libwww - The W3C Protocol Library

transcript

Libwww, the W3C protocol library 29.06.2004

libwww -The W3C Protocol Library

„Großes Schwerpunktseminar WI“University of Applied Sciences Gießen-Friedberg

Stefan Sabatzki

Contents

1. Introduction

2. Structure libwww

3. Programming with libwww

4. Conclusion

Contents

1. Introduction– What is libwww?– Why libwww?

2. Structure libwww

4. Conclusion

What is libwww?

• Generic framework for building web applications• Written in C• Pluggable modularity• Means to provide most common Internet access methods• Transmit data in many different media formats• Dataflow to and from the server

What is libwww? (2)

• First version implemented 1992 by Tim Berners-Lee• Development at CERN• 1994 libwww moved from CERN to W3C• 1998 released as opensource• As of September 2003 W3C stopped work on libwww• As of January 2004 libwww officially belongs to the „Open

Source Community“

Why libwww?

• Experimenting and prototyping• Performance, modularity and extensibility• Free and open source code• Mailing lists and active community

Contents

1. Introduction

2. Structure libwww– Design Model– Request/Response Paradigm– Data Flow– Threads, Eventloops and Filters– Modules as Statemachines

4. Conclusion

Design Model

• Layering as design model

Design Model (2)

• More demonstrative

Request/Response Paradigm

• Application issues request • Libwww fulfills request• Presented to application on arrival• Simultaneous requests handled by Librarycore

Data Flow

• Streams are used to transport data• Derived from generic stream

– Protocol streams– Converters– Presenters– I/O streams– Basic streams

Data Flow (2)

• Structured streams– Derived from generic stream– Accepts structured document– Ordered tree-structured arrangement of data– Each instance is associated with SMGL parser– Each instance is associated with corresponding DTD

Data Flow (3)

• Cascaded streams– Stream chains– Setup before data arrives

Data Flow (4)

– Setup after data arrives

Threads, Eventloops and Filters

• Not thread-save• Implements pseudo-thread model

– Uses non-blocking sockets– Based on callback functions

• Before/After-Filter– Global and local filters– Registered at runtime

Threads, Eventloops and Filters (2)

Modules as Statemachines

• Since libwww 3.0• Protocol modules implemented as statemachines• Part of thread-model• Keep track of current state in communication interface

Modules as Statemachines (2)

Contents

1. Introduction

2. Structure libwww

3. Programming with libwww– C++ Simulation– APIs and Library Interfaces– Simple Example– More Complex Example

4. Conclusion

C++ Simulation

• Construction/destruction– *_new / *_delete (HTRequest_new / HTRequest_delete)

• Data hiding • Inheritance

– Explicit pointer casting

• PRIVATE, PUBLIC Makros

APIs and Library Interfaces

• Set of APIs called packages• Win32: DLLs• Unix: separate static libraries • Package interface exported via single include file: WWW*.h • Some important packages

– Basic Utility Packages– Core Packages – Initialization Packages– Transport Packages– Protocol Packages– Parser Packages

Simple Example

• Displays all links in document• Applicable to text, html/xml tags, etc.

// snippet...HText_registerLinkCallback(foundLink); .HTEventList_loop(request); ... foundLink (...) {

HTAnchor * dest = HTAnchor_followMainLink(...); char * address = HTAnchor_address(dest); HTPrint("Found link `%s\'\n", address); HT_FREE(address);

More Complex Example

• Rudimentary commandline browser• See project www.dsw

Contents

1. Introduction

2. Structure libwww

4. Conclusion– What‘s missing?– Facts about libwww– Personal Opinon

What‘s missing?

• Not thread-safe• No cookie-jar, only parsing/generation• Consistent usage of RegEx• C++ representation

Facts about libwww

• Who uses libwww? No one?• Sample applications on project homepage• No reviews, benchmarks, comparisons• Not ‚bug free‘• ‚Competitors‘ (mostly UNIX)

– WinInet– Libghttp– Libcurl– Libhttp – Neon

Personal Opinion

• Typical opensource project• Tricky installation• ‚Feels‘ old < – > IS old• Desperate attempt to reach OOP• Non-trivial usage, but very flexible and potent

Thank you for your attention

libwww - The W3C Protocol Library

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