diff options
| -rw-r--r-- | dns.c | 110 | ||||
| -rw-r--r-- | dns_example.c | 4 |
2 files changed, 96 insertions, 18 deletions
@@ -18,6 +18,7 @@ struct header { int is_response: 1; int opcode: 4; int is_authanswer: 1; + int is_truncated: 1; int is_recursion_desired: 1; */ @@ -80,7 +81,7 @@ static void fill_question(char **writer, int query_type) *writer += sizeof(*q); } -static int ask(const char *s, const char *h, int qt, struct sockaddr_in *a) +static int askudp(const char *s, const char *h, int qt, struct sockaddr_in *a) { int sent; int plen = sizeof(struct header) + strlen(h) + 2 + @@ -88,6 +89,9 @@ static int ask(const char *s, const char *h, int qt, struct sockaddr_in *a) char *packet = malloc(plen); char *writer = packet; int sock = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP); + if (sock < 0) { + return 0; + } a->sin_family = AF_INET; a->sin_port = htons(53); a->sin_addr.s_addr = inet_addr(s); @@ -104,6 +108,84 @@ static int ask(const char *s, const char *h, int qt, struct sockaddr_in *a) return sock; } +static int asktcp(const char *s, const char *h, int qt) +{ + struct sockaddr_in a; + int sent; + int plen = sizeof(struct header) + strlen(h) + 4 + + sizeof(struct question_header); + char *packet = malloc(plen); + char *writer = packet; + int sock = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP); + if (sock < 0) { + return 0; + } + a.sin_family = AF_INET; + a.sin_port = htons(53); + a.sin_addr.s_addr = inet_addr(s); + if (connect(sock, (struct sockaddr *) &a, sizeof(a))) { + return 0; + } + + writer += 2; + fill_header(&writer); + fill_name(&writer, h); + fill_question(&writer, qt); + *((unsigned short *) packet) = htons(writer - packet - 2); + + sent = write(sock, packet, plen); + free(packet); + if (sent != plen) { + return 0; + } + return sock; +} + +static char *gettcp(int sock) +{ + short size; + char *packet; + if (!sock) { + return 0; + } + if (read(sock, &size, 2) < 0) { + close(sock); + return 0; + } + size = ntohs(size); + packet = malloc(size); + if (read(sock, packet, size) < 0) { + close(sock); + free(packet); + return 0; + } + close(sock); + return packet; +} + +static char *get(const char *s, const char *h, int qt) +{ + struct sockaddr_in a; + char *packet; + socklen_t slen = sizeof(a); + int sock = askudp(s, h, qt, &a); + if (!sock) { + return 0; + } + packet = malloc(512); + if (recvfrom(sock, packet, 512, 0, (struct sockaddr *) &a, &slen) < 0) { + free(packet); + close(sock); + return 0; + } else if (packet[2] & 0b10) { + free(packet); + close(sock); + return gettcp(asktcp(s, h, qt)); + } + close(sock); + return packet; +} + static void skip_questions(char **reader, int num) { @@ -205,24 +287,21 @@ static struct dns_answers *get_answers(char **reader, char *packet, int num) return res; } -static struct dns_answers *get(int sock, struct sockaddr_in *a) +static struct dns_answers *parse(char *packet) { - char packet[512]; + struct dns_answers *res; char *reader = packet; - struct header *head; - socklen_t slen = sizeof(*a); - if (!sock) { - return 0; - } - if (recvfrom(sock, packet, 512, 0, (struct sockaddr *) a, &slen) < 0) { + struct header *head = (struct header *) reader; + if (!packet) { return 0; } - head = (struct header *) reader; - head->questions = ntohs(head->questions); - head->answers = ntohs(head->answers); - reader += sizeof(*head); + head->questions = ntohs(head->questions); + head->answers = ntohs(head->answers); + reader += sizeof(*head); skip_questions(&reader, head->questions); - return get_answers(&reader, packet, head->answers); + res = get_answers(&reader, packet, head->answers); + free(packet); + return res; } @@ -260,8 +339,7 @@ int dns_srv_weight(void *data) struct dns_answers *dns_get(const char *server, const char *host, int query) { - struct sockaddr_in addr; - return get(ask(server, host, query, &addr), &addr); + return parse(get(server, host, query)); } void dns_free(struct dns_answers *answers) diff --git a/dns_example.c b/dns_example.c index 9f16dc0..fb0c74a 100644 --- a/dns_example.c +++ b/dns_example.c @@ -5,8 +5,8 @@ int main() { struct dns_answers *cur; - const char *router = "10.1.1.1"; /* place here your one */ - struct dns_answers *ans = dns_get(router, "veresov.pro", dns_type_a); + const char *server = "8.8.8.8"; /* place your favourite one */ + struct dns_answers *ans = dns_get(server, "veresov.pro", dns_type_txt); for (cur = ans; cur; cur = cur->next) { if (cur->type == dns_type_a) { unsigned char *ip = cur->data; |