DNSServiceQueryRecord MacOS

README.md

TODO: Add compilation command

query.cpp

#include <iostream>
#include <thread>
#include <vector>
#include <dns_sd.h>
#include <unistd.h>
#include <cstring>

using std::string;

void queryRecordCallback(
    DNSServiceRef sdRef,
    DNSServiceFlags flags,
    uint32_t interfaceIndex,
    DNSServiceErrorType errorCode,
    const char *fullname,
    uint16_t rrtype,
    uint16_t rrclass,
    uint16_t rdlen,
    const void *rdata,
    uint32_t ttl,
    void *context
) {
    if (errorCode == kDNSServiceErr_NoError) {
        printf("Received record for: %s\n", fullname);
    } else {
        printf("Error querying record: %d\n", errorCode);
    }
}

void performDNSQuery(const std::string& hostname) {
    std::string host = hostname;
    printf("starting query :%s\n", host.c_str());

    DNSServiceRef sdRef;
    DNSServiceErrorType error = DNSServiceQueryRecord(
        &sdRef,
        0,
        0,
        host.c_str(),
        1,
        kDNSServiceClass_IN,
        queryRecordCallback,
        nullptr
    );

    if (error != kDNSServiceErr_NoError) {
        printf("Error starting query: %d\n", error);
        return;
    }

    int fd = DNSServiceRefSockFD(sdRef);
    fd_set readfds;
    FD_ZERO(&readfds);
    FD_SET(fd, &readfds);

    struct timeval timeout;
    timeout.tv_sec = 5;  // 5-second timeout
    timeout.tv_usec = 0;

    printf("selecting\n");

    struct timeval* select_timeout = NULL;
    // select_timeout = &timeout;

    // If the target domain doesn't have an HTTPS record
    // the callback never gets called and select hangs forever.
    // If this isn't a bug in the implementation this is the worst
    // API design ever!
    int result = select(fd + 1, &readfds, NULL, NULL, select_timeout);
    if (result > 0 && FD_ISSET(fd, &readfds)) {
        // Process the result
        DNSServiceProcessResult(sdRef);
    } else if (result == 0) {
        printf("select() timed out\n");
    } else if (result < 0) {
        printf("select() failed\n");
    }

    DNSServiceRefDeallocate(sdRef);
    printf("done query :%s\n", host.c_str());
}

int main(int argc, char* argv[]) {
    // If an argument is passed, resolve only that domain
    std::string hostname = argv[1];
    printf("Resolving single domain: %s\n", hostname.c_str());
    performDNSQuery(hostname);

    return 0;
}