Merge remote-tracking branch 'tor-github/pr/699'

7 files changed, 178 insertions, 27 deletions

diff --git a/changes/ticket26698 b/changes/ticket26698
new file mode 100644
index 0000000000..6b029a1b73
--- /dev/null
+++ b/changes/ticket26698
@@ -0,0 +1,4 @@
+  o Minor features (directory authority):
+    - When a directory authority is using a bandwidth file to obtain the
+      bandwidth values, include the digest of the file in the vote.
+      Closes ticket 26698.
diff --git a/src/app/config/config.c b/src/app/config/config.c
index 8e4794315f..7734c19a04 100644
--- a/src/app/config/config.c
+++ b/src/app/config/config.c
@@ -3554,7 +3554,8 @@ options_validate(or_options_t *old_options, or_options_t *options,
              "(Bridge/V3)AuthoritativeDir is set.");
     /* If we have a v3bandwidthsfile and it's broken, complain on startup */
     if (options->V3BandwidthsFile && !old_options) {
-      dirserv_read_measured_bandwidths(options->V3BandwidthsFile, NULL, NULL);
+      dirserv_read_measured_bandwidths(options->V3BandwidthsFile, NULL, NULL,
+                                       NULL);
     }
     /* same for guardfraction file */
     if (options->GuardfractionFile && !old_options) {
diff --git a/src/feature/dirauth/bwauth.c b/src/feature/dirauth/bwauth.c
index a31050ff9c..7d7dea4dfa 100644
--- a/src/feature/dirauth/bwauth.c
+++ b/src/feature/dirauth/bwauth.c
@@ -20,6 +20,7 @@
 #include "feature/nodelist/routerinfo_st.h"
 #include "feature/nodelist/vote_routerstatus_st.h"
 
+#include "lib/crypt_ops/crypto_format.h"
 #include "lib/encoding/keyval.h"
 
 /** Total number of routers with measured bandwidth; this is set by
@@ -205,7 +206,8 @@ dirserv_get_credible_bandwidth_kb(const routerinfo_t *ri)
 int
 dirserv_read_measured_bandwidths(const char *from_file,
                                  smartlist_t *routerstatuses,
-                                 smartlist_t *bw_file_headers)
+                                 smartlist_t *bw_file_headers,
+                                 uint8_t *digest_out)
 {
   FILE *fp = tor_fopen_cloexec(from_file, "r");
   int applied_lines = 0;
@@ -219,6 +221,7 @@ dirserv_read_measured_bandwidths(const char *from_file,
   int rv = -1;
   char *line = NULL;
   size_t n = 0;
+  crypto_digest_t *digest = crypto_digest256_new(DIGEST_SHA256);
 
   /* Initialise line, so that we can't possibly run off the end. */
 
@@ -233,11 +236,14 @@ dirserv_read_measured_bandwidths(const char *from_file,
     log_warn(LD_DIRSERV, "Empty bandwidth file");
     goto err;
   }
+  /* If the line could be gotten, add it to the digest */
+  crypto_digest_add_bytes(digest, (const char *) line, strlen(line));
 
   if (!strlen(line) || line[strlen(line)-1] != '\n') {
     log_warn(LD_DIRSERV, "Long or truncated time in bandwidth file: %s",
              escaped(line));
-    goto err;
+    /* Continue adding lines to the digest. */
+    goto continue_digest;
   }
 
   line[strlen(line)-1] = '\0';
@@ -245,14 +251,14 @@ dirserv_read_measured_bandwidths(const char *from_file,
   if (!ok) {
     log_warn(LD_DIRSERV, "Non-integer time in bandwidth file: %s",
              escaped(line));
-    goto err;
+    goto continue_digest;
   }
 
-  now = time(NULL);
+  now = approx_time();
   if ((now - file_time) > MAX_MEASUREMENT_AGE) {
     log_warn(LD_DIRSERV, "Bandwidth measurement file stale. Age: %u",
              (unsigned)(time(NULL) - file_time));
-    goto err;
+    goto continue_digest;
   }
 
