311 lines
8.1 KiB
C
311 lines
8.1 KiB
C
/*
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* Domain search option for DHCP (RFC 3397)
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*
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* Copyright (c) 2012 Klaus Stengel
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*
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* Permission is hereby granted, free of charge, to any person obtaining a copy
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* of this software and associated documentation files (the "Software"), to deal
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* in the Software without restriction, including without limitation the rights
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* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
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* copies of the Software, and to permit persons to whom the Software is
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* furnished to do so, subject to the following conditions:
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*
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* The above copyright notice and this permission notice shall be included in
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* all copies or substantial portions of the Software.
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*
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* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
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* THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
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* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
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* THE SOFTWARE.
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*/
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#include "slirp.h"
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static const uint8_t RFC3397_OPT_DOMAIN_SEARCH = 119;
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static const uint8_t MAX_OPT_LEN = 255;
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static const uint8_t OPT_HEADER_LEN = 2;
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static const uint8_t REFERENCE_LEN = 2;
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struct compact_domain;
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typedef struct compact_domain {
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struct compact_domain *self;
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struct compact_domain *refdom;
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uint8_t *labels;
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size_t len;
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size_t common_octets;
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} CompactDomain;
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static size_t
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domain_suffix_diffoff(const CompactDomain *a, const CompactDomain *b)
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{
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size_t la = a->len, lb = b->len;
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uint8_t *da = a->labels + la, *db = b->labels + lb;
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size_t i, lm = (la < lb) ? la : lb;
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for (i = 0; i < lm; i++) {
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da--; db--;
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if (*da != *db) {
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break;
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}
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}
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return i;
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}
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static int domain_suffix_ord(const void *cva, const void *cvb)
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{
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const CompactDomain *a = cva, *b = cvb;
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size_t la = a->len, lb = b->len;
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size_t doff = domain_suffix_diffoff(a, b);
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uint8_t ca = a->labels[la - doff];
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uint8_t cb = b->labels[lb - doff];
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if (ca < cb) {
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return -1;
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}
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if (ca > cb) {
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return 1;
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}
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if (la < lb) {
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return -1;
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}
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if (la > lb) {
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return 1;
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}
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return 0;
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}
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static size_t domain_common_label(CompactDomain *a, CompactDomain *b)
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{
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size_t res, doff = domain_suffix_diffoff(a, b);
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uint8_t *first_eq_pos = a->labels + (a->len - doff);
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uint8_t *label = a->labels;
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while (*label && label < first_eq_pos) {
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label += *label + 1;
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}
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res = a->len - (label - a->labels);
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/* only report if it can help to reduce the packet size */
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return (res > REFERENCE_LEN) ? res : 0;
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}
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static void domain_fixup_order(CompactDomain *cd, size_t n)
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{
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size_t i;
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for (i = 0; i < n; i++) {
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CompactDomain *cur = cd + i, *next = cd[i].self;
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while (!cur->common_octets) {
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CompactDomain *tmp = next->self; /* backup target value */
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next->self = cur;
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cur->common_octets++;
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cur = next;
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next = tmp;
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}
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}
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}
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static void domain_mklabels(CompactDomain *cd, const char *input)
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{
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uint8_t *len_marker = cd->labels;
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uint8_t *output = len_marker; /* pre-incremented */
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const char *in = input;
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char cur_chr;
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size_t len = 0;
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if (cd->len == 0) {
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goto fail;
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}
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cd->len++;
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do {
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cur_chr = *in++;
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if (cur_chr == '.' || cur_chr == '\0') {
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len = output - len_marker;
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if ((len == 0 && cur_chr == '.') || len >= 64) {
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goto fail;
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}
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*len_marker = len;
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output++;
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len_marker = output;
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} else {
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output++;
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*output = cur_chr;
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}
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} while (cur_chr != '\0');
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/* ensure proper zero-termination */
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if (len != 0) {
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*len_marker = 0;
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cd->len++;
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}
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return;
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fail:
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g_warning("failed to parse domain name '%s'\n", input);
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cd->len = 0;
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}
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static void
