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Add captive dns server example

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This commit is contained in:
cpq 2020-12-28 05:25:29 +00:00
parent 788b577d65
commit a882aab30e
7 changed files with 250 additions and 102 deletions
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11
examples/captive-dns-server/Makefile Normal file
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@ -0,0 +1,11 @@
PROG ?= example
CFLAGS ?= -DMG_IO_SIZE=8192 -DMG_ENABLE_LINES
all: $(PROG)
$(DEBUGGER) ./$(PROG) $(ARGS)
$(PROG): main.c
$(CC) ../../mongoose.c -I../.. -W -Wall $(CFLAGS) -o $(PROG) main.c
clean:
rm -rf $(PROG) *.o *.dSYM *.gcov *.gcno *.gcda *.obj *.exe *.ilk *.pdb

55
examples/captive-dns-server/main.c Normal file
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@ -0,0 +1,55 @@
// Copyright (c) 2020 Cesanta Software Limited
// All rights reserved
//
// Example captive DNS server (captive portal).
// 1. Run `make`. This builds and starts a server on port 5533
// 2. Run `dig -t A www.google.com -4 @localhost -p 5533`
#include "mongoose.h"
static const char *s_listen_url = "udp://0.0.0.0:5533";
// DNS answer section. We response with IP 1.2.3.4 - you can change it
// in the last 4 bytes of this array
uint8_t answer[] = {
0xc0, 0x0c, // Point to the name in the DNS question
0, 1, // 2 bytes - record type, A
0, 1, // 2 bytes - address class, INET
0, 0, 0, 120, // 4 bytes - TTL
0, 4, // 2 bytes - address length
1, 2, 3, 4 // 4 bytes - IP address
};
static void fn(struct mg_connection *c, int ev, void *ev_data, void *fn_data) {
if (ev == MG_EV_READ) {
struct mg_dns_rr rr; // Parse first question, offset 12 is header size
size_t n = mg_dns_parse_rr(c->recv.buf, c->recv.len, 12, true, &rr);
if (n > 0) {
char buf[12 + n + sizeof(answer)];
struct mg_dns_header *h = (struct mg_dns_header *) buf;
memset(buf, 0, sizeof(buf)); // Clear the whole datagram
h->txnid = ((struct mg_dns_header *) c->recv.buf)->txnid; // Copy tnxid
h->num_questions = mg_htons(1); // We use only the 1st question
h->num_answers = mg_htons(1); // And only one answer
h->flags = mg_htons(0x8400); // Authoritative response
memcpy(buf + sizeof(*h), c->recv.buf + sizeof(*h), n); // Copy question
memcpy(buf + sizeof(*h) + n, answer, sizeof(answer)); // And answer
mg_send(c, buf, sizeof(buf)); // And send it!
}
mg_iobuf_delete(&c->recv, c->recv.len);
}
(void) fn_data;
(void) ev_data;
}
int main(void) {
struct mg_mgr mgr;
mg_log_set("3"); // Set log level
mg_mgr_init(&mgr); // Initialise event manager
mg_listen(&mgr, s_listen_url, fn, NULL); // Start DNS server
for (;;) mg_mgr_poll(&mgr, 1000); // Event loop
mg_mgr_free(&mgr);
return 0;
}

