Introduction

This is a proof-of-concept async DNS resolver library for the Janet programming language. This code is not at all production ready, as it only implements the happy path and has virtually no error handling.

Description

Address resolution is a complicated task that is usually performed by the libc standard library using getaddrinfo() or similar calls. The Janet standard library also uses this call for resolving when calling net/address; this can be problematic because getaddrinfo() can potentially block for several seconds, effectively blocking the current Janet thread and it's event loop as well.

This library implements a very simply DNS resolver that does not rely on the libc standard library functions; instead it communicates directly with DNS servers to perform the lookup, allowing for proper async behavior that will not block the event loop.

Note that the resolving behavior of this library is by no means standard and might differ from the underlying libc implementation; also, it will only use DNS for resolution and does not implement any other source like a local hosts file.

Example

(import ./resolver)

# Create resolver instance

(def res (resolver/new "8.8.4.4"))

# Call the :resolve method to perform a DNS lookup

(defn test[]
  (ev/sleep 0.1)
  (pp (:resolve res "nyt.com"))
  (ev/sleep 0.1)
  (pp (:resolve res "google.com" :AAAA)))


(ev/call test)

TODO and Open questions

• Improve error handling
• Acquire DNS server IPs from system resolver configuration
• Cache resceived answers with proper time-to-live
• Implement TCP/53
• Primary/secondary server fallback