XMLValidator

A CLI tool that checks whether or not a given XML is valid. Supports strings and files.

Run

Using dotnet CLI

Change directory to XMLValidator.CLI

cd XMLValidator.CLI

To test strings:

dotnet run -i "<Design><Code>hello world</Code></Design>"

To test files:

dotnet run -f input.xml

Using MSBuild

After building the solution with XMLValidator.CLI as the Startup Project, change directory to:

cd XMLValidator.CLI\bin\Release\net6.0

To test strings:

XMLValidator.CLI.exe -i "<Design><Code>hello world</Code></Design>"

To test files:

XMLValidator.CLI.exe -f input.xml

How it works

XMLValidator is divided in two main parts, the Parser and Validator. The Parser reads the input and create a list of Element objects, which is consumed by the Validator to decide if what was received is a valid XML or not.

Parser

The parser reads the input string and uses a Finite State Machine to create Element objects. Elements are records with a name and a type (Opening or Closing).

The FSM is defined as follows.

Validator

The validator receives the list of Elements and uses a stack to decide if the input is valid. Elements are stored in the stack if they have the type Opening. When a matching element with type Closing is received, that element is removed from the stack, which guarantees the nesting order of the elements. If a new element, that doesn't match the element at the top of the stack, is received, the XML is invalid. After all elements are processed, if there are no elements left in the stack, the XML is valid.

input: "<Design><Code>hello world</Code></Design>"

<Design>   <Code>       </Code>       </Design>
   [] -> [<Design>] -> [ <Code> ] -> [<Design>] -> []
                       [<Design>]

output: true
explanation: stack is empty

input: "<Design><Code>hello world</Code></Design><People>"

<Design>   <Code>       </Code>       </Design>     <People>
   [] -> [<Design>] -> [ <Code> ] -> [<Design>] -> [<People>]
                       [<Design>]

output: false
explanation: stack is not empty

input: "<People><Design><Code>hello world</People></Code></Design>"

<People>  <Design>       <Code>       </People>     
   [] -> [<People>] -> [<Design>] -> [ <Code> ]
                       [<People>]    [<Design>] 
                                     [<People>] 

output: false
explanation: </People> closing Element did not match the Opening Element <Code> at the top of the stack