123
mongoose.c
View File

@ -131,15 +131,6 @@ int mg_base64_decode(const char *src, int n, char *dst) {
struct mg_dns_header {
uint16_t transaction_id;
uint16_t flags;
uint16_t num_questions;
uint16_t num_answers;
uint16_t num_authority_prs;
uint16_t num_other_prs;
};
struct dns_data {
struct dns_data *next;
struct mg_connection *c;
@ -165,73 +156,103 @@ void mg_resolve_cancel(struct mg_connection *c) {
}
}
static size_t mg_dns_parse_name(const uint8_t *s, const uint8_t *e, size_t off,
char *to, size_t tolen, int depth) {
static size_t mg_dns_parse_name_depth(const uint8_t *s, size_t len, size_t ofs,
char *to, size_t tolen, int depth) {
size_t i = 0, j = 0;
if (tolen > 0) to[0] = '\0';
if (depth > 5) return 0;
while (&s[off + i + 1] < e && s[off + i] > 0) {
size_t n = s[off + i];
if (n & 0xc0) {
size_t ptr = (((n & 0x3f) << 8) | s[off + i + 1]) - 12; // 12 is hdr len
if (&s[ptr + 1] < e && (s[ptr] & 0xc0) == 0) {
mg_dns_parse_name(s, e, ptr, to, tolen, depth + 1);
}
while (ofs + i + 1 < len) {
size_t n = s[ofs + i];
if (n == 0) {
i++;
break;
}
if (&s[off + i + n + 1] >= e) break;
if (j + n + 1 >= tolen) return 0; // Error - overflow
if (j > 0) to[j++] = '.';
memcpy(&to[j], &s[off + i + 1], n);
if (n & 0xc0) {
size_t ptr = (((n & 0x3f) << 8) | s[ofs + i + 1]); // 12 is hdr len
if (ptr + 1 < len && (s[ptr] & 0xc0) == 0 &&
mg_dns_parse_name_depth(s, len, ptr, to, tolen, depth + 1) == 0)
return 0;
i += 2;
break;
}
if (ofs + i + n + 1 >= len) return 0;
if (j > 0) {
if (j < tolen) to[j] = '.';
j++;
}
if (j + n < tolen) memcpy(&to[j], &s[ofs + i + 1], n);
j += n;
i += n + 1;
to[j] = '\0'; // Zero-terminate this chunk
// LOG(LL_DEBUG, ("-- %zu/%zu %zu %zu", i, e - s, j, n));
if (j < tolen) to[j] = '\0'; // Zero-terminate this chunk
}
if (tolen > 0) to[tolen - 1] = '\0'; // Make sure make sure it is nul-term
return i;
}
// txid flags numQ numA numAP numOP
// 0000 00 01 81 80 00 01 00 01 00 00 00 00 07 63 65 73 .............ces
// 0010 61 6e 74 61 03 63 6f 6d 00 00 01 00 01 c0 0c 00 anta.com........
// 0020 01 00 01 00 00 02 57 00 04 94 fb 36 ec ......W....6.
bool mg_dns_parse(const uint8_t *buf, size_t len, struct mg_dns_message *dm) {
struct mg_dns_header *h = (struct mg_dns_header *) buf;
const uint8_t *s = buf + sizeof(*h), *e = &buf[len];
uint16_t atype, aclass;
size_t i, j = 0, n;
memset(dm, 0, sizeof(*dm));
size_t mg_dns_parse_name(const uint8_t *s, size_t n, size_t ofs, char *dst,
size_t dstlen) {
return mg_dns_parse_name_depth(s, n, ofs, dst, dstlen, 0);
}
size_t mg_dns_parse_rr(const uint8_t *buf, size_t len, size_t ofs,
bool is_question, struct mg_dns_rr *rr) {
const struct mg_dns_header *h = (struct mg_dns_header *) buf;
const uint8_t *s = buf + ofs, *e = &buf[len];
memset(rr, 0, sizeof(*rr));
if (len < sizeof(*h)) return 0; // Too small, headers dont fit
if (len > 512) return 0; // Too large, we don't expect that
if (s >= e) return 0; // Overflow
if ((rr->nlen = mg_dns_parse_name(buf, len, ofs, NULL, 0)) == 0) return 0;
// LOG(LL_INFO, ("%zu %zu %hu %d", ofs, len, rr->nlen, is_question));
s += rr->nlen + 4;
if (s > e) return 0;
rr->atype = ((uint16_t) s[-4] << 8) | s[-3];
rr->aclass = ((uint16_t) s[-2] << 8) | s[-1];
if (is_question) return rr->nlen + 4;
s += 6;
if (s > e) return 0;
rr->alen = ((uint16_t) s[-2] << 8) | s[-1];
if (s + rr->alen > e) return 0;
return rr->nlen + rr->alen + 10;
}
bool mg_dns_parse(const uint8_t *buf, size_t len, struct mg_dns_message *dm) {
const struct mg_dns_header *h = (struct mg_dns_header *) buf;
struct mg_dns_rr rr;
size_t i, n, ofs = sizeof(*h);
memset(dm, 0, sizeof(*dm));
if (len < sizeof(*h)) return 0; // Too small, headers dont fit
if (mg_ntohs(h->num_questions) > 1) return 0; // Sanity
if (mg_ntohs(h->num_answers) > 10) return 0; // Sanity
dm->txnid = mg_ntohs(h->transaction_id);
dm->txnid = mg_ntohs(h->txnid);
for (i = 0; i < mg_ntohs(h->num_questions); i++) {
j += mg_dns_parse_name(s, e, j, dm->name, sizeof(dm->name), 0) + 5;
// LOG(LL_INFO, ("QUE %zu %zu [%s]", i, j, dm->name));
if ((n = mg_dns_parse_rr(buf, len, ofs, true, &rr)) == 0) return false;
// LOG(LL_INFO, ("Q %zu %zu", ofs, n));
ofs += n;
}
for (i = 0; i < mg_ntohs(h->num_answers); i++) {
j += mg_dns_parse_name(s, e, j, dm->name, sizeof(dm->name), 0) + 9;
if (&s[j] + 2 > e) break;
atype = ((int) s[j - 8] << 8) | s[j - 7];
aclass = ((int) s[j - 6] << 8) | s[j - 5];
n = ((int) s[j] << 8) | s[j + 1];
LOG(LL_VERBOSE_DEBUG, ("%s %d %hu %hu", dm->name, (int) n, atype, aclass));
if (&s[j] + 2 + n > e) break;
if (n == 4 && atype == 1 && aclass == 1) {
// LOG(LL_INFO, ("A -- %zu %zu %s", ofs, n, dm->name));
if ((n = mg_dns_parse_rr(buf, len, ofs, false, &rr)) == 0) return false;
mg_dns_parse_name(buf, len, ofs, dm->name, sizeof(dm->name));
LOG(LL_INFO, ("A %zu %zu %s", ofs, n, dm->name));
ofs += n;
if (rr.alen == 4 && rr.atype == 1 && rr.aclass == 1) {
dm->addr.is_ip6 = false;
memcpy(&dm->addr.ip, &s[j + 2], n);
memcpy(&dm->addr.ip, &buf[ofs - 4], 4);
dm->resolved = true;
break; // Return success
} else if (n == 16 && atype == 28 && aclass == 1) {
} else if (rr.alen == 16 && rr.atype == 28 && rr.aclass == 1) {
dm->addr.is_ip6 = true;
memcpy(&dm->addr.ip6, &s[j + 2], n);
memcpy(&dm->addr.ip6, &buf[ofs - 16], 16);
dm->resolved = true;
break; // Return success
}
j += 2 + n;
}
return true;
}
@ -298,7 +319,7 @@ void mg_dns_send(struct mg_connection *c, const struct mg_str *name,
} pkt;
size_t i, n;
memset(&pkt, 0, sizeof(pkt));
pkt.header.transaction_id = mg_htons(txnid);
pkt.header.txnid = mg_htons(txnid);
pkt.header.flags = mg_htons(0x100);
pkt.header.num_questions = mg_htons(1);
for (i = n = 0; i < sizeof(pkt.data) - 5; i++) {
@ -2947,7 +2968,7 @@ void mg_mgr_poll(struct mg_mgr *mgr, int ms) {
c->is_resolving ? 'R' : 'r', c->is_closing ? 'C' : 'c'));
if (c->is_resolving || c->is_closing) {
// Do nothing
} else if (c->is_listening) {
} else if (c->is_listening && c->is_udp == 0) {
if (c->is_readable) accept_conn(mgr, c);
} else if (c->is_connecting) {
if (c->is_readable || c->is_writable) connect_conn(c);