   /* If timestamp was correct and bw_file_headers is not NULL,
@@ -267,6 +273,7 @@ dirserv_read_measured_bandwidths(const char *from_file,
   while (!feof(fp)) {
     measured_bw_line_t parsed_line;
     if (tor_getline(&line, &n, fp) >= 0) {
+      crypto_digest_add_bytes(digest, (const char *) line, strlen(line));
       if (measured_bw_line_parse(&parsed_line, line,
                                  line_is_after_headers) != -1) {
         /* This condition will be true when the first complete valid bw line
@@ -305,6 +312,14 @@ dirserv_read_measured_bandwidths(const char *from_file,
            "Applied %d measurements.", applied_lines);
   rv = 0;
 
+ continue_digest:
+  /* Continue parsing lines to return the digest of the Bandwidth File. */
+  while (!feof(fp)) {
+    if (tor_getline(&line, &n, fp) >= 0) {
+      crypto_digest_add_bytes(digest, (const char *) line, strlen(line));
+    }
+  }
+
  err:
   if (line) {
     // we need to raw_free this buffer because we got it from tor_getdelim()
@@ -312,6 +327,9 @@ dirserv_read_measured_bandwidths(const char *from_file,
   }
   if (fp)
     fclose(fp);
+  if (digest_out)
+    crypto_digest_get_digest(digest, (char *) digest_out, DIGEST256_LEN);
+  crypto_digest_free(digest);
   return rv;
 }
 
diff --git a/src/feature/dirauth/bwauth.h b/src/feature/dirauth/bwauth.h
index 4507728458..8b7acc4a1c 100644
--- a/src/feature/dirauth/bwauth.h
+++ b/src/feature/dirauth/bwauth.h
@@ -21,8 +21,8 @@
 
 int dirserv_read_measured_bandwidths(const char *from_file,
                                      smartlist_t *routerstatuses,
-                                     smartlist_t *bw_file_headers);
-
+                                     smartlist_t *bw_file_headers,
+                                     uint8_t *digest_out);
 int dirserv_query_measured_bw_cache_kb(const char *node_id,
                                        long *bw_out,
                                        time_t *as_of_out);
diff --git a/src/feature/dirauth/dirvote.c b/src/feature/dirauth/dirvote.c
index 9587f36550..ba7b2f1de6 100644
--- a/src/feature/dirauth/dirvote.c
+++ b/src/feature/dirauth/dirvote.c
@@ -61,6 +61,9 @@
 #include "lib/encoding/confline.h"
 #include "lib/crypt_ops/crypto_format.h"
 
+/* Algorithm to use for the bandwidth file digest. */
+#define DIGEST_ALG_BW_FILE DIGEST_SHA256
+
 /**
  * \file dirvote.c
  * \brief Functions to compute directory consensus, and schedule voting.
@@ -269,6 +272,7 @@ format_networkstatus_vote(crypto_pk_t *private_signing_key,
     char *flag_thresholds = dirserv_get_flag_thresholds_line();
     char *params;
     char *bw_headers_line = NULL;
+    char *bw_file_digest = NULL;
     authority_cert_t *cert = v3_ns->cert;
     char *methods =
       make_consensus_method_list(MIN_SUPPORTED_CONSENSUS_METHOD,
@@ -308,6 +312,28 @@ format_networkstatus_vote(crypto_pk_t *private_signing_key,
       tor_free(bw_file_headers);
     }
 
