Found a really helpful repo to make ESP32 act as DNS server.
/*
* ----------------------------------------------------------------------------
* "THE BEER-WARE LICENSE" (Revision 42):
* Jeroen Domburg <jeroen@spritesmods.com> wrote this file. As long as you retain
* this notice you can do whatever you want with this stuff. If we meet some day,
* and you think this stuff is worth it, you can buy me a beer in return.
*
* modified for ESP32 by Cornelis
*
* ----------------------------------------------------------------------------
*/
/*
This is a 'captive portal' DNS server: it basically replies with a fixed IP (in this case:
the one of the SoftAP interface of this ESP module) for any and all DNS queries. This can
be used to send mobile phones, tablets etc which connect to the ESP in AP mode directly to
the internal webserver.
*/
#include "freertos/FreeRTOS.h"
#include "freertos/task.h"
#include "freertos/queue.h"
#include "lwip/sockets.h"
#include "lwip/err.h"
#include "tcpip_adapter.h"
#include "string.h"
static int sockFd;
#define DNS_LEN 512
typedef struct __attribute__ ((packed)) {
uint16_t id;
uint8_t flags;
uint8_t rcode;
uint16_t qdcount;
uint16_t ancount;
uint16_t nscount;
uint16_t arcount;
} DnsHeader;
typedef struct __attribute__ ((packed)) {
uint8_t len;
uint8_t data;
} DnsLabel;
typedef struct __attribute__ ((packed)) {
//before: label
uint16_t type;
uint16_t class;
} DnsQuestionFooter;
typedef struct __attribute__ ((packed)) {
//before: label
uint16_t type;
uint16_t class;
uint32_t ttl;
uint16_t rdlength;
//after: rdata
} DnsResourceFooter;
typedef struct __attribute__ ((packed)) {
uint16_t prio;
uint16_t weight;
} DnsUriHdr;
#define FLAG_QR (1<<7)
#define FLAG_AA (1<<2)
#define FLAG_TC (1<<1)
#define FLAG_RD (1<<0)
#define QTYPE_A 1
#define QTYPE_NS 2
#define QTYPE_CNAME 5
#define QTYPE_SOA 6
#define QTYPE_WKS 11
#define QTYPE_PTR 12
#define QTYPE_HINFO 13
#define QTYPE_MINFO 14
#define QTYPE_MX 15
#define QTYPE_TXT 16
#define QTYPE_URI 256
#define QCLASS_IN 1
#define QCLASS_ANY 255
#define QCLASS_URI 256
//Function to put unaligned 16-bit network values
static void setn16(void *pp, int16_t n) {
char *p=pp;
*p++=(n>>8);
*p++=(n&0xff);
}
//Function to put unaligned 32-bit network values
static void setn32(void *pp, int32_t n) {
char *p=pp;
*p++=(n>>24)&0xff;
*p++=(n>>16)&0xff;
*p++=(n>>8)&0xff;
*p++=(n&0xff);
}
static uint16_t my_ntohs(uint16_t *in) {
char *p=(char*)in;
return ((p[0]<<8)&0xff00)|(p[1]&0xff);
}
//Parses a label into a C-string containing a dotted
//Returns pointer to start of next fields in packet
static char* labelToStr(char *packet, char *labelPtr, int packetSz, char *res, int resMaxLen) {
int i, j, k;
char *endPtr=NULL;
i=0;
do {
if ((*labelPtr&0xC0)==0) {
j=*labelPtr++; //skip past length
//Add separator period if there already is data in res
if (i<resMaxLen && i!=0) res[i++]='.';
//Copy label to res
for (k=0; k<j; k++) {
if ((labelPtr-packet)>packetSz) return NULL;
if (i<resMaxLen) res[i++]=*labelPtr++;
}
} else if ((*labelPtr&0xC0)==0xC0) {
//Compressed label pointer
endPtr=labelPtr+2;
int offset=my_ntohs(((uint16_t *)labelPtr))&0x3FFF;
//Check if offset points to somewhere outside of the packet
if (offset>packetSz) return NULL;
labelPtr=&packet[offset];
}
//check for out-of-bound-ness
if ((labelPtr-packet)>packetSz) return NULL;
} while (*labelPtr!=0);
res[i]=0; //zero-terminate
if (endPtr==NULL) endPtr=labelPtr+1;
return endPtr;
}
//Converts a dotted hostname to the weird label form dns uses.
