOREACH(entry->ranges, proto_range_t *, r, tor_free(r));
+  smartlist_free(entry->ranges);
+  tor_free(entry);
+}
+
+/** The largest possible protocol version. */
+#define MAX_PROTOCOL_VERSION (UINT32_MAX-1)
+
+/**
+ * Given a string <b>s</b> and optional end-of-string pointer
+ * <b>end_of_range</b>, parse the protocol range and store it in
+ * <b>low_out</b> and <b>high_out</b>.  A protocol range has the format U, or
+ * U-U, where U is an unsigned 32-bit integer.
+ */
+static int
+parse_version_range(const char *s, const char *end_of_range,
+                    uint32_t *low_out, uint32_t *high_out)
+{
+  uint32_t low, high;
+  char *next = NULL;
+  int ok;
+
+  tor_assert(high_out);
+  tor_assert(low_out);
+
+  if (BUG(!end_of_range))
+    end_of_range = s + strlen(s); // LCOV_EXCL_LINE
+
+  /* A range must start with a digit. */
+  if (!TOR_ISDIGIT(*s)) {
+    goto error;
+  }
+
+  /* Note that this wouldn't be safe if we didn't know that eventually,
+   * we'd hit a NUL */
+  low = (uint32_t) tor_parse_ulong(s, 10, 0, MAX_PROTOCOL_VERSION, &ok, &next);
+  if (!ok)
+    goto error;
+  if (next > end_of_range)
+    goto error;
+  if (next == end_of_range) {
+    high = low;
+    goto done;
+  }
+
+  if (*next != '-')
+    goto error;
+  s = next+1;
+
+  /* ibid */
+  if (!TOR_ISDIGIT(*s)) {
+    goto error;
+  }
+  high = (uint32_t) tor_parse_ulong(s, 10, 0,
+                                    MAX_PROTOCOL_VERSION, &ok, &next);
+  if (!ok)
+    goto error;
+  if (next != end_of_range)
+    goto error;
+
+  if (low > high)
+    goto error;
+
+ done:
+  *high_out = high;
+  *low_out = low;
+  return 0;
+
+ error:
+  return -1;
+}
+
+/** Parse a single protocol entry from <b>s</b> up to an optional
+ * <b>end_of_entry</b> pointer, and return that protocol entry. Return NULL
+ * on error.
+ *
+ * A protocol entry has a keyword, an = sign, and zero or more ranges. */
+static proto_entry_t *
+parse_single_entry(const char *s, const char *end_of_entry)
+{
+  proto_entry_t *out = tor_malloc_zero(sizeof(proto_entry_t));
+  const char *equals;
+
+  out->ranges = smartlist_new();
+
+  if (BUG (!end_of_entry))
+    end_of_entry = s + strlen(s); // LCOV_EXCL_LINE
+
+  /* There must be an =. */
+  equals = memchr(s, '=', end_of_entry - s);
+  if (!equals)
+    goto error;
+
+  /* The name must be nonempty */
+  if (equals == s)
+    goto error;
+
+  /* The name must not be longer than MAX_PROTOCOL_NAME_LENGTH. */
+  if (equals - s > (int)MAX_PROTOCOL_NAME_LENGTH) {
+    log_warn(LD_NET, "When parsing a protocol entry, I got a very large "
+             "protocol name. This is possibly an attack or a bug, unless "
+             "the Tor network truly supports protocol names larger than "
+             "%ud characters. The offending string was: %s",
+             MAX_PROTOCOL_NAME_LENGTH, escaped(out->name));
+    goto error;
+  }
+  out->name = tor_strndup(s, equals-s);
+
+  tor_assert(equals < end_of_entry);
+
+  s = equals + 1;
+  while (s < end_of_entry) {
+    const char *comma = memchr(s, ',', end_of_entry-s);
+    proto_range_t *range = tor_malloc_zero(sizeof(proto_range_t));
+    if (! comma)
+      comma = end_of_entry;
+
+    smartlist_add(out->ranges, range);
+    if (parse_version_range(s, comma, &range->low, &range->high) < 0) {
+      goto error;
+    }
+
+    s = comma;
+    while (*s == ',' && s < end_of_entry)
+      ++s;
+  }
+
+  return out;
+
+ error:
+  proto_entry_free(out);
+  return NULL;
+}
+
+/**
+ * Parse the protocol list from <b>s</b> and return it as a smartlist of
+ * proto_entry_t
+ */
+STATIC smartlist_t *
+parse_protocol_list(const char *s)
+{
+  smartlist_t *entries = smartlist_new();
+
+  while (*s) {
+    /* Find the next space or the NUL. */
+    const char *end_of_entry = strchr(s, ' ');
+    proto_entry_t *entry;
+    if (!end_of_entry)
+      end_of_entry = s + strlen(s);
+
+    entry = parse_single_entry(s, end_of_entry);
+
+    if (! entry)
+      goto error;
+
+    smartlist_add(entries, entry);
+
+    s = end_of_entry;
+    while (*s == ' ')
+      ++s;
+  }
+
+  return entries;
+
+ error:
+  SMARTLIST_FOREACH(entries, proto_entry_t *, ent, proto_entry_free(ent));
+  smartlist_free(entries);
+  return NULL;
+}
+
+/**
+ * Return true if the unparsed protover in <b>s</b> would contain a protocol
+ * name longer than MAX_PROTOCOL_NAME_LENGTH, and false otherwise.