+    /* Create bandwidth-file-digest if applicable.
+     * v3_ns->b64_digest_bw_file will contain the digest when V3BandwidthsFile
+     * is configured and the bandwidth file could be read, even if it was not
+     * parseable.
+     */
+    if (!tor_digest256_is_zero((const char *)v3_ns->bw_file_digest256)) {
+      /* Encode the digest. */
+      char b64_digest_bw_file[BASE64_DIGEST256_LEN+1] = {0};
+      if (digest256_to_base64(b64_digest_bw_file,
+                              (const char *)v3_ns->bw_file_digest256)>0) {
+        /* "bandwidth-file-digest" 1*(SP algorithm "=" digest) NL */
+        char *digest_algo_b64_digest_bw_file = NULL;
+        tor_asprintf(&digest_algo_b64_digest_bw_file, "%s=%s",
+                     crypto_digest_algorithm_get_name(DIGEST_ALG_BW_FILE),
+                     b64_digest_bw_file);
+        /* No need for tor_strdup(""), format_line_if_present does it. */
+        bw_file_digest = format_line_if_present(
+          "bandwidth-file-digest", digest_algo_b64_digest_bw_file);
+        tor_free(digest_algo_b64_digest_bw_file);
+      }
+    }
+
     smartlist_add_asprintf(chunks,
                  "network-status-version 3\n"
                  "vote-status %s\n"
@@ -327,6 +353,7 @@ format_networkstatus_vote(crypto_pk_t *private_signing_key,
                  "contact %s\n"
                  "%s" /* shared randomness information */
                  "%s" /* bandwidth file headers */
+                 "%s" /* bandwidth file */
                  ,
                  v3_ns->type == NS_TYPE_VOTE ? "vote" : "opinion",
                  methods,
@@ -345,7 +372,8 @@ format_networkstatus_vote(crypto_pk_t *private_signing_key,
                  shared_random_vote_str ?
                            shared_random_vote_str : "",
                  bw_headers_line ?
-                           bw_headers_line : "");
+                           bw_headers_line : "",
+                 bw_file_digest ? bw_file_digest: "");
 
     tor_free(params);
     tor_free(flags);
@@ -353,6 +381,7 @@ format_networkstatus_vote(crypto_pk_t *private_signing_key,
     tor_free(methods);
     tor_free(shared_random_vote_str);
     tor_free(bw_headers_line);
+    tor_free(bw_file_digest);
 
     if (!tor_digest_is_zero(voter->legacy_id_digest)) {
       char fpbuf[HEX_DIGEST_LEN+1];
@@ -4425,6 +4454,7 @@ dirserv_generate_networkstatus_vote_obj(crypto_pk_t *private_key,
   const int vote_on_reachability = running_long_enough_to_decide_unreachable();
   smartlist_t *microdescriptors = NULL;
   smartlist_t *bw_file_headers = NULL;
+  uint8_t bw_file_digest256[DIGEST256_LEN] = {0};
 
   tor_assert(private_key);
   tor_assert(cert);
@@ -4462,7 +4492,8 @@ dirserv_generate_networkstatus_vote_obj(crypto_pk_t *private_key,
    * set_routerstatus_from_routerinfo() see up-to-date bandwidth info.
    */
   if (options->V3BandwidthsFile) {
-    dirserv_read_measured_bandwidths(options->V3BandwidthsFile, NULL, NULL);
+    dirserv_read_measured_bandwidths(options->V3BandwidthsFile, NULL, NULL,
+                                     NULL);
   } else {
     /*
      * No bandwidths file; clear the measured bandwidth cache in case we had
@@ -4567,7 +4598,9 @@ dirserv_generate_networkstatus_vote_obj(crypto_pk_t *private_key,
     /* Only set bw_file_headers when V3BandwidthsFile is configured */
     bw_file_headers = smartlist_new();
     dirserv_read_measured_bandwidths(options->V3BandwidthsFile,
-                                     routerstatuses, bw_file_headers);
+                                     routerstatuses, bw_file_headers,
+                                     bw_file_digest256);
+
   } else {
     /*
      * No bandwidths file; clear the measured bandwidth cache in case we had
@@ -4664,6 +4697,7 @@ dirserv_generate_networkstatus_vote_obj(crypto_pk_t *private_key,
     smartlist_sort_strings(v3_out->net_params);
   }
   v3_out->bw_file_headers = bw_file_headers;
+  memcpy(v3_out->bw_file_digest256, bw_file_digest256, DIGEST256_LEN);
 
