commit 3287cae68c8e6f2f72967bf6fb07e601792ecd2c
Merge: a57e168ca 669ec6432
Author: teor <teor(a)torproject.org>
Date: Mon Aug 12 09:38:46 2019 +1000
Merge remote-tracking branch 'tor-github/pr/848' into maint-0.3.5
changes/cid1444119 | 3 +++
src/feature/dircommon/consdiff.c | 2 +-
2 files changed, 4 insertions(+), 1 deletion(-)
diff --cc src/feature/dircommon/consdiff.c
index 785205cb6,000000000..d0f7594ce
mode 100644,000000..100644
--- a/src/feature/dircommon/consdiff.c
+++ b/src/feature/dircommon/consdiff.c
@@@ -1,1414 -1,0 +1,1414 @@@
+/* Copyright (c) 2014, Daniel Martí
+ * Copyright (c) 2014-2019, The Tor Project, Inc. */
+/* See LICENSE for licensing information */
+
+/**
+ * \file consdiff.c
+ * \brief Consensus diff implementation, including both the generation and the
+ * application of diffs in a minimal ed format.
+ *
+ * The consensus diff application is done in consdiff_apply_diff, which relies
+ * on apply_ed_diff for the main ed diff part and on some digest helper
+ * functions to check the digest hashes found in the consensus diff header.
+ *
+ * The consensus diff generation is more complex. consdiff_gen_diff generates
+ * it, relying on gen_ed_diff to generate the ed diff and some digest helper
+ * functions to generate the digest hashes.
+ *
+ * gen_ed_diff is the tricky bit. In it simplest form, it will take quadratic
+ * time and linear space to generate an ed diff given two smartlists. As shown
+ * in its comment section, calling calc_changes on the entire two consensuses
+ * will calculate what is to be added and what is to be deleted in the diff.
+ * Its comment section briefly explains how it works.
+ *
+ * In our case specific to consensuses, we take advantage of the fact that
+ * consensuses list routers sorted by their identities. We use that
+ * information to avoid running calc_changes on the whole smartlists.
+ * gen_ed_diff will navigate through the two consensuses identity by identity
+ * and will send small couples of slices to calc_changes, keeping the running
+ * time near-linear. This is explained in more detail in the gen_ed_diff
+ * comments.
+ *
+ * The allocation strategy tries to save time and memory by avoiding needless
+ * copies. Instead of actually splitting the inputs into separate strings, we
+ * allocate cdline_t objects, each of which represents a line in the original
+ * object or in the output. We use memarea_t allocators to manage the
+ * temporary memory we use when generating or applying diffs.
+ **/
+
+#define CONSDIFF_PRIVATE
+
+#include "core/or/or.h"
+#include "feature/dircommon/consdiff.h"
+#include "lib/memarea/memarea.h"
+#include "feature/dirparse/ns_parse.h"
+
+static const char* ns_diff_version = "network-status-diff-version 1";
+static const char* hash_token = "hash";
+
+static char *consensus_join_lines(const smartlist_t *inp);
+
+/** Return true iff a and b have the same contents. */
+STATIC int
+lines_eq(const cdline_t *a, const cdline_t *b)
+{
+ return a->len == b->len && fast_memeq(a->s, b->s, a->len);
+}
+
+/** Return true iff a has the same contents as the nul-terminated string b. */
+STATIC int
+line_str_eq(const cdline_t *a, const char *b)
+{
+ const size_t len = strlen(b);
+ tor_assert(len <= UINT32_MAX);
+ cdline_t bline = { b, (uint32_t)len };
+ return lines_eq(a, &bline);
+}
+
+/** Return true iff a begins with the same contents as the nul-terminated
+ * string b. */
+static int
+line_starts_with_str(const cdline_t *a, const char *b)
+{
+ const size_t len = strlen(b);
+ tor_assert(len <= UINT32_MAX);
+ return a->len >= len && fast_memeq(a->s, b, len);
+}
+
+/** Return a new cdline_t holding as its contents the nul-terminated
+ * string s. Use the provided memory area for storage. */
+static cdline_t *
+cdline_linecpy(memarea_t *area, const char *s)
+{
+ size_t len = strlen(s);
+ const char *ss = memarea_memdup(area, s, len);
+ cdline_t *line = memarea_alloc(area, sizeof(cdline_t));
+ line->s = ss;
+ line->len = (uint32_t)len;
+ return line;
+}
+
+/** Add a cdline_t to <b>lst</b> holding as its contents the nul-terminated
+ * string s. Use the provided memory area for storage. */
+STATIC void
+smartlist_add_linecpy(smartlist_t *lst, memarea_t *area, const char *s)
+{
+ smartlist_add(lst, cdline_linecpy(area, s));
+}
+
+/** Compute the digest of <b>cons</b>, and store the result in
+ * <b>digest_out</b>. Return 0 on success, -1 on failure. */
+/* This is a separate, mockable function so that we can override it when
+ * fuzzing. */
+MOCK_IMPL(STATIC int,
+consensus_compute_digest,(const char *cons,
+ consensus_digest_t *digest_out))
+{
+ int r = crypto_digest256((char*)digest_out->sha3_256,
+ cons, strlen(cons), DIGEST_SHA3_256);
+ return r;
+}
+
+/** Compute the digest-as-signed of <b>cons</b>, and store the result in
+ * <b>digest_out</b>. Return 0 on success, -1 on failure. */
+/* This is a separate, mockable function so that we can override it when
+ * fuzzing. */
+MOCK_IMPL(STATIC int,
+consensus_compute_digest_as_signed,(const char *cons,
+ consensus_digest_t *digest_out))
+{
+ return router_get_networkstatus_v3_sha3_as_signed(digest_out->sha3_256,
+ cons);
+}
+
+/** Return true iff <b>d1</b> and <b>d2</b> contain the same digest */
+/* This is a separate, mockable function so that we can override it when
+ * fuzzing. */
+MOCK_IMPL(STATIC int,
+consensus_digest_eq,(const uint8_t *d1,
+ const uint8_t *d2))
+{
+ return fast_memeq(d1, d2, DIGEST256_LEN);
+}
+
+/** Create (allocate) a new slice from a smartlist. Assumes that the start
+ * and the end indexes are within the bounds of the initial smartlist. The end
+ * element is not part of the resulting slice. If end is -1, the slice is to
+ * reach the end of the smartlist.
+ */
+STATIC smartlist_slice_t *
+smartlist_slice(const smartlist_t *list, int start, int end)
+{
+ int list_len = smartlist_len(list);
+ tor_assert(start >= 0);
+ tor_assert(start <= list_len);
+ if (end == -1) {
+ end = list_len;
+ }
+ tor_assert(start <= end);
+
+ smartlist_slice_t *slice = tor_malloc(sizeof(smartlist_slice_t));
+ slice->list = list;
+ slice->offset = start;
+ slice->len = end - start;
+ return slice;
+}
+
+/** Helper: Compute the longest common subsequence lengths for the two slices.