+ */
+bool
+protover_contains_long_protocol_names(const char *s)
+{
+  smartlist_t *list = parse_protocol_list(s);
+  if (!list)
+    return true; /* yes, has a dangerous name */
+  SMARTLIST_FOREACH(list, proto_entry_t *, ent, proto_entry_free(ent));
+  smartlist_free(list);
+  return false; /* no, looks fine */
+}
+
+/**
+ * Given a protocol type and version number, return true iff we know
+ * how to speak that protocol.
+ */
+int
+protover_is_supported_here(protocol_type_t pr, uint32_t ver)
+{
+  const smartlist_t *ours = get_supported_protocol_list();
+  return protocol_list_contains(ours, pr, ver);
+}
+
+/**
+ * Return true iff "list" encodes a protocol list that includes support for
+ * the indicated protocol and version.
+ */
+int
+protocol_list_supports_protocol(const char *list, protocol_type_t tp,
+                                uint32_t version)
+{
+  /* NOTE: This is a pretty inefficient implementation. If it ever shows
+   * up in profiles, we should memoize it.
+   */
+  smartlist_t *protocols = parse_protocol_list(list);
+  if (!protocols) {
+    return 0;
+  }
+  int contains = protocol_list_contains(protocols, tp, version);
+
+  SMARTLIST_FOREACH(protocols, proto_entry_t *, ent, proto_entry_free(ent));
+  smartlist_free(protocols);
+  return contains;
+}
+
+/**
+ * Return true iff "list" encodes a protocol list that includes support for
+ * the indicated protocol and version, or some later version.
+ */
+int
+protocol_list_supports_protocol_or_later(const char *list,
+                                         protocol_type_t tp,
+                                         uint32_t version)
+{
+  /* NOTE: This is a pretty inefficient implementation. If it ever shows
+   * up in profiles, we should memoize it.
+   */
+  smartlist_t *protocols = parse_protocol_list(list);
+  if (!protocols) {
+    return 0;
+  }
+  const char *pr_name = protocol_type_to_str(tp);
+
+  int contains = 0;
+  SMARTLIST_FOREACH_BEGIN(protocols, proto_entry_t *, proto) {
+    if (strcasecmp(proto->name, pr_name))
+      continue;
+    SMARTLIST_FOREACH_BEGIN(proto->ranges, const proto_range_t *, range) {
+      if (range->high >= version) {
+        contains = 1;
+        goto found;
+      }
+    } SMARTLIST_FOREACH_END(range);
+  } SMARTLIST_FOREACH_END(proto);
+
+ found:
+  SMARTLIST_FOREACH(protocols, proto_entry_t *, ent, proto_entry_free(ent));
+  smartlist_free(protocols);
+  return contains;
+}
+
+/** Return the canonical string containing the list of protocols
+ * that we support. */
+/// C_RUST_COUPLED: src/rust/protover/protover.rs `SUPPORTED_PROTOCOLS`
+const char *
+protover_get_supported_protocols(void)
+{
+  return
+    "Cons=1-2 "
+    "Desc=1-2 "
+    "DirCache=1-2 "
+    "HSDir=1-2 "
+    "HSIntro=3-4 "
+    "HSRend=1-2 "
+    "Link=1-5 "
+    "LinkAuth=1,3 "
+    "Microdesc=1-2 "
+    "Relay=1-2";
+}
+
+/** The protocols from protover_get_supported_protocols(), as parsed into a
+ * list of proto_entry_t values. Access this via
+ * get_supported_protocol_list. */
+static smartlist_t *supported_protocol_list = NULL;
+
+/** Return a pointer to a smartlist of proto_entry_t for the protocols
+ * we support. */
+static const smartlist_t *
+get_supported_protocol_list(void)
+{
+  if (PREDICT_UNLIKELY(supported_protocol_list == NULL)) {
+    supported_protocol_list =
+      parse_protocol_list(protover_get_supported_protocols());
+  }
+  return supported_protocol_list;
+}
+
+/**
+ * Given a protocol entry, encode it at the end of the smartlist <b>chunks</b>
+ * as one or more newly allocated strings.
