[fpc-pascal] netdb and DNS queries for MX, TXT, and other resource types

[Noel Duffy]

On 16/09/20 8:43 pm, Michael Van Canneyt via fpc-pascal wrote:
> 
> 
> On Wed, 16 Sep 2020, Noel Duffy via fpc-pascal wrote:
> 
>> I'm in need of a library to perform DNS lookups for a range of different resource types such as MX, TXT, PTR and so on. At first I thought that netdb would do the job, but it turns out that it only supports direct A and AAA lookups. However, the code actually has the ability to query all resource types, but the module's API doesn't expose this functionality. The functions Query and BuildQuery, and the types TQueryData and TRRData are not made available to callers.
>>
>> cnetdb is similar in that it exposes just a subset of what libresolv provides. There's no interface to things like res_nquery, for instance. While it's theoretically possible for me to interface directly to libresolv, in reality the API is a horrible hairball of C macros and pointers and this is not a path I want to go down.
>>
>> Is it intended that netdb will be capable of querying all resource types? It appears that most of the work is already done, with the only major pieces missing the parsing of the additional resource records and the exposure of additional functions for the public API.
> 
> It was intended, but in practice I just added the records I needed.
> If you feel like adding new records, I'll gladly accept patches.
> 

I can certainly do that. The first question, though, is what should the API look like? From my initial reading of the code the simplest path might be to expose Query and BuildQuery publicly, so that users can compose queries for arbitrary resource types similarly to libresolv, but there will still need to be new methods to parse the RR data. Such an API is low-level but offers the most flexibility. That's what a number of other languages do.

I'll need to do a close read of RFC 1035 to get a clearer idea of the RR data parsing requirements before I can suggest anything useful there.