DNSGrep

A utility for quickly searching presorted DNS names. Built around the Rapid7 rdns & fdns dataset.

How does it work?

This utility assumes the file provided is presorted (both alphabetical, and symbols).

The algorithm is pretty simple:

1. Use a binary search algorithm to seek through the file, looking for a substring match against the query.
2. Once a match is found, the file is scanned backwards in 10KB increments looking for a non-matching substring.
3. Once a non-matching substring is found, the file is scanned forwards until all exact matches are returned.

Limits

There is a built-in limit system. This prevents 2 things:

1. scanning too far backwards (MaxScan)
2. scanning too far forwards after scanning backwards (MaxOutputLines)

This allows for any input while stopping requests that are taking too long.

Additionally, this utility does not handle the edge cases(start/end) of files and will return an error if encountered.

Install

# used for dnsgrep cli flags
go get “github.com/jessevdk/go-flags”
# used by the experimental server for http routing
go get “github.com/gorilla/mux”
# pull in a string reversal function
go get “github.com/golang/example/stringutil”

Use

Generate fdns_a.sort.txt and rdns.sort.txt first using the scripts found in the scripts/ folder:

# Each of these scripts requires:
# * 3 hours+ on an SSD
# * 300GB+ temp disk space (under the same folder)
# * ~65GB for output output (under the same folder)
# * jq to be installed
./scripts/fdns_a.sh
./scripts/rdns.sh

Run the command line utility:

go run dnsgrep.go -f DNSBinarySearch/test_data.txt -i “amiccom.com.tw”

Run the experimental server in the same folder as fdns_a.sort & rdns.sort.txt:

go run experimentalServer.go

Copyright (c) 2019 Samuel Erb

Source: https://github.com/erbbysam/