+ */
+static void
+proto_entry_encode_into(smartlist_t *chunks, const proto_entry_t *entry)
+{
+  smartlist_add_asprintf(chunks, "%s=", entry->name);
+
+  SMARTLIST_FOREACH_BEGIN(entry->ranges, proto_range_t *, range) {
+    const char *comma = "";
+    if (range_sl_idx != 0)
+      comma = ",";
+
+    if (range->low == range->high) {
+      smartlist_add_asprintf(chunks, "%s%lu",
+                             comma, (unsigned long)range->low);
+    } else {
+      smartlist_add_asprintf(chunks, "%s%lu-%lu",
+                             comma, (unsigned long)range->low,
+                             (unsigned long)range->high);
+    }
+  } SMARTLIST_FOREACH_END(range);
+}
+
+/** Given a list of space-separated proto_entry_t items,
+ * encode it into a newly allocated space-separated string. */
+STATIC char *
+encode_protocol_list(const smartlist_t *sl)
+{
+  const char *separator = "";
+  smartlist_t *chunks = smartlist_new();
+  SMARTLIST_FOREACH_BEGIN(sl, const proto_entry_t *, ent) {
+    smartlist_add_strdup(chunks, separator);
+
+    proto_entry_encode_into(chunks, ent);
+
+    separator = " ";
+  } SMARTLIST_FOREACH_END(ent);
+
+  char *result = smartlist_join_strings(chunks, "", 0, NULL);
+
+  SMARTLIST_FOREACH(chunks, char *, cp, tor_free(cp));
+  smartlist_free(chunks);
+
+  return result;
+}
+
+/* We treat any protocol list with more than this many subprotocols in it
+ * as a DoS attempt. */
+/// C_RUST_COUPLED: src/rust/protover/protover.rs
+///                 `MAX_PROTOCOLS_TO_EXPAND`
+static const int MAX_PROTOCOLS_TO_EXPAND = (1<<16);
+
+/** Voting helper: Given a list of proto_entry_t, return a newly allocated
+ * smartlist of newly allocated strings, one for each included protocol
+ * version. (So 'Foo=3,5-7' expands to a list of 'Foo=3', 'Foo=5', 'Foo=6',
+ * 'Foo=7'.)
+ *
+ * Do not list any protocol version more than once.
+ *
+ * Return NULL if the list would be too big.