   voter = tor_malloc_zero(sizeof(networkstatus_voter_info_t));
   voter->nickname = tor_strdup(options->Nickname);
diff --git a/src/feature/nodelist/networkstatus_st.h b/src/feature/nodelist/networkstatus_st.h
index 6160f12361..5c1eea3259 100644
--- a/src/feature/nodelist/networkstatus_st.h
+++ b/src/feature/nodelist/networkstatus_st.h
@@ -99,6 +99,9 @@ struct networkstatus_t {
 
   /** List of key=value strings from the headers of the bandwidth list file */
   smartlist_t *bw_file_headers;
+
+  /** A SHA256 digest of the bandwidth file used in a vote. */
+  uint8_t bw_file_digest256[DIGEST256_LEN];
 };
 
 #endif
diff --git a/src/test/test_dir.c b/src/test/test_dir.c
index dab0b7444a..4132d42d12 100644
--- a/src/test/test_dir.c
+++ b/src/test/test_dir.c
@@ -91,6 +91,9 @@
 #ifdef HAVE_SYS_STAT_H
 #include <sys/stat.h>
 #endif
+#ifdef HAVE_UNISTD_H
+#include <unistd.h>
+#endif
 
 #define NS_MODULE dir
 
@@ -1765,7 +1768,8 @@ test_dir_dirserv_read_measured_bandwidths(void *arg)
   write_str_to_file(fname, "", 0);
   setup_capture_of_logs(LOG_WARN);
   tt_int_op(-1, OP_EQ, dirserv_read_measured_bandwidths(fname, NULL,
-                                                        bw_file_headers));
+                                                        bw_file_headers,
+                                                        NULL));
   expect_log_msg("Empty bandwidth file\n");
   teardown_capture_of_logs();
   bw_file_headers_str = smartlist_join_strings(bw_file_headers, " ", 0, NULL);
@@ -1781,7 +1785,9 @@ test_dir_dirserv_read_measured_bandwidths(void *arg)
   write_str_to_file(fname, content, 0);
   tor_free(content);
   tt_int_op(-1, OP_EQ, dirserv_read_measured_bandwidths(fname, NULL,
-                                                        bw_file_headers));
+                                                        bw_file_headers,
+                                                        NULL));
+
   bw_file_headers_str = smartlist_join_strings(bw_file_headers, " ", 0, NULL);
   tt_str_op("", OP_EQ, bw_file_headers_str);
   SMARTLIST_FOREACH(bw_file_headers, char *, c, tor_free(c));
@@ -1792,7 +1798,9 @@ test_dir_dirserv_read_measured_bandwidths(void *arg)
   write_str_to_file(fname, header_lines_v100, 0);
   bw_file_headers = smartlist_new();
   tt_int_op(0, OP_EQ, dirserv_read_measured_bandwidths(fname, NULL,
-                                                       bw_file_headers));
+                                                       bw_file_headers,
+                                                       NULL));
+
   bw_file_headers_str = smartlist_join_strings(bw_file_headers, " ", 0, NULL);
   tt_str_op(bw_file_headers_str_v100, OP_EQ, bw_file_headers_str);
   SMARTLIST_FOREACH(bw_file_headers, char *, c, tor_free(c));
@@ -1805,7 +1813,9 @@ test_dir_dirserv_read_measured_bandwidths(void *arg)
   write_str_to_file(fname, content, 0);
   tor_free(content);
   tt_int_op(0, OP_EQ, dirserv_read_measured_bandwidths(fname, NULL,
-                                                       bw_file_headers));
+                                                       bw_file_headers,
+                                                       NULL));
+
   bw_file_headers_str = smartlist_join_strings(bw_file_headers, " ", 0, NULL);
   tt_str_op(bw_file_headers_str_v100, OP_EQ, bw_file_headers_str);
   SMARTLIST_FOREACH(bw_file_headers, char *, c, tor_free(c));
@@ -1816,7 +1826,8 @@ test_dir_dirserv_read_measured_bandwidths(void *arg)
   tor_asprintf(&content, "%s%s", header_lines_v100, relay_lines_v100);
   write_str_to_file(fname, content, 0);
   tor_free(content);
-  tt_int_op(0, OP_EQ, dirserv_read_measured_bandwidths(fname, NULL, NULL));
+  tt_int_op(0, OP_EQ, dirserv_read_measured_bandwidths(fname, NULL, NULL,
+                                                       NULL));
 
