CSC/ECE 517 Fall 2015/oss/M1503/IntegrateXMLParser

Rust

Rust is a general-purpose, compiled programming language developed by Mozilla Research. The syntax of Rust is somewhat similar to C and C++, with blocks of code delimited by curly brackets, and control flow and structure. Rust does not use automatic garbage collection mechanism similar to java. It accomplishes the goals of memory safe without using garbage collection and it supports concurrency and parallelism in building platforms.

Servo

Servo is web browser layout engine developed by Mozilla Research. It was developed in Rust. Servo handles parallel environments such as rendering, layout, image decoding as a separate tasks. Servo provides APIs, JavaScript support. Servo was not developed explicitly to create full web browser but to achieve maximum parallelism.

Compilation and Build

Code link: https://github.com/servo/servo/ . This repository is forked to https://github.com/ronak6892/servo . Build success is ensured by commands ./mach build --dev and ./mach run tests/html/about-mozilla.html.

Project Description

Servo currently lacks a parser for XML documents, which prevents implementation of several APIs. The goal of the project is to integrate xml5ever parser into Servo.

Design

To integrate XML5ever, dependency was added for XML5ever parser similar to HTML5ever.A separate interface was defined in ServoXMLParser webidl file and this interface was implemented in its corresponding rust file along with necessary stubs to parse XML. The Adapter Design Pattern was applied to enhance parsing mechanism for XML5 in Servo. Interface defined using adapter pattern closely resembles servoHTMLParser interface as this will facilitate parsing or modifying any code for both XML and HTML documents and future reader don't have to understand code for both separately as they are related in their functionality.

Initial implementation

To achieve project goal we have done following initial steps.

Complied servo and add xml5ever as a dependency to the script using cargo package manager. To do this we edited Cargo.toml located at components/script by adding xml5ever as a dependency.

Added xml.rs at components/script/parse with parse_xml() as a function. mod.rs also need to be modified in order to declare file.

Added ServoXMLParser interface with necessary stubs in servoxmlparser.rs located at components/script/dom. Also servoxmlparser need to be declared in mod.rs located at components/script/dom.

Called parse_xml from domparser.rs located at components/script/dom this will help compile.

Challenges

Primary challenge is to continuously sync with the latest commits of servo and ensuring build success after integrating each step. And keep on adding of necessary stubs as per the new changes in parsing mechanism also need continuous and careful efforts.

Testing

To integrate the model of XML parser into current servo code, no extra test cases were added. We have added interface files and method stubs, XML parser functionality will be implemented as subsequent steps in final project. Integration success is tested by successful compilation and build after adding our changes. Following commands are used to check that all test cases were passed.

./mach run tests/html/about-mozilla.html

./mach test-tidy

All the modifications which were suggested by servo community through comments on pull request, have been incorporated and pull request has been merged successfully.

Subsequent steps for final project

• modify ScriptTask::load in script_task.rs to recognize the text/xml content type and call parse_xml instead of parse_html as appropriate, while passing the appropriate flag to the Document constructor.
• implement a TreeSink for the XML parser that performs appropriate tree modifications for each action (see the implementation in parse/html.rs for an excellent model).
• implement support in xmlhttprequest.rs for XML document responses (see step 7 in https://xhr.spec.whatwg.org/#document-response).
• implement XMLDocument API by following the documentation and implementing the steps laid out in the specification for the load method.

External Links

HTML5ever - https://github.com/servo/html5ever/

XML5ever - https://github.com/Ygg01/xml5ever

Pull request - https://github.com/servo/servo/pull/8278

YouTube - https://youtu.be/i8dONOzYwlc

References

Servo Documentation - http://doc.servo.org/servo/index.html

Project Definition - https://github.com/servo/servo/wiki/Integrate-xml5ever

Rust Documentation - https://doc.rust-lang.org/nightly/index.html

XML specs - https://xhr.spec.whatwg.org/#document-response