Scriptling Scriptling

scriptling.net.resolve

DNS resolution library for hostname lookup, SRV record resolution, and srv+http(s):// URL resolution.

Overview

The scriptling.net.resolve library provides DNS resolution utilities. It uses the system resolver by default, or custom nameservers when configured by the host application (e.g. knot).

Available Functions

Function Description
lookup_ip(host) Resolve a hostname to a list of IP addresses.
lookup_srv(service) Resolve an SRV record to a list of addresses.
resolve_srv_http(uri) Resolve a srv+http(s):// URI to a concrete URL.

Functions

lookup_ip(host)

Resolves a hostname to a list of IP address strings (A and AAAA records).

Parameters:

  • host (str): The hostname to resolve.

Returns: list[str]: list of IP address strings.

import scriptling.net.resolve as resolve

ips = resolve.lookup_ip("example.com")
print(ips)  # ["93.184.216.34"]

for ip in ips:
    print(ip)

lookup_srv(service)

Resolves an SRV service name to a list of address dicts, ordered by priority and weighted random selection per RFC 2782.

Parameters:

  • service (str): The SRV service name, e.g. "_myservice._tcp.example.com".

Returns: list[dict]: list of address dicts, each with ip (str, the resolved IP address) and port (int, the port number from the SRV record).

import scriptling.net.resolve as resolve

addrs = resolve.lookup_srv("_myservice._tcp.example.com")
for addr in addrs:
    print(f"{addr['ip']}:{addr['port']}")

resolve_srv_http(uri)

Resolves a srv+http(s):// URI to a concrete URL. Strips the srv+ prefix, resolves the SRV record for the host, and substitutes the resolved port. The original hostname is preserved for SNI/TLS.

If uri does not start with srv+, it is returned unchanged, with an https:// prefix added if no scheme is present.

Parameters:

  • uri (str): The URI to resolve.

Returns: str: the resolved URL.

import scriptling.net.resolve as resolve

url = resolve.resolve_srv_http("srv+https://api.example.com/v1")
print(url)  # "https://api.example.com:8443/v1"

# Non-SRV URIs pass through
url = resolve.resolve_srv_http("https://plain.example.com/path")
print(url)  # "https://plain.example.com/path"

Security Considerations

This is an extended library, requiring registration in Go, see Library Registration.

scriptling.net.resolve performs DNS lookups against the system resolver, or against custom nameservers if the embedder injects one. DNS responses are not validated against any allowlist, so a script can trigger lookups for arbitrary hostnames, which can be used for network reconnaissance or to exfiltrate data via DNS queries. Host applications can restrict or monitor this by passing a custom resolver to resolve.Register(env, resolver): see Host Application Integration below. See Security Considerations for a full breakdown of network-enabled libraries.

Host Application Integration

Host applications can inject a custom resolver by passing it to resolve.Register(env, resolver). This allows applications like knot to configure custom nameservers, caching, and domain-specific routing. The resolver argument is required; Register panics if it is nil.

See Also