+ */
+static smartlist_t *
+expand_protocol_list(const smartlist_t *protos)
+{
+  smartlist_t *expanded = smartlist_new();
+  if (!protos)
+    return expanded;
+
+  SMARTLIST_FOREACH_BEGIN(protos, const proto_entry_t *, ent) {
+    const char *name = ent->name;
+    if (strlen(name) > MAX_PROTOCOL_NAME_LENGTH) {
+      log_warn(LD_NET, "When expanding a protocol entry, I got a very large "
+               "protocol name. This is possibly an attack or a bug, unless "
+               "the Tor network truly supports protocol names larger than "
+               "%ud characters. The offending string was: %s",
+               MAX_PROTOCOL_NAME_LENGTH, escaped(name));
+      continue;
+    }
+    SMARTLIST_FOREACH_BEGIN(ent->ranges, const proto_range_t *, range) {
+      uint32_t u;
+      for (u = range->low; u <= range->high; ++u) {
+        smartlist_add_asprintf(expanded, "%s=%lu", name, (unsigned long)u);
+        if (smartlist_len(expanded) > MAX_PROTOCOLS_TO_EXPAND)
+          goto too_many;
+      }
+    } SMARTLIST_FOREACH_END(range);
+  } SMARTLIST_FOREACH_END(ent);
+
+  smartlist_sort_strings(expanded);
+  smartlist_uniq_strings(expanded); // This makes voting work. do not remove
+  return expanded;
+
+ too_many:
+  SMARTLIST_FOREACH(expanded, char *, cp, tor_free(cp));
+  smartlist_free(expanded);
+  return NULL;
+}
+
+/** Voting helper: compare two singleton proto_entry_t items by version
+ * alone. (A singleton item is one with a single range entry where
+ * low==high.) */
+static int
+cmp_single_ent_by_version(const void **a_, const void **b_)
+{
+  const proto_entry_t *ent_a = *a_;
+  const proto_entry_t *ent_b = *b_;
+
+  tor_assert(smartlist_len(ent_a->ranges) == 1);
+  tor_assert(smartlist_len(ent_b->ranges) == 1);
+
+  const proto_range_t *a = smartlist_get(ent_a->ranges, 0);
+  const proto_range_t *b = smartlist_get(ent_b->ranges, 0);
+
+  tor_assert(a->low == a->high);
+  tor_assert(b->low == b->high);
+
+  if (a->low < b->low) {
+    return -1;
+  } else if (a->low == b->low) {
+    return 0;
+  } else {
+    return 1;
+  }
+}
+
+/** Voting helper: Given a list of singleton protocol strings (of the form
+ * Foo=7), return a canonical listing of all the protocol versions listed,
+ * with as few ranges as possible, with protocol versions sorted lexically and
+ * versions sorted in numerically increasing order, using as few range entries
+ * as possible.
+ **/
+static char *
+contract_protocol_list(const smartlist_t *proto_strings)
+{
+  if (smartlist_len(proto_strings) == 0) {
+    return tor_strdup("");
+  }
+
+  // map from name to list of single-version entries
+  strmap_t *entry_lists_by_name = strmap_new();
+  // list of protocol names
+  smartlist_t *all_names = smartlist_new();
+  // list of strings for the output we're building
+  smartlist_t *chunks = smartlist_new();
+
+  // Parse each item and stick it entry_lists_by_name. Build
+  // 'all_names' at the same time.
+  SMARTLIST_FOREACH_BEGIN(proto_strings, const char *, s) {
+    if (BUG(!s))
+      continue;// LCOV_EXCL_LINE
+    proto_entry_t *ent = parse_single_entry(s, s+strlen(s));
+    if (BUG(!ent))
+      continue; // LCOV_EXCL_LINE
+    smartlist_t *lst = strmap_get(entry_lists_by_name, ent->name);
+    if (!lst) {
+      smartlist_add(all_names, ent->name);
+      lst = smartlist_new();
+      strmap_set(entry_lists_by_name, ent->name, lst);
+    }
+    smartlist_add(lst, ent);
+  } SMARTLIST_FOREACH_END(s);
+
+  // We want to output the protocols sorted by their name.
+  smartlist_sort_strings(all_names);
+
+  SMARTLIST_FOREACH_BEGIN(all_names, const char *, name) {
+    const int first_entry = (name_sl_idx == 0);
+    smartlist_t *lst = strmap_get(entry_lists_by_name, name);
+    tor_assert(lst);
+    // Sort every entry with this name by version. They are
+    // singletons, so there can't be overlap.
+    smartlist_sort(lst, cmp_single_ent_by_version);
+
+    if (! first_entry)
+      smartlist_add_strdup(chunks, " ");
+
+    /* We're going to construct this entry from the ranges. */
+    proto_entry_t *entry = tor_malloc_zero(sizeof(proto_entry_t));
+    entry->ranges = smartlist_new();
+    entry->name = tor_strdup(name);
+
+    // Now, find all the ranges of versions start..end where
+    // all of start, start+1, start+2, ..end are included.
+    int start_of_cur_series = 0;
+    while (start_of_cur_series < smartlist_len(lst)) {
+      const proto_entry_t *ent = smartlist_get(lst, start_of_cur_series);
+      const proto_range_t *range = smartlist_get(ent->ranges, 0);
+      const uint32_t ver_low = range->low;
+      uint32_t ver_high = ver_low;
+
+      int idx;
+      for (idx = start_of_cur_series+1; idx < smartlist_len(lst); ++idx) {
+        ent = smartlist_get(lst, idx);
+        range = smartlist_get(ent->ranges, 0);
+        if (range->low != ver_high + 1)
+          break;
+        ver_high += 1;
+      }
+
+      // Now idx is either off the end of the list, or the first sequence
+      // break in the list.
