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https://github.com/pi-hole/dnsmasq.git
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Add packet-dump debugging facility.
This commit is contained in:
Simon Kelley
210
src/dump.c
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210
src/dump.c
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/* dnsmasq is Copyright (c) 2000-2018 Simon Kelley
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This program is free software; you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; version 2 dated June, 1991, or
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(at your option) version 3 dated 29 June, 2007.
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This program is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with this program. If not, see <http://www.gnu.org/licenses/>.
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*/
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#include "dnsmasq.h"
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#ifdef HAVE_DUMPFILE
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static u32 packet_count;
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/* https://wiki.wireshark.org/Development/LibpcapFileFormat */
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struct pcap_hdr_s {
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u32 magic_number; /* magic number */
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u16 version_major; /* major version number */
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u16 version_minor; /* minor version number */
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u32 thiszone; /* GMT to local correction */
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u32 sigfigs; /* accuracy of timestamps */
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u32 snaplen; /* max length of captured packets, in octets */
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u32 network; /* data link type */
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};
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struct pcaprec_hdr_s {
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u32 ts_sec; /* timestamp seconds */
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u32 ts_usec; /* timestamp microseconds */
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u32 incl_len; /* number of octets of packet saved in file */
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u32 orig_len; /* actual length of packet */
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};
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void dump_init(void)
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{
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struct stat buf;
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struct pcap_hdr_s header;
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struct pcaprec_hdr_s pcap_header;
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packet_count = 0;
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if (stat(daemon->dump_file, &buf) == -1)
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{
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/* doesn't exist, create and add header */
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header.magic_number = 0xa1b2c3d4;
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header.version_major = 2;
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header.version_minor = 4;
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header.thiszone = 0;
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header.sigfigs = 0;
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header.snaplen = daemon->edns_pktsz + 200; /* slop for IP/UDP headers */
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header.network = 101; /* DLT_RAW http://www.tcpdump.org/linktypes.html */
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if (errno != ENOENT ||
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(daemon->dumpfd = creat(daemon->dump_file, S_IRUSR | S_IWUSR)) == -1 ||
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!read_write(daemon->dumpfd, (void *)&header, sizeof(header), 0))
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die(_("cannot create %s: %s"), daemon->dump_file, EC_FILE);
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}
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else if ((daemon->dumpfd = open(daemon->dump_file, O_APPEND | O_RDWR)) == -1 ||
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!read_write(daemon->dumpfd, (void *)&header, sizeof(header), 1) ||
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header.magic_number != 0xa1b2c3d4)
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die(_("cannot access %s: %s"), daemon->dump_file, EC_FILE);
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else
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{
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/* count existing records */
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while (read_write(daemon->dumpfd, (void *)&pcap_header, sizeof(pcap_header), 1))
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{
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lseek(daemon->dumpfd, pcap_header.incl_len, SEEK_CUR);
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packet_count++;
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}
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}
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}
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void dump_packet(int mask, void *packet, size_t len, union mysockaddr *src, union mysockaddr *dst)
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{
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struct ip ip;
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#ifdef HAVE_IPV6
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struct ip6_hdr ip6;
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int family;
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#endif
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struct udphdr {
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u16 uh_sport; /* source port */
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u16 uh_dport; /* destination port */
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u16 uh_ulen; /* udp length */
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u16 uh_sum; /* udp checksum */
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} udp;
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struct pcaprec_hdr_s pcap_header;
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struct timeval time;
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u32 i, sum;
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void *iphdr;
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size_t ipsz;
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int rc;
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if (daemon->dumpfd == -1 || !(mask & daemon->dump_mask))
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return;
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/* So wireshark can Id the packet. */