20
mongoose.h
View File

@ -809,6 +809,26 @@ struct mg_dns_message {
char name[256]; // Host name
};
struct mg_dns_header {
uint16_t txnid; // Transaction ID
uint16_t flags;
uint16_t num_questions;
uint16_t num_answers;
uint16_t num_authority_prs;
uint16_t num_other_prs;
};
// DNS resource record
struct mg_dns_rr {
uint16_t nlen; // Name or pointer length
uint16_t atype; // Address type
uint16_t aclass; // Address class
uint16_t alen; // Address length
};
void mg_resolve(struct mg_connection *, struct mg_str *, int);
void mg_resolve_cancel(struct mg_connection *);
bool mg_dns_parse(const uint8_t *buf, size_t len, struct mg_dns_message *);
size_t mg_dns_parse_rr(const uint8_t *buf, size_t len, size_t ofs,
bool is_question, struct mg_dns_rr *);
size_t mg_dns_decode_name(const uint8_t *, size_t, size_t, char *, size_t);

121
src/dns.c
View File

@ -5,15 +5,6 @@
#include "timer.h"
#include "util.h"
struct mg_dns_header {
uint16_t transaction_id;
uint16_t flags;
uint16_t num_questions;
uint16_t num_answers;
uint16_t num_authority_prs;
uint16_t num_other_prs;
};
struct dns_data {
struct dns_data *next;
struct mg_connection *c;
@ -39,73 +30,103 @@ void mg_resolve_cancel(struct mg_connection *c) {
}
}
static size_t mg_dns_parse_name(const uint8_t *s, const uint8_t *e, size_t off,
char *to, size_t tolen, int depth) {
static size_t mg_dns_parse_name_depth(const uint8_t *s, size_t len, size_t ofs,
char *to, size_t tolen, int depth) {
size_t i = 0, j = 0;
if (tolen > 0) to[0] = '\0';
if (depth > 5) return 0;
while (&s[off + i + 1] < e && s[off + i] > 0) {
size_t n = s[off + i];
if (n & 0xc0) {
size_t ptr = (((n & 0x3f) << 8) | s[off + i + 1]) - 12; // 12 is hdr len
if (&s[ptr + 1] < e && (s[ptr] & 0xc0) == 0) {
mg_dns_parse_name(s, e, ptr, to, tolen, depth + 1);
}
while (ofs + i + 1 < len) {
size_t n = s[ofs + i];
if (n == 0) {
i++;
break;
}
if (&s[off + i + n + 1] >= e) break;
if (j + n + 1 >= tolen) return 0; // Error - overflow
if (j > 0) to[j++] = '.';
memcpy(&to[j], &s[off + i + 1], n);
if (n & 0xc0) {
size_t ptr = (((n & 0x3f) << 8) | s[ofs + i + 1]); // 12 is hdr len
if (ptr + 1 < len && (s[ptr] & 0xc0) == 0 &&
mg_dns_parse_name_depth(s, len, ptr, to, tolen, depth + 1) == 0)
return 0;
i += 2;
break;
}
if (ofs + i + n + 1 >= len) return 0;
if (j > 0) {
if (j < tolen) to[j] = '.';
j++;
}
if (j + n < tolen) memcpy(&to[j], &s[ofs + i + 1], n);
j += n;
i += n + 1;
to[j] = '\0'; // Zero-terminate this chunk
// LOG(LL_DEBUG, ("-- %zu/%zu %zu %zu", i, e - s, j, n));
if (j < tolen) to[j] = '\0'; // Zero-terminate this chunk
}
if (tolen > 0) to[tolen - 1] = '\0'; // Make sure make sure it is nul-term
return i;
}
// txid flags numQ numA numAP numOP
// 0000 00 01 81 80 00 01 00 01 00 00 00 00 07 63 65 73 .............ces
// 0010 61 6e 74 61 03 63 6f 6d 00 00 01 00 01 c0 0c 00 anta.com........
// 0020 01 00 01 00 00 02 57 00 04 94 fb 36 ec ......W....6.
bool mg_dns_parse(const uint8_t *buf, size_t len, struct mg_dns_message *dm) {
struct mg_dns_header *h = (struct mg_dns_header *) buf;
const uint8_t *s = buf + sizeof(*h), *e = &buf[len];
uint16_t atype, aclass;
size_t i, j = 0, n;
memset(dm, 0, sizeof(*dm));
size_t mg_dns_parse_name(const uint8_t *s, size_t n, size_t ofs, char *dst,