+ * Used as part of the diff generation to find the column at which to split
+ * slice2 while still having the optimal solution.
+ * If direction is -1, the navigation is reversed. Otherwise it must be 1.
+ * The length of the resulting integer array is that of the second slice plus
+ * one.
+ */
+STATIC int *
+lcs_lengths(const smartlist_slice_t *slice1, const smartlist_slice_t *slice2,
+ int direction)
+{
+ size_t a_size = sizeof(int) * (slice2->len+1);
+
+ /* Resulting lcs lengths. */
+ int *result = tor_malloc_zero(a_size);
+ /* Copy of the lcs lengths from the last iteration. */
+ int *prev = tor_malloc(a_size);
+
+ tor_assert(direction == 1 || direction == -1);
+
+ int si = slice1->offset;
+ if (direction == -1) {
+ si += (slice1->len-1);
+ }
+
+ for (int i = 0; i < slice1->len; ++i, si+=direction) {
+
+ const cdline_t *line1 = smartlist_get(slice1->list, si);
+ /* Store the last results. */
+ memcpy(prev, result, a_size);
+
+ int sj = slice2->offset;
+ if (direction == -1) {
+ sj += (slice2->len-1);
+ }
+
+ for (int j = 0; j < slice2->len; ++j, sj+=direction) {
+
+ const cdline_t *line2 = smartlist_get(slice2->list, sj);
+ if (lines_eq(line1, line2)) {
+ /* If the lines are equal, the lcs is one line longer. */
+ result[j + 1] = prev[j] + 1;
+ } else {
+ /* If not, see what lcs parent path is longer. */
+ result[j + 1] = MAX(result[j], prev[j + 1]);
+ }
+ }
+ }
+ tor_free(prev);
+ return result;
+}
+
+/** Helper: Trim any number of lines that are equally at the start or the end
+ * of both slices.
+ */
+STATIC void
+trim_slices(smartlist_slice_t *slice1, smartlist_slice_t *slice2)
+{
+ while (slice1->len>0 && slice2->len>0) {
+ const cdline_t *line1 = smartlist_get(slice1->list, slice1->offset);
+ const cdline_t *line2 = smartlist_get(slice2->list, slice2->offset);
+ if (!lines_eq(line1, line2)) {
+ break;
+ }
+ slice1->offset++; slice1->len--;
+ slice2->offset++; slice2->len--;
+ }
+
+ int i1 = (slice1->offset+slice1->len)-1;
+ int i2 = (slice2->offset+slice2->len)-1;
+
+ while (slice1->len>0 && slice2->len>0) {
+ const cdline_t *line1 = smartlist_get(slice1->list, i1);
+ const cdline_t *line2 = smartlist_get(slice2->list, i2);
+ if (!lines_eq(line1, line2)) {
+ break;
+ }
+ i1--;
+ slice1->len--;
+ i2--;
+ slice2->len--;
+ }
+}
+
+/** Like smartlist_string_pos, but uses a cdline_t, and is restricted to the
+ * bounds of the slice.
+ */
+STATIC int
+smartlist_slice_string_pos(const smartlist_slice_t *slice,
+ const cdline_t *string)
+{
+ int end = slice->offset + slice->len;
+ for (int i = slice->offset; i < end; ++i) {
+ const cdline_t *el = smartlist_get(slice->list, i);
+ if (lines_eq(el, string)) {
+ return i;
+ }
+ }
+ return -1;
+}
+
+/** Helper: Set all the appropriate changed booleans to true. The first slice
+ * must be of length 0 or 1. All the lines of slice1 and slice2 which are not
+ * present in the other slice will be set to changed in their bool array.
+ * The two changed bool arrays are passed in the same order as the slices.
+ */
+STATIC void
+set_changed(bitarray_t *changed1, bitarray_t *changed2,
+ const smartlist_slice_t *slice1, const smartlist_slice_t *slice2)
+{
+ int toskip = -1;
+ tor_assert(slice1->len == 0 || slice1->len == 1);
+
+ if (slice1->len == 1) {
+ const cdline_t *line_common = smartlist_get(slice1->list, slice1->offset);
+ toskip = smartlist_slice_string_pos(slice2, line_common);
+ if (toskip == -1) {
+ bitarray_set(changed1, slice1->offset);
+ }
+ }
+ int end = slice2->offset + slice2->len;
+ for (int i = slice2->offset; i < end; ++i) {
+ if (i != toskip) {
+ bitarray_set(changed2, i);
+ }
+ }
+}
+
+/*
+ * Helper: Given that slice1 has been split by half into top and bot, we want
+ * to fetch the column at which to split slice2 so that we are still on track
+ * to the optimal diff solution, i.e. the shortest one. We use lcs_lengths
+ * since the shortest diff is just another way to say the longest common
+ * subsequence.
+ */
+static int
+optimal_column_to_split(const smartlist_slice_t *top,
+ const smartlist_slice_t *bot,
+ const smartlist_slice_t *slice2)
+{
+ int *lens_top = lcs_lengths(top, slice2, 1);
+ int *lens_bot = lcs_lengths(bot, slice2, -1);
+ int column=0, max_sum=-1;
+
+ for (int i = 0; i < slice2->len+1; ++i) {
+ int sum = lens_top[i] + lens_bot[slice2->len-i];
+ if (sum > max_sum) {
+ column = i;
+ max_sum = sum;
+ }
+ }
+ tor_free(lens_top);
+ tor_free(lens_bot);
+
+ return column;
+}
+
+/**
+ * Helper: Figure out what elements are new or gone on the second smartlist
+ * relative to the first smartlist, and store the booleans in the bitarrays.
+ * True on the first bitarray means the element is gone, true on the second
+ * bitarray means it's new.
+ *
+ * In its base case, either of the smartlists is of length <= 1 and we can
+ * quickly see what elements are new or are gone. In the other case, we will
+ * split one smartlist by half and we'll use optimal_column_to_split to find
+ * the optimal column at which to split the second smartlist so that we are
+ * finding the smallest diff possible.