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udp.uh_sport = udp.uh_dport = htons(NAMESERVER_PORT);
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#ifdef HAVE_IPV6
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if (src)
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family = src->sa.sa_family;
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else
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family = dst->sa.sa_family;
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if (family == AF_INET6)
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{
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iphdr = &ip6;
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ipsz = sizeof(ip6);
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memset(&ip6, 0, sizeof(ip6));
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ip6.ip6_vfc = 6 << 4;
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ip6.ip6_plen = htons(sizeof(struct udphdr) + len);
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ip6.ip6_nxt = IPPROTO_UDP;
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ip6.ip6_hops = 64;
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if (src)
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{
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memcpy(&ip6.ip6_src, &src->in6.sin6_addr, IN6ADDRSZ);
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udp.uh_sport = src->in6.sin6_port;
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}
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if (dst)
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{
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memcpy(&ip6.ip6_dst, &dst->in6.sin6_addr, IN6ADDRSZ);
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udp.uh_dport = dst->in6.sin6_port;
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}
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/* start UDP checksum */
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for (sum = 0, i = 0; i < IN6ADDRSZ; i++)
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sum += ((u16 *)&ip6.ip6_src)[i];
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}
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else
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#endif
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{
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iphdr = &ip;
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ipsz = sizeof(ip);
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memset(&ip, 0, sizeof(ip));
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ip.ip_v = IPVERSION;
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ip.ip_hl = sizeof(struct ip) / 4;
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ip.ip_len = htons(sizeof(struct ip) + sizeof(struct udphdr) + len);
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ip.ip_ttl = IPDEFTTL;
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ip.ip_p = IPPROTO_UDP;
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if (src)
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{
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ip.ip_src = src->in.sin_addr;
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udp.uh_sport = src->in.sin_port;
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}
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if (dst)
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{
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ip.ip_dst = dst->in.sin_addr;
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udp.uh_dport = dst->in.sin_port;
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}
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ip.ip_sum = 0;
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for (sum = 0, i = 0; i < sizeof(struct ip) / 2; i++)
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sum += ((u16 *)&ip)[i];
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while (sum >> 16)
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sum = (sum & 0xffff) + (sum >> 16);
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ip.ip_sum = (sum == 0xffff) ? sum : ~sum;
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/* start UDP checksum */
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sum = ip.ip_src.s_addr & 0xffff;
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sum += (ip.ip_src.s_addr >> 16) & 0xffff;
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sum += ip.ip_dst.s_addr & 0xffff;
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sum += (ip.ip_dst.s_addr >> 16) & 0xffff;
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}
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if (len & 1)
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((unsigned char *)packet)[len] = 0; /* for checksum, in case length is odd. */
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udp.uh_sum = 0;
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udp.uh_ulen = htons(sizeof(struct udphdr) + len);
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sum += htons(IPPROTO_UDP);
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sum += htons(sizeof(struct udphdr) + len);
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for (i = 0; i < sizeof(struct udphdr)/2; i++)
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sum += ((u16 *)&udp)[i];
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for (i = 0; i < (len + 1) / 2; i++)
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sum += ((u16 *)packet)[i];
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while (sum >> 16)
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sum = (sum & 0xffff) + (sum >> 16);
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udp.uh_sum = (sum == 0xffff) ? sum : ~sum;
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rc = gettimeofday(&time, NULL);
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pcap_header.ts_sec = time.tv_sec;
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pcap_header.ts_usec = time.tv_usec;
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pcap_header.incl_len = pcap_header.orig_len = ipsz + sizeof(udp) + len;
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if (rc == -1 ||
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!read_write(daemon->dumpfd, (void *)&pcap_header, sizeof(pcap_header), 0) ||
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!read_write(daemon->dumpfd, iphdr, ipsz, 0) ||
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!read_write(daemon->dumpfd, (void *)&udp, sizeof(udp), 0) ||
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!read_write(daemon->dumpfd, (void *)packet, len, 0))
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my_syslog(LOG_ERR, _("failed to write packet dump"));
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else
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my_syslog(LOG_INFO, _("dumping UDP packet %u mask 0x%04x"), ++packet_count, mask);
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}
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#endif
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