   /* Test bandwidth file including v1.1.0 bandwidth headers and
    * v1.0.0 relay lines. bw_file_headers will contain the v1.1.0 headers. */
@@ -1826,7 +1837,9 @@ test_dir_dirserv_read_measured_bandwidths(void *arg)
   write_str_to_file(fname, content, 0);
   tor_free(content);
   tt_int_op(0, OP_EQ, dirserv_read_measured_bandwidths(fname, NULL,
-                                                       bw_file_headers));
+                                                       bw_file_headers,
+                                                       NULL));
+
   bw_file_headers_str = smartlist_join_strings(bw_file_headers, " ", 0, NULL);
   tt_str_op(bw_file_headers_str_v110, OP_EQ, bw_file_headers_str);
   SMARTLIST_FOREACH(bw_file_headers, char *, c, tor_free(c));
@@ -1842,7 +1855,9 @@ test_dir_dirserv_read_measured_bandwidths(void *arg)
   write_str_to_file(fname, content, 0);
   tor_free(content);
   tt_int_op(0, OP_EQ, dirserv_read_measured_bandwidths(fname, NULL,
-                                                       bw_file_headers));
+                                                       bw_file_headers,
+                                                       NULL));
+
   bw_file_headers_str = smartlist_join_strings(bw_file_headers, " ", 0, NULL);
   tt_str_op(bw_file_headers_str_v100, OP_EQ, bw_file_headers_str);
   SMARTLIST_FOREACH(bw_file_headers, char *, c, tor_free(c));
@@ -1859,7 +1874,9 @@ test_dir_dirserv_read_measured_bandwidths(void *arg)
   write_str_to_file(fname, content, 0);
   tor_free(content);
   tt_int_op(0, OP_EQ, dirserv_read_measured_bandwidths(fname, NULL,
-                                                       bw_file_headers));
+                                                       bw_file_headers,
+                                                       NULL));
+
   bw_file_headers_str = smartlist_join_strings(bw_file_headers, " ", 0, NULL);
   tt_str_op(bw_file_headers_str_v100, OP_EQ, bw_file_headers_str);
   SMARTLIST_FOREACH(bw_file_headers, char *, c, tor_free(c));
@@ -1870,7 +1887,9 @@ test_dir_dirserv_read_measured_bandwidths(void *arg)
   bw_file_headers = smartlist_new();
   write_str_to_file(fname, header_lines_v110_no_terminator, 0);
   tt_int_op(0, OP_EQ, dirserv_read_measured_bandwidths(fname, NULL,
-                                                       bw_file_headers));
+                                                       bw_file_headers,
+                                                       NULL));
+
   bw_file_headers_str = smartlist_join_strings(bw_file_headers, " ", 0, NULL);
   tt_str_op(bw_file_headers_str_v110, OP_EQ, bw_file_headers_str);
   SMARTLIST_FOREACH(bw_file_headers, char *, c, tor_free(c));
@@ -1881,7 +1900,9 @@ test_dir_dirserv_read_measured_bandwidths(void *arg)
   bw_file_headers = smartlist_new();
   write_str_to_file(fname, header_lines_v110, 0);
   tt_int_op(0, OP_EQ, dirserv_read_measured_bandwidths(fname, NULL,
-                                                       bw_file_headers));
+                                                       bw_file_headers,
+                                                       NULL));
+
   bw_file_headers_str = smartlist_join_strings(bw_file_headers, " ", 0, NULL);
   tt_str_op(bw_file_headers_str_v110, OP_EQ, bw_file_headers_str);
   SMARTLIST_FOREACH(bw_file_headers, char *, c, tor_free(c));
@@ -1896,7 +1917,9 @@ test_dir_dirserv_read_measured_bandwidths(void *arg)
   write_str_to_file(fname, content, 0);
   tor_free(content);
   tt_int_op(0, OP_EQ, dirserv_read_measured_bandwidths(fname, NULL,