size_t dstlen) {
return mg_dns_parse_name_depth(s, n, ofs, dst, dstlen, 0);
}
size_t mg_dns_parse_rr(const uint8_t *buf, size_t len, size_t ofs,
bool is_question, struct mg_dns_rr *rr) {
const struct mg_dns_header *h = (struct mg_dns_header *) buf;
const uint8_t *s = buf + ofs, *e = &buf[len];
memset(rr, 0, sizeof(*rr));
if (len < sizeof(*h)) return 0; // Too small, headers dont fit
if (len > 512) return 0; // Too large, we don't expect that
if (s >= e) return 0; // Overflow
if ((rr->nlen = mg_dns_parse_name(buf, len, ofs, NULL, 0)) == 0) return 0;
// LOG(LL_INFO, ("%zu %zu %hu %d", ofs, len, rr->nlen, is_question));
s += rr->nlen + 4;
if (s > e) return 0;
rr->atype = ((uint16_t) s[-4] << 8) | s[-3];
rr->aclass = ((uint16_t) s[-2] << 8) | s[-1];
if (is_question) return rr->nlen + 4;
s += 6;
if (s > e) return 0;
rr->alen = ((uint16_t) s[-2] << 8) | s[-1];
if (s + rr->alen > e) return 0;
return rr->nlen + rr->alen + 10;
}
bool mg_dns_parse(const uint8_t *buf, size_t len, struct mg_dns_message *dm) {
const struct mg_dns_header *h = (struct mg_dns_header *) buf;
struct mg_dns_rr rr;
size_t i, n, ofs = sizeof(*h);
memset(dm, 0, sizeof(*dm));
if (len < sizeof(*h)) return 0; // Too small, headers dont fit
if (mg_ntohs(h->num_questions) > 1) return 0; // Sanity
if (mg_ntohs(h->num_answers) > 10) return 0; // Sanity
dm->txnid = mg_ntohs(h->transaction_id);
dm->txnid = mg_ntohs(h->txnid);
for (i = 0; i < mg_ntohs(h->num_questions); i++) {
j += mg_dns_parse_name(s, e, j, dm->name, sizeof(dm->name), 0) + 5;
// LOG(LL_INFO, ("QUE %zu %zu [%s]", i, j, dm->name));
if ((n = mg_dns_parse_rr(buf, len, ofs, true, &rr)) == 0) return false;
// LOG(LL_INFO, ("Q %zu %zu", ofs, n));
ofs += n;
}
for (i = 0; i < mg_ntohs(h->num_answers); i++) {
j += mg_dns_parse_name(s, e, j, dm->name, sizeof(dm->name), 0) + 9;
if (&s[j] + 2 > e) break;
atype = ((int) s[j - 8] << 8) | s[j - 7];
aclass = ((int) s[j - 6] << 8) | s[j - 5];
n = ((int) s[j] << 8) | s[j + 1];
LOG(LL_VERBOSE_DEBUG, ("%s %d %hu %hu", dm->name, (int) n, atype, aclass));
if (&s[j] + 2 + n > e) break;
if (n == 4 && atype == 1 && aclass == 1) {
// LOG(LL_INFO, ("A -- %zu %zu %s", ofs, n, dm->name));
if ((n = mg_dns_parse_rr(buf, len, ofs, false, &rr)) == 0) return false;
mg_dns_parse_name(buf, len, ofs, dm->name, sizeof(dm->name));
LOG(LL_INFO, ("A %zu %zu %s", ofs, n, dm->name));
ofs += n;
if (rr.alen == 4 && rr.atype == 1 && rr.aclass == 1) {
dm->addr.is_ip6 = false;
memcpy(&dm->addr.ip, &s[j + 2], n);
memcpy(&dm->addr.ip, &buf[ofs - 4], 4);
dm->resolved = true;
break; // Return success
} else if (n == 16 && atype == 28 && aclass == 1) {
} else if (rr.alen == 16 && rr.atype == 28 && rr.aclass == 1) {
dm->addr.is_ip6 = true;
memcpy(&dm->addr.ip6, &s[j + 2], n);
memcpy(&dm->addr.ip6, &buf[ofs - 16], 16);
dm->resolved = true;
break; // Return success
}
j += 2 + n;
}
return true;
}
@ -172,7 +193,7 @@ void mg_dns_send(struct mg_connection *c, const struct mg_str *name,
} pkt;
size_t i, n;
memset(&pkt, 0, sizeof(pkt));
pkt.header.transaction_id = mg_htons(txnid);
pkt.header.txnid = mg_htons(txnid);
pkt.header.flags = mg_htons(0x100);
pkt.header.num_questions = mg_htons(1);
for (i = n = 0; i < sizeof(pkt.data) - 5; i++) {