+ */
+STATIC void
+calc_changes(smartlist_slice_t *slice1,
+ smartlist_slice_t *slice2,
+ bitarray_t *changed1, bitarray_t *changed2)
+{
+ trim_slices(slice1, slice2);
+
+ if (slice1->len <= 1) {
+ set_changed(changed1, changed2, slice1, slice2);
+
+ } else if (slice2->len <= 1) {
+ set_changed(changed2, changed1, slice2, slice1);
+
+ /* Keep on splitting the slices in two. */
+ } else {
+ smartlist_slice_t *top, *bot, *left, *right;
+
+ /* Split the first slice in half. */
+ int mid = slice1->len/2;
+ top = smartlist_slice(slice1->list, slice1->offset, slice1->offset+mid);
+ bot = smartlist_slice(slice1->list, slice1->offset+mid,
+ slice1->offset+slice1->len);
+
+ /* Split the second slice by the optimal column. */
+ int mid2 = optimal_column_to_split(top, bot, slice2);
+ left = smartlist_slice(slice2->list, slice2->offset, slice2->offset+mid2);
+ right = smartlist_slice(slice2->list, slice2->offset+mid2,
+ slice2->offset+slice2->len);
+
+ calc_changes(top, left, changed1, changed2);
+ calc_changes(bot, right, changed1, changed2);
+ tor_free(top);
+ tor_free(bot);
+ tor_free(left);
+ tor_free(right);
+ }
+}
+
+/* This table is from crypto.c. The SP and PAD defines are different. */
+#define NOT_VALID_BASE64 255
+#define X NOT_VALID_BASE64
+#define SP NOT_VALID_BASE64
+#define PAD NOT_VALID_BASE64
+static const uint8_t base64_compare_table[256] = {
+ X, X, X, X, X, X, X, X, X, SP, SP, SP, X, SP, X, X,
+ X, X, X, X, X, X, X, X, X, X, X, X, X, X, X, X,
+ SP, X, X, X, X, X, X, X, X, X, X, 62, X, X, X, 63,
+ 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, X, X, X, PAD, X, X,
+ X, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14,
+ 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, X, X, X, X, X,
+ X, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40,
+ 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, X, X, X, X, X,
+ X, X, X, X, X, X, X, X, X, X, X, X, X, X, X, X,
+ X, X, X, X, X, X, X, X, X, X, X, X, X, X, X, X,
+ X, X, X, X, X, X, X, X, X, X, X, X, X, X, X, X,
+ X, X, X, X, X, X, X, X, X, X, X, X, X, X, X, X,
+ X, X, X, X, X, X, X, X, X, X, X, X, X, X, X, X,
+ X, X, X, X, X, X, X, X, X, X, X, X, X, X, X, X,
+ X, X, X, X, X, X, X, X, X, X, X, X, X, X, X, X,
+ X, X, X, X, X, X, X, X, X, X, X, X, X, X, X, X,
+};
+
+/** Helper: Get the identity hash from a router line, assuming that the line
+ * at least appears to be a router line and thus starts with "r ".
+ *
+ * If an identity hash is found, store it (without decoding it) in
+ * <b>hash_out</b>, and return 0. On failure, return -1.
+ */
+STATIC int
+get_id_hash(const cdline_t *line, cdline_t *hash_out)
+{
+ if (line->len < 2)
+ return -1;
+
+ /* Skip the router name. */
+ const char *hash = memchr(line->s + 2, ' ', line->len - 2);
+ if (!hash) {
+ return -1;
+ }
+
+ hash++;
+ const char *hash_end = hash;
+ /* Stop when the first non-base64 character is found. Use unsigned chars to
+ * avoid negative indexes causing crashes.
+ */
+ while (base64_compare_table[*((unsigned char*)hash_end)]
+ != NOT_VALID_BASE64 &&
+ hash_end < line->s + line->len) {
+ hash_end++;
+ }
+
+ /* Empty hash. */
+ if (hash_end == hash) {
+ return -1;
+ }
+
+ hash_out->s = hash;
+ /* Always true because lines are limited to this length */
+ tor_assert(hash_end >= hash);
+ tor_assert((size_t)(hash_end - hash) <= UINT32_MAX);
+ hash_out->len = (uint32_t)(hash_end - hash);
+
+ return 0;
+}
+
+/** Helper: Check that a line is a valid router entry. We must at least be
+ * able to fetch a proper identity hash from it for it to be valid.
+ */
+STATIC int
+is_valid_router_entry(const cdline_t *line)
+{
+ if (line->len < 2 || fast_memneq(line->s, "r ", 2))
+ return 0;
+ cdline_t tmp;
+ return (get_id_hash(line, &tmp) == 0);
+}
+
+/** Helper: Find the next router line starting at the current position.
+ * Assumes that cur is lower than the length of the smartlist, i.e. it is a
+ * line within the bounds of the consensus. The only exception is when we
+ * don't want to skip the first line, in which case cur will be -1.
+ */
+STATIC int
+next_router(const smartlist_t *cons, int cur)
+{
+ int len = smartlist_len(cons);
+ tor_assert(cur >= -1 && cur < len);
+
+ if (++cur >= len) {
+ return len;
+ }
+
+ const cdline_t *line = smartlist_get(cons, cur);
+ while (!is_valid_router_entry(line)) {
+ if (++cur >= len) {
+ return len;
+ }
+ line = smartlist_get(cons, cur);
+ }
+ return cur;
+}
+
+/** Helper: compare two base64-encoded identity hashes, which may be of
+ * different lengths. Comparison ends when the first non-base64 char is found.
+ */
+STATIC int
+base64cmp(const cdline_t *hash1, const cdline_t *hash2)
+{
+ /* NULL is always lower, useful for last_hash which starts at NULL. */
+ if (!hash1->s && !hash2->s) {
+ return 0;
+ }
+ if (!hash1->s) {
+ return -1;
+ }
+ if (!hash2->s) {
+ return 1;
+ }
+
+ /* Don't index with a char; char may be signed. */
+ const unsigned char *a = (unsigned char*)hash1->s;
+ const unsigned char *b = (unsigned char*)hash2->s;
+ const unsigned char *a_end = a + hash1->len;
+ const unsigned char *b_end = b + hash2->len;
+ while (1) {
+ uint8_t av = base64_compare_table[*a];
+ uint8_t bv = base64_compare_table[*b];
+ if (av == NOT_VALID_BASE64) {
+ if (bv == NOT_VALID_BASE64) {
+ /* Both ended with exactly the same characters. */
+ return 0;
+ } else {
+ /* hash2 goes on longer than hash1 and thus hash1 is lower. */
+ return -1;
+ }
+ } else if (bv == NOT_VALID_BASE64) {
+ /* hash1 goes on longer than hash2 and thus hash1 is greater. */
+ return 1;
+ } else if (av < bv) {
+ /* The first difference shows that hash1 is lower. */
+ return -1;
+ } else if (av > bv) {
+ /* The first difference shows that hash1 is greater. */
+ return 1;
+ } else {
+ a++;
+ b++;
+ if (a == a_end) {
+ if (b == b_end) {
+ return 0;
+ } else {
+ return -1;
+ }
+ } else if (b == b_end) {
+ return 1;
+ }
+ }
+ }
+}
+
+/** Structure used to remember the previous and current identity hash of
+ * the "r " lines in a consensus, to enforce well-ordering. */
+typedef struct router_id_iterator_t {
+ cdline_t last_hash;
+ cdline_t hash;
+} router_id_iterator_t;
+
+/**
+ * Initializer for a router_id_iterator_t.
