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README.md

ROS Message Parser for .Net

Hanlde ROS message files with ease

ROS Message Parser allows you to parse ROS message/service/action files.

You can either use one built in Parser for

  • Messages (*.msg)
  • Services (*.srv)
  • Actions (*.action)

or build your own visitors or listeners on top of the generated parse tree.

Installation

ROS Message Parser for .Net is available as NuGet Package.

TODO Publish as nuget.

Usage

Built in Parsers

Use the built in parsers if you want to get a structured representation of a ROS message.

Parsing a message file

var descriptor = new MessageParser(File.ReadAllText(filePath)).Parse();

or

MessageDescriptor descriptor;
            
using (var file = File.OpenRead(filePath))
{
    var parser = new MessageParser(file)
    descriptor = parser.Parse();
}

Parsing a service file

var descriptor = new ServiceParser(File.ReadAllText(filePath)).Parse();

or

ServiceDescriptor descriptor;
            
using (var file = File.OpenRead(filePath))
{
    var parser = new ServiceParser(file);
    descriptor = parser.Parse();
}

Parsing an action file

var descriptor = new ActionParser(File.ReadAllText(filePath)).Parse();

or

ActionDescriptor descriptor;
            
using (var file = File.OpenRead(filePath))
{
    var parser = new ActionParser(file);
    descriptor = parser.Parse();
}

What you get from the parsers is a either a MessageDescriptor, ServiceDescriptor or a ActionDescriptor representing the structure of the ROS message file. You can then operate on these message structures.

Have a look on the UML diagram below for a detailed description.

Message Parsers UML diagram

Intercepting descriptor creation

You can intercept the descriptor creation by creating a class which implements Joanneum.Robotics.Ros.MessageParser.IRosMessageVisitorListener. This allows you to implement the following methods used in the object tree creation:

  • void OnVisitRosMessage(MessageDescriptor messageDescriptor)
  • void OnVisitRosService(ServiceDescriptor serviceDescriptor)
  • void OnVisitRosAction(ActionDescriptor actionDescriptor)
  • void OnVisitFieldDeclaration(FieldDescriptor fieldDescriptor)
  • void OnVisitConstantDeclaration(ConstantDescriptor constDescriptor)
  • void OnVisitComment(string comment)
  • void OnVisitIdentifier(string identifier)
  • void OnVisitRosType(RosTypeInfo typeInfo)
  • void OnVisitPrimitiveType(PrimitiveTypeInfo typeInfoDescriptor)
  • void OnVisitArrayType(ArrayTypeInfo arrayTypeInfo)
  • void OnVisitRosbagInput(RosbagMessageDefinitionDescriptor rosbag)
  • void OnVisitRosbagNestedType(NestedTypeDescriptor descriptor);

You can then pass this listener to the Parse(IRosMessageVisitorListener listener) method of the Parser.

Create your own parse tree Visitor or Listener

Used for low level parse tree processing.

Build your own ANTLR visitor or listener to process the abstract syntax tree. Extend Joanneum.Robotics.Ros.MessageParser.Antlr.RosMessageParserBaseListener or Joanneum.Robotics.Ros.MessageParser.Antlr.RosMessageParserBaseVisitor respectively.

Having ANTLR IDE Support displaying the parse tree will make this expedition much more comfortable. See https://www.antlr.org/tools.html for a list of supported IDE plugins

Example Assume the following ros message file:

#This is a comment
int32 CONST_DECLARATION = 99
int8 myIntValue

The Parser creates the following abstract syntax tree based on the input message:

Message Parsers UML diagram

The base visitor and listener classes implement methods for all tree node types which you can override. The grammar defines these tree node types.

Contributing

ROS Message Parser for .Net is based on ANTLRv4. If you are not familiar with ANTLR there is a good tutorial from Gabriele Tomasetti (https://tomassetti.me/antlr-mega-tutorial/)

License

This project is licensed under the BSD 3-clause license. Learn more

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