+      start_of_cur_series = idx;
+
+      proto_range_t *new_range = tor_malloc_zero(sizeof(proto_range_t));
+      new_range->low = ver_low;
+      new_range->high = ver_high;
+      smartlist_add(entry->ranges, new_range);
+    }
+    proto_entry_encode_into(chunks, entry);
+    proto_entry_free(entry);
+
+  } SMARTLIST_FOREACH_END(name);
+
+  // Build the result...
+  char *result = smartlist_join_strings(chunks, "", 0, NULL);
+
+  // And free all the stuff we allocated.
+  SMARTLIST_FOREACH_BEGIN(all_names, const char *, name) {
+    smartlist_t *lst = strmap_get(entry_lists_by_name, name);
+    tor_assert(lst);
+    SMARTLIST_FOREACH(lst, proto_entry_t *, e, proto_entry_free(e));
+    smartlist_free(lst);
+  } SMARTLIST_FOREACH_END(name);
+
+  strmap_free(entry_lists_by_name, NULL);
+  smartlist_free(all_names);
+  SMARTLIST_FOREACH(chunks, char *, cp, tor_free(cp));
+  smartlist_free(chunks);
+
+  return result;
+}
+
+/**
+ * Protocol voting implementation.
+ *
+ * Given a list of strings describing protocol versions, return a newly
+ * allocated string encoding all of the protocols that are listed by at
+ * least <b>threshold</b> of the inputs.
+ *
+ * The string is minimal and sorted according to the rules of
+ * contract_protocol_list above.
+ */
+char *
+protover_compute_vote(const smartlist_t *list_of_proto_strings,
+                      int threshold)
+{
+  if (smartlist_len(list_of_proto_strings) == 0) {
+    return tor_strdup("");
+  }
+
+  smartlist_t *all_entries = smartlist_new();
+
+  // First, parse the inputs and break them into singleton entries.
+  SMARTLIST_FOREACH_BEGIN(list_of_proto_strings, const char *, vote) {
+    smartlist_t *unexpanded = parse_protocol_list(vote);
+    if (! unexpanded) {
+      log_warn(LD_NET, "I failed with parsing a protocol list from "
+               "an authority. The offending string was: %s",
+               escaped(vote));
+      continue;
+    }
+    smartlist_t *this_vote = expand_protocol_list(unexpanded);
+    if (this_vote == NULL) {
+      log_warn(LD_NET, "When expanding a protocol list from an authority, I "
+               "got too many protocols. This is possibly an attack or a bug, "
+               "unless the Tor network truly has expanded to support over %d "
+               "different subprotocol versions. The offending string was: %s",
+               MAX_PROTOCOLS_TO_EXPAND, escaped(vote));
+    } else {
+      smartlist_add_all(all_entries, this_vote);
+      smartlist_free(this_vote);
+    }
+    SMARTLIST_FOREACH(unexpanded, proto_entry_t *, e, proto_entry_free(e));
+    smartlist_free(unexpanded);
+  } SMARTLIST_FOREACH_END(vote);
+
+  if (smartlist_len(all_entries) == 0) {
+    smartlist_free(all_entries);
+    return tor_strdup("");
+  }
+
+  // Now sort the singleton entries
+  smartlist_sort_strings(all_entries);
+
+  // Now find all the strings that appear at least 'threshold' times.
+  smartlist_t *include_entries = smartlist_new();
+  const char *cur_entry = smartlist_get(all_entries, 0);
+  int n_times = 0;
+  SMARTLIST_FOREACH_BEGIN(all_entries, const char *, ent) {
+    if (!strcmp(ent, cur_entry)) {
+      n_times++;
+    } else {
+      if (n_times >= threshold && cur_entry)
+        smartlist_add(include_entries, (void*)cur_entry);
+      cur_entry = ent;
+      n_times = 1 ;
+    }
+  } SMARTLIST_FOREACH_END(ent);
+
+  if (n_times >= threshold && cur_entry)
+    smartlist_add(include_entries, (void*)cur_entry);
+
+  // Finally, compress that list.
