About

I was asked to provide an example client for ingesting UDP datagrams, computing statistics about those datagrams, and outputting the results to standard output. Since this is a command line client, I used ANSI colors and animation to make it a bit more pleasant to use.

I don't contend this is the best way to ingest UDP packets, but it's a viable way to do so. Because I was having fun with this, I used a lexer and parser to parse the payload. That's a bit overkill for simple payloads, but it scales well as payload complexity increases.

Protocol

The server sends events over UDP that conform to this binary (BigEndian) structure:

Description	Bytes
Node ID	2
EPOC TimeStamp	4
Payload Size	2
UUID	16
Payload	payload size
Protocol1	2
Submitter IP	4
CRC32	4

¹ Protocol constants

Assumptions

• The client runs on Linux or macOS, primarily because the server binaries used to create this client were targeted at these OSes
  • The only likely Windows limitation in the client code are system calls to determine terminal window sizing
• Go 1s .19+ is in the PATH
  • Go 1.19 is required due to use of new AppendByteOrder interface

Build and Run the Client

Nothing special is required here. Simply go build the source code.

$ go build -o bin/client *.go
$ ./bin/client -h
This client initiates communication with an event server and parses a finite 
number of events. After parsing all events, the client prints a report of 
findings answering the following questions:

        * What are the top 5 SSH passwords?
        * What are the top 5 SSH usernames?
        * What are the top 5 TELNET passwords?
        * What are the top 5 TELNET usernames?
        * What are the top 30 user-agents in HTTP events?
        * What are the top 20 emails in SMTP?
        * Who are the top 15 submitters?
        * What events did <ip-detail> submit?

Usage of ./bin/client:
  -address string
        event server host:port (default "localhost:1035")
  -cache int
        MB of RAM to use for caching datagrams (min 1) (default 20)
  -datagram-size int
        maximum UDP datagram size (min 512; max 65535) (default 512)
  -datagrams int
        datagrams to read from event server (default 37529)
  -ip-detail string
        detail events submitted by a given IP (default "1.2.3.4")
  -v    enable verbose (debug) output

The flag defaults should be sufficient if you're running the emitter server using its defaults on the same system.

Bonus

The CRC32 validation occurs in the protocol.Event.Valid() method.