static char *strToLabel(char *str, char *label, int maxLen) {
char *len=label; //ptr to len byte
char *p=label+1; //ptr to next label byte to be written
while (1) {
if (*str=='.' || *str==0) {
*len=((p-len)-1); //write len of label bit
len=p; //pos of len for next part
p++; //data ptr is one past len
if (*str==0) break; //done
str++;
} else {
*p++=*str++; //copy byte
//if ((p-label)>maxLen) return NULL; //check out of bounds
}
}
*len=0;
return p; //ptr to first free byte in resp
}
//Receive a DNS packet and maybe send a response back
static void captdnsRecv(struct sockaddr_in *premote_addr, char *pusrdata, unsigned short length) {
char buff[DNS_LEN];
char reply[DNS_LEN];
int i;
char *rend=&reply[length];
char *p=pusrdata;
DnsHeader *hdr=(DnsHeader*)p;
DnsHeader *rhdr=(DnsHeader*)&reply[0];
p+=sizeof(DnsHeader);
// printf("DNS packet: id 0x%X flags 0x%X rcode 0x%X qcnt %d ancnt %d nscount %d arcount %d len %d\n",
// my_ntohs(&hdr->id), hdr->flags, hdr->rcode, my_ntohs(&hdr->qdcount), my_ntohs(&hdr->ancount), my_ntohs(&hdr->nscount), my_ntohs(&hdr->arcount), length);
//Some sanity checks:
if (length>DNS_LEN) return; //Packet is longer than DNS implementation allows
if (length<sizeof(DnsHeader)) return; //Packet is too short
if (hdr->ancount || hdr->nscount || hdr->arcount) return; //this is a reply, don't know what to do with it
if (hdr->flags&FLAG_TC) return; //truncated, can't use this
//Reply is basically the request plus the needed data
memcpy(reply, pusrdata, length);
rhdr->flags|=FLAG_QR;
for (i=0; i<my_ntohs(&hdr->qdcount); i++)
{
//Grab the labels in the q string
p=labelToStr(pusrdata, p, length, buff, sizeof(buff));
if (p==NULL) return;
DnsQuestionFooter *qf=(DnsQuestionFooter*)p;
p+=sizeof(DnsQuestionFooter);
printf("DNS: Q (type 0x%X class 0x%X) for %s\n", my_ntohs(&qf->type), my_ntohs(&qf->class), buff);
if (my_ntohs(&qf->type)==QTYPE_A) {
//They want to know the IPv4 address of something.
//Build the response.
rend=strToLabel(buff, rend, sizeof(reply)-(rend-reply)); //Add the label
if (rend==NULL) return;
DnsResourceFooter *rf=(DnsResourceFooter *)rend;
rend+=sizeof(DnsResourceFooter);
setn16(&rf->type, QTYPE_A);
setn16(&rf->class, QCLASS_IN);
setn32(&rf->ttl, 0);
setn16(&rf->rdlength, 4); //IPv4 addr is 4 bytes;
//Grab the current IP of the softap interface
tcpip_adapter_ip_info_t info;
//tcpip_adapter_get_ip_info(TCPIP_ADAPTER_IF_ETH, &info);
tcpip_adapter_get_ip_info(TCPIP_ADAPTER_IF_AP, &info);
//struct ip_info info;
//wifi_get_ip_info(SOFTAP_IF, &info);
*rend++=ip4_addr1(&info.ip);
*rend++=ip4_addr2(&info.ip);
*rend++=ip4_addr3(&info.ip);
*rend++=ip4_addr4(&info.ip);
setn16(&rhdr->ancount, my_ntohs(&rhdr->ancount)+1);
//printf("IP Address: %s\n", ip4addr_ntoa(&info.ip));
//printf("Added A rec to resp. Resp len is %d\n", (rend-reply));
} else if (my_ntohs(&qf->type)==QTYPE_NS) {
//Give ns server. Basically can be whatever we want because it'll get resolved to our IP later anyway.