+ */
+#define ROUTER_ID_ITERATOR_INIT { { NULL, 0 }, { NULL, 0 } }
+
+/** Given an index *<b>idxp</b> into the consensus at <b>cons</b>, advance
+ * the index to the next router line ("r ...") in the consensus, or to
+ * an index one after the end of the list if there is no such line.
+ *
+ * Use <b>iter</b> to record the hash of the found router line, if any,
+ * and to enforce ordering on the hashes. If the hashes are mis-ordered,
+ * return -1. Else, return 0.
+ **/
+static int
+find_next_router_line(const smartlist_t *cons,
+ const char *consname,
+ int *idxp,
+ router_id_iterator_t *iter)
+{
+ *idxp = next_router(cons, *idxp);
+ if (*idxp < smartlist_len(cons)) {
+ memcpy(&iter->last_hash, &iter->hash, sizeof(cdline_t));
+ if (get_id_hash(smartlist_get(cons, *idxp), &iter->hash) < 0 ||
+ base64cmp(&iter->hash, &iter->last_hash) <= 0) {
+ log_warn(LD_CONSDIFF, "Refusing to generate consensus diff because "
+ "the %s consensus doesn't have its router entries sorted "
+ "properly.", consname);
+ return -1;
+ }
+ }
+ return 0;
+}
+
+/** Line-prefix indicating the beginning of the signatures section that we
+ * intend to delete. */
+#define START_OF_SIGNATURES_SECTION "directory-signature "
+
+/** Pre-process a consensus in <b>cons</b> (represented as a list of cdline_t)
+ * to remove the signatures from it. If the footer is removed, return a
+ * cdline_t containing a delete command to delete the footer, allocated in
+ * <b>area</>. If no footer is removed, return NULL.
+ *
+ * We remove the signatures here because they are not themselves signed, and
+ * as such there might be different encodings for them.
+ */
+static cdline_t *
+preprocess_consensus(memarea_t *area,
+ smartlist_t *cons)
+{
+ int idx;
+ int dirsig_idx = -1;
+ for (idx = 0; idx < smartlist_len(cons); ++idx) {
+ cdline_t *line = smartlist_get(cons, idx);
+ if (line_starts_with_str(line, START_OF_SIGNATURES_SECTION)) {
+ dirsig_idx = idx;
+ break;
+ }
+ }
+ if (dirsig_idx >= 0) {
+ char buf[64];
+ while (smartlist_len(cons) > dirsig_idx)
+ smartlist_del(cons, dirsig_idx);
+ tor_snprintf(buf, sizeof(buf), "%d,$d", dirsig_idx+1);
+ return cdline_linecpy(area, buf);
+ } else {
+ return NULL;
+ }
+}
+
+/** Generate an ed diff as a smartlist from two consensuses, also given as
+ * smartlists. Will return NULL if the diff could not be generated, which can
+ * happen if any lines the script had to add matched "." or if the routers
+ * were not properly ordered.
+ *
+ * All cdline_t objects in the resulting object are either references to lines
+ * in one of the inputs, or are newly allocated lines in the provided memarea.
+ *
+ * This implementation is consensus-specific. To generate an ed diff for any
+ * given input in quadratic time, you can replace all the code until the
+ * navigation in reverse order with the following:
+ *
+ * int len1 = smartlist_len(cons1);
+ * int len2 = smartlist_len(cons2);
+ * bitarray_t *changed1 = bitarray_init_zero(len1);
+ * bitarray_t *changed2 = bitarray_init_zero(len2);
+ * cons1_sl = smartlist_slice(cons1, 0, -1);
+ * cons2_sl = smartlist_slice(cons2, 0, -1);
+ * calc_changes(cons1_sl, cons2_sl, changed1, changed2);
+ */
+STATIC smartlist_t *
+gen_ed_diff(const smartlist_t *cons1_orig, const smartlist_t *cons2,
+ memarea_t *area)
+{
+ smartlist_t *cons1 = smartlist_new();
+ smartlist_add_all(cons1, cons1_orig);
+ cdline_t *remove_trailer = preprocess_consensus(area, cons1);
+
+ int len1 = smartlist_len(cons1);
+ int len2 = smartlist_len(cons2);
+ smartlist_t *result = smartlist_new();
+
+ if (remove_trailer) {
+ /* There's a delete-the-trailer line at the end, so add it here. */
+ smartlist_add(result, remove_trailer);
+ }
+
+ /* Initialize the changed bitarrays to zero, so that calc_changes only needs
+ * to set the ones that matter and leave the rest untouched.
+ */
+ bitarray_t *changed1 = bitarray_init_zero(len1);
+ bitarray_t *changed2 = bitarray_init_zero(len2);
+ int i1=-1, i2=-1;
+ int start1=0, start2=0;
+
+ /* To check that hashes are ordered properly */
+ router_id_iterator_t iter1 = ROUTER_ID_ITERATOR_INIT;
+ router_id_iterator_t iter2 = ROUTER_ID_ITERATOR_INIT;
+
+ /* i1 and i2 are initialized at the first line of each consensus. They never
+ * reach past len1 and len2 respectively, since next_router doesn't let that
+ * happen. i1 and i2 are advanced by at least one line at each iteration as
+ * long as they have not yet reached len1 and len2, so the loop is
+ * guaranteed to end, and each pair of (i1,i2) will be inspected at most
+ * once.
+ */
+ while (i1 < len1 || i2 < len2) {
+
+ /* Advance each of the two navigation positions by one router entry if not
+ * yet at the end.
+ */
+ if (i1 < len1) {
+ if (find_next_router_line(cons1, "base", &i1, &iter1) < 0) {
+ goto error_cleanup;
+ }
+ }
+
+ if (i2 < len2) {
+ if (find_next_router_line(cons2, "target", &i2, &iter2) < 0) {
+ goto error_cleanup;
+ }
+ }
+
+ /* If we have reached the end of both consensuses, there is no need to
+ * compare hashes anymore, since this is the last iteration.
+ */
+ if (i1 < len1 || i2 < len2) {
+
+ /* Keep on advancing the lower (by identity hash sorting) position until
+ * we have two matching positions. The only other possible outcome is
+ * that a lower position reaches the end of the consensus before it can
+ * reach a hash that is no longer the lower one. Since there will always
+ * be a lower hash for as long as the loop runs, one of the two indexes
+ * will always be incremented, thus assuring that the loop must end
+ * after a finite number of iterations. If that cannot be because said
+ * consensus has already reached the end, both are extended to their
+ * respecting ends since we are done.