20
src/dns.h
View File

@ -14,6 +14,26 @@ struct mg_dns_message {
char name[256]; // Host name
};
struct mg_dns_header {
uint16_t txnid; // Transaction ID
uint16_t flags;
uint16_t num_questions;
uint16_t num_answers;
uint16_t num_authority_prs;
uint16_t num_other_prs;
};
// DNS resource record
struct mg_dns_rr {
uint16_t nlen; // Name or pointer length
uint16_t atype; // Address type
uint16_t aclass; // Address class
uint16_t alen; // Address length
};
void mg_resolve(struct mg_connection *, struct mg_str *, int);
void mg_resolve_cancel(struct mg_connection *);
bool mg_dns_parse(const uint8_t *buf, size_t len, struct mg_dns_message *);
size_t mg_dns_parse_rr(const uint8_t *buf, size_t len, size_t ofs,
bool is_question, struct mg_dns_rr *);
size_t mg_dns_decode_name(const uint8_t *, size_t, size_t, char *, size_t);

2
src/sock.c
View File

@ -538,7 +538,7 @@ void mg_mgr_poll(struct mg_mgr *mgr, int ms) {
c->is_resolving ? 'R' : 'r', c->is_closing ? 'C' : 'c'));
if (c->is_resolving || c->is_closing) {
// Do nothing
} else if (c->is_listening) {
} else if (c->is_listening && c->is_udp == 0) {
if (c->is_readable) accept_conn(mgr, c);
} else if (c->is_connecting) {
if (c->is_readable || c->is_writable) connect_conn(c);