This is a getaddrinfo-based DNS server. Useful if you have an uncommon way to resolve DNS and want to turn that into a proper nameserver.
The server itself parses incoming DNS requests, queries getaddrinfo for the IP addresses, and crafts a valid DNS response with those addresses. This means that it can only resolve A and AAAA records, not TXT or anything else.
Just type make to build gaidns
gaidns binds to port 53/udp on all available network interfaces. TCP is not supported, as it's not necessary for name resolving to work.
The server consists of two files: the protocol implementation in main.c, and the business logic in handlers.c. The API used by handlers.c is as follows:
void handle(char* domain, int record_type, void* opaque);
This function is called on each incoming request. domain is a dot-separated domain name without a trailing dot. record_type is the DNS record type of the request.
int write_record(void* opaque, int domain, int record_type, void* data, int len);
This function can be used to add a record into the response for the current request.
opaque must be the same that has been passed to handle.
domain refers to the domain name the record belongs to. Must be 0 for the actually-requested domain.
record_type is the DNS record type of the record.
data is the actual data carried in the record. For A and AAAA records that is the address itself.
len is the length of data.
If data is another hostname, then the return value of write_record can be passed as the domain argument for subsequent calls.