+ */
+ int cmp = base64cmp(&iter1.hash, &iter2.hash);
+ while (cmp != 0) {
+ if (i1 < len1 && cmp < 0) {
+ if (find_next_router_line(cons1, "base", &i1, &iter1) < 0) {
+ goto error_cleanup;
+ }
+ if (i1 == len1) {
+ /* We finished the first consensus, so grab all the remaining
+ * lines of the second consensus and finish up.
+ */
+ i2 = len2;
+ break;
+ }
+ } else if (i2 < len2 && cmp > 0) {
+ if (find_next_router_line(cons2, "target", &i2, &iter2) < 0) {
+ goto error_cleanup;
+ }
+ if (i2 == len2) {
+ /* We finished the second consensus, so grab all the remaining
+ * lines of the first consensus and finish up.
+ */
+ i1 = len1;
+ break;
+ }
+ } else {
+ i1 = len1;
+ i2 = len2;
+ break;
+ }
+ cmp = base64cmp(&iter1.hash, &iter2.hash);
+ }
+ }
+
+ /* Make slices out of these chunks (up to the common router entry) and
+ * calculate the changes for them.
+ * Error if any of the two slices are longer than 10K lines. That should
+ * never happen with any pair of real consensuses. Feeding more than 10K
+ * lines to calc_changes would be very slow anyway.
+ */
+#define MAX_LINE_COUNT (10000)
+ if (i1-start1 > MAX_LINE_COUNT || i2-start2 > MAX_LINE_COUNT) {
+ log_warn(LD_CONSDIFF, "Refusing to generate consensus diff because "
+ "we found too few common router ids.");
+ goto error_cleanup;
+ }
+
+ smartlist_slice_t *cons1_sl = smartlist_slice(cons1, start1, i1);
+ smartlist_slice_t *cons2_sl = smartlist_slice(cons2, start2, i2);
+ calc_changes(cons1_sl, cons2_sl, changed1, changed2);
+ tor_free(cons1_sl);
+ tor_free(cons2_sl);
+ start1 = i1, start2 = i2;
+ }
+
+ /* Navigate the changes in reverse order and generate one ed command for
+ * each chunk of changes.
+ */
+ i1=len1-1, i2=len2-1;
+ char buf[128];
+ while (i1 >= 0 || i2 >= 0) {
+
+ int start1x, start2x, end1, end2, added, deleted;
+
+ /* We are at a point were no changed bools are true, so just keep going. */
+ if (!(i1 >= 0 && bitarray_is_set(changed1, i1)) &&
+ !(i2 >= 0 && bitarray_is_set(changed2, i2))) {
+ if (i1 >= 0) {
+ i1--;
+ }
+ if (i2 >= 0) {
+ i2--;
+ }
+ continue;
+ }
+
+ end1 = i1, end2 = i2;
+
+ /* Grab all contiguous changed lines */
+ while (i1 >= 0 && bitarray_is_set(changed1, i1)) {
+ i1--;
+ }
+ while (i2 >= 0 && bitarray_is_set(changed2, i2)) {
+ i2--;
+ }
+
+ start1x = i1+1, start2x = i2+1;
+ added = end2-i2, deleted = end1-i1;
+
+ if (added == 0) {
+ if (deleted == 1) {
+ tor_snprintf(buf, sizeof(buf), "%id", start1x+1);
+ smartlist_add_linecpy(result, area, buf);
+ } else {
+ tor_snprintf(buf, sizeof(buf), "%i,%id", start1x+1, start1x+deleted);
+ smartlist_add_linecpy(result, area, buf);
+ }
+ } else {
+ int i;
+ if (deleted == 0) {
+ tor_snprintf(buf, sizeof(buf), "%ia", start1x);
+ smartlist_add_linecpy(result, area, buf);
+ } else if (deleted == 1) {
+ tor_snprintf(buf, sizeof(buf), "%ic", start1x+1);
+ smartlist_add_linecpy(result, area, buf);
+ } else {
+ tor_snprintf(buf, sizeof(buf), "%i,%ic", start1x+1, start1x+deleted);
+ smartlist_add_linecpy(result, area, buf);
+ }
+
+ for (i = start2x; i <= end2; ++i) {
+ cdline_t *line = smartlist_get(cons2, i);
+ if (line_str_eq(line, ".")) {
+ log_warn(LD_CONSDIFF, "Cannot generate consensus diff because "
+ "one of the lines to be added is \".\".");
+ goto error_cleanup;
+ }
+ smartlist_add(result, line);
+ }
+ smartlist_add_linecpy(result, area, ".");
+ }
+ }
+
+ smartlist_free(cons1);
+ bitarray_free(changed1);
+ bitarray_free(changed2);
+
+ return result;
+
+ error_cleanup:
+
+ smartlist_free(cons1);
+ bitarray_free(changed1);
+ bitarray_free(changed2);
+
+ smartlist_free(result);
+
+ return NULL;
+}
+
+/* Helper: Read a base-10 number between 0 and INT32_MAX from <b>s</b> and
+ * store it in <b>num_out</b>. Advance <b>s</b> to the characer immediately
+ * after the number. Return 0 on success, -1 on failure. */
+static int
+get_linenum(const char **s, int *num_out)
+{
+ int ok;
+ char *next;
+ if (!TOR_ISDIGIT(**s)) {
+ return -1;
+ }
+ *num_out = (int) tor_parse_long(*s, 10, 0, INT32_MAX, &ok, &next);
+ if (ok && next) {
+ *s = next;
+ return 0;
+ } else {
+ return -1;
+ }
+}
+
+/** Apply the ed diff, starting at <b>diff_starting_line</b>, to the consensus
+ * and return a new consensus, also as a line-based smartlist. Will return
+ * NULL if the ed diff is not properly formatted.
+ *
+ * All cdline_t objects in the resulting object are references to lines
+ * in one of the inputs; nothing is copied.
