Design

Uses a simple design with 2 buffers which are extensible (currently using go channels) and can be replaced by any suitable API. Similarly, sendData is also extensible.

Code

.
|-- go.mod
|-- go.sum
|-- handler
|   |-- packetHandler.go              // contains packet handling and filtering
|   `-- sendData.go                   // contains send data
`-- main.go                           // contains packet capture using gopcap

To build and run :

Obtain the following first:

• Whitelist file URL ( a regex based list on a remote location which can be fetched. Example list is provided in the file whitelistDns )

• The whitelist resource must change it's Etag if whitelist changes on the remote resource as the code checks for changes in etag for updating the whitelist.

Place these values in build.sh and run:

$ go mod init dnslog
$ go mod tidy
$ ./build.sh

# Run as sudo
$ sudo ./bin/dnslog

Performance

• Here golang package gopcap is being used which is a wrapper around libpcap. This is slower than direct implementation using libpcap in C.

• Here pcap is being used. Much better solutions like tc-bpf could have been used for better performance in case of large number of packet transfers. Using kernel tracepoints in the kernel would have been much faster as pcap processes raw packets which are generally used for processing packets. For logging we don't need to process the packets.