Project 2, CMSC 621, Spring 2022, UMBC

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Client-Server Token Manager

You are to implement a client-server application in Go for the management of tokens. Token ADT

A token is an abstract data type, with the following properties: id, name, domain, and state. Tokens are uniquely identified by their id, which is a string. The name of a token is another string. The domain of a token consists of three uint64 integers: low, mid, and high. The state of a token consists of two unit64 integers: a partial value and a final value, which is defined at the integer x in the range [low, mid) and [low, high), respectively, that minimizes h(name, x) for a hash function

h. The hash h to use for this project is the SHA256 as below:

import (

"crypto/sha256" "encoding/binary" "fmt"

)

// Hash concatentates a message and a nonce and generates a hash value. func Hash(name string, nonce uint64) uint64 {

hasher := sha256.New() hasher.Write([]byte(fmt.Sprintf("%s %d", name, nonce))) return binary.BigEndian.Uint64(hasher.Sum(nil))

}

Tokens support the following methods:

• create(id): create a token with the given id. Reset the token’s state to “undefined/null”. Return a success or fail response.
• drop(id): to destroy/delete the token with the given id
• write(id, name, low, high, mid):

1. set the properties name, low, mid, and high for the token with the given id. Assume uint64 integers low <= mid < high.
2. compute the partial value of the token as argmin_x H(name, x) for x in [low, mid), and reset the final value of the token.
3. return the partial value on success or fail response

• read(id):

1. find argmin_x H(name, x) for x in [mid, high)
2. set the token’s final value to the minimum of the value in step#1 and its partial value
3. return the token’s final value on success or fail response

Task

Implement a client-server solution for managing tokens. Your server should maintain an initially empty (non-persistent) collection of tokens. Clients issue RPC calls to the server to execute create, drop, read-write methods on tokens. The server executes such RPCs and returns an appropriate response to each call. Client-server communication is assumed synchronous.

Your solution should in developed in Go and utilize the gRPC and Google Protocol Buffer

frameworks.

Your server, upon completing an RPC call by a client for a token, it should “dump” on stderr or stdout all the information it has for that token, followed by a list of the ids of all of its tokens. The server upon starting, it gets the port number to listen to from the command line arguments/flags, eg.

tokenserver -port 50051

The server terminates upon receiving a CTRL-C (SIGINT) signal. Your server should allow for maximum concurrency among non-conflicting RPC calls (eg any pair of concurrent RPC calls on the same token conflict unless both are read); conflicting RPC calls should be executed in a serial manner.

Your client executes a single RPC call (to a server on the specified host and port) upon fetching the command line arguments/flags, eg

tokenclient -create -id 1234 -host localhost -port 50051

tokenclient -write -id 1234 -name abc -low 0 -mid 10 -high 100 -host localhost -port 50051 tokenclient -read -id 1234 -host localhost -port 50051

tokenclient -drop 1234 -host localhost -port 50051

Your client should print on stdout the response it received from the RPC call to the server, and then terminate.

Alternatively, you may have a -config command line flag to specify the filename of a simple YAML (configuration) file with the intended server’s connection information, eg.

host: localhost port: 50051

What to submit:

Submit a .tar.gz archive with your

• complete Go code (and any supporting files)
• a bash script demonstrating running your server and sequence of client executions.
• README file (with relevant documentation and usage guide)

References

• • Quickstart for the gRPC Framework
  • Tutorial on Google Protocol Buffers
  • gRPC with ProtoBuf Basics Tutorial
  • Goroutines and gRPC Serve() method of gRPC Server
  • sync package: Mutexes in Go or Mutex Tour or RWMutex or Map

• • Command Line Flags in Go
  • YAML configurations for Go

This project was inspired from a similar project of the 15-440/640, Distributed Systems class at CMU.