+ */
+STATIC smartlist_t *
+apply_ed_diff(const smartlist_t *cons1, const smartlist_t *diff,
+ int diff_starting_line)
+{
+ int diff_len = smartlist_len(diff);
+ int j = smartlist_len(cons1);
+ smartlist_t *cons2 = smartlist_new();
+
+ for (int i=diff_starting_line; i<diff_len; ++i) {
+ const cdline_t *diff_cdline = smartlist_get(diff, i);
+ char diff_line[128];
+
+ if (diff_cdline->len > sizeof(diff_line) - 1) {
+ log_warn(LD_CONSDIFF, "Could not apply consensus diff because "
+ "an ed command was far too long");
+ goto error_cleanup;
+ }
+ /* Copy the line to make it nul-terminated. */
+ memcpy(diff_line, diff_cdline->s, diff_cdline->len);
+ diff_line[diff_cdline->len] = 0;
+ const char *ptr = diff_line;
+ int start = 0, end = 0;
+ int had_range = 0;
+ int end_was_eof = 0;
+ if (get_linenum(&ptr, &start) < 0) {
+ log_warn(LD_CONSDIFF, "Could not apply consensus diff because "
+ "an ed command was missing a line number.");
+ goto error_cleanup;
+ }
+ if (*ptr == ',') {
+ /* Two-item range */
+ had_range = 1;
+ ++ptr;
+ if (*ptr == '$') {
+ end_was_eof = 1;
+ end = smartlist_len(cons1);
+ ++ptr;
+ } else if (get_linenum(&ptr, &end) < 0) {
+ log_warn(LD_CONSDIFF, "Could not apply consensus diff because "
+ "an ed command was missing a range end line number.");
+ goto error_cleanup;
+ }
+ /* Incoherent range. */
+ if (end <= start) {
+ log_warn(LD_CONSDIFF, "Could not apply consensus diff because "
+ "an invalid range was found in an ed command.");
+ goto error_cleanup;
+ }
+ } else {
+ /* We'll take <n1> as <n1>,<n1> for simplicity. */
+ end = start;
+ }
+
+ if (end > j) {
+ log_warn(LD_CONSDIFF, "Could not apply consensus diff because "
+ "its commands are not properly sorted in reverse order.");
+ goto error_cleanup;
+ }
+
+ if (*ptr == '\0') {
+ log_warn(LD_CONSDIFF, "Could not apply consensus diff because "
+ "a line with no ed command was found");
+ goto error_cleanup;
+ }
+
+ if (*(ptr+1) != '\0') {
+ log_warn(LD_CONSDIFF, "Could not apply consensus diff because "
+ "an ed command longer than one char was found.");
+ goto error_cleanup;
+ }
+
+ char action = *ptr;
+
+ switch (action) {
+ case 'a':
+ case 'c':
+ case 'd':
+ break;
+ default:
+ log_warn(LD_CONSDIFF, "Could not apply consensus diff because "
+ "an unrecognised ed command was found.");
+ goto error_cleanup;
+ }
+
+ /** $ is not allowed with non-d actions. */
+ if (end_was_eof && action != 'd') {
+ log_warn(LD_CONSDIFF, "Could not apply consensus diff because "
+ "it wanted to use $ with a command other than delete");
+ goto error_cleanup;
+ }
+
+ /* 'a' commands are not allowed to have ranges. */
+ if (had_range && action == 'a') {
+ log_warn(LD_CONSDIFF, "Could not apply consensus diff because "
+ "it wanted to add lines after a range.");
+ goto error_cleanup;
+ }
+
+ /* Add unchanged lines. */
+ for (; j && j > end; --j) {
+ cdline_t *cons_line = smartlist_get(cons1, j-1);
+ smartlist_add(cons2, cons_line);
+ }
+
+ /* Ignore removed lines. */
+ if (action == 'c' || action == 'd') {
+ while (--j >= start) {
+ /* Skip line */
+ }
+ }
+
+ /* Add new lines in reverse order, since it will all be reversed at the
+ * end.
+ */
+ if (action == 'a' || action == 'c') {
+ int added_end = i;
+
+ i++; /* Skip the line with the range and command. */
+ while (i < diff_len) {
+ if (line_str_eq(smartlist_get(diff, i), ".")) {
+ break;
+ }
+ if (++i == diff_len) {
+ log_warn(LD_CONSDIFF, "Could not apply consensus diff because "
+ "it has lines to be inserted that don't end with a \".\".");
+ goto error_cleanup;
+ }
+ }
+
+ int added_i = i-1;
+
+ /* It would make no sense to add zero new lines. */
+ if (added_i == added_end) {
+ log_warn(LD_CONSDIFF, "Could not apply consensus diff because "
+ "it has an ed command that tries to insert zero lines.");
+ goto error_cleanup;
+ }
+
+ while (added_i > added_end) {
+ cdline_t *added_line = smartlist_get(diff, added_i--);
+ smartlist_add(cons2, added_line);
+ }
+ }
+ }
+
+ /* Add remaining unchanged lines. */
+ for (; j > 0; --j) {
+ cdline_t *cons_line = smartlist_get(cons1, j-1);
+ smartlist_add(cons2, cons_line);
+ }
+
+ /* Reverse the whole thing since we did it from the end. */
+ smartlist_reverse(cons2);
+ return cons2;
+
+ error_cleanup:
+
+ smartlist_free(cons2);
+
+ return NULL;
+}
+
+/** Generate a consensus diff as a smartlist from two given consensuses, also
+ * as smartlists. Will return NULL if the consensus diff could not be
+ * generated. Neither of the two consensuses are modified in any way, so it's
+ * up to the caller to free their resources.
+ */
+smartlist_t *
+consdiff_gen_diff(const smartlist_t *cons1,
+ const smartlist_t *cons2,
+ const consensus_digest_t *digests1,
+ const consensus_digest_t *digests2,
+ memarea_t *area)
+{
+ smartlist_t *ed_diff = gen_ed_diff(cons1, cons2, area);
+ /* ed diff could not be generated - reason already logged by gen_ed_diff. */
+ if (!ed_diff) {
+ goto error_cleanup;
+ }
+
+ /* See that the script actually produces what we want. */
+ smartlist_t *ed_cons2 = apply_ed_diff(cons1, ed_diff, 0);
+ if (!ed_cons2) {
+ /* LCOV_EXCL_START -- impossible if diff generation is correct */
+ log_warn(LD_BUG|LD_CONSDIFF, "Refusing to generate consensus diff because "
+ "the generated ed diff could not be tested to successfully generate "
+ "the target consensus.");
+ goto error_cleanup;
+ /* LCOV_EXCL_STOP */
+ }
+
+ int cons2_eq = 1;
+ if (smartlist_len(cons2) == smartlist_len(ed_cons2)) {
+ SMARTLIST_FOREACH_BEGIN(cons2, const cdline_t *, line1) {
+ const cdline_t *line2 = smartlist_get(ed_cons2, line1_sl_idx);
+ if (! lines_eq(line1, line2) ) {
+ cons2_eq = 0;
+ break;
+ }
+ } SMARTLIST_FOREACH_END(line1);
+ } else {
+ cons2_eq = 0;
+ }
+ smartlist_free(ed_cons2);
+ if (!cons2_eq) {
+ /* LCOV_EXCL_START -- impossible if diff generation is correct. */
+ log_warn(LD_BUG|LD_CONSDIFF, "Refusing to generate consensus diff because "
+ "the generated ed diff did not generate the target consensus "
+ "successfully when tested.");
+ goto error_cleanup;
+ /* LCOV_EXCL_STOP */
+ }
+
+ char cons1_hash_hex[HEX_DIGEST256_LEN+1];
+ char cons2_hash_hex[HEX_DIGEST256_LEN+1];
+ base16_encode(cons1_hash_hex, HEX_DIGEST256_LEN+1,
+ (const char*)digests1->sha3_256, DIGEST256_LEN);
+ base16_encode(cons2_hash_hex, HEX_DIGEST256_LEN+1,
+ (const char*)digests2->sha3_256, DIGEST256_LEN);
+
+ /* Create the resulting consensus diff. */
+ char buf[160];
+ smartlist_t *result = smartlist_new();
+ tor_snprintf(buf, sizeof(buf), "%s", ns_diff_version);
+ smartlist_add_linecpy(result, area, buf);
+ tor_snprintf(buf, sizeof(buf), "%s %s %s", hash_token,
+ cons1_hash_hex, cons2_hash_hex);
+ smartlist_add_linecpy(result, area, buf);
+ smartlist_add_all(result, ed_diff);
+ smartlist_free(ed_diff);
+ return result;
+
+ error_cleanup:
+
+ if (ed_diff) {
+ /* LCOV_EXCL_START -- ed_diff is NULL except in unreachable cases above */
+ smartlist_free(ed_diff);
+ /* LCOV_EXCL_STOP */
+ }
+
+ return NULL;
+}
+
+/** Fetch the digest of the base consensus in the consensus diff, encoded in
+ * base16 as found in the diff itself. digest1_out and digest2_out must be of
+ * length DIGEST256_LEN or larger if not NULL.