+  char *result = contract_protocol_list(include_entries);
+  smartlist_free(include_entries);
+  SMARTLIST_FOREACH(all_entries, char *, cp, tor_free(cp));
+  smartlist_free(all_entries);
+
+  return result;
+}
+
+/** Return true if every protocol version described in the string <b>s</b> is
+ * one that we support, and false otherwise.  If <b>missing_out</b> is
+ * provided, set it to the list of protocols we do not support.
+ *
+ * NOTE: This is quadratic, but we don't do it much: only a few times per
+ * consensus. Checking signatures should be way more expensive than this
+ * ever would be.
+ **/
+int
+protover_all_supported(const char *s, char **missing_out)
+{
+  int all_supported = 1;
+  smartlist_t *missing_some;
+  smartlist_t *missing_completely;
+  smartlist_t *missing_all;
+
+  if (!s) {
+    return 1;
+  }
+
+  smartlist_t *entries = parse_protocol_list(s);
+  if (BUG(entries == NULL)) {
+    log_warn(LD_NET, "Received an unparseable protocol list %s"
+             " from the consensus", escaped(s));
+    return 1;
+  }
+
+  missing_some = smartlist_new();
+  missing_completely = smartlist_new();
+
+  SMARTLIST_FOREACH_BEGIN(entries, const proto_entry_t *, ent) {
+    protocol_type_t tp;
+    if (str_to_protocol_type(ent->name, &tp) < 0) {
+      if (smartlist_len(ent->ranges)) {
+        goto unsupported;
+      }
+      continue;
+    }
+
+    SMARTLIST_FOREACH_BEGIN(ent->ranges, const proto_range_t *, range) {
+      proto_entry_t *unsupported = tor_malloc_zero(sizeof(proto_entry_t));
+      proto_range_t *versions = tor_malloc_zero(sizeof(proto_range_t));
+      uint32_t i;
+
+      unsupported->name = tor_strdup(ent->name);
+      unsupported->ranges = smartlist_new();
+
+      for (i = range->low; i <= range->high; ++i) {
+        if (!protover_is_supported_here(tp, i)) {
+          if (versions->low == 0 && versions->high == 0) {
+            versions->low = i;
+            /* Pre-emptively add the high now, just in case we're in a single
+             * version range (e.g. "Link=999"). */
+            versions->high = i;
+          }
+          /* If the last one to be unsupported is one less than the current
+           * one, we're in a continuous range, so set the high field. */
+          if ((versions->high && versions->high == i - 1) ||
+              /* Similarly, if the last high wasn't set and we're currently
+               * one higher than the low, add current index as the highest
+               * known high. */
+              (!versions->high && versions->low == i - 1)) {
+            versions->high = i;
+            continue;
+          }
+        } else {
+          /* If we hit a supported version, and we previously had a range,
+           * we've hit a non-continuity. Copy the previous range and add it to
+           * the unsupported->ranges list and zero-out the previous range for
+           * the next iteration. */
+          if (versions->low != 0 && versions->high != 0) {
+            proto_range_t *versions_to_add = tor_malloc(sizeof(proto_range_t));
+
+            versions_to_add->low = versions->low;
+            versions_to_add->high = versions->high;
+            smartlist_add(unsupported->ranges, versions_to_add);
+
+            versions->low = 0;
+            versions->high = 0;
+          }
+        }
+      }
+      /* Once we've run out of versions to check, see if we had any unsupported
+       * ones and, if so, add them to unsupported->ranges. */
+      if (versions->low != 0 && versions->high != 0) {
+        smartlist_add(unsupported->ranges, versions);
+      }
+      /* Finally, if we had something unsupported, add it to the list of
+       * missing_some things and mark that there was something missing. */
+      if (smartlist_len(unsupported->ranges) != 0) {
+        smartlist_add(missing_some, (void*) unsupported);
+        all_supported = 0;