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domain_mkxrefs(CompactDomain *doms, CompactDomain *last, size_t depth)
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{
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CompactDomain *i = doms, *target = doms;
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do {
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if (i->labels < target->labels) {
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target = i;
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}
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} while (i++ != last);
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for (i = doms; i != last; i++) {
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CompactDomain *group_last;
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size_t next_depth;
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if (i->common_octets == depth) {
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continue;
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}
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next_depth = -1;
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for (group_last = i; group_last != last; group_last++) {
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size_t co = group_last->common_octets;
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if (co <= depth) {
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break;
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}
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if (co < next_depth) {
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next_depth = co;
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}
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}
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domain_mkxrefs(i, group_last, next_depth);
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i = group_last;
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if (i == last) {
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break;
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}
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}
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if (depth == 0) {
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return;
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}
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i = doms;
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do {
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if (i != target && i->refdom == NULL) {
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i->refdom = target;
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i->common_octets = depth;
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}
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} while (i++ != last);
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}
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static size_t domain_compactify(CompactDomain *domains, size_t n)
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{
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uint8_t *start = domains->self->labels, *outptr = start;
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size_t i;
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for (i = 0; i < n; i++) {
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CompactDomain *cd = domains[i].self;
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CompactDomain *rd = cd->refdom;
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if (rd != NULL) {
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size_t moff = (rd->labels - start)
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+ (rd->len - cd->common_octets);
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if (moff < 0x3FFFu) {
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cd->len -= cd->common_octets - 2;
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cd->labels[cd->len - 1] = moff & 0xFFu;
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cd->labels[cd->len - 2] = 0xC0u | (moff >> 8);
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}
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}
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if (cd->labels != outptr) {
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memmove(outptr, cd->labels, cd->len);
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cd->labels = outptr;
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}
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outptr += cd->len;
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}
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return outptr - start;
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}
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int translate_dnssearch(Slirp *s, const char **names)
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{
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size_t blocks, bsrc_start, bsrc_end, bdst_start;
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size_t i, num_domains, memreq = 0;
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uint8_t *result = NULL, *outptr;
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CompactDomain *domains = NULL;
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const char **nameptr = names;
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while (*nameptr != NULL) {
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nameptr++;
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}
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num_domains = nameptr - names;
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if (num_domains == 0) {
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return -2;
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}
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domains = g_malloc(num_domains * sizeof(*domains));
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for (i = 0; i < num_domains; i++) {
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size_t nlen = strlen(names[i]);
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memreq += nlen + 2; /* 1 zero octet + 1 label length octet */
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domains[i].self = domains + i;
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domains[i].len = nlen;
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domains[i].common_octets = 0;
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domains[i].refdom = NULL;
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}
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/* reserve extra 2 header bytes for each 255 bytes of output */
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memreq += DIV_ROUND_UP(memreq, MAX_OPT_LEN) * OPT_HEADER_LEN;
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result = g_malloc(memreq * sizeof(*result));
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outptr = result;
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for (i = 0; i < num_domains; i++) {
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domains[i].labels = outptr;
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domain_mklabels(domains + i, names[i]);
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outptr += domains[i].len;
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}
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if (outptr == result) {
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g_free(domains);
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g_free(result);
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return -1;
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}
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qsort(domains, num_domains, sizeof(*domains), domain_suffix_ord);
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domain_fixup_order(domains, num_domains);
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for (i = 1; i < num_domains; i++) {
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size_t cl = domain_common_label(domains + i - 1, domains + i);
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domains[i - 1].common_octets = cl;
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}
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domain_mkxrefs(domains, domains + num_domains - 1, 0);
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memreq = domain_compactify(domains, num_domains);
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blocks = DIV_ROUND_UP(memreq, MAX_OPT_LEN);
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bsrc_end = memreq;
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bsrc_start = (blocks - 1) * MAX_OPT_LEN;
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bdst_start = bsrc_start + blocks * OPT_HEADER_LEN;
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memreq += blocks * OPT_HEADER_LEN;
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while (blocks--) {
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size_t len = bsrc_end - bsrc_start;
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memmove(result + bdst_start, result + bsrc_start, len);
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result[bdst_start - 2] = RFC3397_OPT_DOMAIN_SEARCH;
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result[bdst_start - 1] = len;
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bsrc_end = bsrc_start;
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bsrc_start -= MAX_OPT_LEN;
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bdst_start -= MAX_OPT_LEN + OPT_HEADER_LEN;
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}
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g_free(domains);
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s->vdnssearch = result;
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s->vdnssearch_len = memreq;
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return 0;
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}
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