+ */
+int
+consdiff_get_digests(const smartlist_t *diff,
+ char *digest1_out,
+ char *digest2_out)
+{
+ smartlist_t *hash_words = NULL;
+ const cdline_t *format;
+ char cons1_hash[DIGEST256_LEN], cons2_hash[DIGEST256_LEN];
+ char *cons1_hash_hex, *cons2_hash_hex;
+ if (smartlist_len(diff) < 2) {
+ log_info(LD_CONSDIFF, "The provided consensus diff is too short.");
+ goto error_cleanup;
+ }
+
+ /* Check that it's the format and version we know. */
+ format = smartlist_get(diff, 0);
+ if (!line_str_eq(format, ns_diff_version)) {
+ log_warn(LD_CONSDIFF, "The provided consensus diff format is not known.");
+ goto error_cleanup;
+ }
+
+ /* Grab the base16 digests. */
+ hash_words = smartlist_new();
+ {
+ const cdline_t *line2 = smartlist_get(diff, 1);
+ char *h = tor_memdup_nulterm(line2->s, line2->len);
+ smartlist_split_string(hash_words, h, " ", 0, 0);
+ tor_free(h);
+ }
+
+ /* There have to be three words, the first of which must be hash_token. */
+ if (smartlist_len(hash_words) != 3 ||
+ strcmp(smartlist_get(hash_words, 0), hash_token)) {
+ log_info(LD_CONSDIFF, "The provided consensus diff does not include "
+ "the necessary digests.");
+ goto error_cleanup;
+ }
+
+ /* Expected hashes as found in the consensus diff header. They must be of
+ * length HEX_DIGEST256_LEN, normally 64 hexadecimal characters.
+ * If any of the decodings fail, error to make sure that the hashes are
+ * proper base16-encoded digests.
+ */
+ cons1_hash_hex = smartlist_get(hash_words, 1);
+ cons2_hash_hex = smartlist_get(hash_words, 2);
+ if (strlen(cons1_hash_hex) != HEX_DIGEST256_LEN ||
+ strlen(cons2_hash_hex) != HEX_DIGEST256_LEN) {
+ log_info(LD_CONSDIFF, "The provided consensus diff includes "
+ "base16-encoded digests of incorrect size.");
+ goto error_cleanup;
+ }
+
+ if (base16_decode(cons1_hash, DIGEST256_LEN,
+ cons1_hash_hex, HEX_DIGEST256_LEN) != DIGEST256_LEN ||
+ base16_decode(cons2_hash, DIGEST256_LEN,
+ cons2_hash_hex, HEX_DIGEST256_LEN) != DIGEST256_LEN) {
+ log_info(LD_CONSDIFF, "The provided consensus diff includes "
+ "malformed digests.");
+ goto error_cleanup;
+ }
+
+ if (digest1_out) {
+ memcpy(digest1_out, cons1_hash, DIGEST256_LEN);
+ }
+ if (digest2_out) {
+ memcpy(digest2_out, cons2_hash, DIGEST256_LEN);
+ }
+
+ SMARTLIST_FOREACH(hash_words, char *, cp, tor_free(cp));
+ smartlist_free(hash_words);
+ return 0;
+
+ error_cleanup:
+
+ if (hash_words) {
+ SMARTLIST_FOREACH(hash_words, char *, cp, tor_free(cp));
+ smartlist_free(hash_words);
+ }
+ return 1;
+}
+
+/** Apply the consensus diff to the given consensus and return a new
+ * consensus, also as a line-based smartlist. Will return NULL if the diff
+ * could not be applied. Neither the consensus nor the diff are modified in
+ * any way, so it's up to the caller to free their resources.