+      } else {
+        proto_entry_free(unsupported);
+        tor_free(versions);
+      }
+    } SMARTLIST_FOREACH_END(range);
+
+    continue;
+
+  unsupported:
+    all_supported = 0;
+    smartlist_add(missing_completely, (void*) ent);
+  } SMARTLIST_FOREACH_END(ent);
+
+  /* We keep the two smartlists separate so that we can free the proto_entry_t
+   * we created and put in missing_some, so here we add them together to build
+   * the string. */
+  missing_all = smartlist_new();
+  smartlist_add_all(missing_all, missing_some);
+  smartlist_add_all(missing_all, missing_completely);
+
+  if (missing_out && !all_supported) {
+    tor_assert(smartlist_len(missing_all) != 0);
+    *missing_out = encode_protocol_list(missing_all);
+  }
+  SMARTLIST_FOREACH(missing_some, proto_entry_t *, ent, proto_entry_free(ent));
+  smartlist_free(missing_some);
+  smartlist_free(missing_completely);
+  smartlist_free(missing_all);
+
+  SMARTLIST_FOREACH(entries, proto_entry_t *, ent, proto_entry_free(ent));
+  smartlist_free(entries);
+
+  return all_supported;
+}
+
+/** Helper: Given a list of proto_entry_t, return true iff
+ * <b>pr</b>=<b>ver</b> is included in that list. */
+static int
+protocol_list_contains(const smartlist_t *protos,
+                       protocol_type_t pr, uint32_t ver)
+{
+  if (BUG(protos == NULL)) {
+    return 0; // LCOV_EXCL_LINE
+  }
+  const char *pr_name = protocol_type_to_str(pr);
+  if (BUG(pr_name == NULL)) {
+    return 0; // LCOV_EXCL_LINE
+  }
+
+  SMARTLIST_FOREACH_BEGIN(protos, const proto_entry_t *, ent) {
+    if (strcasecmp(ent->name, pr_name))
+      continue;
+    /* name matches; check the ranges */
+    SMARTLIST_FOREACH_BEGIN(ent->ranges, const proto_range_t *, range) {
+      if (ver >= range->low && ver <= range->high)
+        return 1;
+    } SMARTLIST_FOREACH_END(range);
+  } SMARTLIST_FOREACH_END(ent);
+
+  return 0;
+}
+
+/** Return a string describing the protocols supported by tor version
+ * <b>version</b>, or an empty string if we cannot tell.
+ *
+ * Note that this is only used to infer protocols for Tor versions that
+ * can't declare their own.
+ **/
+/// C_RUST_COUPLED: src/rust/protover/protover.rs `compute_for_old_tor`
+const char *
+protover_compute_for_old_tor(const char *version)
+{
+  if (version == NULL) {
+    /* No known version; guess the oldest series that is still supported. */
+    version = "0.2.5.15";
+  }
+
+  if (tor_version_as_new_as(version,
+                            FIRST_TOR_VERSION_TO_ADVERTISE_PROTOCOLS)) {
+    return "";
+  } else if (tor_version_as_new_as(version, "0.2.9.1-alpha")) {
+    /* 0.2.9.1-alpha HSRend=2 */
+    return "Cons=1-2 Desc=1-2 DirCache=1 HSDir=1 HSIntro=3 HSRend=1-2 "
+      "Link=1-4 LinkAuth=1 "
+      "Microdesc=1-2 Relay=1-2";
+  } else if (tor_version_as_new_as(version, "0.2.7.5")) {
+    /* 0.2.7-stable added Desc=2, Microdesc=2, Cons=2, which indicate
+     * ed25519 support.  We'll call them present only in "stable" 027,
+     * though. */
+    return "Cons=1-2 Desc=1-2 DirCache=1 HSDir=1 HSIntro=3 HSRend=1 "
+      "Link=1-4 LinkAuth=1 "
+      "Microdesc=1-2 Relay=1-2";
+  } else if (tor_version_as_new_as(version, "0.2.4.19")) {
+    /* No currently supported Tor server versions are older than this, or
+     * lack these protocols. */
+    return "Cons=1 Desc=1 DirCache=1 HSDir=1 HSIntro=3 HSRend=1 "
+      "Link=1-4 LinkAuth=1 "
+      "Microdesc=1 Relay=1-2";
+  } else {
+    /* Cannot infer protocols. */
+    return "";
+  }
+}
+
+/**
+ * Release all storage held by static fields in protover.c
+ */
+void
+protover_free_all(void)
+{
+  if (supported_protocol_list) {
+    smartlist_t *entries = supported_protocol_list;
+    SMARTLIST_FOREACH(entries, proto_entry_t *, ent, proto_entry_free(ent));
+    smartlist_free(entries);
+    supported_protocol_list = NULL;
+  }
+}
+
+#endif /* !defined(HAVE_RUST) */
+