-                                                       bw_file_headers));
+                                                       bw_file_headers,
+                                                       NULL));
+
   bw_file_headers_str = smartlist_join_strings(bw_file_headers, " ", 0, NULL);
   tt_str_op(bw_file_headers_str_v110, OP_EQ, bw_file_headers_str);
   SMARTLIST_FOREACH(bw_file_headers, char *, c, tor_free(c));
@@ -1911,7 +1934,9 @@ test_dir_dirserv_read_measured_bandwidths(void *arg)
   write_str_to_file(fname, content, 0);
   tor_free(content);
   tt_int_op(0, OP_EQ, dirserv_read_measured_bandwidths(fname, NULL,
-                                                       bw_file_headers));
+                                                       bw_file_headers,
+                                                       NULL));
+
   bw_file_headers_str = smartlist_join_strings(bw_file_headers, " ", 0, NULL);
   tt_str_op(bw_file_headers_str_v110, OP_EQ, bw_file_headers_str);
   SMARTLIST_FOREACH(bw_file_headers, char *, c, tor_free(c));
@@ -1927,7 +1952,9 @@ test_dir_dirserv_read_measured_bandwidths(void *arg)
   write_str_to_file(fname, content, 0);
   tor_free(content);
   tt_int_op(0, OP_EQ, dirserv_read_measured_bandwidths(fname, NULL,
-                                                       bw_file_headers));
+                                                       bw_file_headers,
+                                                       NULL));
+
   bw_file_headers_str = smartlist_join_strings(bw_file_headers, " ", 0, NULL);
   tt_str_op(bw_file_headers_str_v110, OP_EQ, bw_file_headers_str);
   SMARTLIST_FOREACH(bw_file_headers, char *, c, tor_free(c));
@@ -1944,7 +1971,9 @@ test_dir_dirserv_read_measured_bandwidths(void *arg)
   write_str_to_file(fname, content, 0);
   tor_free(content);
   tt_int_op(0, OP_EQ, dirserv_read_measured_bandwidths(fname, NULL,
-                                                       bw_file_headers));
+                                                       bw_file_headers,
+                                                       NULL));
+
   bw_file_headers_str = smartlist_join_strings(bw_file_headers, " ", 0, NULL);
   tt_str_op(bw_file_headers_str_bad, OP_EQ, bw_file_headers_str);
   SMARTLIST_FOREACH(bw_file_headers, char *, c, tor_free(c));
@@ -1962,7 +1991,9 @@ test_dir_dirserv_read_measured_bandwidths(void *arg)
   write_str_to_file(fname, content, 0);
   tor_free(content);
   tt_int_op(0, OP_EQ, dirserv_read_measured_bandwidths(fname, NULL,
-                                                       bw_file_headers));
+                                                       bw_file_headers,
+                                                       NULL));
+
   tt_int_op(MAX_BW_FILE_HEADER_COUNT_IN_VOTE, OP_EQ,
             smartlist_len(bw_file_headers));
   bw_file_headers_str = smartlist_join_strings(bw_file_headers, " ", 0, NULL);
@@ -1983,7 +2014,9 @@ test_dir_dirserv_read_measured_bandwidths(void *arg)
   write_str_to_file(fname, content, 0);
   tor_free(content);
   tt_int_op(0, OP_EQ, dirserv_read_measured_bandwidths(fname, NULL,
-                                                       bw_file_headers));
+                                                       bw_file_headers,
+                                                       NULL));
+
   tt_int_op(MAX_BW_FILE_HEADER_COUNT_IN_VOTE, OP_EQ,
             smartlist_len(bw_file_headers));
   /* force bw_file_headers to be bigger than
@@ -1997,6 +2030,7 @@ test_dir_dirserv_read_measured_bandwidths(void *arg)
   tor_free(bw_file_headers_str);
 