+ */
+char *
+consdiff_apply_diff(const smartlist_t *cons1,
+ const smartlist_t *diff,
+ const consensus_digest_t *digests1)
+{
+ smartlist_t *cons2 = NULL;
+ char *cons2_str = NULL;
+ char e_cons1_hash[DIGEST256_LEN];
+ char e_cons2_hash[DIGEST256_LEN];
+
+ if (consdiff_get_digests(diff, e_cons1_hash, e_cons2_hash) != 0) {
+ goto error_cleanup;
+ }
+
+ /* See that the consensus that was given to us matches its hash. */
+ if (!consensus_digest_eq(digests1->sha3_256,
+ (const uint8_t*)e_cons1_hash)) {
+ char hex_digest1[HEX_DIGEST256_LEN+1];
+ char e_hex_digest1[HEX_DIGEST256_LEN+1];
+ log_warn(LD_CONSDIFF, "Refusing to apply consensus diff because "
+ "the base consensus doesn't match the digest as found in "
+ "the consensus diff header.");
+ base16_encode(hex_digest1, HEX_DIGEST256_LEN+1,
+ (const char *)digests1->sha3_256, DIGEST256_LEN);
+ base16_encode(e_hex_digest1, HEX_DIGEST256_LEN+1,
+ e_cons1_hash, DIGEST256_LEN);
+ log_warn(LD_CONSDIFF, "Expected: %s; found: %s",
+ hex_digest1, e_hex_digest1);
+ goto error_cleanup;
+ }
+
+ /* Grab the ed diff and calculate the resulting consensus. */
+ /* Skip the first two lines. */
+ cons2 = apply_ed_diff(cons1, diff, 2);
+
+ /* ed diff could not be applied - reason already logged by apply_ed_diff. */
+ if (!cons2) {
+ goto error_cleanup;
+ }
+
+ cons2_str = consensus_join_lines(cons2);
+
+ consensus_digest_t cons2_digests;
+ if (consensus_compute_digest(cons2_str, &cons2_digests) < 0) {
+ /* LCOV_EXCL_START -- digest can't fail */
+ log_warn(LD_CONSDIFF, "Could not compute digests of the consensus "
+ "resulting from applying a consensus diff.");
+ goto error_cleanup;
+ /* LCOV_EXCL_STOP */
+ }
+
+ /* See that the resulting consensus matches its hash. */
+ if (!consensus_digest_eq(cons2_digests.sha3_256,
+ (const uint8_t*)e_cons2_hash)) {
+ log_warn(LD_CONSDIFF, "Refusing to apply consensus diff because "
+ "the resulting consensus doesn't match the digest as found in "
+ "the consensus diff header.");
+ char hex_digest2[HEX_DIGEST256_LEN+1];
+ char e_hex_digest2[HEX_DIGEST256_LEN+1];
+ base16_encode(hex_digest2, HEX_DIGEST256_LEN+1,
+ (const char *)cons2_digests.sha3_256, DIGEST256_LEN);
+ base16_encode(e_hex_digest2, HEX_DIGEST256_LEN+1,
+ e_cons2_hash, DIGEST256_LEN);
+ log_warn(LD_CONSDIFF, "Expected: %s; found: %s",
+ hex_digest2, e_hex_digest2);
+ goto error_cleanup;
+ }
+
+ goto done;
+
+ error_cleanup:
+ tor_free(cons2_str); /* Sets it to NULL */
+
+ done:
+ if (cons2) {
+ smartlist_free(cons2);
+ }
+
+ return cons2_str;
+}
+
+/** Any consensus line longer than this means that the input is invalid. */
+#define CONSENSUS_LINE_MAX_LEN (1<<20)
+
+/**
+ * Helper: For every NL-terminated line in <b>s</b>, add a cdline referring to
+ * that line (without trailing newline) to <b>out</b>. Return -1 if there are
+ * any non-NL terminated lines; 0 otherwise.
+ *
+ * Unlike tor_split_lines, this function avoids ambiguity on its
+ * handling of a final line that isn't NL-terminated.
+ *
+ * All cdline_t objects are allocated in the provided memarea. Strings
+ * are not copied: if <b>s</b> changes or becomes invalid, then all
+ * generated cdlines will become invalid.
+ */
+STATIC int
+consensus_split_lines(smartlist_t *out, const char *s, memarea_t *area)
+{
+ const char *end_of_str = s + strlen(s);
+ tor_assert(*end_of_str == '\0');
+
+ while (*s) {
+ const char *eol = memchr(s, '\n', end_of_str - s);
+ if (!eol) {
+ /* File doesn't end with newline. */
+ return -1;
+ }
+ if (eol - s > CONSENSUS_LINE_MAX_LEN) {
+ /* Line is far too long. */
+ return -1;
+ }
+ cdline_t *line = memarea_alloc(area, sizeof(cdline_t));
+ line->s = s;
+ line->len = (uint32_t)(eol - s);
+ smartlist_add(out, line);
+ s = eol+1;
+ }
+ return 0;
+}
+
+/** Given a list of cdline_t, return a newly allocated string containing
+ * all of the lines, terminated with NL, concatenated.
+ *
+ * Unlike smartlist_join_strings(), avoids lossy operations on empty
+ * lists. */
+static char *
+consensus_join_lines(const smartlist_t *inp)
+{
+ size_t n = 0;
+ SMARTLIST_FOREACH(inp, const cdline_t *, cdline, n += cdline->len + 1);
+ n += 1;
+ char *result = tor_malloc(n);
+ char *out = result;
+ SMARTLIST_FOREACH_BEGIN(inp, const cdline_t *, cdline) {
+ memcpy(out, cdline->s, cdline->len);
+ out += cdline->len;
+ *out++ = '\n';
+ } SMARTLIST_FOREACH_END(cdline);
+ *out++ = '\0';
+ tor_assert(out == result+n);
+ return result;
+}
+
+/** Given two consensus documents, try to compute a diff between them. On
+ * success, retun a newly allocated string containing that diff. On failure,
+ * return NULL. */
+char *
+consensus_diff_generate(const char *cons1,
+ const char *cons2)
+{
+ consensus_digest_t d1, d2;
+ smartlist_t *lines1 = NULL, *lines2 = NULL, *result_lines = NULL;
+ int r1, r2;
+ char *result = NULL;
+
+ r1 = consensus_compute_digest_as_signed(cons1, &d1);
+ r2 = consensus_compute_digest(cons2, &d2);
+ if (BUG(r1 < 0 || r2 < 0))
+ return NULL; // LCOV_EXCL_LINE
+
+ memarea_t *area = memarea_new();
+ lines1 = smartlist_new();
+ lines2 = smartlist_new();
+ if (consensus_split_lines(lines1, cons1, area) < 0)
+ goto done;
+ if (consensus_split_lines(lines2, cons2, area) < 0)
+ goto done;
+
+ result_lines = consdiff_gen_diff(lines1, lines2, &d1, &d2, area);
+
+ done:
+ if (result_lines) {
+ result = consensus_join_lines(result_lines);
+ smartlist_free(result_lines);
+ }
+
+ memarea_drop_all(area);
+ smartlist_free(lines1);
+ smartlist_free(lines2);
+
+ return result;
+}
+
+/** Given a consensus document and a diff, try to apply the diff to the
+ * consensus. On success return a newly allocated string containing the new
+ * consensus. On failure, return NULL. */
+char *
+consensus_diff_apply(const char *consensus,
+ const char *diff)
+{
+ consensus_digest_t d1;
+ smartlist_t *lines1 = NULL, *lines2 = NULL;
+ int r1;
+ char *result = NULL;
+ memarea_t *area = memarea_new();
+
+ r1 = consensus_compute_digest_as_signed(consensus, &d1);
+ if (BUG(r1 < 0))
- return NULL; // LCOV_EXCL_LINE
++ goto done;
+
+ lines1 = smartlist_new();
+ lines2 = smartlist_new();
+ if (consensus_split_lines(lines1, consensus, area) < 0)
+ goto done;
+ if (consensus_split_lines(lines2, diff, area) < 0)
+ goto done;
+
+ result = consdiff_apply_diff(lines1, lines2, &d1);
+
+ done:
+ smartlist_free(lines1);
+ smartlist_free(lines2);
+ memarea_drop_all(area);
+
+ return result;
+}
+
+/** Return true iff, based on its header, <b>document</b> is likely
+ * to be a consensus diff. */
+int
+looks_like_a_consensus_diff(const char *document, size_t len)
+{
+ return (len >= strlen(ns_diff_version) &&
+ fast_memeq(document, ns_diff_version, strlen(ns_diff_version)));
+}
