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🗽 Sync 2026-06-03 14:05:40
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@@ -6,7 +6,7 @@ include $(TOPDIR)/rules.mk
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PKG_NAME:=dns2tcp
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PKG_VERSION:=1.1.2
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PKG_RELEASE:=2
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PKG_RELEASE:=3
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PKG_SOURCE:=$(PKG_NAME)-$(PKG_VERSION).tar.gz
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PKG_SOURCE_URL:=https://codeload.github.com/zfl9/dns2tcp/tar.gz/v$(PKG_VERSION)?
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@@ -1,210 +0,0 @@
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diff --git a/dns2tcp.c b/dns2tcp.c
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index b289598..542f839 100644
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--- a/dns2tcp.c
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+++ b/dns2tcp.c
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@@ -35,6 +35,10 @@
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#define PORTSTRLEN 6 /* "65535" (include \0) */
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#define DNS_MSGSZ 1472 /* mtu:1500 - iphdr:20 - udphdr:8 */
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+#define DNS_HDRLEN 12
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+
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+#define DNS_TYPE_A 1
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+#define DNS_TYPE_AAAA 28
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/* ======================== helper ======================== */
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@@ -128,6 +132,14 @@ typedef struct {
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union skaddr srcaddr;
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} ctx_t;
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+typedef struct {
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+ size_t start;
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+ size_t end;
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+ uint16_t type;
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+ uint8_t section;
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+ bool drop;
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+} dns_rr_t;
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+
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/* ======================== global-vars ======================== */
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enum {
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@@ -135,6 +147,7 @@ enum {
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FLAG_REUSE_PORT = 1 << 1, /* udp listen */
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FLAG_VERBOSE = 1 << 2, /* logging */
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FLAG_LOCAL_ADDR = 1 << 3, /* tcp local addr */
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+ FLAG_FILTER_AAAA = 1 << 4, /* strip all AAAA records from dns response */
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};
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#define has_flag(flag) (g_flags & (flag))
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@@ -166,6 +179,126 @@ static void tcp_connect_cb(evloop_t *evloop, evio_t *watcher, int events);
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static void tcp_sendmsg_cb(evloop_t *evloop, evio_t *watcher, int events);
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static void tcp_recvmsg_cb(evloop_t *evloop, evio_t *watcher, int events);
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+static uint16_t read_be16(const void *ptr) {
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+ const uint8_t *bytes = ptr;
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+ return ((uint16_t)bytes[0] << 8) | bytes[1];
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+}
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+
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+static void write_be16(void *ptr, uint16_t value) {
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+ uint8_t *bytes = ptr;
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+ bytes[0] = value >> 8;
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+ bytes[1] = value & 0xff;
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+}
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+
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+static bool dns_skip_name(const uint8_t *msg, size_t msglen, size_t offset, size_t *next_offset) {
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+ while (offset < msglen) {
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+ uint8_t len = msg[offset];
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+ if (len == 0) {
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+ *next_offset = offset + 1;
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+ return true;
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+ }
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+ if ((len & 0xc0) == 0xc0) {
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+ if (offset + 1 >= msglen)
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+ return false;
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+ *next_offset = offset + 2;
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+ return true;
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+ }
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+ if ((len & 0xc0) || offset + 1 + len > msglen)
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+ return false;
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+ offset += 1 + len;
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+ }
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+
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+ return false;
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+}
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+
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+static size_t filter_aaaa_records(uint8_t *msg, size_t msglen) {
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+ if (!has_flag(FLAG_FILTER_AAAA) || msglen < DNS_HDRLEN)
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+ return msglen;
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+
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+ uint16_t qdcount = read_be16(msg + 4);
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+ uint16_t counts[] = {
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+ read_be16(msg + 6),
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+ read_be16(msg + 8),
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+ read_be16(msg + 10),
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+ };
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+ uint32_t rrcount = counts[0] + counts[1] + counts[2];
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+
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+ if (rrcount == 0 || qdcount > msglen / 5 || rrcount > msglen / 11)
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+ return msglen;
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+
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+ size_t offset = DNS_HDRLEN;
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+ for (uint16_t i = 0; i < qdcount; i++) {
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+ if (!dns_skip_name(msg, msglen, offset, &offset) || offset + 4 > msglen)
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+ return msglen;
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+ offset += 4;
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+ }
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+
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+ size_t rr_start = offset;
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+ dns_rr_t *rrs = calloc(rrcount, sizeof(*rrs));
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+ if (!rrs)
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+ return msglen;
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+
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+ uint32_t rridx = 0;
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+ for (uint8_t section = 0; section < 3; section++) {
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+ for (uint16_t i = 0; i < counts[section]; i++) {
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+ dns_rr_t *rr = &rrs[rridx++];
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+ rr->start = offset;