rend=strToLabel(buff, rend, sizeof(reply)-(rend-reply)); //Add the label
DnsResourceFooter *rf=(DnsResourceFooter *)rend;
rend+=sizeof(DnsResourceFooter);
setn16(&rf->type, QTYPE_NS);
setn16(&rf->class, QCLASS_IN);
setn16(&rf->ttl, 0);
setn16(&rf->rdlength, 4);
*rend++=2;
*rend++='n';
*rend++='s';
*rend++=0;
setn16(&rhdr->ancount, my_ntohs(&rhdr->ancount)+1);
//printf("Added NS rec to resp. Resp len is %d\n", (rend-reply));
} else if (my_ntohs(&qf->type)==QTYPE_URI) {
//Give uri to us
rend=strToLabel(buff, rend, sizeof(reply)-(rend-reply)); //Add the label
DnsResourceFooter *rf=(DnsResourceFooter *)rend;
rend+=sizeof(DnsResourceFooter);
DnsUriHdr *uh=(DnsUriHdr *)rend;
rend+=sizeof(DnsUriHdr);
setn16(&rf->type, QTYPE_URI);
setn16(&rf->class, QCLASS_URI);
setn16(&rf->ttl, 0);
setn16(&rf->rdlength, 4+16);
setn16(&uh->prio, 10);
setn16(&uh->weight, 1);
memcpy(rend, "http://esp.nonet", 16);
rend+=16;
setn16(&rhdr->ancount, my_ntohs(&rhdr->ancount)+1);
//printf("Added NS rec to resp. Resp len is %d\n", (rend-reply));
}
}
//Send the response
//printf("Send response\n");
sendto(sockFd,(uint8_t*)reply, rend-reply, 0, (struct sockaddr *)premote_addr, sizeof(struct sockaddr_in));
}
static void captdnsTask(void *pvParameters) {
struct sockaddr_in server_addr;
uint32_t ret;
struct sockaddr_in from;
socklen_t fromlen;
//struct tcpip_adapter_ip_info_t ipconfig;
char udp_msg[DNS_LEN];
//memset(&ipconfig, 0, sizeof(ipconfig));
memset(&server_addr, 0, sizeof(server_addr));
server_addr.sin_family = AF_INET;
server_addr.sin_addr.s_addr = INADDR_ANY;
server_addr.sin_port = htons(53);
server_addr.sin_len = sizeof(server_addr);
do {
sockFd=socket(AF_INET, SOCK_DGRAM, 0);
if (sockFd==-1) {
printf("captdns_task failed to create sock!\n");
vTaskDelay(1000/portTICK_RATE_MS);
}
} while (sockFd==-1);
do {
ret=bind(sockFd, (struct sockaddr *)&server_addr, sizeof(server_addr));
if (ret!=0) {
printf("captdns_task failed to bind sock!\n");
vTaskDelay(1000/portTICK_RATE_MS);
}
} while (ret!=0);
printf("CaptDNS inited.\n");
while(1) {
memset(&from, 0, sizeof(from));
fromlen=sizeof(struct sockaddr_in);
ret=recvfrom(sockFd, (uint8_t *)udp_msg, DNS_LEN, 0,(struct sockaddr *)&from,(socklen_t *)&fromlen);
if (ret>0) captdnsRecv(&from,udp_msg,ret);
}
close(sockFd);
vTaskDelete(NULL);
}
void captdnsInit(void)
{
xTaskCreate(captdnsTask, (const char *)"captdns_task", 10000, NULL, 3, NULL);
}
- End of all, type with ❤️ -
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