  done:
+  unlink(fname);
   tor_free(fname);
   tor_free(header_lines_v100);
   tor_free(header_lines_v110_no_terminator);
@@ -3830,6 +3864,62 @@ mock_get_options(void)
   return mock_options;
 }
 
+/**
+ * Test dirauth_get_b64_digest_bw_file.
+ * This function should be near the other bwauth functions, but it needs
+ * mock_get_options, that is only defined here.
+ */
+
+static void
+test_dir_bwauth_bw_file_digest256(void *arg)
+{
+  (void)arg;
+  const char *content =
+    "1541171221\n"
+    "node_id=$68A483E05A2ABDCA6DA5A3EF8DB5177638A27F80 "
+    "master_key_ed25519=YaqV4vbvPYKucElk297eVdNArDz9HtIwUoIeo0+cVIpQ "
+    "bw=760 nick=Test time=2018-05-08T16:13:26\n";
+
+  char *fname = tor_strdup(get_fname("V3BandwidthsFile"));
+  /* Initialize to a wrong digest. */
+  uint8_t digest[DIGEST256_LEN] = "01234567890123456789abcdefghijkl";
+
+  /* Digest of an empty string. Initialize to a wrong digest. */
+  char digest_empty_str[DIGEST256_LEN] = "01234567890123456789abcdefghijkl";
+  crypto_digest256(digest_empty_str, "", 0, DIGEST_SHA256);
+
+  /* Digest of the content. Initialize to a wrong digest. */
+  char digest_expected[DIGEST256_LEN] = "01234567890123456789abcdefghijkl";
+  crypto_digest256(digest_expected, content, strlen(content), DIGEST_SHA256);
+
+  /* When the bandwidth file can not be found. */
+  tt_int_op(-1, OP_EQ,
+            dirserv_read_measured_bandwidths(fname,
+                                             NULL, NULL, digest));
+  tt_mem_op(digest, OP_EQ, digest_empty_str, DIGEST256_LEN);
+
+  /* When there is a timestamp but it is too old. */
+  write_str_to_file(fname, content, 0);
+  tt_int_op(-1, OP_EQ,
+            dirserv_read_measured_bandwidths(fname,
+                                             NULL, NULL, digest));
+  /* The digest will be correct. */
+  tt_mem_op(digest, OP_EQ, digest_expected, DIGEST256_LEN);
+
+  update_approx_time(1541171221);
+
+  /* When there is a bandwidth file and it can be read. */
+  tt_int_op(0, OP_EQ,
+            dirserv_read_measured_bandwidths(fname,
+                                             NULL, NULL, digest));
+  tt_mem_op(digest, OP_EQ, digest_expected, DIGEST256_LEN);
+
+ done:
+  unlink(fname);
+  tor_free(fname);
+  update_approx_time(time(NULL));
+}
+
 static void
 reset_routerstatus(routerstatus_t *rs,
                    const char *hex_identity_digest,
@@ -6411,6 +6501,7 @@ struct testcase_t dir_tests[] = {
   DIR_LEGACY(measured_bw_kb_line_is_after_headers),
   DIR_LEGACY(measured_bw_kb_cache),
   DIR_LEGACY(dirserv_read_measured_bandwidths),
+  DIR(bwauth_bw_file_digest256, 0),
   DIR_LEGACY(param_voting),
   DIR(param_voting_lookup, 0),
   DIR_LEGACY(v3_networkstatus),