INFO314-XMLRPC

A homework assignment for my INFO314 course.

Goal

You must build a client and server for a calculator application using the XML-RPC "standard". You are free to do this in Java, Python, or any other language you prefer, but it must follow the structure and format dictated by the XML-RPC website.

Background

XML-RPC was an early candidate during the "early web services" era, when we were just getting started exploring sending XML over HTTP. All endpoints are HTTP POST requests containing an XML payload that must follow the description given on the XML-RPC website.

POST /RPC2 HTTP/1.0
User-Agent: Frontier/5.1.2 (WinNT)
Host: betty.userland.com
Content-Type: text/xml
Content-length: 181

<?xml version="1.0"?>
<methodCall>
    <methodName>examples.getStateName</methodName>
    <params>
        <param>
            <value><i4>41</i4></value>
        </param>
    </params>
</methodCall>

The XML-RPC website has complete details, but in essence, all of the information about a remote call (or reponse) comes in the XML payload--it does not care about most of the rest of the HTTP layer.

Server rubric (5 pts)

A basic scaffolded HTTP server (using the SparkJava project) is provided for you in the JavaServer directory. You are free to use this, or you can use a different project if you choose. Whatever you use, your HTTP endpoint must:

• listen on port 8080
• return a 404 for any URL other than "/RPC"
• return a 405 (Method Not Supported) for any operation other than POST
• the Host must reflect the hostname it is running on

Your XML-RPC endpoint must support five method names:

• add: it should take zero to any number of i4 parameters, returning one i4 result, adding the values together. add with 0 parameters should return 0; add with 1 parameter should return that original value. Otherwise, sum all the parameters.
• subtract: it should take two i4 parameters, returning one i4 result, subtracting the second from the first.
• multiply: it should take zero to any number of i4 parameters, returning one i4 result, multiplying the values together. multiply with 0 parameters should return 1; multiply with 1 parameter should return that original value. Otherwise, multiply all the parameters.
• divide: it should take two i4 parameters, returning one i4 result, dividing the first by the second. If the second parameter is a 0, return a faultCode of 1 and a faultString of "divide by zero".
• modulo: it should take two i4 parameters, returning one i4 result, doing the modulo (remainder) operation. If the second parameter is a 0, return a faultCode of 1 and a faultString of "divide by zero".

To be more clear about add and multiply, an add of 1, 2, 3, 4 should be 1 + 2 + 3 + 4, or 10, and a multiply of 1, 2, 3, 4 would be 1 * 2 * 3 * 4, or 24.

If anything than an i4 is passed to any of these endpoints, return a faultCode of 3 and a faultString of "illegal argument type".

Client rubric (3 pts)

Your client must be a console application that takes command-line parameters like so:

java CalcClient localhost 8080

In other words, args[0] should be the server, and args[1] the port. The User-Agent header should be the name of your group. The client then needs to exercise all five of the operations, like so:

• subtract(12, 6) = 6
• multiply(3, 4) = 12
• divide(10, 5) = 2
• modulo(10, 5) = 0
• add(0) = 0
• add(1, 2, 3, 4, 5) = 15
• multiply(1, 2, 3, 4, 5) = 120

In addition, the client should make sure the server responds with errors appropriately:

• add two very large numbers such that it triggers an overflow
• multiply two very large numbers and trigger an overflow
• subtract taking two string parameters should trigger illegal argument faults
• divide any number by 0 and trigger a divide-by-zero fault

Interoperability rubric (2 pts)

In order to ensure that your use of XML-RPC is correct, you must demonstrate that your XML-RPC client can work against another person's XML-RPC server, and similarly that another (different) person's client can work against your server. In your project's README, document which other server you interop'ed against, and which client.

Client calling another server, 1 pt. Server called by another client, 1 pt.

A note about Gradle

In the JavaServer directory, you will find a Gradle project: specifically, there is a pair of files, gradlew and gradlew.bat which are shell scripts for *nix-like shells (macOS and Linux, primarily) and Windows, respectively, and use the binaries and configuration stored in the gradle directory to boostrap the necessary components on your machine to do a build.

Breaking all of that down, what it means is that so long as you have a recent Java SDK installed on your machine, you can just type "gradlew run" and Gradle will build and run the code. The source is located in JavaServer/app/src/main/java/edu/uw/info314/xmlrpc/server, and most tools (like VSCode) will recognize the directory structure and treat it as a Gradle project.

If this is your first experience with a Gradle project, don't stress. Just have a Terminal window open, and from the JavaServer directory, type gradlew run to compile-and-run the Java server code. If it fails to build, it will give you the compile errors, otherwise it will show you the running output.

Extra credit: REST (5 pts)

• Write a REST calculator server
• Create an entirely separate HTTP endpoint
• Same five calculator operations
• Same sort of error handling