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+ rr->section = section;
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+
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+ if (!dns_skip_name(msg, msglen, offset, &offset) || offset + 10 > msglen)
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+ goto out;
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+
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+ rr->type = read_be16(msg + offset);
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+ uint16_t rdlen = read_be16(msg + offset + 8);
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+ rr->end = offset + 10 + rdlen;
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+ if (rr->end > msglen)
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+ goto out;
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+
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+ offset = rr->end;
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+ }
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+ }
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+
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+ size_t rest_start = offset;
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+ bool changed = false;
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+ uint16_t keep_counts[] = { counts[0], counts[1], counts[2] };
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+
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+ for (uint32_t i = 0; i < rrcount; i++) {
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+ if (rrs[i].type == DNS_TYPE_AAAA) {
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+ rrs[i].drop = true;
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+ keep_counts[rrs[i].section]--;
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+ changed = true;
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+ }
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+ }
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+
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+ if (changed) {
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+ size_t write_offset = rr_start;
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+
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+ for (uint32_t i = 0; i < rrcount; i++) {
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+ if (rrs[i].drop)
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+ continue;
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+
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+ size_t rrlen = rrs[i].end - rrs[i].start;
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+ if (write_offset != rrs[i].start)
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+ memmove(msg + write_offset, msg + rrs[i].start, rrlen);
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+ write_offset += rrlen;
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+ }
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+
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+ if (write_offset != rest_start)
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+ memmove(msg + write_offset, msg + rest_start, msglen - rest_start);
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+
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+ msglen = write_offset + (msglen - rest_start);
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+ write_be16(msg + 6, keep_counts[0]);
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+ write_be16(msg + 8, keep_counts[1]);
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+ write_be16(msg + 10, keep_counts[2]);
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+ log_verbose("filter AAAA records, answer:%hu -> %hu, authority:%hu -> %hu, additional:%hu -> %hu",
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+ counts[0], keep_counts[0], counts[1], keep_counts[1], counts[2], keep_counts[2]);
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+ }
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+
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+out:
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+ free(rrs);
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+ return msglen;
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+}
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+
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static void print_help(void) {
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printf("usage: dns2tcp <-L listen> <-R remote> [options...]\n"
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" -L <ip[#port]> udp listen address, port default to 53\n"
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@@ -174,6 +307,7 @@ static void print_help(void) {
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" -s <syncnt> set TCP_SYNCNT option for tcp socket\n"
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" -6 set IPV6_V6ONLY option for udp socket\n"
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" -r set SO_REUSEPORT option for udp socket\n"
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+ " -A strip all AAAA records from dns response\n"
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" -v print verbose log, used for debugging\n"
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" -V print version number of dns2tcp and exit\n"
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" -h print help information of dns2tcp and exit\n"
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@@ -257,7 +391,7 @@ static void parse_opt(int argc, char *argv[]) {
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opterr = 0;
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int shortopt;
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- const char *optstr = "L:R:l:s:6rafvVh";
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+ const char *optstr = "L:R:l:s:6rAafvVh";
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while ((shortopt = getopt(argc, argv, optstr)) != -1) {
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switch (shortopt) {
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case 'L':
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@@ -295,6 +429,9 @@ static void parse_opt(int argc, char *argv[]) {
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case 'r':
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add_flag(FLAG_REUSE_PORT);
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break;
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+ case 'A':
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+ add_flag(FLAG_FILTER_AAAA);
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+ break;
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case 'a':
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/* nop */
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break;
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@@ -399,6 +536,7 @@ int main(int argc, char *argv[]) {
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if (g_syn_cnt) log_info("enable TCP_SYNCNT:%hhu sockopt", g_syn_cnt);
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if (has_flag(FLAG_IPV6_V6ONLY)) log_info("enable IPV6_V6ONLY sockopt");
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if (has_flag(FLAG_REUSE_PORT)) log_info("enable SO_REUSEPORT sockopt");
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+ if (has_flag(FLAG_FILTER_AAAA)) log_info("enable AAAA record filter");
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log_verbose("print the verbose log");
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g_listen_fd = create_socket(skaddr_family(&g_listen_skaddr), SOCK_DGRAM);
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@@ -532,6 +670,9 @@ static void tcp_recvmsg_cb(evloop_t *evloop, evio_t *watcher, int events __unuse
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uint16_t msglen;
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if (ctx->nbytes < 2 || ctx->nbytes < 2 + (msglen = ntohs(*(uint16_t *)buffer))) return;
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+ msglen = filter_aaaa_records((uint8_t *)buffer + 2, msglen);
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+ *(uint16_t *)buffer = htons(msglen);
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+
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ssize_t nsend = sendto(g_listen_fd, buffer + 2, msglen, 0, &ctx->srcaddr.sa, skaddr_len(&ctx->srcaddr));
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if (nsend < 0 || verbose) {
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char ip[IP6STRLEN];
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