uri-rewriter

A small Go command-line utility to rewrite the hostname component of a URI using DNS CNAME records.

Usage

uri-rewriter hostname-cname [--cname-level N] <uri>

• --cname-level, -l: The step in the CNAME chain to use for replacement.
  • 1 = the first CNAME target (closest to the original hostname)
  • If the requested level exceeds the available CNAME chain length, the last available CNAME target is used.
  • If there is no CNAME for the hostname, the URI is output unchanged.

Examples

Assume DNS has the following CNAME chain:

www.example.com -> www.example.net -> origin.example.org

• Level 1 (first CNAME):

uri-rewriter hostname-cname -l 1 "https://www.example.com/path?x=1"
# https://www.example.net/path?x=1

• Level 2 (second CNAME):

uri-rewriter hostname-cname -l 2 "https://www.example.com/path?x=1"
# https://origin.example.org/path?x=1

• With port preservation:

uri-rewriter hostname-cname -l 1 "https://www.example.com:8443/path"
# https://www.example.net:8443/path

Notes

• Only the rewritten URI is printed to stdout. Errors (e.g., invalid URI, DNS failures) are written to stderr with a non-zero exit code.
• The tool follows the system resolver configuration (/etc/resolv.conf) to query CNAME records. If it is unavailable, it falls back to public resolvers (Cloudflare 1.1.1.1 and Google 8.8.8.8).
• Trailing dots in DNS names (e.g., example.com.) are removed in the output for URI compatibility.

Install

git clone https://github.com/dpc-sdp/uri-rewriter.git
cd uri-rewriter
go build .
# The binary will be at ./uri-rewriter

Or install directly with Go:

go install github.com/dpc-sdp/uri-rewriter@latest

License

MIT